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- Создано: 05-01-22
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The Benefits and Application of Steel Pipes
Описание: The Benefits and Application of Steel Pipes Steel pipes are the most commonly used pipes in water supply systems. They are also used in pipelines for natural gas, and sewerage systems. Although comparatively expensive to other pipes, they hold the advantage of being able to withstand high pressures and are available in more convenient lengths, and can also be welded easily, thereby resulting in lower installation and transportation costs. These types of pipes are highly efficient and can be used in small diameters as needed and are 100% recyclable compared to other materials. The pipes can further be melted down and turned into other usable material in industry. Furthermore, the high strength of these pipes and resistance to damage caused by human errors, tree roots, and extreme weather conditions make these pipes the ideal choice for most water and sewerage supply systems. The disadvantages of steel pipes include thermal conductivity, which is very poor as there is a difference in heat transfer. These types of pipes are usually bonded with aluminum or copper to increase thermal conductivity and improve heat transfer. Cost is another issue, as these pipes are expensive and this is guided by the misconception of being a one-time purchase. However, Carbon steel pipes are difficult to fabricate and lack the malleable qualities that other materials have, therefore repairs and replacements of steel pipes are extra difficult. Steel pipe is required in the majority of oil and gas production and pipeline applications. ASME A53 and A106 and API 5L seamless, electric resistance welding (ERW), and submerged arc welding (SAW) steel pipe are commercially available and most commonly used in pipeline systems. PVC, fiberglass, polypropylene, and other materials may be used in low-pressure and utility applications. ASME B31.4 and B31.8 allow the use of alternate materials in very restricted applications. Seamless pipe is seldom used in pipeline applications because of the higher cost and limited availability. From a design and regulatory perspective, pipe made with ERW and SAW seams is equivalent to seamless pipe and is less costly. Note: This is not true for piping systems designed in accordance with ASME B31.3. For high-pressure pipeline, high-grade pipe, such as API 5L grades X42, X52, X60, and X65, is selected because much thinner wall pipe can be used, which significantly reduces pipe costs. Construction cost savings also are realized, as the welding time is reduced and material shipping/handling costs are reduced. Steel pipe is normally used for pipelines operating at a pressure of 100 psig or more. Steel pipe withstands high pressures, is durable, and has a long operating life cycle. Fiberglass, PVC, or high-density polyethylene (HDPE) pipe is used in certain instances for low-pressure gas gathering pipelines. Components of the pipeline include the following: pipes, valves, fittings, and equipment such as metering, pumps, and compressors. In this book, we are concerned only with transporting hydrocarbons such as natural gas, refined petroleum products, crude oil, and liquefied petroleum gas in steel pipelines. Therefore, we will not deal with materials such as PVC pipe. Hot rolled steel pipe is generally used aboveground for firewater lines. Underground piping systems can be constructed of steel, cement-lined steel, or high-density polyethylene (HDPE). Concrete is sometimes used but is seldom economical except in large diameters. HDPE does not corrode, resists accumulation of scale, and is very ductile and lightweight. But, because it fails when heated, it can only be used in buried installations, where it is also protected from mechanical damage and radiant heat. High-performance butterfly valves and gate valves are recommended for block valves in firewater distribution systems. They should provide reasonably tight shutoff and use sealing materials that do not swell or deteriorate with age. Any valve that may be buried, and that may therefore not receive frequent maintenance, should be very durable. Steel pipe should be used aboveground for firewater lines. Underground piping systems can be constructed of steel, cement-lined steel, or high-density polyethylene (HDPE). Concrete is sometimes used but is seldom economical except in large diameters. HDPE does not corrode, resists accumulation of scale, and is very ductile and lightweight. Because it fails when heated, HDPE pipe can only be used in buried installations. Burial also provides protection from mechanical damage. Layout The topic of equipment and piping layout is discussed in Chapter 11. Issues to do with the layout of a firewater system are described below. In climates where freezing does not occur, above-ground installation of steel firewater distribution lines has the advantages of low first cost and ease of inspection and repair. In cold climates, distribution lines should be buried below the frost line. When possible, firewater mains should be arranged in loops around process facility and tank farms. Shutoff valves should be located to allow isolation of system segments for maintenance while still providing water for all facilities. The minimum water rate with a section of pipe out of service should be at least 60% of the design rate at design pressure for that area. A firewater header should be provided in each process facility area to serve hose stations. Steel pipes have various advantages for your next industrial or residential project. Steel tubing is used in a variety of industries, from industrial manufacturing to sculpture. One of the applications for steel tube is in plumbing, where it is used to replace traditional plastic pipes with stainless steel pipes. Stainless steel piping is more expensive than plastic piping, but it has a number of advantages over the latter. Steel pipe buyers consider these advantages - ANTI-STAIN AND ANTI-CORROSION Corrosion is the number one adversary of metal piping. The exterior of iron, steel and concrete pipework will deteriorate due to soil and UV rays. Other types of piping inside walls appear to rust, become damaged by abrasion, or accumulate debris. However, due to corrosion resistance of stainless steel, this happens rarely. This gives stainless steel an advantage in areas such as sanitary water distribution and hospital applications. When you buy stainless steel 316 pipes, you're getting a durable product that will last for decades. It is a long-lasting substance that is simple to maintain and install. Because of its corrosion-resistant qualities, stainless steel is low-maintenance and unlikely to need to be replaced for decades. STABILITY AND ADAPTABILITY Stainless steel can be treated with various elements such as molybdenum, nickel, or nitrogen to improve its corrosion resistance. Stainless steel can endure high temperatures. By adding various materials to stainless steel, thin pipe walls can be achieved, resulting in a lighter finished product that is suited for a wide range of commercial and industrial applications. ATTRACTIVENESS Exposed precision steel pipe and fittings are a good choice for commercial premises because the material is naturally bright and attractive. ENVIRONMENT-FRIENDLY Stainless steel is not a petroleum-based product. Unlike other pipe materials, it does not require any type of coating or lining. When you require disposing of or repairing stainless steel piping, it is 100% recyclable, reducing the environmental impact. Steel, like iron, has helped building in particular since it is a more practical alternative to other metals. Steel is corrosion-resistant, making it more long-lasting and cost-effective. It also means that, because they can survive them, these pipes can be used in regions that are constantly exposed to the elements. Steel pipes can be used for a variety of purposes. DOMESTIC BUSINESS Stainless steel 304 pipes are a popular choice in many homes since they are more durable, which means you won't have to replace them every few seasons. Any plumber would recommend stainless steel pipe for your tub, tap, and the rest of the structure, especially exposed pipes, because it is more resistant to the elements. They're also thought to be hardier. INDUSTRY OF MEDICINE If doctors use it, it must be safe, therefore that's another steel tick. Steel pipes have been utilized for everything in the medical field, including shattered bones, medical equipment, surgical tools, dental treatments, and even pharmaceutical assistance. Steel's versatility is a testament to its durability, protection, and adaptability. INDUSTRY OF CONSTRUCTION This is one of the most obvious uses for Q235 seamless steel pipe. They are preferred by many construction companies because they are both pliable and sturdy. Steel pipes are utilized as building piles when the soil is too thin to support the weight of big structures. The structure itself, as well as its architectural style, are frequently included. In fact, construction companies are one of the major steel pipe buyers. Steel pipes are frequently used in the construction of ships, oil refineries, and even space stations, and they are housed in a shipyard. Steel pipes are a good choice for building on the ground, in the ocean, or in space. Get it from authentic and reputed industrial pipe suppliers. For such requirement visit International Pipe and Supply in OKC.
Дата Публикации: 05-01-22
A review of rapid prototyping integrated investment casting processes
Описание: A review of rapid prototyping integrated investment casting processes Investment casting has been used to manufacture weapons, jewellery and investment casting during the ancient civilization. Today, its applications include jewellery/art castings, turbine blades and many more industrial/scientific components. The present paper reviews various investigations made by researchers in different stages of investment casting and highlights their importance. The paper initially highlights the investigations made on pattern wax properties, effects of blending, additives and fillers. Different ways through which pattern properties (like surface finish, dimensional accuracy, etc.) could be enhanced by properly controlling the injection processing parameters are thoroughly discussed. The paper also looks into the investigations made to enhance the strength, surface finish, etc. of ceramic shell for ferrous alloys/non-ferrous alloys as well as superalloys in investment casting. Investigations made on incorporation of nylon fibers and polymer additions confirm that a ceramic shell reinforced with nylon fibers attains additional permeability compared to the one with polymer additions. Different investigations carried out on autoclave dewaxing and microwave dewaxing conclude that the wax properties are less altered with microwave dewaxing when compared to an autoclave dewaxing. Some recent investigations carried out on pouring and post-treatment operations are also discussed in the paper. The advent and emergence of rapid prototyping in shell mold casting are broadly exposed in the subsequent sections of the paper. Various aspects of rapid prototyping like rapid investment casting, rapid freeze prototyping, etc., along with their advantages are projected. The emerging areas of applications of rapid prototyping like dentistry, etc., are duly discussed. The casting of titanium based alloys presents considerable problems, including the extensive interactions that occur between the metal and refractory. In this work, CaO stabilised zirconia was used as a primary coat material on the investment casting mould. The reaction between the zirconia face-coat and a Ti-46Al-8Nb-1B alloy was evaluated at three mould pre-heating temperatures: 500°C, 1000°C and 1200 °C. The effect of casting dimensions on interaction was also included in this work and the computer simulation of metal cooling profiles was carried out to assist the analysis. Higher mould pre-heat temperature and larger casting dimensions enhanced the interaction between the shell and the TiAl alloy associated with longer metal solidification time. During the high temperature casting process, not only were O and Zr observed penetrating into the metal from the decomposition of the face-coat materials, but also Si which had penetrated from the backup coat was found to have interacted with the metal. Investment casting is competitive with all other casting processes where the size of the product is within a mutually castable range. Though investment casting is used to produce metal parts of any intricate shapes with excellent surface finish, it suffers from long lead time and high tooling costs, which makes it uneconomical for the production of either single casting, or small and medium production units. These problems could be overcome by the applications of rapid prototyping and rapid tooling technologies for low-volume investment casting production runs. The present article analyzes different classifications of rapid prototyping techniques and it reviews various investigations made on the usability of rapid prototyping- and rapid tooling-integrated investment casting process, with their advantages and limitations. The emerging areas of applications of rapid prototyping like dentistry, jewelry, surgical implants, turbine blades, etc., are accordingly discussed. Further, an elaborate discussion is made on the application of newer technologies for directly developing ceramic shells. This article also emphasizes on various future scopes possible in rapid prototyping-integrated investment casting process. Investment casting process is known to its capability of producing clear net shape, high-dimensional accuracy and intricate design. Consistent research effort has been made by various researchers with an objective to explore the world of investment casting. Literature review revealed the effect of processing parameters on output parameters of cast specimen. This article highlights the advancements made and proposed at each step of investment casting and its hybridization with other process. Besides, investment casting has always been known to manufacture parts such as weapons, jewellery item, idols and statues of god and goddess since 3000 BC; this article reviews the present applications and trends in combination of rapid prototyping technique as integrated investment casting to serve in medical science. Advancements in shell moulding with incorporation of fibre and polymer, development of alternative feedstock filament to fused deposition modelling are duly discussed. The aim of this review article is to present state of art review of investment casting since 3200 BC. This article is organized as follows: in section ‘Introduction’, introduction to investment casting steps is given along with researches undertaken at each step; in section ‘Rapid prototyping technique’, background is given on the concept of rapid prototyping technique by examining the various approaches taken in the literature for defining rapid prototyping technique; section ‘Biomedical applications of RPT’ presents the medicine or biomedical applications of investment casting and rapid prototyping technique; section ‘Future trends’ provides some perspectives on future research and section ‘Conclusion’ closes the article by offering conclusions. In order to improve the properties of silicon sol shell for shell mold casting process, natural plant fibers combined with aluminum silicate fibers at natural-to-aluminum silicate fibers mass ratio of 1:1 were mixed into the slurries preparing for fiber-reinforced shell. The flexural strength of specimens of green shells, fired shells at different temperatures and the self-loaded deformation of the latter at elevated temperature were investigated. The fracture surface of shell specimens was observed by SEM. The results show that the green strength of shell specimens increases firstly and then decreases with variation of content of fiber from 0.2% to 1.0%. However, the self-loaded deformation at elevated temperature firstly decreases and then increases. The green strength of shell specimens reinforced with 0.6% fibers reaches the maximum of 2.94 MPa. The bending strength of shell specimens reinforced with 0.6% fibers fired at 900℃ reaches 4.04 MPa, approaching that of the non-reinforced shell specimens. It is found by SEM that the failure of the fiber-reinforced shell specimens at the applied load is resulted in breakdown of silicon sol films and pulling-out, fracturing and debonding of fibers in the shell. The development of manufacturing processes for high-performance investment casting components in turbomachinery is an iterative process, which takes a lot of development time for engineers and foundry occupation. The reduction of these expensive preliminary tests is possible by combining probabilistic methods with modern simulation tools for the numerical description of the what is investment casting and solidification processes. Starting from the deterministic simulation of the casting process, the casting and solidification parameters including their production tolerances are taken into account in the probabilistic simulation. Through a multi-dimensional statistical analysis of the numerous parameters of the casting process and the achieved virtual casting results, the correlations between the process parameters and component quality can be worked out. Furthermore, a design of experiment (DoE) was performed with real castings to confirm the influence of the main parameters on the result quantities. Mechanical and microstructural characterizations of appropriate cast specimens allow a validation of the simulation results and the formulation of casting parameter–microstructure–property relations. The mechanical properties are studied by uniaxial hot tensile tests using standard and small-scale specimens. Furthermore, the uniaxial fatigue behavior and the life times at elevated temperatures are investigated. In order to reduce the interaction between the Ti alloys and ceramic shell during the casting, materials with high thermal and chemical inertness were used in investment casting. An investigation was undertaken to analyze the influence of the change of binder systems on the slurries, facecoats and the thermo-chemical properties of the facecoat systems using an Y2O3–ZrO2 filler material. The results showed that, using alumina-sol as the binder in the slurry gave the longest life of around three days followed by that using the commercially available zirconia-sol at around 6 h, and the yttria sol based slurry giving a shortest life of around 1.5 h. Meanwhile using the alumina-sol can also enhance the facecoat sintering properties. There was no obvious evidence observed that the change of the binder system influenced the facecoat chemical inertness.
Дата Публикации: 05-01-22
A study on the flow characteristics of butterfly valve with baffles
Описание: A study on the flow characteristics of butterfly valve with baffles The butterfly valve was originally used where a tight closure was not absolutely necessary. However, over the years, these valves have been manufactured with fairly tight seals made of rubber or elastomeric materials that provide good shut off similar to other types of valves. Butterfly valves are used where space is limited. Unlike gate valves, butterfly valves can be used for throttling or regulating flow as well as in the full open and fully closed position. The pressure loss through a butterfly valve is small in comparison with the gate valve. The L/D ratio for this type of valve is approximately one-third of that of a gate valve. Butterfly valves are used in large and small sizes. They may be hand wheel–operated or operated using a wrench or gearing mechanism. Concentric butterfly valves are bidirectional. Double offset and triple offset bi-offset butterfly are also bidirectional but with preferred flow (pressure) direction, such as flow from the stem side. Fig. 2.96 shows the preferred flow direction of a flanged end double offset butterfly valve. Butterfly valves tend to be cheaper than gate valves because they require less material and less civil works. They are also easier to operate against unbalanced water pressures as the disc pivots about an axis on or near the pipe axis. Consequently butterfly valves are now commonly used in water distribution systems. Butterfly valves can be metal seated or resilient seated; in the latter case the seat is usually made of natural or synthetic rubber and is commonly fixed to the body of valves of smaller sizes or to the disc. Plate 28(b) shows a resilient seated butterfly valve. Resilient seated valves can remain virtually watertight, even after prolonged use in silty water. Therefore, resilient seats are usually specified for isolating valves in distribution systems. Resilient seated valves may also be used for control purposes but, if operated at small openings, the seal may be damaged. Solid rubber is the material usually used for resilient seatings: inflatable seals have been used on very large valves but not always with success. Metal seated butterfly valves do not have tight shut-off characteristics and are mainly intended for flow control purposes where they need to be held in the partially open position. Distribution network pipe systems are now designed to produce self-cleaning velocities at least once every 24 hours and should not need swabbing as part of normal operation. A transfer pipeline may need to be swabbed periodically. Butterfly valves on the line prevent the passage of foam swabs (except for very soft ones) but this does not usually pose a problem if the valves are spaced sufficiently far apart to allow the pipe to be cleaned in sections. Short lengths of pipe either side of the valve are Butterfly valves should normally be mounted with the spindle horizontal since this allows debris in the pipe invert to be swept clear as the valve is closed. Where the spindle is vertical solids can lodge under the disc at the spindle and cause damage to the seal. Disc position indicators are useful and strong disc stops integral with the body should be specified, so that the operator can feel with certainty when the disc is fully closed or fully open. Butterfly valves have been made to very large diameters (10 m or more) operating under very high heads and at high water velocities (20 m/s or more) and have proved successful in use. However, when a centre-pivoted butterfly valve is to be used for flow control purposes the maximum velocity of approach to the valve should be limited to 5 m/s. Resilient seated valves can be specified to have no visible leakage on seat test but the range of acceptable seat leakage rates for metal seated valves varies from about 0.004 to 0.04 l/h per 100 mm of nominal diameter (DN), at the specifier’s choice. However, a low rate for a high pressure differential would be expensive to achieve and difficult to maintain with metal seats. For some control applications, an acceptable seat leakage rate of about 0.4 l/h per 100 mm DN may be appropriate. If a valve may be required to remain in place closed on removal of the pipe on one side for a temporary operation, it must be flanged for bolting to a pipe flange on the other side. ‘Wafer’ butterfly valves whose bodies are sandwiched between pipe flanges do not achieve this. Use of such valves for isolation of air valves allows maintenance to be carried out on the air valve in situ with the pipeline in service but does not allow removal and replacement of the air valve under pressure. Since replacement of air valves is likely to be cheaper than in situ refurbishment, flanged isolating valves are preferred in such situations. The butterfly valve is a rotary valve in which a disk-shaped seating element is rotated 90° to open or close the flow passage. They are used in throttling service, particularly where large-size valves with automatic actuators are required. Butterfly valves cannot be used where a nonobstructed, full opening is needed. They offer a size and weight advantage over plug and ball valves. Conventional butterfly valves are used mainly in low-pressure water service and throttling applications. The seats, disk, and shaft are in the same plane. The seat is obtained by an interference fit between the disk and resilient (flexible) liner. This type of fit is shown in Figure 4.64. The tightness of the seat is limited by the operating torque of valve and the seal between the shaft and the liner. The sealing characteristics of this valve are poor and leakage usually occurs. The high-performance butterfly valve provides good sealing characteristics and a tight shutoff. The disk is essentially an off-center slice of a ball, and the seating mechanism of this valve is similar to that of a ball valve. The disk and seats of this valve are offset from the shaft and shaft sealing in this valve is not critical. Many valves offer a primary seat made of a resilient material and a secondary metal-to-metal seal making them “fire-safe.” High-performance butterfly valves are available in pressure classes as high as ANSI 900 and can be used in applications requiring tight shutoff. The gate valve has a unique body style unlike the other valves we have discussed. The butterfly uses a circular plate or wafer operated by a wrench to control flow. A 90° turn of the wrench moves the wafer from a fully open position to a fully closed position. The wafer remains in the stream of flow and rotates around a shaft connected to the wrench. As the valve is being closed, the wafer rotates to become perpendicular to the direction of flow and acts as a dam to reduce or stop the flow. Traditional butterfly valves now work at high pressure drops across the disc which can be both metallic and “soft”. Upper and lower temperature limits are the same, by and large, as those for globe valves, depending on duty and material of construction. The butterfly construction is especially suitable for high temperatures. Bodies can be fabricated from bar and plate and the seals can be mounted on cooling extensions away from the main flow. Butterfly valves can be used as a control valve and also as a shut-off valve, as discussed in Chapter 3, Section 3.3.3, against high pressure drops of regularly up to 415 barg. Depending upon the materials of construction and the seat design a butterfly control valve may have very limited shut-off pressure drops. Some 100 barg valves are only rated for 4 barg shut-off differential. A globe valve should have a range of possible shaft diameters for each nominal valve size in order to handle the variation in torque due to various operating pressure conditions and packing box friction. Shafts should not be made of material prone to creep, such as some austenitic stainless steels. In these situations a precipitation hardening stainless steel such as 17-4PH is preferred. The corrosion resistance of such materials, equivalent to AISI 304, must be borne in mind. The disc must withstand high differential pressures. Some valves do have restrictions on the maximum throttling differential pressure, 35% of pressure rating in some cases. Generally, butterfly valves are used for the inlet control and bypass valves. They are inexpensive to manufacture, and their actuators are able to operate in accordance with the requisite response times. Butterfly valves do, however, have the disadvantage of a tightly curved characteristic. Additional non-linearities arise from the fact that valves of different nominal sizes are operated in sequence. An initial improvement in the control response was achieved in that the steady-state duty point characteristics for operation with and without the expander were stored in function generators in the controller. Depending on the operational state, the output of the process controller (regenerator pressure, or differential pressure, between the regenerator and the reactor) is applied to one or the other of these characteristics. In the event of an expander trip, the system immediately switches from one characteristic to the other. This results in linearization of the characteristic profile, so that the process controller is able to operate independent of the duty point concerned and independent of the operating mode (i.e., with or without the expander). This switching between characteristics in the event of an emergency trip also ensures that the bypass valves are always driven at maximum actuating speed to their new steady-state position in accordance with the prevailing operating conditions. All this is performed independent of the prevailing duty point (i.e., whether the system is operating at partial load or at overload). In the industry, globe valves, which are commonly used to precise control the flow rate along with opening and closing flow in pipes, are technically and economically limited in valve size due to structural instability related to complex internal flow passage. Butterfly valves, on the other hand, have advantages such as low weight and low manufacturing costs, but it is difficult to control the flow rate at an opening angle of 60°or higher and flow is unstable in the case of butterfly valve. Therefore, the purpose of this study is to have characteristics of flow rate of the globe valve that is used in the industry at the same diameter of pipeline and flow stability due to uniformity of flow through the baffle hole by adding 1/2 baffle to forged valve. Hole size of baffles were set at 5, 7 and 9 mm and baffles were set at the rear of the butterfly valve. To verify the method of numerical analysis, the results of experimental study were compared with the results of numerical study. As a results, it is confirmed that characteristics of flow rate of butterfly valve with baffle is similar to globe valve in the case of hole size 5 mm. In addition, flow pattern is to be stable by analyzing turbulence energy. Consequently, when applying baffle to butterfly valve, it is possible to reduce the flow unstability and change the flow rate of butterfly valve.
Дата Публикации: 05-01-22
What are the different types of nuts and bolts?
Описание: What are the different types of nuts and bolts? What does a bolt look like? Let’s start with a nuts-and-bolts definition. Bolts are threaded fasteners with external male threads. They mate with nuts, which have female – meaning, internal – threads. What are nuts used for? Both the bolt and the nut grip the materials being fastened, creating a bolt joint, with the nut also preventing axial movement. The effect of the bolt joint comes down to the axial clamping force provided by the nut and the shank of the bolt, which acts as a rod that presses the joint against sideways shear forces. This is why so many bolt shanks are threadless – it makes for a stronger rod. When to use bolts vs screws It’s often assumed that the difference between hex bolts and screws lies in the tools used to install each – a screwdriver for a screw and a wrench for a bolt. This isn’t always the case, however. Bolts can have heads that we associate with screws and require a screwdriver for installation. Even some screws use nuts, so we’re dealing with gray areas. The decision of which you choose really comes down to the application and the materials you’re fastening. For lightweight materials, such as plastics, plywood and drywall, screws are best. Most of the time, that is. Bolts also come in plastics, but these are mostly used for electronics, as they’re lightweight, corrosion resistant and provide excellent insulation. For heavy-duty applications and heavier materials, such as concrete and metals, go with bolts. Bolt head styles are designed for the bolt’s intended function while enabling the installation tool to grip the head. Below are examples of different types of bolt heads. As seen here, bolts can have slots or drives, just as screws do. The vast majority of nuts, no matter what type, are hex shaped. This is because the six sides make it easy to turn. It only takes a one-sixth turn for the nut to reach the next flat parallel. A nut with fewer sides takes more time to install. Other shapes are available, which are for specific needs. For the same reason you use them with screws. Technically you don’t need washers for nuts and heavy hex bolts, but we recommend that you still use them. a silver washer How do washers work with bolts? Washers evenly distribute the nut’s load and protect the surface that you’re fastening from damage. It also gives your nut a smooth surface to push against, which helps the fasteners remain tight instead of loosening. In a few cases, you’ll need to put the washer on the bolt side, but only if it’s the bolt that requires How to choose the right nut for your bolt Nuts and bolts fasten together with their threads. The weakest shear plane in the thread profile is where failure can start. That is, the weakest material determines the strength of the connection. The point is, nuts and bolts should be made of the same alloys. Not only that, but your nut should meet or exceed the maximum tensile strength of the bolt, which is the amount of pull the bolt can withstand. If safety is a key consideration in your application, then you want your nut to be stronger than your bolt. In these instances, the Industrial Fastener Institute (IFI) recommends that your nut should exceed your bolt’s tensile strength by 20%. How to tell the grade of a bolt Bolt grades indicate the strength of your fastener. Understanding bolt grades is critical to choosing the right fastener. Typically, identification markings on bolt heads include the grade and the manufacturer’s mark. The grades are indicated by raised dashes or numbers. Bolts are one of the most common elements used in construction and machine design. They hold every-thing together – from screws in electric toothbrushes and door hinges to massive bolts that secure concrete pillars in buildings. Yet, have you ever stopped to wonder where they actually came from? When was the first bolt made? While the history of threads can be traced back to 400 BC, the most significant developments in the modern-day bolt and screw processes were made during the last 150 years. Experts differ as to the origins of the humble nut and bolt. In his article “Nuts and Bolts”, Frederick E. Graves argues that a threaded bolt and a matching nut serving as a fastener only dates back to the 15th century. He bases this conclusion on the first printed record of screws appearing in a book in the early 15th century. However, Graves also acknowledges that even though the threaded bolt dates back to the 15th century, the unthreaded bolt goes back to Roman times when it was used for “barring doors, as pivots for opening and closing doors and as wedge bolts: a bar or a rod with a slot in which a wedge was inserted so that the bolt could not be moved.” He also implies that the Romans developed the first screw, which was made out of bronze, or even silver. The threads were filed by hand or consisted of a wire wound around a rod and soldered on. According to bolt expert Bill Eccles’ research, the history of the screw thread goes back much further. Archimedes (287 BC–212 BC) developed the screw principle and used it to construct devices to raise water. However, there are signs that the water screw may have originated in Egypt before the time of Archimedes. It was constructed from wood and was used to irrigate land and remove bilge water from ships. “But many consider that the screw thread was invented around 400 BC by Archytas of Tarentum, who has often been called the founder of mechanics and considered a contemporary of Plato,” Eccles writes on his website. The history can be broken down into two parts: the threads themselves that date back to around 400 BC when they were used for items such as a spiral for lifting water, presses for grapes to make wine, and the fasteners themselves, which have been in use for around 400 years. Moving forward to the 15th century, Johann Gutenberg used screws in the fastenings on his printing presses. The tendency to use screws gained momentum with their use being extended to items such as clocks and armor. According to Graves, Leonardo da Vinci’s notebooks from the late 15th and early 16th centuries include several designs for screw-cutting machines. What the majority of researchers on this topic do agree on, though, is that it was the Industrial Revolution that sped up the development of the nut and bolt and put them firmly on the map as an important component in the engineering and construction world. The first industrial production of bolts The “History of the Nut and Bolt Industry in America” by W.R. Wilbur in 1905 acknowledges that the first machine for making carriage bolts and screws was made by Besson in France in 1568, who later introduced a screw-cutting gauge or plate to be used on lathes. In 1641, the English firm, Hindley of York, improved this device and it became widely used. Across the Atlantic in the USA, some of the documented histories of the bolt may be found in the Carriage Museum of America. Nuts on vehicles built in the early 1800s were flatter and squarer than later vehicles, which had chamfered corners on the nuts and the flush was trimmed off the bolts. Making bolts at this time was a cumbersome and painstaking process. n Britain in 1760, J and W Wyatt introduced a factory process for the mass production of screw threads. However, this milestone led to another challenge: each company manufactured its own threads, nuts, and bolts so there was a huge range of different sized screw threads on the market, causing problems for machinery manufacturers. When were screw threads first standardized? It wasn’t until 1841 that Joseph Whitworth managed to find a solution. After years of research collecting sample screws from many British workshops, he suggested standardizing the size of the screw threads in Britain so that, for example, someone could make a bolt in England and someone in Glasgow could make the nut and they would both fit together. His proposal was that the angle of the thread flanks was standardized at 55 degrees, and the number of threads per inch, should be defined for various diameters. While this issue was being addressed in Britain, the Americans were trying to do likewise and initially started using the Whitworth thread. In 1864, William Sellers proposed a 60-degree thread form and various thread pitches for different diameters. This developed into the American Standard Coarse Series and the Fine Series. One advantage the Americans had over the British was that their thread form had flat roots and crests. This made it easier to manufacture than the Whitworth standard, which had rounded roots and crests. It was found, however, that the Whitworth thread performed better in dynamic applications and the rounded root of the Whitworth thread improved fatigue performance. Introducing the ISO metric During World War I, the lack of consistency between screw threads in different countries became a huge obstacle to the war effort; during World War II it became an even bigger problem for the Allied forces. In 1948, Britain, the USA and Canada agreed on the Unified thread as the standard for all countries that used imperial measurements. It uses a similar profile as the DIN metric thread previously developed in Germany in 1919. This was a combination of the best of the Whitworth thread form (the rounded root to improve fatigue performance) and the Sellers thread (60-degree flank angle and flat crests). However, the larger root radius of the Unified thread proved to be advantageous over the DIN metric profile. This led to the ISO metric thread which is used in all industrialized countries today. Those working in the industry have witnessed much fine-tuning of bolts during recent decades. “When I started in the industry 35 years ago the strength of the bolts was not as fully defined as it is today,” recalls Eccles. “With the introduction of the modern metric property classes and the recent updates to the relevant ISO standards, the description of a bolt’s strength and the test methods used to establish their properties is now far better defined.” As the raw materials industry has become more sophisticated, the DNA of bolts has changed from steel to other more exotic materials to meet changing industry needs. What metals are used to produce bolts? Over the last 20 years, there have been developments in nickel-based alloys that can work in high-temperature environments such as turbochargers and engines in which steel doesn’t perform as well. Recent research focuses on light metal bolts such as aluminium, magnesium, and titanium. Today’s bolt technology has come a long way since the days when bolts and screws were made by hand and customers could only choose between basic steel nuts and bolts. These days, solutions like Nord-Lock have invented significant improvements in bolting technology, including wedge-locking systems. Customers can select pre-assembled zinc flake coated or stainless-steel washers, wheel nuts designed for flat-faced steel rims, or combi bolts, which are customized for different applications. Superbolt multi-jackbolt tensioners and Boltight hydraulic tensioners have also been added for use in heavy industries, such as offshore, energy, and mining, taking a huge step in becoming a world leader in bolt securing.
Дата Публикации: 05-01-22
Bags of style: how the backpack became a fashion essential
Описание: Bags of style: how the backpack became a fashion essential They used to be carried by the slightly awkward-looking kids in the school playground or hikers and were much more likely to be sported by men than women. But now, go to any high street, office or packed rush-hour bus and the humble backpack bag is everywhere. Fashion searches for rucksacks are up 37% month-on-month, according to global fashion search platform Lyst. In the UK the annual amount spent on backpacks has risen every year since 2014 when, according to global market research company Euromonitor International, the retail spend was ￡112m – it forecasts the 2019 figure will be ￡219.5m. “There has been an enormous change in attitudes towards day packs,” says Ralph White, UK managing director of the Swedish rucksack brand Fj?llr?ven. According to Domitille Parent, product director at Eastpak, a brand that has been making rucksacks for over 40 years, an increasing number of commute backpack buyers are women: nearly 60% of online sales in the UK are made by women, and that number has been rising year-on-year. In the US, according to the market research firm NPD, sales of what they label women’s backpacks are up by 28% in the past year – with New York, Los Angeles and San Francisco the top three growth regions – while sales of men’s backpacks are down. Of course, it should be no surprise that women are using a style of bag that is practical and – increasingly – stylish, too. But it has taken something of a shift in attitudes for the backpack to find mainstream traction in workplaces – and gender parity. As with many things, Miuccia Prada was a pioneer: when she released a nylon rucksack, made from military parachute fabric, in 1984, it was considered radical. All the other bags around were, she said in a recent interview with Vogue magazine, “so formal, so lady, so traditional”. In the past, style blogger and backpack-wearer Susie Lau, aka Susie Bubble, has cited the Phoebe Philo effect. As former designer at Celine, Philo led the charge for what many brand “ugly” fashion, from Birkenstocks and clogs to backpacks. Skipping forward to 2016, Burberry’s monogrammed backpacks were the elevated version that convinced the likes of Cara Delevingne to embrace the look. At the Tribeca film festival last year Sarah Jessica Parker, the woman to thank for sparking many an impractical tiny handbag trend, was spotted wearing a rucksack on the red carpet. On the Prada men’s AW19 catwalk they were worn by Gigi Hadid and Kaia Gerber, and Chanel’s 2020 Cruise show featured a outdoor backpack. With many high-fashion brands, from Gucci to Coach, making rucksacks; the mid range of the market seeing a proliferation of more sophisticated designs – from the likes of Herschel to Dr Martens – and more than 400 styles offered on Asos, backpacks have come a long way from the days of Power Rangers or My Little Pony bags. The rucksack’s fashion credentials have been bolstered by the rise of gorpcore – a neologism coined in 2017 from the acronym “gorp”, which stands for “granola, oats, raisins, peanuts”, aka trail mix, and encompasses all manner of camping attire. The ongoing popularity of luxury sportswear has helped make rucksacks less back-of-the-bus and more chia seeds and balasana. With the rise of the urban hiker look last year, the field trip look went high-fashion. “The outdoors as a whole has definitely got more fashionable,” says White. Plus it’s come into cities. With some of the most popular brands hailing from Sweden, they play into our era’s love of all things Scandi. As White explains: “There has definitely been a rise in the popularity of Scandinavian culture – from hygge to fika. Fj?llr?ven takes a very Scandinavian approach to its product design.” Its now-iconic K?nken, was introduced as a bag for Swedish children in 1978. The sheer practicality of the rucksack is a plus point, too. Backpacks are “easy to wear, hands-free, fuss-free and comfy,” says Georgie Tym, a lecturer at Cordwainers, the shoes and accessories brand of London College of Fashion. Function appears to be winning over any lingering competition from archaic, gendered double standards. If Danielle Drake, PR manager at Sandqvist, a high-end Swedish bag brand, is to be believed, the backpack is to bags what flats are to high heels. “The past pressure of having to cram all of your gear into a shoulder bag just for the sake of dated perceptions on women’s workplace attire has no place in today’s world.” As we approach the end of the year in Singapore, we have a small favour to ask. We’d like to thank you for putting your trust in our journalism this year - and invite you to join the million-plus people in 180 countries who have recently taken the step to support us financially, keeping us open to all, and fiercely independent. In 2021, this support sustained investigative work into offshore wealth, spyware, sexual harassment, labour abuse, environmental plunder, crony coronavirus contracts, and Big Tech. The new year, like all new years, will hopefully herald a fresh sense of cautious optimism, and there is certainly much for us to focus on in 2022 - a volley of elections, myriad economic challenges, the next round in the struggle against the pandemic and a World Cup. With no shareholders or billionaire owner, we can set our own agenda and provide trustworthy journalism that’s free from commercial and political influence, offering a counterweight to the spread of misinformation. When it’s never mattered more, we can investigate and challenge without fear or favour. Unlike many other media organisations, Guardian journalism is available for everyone to read, regardless of what they can afford to pay. We do this because we believe in information equality. Greater numbers of people can keep track of global events, understand their impact on people and communities, and become inspired to take meaningful action. If there were ever a time to join us, it is now. Every contribution, however big or small, powers our journalism and sustains our future. Support the Guardian from as little as $1 – it only takes a minute. If you can, please consider supporting us with a regular amount each month. Thank you. Backpacks were once considered casual and suited only for travel or for students who needed to lug books by the kilos. It was a hard-working bag meant for the wearer’s comfort. But as offices become more mobile with laptops and assorted gadgetry (chargers, tabs, power banks and mobile phones), a foldable backpack has become the goto workbag. Add to this the rise of a casual corporate culture, where athleisure is kosher at the workplace and sneakers are subbing in for high heels for women and dress shoes for men, and backpacks are strictly formal now. Making and selling backpacks and travel bags — of burlap and vegan leather — is how Samriddh Burman, Karuna Parikh and Rewant Lokesh of Kolkata came together to start The Burlap People. Parikh says each of them chose backpacks as their daily work or office bags and the backpacks came naturally to them. Backpack loads of school students during school days have been suggested to range from 10% to as high as 25% of their body weight and may have a negative impact on their body. The aim of this review was to identify and review studies that have examined impacts of contemporary backpack loads on school children. Methods: A systematic search was conducted of the literature using key search terms. After relevant studies published in recent years were selected using strict inclusion and exclusion criteria, the studies were critically appraised and relevant data were extracted and tabulated prior to conducting a critical narrative synthesis of findings. Results: Twenty-one studies were included, ranging in methodological quality from poor to good (critical appraisal scores 22% to 77%). Students carried on average over 15% of their own body weight, which caused biomechanical and physiological adaptations that could increase musculoskeletal injury risk, fatigue, redness, swelling and discomfort. Conclusion: Considering the limited methodological quality and variations in foci across studies, further research is needed to elucidate: (1) the loads students carry around on a school day in their school backpacks and; (2) the biomechanical, physiological and physical effects of load carriage on students. A review by Mackenzie et al. in 2003 of drawstring backpack loads carried by school students during a school day identified that children were carrying as much as 30% to 40% of their body weight. This review, while acknowledging that no critical maximal load had been established (to address back pain), recommended around 10% of the child’s bodyweight as a maximum limit. The following year, a review by Brackley and Stevenson stated that the majority of work considered the loads carried by children to be above recommended limits, likewise recommending a maximal load of between 10 to 15% of the child’s bodyweight. Since these reviews, more recent research has suggested that these loads are lighter and in some instances may be meeting this recommendation, with loads ranging from 10% to 25% of the school child’s bodyweight. However, this recent research, in agreement with the earlier reviews, also suggests that these loads have a negative impact (e.g., increased forward lean, pain, skin pressure) on children’s bodies .
Дата Публикации: 05-01-22
The Effect of a Wrist Brace on Injury Patterns
Описание: The Effect of a Wrist Brace on Injury Patterns We compared patterns of bony and ligamentous injury with distal radial fractures in braced and unbraced wrists using 20 paired fresh cadaveric upper extremi ties. A commercially available wrist brace was placed on one wrist in each pair. Specimens were then placed in a fast-loading gravity-driven device and subjected to loads averaging 16 kg from an average height of 78 cm. Postfracture radiographs were obtained, the spec imens were dissected, and fracture patterns and liga mentous integrity were assessed. The following frac ture types were produced: distal radial fractures (eight unbraced, seven braced) and intraarticular (seven un braced, four braced). Radiographically, seven un braced wrists demonstrated carpal bone fracture and one braced wrist demonstrated carpal fractures. Eight unbraced and three braced wrists sustained carpal intrinsic ligament injuries, four unbraced and one braced wrists demonstrated extrinsic ligament injuries. More capsular tears occurred in the unbraced group (N = 8) than in the braced group (N = 1). This model demonstrated a difference in the patterns of injury in unbraced and braced wrists subjected to the same mechanical conditions, which suggests that use of a wrist brace may alter patterns of wrist injury. Braces and splints can be useful for acute injuries, chronic conditions, and the prevention of injury. There is good evidence to support the use of some braces and splints; others are used because of subjective reports from patients, relatively low cost, and few adverse effects, despite limited data on their effectiveness. The unloader (valgus) knee brace is recommended for pain reduction in patients with osteoarthritis of the medial compartment of the knee. Use of the patellar brace for patellofemoral pain syndrome is neither recommended nor discouraged because good evidence for its effectiveness is lacking. A knee immobilizer may be used for a limited number of acute traumatic knee injuries. Functional ankle braces are recommended rather than immobilization for the treatment of acute ankle sprains, and semirigid ankle braces decrease the risk of future ankle sprains in patients with a history of ankle sprain. A neutral wrist splint worn full-time improves symptoms of carpal tunnel syndrome. Close follow-up after bracing or splinting is essential to ensure proper fit and use. Am Fam Physician 2007;75:342–8. Copyright ? 2007 American Academy of Family Physicians.) Family physicians often must make decisions regarding the use of braces or splints in the management of musculoskeletal disorders. Bracing can be useful for acute injuries, and also for chronic conditions and in the prevention of injury. The purpose of braces and splints is to improve physical function, slow disease progression, and diminish pain. They can be used to immobilize an unstable joint or fracture, to unload a portion of a joint and improve pain and function, to eliminate range of motion in one direction, or to modify range of motion in one or more directions. They do not replace a good rehabilitative program, and the entire spectrum of treatment options should be explored and used as needed. Accurate diagnosis of the injury is important in determining whether a brace or splint is indicated. Generally, splints are for short-term use. Excessive, continuous use of a brace or splint can lead to chronic pain and stiffness of a joint or to muscle weakness. However, long-term use of some braces, such as a knee support, can help prevent progression of pain attributable to osteoarthritis of the knee. Given the limited evidence on the use of braces and splints, it is particularly important to use a patient-centered approach, with consideration for individual patient's expectations and concerns and an understanding of the nature of their activity. For example, for high school and collegiate athletes, there are specific rules on the types of protective equipment, splints, and braces that may be worn during competition.1 Close follow-up after bracing or splinting is essential to ensure proper fit and use. The most common types of braces and splints used in primary care and the quality of evidence to support current recommendations are discussed in the following. Relatively few studies on bracing have been published, and most are not randomized controlled trials. A Cochrane systematic review4 identified only one randomized controlled trial.2 In this study, 119 patients who had osteoarthritis associated with varus deformity of the knee were randomized to receive usual treatment, unloader knee brace, or neoprene sleeve to evaluate the effect of these therapies on functional status and quality of life.2 Although both the sleeve and the brace reduced pain and improved function, greater benefit was found with the unloader brace. In a randomized crossover trial, 12 patients with varus osteoarthritis were given a simple hinged brace or an unloader brace during two six-month periods. Because patients acted as their own controls, it was possible to identify statistically and clinically significant benefits for the unloader brace that were greater than those of the hinged brace despite the small number of patients involved in the study.5 The American Academy of Orthopaedic Surgeons recommends unloader braces for the reduction of pain in patients with osteoarthritis of the knee.6 This conservative option is thought to extend the time before patients need to undergo knee arthroplasty; it also can be considered for those who are not candidates for surgery. ANTERIOR KNEE PAIN BRACE Anterior knee pain, also called patellofemoral pain syndrome (PFPS), is a common complaint among young, active patients. Its etiology is multifactorial and controversial, and the treatment can be frustrating for the physician and the patient. Braces have been developed to address the most commonly accepted etiology: malalignment of the patellofemoral joint. Typically, these braces are made of neoprene or a similar elastic material, with additional straps or a buttress for patellar support. The buttress can be circular, C-shaped, J-shaped, or H-shaped to help maintain tracking of the patella in the femoral groove. These braces are reasonably priced, and off-the-shelf models are adequate (Figure 2). Evidence of the effectiveness of braces for treatment or prevention of PFPS is limited because of methodologic differences and shortcomings across studies. Two systematic reviews published in 2002 and 2003 concluded that, because of the low quality of available studies, there is insufficient evidence to support or to discourage the use of patellar bracing for PFPS.7,8 Likewise, an American Academy of Pediatricians technical report stated that there is no scientific evidence to support the use of knee sleeves. Two studies, published after the systematic reviews, produced contradictory results.10,11 In one small, anatomic study using magnetic resonance imaging, researchers examined patellar alignment, patellofemoral joint contact area, and pain response in patients with and those without bracing.10 They found significant changes in contact area and improvement in pain in the braced group but little change in patellar alignment. In a prospective randomized clinical trial published in 2005, researchers randomized 136 patients with anterior knee pain to treatment with home exercises, patellar bracing, exercises plus bracing, or exercises plus knee sleeve, and found no difference in pain ratings between the four groups after 12 weeks.11 Small studies on military recruits have reported a decrease in the incidence of anterior knee pad with patellar bracing.12,13 Because of the limited data and lack of clear recommendations and consensus on the effectiveness of patellar braces for the treatment or prevention of anterior knee pain, decisions regarding their use must be made on an individual basis. Some patients may feel benefits; therefore, patients should be told that study results are inconclusive or mixed. A therapeutic trial of braces may be worthwhile because the braces are not expensive and no harmful effects have been found. Nonetheless, a brace is no substitute for a good rehabilitative program that includes strengthening, range-of-motion, and proprioceptive exercises.14–17 KNEE IMMOBILIZER Complete immobilization of the knee for an extended period is generally contraindicated because of the prolonged stiffness, muscle atrophy, and chronic pain that result. However, there are exceptions. Indications for the use of a knee immobilizer (Figure 3) include the acute (or presurgical) management of quadriceps rupture, patellar tendon rupture, medial collateral ligament rupture, patellar fracture or dislocation, and a limited number of other acute traumatic knee injuries. The duration of immobilization and management of these conditions is variable and beyond the scope of this article. Other knee braces include prophylactic braces designed to prevent or limit the severity of knee injuries. These braces are used commonly by football players to help protect against medial collateral ligament injury. Functional knee braces are designed to provide stability to a ligament-deficient knee (e.g., in a patient with an anterior cruciate ligament tear before surgery) and also can be used for postsurgical repair. Rehabilitative knee sleeve are used postoperatively to allow protected range of motion.6 Recommendations for the proper selection and use of these braces are highly variable, complex, and often inconsistent; the choice seems to be based on anecdotal experience and trial and error. Ankle Braces Ankle sprains are one of the most common acute musculoskeletal injuries. The treatment of lateral ankle sprains can be confusing because of the many braces and splints that are available for this injury. Ankle braces can be divided into two categories: rigid and functional. Rigid braces essentially immobilize the entire ankle. Functional braces, which include semirigid (e.g., Aircast) and soft, lace-up braces, allow some plantar and dorsiflexion at the ankle while controlling for inversion and eversion. Semirigid braces are made of thermoplastic contoured lateral stirrups lined with air-filled foam pads for support of the medial and lateral malleoli. Supplemental air can be added to these air cells through an inlet port.18 Soft, lace-up braces are usually made of canvas. Semirigid stirrup braces restrict ankle inversion and eversion more than lace-up braces19 (Figures 4 and 5). External ankle support also has been shown to improve proprioception, an important component in the reduction of recurrent ankle sprains. Complete immobilization of the ankle following an acute ankle sprain is no longer recommended. Early mobilization using functional treatment is preferred.20 A Cochrane systematic review concluded that treatment of acute ankle sprains with functional braces leads to better outcomes (e.g., shorter time taken to return to work or sport, less swelling and instability, greater overall satisfaction) compared with immobilization.21 A systematic review identified nine randomized trials that compared different functional treatment strategies (e.g., lace-up or semirigid brace, elastic bandage) for acute lateral ankle ligament injuries.20 Because of the variety of treatments and inconsistently reported follow-up times, the most effective functional treatment brace could not be identified. However, lace-up ankle braces more effectively reduced short-term swelling than did semirigid ankle braces. The most recent randomized controlled study, published in 2005, demonstrated improvement in ankle joint function after a moderate to severe inversion injury using a semirigid (Aircast) brace.18 Thus, the evidence supports a functional treatment approach to inversion ankle sprains with the use of a semirigid or soft, lace-up brace. PROPHYLACTIC ANKLE BRACES Multiple studies have evaluated the effectiveness of ankle braces for the prevention of ankle sprains. There is good evidence that semirigid braces help to prevent ankle sprains during high-risk sports such as soccer and basketball. According to a Cochrane systematic review, patients with a history of ankle sprain can be advised that wearing such a brace reduces their risk of future ankle sprains.22 Few studies recommend the duration for which wrist brace should be used. However, one systematic review on the prevention of ankle sprains in sports recommends that patients who sustain moderate or severe ankle sprains should wear an ankle brace during sports activity for at least six months following the injury.23 Wrist splints Carpal tunnel syndrome is a common compression neuropathy, often treated initially with a splint to relieve pressure on the median nerve. Few recent studies have addressed the effectiveness of wrist splints in the treatment of carpal tunnel syndrome, and no randomized controlled trials have compared wrist splinting with no treatment. One systematic review concluded that there is limited evidence to support the use of splinting for up to six months,24 whereas a second review found that a hand brace improved symptoms and function after four weeks.25 There are various options when prescribing a wrist splint, including neutral versus cock-up (extension) splints, nighttime versus full-time wear, duration of wear, and custom versus prefabricated splints. One prospective study found that neutral splints relieved symptoms more than cock-up splints (20 degrees of extension).26 The authors also found that symptom relief was evident in the first two weeks of wearing the splint; no additional improvement was noted between weeks 2 and 8 of wear.26 The first long-term prospective randomized study to compare nighttime splint wear with steroid injection found improvements in symptoms as well as motor and sensory nerve conduction velocities after one year of wearing a splint at night.27 Another randomized clinical trial, comparing symptoms and functional deficits in nighttime versus full-time splint wear, found the most significant improvements at six-week follow-up in the group instructed to wear the splints full-time.28 Splints come with a dorsal or volar compartment in which metal or thermoplastic inserts can be placed. It is easier to mold a custom insert than it is to mold a prefabricated metal one29 (Figure 6). When fitting a prefabricated wrist splint, it is important to observe the wrist position, because off-the-shelf wrist splints may have significant extension. Prefabricated splints, which tend to be more rigid and less comfortable than thermoplastic custom splints, typically are made to have 10 to 30 degrees of extension. Patients wearing prefabricated splints should return with the splint so that the angle can be adjusted to the neutral position if necessary. Researchers suggest that prefabricated splints must be adjusted to the neutral posi
Дата Публикации: 05-01-22
Acrylic Nails: Everything You’ve Ever Wanted to Know
Описание: Acrylic Nails: Everything You’ve Ever Wanted to Know Acrylic nails are the definition of glamour in the beauty world, and pretty much anyone with eyes can see that. But are fake nails safe? Do acrylic nails hurt? How much do acrylic nails cost? And what are acrylic nails even made of, anyway? If you’re curious about acrylics and have never tried them before, it’s totally understandable if you have some reservations about the beauty treatment. Find out if acrylic nails are right for you after reading our answers to all your questions about the unique manicure below, and then get inspired by some of the prettiest acrylic nails on the internet today. Acrylic nails are nail enhancements made by combining a liquid acrylic product with a powdered acrylic product, according to Nails magazine. The two products (known as a monomer and a polymer, respectively) together form a soft ball that can be fashioned into a nail shape. Once a nail technician applies this acrylic to a client’s nails, the material hardens and becomes much stronger. And then it can be buffed and filed to the customer’s liking. But wait: Who invented acrylic nails? You might be surprised to learn that acrylics as we know them today were first developed in 1934 by a dentist named Maxwell Lappe. He created these artificial nails in order to help nail-biters curb their habit. Who would’ve guessed that they’d become such a huge fashion statement in the decades following? Considering the fact that chemists have developed much better techniques to make acrylic nails look more natural, it’s no surprise that this beauty treatment still has such an enormous staying power to this day. How to Remove Acrylic Nails at Home It is highly recommended to go back to the nail technician or salon where you got your long coffin fake nails done to have them removed. After all, the professionals are the ones that are most experienced in knowing exactly how to soak off acrylic nails and file them down in an efficient manner. However, sometimes going to the salon right away isn’t possible and you absolutely need to know how to remove acrylic nails at home for one reason or another. (Hey, life happens!) If you must learn how to take off acrylic nails at home, you want to be sure you do it safely: Beauty experts at Makeup.com say your best move is to soak your nails into acetone until they’re totally soft and then file the acrylics off one by one. As you can imagine, these instructions about how to get acrylic nails off can take quite a bit of time to complete in real life. But it’s a much better method of removing acrylic nails than trying to pull them off manually. Overall, trying to learn how to remove acrylic nails without acetone or a file is a pretty bad idea. If you try to do that — especially while your acrylics are still hard — you can say hello to some seriously brittle and weak natural nails in the future. No one wants that! How are acrylic nails applied? After you choose your preferred nail shape, length, and color, your technician should begin your acrylics appointment by cleaning, soaking, and filing your natural nails. If you requested length to be added to your nails, they’ll add artificial tips after that. (If you requested very short acrylic nails, they will skip this step.) Next, nail techs will apply an adhesive before attaching the acrylic nails to all your nail beds. Then, they sand down and shape the acrylics. Finally, they add any additional polish, accessories, or nail art that you asked for at the beginning of the appointment. If you’re wondering how to apply acrylic nails at home, this can vary depending on what type you’re using. Luckily most kits, such as Kiss Products Salon Acrylic French Nail Kit ($6.49, Amazon), include instructions about how to do acrylic nails safely and effectively on your own. Gel Nails vs. Acrylic Nails: Should I get acrylic nails? If you’re considering getting acrylic nails, you’ve probably heard some folks suggest that you try gel nails instead. Considering that gel nails are often grouped in the same type of beauty treatment as acrylic nails, it’s easy to confuse the two, or even mistake them as terms that could be used interchangeably. In reality, they’re quite a bit different — and they both have pros and cons. While acrylics are nail enhancements made by combining a liquid acrylic product with a powdered acrylic product, gel nails are part of a more homogenous gel product that needs to be “cured” or “sealed” onto the nail with the use of a UV light between each layer. According to Nails, a helpful way to understand the difference between gel and medium coffin fake nails is to think of gel as premixed acrylic. While acrylic nails are more strong and durable than gel nails, gel can actually be used to strengthen the natural nail and helps protect it as it grows. That said, acrylic nails are a bit easier for you to maintain at home, because you can both fix them soak them off without the help of a nail technician, unlike most gel nails. However, gel nails may be a more practical choice for people who use their hands quite a bit; they are far more flexible than acrylics. Gel is generally pretty odorless, and the same cannot be said for acrylics. Wondering, “Should I get acrylic nails or gels?” When it comes to the debate about gel nails vs acrylic nails, there’s not really a way to say which one is the actual “winner.” At the end of the day, it’s totally up to you whether you want to opt for acrylic nails or gel nails — it’s all personal preference about which method works best for you and your lifestyle. Goodness knows that both beauty treatments boast a wide variety of fans, and either group would be more than happy to have you join them for the fun. How much do acrylic nails cost? The price of acrylic nails varies widely between nail technicians. According to Cost Helper Health, the typical cost for a mid-range acrylic manicure at a spa or salon ranges from $35 to $45 for a standard set. For colors like pink or white, that price can increase to $50 or $60. But how much are acrylic nails that feature an elaborate design? Don’t be shocked when you see that especially creative acrylic nails can cost up to $100 or even $120. For example, if you’re getting fancy coffin acrylic nails or holiday-themed acrylic nails, you can expect to pay a premium price. Remember: It might be tempting to pay a low price for acrylics, especially since there are “deals” of prices as low as $10 floating around out there. But when it comes to your nails — and everywhere else on your body — your health comes first. And there’s a much higher risk of your nails suffering in the long run from a low-quality acrylic set. Not worth it! How long do acrylic nails last? The lifespan of acrylic nails varies widely from person to person. For example, if someone uses his or her hands for work quite a bit — especially for manual labor — that person might learn pretty quickly that acrylic nails won’t last too long compared to someone who uses their hands for little more than typing. But how long do acrylic nails last in a general sense? Experts say you need to return to the salon every two to three weeks to fill in the gaps that appear as your natural nails grow. So that’s a good rule of thumb (and all the rest of your fingers!) to follow for how long you can expect your short coffin fake nails to look fabulous. But how often should acrylic nails be replaced? If you love wearing acrylic nails often, it might be worth considering removing them every two to three months to let them “breathe” in between sets. Are acrylic nails safe? In a piece for Mayo Clinic, dermatologist Lawrence E. Gibson, MD, says that artificial nails are unlikely to harm natural nails — as long as they’re healthy. That said, it is possible to encounter some problems if you’re not careful while maintaining them. If your artificial nail is damaged or if you let your nails grow too long, a gap can develop between your acrylic and your actual nail. The warm and moist environment there is basically a breeding ground for an icky infection. An infection might also happen if you request very long or rigid acrylics. Of course, if your technician uses unsanitary tools, this will put you more at risk for an adverse reactions (as is the case with just about every beauty treatment out there). Luckily, there are ways for fans of acrylic nails to keep themselves as safe as possible. Other than making sure that your nail technician properly sterilizes all tools used during the treatment, it’s also a good idea to select salons that display a current license and technicians who are licensed by the state board. For optimum safety, request a new nail file or bring your own (nail files cannot be sterilized like other nail tools). If you spot signs of a nail infection — such as redness, swelling, and Why do acrylic nails hurt the first day? According to licensed nail technicians, there are a few possible reasons why your acrylic nails might be hurting right after you get them done. For instance, the nail technician might have applied a tip that was too small for your nails. Maybe they accidentally pinched the nail during the application. Or perhaps your nail might have been over-filed. Although this can happen every now and then, it’s not a good sign if your acrylic nails hurt every single time you get them done. If you’re still wondering, “Why do acrylic nails hurt?” a day after your appointment, it might be time to find a different technician for the job. Are acrylic nails vegan? If you’re a strict vegan, acrylic nails might not be the best choice for you. According to The Beauty Academy, the brushes often used for stiletto fake nails are typically made from “kolinsky,” which is sometimes called sable hair. This kolinsky is real hair gathered from an animal — a type of weasel found in particularly cold places in Russia and China, to be specific. This natural hair from the weasel is the preferred brush option for many technicians because it has a certain thickness to it that helps it hold the acrylic liquid effectively. It’s also quite strong and flexible. That said, it’s worth noting that some technicians are starting to use synthetic bristles in their brushes for acrylics. As with technology in general, this “vegan” method is improving. But many nail technicians still prefer the brushes made with natural hair instead. If you’re not sure which type of brush — or which type of nail products in general — that your technician uses, always ask first. You might be surprised! Do acrylic nails damage your nails? According to Thomas Knackstedt, MD, of Cleveland Clinic, most folks can use acrylic nails without it affecting the overall health of the natural nails. However, it is possible that some people can develop a contact allergy to dyes or glues used during the appointment. But if you don’t get a reaction after the treatment, do acrylic nails damage your nails after you get them removed? As is the case with many beauty treatments, the part of the process that can actually be the most irritating is the removal of acrylic nails. If you take good care of your nails and keep them in generally good health, the irritation should be fairly minimal. That said, a few people might notice that their nails are particularly sensitive afterward and visibly brittle or discolored. If you’re part of that population, you may want to consider alternate options for your next manicure. But if not, feel free to get those bad boys glued on — especially if you have a special occasion coming up where it’s time to impress. Scroll below to see some of the most stunning types of acrylic nails out there, then click on a circular button below your favorite image to share it instantly with family and friends on Facebook, Twitter, or Pinterest! Coffin nails are a great way to add some edge to your mani when go-to shapes like square and almond just aren't cutting it. Coffin fall nails are even better when spooky season hits. Don't let the eerie name put you off—this shape is fierce and fun. If you're into the technical stuff, let's start off with the basics: What are coffin nails? “Traditionally coffin shaped nails are longer nails that have a square or straight top and often taper slight towards the tip," explains Emily Rudman, founder of Emilie Heathe. “Another popular shape is the ballerina which is a longer coffin shape—often the two are used interchangeably.” For those who want to give their fingers a more elongated shape as the leaves start to fall, coffin fall nail designs are a great option. The length is guaranteed to make a beauty statement, and the right autumn nail designs won't leave you feeling like you're cosplaying a pumpkin spice latte. And for years, longer nails have been used as a tool for creative expression and personal style, explains Rudman. “The longer the almond fake nails, the more of a canvas one has to work with. From a cultural standpoint, many of the trends we see in nails comes from Black, Asian, and Latinx cultures. And with those cultures in America making more of a statement while taking ownership of their contributions to society, those styles have also become more popularized.” Artists like Cardi B have been adorning their hands with extensions way before the fame and have continued to showcase new styles, while also helping put the people behind their eye-catching work on the map. Jenny Bui, the long-time nail artist responsible for many of Cardi and sister Hennessy's blinged-out manis is known for dazzling extensions drenched in technicolor Swarovski crystals. But while long nails seem to be everywhere, as seen on celebrities from Kylie Jenner to Dua Lipa, that wasn't always the case. In fact, not too long ago “claws” weren't a compliment. “There is also always appropriation, in this case, traditionally longer nails were viewed as ‘inappropriate’ or 'not classy,” says Rudman. "But as the world has shifted and as white cultures have accepted these beauty trends, it has lead to wider acceptance amongst the majority. It’s neither OK or fair, but it often happens this way." As beauty continues to evolve it's important to keep in mind the history of how the latest trends came to be to give credit where it's due. A marker for showcasing your personality while also adorning yourself, coffin nails are here to stay. If you've decided to swap out your go-to shape to give it a spin but are looking for some fall acrylic nails inspiration, read on. From jeweled tips to a classic french with a tropical twist, we've rounded up 10 of the cutest coffin fall nails to bookmark for your next salon visit.
Дата Публикации: 05-01-22
Water Well Maintenance and Rehabilitation
Описание: Water Well Maintenance and Rehabilitation The purpose of the study to obtained water well screens opening size and gravel packs size, and to access within the groundwater inter through the aquifer to the well screen and prevent running sand from entering the well. The use of properly designed screen and gravels are important and this paper is an important reference for the design of groundwater wells. In this study, the purpose of the circle method is to design water well and the benefits of sand control. The determination of screen slot size and its variation in the opening is often a major aim of hydrogeological studies. However, measurement of hydraulic conductivity (K) at a high spatial resolution in sedimentary aquifers is a challenge. One commonly used approach is to estimate slot size from grain size analysis. The objectives of this study are to compare between curve of grain size analysis, bar graph and circle method used applied different formulas for the determination of slot size from grain-size data and to evaluate how well this method predicts slot size and gravel pack. Correlation between the mechanical analysis curve, bar graph and the circle methods were found for the used applied different formulas. Based on circle results, the applied circle formulas appear to be suitable for an initial assessment of aquifer properties. However, considering the difference in calculated aquifer parameter values, results are smaller significantly and reliable for the high analysis of aquifer materials. The well screen is the component of a well which provides an opening through which water enters the well casing from the aquifer, as well as stabilizing the material in the “near-well zone” and preventing it from entering the well. Screens may be constructed with a variety of different materials and designs, as appropriate to the design of the well and its aquifers. Typical types of screen are: Horizontal bridge slot screen, a pipe-based well screen with punch-formed downward facing louver-shaped openings. Continuous wire wrap screens, manufactured by wrapping shaped wire around an internal array of rods. Bridge slot screens, produced by rolling and welding perforated steel plates or sheets. Machine-slotted (milled) screens, manufactured by milling casing with axially oriented precision cutters. Well casing perforated in place with a mills knife or a hydraulic perforator lowered down the cased borehole. Different wedge wire screen may by evaluated for a particular well design based on the material, size of perforations, percent of open area, cost, susceptibility to corrosion, and collapse strength. A properly designed screen allows sand-free water to flow into the well with a minimum drawdown. As a water well ages, the rate at which water may be pumped (commonly referred to as the well yield, flow or performance) tends to decrease, especially in wells that were not properly developed when first drilled. This fact sheet briefly describes common well problems and discusses prevention and rehabilitation measures. Water Well Maintenance Water wells require regular maintenance to ensure adequate water flow and continued drinking water safety. To ensure water quality, well water should be tested annually for total coliform bacteria and E. coli bacteria by a state accredited testing laboratory. Every three years, additional testing is recommended for pH and total dissolved solids as well as tests related to land uses occurring or expected to occur within sight of the well. Additionally, if there are obvious stains, tastes, or odors in water, seek testing that will help identify the source of these symptoms. Water wells should also be inspected annually for obvious signs of damage or contamination. Be sure the area within 100 feet around the continuous slot screen is clear of debris or items that might pollute the water supply. Get the well professionally inspected by a water well contractor every ten years. Keep all records related to the water well including: Water well completion report or log (if you have it) which should include information such as water well depth, date drilled, construction (including casing specifications, grouting and screen), and water well yield or flow rate in gallons per minute (gpm) Water quality test reports Past inspection reports Invoices from work done by water well contractors (including pump replacement) Water treatment equipment warranties, invoices and manuals To find some of this information you can check with the Pennsylvania Department of Conservation and Natural Resources (PA DCNR) Pennsylvania Groundwater Information System (PaGWIS) or contact a local well driller. Well Performance As a water well ages, the rate at which water may be pumped (commonly referred to as the well yield, flow or performance) tends to decrease, especially in wells that were not properly developed when first drilled. A drop or complete loss of water production from a well can sometimes occur even in relatively new wells due to a lowered water level from persistent drought or over-pumping of the well which can dewater the water-bearing zones. More often, reduced well yield over time can be related to changes in the water well itself including: Incrustation from mineral deposits Bio-fouling by the growth of microorganisms Physical plugging of "aquifer" (the saturated layer of sand, gravel, or rock through which water is transmitted) by sediment Sand pumping Well screen or casing corrosion Pump damage This fact sheet briefly describes these common problems and discusses alternative prevention and rehabilitation measures. Water Well Rehabilitation Measures taken to correct these problems are referred to as well rehabilitation or restoration. A successful well rehabilitation will maximize the flow of water from the well. The chances for successful rehabilitation are dependent on the cause(s) of poor well performance and the degree to which the problem has progressed. Upon noticing loss of performance in your well have a professional water well contractor inspect your well, preferably with a downhole camera. A common measure of the delivery of water by a water well is referred to as the "specific capacity" which is defined as the pumping rate (gallons per minute) divided by the drawdown or increased depth to water during pumping (in feet). Generally, a decrease of 25% or more in well yield indicates that rehabilitation is in order. Delaying rehabilitation procedures can significantly increase costs and in some cases make rehabilitation impossible. To detect deterioration of well performance, you must have a point of reference. Often this reference is the original well construction and pump test data which are normally supplied to you by the well driller on a well completion report or well log when the well is installed. However, even if you do not have this information, significant changes in your well are also a warning sign. The principal means used for rehabilitation of chemical incrustation problems involves the use of strong acid solutions to dissolve incrusting materials. Once loosened or dissolved, the incrusting materials are pumped from the well with the acid solution for disposal. The type of acid to be used, its form (liquid, granular, pelletized), the procedures used to introduce and agitate the acid solution, and the severity of incrustation all play a part in determining the success of acid treatment. It is common for acid-treated older wells to completely recover or even exceed the original well yield assuming any material dislodged by the acid is removed from the pre-packed well screen. While acid treatment methods for incrustation removal are very effective, mechanical methods, such as wire brushing or scraping, are often used in conjunction with acid treatment to improve results. A less common mechanical approach is the use of controlled blasting. Controlled blasting involves the use of explosives, carefully set at specific locations in the well bore, to fracture consolidated rock aquifer and incrusting materials. Experience has shown this technique, when done properly, to be useful for temporary well yield improvement. However, cracks opened by blasting often eventually become incrusted and additional rehabilitation measures are required to maintain well productivity. Rapid growth of these bacteria can quickly clog well screen pores and render a well virtually useless in a matter of months. Once iron bacteria become established in a well, they are extremely difficult to eradicate. Treating iron bacteria colonies in water wells is often a perpetual process that seeks to maintain well performance at an acceptable level. In general, chemical means of control are most effective. However, best results are achieved when chemical bactericides are used in conjunction with physical agitation of the well bore water to remove the biological residue. The chemical of choice for most small diameter wells is chlorine. It has the advantage of being readily available, inexpensive, and is generally accepted by health officials for use in potable water supplies. For general disinfection purposes following routine well and piping construction, repair, or pump installation, a 50 mg/L dose of free chlorine is recommended. For treatment of severe iron bacteria problems concentrations as high as 500 to 2,000 mg/L are used. However, chlorine treatment of iron bacteria problems may not be effective without subsequent agitation of the well water. Turbulent flow causes greater surface area exposure of slime growths to the chlorine solution and assists in dislodging obstructions. For more information on how to shock chlorinate a well, consult our fact sheet Shock Chlorination of Wells and Springs or contract with a professional well driller. Since precipitation of iron in the bacteria biomatting contributes to clogging of flow spaces, rehabilitation results are usually improved when acid treatments are alternated with bactericide treatments. The most important preventative measure to avoid physical plugging is proper well development. Adequate well development will stabilize the aquifer material so that subsequent pumping from the well will not result in excessive sediment removal. Removal of fine silt and clay particles introduced in some drilling fluids, or which naturally occur in certain kinds of aquifers, can only be accomplished with the use of chemical treatments. As with other chemical rehabilitation treatments, agitation of the chemical into and out of the aquifer formation is crucial to success of the operation. This agitation may be provided by a surge plunger, compressed air, well pump, or high-velocity jet. Use of a high-velocity jet is generally recognized as the most effective means of agitation. When water from the well is re-circulated for jetting, sediment should be removed prior to reuse. Continuous removal of dislodged sediment, as done in a re-circulating jet operation, gives the best results as the cleaning solution is able to penetrate more deeply into the aquifer medium.
Дата Публикации: 05-01-22