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- Создано: 26-01-22
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How Tower Cranes Work
Описание: How Tower Cranes Work Tower cranes are extensively used for lifting materials in construction sites. Most construction sites are very confined and close to public. Tower crane accidents not only hazard workers in construction sites, but also pedestrians. This paper investigates tower crane safety in related to the understanding and degree of executing statutory requirements and non-statutory guidelines for the use of tower cranes in the Hong Kong construction industry. A questionnaire survey and structured interviews are conducted. It is found that human factors are attributed to tower crane safety. Indolent performance of requirements or responsibilities of practitioners in tower crane operations is found. Inadequate training and fatigue of practitioners are one of the main reasons causing unsafe practices of tower crane operations. Recommendations for improving safety performance in tower crane operations are also discussed. Research highlights This paper investigates tower crane safety in related to the understanding and degree of executing statutory requirements and non-statutory guidelines for the use of flat top tower crane in the Hong Kong construction industry. It is found that human factors are attributed to tower crane safety. Indolent performance of requirements or responsibilities of practitioners in tower crane operations is found. Inadequate training and fatigue of practitioners are one of the main reasons causing unsafe practices of tower crane operations. Tower cranes are a common fixture at any major construction site. They're pretty hard to miss -- they often rise hundreds of feet into the air, and can reach out just as far. The construction crew uses the tower crane to lift , concrete, large tools like acetylene torches and generators, and a wide variety of other building materials. When you look at one of these cranes, what it can do seems nearly impossible: Why doesn't it tip over? How can such a long boom lift so much weigh-t? How is it able to grow taller as the building grows taller? If you have ever wondered about how tower cranes work, then this article is for you. In this article, you'll find out the answers to all of these questions and more! Weather monitoring in construction sites is important, but especially when luffing jib tower crane are used. A strong gust of wind can destabilize the load and structure, causing a collapse. Project managers should constantly check weather forecasts, and avoid lifting operations with unfavorable weather. A weather monitoring system at the project sites can warn about dangerous wind conditions that are not covered in forecasts. Tower Crane Support System One of the first questions that may be asked by someone looking at a tower crane is these structures stand upright. There are several elements that contribute to the tower crane’s stability. The concrete pad is a concrete foundation made by the construction company several weeks prior to the crane’s arrival. Typical measurements for the pad are 30x30x4 feet (10x10x1.3 meters), with a weight of around 400,000 pounds. Large anchor bolts are deeply embedded in the concrete pad, and these elements support the base of the crane. Tower cranes are delivered to construction projects in parts, which are then assembled on-site. Qualified installers assemble the jib and the machinery section, these horizontal elements are then positioned on the mast, which is only 40 feet tall initially. Once this assembly is completed, the counterweights are placed by a mobile crane. The mast rises from the concrete pad, and it remains upright thanks to its triangulated structure. To increase the crane height, the crew adds sections to the mast with a climbing frame: A weight is hung on the jib to balance the counterweight. The slewing unit is detached from the top of the mast and hydraulic rams in the top climber push the slewing unit up 20 feet. The crane operator uses the crane to lift another 20 ft mast section into the gap and then it is bolted in place. These steps are repeated continuously until the desired height is achieved. Once it is time to remove the tower crane from the construction site, the crane disassembles its own mast and smaller cranes are used to disassemble the rest. Tower crane accidents frequently occur in the construction industry, often resulting in casualties. The utilization of tower crane spare parts involves multiple phases including installation, usage, climbing, and dismantling. Moreover, the hazards associated with the use of tower cranes can change and be propagated during phase alternation. However, past studies have paid less attention to the differences and hazard propagations between phases. In this research, these hazards are investigated during different construction phases. The propagation of hazards between phases is analyzed to develop appropriate safety management protocols according to each specific phase. Finally, measures are suggested to avoid an adverse impact between the phases. A combined method is also proposed to identify hazard propagation, which serves as a reference and contributes to safety management and accident prevention during different tower crane phases in the construction process. In construction sites, tower cranes are used for the vertical and horizontal transportation of materials . It is essential equipment for most construction projects, especially for high-rise buildings . Typically, they need to be reinstalled on the construction site once the components of the tower crane leave the factory. As the height of a construction project increases, tower cranes are necessary, and they eventually must be climbed. Furthermore, maintenance and dismantlement must be performed. Thus, a tower crane is not only a piece of auxiliary equipment in construction but also a construction object with complicated processes . This negatively impacts on-site construction safety. In this investigation, 149 accident analysis reports on a tower crane in construction sites in China were collected for the period from 2015 to 2019. The accidents resulted in a total of 216 deaths and 89 injuries and led to adverse social impacts. Therefore, it is essential to analyze the hazards associated with the deployment of tower cranes on construction sites to prevent such accidents. Tower cranes on construction sites consist of the following phases: installation, usage, climbing, and dismantling. According to the investigated accidents, the processes and constructors are not the same for the different construction phases. This results in the occurrence of different types of accidents during different phases. Moreover, hazards propagate between each phase and the propagation also affects the safety of the tower crane. Therefore, it is necessary to analyze the hazards associated with each construction phase and to explore the differences and interrelations between them. Furthermore, although different hazards may occur during different phases, previous works often focused on the usage phase . Some researchers have investigated dynamic structural performance, the interaction effects of multitower crane operation, the load, and the environment of the tower crane in the usage phase . In addition, the factors that impact safety during the installation (including climbing) and dismantling phases have been analyzed . However, there are few comparative studies on the multiple phases of tower crane mast section on the construction site. Equally important are the interrelationships between the hazards associated with different phases, which have not been investigated to date. In this paper, we address the aforementioned limitations in the literature. 2.2. Hazard Analysis The conventional hazard analysis methods include preliminary hazard analysis (PHA), system hazard analysis (SHA), fault tree analysis (FTA), event tree analysis (ETA), failure mode and effects analysis (FMEA), and failure mode effects and criticality analysis (FMECA) . With the development of system thinking, system analysis methods such as AcciMap, STAMP, FRAM, and the 2–4 Model have been increasingly utilized in contemporary studies to analyze hazards . According to one of the main tenets of system thinking, accidents are not caused by a series of linear events. Moreover, the relationships and interactions among the system elements should be considered . A complex system of accidents may be analyzed in detail to define the relationship between several factors at different organizational levels based on the system thinking principle . It is an important method for the analysis of the cause of accidents and safety hazard identification. These system thinking methods have different objectives. A summary of each method is presented in Table 1. These methods have also been compared in several investigations and it was concluded that the STAMP model results in a more comprehensive set of conclusions and is more reliable than other accident system analysis methods . The STAMP model involves various elements of a system, such as the individuals, the objects, the organizations, and the environment . The most important is that the STAMP model concerns the interactions of components and systems. As the tower crane safety system is a complex system with different components and phases, the STAMP model can contribute to the safety system analysis of the tower crane during different construction phases in this study. The personnel involved in the installation, climbing, and dismantling phases of the tower crane are primarily the same. The individuals and components involved in the climbing and dismantling phases are mostly the same as those of the installation phase. The differences are the system input and the working activities. The climbing process involves repeating certain steps of the installation process, namely the installation of the mast section. The dismantling process entails the inverse of the installation process. In consideration of the similar components and interactions in installation, climbing, and dismantling, the installation phase is selected to represent others to analyze internal system hazards. In the usage phase, the lifting system that consists of the tower crane and the lifting object is considered as the controlled object. The personnel in the usage phases mainly include the operator, rigger, and signalman. This is the process in which the operator uses the tower crane to lift the objects and is relatively different from the installation phase. Hazard analysis of the usage phase is therefore performed separately. Moreover, the hazards caused by the interaction among the phases are also analyzed separately. 4.2. System Analysis of Tower Crane with STAMP The STAMP model has good performance for system modeling and safety analysis and is broadly applied to accident analysis in astronautics, fire disasters, traffic incidents, and other industries . However, it is seldom applied to system hazard analysis in the construction industry, and the tower crane in particular. In the following, the STAMP method is adapted to model the installation and usage phases of the tower crane. Moreover, the proposed STPA method based on STAMP is applied to analyze hazards, namely, the unsafe behavior of humans and the unsafe state of the objects. Since the STAMP model is proposed in the context of system theory, the system model is considered as a hierarchical structure in which each layer imposes constraints on its lower layers. In the complete STAMP, several superstructures are involved, including Congress and Legislatures, Government Regulatory Agencies, and Companies. However, in this investigation, only hazards at the construction site are analyzed and superstructures such as government and enterprise are not considered. Thus, the core content of the STAMP model, i.e., the control loop and the process model, is utilized in this work (Figure 5). The interaction between components consists of the feedback of information and the control loops. A dynamic balance is also maintained by the system via the feedback and control of the components. The interactions between the system and the outside world include the process input, the process output, and the disturbance due to the outside world. Generally, the STAMP model is applied to system security analysis related to three aspects: component failure, component interaction failure, and external influence. There are few safety analysis methods that consider system inputs and outputs. They usually consider factors within the system. STAMP can analyze the interaction between phases via the input and output analysis. It is the main reason to choose this method in our research. The process input and output of STAMP can correspond to the IDEF0 interface. Meanwhile, the controls and mechanisms of IDEF0 can help establish the control model of STAMP. Thus, it is feasible to combine IDEF0 and STAMP in this study. This method can analyze the hazard transition between different phases. 4.2.1. Tower Crane STAMP Model for the Installation Phase Tower crane installation is a process that involves rigorous operation steps, short operation time, complicated procedures, and high professional requirements of the workers. Younes and Marzouk analyzed and listed the components required for the installation of the tower crane as the foundation, basic mast, main jib, counter jib, winding gear, and operating room. All these components constitute the tower crane and form the controlled process of the system. The installation processes include sensing, controlling, and execution in the vicinity of the tower crane and its components. The supervisor acts as a sensor and collects on-site information, including the status of the tower crane and the behavior of the operators, which is then fed back to the manager. The manager acts as a controller, which involves making decisions and sending out operational commands based on the installation scheme and the information received from the construction site. Based on the directives of the supervisor, the workers install the tower crane according to the installation scheme and the operational commands from the manager. The workers consist of an installer, operator, signalman, and rigger. The latter three can be the individuals that also operate the tower crane or those who use other lifting machinery to lift the tower crane components. Moreover, the completion of the previous phase, as the process input, affects the installation process. The external disturbance affects the system components, including the construction environment and the weather conditions. Likewise, the completion of the installation phase as the process output also affects the next phase. According to the previous analysis, the system control loop and the process model for the tower crane installation process are constructed using the STAMP method, as illustrated in Figure 6.
Дата Публикации: 26-01-22
A Simple Guide to Outdoor Shade Sails
Описание: A Simple Guide to Outdoor Shade Sails When the hot Australian summer months approach, spending time outdoors can be unpleasant without the proper shade and coverage With an outdoor shade sail, you'll enjoy a beautiful aesthetic and plenty of shade to keep yourself and your guests comfortable and cool. If you're considering a shade sail at home, read on to learn more about choosing and setting up these helpful home accessories. Do You Need Council Approval For Shade Sails? Depending on your location, you may need to obtain council approval before attaching a shade sail to your home or patio. In general, you likely won't need to obtain approval, but there could be some exceptions. For example, if your shade sail is exceptionally large, it's always best to ask beforehand. When you check with your local council in advance, you can avoid the worry or stress about potential issues in the future. Consult with your local council and ask them about size limits, design or style requirements, and more to ensure you're able to use a shade sail. Some councils require that triangle shade sail are no longer than 20 square meters in size and three meters in height. The sail should also not extend past your home's facade in most localities. Anything beyond those guidelines may require prior approval, so it's always best to confirm before you look for a shade sail for your home. If you're still not sure about sizing, feel free to contact us and we can help you work it out. What Size Outdoor Shade Sail do I Need? The size of your specific shade sail can vary depending on the shape and design that you want to install. Always ensure that the shade sail will provide you with ample coverage over an uncovered outdoor space, such as a concrete patio. You'll also want to make sure that you have enough room for maximum tensioning at the corners. Corners that are not taught can wear the shade sail down faster, and you also won't have a tight, secure fit which can cause the material to buckle. Make sure that the sail starts approximately 30 cm or 0.3 meters from each anchor point. If you're using multiple sails, there should be approximately a 45 cm or 0.45-meter gap between each one to keep them from rubbing together on windy days. As for the actual size of the sail itself, many options come in predetermined sizes and shapes such as triangles, squares, and rectangles. You can also opt for a custom-sized shade to meet your exact specifications. As long as the shade sail provides you with the coverage you need, you'll enjoy a cool, comfortable outdoor space. Measure your patio, deck, or porch to get the total dimensions before you decide on the size of your shade sail. Next, measure the distance between each attachment point to give you a clearer idea of the dimensions of the shade sail itself. The final size will be smaller than the total dimensions of your patio or deck since you'll need to keep that distance of 0.3 meters between each anchor point. How to Install a Shade Sail on a Deck Once you've determined the proper size of your outdoor shade sail, you'll need to decide on the location of each anchor point. To install a shade sail on a deck, you'll likely need to add posts to each corner to hold the sail in place. Posts should be made of thick wood and secured either by anchoring them to the deck itself or in holes filled with concrete (footings) on the ground. You may also use a large tree, fence post, or fascia depending on how your deck is oriented. Steel is another option for shade sail posts, but attaching them may require different parts. Once all of your mounting posts are secured, you'll need to add the hardware and make sure that each connection is facing toward the centre of your shade sail. Tighten each connection securely, then lay your rectangle shade sail out in the correct configuration or orientation. Begin by connection each corner of your shade sail to the fixing or anchor points. Hook each one up loosely, then slowly start to tension them using a strapping tensioner. As you tighten the sail, it will begin to look taught and rigid without any wrinkles, which means it's ready to be enjoyed. If your shade sail starts to sag, you can re-tighten it and bring it taught. One way to do this is by using a wire rope that runs through a pocket sewn in the perimeter of your sail. Simply pull the wire rope on each corner until the shade sail retightens and all sagging is removed. Another method to fix the issue is through height variation, where the sails are installed at alternating high and low anchor points. This creates something called a hyperbolic parabola. The opposing high points pull the sail up and out, while the lower points pull it down and out to keep everything tight. You may also use tensioning hardware such as turnbuckles or pulleys. This hardware should be included with the installation, and you can use it to retighten your sail whenever it sags or becomes loose. It's easy to get the comfort level you need to beat the Australian heat with an outdoor shade sail. Not only do these sails look beautiful, but they're an easy way to enjoy a cooler, shaded outdoor space any time of year. Make sure you install durable and secure anchor points before installing the shade sail. Select the proper size and hardware to install your sail and experience the ultimate in cool relaxation. To explore our range of products, be sure to visit our website or get in touch with us today for more information. Please note the contents of this post is information only and general in nature. If you require advice it is best to contact one of our shade specialists who can review your particular circumstances and then provide tailored advice according to your needs. A shade sail is a patio or deck covering made from durable outdoor fabric that provides protection from the sun. Shade sails are installed by stretching the fabric and using tension to affix the corners of the shade to mounting points (like a pergola, post, tree or wall). Shade sails are considered a more affordable and versatile alternative to a hard-structure roof. Shade sails come in various shapes, sizes and colors to fit any style backyard. Of course the main benefit of rectractable shade sail is sun protection. Most shade sails block between 90 to 95 percent of UV rays. There are some variations in UV absorption depending on the shade material’s weight color and the tightness of the weave, but the differences are typically less than five percent. But if you want maximum sun protection, know that heavier fabric, a tighter weave and darker colors generally block the most UV rays. You also might want your shade sail to block rain. Triangle sun shade sail are water resistant but not waterproof. A light sprinkle will roll off the shade, so it’s important to install it at an angle. In a heavy downpour, water will drip through the shade because it’s made from breathable woven fabric, which allows air to pass through and keep the shaded area cool. If you want full rain protection, look for a shade specifically categorized as waterproof. Skin cancer is among the most common cancers in light-skinned populations worldwide, and melanoma incidence has increased beyond that expected because of population growth and aging.1 There will be an estimated 87?110 cases of melanoma in the United States2 and 13?941 cases of melanoma in Australia3 in 2017. The primary risk factor for skin cancer, and the most avoidable, is exposure to solar ultraviolet (UV) radiation.4 To prevent skin cancer, individuals are advised to minimize UV exposure by staying in the shade.2,5 Permanent purpose-built shade can provide known amounts of reduction of UV exposure.6 Shade is part of the built environment,7 which according to social-ecological models8 can have direct effects on behaviors (e.g., increasing individuals shaded, providing a visible cue for sun protection, and enabling access to protection without planning9,10). Shade may attract high-risk individuals with unfavorable attitudes toward sun safety to use shade for maintaining comfortable body temperatures.11 Identifying environmental features amenable to change holds promise for improving population health7; however, evidence is limited mainly to cross-sectional or quasi-experimental designs with scant prospective trials.12 The prevalence of, trends in,13,14 and demographic and attitudinal correlates of shade use, along with the association of shade with temperature and sunburn incidence, have been reported.15–17 A study in Melbourne, Australia, secondary schools remains the only prospective randomized trial of purpose-built shade for sun protection9,11; it found that students used rather than avoided shade.11 The ability to improve sun protection by introducing shade needs to be tested in other locations and with adults. Public parks are popular for outdoor recreation, and shade is a desirable feature in parks.10 The present trial prospectively tested the effect of purpose-built shade on use of passive recreation areas (PRAs) in public parks (i.e., areas used for sitting or standing while socializing, preparing or eating a meal, watching or coaching sports, watching a concert, taking a class, or waiting, or areas where people stroll for sightseeing or while observing outdoor displays). We hypothesized that the introduction of triangle patio shade sail over PRAs would increase the use of the PRAs by park visitors compared with unshaded control PRAs (hypothesis 1). Social-ecological models suggest that built environmental features influence health risks through their interplay with the social environment. Australia has a longer history of comprehensive efforts to prevent skin cancer than the United States.18,19 Accordingly, stronger norms for sun safety in Australia than in the United States are expected, so we hypothesized that the increase in use of PRAs at shaded PRAs would be larger in Melbourne, Australia than in Denver, Colorado (hypothesis 2). We included a sample of 144 study PRAs, together with 144 comparison PRAs, in the trial in 2010 to 2014 in public parks in 4 municipalities in the Melbourne area (Manningham, Monash, Whittlesea, and Shire of Nillumbik) and Denver. Lists of public parks were provided by municipal staff, who designated some parks as ineligible because of location, amenities, or scheduled construction or renovation. Each park was audited by research staff to identify suitable PRAs.20 To be eligible, PRAs had to (1) be located in public parks containing at least 2 unshaded PRAs, (2) meet the definition of a PRA, and (3) be in full sun (i.e., no shade) at pretest; 1 of the 2 PRAs had to (4) contain a space where a shade sail could be constructed (i.e., free from underground or above ground obstructions, relatively level, and large enough to accommodate the shade sail), and (5) be approved by parks department staff for shade sail construction. We excluded PRAs when major construction or redevelopment was planned within the study period. We selected a single study PRA for full assessment and potential randomization to shade construction, which avoided bias because of clustering of PRAs within a park. We selected a second unshaded comparison PRA (if more than 1 was available, the PRA closest to the study PRA was selected) and assessed it as in use or not to provide a measure of how extensively PRAs were being used in the park. Trial Design and Procedures We conducted a stratified randomized pretest–posttest controlled design study by enrolling PRAs within public parks in 3 annual waves. After completion of the pretest assessment, parks were randomized by an independent biostatistician in an unequal 1:3 allocation ratio to treatment (shaded) versus control (unshaded) stratified by city, wave, and pretest use of the study PRA. The project biostatistician was blinded to conditions, and the independent biostatistician had no further role in the project. At treatment PRAs, shade sails were built to similar designs in both cities, with some variation to fit the site requirements and preference of the municipalities, between pretest and posttest assessments, by working with parks department staff and shade sail vendors. The PRAs were observed by trained observers for 30-minute periods on 4 weekend days during a 20-week period in the summer months (June to September in Denver; December to March in Melbourne) at pretest and posttest. Study condition was apparent to data collection staff at posttest because shade sails were impossible to conceal. Treatment Using Shade Sails Shade sails were designed to create attractive shade structures that maximized available shade from 11 am to 3 pm in summer and complied with local engineering, building, and planning codes.20 Shade cloth had a minimum ultraviolet protection factor (UPF) rating that reduced UV exposure by at least 94% and exceeded the minimum safety requirements for strength and resistance to light degradation. Project staff recommended that the shade sail be the largest size acceptable to the municipalities. Ownership of the shade sails was transferred to the municipalities once built and thereby compensated them for work on the project. Nearly all shade sails were completed before the following summer. Completion of a few shade sails was delayed until part way through the summer because of permitting and construction delays and unanticipated underground obstructions, so the posttest observations occurred after construction finished.
Дата Публикации: 26-01-22
Hooded Baby Towels – Softest Baby Bath Towels With Caps For Newborns Launched
Описание: Hooded Baby Towels – Softest Baby Bath Towels With Caps For Newborns Launched The company’s latest launch is part of its comprehensive range of ethically sourced and expertly crafted bedding and accessories for infants. Malabar Baby is committed to environmentally-friendly production practices, working closely with factories that have a vested interest in preserving water and recycling resources through the manufacturing processes. According to cotton.org, cotton was first grown, spun, and woven as far back as 3000 B.C in the Indus River Valley. While bamboo has been used for centuries to make paper and household goods, its commercial use in a cellulosic form for fabric production has only become widespread since the early 2000s. The baby hooded bath towel range is manufactured in sites across India and China. Meticulous research ensures only the highest-quality raw materials are sourced and used in production. Many of the designs feature traditional patterns or iconic architecture, rendered onto fabric using a block print process. The hooded towels measure 34 x 34 inches, allowing easy coverage for children up to 5 years of age. Malabar Baby’s stringent quality controls and durable fabrics ensure that all of its products will last for years. The block-printed towel range comes in a variety of styles and colors including the Miami Collection, which features a block-printed motif leaf print with a deep coral trim. The Erawan Collection has a honeycomb-style pattern with a mustard yellow-colored outer strip. All of the towels in the collection have a dual fabric construction with Indian cotton voile on one side and cotton terry on the other. A Bamboo Cotton Pom Pom Hooded towel is also available and offers a stretchy, silk-like feel without compromising strength or durability. The soft pom pom trim adds another unique design feature. A bathed little one, fresh out of the tub, is one of parenting’s precious moments, even if you end up wetter than intended. Investing in a good hooded towel will make drying your tot not only a simpler task, but you may even get a cuddle or two and avoid post-bath chills. We put a range of bamboo fiber baby hooded bath towel to the test with the help of our mini bathers. But what do you need to look for when making your fluffy choice? Naturally, the material in question will affect its ability to try your little one. The majority of towels on the market, particularly when using on a child’s delicate skin, will be a cotton terry towelling; a fabric woven with many protruding loops of thread which can absorb large amounts of water, but look out for variations of this such as a bamboo blend which is more absorbent. Bath time should be fun, so opt for a towel with an interesting character or animal design. The giggles and appeal will be worth it, plus it’ll encourage imaginative play once they’re running around the house. Many baby-specific hooded towels come at a standard size (75cm x 75cm), and while these are lovely for the early months, you may find your baby grows out of these at super speed and you’re soon after more material. Hop little bunny, or just give us plenty of cuddles in this adorable hooded towel from British brand Cuddledry. There’s plenty to interest a curious toddler, from the sweet star-detailed trim to the squidgy tail and floppy ears... our toddler tester didn’t want to take it off, and unlike others we tested it wouldn’t fall off because there’s a clever popper at the neck to keep it on, making it great for the beach too. It’s made from a blend of bamboo and cotton towelling, which washes incredibly well and maintains its softness. Known for its anti-bacterial properties, the brand claims that this material mix is 60 per cent more absorbent than using pure cotton on its own. Plus, any bamboo used (over half of the composition) has been sustainably grown and certified by Oekotex. We also found it was more absorbent once we’d washed it. It comes in two sizes, three to six years or one to three years, which is what we tested. It’s 60cm long from the neck to the bottom edge of the cotton baby hooded bath towel, but there’s 20cm height in the hood, and it’s 130cm wide, which means there’s more than enough material to dry them off, but not too much length that they’ll trip over when they’re on the move. You can trust our independent reviews. We may earn commission from some of the retailers, but we never allow this to influence selections, which are formed from real-world testing and expert advice. This revenue helps to fund journalism across The Independent. Belgian kids brand Trixie is big on sustainability. It exclusively uses organic cotton and ensures manufacturing is carefully thought out, but the brand is also passionate about sparking imagination so you can always expect fun animal characters and bright colours in its products. Made from organic terry cotton, Mrs Elephant is a welcome addition to bath time, we love the trunk detail and elephant ears on the hood, while the spotted splash print feels appropriate for post tub snuggles. There’s a matching bath mitt and dressing gown which is great for older siblings. We have to praise Mori on creating the embroidered bamboo fiber hooded bath towel of all those we tested, but then we expected nothing less from the British baby brand which produces such delightful baby essentials, typically made from its signature cotton and bamboo blend. This toddler towel however is made from 100 per cent organic micro cotton, which is a variety of cotton yarn laced into longer loops that gives towels extra absorbency and a luxurious feel. In fact, it claims to absorb 250 times more water than regular cotton, resulting in a fantastic hooded towel. Due to its size (100 x 63cm), it’s bigger and not square like a baby towel. Designed for those aged roughly one to three years, there’s plenty of material to wrap your little one up, and our toddler tester loved the bunny ears and tail at the back. This hooded towel is certainly the thickest of all those we tested and that’s thanks to the 550gsm Egyptian cotton towelling used, which of course makes it wonderfully soft too. The sizing is a little different too, as you choose from standard (90cm long) or jumbo (120cm long). We tested the the standard size which was perfect for our four-year-old reviewer, but it’s designed to be used until approximately seven years and we’re sure the quality would stand the test of time even using it from baby age. The hood has double the thickness, which is great if your child has a healthy head of hair. We love the simple ribbon detailing on the hood, and opted for a yellow superhero strip on a grey towel for our Batman fanatic which looks striking, but you can choose from sharks and dinosaurs to mermaids and unicorns. There’s a handy pop fastener in a star shape which turns it into a great poncho for the beach. A smidge larger than standard baby towels (80 x 80 cm), it’s surprising how much bigger this towel looks so it should be able to provide service for a little longer. Designed by Swedish brand Elodie, this hooded towel has been Oeko-Tex certified, which means it’s been tested to ensure it’s free from harmful substances. On the interior it’s made from a super soft, absorbent 100 per cent cotton terry cloth, with a velour material on the reverse, which is smooth for optimum cuddling comfort. We love the gold mustard colour, which seems to wash really well, and the bow is a cute playful addition. British designer Rachel Riley is known for her traditional baby and childrenswear, which has graced mini royals and celebrities globally. You can now add a touch of charm to your baby’s bathroom routine with one of her best-selling, cute-as-can-be grey bunny prints. Made from a premium 100 per cent cotton terry-towelling, it’s soft to the touch and washes exceptionally well. The beautiful grey bunny print looks adorable atop your baby’s face, and the towel is completed with a matching trim which makes this feel like a real luxury product. There are so many pieces in the layette that sometimes it gets confusing, even more so in the first pregnancy! But one of the indispensable items is the hooded towel. They are soft, nice pieces, like the white diapers we use for the mouth and shoulder. Then you ask yourself: so, what’s the difference between the towel and the diapers: and the answer is simple. The difference is in the size and usefulness of the pieces. Towels are bigger and are usually made of very thin, pleasant fabric to dry the baby’s skin without hurting it. It absorbs the water and protects the baby when we take him out of the bathtub to get to the room and, later, until we change him completely and get him ready! Especially in winter, prefer hooded towels that help dry the hair and protect the baby’s head. Another important thing: depending on the size of the hooded towel, your child can enjoy it up to the age of 3. Useful and long-lasting, right! Why should you buy a hooded bath towel? Baby towels are specifically designed with your child’s small body and sensitive skin in mind and are almost universally leaps and bounds cuter than regular adult-sized towels. They also often have hoods to help keep your baby’s head warm, especially during the early months of his life when he’s not able to regulate his body temperature. When it comes to drying your baby after his bath time, the type of towel you use is mostly dependent on what works better for you and your little one. If you do not have the budget, space, or inclination to purchase special towels that your child will grow out of in just a few years, regular towels can be used with care. Of course, if you take the cuteness factor into consideration then you’ll understand its almost impossible to resist a baby that looks like an elephant, giraffe, or panda! Temperature Regulating Hood The feature that makes hooded baby towels an essential for all mums-to-be and new mums is the hood design. Not only do they look lovely, but they also make sure your little one is safe and stays healthy after bathing. Regulating baby’s temperature is not only vital, but it’s also not as easy as you would think. You’ve just taken little one out the bath, which means they’re going to get cold quite soon, so you need them be dry and warm as soon as possible. As heat is lost through the head instantaneously, a hood is the ideal way to keep your baby at a safe temperature after bath time and during bed time. You’ll have peace of mind and will be able to unwind at the end of a busy day. Baby Feels Secure Newborns have just been welcomed into the world, so they need to feel secure at all times to be comfortable and content. Replicating the feeling of being inside the womb is a tried and tested way to make sure they’re happy, which you can do by snugly wrapping your little one up in a dyed bamboo fiber hooded bath towel. Experts have confirmed that babies are generally more placid if they feel reassured from similar womb feelings. You’ll Both Sleep Easier With a hooded towel you can cocoon them from head to toe to keep them feeling relaxed and restful. They’re an essential for every mum as they make looking after little one simple and give you the knowledge that you’ll be sleeping sooner rather than later. Sleeping well helps to promote better relationships between mum, baby and the rest of the family, which is so important to development. Protects Little One’s Skin When choosing a baby bath towel for your newborn, you should always decide on one crafted from natural & pure materials as their skin is very delicate and sensitive. Bacteria can be transferred easily, but with fabrics such as micro-cotton, they aren’t harboured like other materials so it is much safer for little one. Micro-cotton is also more sustainable, meaning it helps to protect the planet too. Absorbs and Dries Quickly As we already mentioned (but it really is super important) you must always keep baby’s head dry and warm, so micro-cotton truly is the perfect fabric for a baby towel. By absorbing 250x more moisture and drying in half the time than towels made from normal cotton, you’ll know that baby will be feeling fresh in the fastest time. Whether you’re a mum-to-be or a first-time mum, you can be safe in the knowledge that a hooded baby towel will be on your newborn essentials checklist. One step closer to feeling like the superhero your little one will always know you are!
Дата Публикации: 26-01-22
Understanding the Differences Between Base Oil Formulations
Описание: Understanding the Differences Between Base Oil Formulations All lubricants contain a base oil. It serves as the foundation of the lubricant before it is blended with additives or a thickener in the case of a grease. But how do you know which base oil is best? Trying to choose between mineral oils and synthetics can be confusing. This article will break down the complexity between base oil distillation equipment formulations so you can make the right decision for each application. Base Oil CategoriesLubricants can be categorized in many different ways. One of the most common classifications is by the constituent base oil: mineral, synthetic or vegetable. Mineral oil, which is derived from crude oil, can be produced to a range of qualities associated with the oil’s refining process. Synthetics are man-made through a synthesizing process and come in a number of formulations with unique properties for their intended purpose. Vegetable base oils, which are derived from plant oils, represent a very small percentage of lubricants and are used primarily for renewable and environmental interests. All base oils have characteristics that determine how they will hold up against a variety of lubrication challenges. For a mineral oil, the goal of the refining process is to optimize the resulting properties to produce a superior lubricant. For synthetically generated oils, the objective of the various formulations is to create a lubricant with properties that may not be achievable in a mineral oil. Whether mineral-based or synthetic-based, each waste engine oil to base oil machine is designed to have a specific application. Some of the most important base oil properties include the viscosity limitations and viscosity index, pour point, volatility, oxidation and thermal stability, aniline point (a measure of the base oil’s solvency toward other materials including additives), and hydrolytic stability (the lubricant’s resistance to chemical decomposition in the presence of water). The 20th century saw a number of improvements in the refining process used for mineral oils along with the introduction of a variety of synthetics. By the early 1990s, the American Petroleum Institute (API) had categorized all base oils into five groups, with the first three groups dedicated to mineral oils and the remaining two groups predominantly synthetic base oils. Groups I, II and III are all mineral oils with an increasing severity of the refining process. Group I base oils are created using the solvent-extraction or solvent-refining technology. This technology, which has been employed since the early days of mineral oil refining, aims to extract the undesirable components within the oil such as ring structures and aromatics. Group II base oils are produced using hydrogen gas in a process called hydrogenation or hydrotreating. The goal of this process is the same as for solvent-refining, but it is more effective in converting undesirable components like aromatics into desirable hydrocarbon structures. Group III base oils are made in much the same way as Group II mineral oils, except the hydrogenation process is coupled with high temperatures and high pressures. As a result, nearly all undesirable components within the oil are converted into desirable hydrocarbon structures. When comparing properties among the waste motor oil to base oil machine groups, you typically will see greater benefits with those that are more highly refined, including those with enhanced oxidation stability, thermal stability, viscosity index, pour point and higher operating temperatures. Of course, as the oil becomes more refined, some key weaknesses also occur, which can affect additive solubility and biodegradability. Group IV is dedicated to a single type of synthetic called polyalphaolefin (PAO). It is the most widely used synthetic base oil. PAOs are synthetically generated hydrocarbons with an olefinic tail formed through a polymerization process involving ethylene gas. The result is a structure that looks very much like the purest form of the mineral oils described in Group III. The advantages of PAOs over mineral oil include a higher viscosity index, excellent low- and high-temperature performance, superior oxidation stability, and lower volatility. However, these synthetic lubricants can also have deficiencies when it comes to additive solubility, lubricity, seal shrinkage and film strength. Much like mineral oils, PAOs are widely employed for lubricating applications and are often the preferred option when higher temperatures are expected. Group V is assigned to all other base oils, particularly synthetics. Some of the most common oils in this group include diesters, polyolesters, polyalkylene glycols, phosphate esters and silicones. Diester (dibasic acid ester) is manufactured through a reaction of dibasic acid with alcohol. The resulting properties can be adjusted based on the types of dibasic acid and alcohol used. Polyolester is made through a reaction of monobasic acid with a polyhydric alcohol. Much like diesters, the resulting properties will depend on these two constituent types. Polyalkylene glycol (PAG) is produced through a reaction involving ethylene or propylene oxides and alcohol to form various polymers. A number of PAG products are developed based on the oxide used, which will ultimately influence the base oil’s water solubility. Phosphate ester is created through a reaction of phosphoric acid and alcohol, while silicones are formulated to have a silicon-oxygen structure with organic chains attached. Each of these synthetics has specific strengths and weaknesses, as shown in the table above. In general, synthetics can provide greater benefits when it comes to properties influenced by extreme temperatures, such as oxidative and thermal stability, which can contribute to an extended service life. In situations where the lubricant will encounter cold startups or high operating temperatures, synthetics like PAOs typically will perform better than mineral oils. PAOs also exhibit improved characteristics in relation to demulsibility and hydrolytic stability, which influence the lubricant’s ability to handle water contamination. While PAOs are ideal for applications like engine oils, gear oils, bearing oils and other applications, mineral oil remains the predominant oil of choice due to its lower cost and reasonable service capabilities. With more than 90 percent usage in the industrial and automotive markets, mineral oil has solidified its place as the most common diesel distillation equipment in the majority of applications. Paraffinic mineral oil, which is represented in Groups I, II and III, can offer a higher viscosity index and a higher flash point in comparison to naphthenic mineral oils, which have lower pour points and better additive solvency. Even though naphthenic oil is mineral-based, it is considered a Group V oil because it does not satisfy the API’s qualifications for Group I, II and III. The unique characteristics of naphthenic mineral oils have often made them good lubricants for locomotive engine oils, refrigerant oils, compressor oils, transformer oils and process oils. Nevertheless, paraffinic oils continue to be the preferred option for high-temperature applications and when longer lubricant life is required. Ester-based synthetics, such as diesters and polyolesters, have advantages when it comes to biodegradability and miscibility with other oils. In fact, it is common for diesters and polyolesters to be mixed with PAOs during additive blending to help accept more significant additive packages. Diesters and polyolesters are often deployed as the waste oil filtration equipment for compressor fluids, high-temperature grease applications and even bearing or gear oils. Because they are known to perform well at higher temperatures, polyolesters have also been widely used for jet engine oils. Compared to other oils, polyalkylene glycols (PAGs) have a much higher viscosity index and good detergency, lubricity, and oxidative and thermal stability characteristics. PAGs can be formulated to be water soluble or insoluble and do not form deposits or residue during extreme operating conditions. PAGs can be employed in a number of applications, such as compressor oil, brake fluid, high-temperature chain oil, worm gear oil and metalworking fluid, as well as for applications with food-grade, biodegradability or fire-resistant requirements. Phosphate esters are primarily beneficial for fire-resistant applications. They are often utilized in hydraulic turbines and compressors due to their unique properties, including high ignition temperatures, oxidation stability and low vapor pressures. Silicone-based synthetics are infrequently used in industrial applications, but they can be advantageous in extremely high temperatures, when the lubricant will contact chemicals, or when exposed to radiation or oxygen. These synthetics have a very high viscosity index and are among the best options for oxidation and thermal stability because they are chemically inert. Selecting a Base Oil When you are choosing a base oil, there will be tradeoffs in the lubricant properties required for the application. A common example is viscosity. Higher viscosity provides adequate film strength, while lower viscosity offers low-temperature fluidity and lower energy consumption. In some cases, you may prefer to have a balance between the two so there isn’t too much of a compromise on either side. The chart on page 33 shows a comparison of the most essential properties for each base oil. Although it’s not necessarily important to understand the way in which the oil was manufactured, it is critical to know the available base oil options and the advantages and disadvantages they provide. Optimizing your lubricant selection can help minimize the opportunities for machine failure. While synthetics are justifiably more expensive than mineral oil, the cost of equipment failure is typically much higher. If cost is a key factor in your decision, be sure to choose wisely. The quality of feedstock used in base oil processing depends on the source of the crude oil. Moreover, the refinery is fed with various blends of crude oil to meet the demand of the refining products. These circumstances have caused changes of quality of the feedstock for the base oil production. Often the feedstock properties deviate from the original properties measured during the process design phase. To recalculate and remodel using first principal approaches requires significant costs due to the detailed material characterizations and several pilot-plant runs requirements. To perform all material characterization and pilot plant runs every time the refinery receives a different blend of crude oil will simply multiply the costs. Due to economic reasons, only selected lab characterizations are performed, and the base oil processing plant is operated reactively based on the feedback of the lab analysis of the turnbine oil filtration machine product. However, this reactive method leads to loss in production for several hours because of the residence time as well as time required to perform the lab analysis. Hence in this paper, an alternative method is studied to minimize the production loss by reacting proactively utilizing machine learning algorithms. Support Vector Regression (SVR), Decision Tree Regression (DTR), Random Forest Regression (RFR) and Extreme Gradient Boosting (XGBoost) models are developed and studied using historical data of the plant to predict the base oil product kinematic viscosity and viscosity index based on the feedstock qualities and the process operating conditions. The XGBoost model shows the most optimal and consistent performance during validation and a 6.5 months plant testing period. Subsequent deployment at our plant facility and product recovery analysis have shown that the prediction model has facilitated in reducing the production recovery period during product transition by 40%. Lubrication has been around since the invention of the wheel. Horse-drawn carts with wooden axles used meat greases, pine tar and various forms of animal fat as lubricants. Later, Linseed oil, originally a wood preserver, briefly replaced them as the primary lubrication agent. The earliest internal combustion engines used a product derived from refined crude oil. This was the beginning of the modern base oil. As IC engines became more complex and operated at higher speeds and temperatures, there was a need for better lubrication that could keep up with modern engines. So, additives were supplemented with the base oils. This combination had improved viscosity and protected the engines from wear, friction and resisted corrosion better. In modern cars, the base oil is still the primary catalyst for better engine performance. It forms 75%-80% of the finished product while the additives (10%-20%) and the viscosity index improver, which keeps the viscosity within a threshold at higher temperatures, make up the rest of the engine oil composition along with a vari We currently produce base oil by refining crude oil. Less than 1% of the standard 42-gallon barrel of crude oil is used to make lubricants—while the rest becomes gasoline, diesel and kerosene-type jet fuels. Base oils are classified by the American Petroleum Institute into five groups labeled I-V based on how the oils are processed. Group II oils are distinguished from less refined Group I by their higher purity, low levels of sulfur, nitrogen and aromatics, and superior oxidation stability. Pure Group II base oil is actually clear as water – it’s the additives that give finished motor oil its darker color. Group I oils are not suitable for applications requiring premium base oils, and their use is steadily declining. Group II oils can be substituted for many Group I applications. The base oils in these Groups (I and II) are typically referred to as “mineral conventional base oils.”Group III and IV base oils are high quality oils intended for use in high performance, low viscosity motor oils (such as 0W-20) in technically advanced automotive engines. Oils made from these base oils are classified as synthetics. They exhibit superior oxidation properties, support improved fuel economy, and may allow for extended drain intervals. In some parts of the world, Group IV – also known as “poly-alpha olefins” or PAOs – are considered to be the ONLY base oil that is truly synthetic. Automotive manufacturers and lubricant producers have used Groups I to V base oils depending on the application. Demanding applications, like high temperature performance in turbochargers, extreme cold temperature climates, long drain intervals, or even stop and go traffic conditions require a higher level of performance that can be achieved by selecting the “correct base oil” for the engine oil formulation. The key takeaway to remember about base oils is that they provide a large part of the performance characteristics of the finished oil formulation. Selecting the correct base oil type is critical in developing oils that will keep metal parts lubricated and equipment performing at its best. Base oils are only a part of the formulation in oils. Scientists and engineers need to also consider the impact of additive technology as well. The final performance of any lubricant is the combination of base oils, additives, and formulating knowledge for the application. Lubrication is as old as transportation. The horse-drawn wagons of olden times used leftover meat greases and tallow to lubricate wooden axles. Later, pine tar and hog fat were mixed together for use as a lubricant. Eventually, linseed oil, originally developed as a wood preservative, became the lubricant of choice for coachmen. Early automotive engines used an oil derived through the refining of crude oil, and the modern base oil was born. As engine technology advanced, intricate, fast-moving parts and high temperatures called for better lubrication. Additives were introduced to reduce friction and wear, increase viscosity and improve resistance to corrosion. Still, the base oil is the fundamental contributor to the finished product’s performance. In today’s passenger car motor oils, the base oil makes up 75% to 80% of the finished product. The additive package makes up another 10% to 20%. A viscosity index improver, which is added to reduce the degree to which viscosity will decrease due to high temperatures, takes up another 5% to 10%. Various inhibitors make up the remaining less than 1%. Base oil is produced through the refining of crude oil. A 42-gallon barrel of crude oil can actually yield nearly 45 gallons of petroleum products, but only about .4 gallons or less than 1% goes to making lubricants. The bulk goes to gasoline, diesel fuel and kerosene-type jet fuels. Base oils are classified by the American Petroleum Institute into five groups labeled I-V based on how the oils are processed. Group II oils are distinguished from less refined Group I by their higher purity, low levels of sulfur, nitrogen and aromatics, and superior oxidation stability. Pure Group II base oil is actually clear as water – it’s the additives that give finished motor oil its darker color. Group I oils are not suitable for applications requiring premium base oils, and their use is steadily declining. Group II oils can be substituted for many Group I applications. The base oils in these Groups (I and II) are typically referred to as “mineral conventional base oils.” Group III and IV base oils are high quality oils intended for use in high performance, low viscosity motor oils (such as 0W-20) in technically advanced automotive engines. Oils made from these base oils are classified as synthetics. They exhibit superior oxidation properties, support improved fuel economy, and may allow for extended drain intervals. In some parts of the world, Group IV – also known as “poly-alpha olefins” or PAOs – are considered to be the ONLY base oil that is truly synthetic. Automotive manufacturers and lubricant producers have used Groups I to V base oils depending on the application. Demanding applications, like high temperature performance in turbochargers, extreme cold temperature climates, long drain intervals, or even stop and go traffic conditions require a higher level of performance that can be achieved by selecting the “correct base oil” for the engine oil formulation.
Дата Публикации: 26-01-22
Comparison of Bond Strength of Metal and Ceramic Brackets
Описание: Comparison of Bond Strength of Metal and Ceramic Brackets Appropriate bond strength between bracket and tooth surface is one of the most important aspects of orthodontic treatments . Bonding of MIM monoblock metal bracket to enamel started in the mid 1960s . Only auto-polymerizing materials were available at the time. Bonding of orthodontic brackets with visible light-cure adhesives was first reported by Tavas and Watts . The light-cure adhesives were widely accepted due to their advantages in comparison with other chemical-cure adhesives. These advantages include high primary bond strength, better physical characteristics because of air inhibition phenomenon, user friendly application, extended working time for precise bracket placement and better removal of adhesive excess; but they have three major disadvantages namely being time-consuming, hindering light transmission and polymerization shrinkage . Since then, several new methods using different composites and light-curing units have been introduced for this purpose. The halogen lamp, also known as quartz halogen and tungsten halogen lamp, has been used as light-curing unit for many years , and is the most common source of visible blue light for dental applications. This lamp contains a blue filter to produce light of 400–500 nm wavelength . The wide spectrum of action, easy use and low-cost maintenance are the most favorable characteristics of halogen light curing systems . Despite their popularity, halogen light curing units have several disadvantages. For example, their light power output is 1% of the total electric energy consumed . Moreover, the lamp, reflector and filter wear out gradually . Halogen bulbs have a restricted useful lifetime of about 40–100 hours . The power density of light curing unit decreases with increase in distance. The other drawback of application of halogen bulbs is prolonged curing time . Over the past several years, other light sources such as xenon plasma arc, argon laser, and light-emitting diodes (LEDs) have been introduced in orthodontics . According to the results of previous studies , the shear bond strength (SBS) values of orthodontic brackets in curing with halogen lamps and plasma arc are the same but plasma light reduces curing time per tooth from 20–40 seconds to two seconds. Also, argon laser curing unit provides better SBS than halogen lights. But xenon plasma arc and argon laser are too expensive . Mills introduced LED light curing units as a polymerizing light source in 1995. At present, LED sources are among the most reliable light source categories for bracket bonding . Light cure resins set when irradiated with light at wavelengths of 460nm and 480nm in the blue end of visible spectrum with an intensity of 300mW/cm 2 . Also, LED is an effective transducer of electrical power into visible blue light and does not produce a lot of heat . The advantages of LED light curing units include lifetime of several thousand hours without significant degradation of light flux over time, resistant to shock and vibration and no need for filter to produce blue light . Moreover, LED light curing units consume little power and can be run on rechargeable batteries, allowing them to have a lightweight ergonomic design . The new LED curing units were launched simultaneously with the advancement of technology. First, these curing units generated light with an intensity of approximately 800–1000YmW/cm 2 , reducing the required light exposure time to 10 seconds . Currently, some high-power LED curing units are able to emit light radiation with intensity of 1600–2000YmW/cm 2 , allowing shorter exposure times of six seconds for metal brackets . In this study, the effect of conventional and high-power models of LED units on SBS of metal and ceramic brackets to tooth surfaces was evaluated. Forty sound bovine maxillary central incisors were used in this study. After extraction, the teeth were cleaned and immersed in 0.5% chloramine solution at 4°C for one week. They were divided into four groups of 10 teeth in each group. Next, teeth surfaces were etched with 37% phosphoric acid (Reliance; Itasca, IL, USA) for 20 seconds. After etching, the teeth were washed with water spray for approximately 10 seconds. The sample size (n=8 minimum samples for each group) was calculated with a power analysis in order to provide a statistical significance of alpha=0.05 and a standard deviation of 4.2 MPa using Minitab software. Sampling method in the study was consecutive. Bracket model and the type of light curing unit used for teeth were determined randomly. Group A: After checking correct conditioning of the enamel, metal brackets (American Orthodontics, Sheboygan, WI, USA) with a nominal base area of 11.3mm 2 were bonded with Transbond XT (3M ESPE, St. Paul, MN, USA), applying a uniform layer of adhesive primer on the etched enamel, and resin cement on the base of brackets. Brackets were placed in place and were pressed against the surface of the tooth. Excess cement was carefully removed with a dental probe, and the adhesive was high-power light-cured (2700mW/cm 2 ; Dentlight LLC, Plano, TX, USA) for four seconds (two seconds from mesial and two seconds from distal). MIM bondable metal bracket with a nominal base area of 15.1mm 2 were bonded to the etched enamel and other steps were performed similar to group A. The adhesive was high-power light-cured for three seconds (1.5 seconds from mesial and 1.5 seconds from distal). Group C: Metal brackets (American Orthodontics, Sheboygan, WI, USA) with a nominal base area of 11.3mm 2 were bonded to the etched enamel and other steps were performed similar to other groups. The adhesive was light-cured conventionally (600 mW/cm 2 ; Dr’s light, Good Doctors Co., Ltd., Incheon, South Korea) for 20 seconds (10 seconds from mesial and 10 seconds from distal). Group D: Ceramic brackets (American Orthodontics, Radiance Plus, Sheboygan, WI, USA) with a nominal base area of 15.1mm 2 were bonded to the etched enamel and other steps were performed similar to other groups. The adhesive was light-cured conventionally for 20 seconds (10 seconds from mesial and 10 seconds from distal). The samples were mounted in a metal mold containing auto-polymerizing acrylic resin and thermocycled for 2,500 cycles between 5–55°C for 20 seconds at each temperature with 20 seconds of transfer time. Rectangular wires were used to match the central alignment of teeth in acrylic resin. All samples were subjected to SBS test in a universal testing machine (7060; Zwick Roell, Ulm, Germany) at a crosshead speed of 3 mm/minute (Fig. 1). The results were obtained in kilogram-force, converted to Newtons and then to megapascals (MPa). After failure, the samples were observed under a stereomicroscope (SMZ 800; Nikon, Tokyo, Japan) at ×20 magnification to score the amount of remaining adhesive using the adhesive remnant index (ARI) : 0=No adhesive remained on the tooth; 1=Less than 50% of adhesive remained on the tooth; 2=50% or more of the adhesive remained on the tooth surface; 3= 100% of the adhesive remained on the tooth, with a distinct impression of bracket mesh, corresponding to failure at the bracket-adhesive interface. Data were statistically analyzed using SPSS version 22.0.0 (SPSS Inc., Chicago, IL, USA). The mean, standard deviation, minimum and maximum values of SBS of metal and ceramic brackets to tooth surfaces using two models of light-curing units were computed and reported. The SBS data were analyzed using one-way ANOVA, followed by Tukey’s post hoc test. Failure mode data were subjected to Kruskal-Wallis nonparametric test, followed by LSD post hoc test. Statistical significance was set at alpha=0.05. Objective. Clinical comparison of the survival rates between stainless steel and ceramic brackets over a 12-month period. Materials and Methods. The study involved 20 consecutive patients with diagnosed malocclusion that required two-arch fixed appliance treatment. The participants were randomly divided into two 10-member groups. Group 1 was treated with Abzil Agile (3M Unitek) stainless steel brackets; group 2 was treated with Radiance (American Orthodontics) monocrystalline ceramic brackets. All the sapphire brackets were bonded by the same operator. Over the next 12 months, all bracket failures were recorded with each appointment. The received data were processed statistically using the Mantel–Cox test, Kaplan–Meier method, and Cox hazard model. Results. A total of 381 brackets were bonded, 195 of which were metallic brackets and 186 were ceramic ones. In the 12-month observation period, there were 14 metal (7.2%) and 2 ceramic bracket (1.1%) failures. The overall failure rate was 4.2% (n?=?16). The majority of failures (14 brackets; 87.5%) occurred during the first 6 months of the experiment, 12 (83%) of which were metal brackets and 2 (100%) were ceramic brackets. The statistical analysis revealed significant differences between the groups (). Conclusions. Metal brackets demonstrated significantly higher failure rates than ceramic brackets for both 6- and 12-month observation periods (). The 6% difference between the brackets is clinically significant as it corresponds to one additional failure within 12 months. Orthodontic bracket is an essential element of fixed appliance. Its purpose is to transfer forces from the activated archwire to dentition to enable three-dimensional movement of teeth. Currently, stainless steel brackets are most commonly used at the orthodontic office due to their low cost, high corrosion resistance in the mouth, higher modulus of elasticity, and excellent biomechanical properties . Since stainless steel cannot bond chemically with orthodontic adhesives, these brackets have different types of gauge mesh bases for increasing the contact area with the adhesive. During bracket positioning, mesh eyelets are filled with orthodontic adhesive, and the subsequent polymerisation creates a micromechanical bond between the bracket and the adhesive . In addition to numerous advantages, stainless steel brackets also have some drawbacks, which are poor aesthetics and low biocompatibility. Both clinicians and patients are aware of this problem, which leads to increased interest in ceramic brackets due to their cosmetic properties and high biocompatibility . However, ceramic materials, just like stainless steel, do not form chemical compounds with acrylic and diacrylate orthodontic adhesives . Bases of ceramic brackets are usually formed with recesses or covered with additional ceramic particles to ensure a better mechanical interlock to the adhesive. Another method is to coat the ceramic base with silane to provide chemical adhesion . Bond strength of orthodontic brackets is an important factor which can influence the treatment with the use of fixed appliances. Bracket failures may potentially increase the total treatment time and financial costs of the therapy. The optimal bonding force between the bracket and enamel surface should be sufficient to enable a durable bracket position during treatment and to prevent the enamel from iatrogenic damage during the debonding procedure. Bond failures may be caused by numerous factors, including masticatory forces, forces produced by orthodontic appliances, aging of the orthodontic adhesives, mistakes during any step of bonding protocol, or some conservative dentistry therapies performed prior to bonding, such as topical fluoride varnish applications, or bleaching . The range of the desired bonding force has not been determined yet. On the basis of their in vitro study, Reynolds and von Fraunhofer stated that the minimum bond strength of 6–8?MPa is considered appropriate, whereas Bishara suggested that the bonding strength ought to exceed 13.5?MPa. Recently Gauge assumed that the ideal orthodontic adhesive should withstand forces over 20?MPa. The majority of the studies that evaluated the bond strength of zirconia brackets were carried out as in vitro experiments under ideal laboratory conditions that may not reflect all clinical conditions. In vitro experiments provide information about initial bond strength to the enamel but cannot serve as predictors of bracket survivability . Therefore, more accurate guidance on the clinical relevance of adhesion protocols is provided by in vivo tests, which assess the failure rate of the enamel-boding agent-bracket interface during treatment.
Дата Публикации: 26-01-22
Efficiency of Air Purifiers
Описание: Efficiency of Air Purifiers Infectious diseases caused by airborne bacteria and viruses are a major problem for both social and economic reasons. The significance of this phenomenon is particularly noticeable during the time of the coronavirus pandemic. One of the consequences is the increased interest in the air purifier (AP) market, which resulted in a significant increase in sales of these devices. In this study, we tested the efficiency of APs in removing bacterial air contamination in the educational context in the Upper Silesia region of Poland during the “cold season” of 2018/2019. During the 6 months of measuring microbiological air quality, an 18% decrease in the concentration of microbiological pollutants as a result of the action of the APs was recorded. Additionally, the results of the particle size distribution of the bacterial aerosols showed a reduction in the share of the respirable fraction (particles with an aerodynamic diameter below 3.3 μm) by an average of 20%. The dominance of gram-positive cocci in the indoor environment indicates that humans are the main source of most of the bacteria present in the building. We conclude that the use of APs may significantly decrease the level of concentration of microbiological air pollutants and reduce the negative health effects of indoor bioaerosols; however, further work that documents this phenomenon is needed. There is also limited evidence that these decreases result in improved cardiorespiratory health (Fisk, 2013; Morishita et al., 2015). APs usage has been associated with decreased blood pressure, reduced oxidative stress, reduced systemic inflammation, and enhanced lung function in a number of studies (Kelly and Fussell, 2019). The COVID-19 pandemic has forced a significant focus on indoor disinfection and air purification options. The most frequent applications are the local control of the source of pollution, disinfection of rooms and surfaces, and ventilation. The use of APs can be considered an additional complementary and preventive action in the spread of biological contamination. Adequate IAQ can be achieved mainly by reducing and constantly controlling the concentrations of harmful microorganisms in the air. The limited data on IAQ in Polish educational institutions and the lack of generalized standards for bioaerosol levels are the reason why the presented studies can increase awareness and focus more attention on IAQ issues. According to the Air Quality in Europe 2020 report published by the European Environment Agency (EEA), Poland has the European Union’s most polluted air. The report found that the concentration of both PM10 and PM2.5—two types of harmful airborne participate matter—was higher in Poland than in any other European Union (EU) country. The collected data can be used to assess the exposure of children and kindergarten staff in southern Silesia, which is one of the most polluted areas in the EU. The specific aims include (i) the evaluation of the impact of APs on the microbial IAQ, (ii) investigation of the concentration levels of culturable bacteria, (iii) determination of the size distributions with particular attention to the respirable fraction of bacterial aerosols, and (iv) examination of the bacterial community structure. Materials and Methods Sampling SitesThe study was carried out in a kindergarten located in Gliwice (50.324,666 N, 18.711,405 E). Gliwice is a typical example of a city located in the industrial region of Upper Silesia, Poland, with 178.186 thousand occupants. The surrounding area of the measurement point is characterized by compact building development. Buildings, roads, asphalt, etc., cover most of the surfaces in this part of the city. More detailed information about the main characteristics of the studied kindergarten in Gliwice is provided in Table 1. Air sampling was conducted during the “cold season,” from September 2018 to February 2019. The sampling was performed two times each week, with one sample taken outside the building and two indoors, one when the APs were turned off and the other after 60 min from turning the APs on (Table 2). Two sets of measurements were performed with the APs turned on. Samples were collected between 10:00 and 12:00 local time, in order to check the efficiency of the tested device. The kindergarten had natural ventilation and was insulated and windows were kept closed during the sampling. Epidemiologic studies indicate that indoor air pollution is correlated with morbidity caused by allergic diseases. We evaluated the effectiveness of reducing the levels of indoor fine particulate matter
Дата Публикации: 26-01-22
Useful Refrigerator Parts and Accessories
Описание: Useful Refrigerator Parts and Accessories Go to the grocery store. Pay the bills. Make dinner. Pack lunch. As you busily go about your day and check things off your to-do list, you probably give little thought to your . But maybe you should. With advancements in technology, there are parts and refrigerator accessories for your fridge that can make the rest of your daily chores a little easier. Want to cut down on your bill? Curious about how you can make your groceries and produce last longer? Need just a little more organization in your life? If so, these five fridge accessories might be just what you're looking for. Eating fresh fruits and is great for your health, but can be hard on your wallet, especially if you find yourself spending money on produce, only to throw it away when you find it brown and spoiled in your fridge. But that's when our next refrigerator accessory can help -- it's a crisper liner for your refrigerator's produce drawer. Not only does it reduce moisture to help your fruits and veggies last longer, it also provides a soft, cushiony surface that helps prevents bruising. Some are even made to resist to odor and mold as well, so your refrigerator will stay smelling fresh, too. Soda, water, juice, -- are beverages taking over your ? If so, you might want to invest in a beverage dispenser. These handy, compact refrigerator control board stack your drinks neatly, hold them in place and dole them out one at a time. Many are designed with a flat top, so you can stack other groceries on top. While can dispensers are probably the most popular variety, there are also ones designed to hold bottles, as well. And if you frequent tailgate parties, there's even on designed to be used as a tote. Not only does this version fit snuggly in your fridge, it also sports a handle for easy carrying to your next tailgate or picnic. And they're available in large and small sizes to fit your household's needs. Who hasn't gone to rummage through their only to find the door already open, and for who knows how long? Leaving the fridge door open too long can let out all of the cold air, which can spoil your food and add to your . But not if you have a refrigerator alarm. This helpful device will alert you if you leave your refrigerator door open for too long by mistake. Most alarms even allow you to set the specific amount of time that passes before the alarm sounds. So if you like to take your time browsing the contents of your fridge, no problem. You can still do so in peace without worrying about the constant beeping of the alarm. You can just set it to alert you if the door stays open for a longer amount of time. is getting a bad rap these days, but maybe for good reason. Not only does it add 1.5 million tons of waste to landfills each year, it's also expensive. If you want to help the environment and your wallet, consider installing a refrigerator . For a fraction of the cost you would spend on bottled water for a year, you can get clean, filtered water right out of your fridge. For about $30, you can buy a simple system that you can easily install yourself. And, since it's installed at the refrigerator's water line, it filters drinking water, as well as the water used by your icemaker. Once it's in place, you just need to change the filter about every six months for clean, great tasting water and ice. So now you've got nice , but what about your fridge's air? What's worse than having a tall glass of milk that tastes like last night's garlic chicken? If your refrigerator seems to hold on to food odors, forget about that box of . Instead, try installing an air filter. If you're willing to give up a little bit of precious space in your fridge, an air filter can keep those food odors at bay and have your fridge smelling clean for up to nine months. After that, simply change the filter for a new one for about $11. For just a few extra dollars, in addition to eliminating pesky odors, some air filters will even help control your refrigerator's humidity, which can keep your food fresher longer. Compressor is heart of the refrigerator and it is the washing machine spare parts which does the cooling by making changes in pressure. It runs by an electric motor and most of the electricity is consumed by the compressor. It is located back of the refrigerator. Without a compressor, refrigerant, condenser your refrigerator is just an almaara. So all manufactures give good warranty on compressor. While purchasing the refrigerator make sure you have many years of warranty on compressor. It is the most coldest chamber of fridge. You can make ice in this chamber or you can keep frozen meat as well. Best place to keep the ice cream as well. Digital display screen or Temperature Controller Most of the high end especially side by side refrigerators comes with digital display screen, where you can digitally see the temperature and configure the temperature easily. LG 581 LTR GC-B207GLQV Side By Side Refrigerator is one of such very good example. In the low end models there won't be digital display screen to configure the temperature in that case those models comes with a temperature controllers knob to set the temperature. It is not accurate as digital but will do some level of decent job. Refrigerator features and accessories Refrigerator voltage stabilizer Voltage stabilizer protects the refrigerator from voltage fluctuations. Say you have directly connected the refrigerator to the power input and in case of voltage fluctuations and power surges damages the electronic components of refrigerator. The solution is to connect the power input to stabilizer and output of stabilizer to the refrigerator. In this way stabilizer act as a hedge against the voltage fluctuations, protect the refrigerator and increase the lifetime of refrigerator. Before buying the refrigerator please see high end models provide in built stabilizer. The V-Guard VG 50 voltage stabilizer is the most popular one avilable in the market. Refrigerator stand Refrigerator stand makes the fridge elevated and makes you access the fridge easily. Apart from that being the fridge at height it is very easy to clean as well. Ergonomically well designed fridge makes your life better. Make sure the stand fits the measurements of existing refrigerator and can take the heavy load of your refrigerator weight. Few stand models have adjustable length and width to tackle measurement issues. Refrigerator Deodorizer Afraid to put non veg and vegetables in fridge because of smells. Have you faced situation where food smell attacks the room when you open fridge door. Refrigerator deodorizer is at your service to resolve the problem. Deodorizer absorbs the food smells and additionally controls the growth of bacteria. One quick home tip on absorbing smells -keep one slice of bread openly, it will absorb few smells of meat. Air tight refrigerator boxes and bottles Air tights boxes are great way to organize stuff in your refrigerator. Initially it is hailed as space optimizers and soon they are turned as food protectors from frostbites. Yes, when fruits and vegetables are exposed to direct cool air they get frostbites, kind of coldness marks that you can see. To avoid such issues even single door refrigerators comes with vegetables boxes and high end refrigerators comes with so many compartments to protect from frostbites. In case you have so much open space in the fridge this is the best way. Similar to boxes you can buy some bottles to keep the water cold. Most of themodels comes with bottle holders. Of Course high end models comes with water dispensers, but otherwise you can buy some fridge bottles to keep the water. Milano, Tupperware and Cello are few well known brands. Ice trays Basic single door refrigerator comes with couple of ice trays. High end refrigerators comes with ice dispensers. Say you have normal fridge and you have high requirements of ice then you can buy additional ice trays. Look for non breakable ice trays. Well designed ice trays take significantly less time to form the ice. Other spare parts are well know brands in ice tray manufacturing. Ice trays comes in many designs you can have fun choosing different style ice cubes. Refrigerator magnets Refrigerator magnets are decorative items to enrich your creativity and keep you memories. Say you have visited a tourist place like Simla you can buy refrigerator magnet showcasing Simla city and paste it on fridge door. It is magnet hence it directly sticks to fridge door and you can move around on the door easily. Not only that you can capture your special days like birthday and marriage anniversary and paste it on the door. There are many brands like Alchemy Chemicals, Alpha Industries, Barcelona, Bcreative, PosterGuy, meSleep, Thoughtroad, Marvel, Lion Souvenirs, Seven Rays. You can buy these fridge magnets online too. Not only that there are many online websites which sells such magnets exclusively like chumbak.com. There are many colorful and aesthetically pleasing magnets avilabe as well. Water and ice dispensers Few models of Side-by-side, double door and triple door refrigerators comes with water dispensers. Water dispensers enables you to drink water without even opening the refrigerator door. It is very nice to have feature. Videocon 604 Ltr VPL60ZPS Side by Side Refrigerator is one of such good refrigerator with water dispenser. Removable anti fungal gasket Removable anti fungal gasket is amazing feature. As the name suggest it is removable so you can remove and clean them easily. The anti fungal function make sure fungal and bacteria do not grow in the refrigerator It's the smart way to select the products without reading buying guides defrost thermostat Make the best purchase decision with the help of Refrigerator selector.
Дата Публикации: 26-01-22
Engineering Essentials: Types of Hydraulic Hose
Описание: Engineering Essentials: Types of Hydraulic Hose To say that hose is an important part of a hydraulic system is a huge understatement. The flexibility of hose enables components to be positioned in the most efficient or convenient places, because the hose has the ability to bend around corners, through tight spaces, or across long distances. Yet these days, there seems to be as many different types of hose as there are telephone long-distance carriers. How does a designer tell one from the other? Isn't there an easy way to choose or compare hoses? The SAE standards SAE answers those questions with its J517 hydraulic hose standard. This LPG hose standard serves as the most popular benchmark in the realm of industrial hydraulics today. More specifically, J517 is a set of guidelines that applies to the current SAE 100R series of hoses. Currently, 16 such hose styles exist, and they are designated as 100R1 through 100R16 (see descriptions, pages A105 and 106). Each of the styles must meet a set of dimensional and performance characteristics as set forth by SAE. However, SAE issues no approval source lists, certification, or letters of approval-conformance to these standards by manufacturers is strictly voluntary. In short, the standards only Hydraulic hose construction Modern hydraulic hose typically consists of at least three parts: an inner tube that carries the fluid, a reinforcement layer, and a protective outer layer. The inner tube must have some flexibility and needs to be compatible with the type of fluid it will carry. Commonly used compounds include synthetic rubber, thermoplastics, and PTFE, sometimes called Teflon. The reinforcement layer consists of one or more sheaths of braided wire, spiral-wound wire, or textile yarn. The outer layer is often weather-, oil-, or abrasion-resistant, depending upon the type of environment the hose is designed for. Not surprisingly, hydraulic hoses have a finite life. Proper sizing and use of the correct type of TPR LPG hose will certainly extend the life of a hose assembly, but there are many different factors that affect a hose's lifespan. SAE identifies some of the worst offenses as: flexing the hose to less than the specified minimum bend radius twisting, pulling, kinking, crushing, or abrading the hose operating the hydraulic system above maximum or below minimum temperature exposing the hose to rapid or transient rises (surges) in pressure above the maximum operating pressure, and intermixing hose, fittings, or assembly equipment not recommended as compatible by the manufacturer or not following the manufacturer's instructions for fabricating hose assemblies. Selecting the proper hose Here are seven recommended steps the system designer should follow during the hose and coupling selection process. To help determine the proper hose for an application, use the acronym STAMPED - from Size, Temperature, Application, Materials, Pressure, Ends, and Delivery. Here is what to consider in each area: Size - In order to select the proper hose size for replacement, it is important to measure the inside and natural gas hose diameters exactly using a precision-engineered caliper, as well as the length of the hose. Hose OD is particularly important when hose-support clamps are used or when hoses are routed through bulkheads. Check individual hose specification tables for ODs in suppliers' catalogs. When replacing a hose assembly, always cut the new hose the same length as the one being removed. Moving components of the equipment may pinch or even sever too long a hose. If the replacement hose is too short, pressure may cause the hose to contract and be stretched, leading to reduced service life. Changes in hose length when pressurized range between +2% to 4% while hydraulic mechanisms are in operation. Allow for possible shortening of the hose during operation by making the hose lengths slightly longer than the actual distance between the two connections. Temperature - All hoses are rated with a maximum working temperature ranging from 200° to 300° F based on the fluid temperature. Exposure to continuous high temperatures can lead to hoses losing their flexibility. Failure to use hydraulic oil with the proper viscosity to hold up under high temperatures can accelerate this problem. Always follow the hose manufacturer's recommendations. Exceeding these temperature recommendations can reduce hose life by as much as 80%. Depending on materials used, acceptable temperatures may range from -65° F (Hytrel and winterized rubber compounds) to 400° F (PTFE). External temperatures become a factor when hoses are exposed to a turbo manifold or some other heat source. When hoses are exposed to high external and internal temperatures concurrently, there will be a considerable reduction in hose service life. Insulating sleeves can help protect hose from hot equipment parts and other high temperature sources that are potentially hazardous. In these situations, an additional barrier is usually required to shield hydraulic fluid from a potential source of ignition. Application - Will the selected hose meet bend radius requirements? This refers to the minimum bend radius (usually in inches) that a hydraulic hose must meet. Exceeding this bend radius (using a radius smaller than recommended) is likely to injure the hose reinforcement and reduce hose life. Route high-pressure hydraulic lines parallel to machine contours whenever possible. This practice can help save money by reducing line lengths and minimizing the number of hard-angle, flow-restricting bends. Such routing also can protect lines from external damage and promote easier servicing. Materials - It is mandatory to consult a compatibility chart to check that the tube compound is compatible with the fluid used in the system. Elevated temperature, fluid contamination, and concentration will affect the chemical compatibility of the tube and fluid. Most hydraulic hoses are compatible with petroleum-based oils. Note that new readily biodegradeable or green fluids may present a problem for some csa natural gas hose. Pressure capabilities - Hose working pressure must always be chosen so that it is greater than or equal to the maximum system pressure, including pressure spikes. Pressure spikes greater than the published working pressure will significantly shorten hose life. Hose ends - The coupling-to-hose mechanical interface must be compatible with the hose selected. The proper mating thread end must be chosen so that connection of the mating components will result in leak-free sealing. There are two general categories of couplings to connect most types of hose: the permanent type (used primarily by equipment manufacturers, large-scale rebuilders, and maintenance shops) and the field-attachable type. Permanently attached couplings are cold-formed onto the hose with powered machinery. They are available for most rubber and thermoplastic hoses and offer a wide range of dependable connections at low cost. Assemblies made in the field with portable machines are relatively simple; these machines are economical and easy to operate. In most cases, it is not necessary to skive the cover. These couplings are less complicated to install than other types. Field-attachable couplings are classified as screw-together and clamp-type. The screw-together coupling attaches to the hose by turning the outer coupling shell over the outside diameter of the hose. The coupling insert is then screwed into the coupling shell. A clamp-type coupling has a 2-piece outer shell that clamps onto the hose OD with either two or four bolts and nuts. This hose should be used in low pressure and vacuum applications, with petroleum- and water-based hydraulic fluids, within a temperature range from -40° to 100° C. It is constructed with an inner tube of oil-resistant synthetic rubber, a reinforcement consisting of a ply, or plies, of woven or braided textile fibers with a suitable spiral of body wire, and an oil- and weather-resistant synthetic rubber cover. This hose should be used with petroleum- and water-based hydraulic fluids, within a temperature range from -40° to 100° C. It is constructed with an inner tube of oil-resistant synthetic rubber reinforced with two textile braids separated by a high-tensile-strength steel-wire braid. All of the braids are impregnated with an oil- and mildew-resistant synthetic rubber compound. This high-pressure csa natural gas hose kit should be used with synthetic, petroleum- and water-based hydraulic fluids within a temperature range from -40° to 93° C. It consists of a thermoplastic inner tube resistant to hydraulic fluids with suitable synthetic-fiber reinforcement and a hydraulic fluid- and weather-resistant thermoplastic cover. Nonconductive 100R8 is identified with an orange cover and appropriate lay line. Its pressure capacity is similar to that of 100R2. This hose should be used with petroleum- and water-based hydraulic fluids within a temperature range from -40° to 100° C. It consists of an inner tube of oil-resistant synthetic rubber, six spiral plies of heavy wire wrapped in alternating directions, and an oil- and weather-resistant synthetic rubber cover. A ply, or braid, of suitable material may be used over the inner tube and/or over the wire reinforcement to anchor the synthetic rubber to the wire. In either case, the coupling has limited potential for reuse because the threads distort during attachment. To ensure the correct-size coupling is used when replacing an assembly, the number of threads per inch and thread diameter of the original coupling must be determined. Thread pitch gages are available for identifying the number of threads per inch. A caliper can measure both inside and outside dimensions of the threads. ODs are measured on male couplings, while IDs are measured on female couplings. In most situations, the only differences between an SAE coupling and an imported coupling are the thread configuration and the seat angle. International thread ends can be metric, measured in mm, but also include BSP (British Standard Pipe) threads, which are measured in inches. Knowing the country of origin provides a clue as to what type of thread end is used. DIN (Deutsche Industrial Norme) fittings began in Germany and now are found throughout Europe, while BSP is found on British equipment. Japanese Komatsu machinery uses Komatsu fittings with metric threads, while other Japanese equipment most likely uses JIS (Japanese Industrial StandardBSP threads), or, in some cases, BSP with straight or tapered threads. Delivery - How available is the product? Is it unique? How soon can it be delivered to the distributor or end user? It may be preferable to consider several options to maximize flexibility and avoid the delays that can result from relying on components that are unavailable or in short supply.
Дата Публикации: 26-01-22
How Do Air Compressors Work?
Описание: How Do Air Compressors Work? Air compressors are an invaluable tool for both industrial work and DIY at home, and there are several different types to choose from depending on the job you need doing. Air compressors have a number of uses, such as to fill gas cylinders for industrial purposes and scuba diving, to create the power needed to run pneumatic tools and spray guns, for pumping up automotive tyres, and within heating and air conditioning systems. As we’ve touched on here, there are myriad uses for air compressors both in commercial and domestic environments. Within the category of air guns, there are several types, each of which is suitable for a different job. We’ve compiled a guide to all the major types of air compressor, how they work and how they differentiate from one another. Whether you’re an engineering manager or in charge of facilities for your company, being informed about how oil free air compressor function and what they’re used for is handy and can help you make the proper decisions for your business and industry. Get all the information you need to know about air compressors, complete with the infographic below, with our comprehensive guide. We’ll address the benefits of using premium air compressors in your industry, as well as the questions of ‘what are compressors?’ and ‘how does a compressor work?’, covering all the essentials in one convenient place. Since their invention in the 19th Century, mechanical, automated air compressors have continued to be one of the most widely used tools in industrial settings. Air compressors provide a continuous stream of power that is safer and cooler than many other forms of energy. For many industries, such as metal work and mining environments, air compressors are an absolutely essential tool. After the basic utilities of water, gas and electric, compressed air is actually considered to be the fourth utility. Air compressors are also an affordable choice of tool for many manufacturing jobs, as they are durable, and high quality types require minimal maintenance and repairs. Between the two main categories of compressor – the scroll (piston) compressor and the rotary screw (reciprocating) compressor, you have a tool for every type of industrial and commercial setting, as well as various domestic uses. Single Phase vs. Dual Phase Compressors The most common types of air compressors are single and dual phase, both of which operate in the same fundamental way, only dual phase has one more step involved in the compression process. In a single phase compressor, there is one chamber and the air is compressed a single time; in a dual phase, there are two chambers and the air is put through compression twice. Be careful not to confuse single and dual phase compressors with the number of cylinders a compressor has. Both types of compressor use two cylinders; one-cylinder compressors are less common, because air balancing is made easier with two cylinders. The difference between single and dual stage compressors is that in the former the cylinders are both the same size; in the latter they are different sizes. How Do Single and Dual Phase Compressors Operate? Single phase compressors, also referred to as piston silent oil free air compressor, works in a relatively simple and straightforward way. First, air is drawn into the cylinder; from here, it is compressed once by a single piston movement within a vacuum system. The power of this compression is measured in PSI (pounds per square inch) or Bar – the higher the PSI/Bar, the more power the compressor has. In a single stage air compressor, the air is typically compressed at a rate of around 120 PSI (8.2 Bar). After the air has been compressed, it is sent into the storage tank from where it is dispelled into various tools as a source of energy. Dual phase compressors operate the same way, except there are two stages of compression, rather than just one. After the first round of compression, the air is sent into a second chamber, where it is compressed for the second time, at a rate of around 175 PSI (12.1 Bar). After this, the air is sent to a storage tank in which it is cooled down and ready for application. Both types of compressor are typically powered by either an electric or petrol motor, which drives the piston and causes the compression to happen. Single Phase and Dual Phase Applications Both function in fundamentally the same way and can be used for similar tasks, such as operating a pneumatic drill or other high-powered tools such as those found in a manufacturing plant. Single phase compressors tend to be used within domestic settings for smaller workshop jobs done with handheld tools, such as woodwork, metal work and general DIY. Dual phase compressors, on the other hand, are better for larger scale work in operations such as operations needed in vehicle repair shops, pressing factories and other plants where parts are manufactured. Oil-Free vs. Oil-lubricated Air Compressors Another way to compare air compressors is to look at whether they use oil or not – there are oil-free and oil-based / lubricated compressors and both are suited to slightly different jobs. For the air to be drawn into the chamber safely and effectively, the piston needs to be in top working order. To work properly, the piston must be lubricated with oil. With regards to lubrication, there are two main types of compressor to choose from: oil-free and oil-based. The oil is used on the cylinder to ensure the compression goes smoothly. The Difference Between Oil-Free and Oil-Based Compressors Oil-free ac oil free air compressor already have a lubricated cylinder (often with a non-stick material such as Teflon) and therefore require no further maintenance to work properly. Oil-based compressors require oil to be added to the piston area and changed regularly. Just how often you need to change the oil will be outlined in the manufacturer’s manual that came with your compressor. On the whole, oil-free compressors tend to weigh a lot less than oil-based compressors, as not only do they not have the weight of the oil, but they are more compact machines, requiring fewer separate parts to make them work. Oil-free compressors, being less complex in design, also tend to be more affordable than oil-based compressors. However, although they’re more weighty and expensive, oil-based compressors have their benefits. For one thing, they are strong and durable, and usually have a longer lifespan than their oil-free counterparts. This is usually because over time the greasing material (usually Teflon) begins to wear down and lose its lubrication abilities. Another important factor that should be considered when choosing between an oil-free and oil-based compressor is that the oil-less version tends to heat up faster and to a higher temperature than those which use oil. Compressors without oil also make a lot more noise than those with, so if you want a less noisy workplace, this is a factor to consider too. Oil-Free and Oil-based Compressor Applications Oil-free compressors are a great option for those in need of a lightweight, low maintenance tool for home use. Oil-based compressors are better suited to heavy duty jobs and commercial and industrial use, as although they’re generally heavier and require more maintenance, they are also more robust and versatile. For industrial purposes and extensive, day-long use, oil-based compressors are by far the best option. If you’re looking to invest in quality compressors for your business, opting for oil-based machines is almost certainly the best route to take. Within an industrial or commercial setting, there are numerous uses for oil-based air compressors, including: Vehicle painting and repairs Sanding and woodwork Creating snow banks in ski centres Pneumatic construction tools such as nail guns Air cleaning tools such as blowguns Oil-free compressors can be used for domestic use, such as small-scale jobs like blowing up balloons, home workshop and DIY jobs. They are also largely used in industries where there is a need to avoid the product or consumer coming into contact with oil: food and beverage, pharmaceutical and dental, for example. In these sensitive applications, the consequences of having oil contamination in the air are too high to risk, so having an oil free compressor is a must. There is compressed air quality testing from the International Organisation for Standardisation (ISO) which oil-free technology can help you achieve. Fixed vs. Variable Air Compressors Another factor to consider when choosing the right type of air compressor for your industry is whether they’re equipped with fixed or variable speed. Let’s take a closer look at what these different types of compressor can do for you. The main difference between low noise oil free air compressor that use a fixed speed system and those that use variable speed is the manner in which the motor gets its power. The compression element is much the same across all machines, but the way the motor operates has an effect on the usability, efficiency and lifespan of the machine. How Do VSD Compressors Work? Variable speed compressors (often referred to as VSD (Variable Speed Drive) or VFD (Variable Frequency Drive) – compressors) operates by automatically adjusting the motor speed in accordance with the demand for air. This happens through a system that converts voltage from the mains power supply into a variable frequency. Power is drawn through a converter, inside which it is converted twice. First, it converts AC power into DC power using diodes. A capacitor then cleans the AC, and then converts it to DC using a transistor, which acts as switches. These switches control the frequency of power sent to the motor, which in turn controls the speed of the motor. A VSD air compressor contains this technology, allowing the speed of the motor and the amount of air compression used to be closely controlled. There are pros and cons to both variable speed compressors and their counterpart, fixed speed compressors – check them out below to decide which one is best for your industry. Fixed Speed Pros and Cons Fixed speed air compressors send a consistent, continuous stream of power into the motor, which gives you a reliable frequency in all your air compression jobs. The initial cost of fixed speed compressors is lower than that of variable speed compressors, is easier and cheaper to maintain and is a must-have within industries where the power demand is continuous. This type of compressor is, however, less efficient than its variable speed counterpart. It is also less efficient at saving energy, and can therefore be more expensive to run, with fewer incentives available too. Variable Speed Pros and Cons Variable speed air compressors allow you to control the voltage and the frequency of the power in the motor, giving the user more agency over the tool. This type of compressor is more efficient when it comes to power usage, as you can easily control your output and only use what you need. Many industries will find that this type of air compressor is ideal, as it can be used in line with the demand of the job. When less power is needed, you can easily adjust the speed of the compressor, saving money and protecting the environment at the same time. The downsides of a variable speed compressor are that there is a higher initial capital cost to pay, and maintenance and repairs are more expensive too. They are als Piston Compressors, Scroll Compressors & Rotary Screw Compressors So far in this article, all the compressors mentioned are operated using pistons, which is a generic system for one type of compressor – the scroll compressor, also known as a reciprocating air compressor. The other type is the rotary screw compressor, which doesn’t have pistons and operates in a slightly different way. Here’s a quick overview of how scroll compressors and rotary screw / reciprocating compressors work, and what the unique benefits are of each of them. Scroll Compressors Scroll compressors are a type of piston compressor, and are also called reciprocating compressors. These are the most common type of air compressor, due to affordability and general availability. But how does a reciprocating air compressor work? The piston system works by having a piston travel downwards, decreasing the pressure inside its internal cylinder through the creation of a vacuum. The sudden change in pressure causes the door of the cylinder to be forced open, and draw air in. When the piston travels up again, the air is forced out of the cylinder at a much higher pressure point. This continues in a reciprocating, ‘scroll’ pattern, hence its name. One complaint often heard around air compressors is that some of them are noisy due to friction and a power source, which can be distracting and inconvenient for both commercial and domestic use. The industry has risen to deal with these complaints however, and there are several low noise air compressors to choose from, offering a decibel rating of around 40 dB. 40 dB is considered low noise; 60 dB is considered the safest decibel level for compressors; anything over 85 dB could cause long-lasting damage to your hearing, and you should avoid being exposed to this level for extended periods of time. Low noise and silent air compressors are available in both oil-free and oil-based versions, so just how is the silencing effect achieved? As well as choosing compressors with low decibel levels, one aspect of this technology that makes a big difference is the inclusion of an acoustic chamber for containing the noise. Another tip is to opt for electric-powered compressors, rather than gas-powered, as the former type of power source makes for a quieter machine. The Bottom Line Which type of air compressor you go for depends on a variety of factors. You first need to consider what application the compressors will be used for? Do you need it for continuous, ongoing use in large industrial machinery, or will it be used sporadically? Your answers to these questions will help you decide on whether to go for variable or fixed speed compressors. Another question that you must factor into your decision is: how much do you want to spend? Remember that the initial price of a quality compressor is not the only expense associated with a compressor; consider also the cost of the power needed to run the machine, plus any related ongoing maintenance and repair costs. How much time and energy will investing in high quality compressors save your company? These are all important calculations that should be made before making your decision.
Дата Публикации: 26-01-22