tfhj263
- Создано: 07-12-21
- Последний вход: 07-12-21
Профиль пользователя
tfhj263 объявления
Functional Foods: Benefits, Concerns and Challenges
Описание: Functional Foods: Benefits, Concerns and Challenges That foods might provide therapeutic benefits is clearly not a new concept. The tenet, “Let food be thy medicine and medicine be thy food” was embraced 2500 years ago by Hippocrates, the father of medicine. However, this “food as medicine” philosophy fell into relative obscurity in the 19th century with the advent of modern drug therapy. In the 1900s, the important role of diet in disease prevention and health promotion came to the forefront once again. During the first 50 years of the 20th century, scientific focus was on the identification of essential elements, particularly vitamins, and their role in the prevention of various dietary deficiency diseases. This emphasis on nutrient deficiencies or “undernutrition” shifted dramatically, however, during the 1970s when diseases linked to excess and “overnutrition” became a major public health concern. Thus began a flurry of public health guidelines, including the Senate Select (McGovern) Committee's Dietary Goals for the United States (1977), the Dietary Guidelines for Americans (1980, 1985, 1990, 1996, 2000— a joint publication of the USDA and the Department of Health and Human Services), the Surgeon General's Report on Nutrition and Health (1988), the National Research Council's Diet and Health (1989) and Healthy People 2000 and 2010 from the U.S. Public Health Service. All of these reports are aimed at public policy and education emphasizing the importance of consuming a diet that is low in saturated fat, and high in vegetables, fruits, whole grains and legumes to reduce the risk of chronic diseases such as heart disease, cancer, osteoporosis, diabetes and stroke. Scientists also began to identify physiologically active components in foods from both plants and animals (known as phytochemicals and zoochemicals, respectively) that potentially could reduce risk for a variety of chronic diseases. These events, coupled with an aging, health-conscious population, changes in food regulations, numerous technological advances and a marketplace ripe for the introduction of health-promoting products, coalesced in the 1990s to create the trend we now know as “functional foods.” This report includes a discussion of how functional foods are currently defined, the strength of the evidence both required and thus far provided for many of these products, safety considerations in using some of these products, factors driving the functional foods phenomenon, and finally, what the future may hold for this new food category. What are functional foods? All foods are functional to some extent because all foods provide taste, aroma and nutritive value. However, foods are now being examined intensively for added physiologic benefits, which may reduce chronic disease risk or otherwise optimize health. It is these research efforts that have led to the global interest in the growing food category now recognized as “functional foods.” Functional foods have no universally accepted definition. The concept was first developed in Japan in the 1980s when, faced with escalating health care costs, the Ministry of Health and Welfare initiated a regulatory system to approve certain foods with documented health benefits in hopes of improving the health of the nation's aging population (1). These foods, which are eligible to bear a special seal, are now recognized as Foods for Specified Health Use (FOSHU).3 As of July 2002, nearly 300 food products had been granted FOSHU status in Japan. In the United States, functional foods have no such regulatory identity. However, several organizations have proposed definitions for this new food category. In 1994, the National Academy of Sciences' Food and Nutrition Board defined functional foods as “any modified food or food healthcare ingredients that may provide a health benefit beyond the traditional nutrients it contains” (2). The International Life Sciences Institute defines them as “foods that, by virtue of the presence of physiologically-active components, provide a health benefit beyond basic nutrition” (3). In a 1999 position paper, the American Dietetic Association defined functional foods as foods that are “whole, fortified, enriched, or enhanced,” but more importantly, states that such foods must be consumed as “… part of a varied diet on a regular basis, at effective levels ” for consumers to reap their potential health benefits (4). Another term often used interchangeably with functional foods, although it is less favored by consumers, is “nutraceuticals,” a term coined in 1991 by the Foundation for Innovation in Medicine to refer to nearly any bioactive component that delivers a health benefit. In a 1999 policy paper, Zeisel (5) astutely distinguished whole foods from the isolated components derived from them in his following definition of nutraceuticals: “those diet supplements that deliver a concentrated form of a presumed bioactive agent from a food, presented in a nonfood matrix, and used to enhance health in dosages that exceed those that could be obtained from normal food.” Several factors are responsible for the fact that this is one of the most active areas of research in the nutrition sciences today: 1) an emphasis in nutritional and medical research on associations between diet and dietary constituents and health benefits, 2) a favorable regulatory environment, 3) the consumer self-care phenomenon, and 4) rapid growth in the market for health and wellness products. Criteria for sound science According to the Department of Health and Human Services, diet plays a role in 5 of 10 of the leading causes of death, including coronary heart disease (CHD), certain types of cancer, stroke, diabetes (noninsulin dependent or type 2) and atherosclerosis. The dietary pattern that has been linked with these major causes of death in the United States and other developed countries is characterized as relatively high in total and saturated fat, cholesterol, sodium and refined sugars and relatively low in unsaturated fat, grains, legumes, fruits and vegetables. An accumulating body of research now suggests that consumption of certain foods or their associated physiologically active components may be linked to disease risk reduction (6). The great majority of these components derive from plants; however, there are several classes of physiologically active functional food ingredients of animal or microbial origin. Claims linking the consumption of functional foods or food advanced health ingredients with health outcomes require sound scientific evidence and significant scientific agreement. The Food and Drug Administration (FDA) outlined the criteria for “significant scientific agreement” in a guidance document released on December 22, 1999 (7). As summarized in the schematic shown in Figure 1, there is a clear discrepancy between “emerging evidence” (characterized by in vitro or animal studies, uncontrolled human studies, and inconsistent epidemiological evidence) and “significant scientific agreement.” To reach such agreement requires the support of a body of consistent, relevant evidence from well-designed clinical, epidemiologic and laboratory studies, and expert opinions from a body of independent scientists. Claims about the health benefits of functional foods should be based on sound scientific evidence, but too often only so-called “emerging evidence” is the basis for marketing some functional foods or their components. Table 1 categorizes a variety of functional foods according to the type of evidence supporting their functionality, the strength of that evidence and the recommended intake levels. Functional foods of animal origin Probably the most intensively investigated class of physiologically-active components derived from animal products are the (n-3) fatty acids, predominantly found in fatty fish such as salmon, tuna, mackerel, sardines and herring (8). The two primary (n-3) fatty acids are eicosapentaenoic acid (EPA; 20:5) and docosahexaenoic acid (DHA; 22:6). DHA is an essential component of the phospholipids of cellular membranes, especially in the brain and retina of the eye, and is necessary for their proper functioning. DHA is particularly important for the development of these two organs in infants (9), and just recently, the FDA cleared the use of DHA and arachidonic acid for use in formula for full-term infants (10). Hundreds of clinical studies have been conducted investigating the physiologic effects of (n-3) fatty acids in such chronic conditions as cancer, rheumatoid arthritis, psoriasis, Crohn's disease, cognitive dysfunction and cardiovascular disease (11), with the best-documented health benefit being their role in heart health. A recent meta-analysis of 11 randomized control trials suggests that intake of (n-3) fatty acids reduces overall mortality, mortality due to myocardial infarction and sudden death in patients with CHD (12). The 2000 American Heart Association Dietary Guidelines recommend two servings of fatty fish per week for a healthy heart (13), and the FDA authorized a qualified health claim on dietary supplements linking the consumption of EPA and DHA (n-3) fatty acids to a reduction of coronary heart disease risk (14). The qualified claim states: “Consumption of omega-3 fatty acids may reduce the risk of coronary heart disease. FDA evaluated the evidence and determined that, although there is scientific evidence supporting the claim, the evidence is not conclusive.” A “qualified” claim was authorized because of certain safety concerns regarding the consumption of high levels of (n-3) fatty acids, including: 1) increased bleeding times; 2) increased risk for hemorrhagic stroke; 3) the formation of biologically active oxidation products from the oxidation of (n-3) fatty acids; 4) increased levels of LDL cholesterol; and 5) reduced glycemic control among people with diabetes. The FDA concluded that use of (n-3) fatty acid supplements is safe, provided daily intakes of EPA and DHA from supplements do not exceed 2 g/d (14). Another class of biologically active animal-derived components that has received increasing attention in recent years is probiotics. Defined as “viable microorganisms that are beneficial to human health” (15), the health benefits of probiotics have been considered since the turn of the century when the Nobel prize-winning microbiologist Metchnikoff first postulated that lactic acid bacteria contributed to the longevity of Bulgarian peasants (16). It is thought that a wide variety of live microorganisms can contribute to human health, although the evidence is mainly from animal studies. In addition to numerous strains of Lactobacillus acidophilus, other strains of lactobacillus are being incorporated into functional food products, as food additives, now on the market including L. johnsonii La1, L. reuteri, L. GG, and L. casei Shirota. A recent Scientific Status Summary on probiotics from the Institute of Food Technologists summarized the scientific support for the therapeutic and/or preventive use of these functional ingredients for various health concerns including cancer, intestinal tract function, immune function, allergy, stomach health, urogenital health, cholesterol lowering and hypertension (17). The review emphasizes that the future success of probiotics will require strong support from medical and nutrition scientists and that studies documenting these effects in humans are limited. More recently, research efforts have focused on prebiotics, i.e., nondigestible food ingredients that beneficially affect the host by selectively stimulating the growth and/or activity of one or a limited number of beneficial bacteria in the colon, thus improving host health (18). Prebiotics include short-chain carbohydrates such as fructooligosaccharides and inulin, which enter the colon and serve as substrates for the endogenous colonic bacteria. Newer still is the concept of “synbiotics,” which are mixtures of probiotics and prebiotics that beneficially affect the host by improving the survival and implantation of live microbial dietary supplements in the gastrointestinal tract, by selectively stimulating the growth and/or by activating the metabolism of one or a limited number of health-promoting bacteria, and thus improving host welfare (18). Another nonplant ingredient that has been the focus of increased research efforts in recent years is conjugated linoleic acid (CLA). This component, which was first identified as a potent antimutagenic agent in fried ground beef by Pariza and co-workers (19), is a mixture of structurally similar forms of linoleic acid (cis-9, trans-11 octadecadienoic acid). CLA is present in almost all foods, but occurs in particularly large quantities in dairy products and foods derived from ruminant animals (20). For example, uncooked beef contains 2.9–4.3 mg CLA/g fat, whereas lamb, chicken, pork and salmon contain 5.6, 0.9, 0.6, and 0.3 mg CLA/g fat, respectively, and dairy products contain 3.1–6.1 mg CLA/g fat (21). The inhibition of mammary carcinogenesis in animals is the most extensively documented physiologic effect of CLA (22), and there is also emerging evidence that CLA may decrease body fat and increase muscle mass both in rodent models (23) and in humans (24), although not all human studies have been positive in this regard. There is also preliminary evidence that CLA may increase bone density in animal models (25). Functional foods of plant origin (Natural Plant Extract) Numerous plant foods or physiologically active ingredients, such as pharmaceuticals, derived from plants have been investigated for their role in disease prevention and health. However, only a small number of these have had substantive clinical documentation of their health benefits. An even smaller number have surpassed the rigorous standard of “significant scientific agreement” required by the FDA for authorization of a health claim, which will be discussed in further detail below. Those plant foods currently eligible to bear an FDA-approved health claim include oat soluble (β-glucan) fiber (26), soluble fiber from psyllium seed husk (27), soy protein (28) and sterol- and stanol-ester–fortified margarine (29). Some plant-based foods or food constituents currently do not have approved health claims, but have growing clinical research supporting their potential health benefits, and thus would be described as having moderately strong evidence. These include cranberries, garlic, nuts, grapes and chocolate and are discussed briefly below. Cranberries have been recognized since the 1920s for their efficacy in treating urinary tract infections. A landmark clinical trial (30) confirmed this therapeutic effect in a well-controlled study involving 153 elderly women. More recent research has confirmed that condensed tannins (proanthocyanidins) in cranberry are the biologically active component and prevent E. coli from adhering to the epithelial cells lining the urinary tract (31). New preliminary research suggests that the antiadhesion properties of the cranberry may also provide other health benefits, including in the oral cavity (32). Garlic (Allium sativum) has been used for thousands of years for a wide variety of medicinal purposes; its effects are likely attributable to the presence of numerous physiologically active organosulfur components (e.g., allicin, allylic sulfides) (33). Garlic has been shown to have a modest blood pressure–lowering effect in clinical studies (34), while a growing body of epidemiologic data suggests an inverse relationship between garlic consumption and certain types of cancer (35), particularly of the stomach (36). The latter may be due in part to garlic's ability to inhibit the activity of Helicobacter pylori (the bacterium that causes ulcers). The best-documented clinical effect of garlic, however, concerns its ability to reduce blood cholesterol. A meta-analysis of 13 placebo-controlled double blind trials (37) indicated that garlic component(s) (10 mg steam distilled oil or 600–900 mg standardized garlic powder) significantly reduced total cholesterol compared with placebo by 4–6%. However, the Agency for Healthcare Research & Quality (38), which examined randomized, controlled trials at least 1 mo in duration, concluded that, although clinical trials show several promising, modest, short-term effects of garlic supplementation on lipid and antithrombotic factors, “effects on clinical outcomes are not established …” This is likely due to lack of consistency among studies in type of preparation used and overall study design. Although foods high in fat have traditionally not been regarded as “heart-healthy” (except for fatty fish), evidence is accumulating on the cardiovascular benefits of a variety of nuts, when they are part of a diet that is low in saturated fat and cholesterol (39). Clinical trials, which have specifically examined the effect of almonds on blood lipids, have found that these tree nuts significantly reduced total cholesterol by 4–12% and LDL cholesterol by 6–15% (40,41). More recently, a Life Sciences Research Office review of six clinical intervention trials with walnuts consistently demonstrated decreases in total and LDL cholesterol that should lower the risk of CHD (42). In the late 1970s researchers noted that residents in certain areas of France, who were avid drinkers of red wine, had less heart disease than other Western populations even though they consumed more fat in their diet. This observation triggered numerous investigations into this so-called “French Paradox” (43) and subsequent research confirmed the presence of high concentrations of antioxidant polyphenolics in red grape skins. It must be noted however, that moderate consumption of any alcoholic beverage, e.g., beer, wine or distilled spirits, has been shown in a number of studies to reduce the risk of heart disease in selected populations (44). For those wishing to abstain from alcohol, recent clinical trials demonstrate that grape juice may also exert beneficial effects similar to those of red wine because both are rich in phenolic antioxidant compounds. Consumption of grape juice has been shown to reduce platelet aggregation (45). Another food that is a source of polyphenolics and is just beginning to be investigated for its potential benefits to heart health (46) is chocolate. Chocolate contains flavonoids (procyanidins), which may reduce oxidative stress on LDL cholesterol. In a recent clinical trial involving 23 subjects consuming a diet supplemented with chocolate and cocoa powder providing 466 mg procyanidins/d, time to oxidation of LDL cholesterol was increased by 8% compared with subjects consuming a normal American diet (47). Epidemiologic data are accumulating on the health benefits of several additional functional foods or food components of plant origin, including tea (catechins), lycopene from tomatoes, particularly cooked and/or processed tomato products, and the carotenoids lutein and zeaxanthin from green leafy vegetables. The effect of green or black tea consumption on cancer risk (48) has been the focus of numerous studies. Studies in animals consistently show that consumption of green tea reduces the risk of various types of cancers. Only a few studies have thus far assessed the effects of black tea. Green tea is particularly abundant in specific polyphenolic components known as catechins (49). The major catechins in green tea are (?)-epicatechin, (?)-epicatechin-3-gallate, (?)-epigallocatechin and (?)-epigallocatechin-3-gallate (EGCG) (50). One cup (240 mL) of brewed green tea contains up to 200 mg EGCG, the major polyphenolic constituent of green tea. Although 100 epidemiological studies have examined the effect of tea consumption on cancer risk, the data are conflicting (51). A recent study (52) involving 26,311 residents from three municipalities in northern Japan found no association of green tea consumption with the risk of gastric cancer. Phase I clinical trials are currently ongoing at the MD Anderson Cancer Center (Houston, TX) in collaboration with the Memorial Sloan-Kettering Cancer Center in New York on the safety and efficacy of consuming the equivalent of >10 cups of green tea by 30 cancer patients with advanced solid tumors. Tomatoes and tomato products are also being investigated for their role in cancer chemoprevention and are unique because they are the most significant dietary source of lycopene, a non-provitamin A carotenoid that is also a potent antioxidant (53). A comprehensive review of 72 epidemiologic studies (54) found an inverse association between tomato intake or plasma lycopene concentration and the risk of cancer at a defined anatomical site in 57 of the 72 studies reviewed (79%); in 35 of these studies, the inverse associations were statistically significant. No study indicated higher risk with increasing tomato consumption or lycopene blood levels. Further, the risk reduction for about half of all studies reviewed was 40% (i.e., a relative risk estimate of 0.6). Cancers of the prostate, lung and stomach showed the strongest inverse associations, whereas data were suggestive for cancers of the pancreas, colon and rectum, esophagus, oral cavity, breast and cervix. Most ongoing clinical trials involving lycopene and cancer prevention are focused on prostate cancer, in large part because a 1995 study (55) involving > 47,000 participants from the Health Professionals Follow-Up Study (HPFS) followed from 1986 to 1992 found that >10 servings/wk of tomato sauce, tomatoes, tomato juice or pizza could reduce risk of prostate cancer by 35%; advanced prostate cancer (i.e., more aggressive tumors) was reduced by 53%. More importantly, of the 46 fruits and vegetables evaluated, tomato products were the only foods that were associated with reduced risk of prostate cancer. Additional follow-up data from the HPFS through 1998 further supported the earlier observation that lycopene reduces prostate cancer risk and, more specifically, found that that intake of tomato sauce (2+ servings/wk) was associated with a 23% reduction in prostate cancer risk (56). The protective effect of tomato products may result from lycopene's ability to selectively accumulate in the prostate gland, perhaps serving an antioxidant function in that organ (57). This hypothesis was strengthened by a recent study that found that men with localized prostate adenocarcinoma had significantly reduced prostate DNA oxidative damage after consumption of tomato-sauce based meals containing 30 mg lycopene for 3 wk (58). Another carotenoid that has received recent attention for its role in disease risk reduction is lutein, the main pigment in the macula of the eye (an area of the retina responsible for the sharpest vision). More specifically, research is focusing on the role of lutein in eye health due to its ability to neutralize free radicals that can damage the eye and by preventing photooxidation. Thus, individuals who have a diet high in lutein may be less likely to develop age-related macular degeneration (AMD) (59,60) or cataracts (61,62), the two most common causes of vision loss in adults. Because of the increasing evidence for lutein's role in eye health, supplements that contain this carotenoid are now appearing on the market. There is some concern, however, that lutein in supplement form may not provide the same benefit as the lutein found naturally in foods (63). In March 2000, the National Eye Institute of the NIH released a statement on lutein and its role in eye disease prevention (64): “Claims made about an association between lutein and eye health should be approached with caution. The possible benefits of lutein on the eye remain uncertain.” The statement indicates that there is little direct scientific evidence at this time to support a claim that taking supplements containing lutein can decrease the risk of developing AMD or cataract. Nevertheless, the possibility that lutein may reduce the risk of oxidant-related diseases of the eye clearly warrants further research. Good sources of lutein include green leafy vegetables such as spinach (7.4 mg/100 g) and cooked cabbage (14.4 mg/100 g). Although not yet supported by clinical or epidemiologic data, evidence from in vitro and in vivo (animal) studies supports the cancer-preventive benefits of flaxseed lignans (65), citrus fruit limonoids (66) and various cruciferous vegetable phytochemicals, including isothiocyanates and indoles (67). With respect to the latter, broccoli sprouts are currently being marketed both as a dietary supplement, highlighting the potential cancer-preventive action of one purported physiologically active component, sulforaphane, and as a food containing high levels of sulforaphane. In vitro and in vivo, this component has been shown to be a potent inducer of Phase II detoxifying enzymes in the liver. Such enzymes speed the inactivation of toxic substances and thus accelerate their elimination from the body (68). The marketing of conventional foods as dietary supplements has engendered controversy, however, as will be discussed below. Safety considerations Although there is evidence that certain functional foods or food ingredients can play a role in disease prevention and health promotion, safety considerations should be paramount. Safety concerns have recently been raised, particularly with regard to the seemingly indiscriminate addition of botanicals to foods. A plethora of “functional” bars, beverages, cereals and soups are being enhanced with botanicals, some of which may pose a risk to certain consumers. The safety issues related to herbs are complex and the issue of herb-drug interaction has received increasing attention. One example is St John's wort, a popular herb utilized for treating mild depression. Hypericum extract from St. John's wort significantly increases the metabolic activity of liver cytochrome P450. This enzyme inactivates several drugs, and thus would be expected to decrease their levels and activities in the body. Consuming St. John's wort has been shown to cause concomitant decreases in plasma concentrations of theophylline, cyclosporine, warfarin and ethinylestradiol/desogestrel (oral contraceptives) (69). Such data prompted the FDA to issue a Public Health Advisory about St. John's wort in February of 2000, as have Canadian authorities. In the United States, some consumer groups have lobbied the FDA to halt the sale of 75 functional foods enhanced with St. John's wort as well as the following additional herbs: guarana, gotu kola, ginseng, ginkgo biloba, echinacea, kava kava and spirulina. Also in 2000, the General Accounting Office (GAO) released a report that raised concerns about the safety of certain functional foods (70). The GAO report stated that the FDA “has not developed regulations or provided guidance to companies on the type of safety-related information that should be included on their labels for functional foods and dietary supplements. The absence of such safety information poses a significant safety risk to some consumers.” In June of 2001, the FDA issued warning letters to the food industry concerning the use of “novel ingredients” such as St. John's wort in conventional food (71). The GAO has made the following recommendations regarding the safety of functional foods: Develop and promulgate regulations or other guidance for industry on the evidence needed to document the safety of new dietary ingredients in dietary supplements Develop and promulgate regulations or other guidance for industry on the safety-related information required on labels for dietary supplements and functional foods Develop an enhanced system to record and analyze reports of health problems associated with functional foods and dietary supplements A favorable regulatory environment Three important changes that affected the dissemination of information to consumers about the relationship between diet and health in food regulations occurred in 1990, 1994 and 1997. The first of these is the Nutrition Labeling and Education Act of 1990 (NLEA). The NLEA allows statements on food labels that characterize the relationship of any food or food component to a disease or health-related condition. Such “health claims” must be preapproved by the FDA before their use. Under the NLEA, the FDA was mandated by Congress to review 10 diet-disease relationships, eight of which were eventually approved as health claims.
Дата Публикации: 07-12-21
Paper Tubes
Описание: Paper Tubes Introduction This article provides comprehensive information about paper tubes, paper core and composite cans. You will learn how these paper and paperboard products are made and their materials of construction as well as paper tube applications, advantages and drawbacks. Read further to answer questions like: What‘s the difference between paper tubes, paper tubes and composite cans? Why should you select paper tube containers instead of plastic, glass, or metal packaging? What types and sizes of paper tubes are available from leading manufacturers? How do I specify paper tubes when ordering or submitting an RFQ? How is the quality of paper tube products I am buying tested and assured? How easily can I dispose of or recycle used paper tubes and paper cores? And much more... Paper Tubes Paper Tubes from Ace Paper Tube I. What is a Paper Tube? Paper tubes consist of paper or paperboard sheet layers wound together to form strong, hollow, and usually cylindrical shapes. The paper layers are laminated or bonded together using adhesives. The wall thickness of the tube can vary depending on the number of layers wrapped during manufacturing. Paper tubes are also known as paper cores, paperboard tubes, paper cans, fiber drums with paper drum machine, fiber tubes, paper tubing, wound tubes, composite cans, coreboard tubes, and cardboard tubes. While widely used everywhere, the term "cardboard tube" is a misnomer. Cardboard consists of three kraft layers with the central layer corrugated. II. Paper Tube Types and Shapes Paper Tube and Core Types While paper tubes, paper cores and related products are all made from wound plies of paper or paperboard. Paper tubes with paper tube cutting machine or cores can be constructed from one, two or many plies of brown kraft paper or paperboard. The innermost layer or ply, the liner, and the outermost layer, the wrap, can consist of different materials (foil, film, etc.) or specialized paper. The specialized paper and materials can provide water resistance, graphics or labeling, or a specific color. The two main types of paper tubes and cores include spiral wound and convolute or parallel wound paper tubes. Convolute wound tubes are used in applications requiring high bend strength, crush resistance and dynamic strength. A spiral wound tube has the paper ply or plies wrapped around at an angle to the tube's axis. In convolute tubes, the outer two edges of the paper strip are wrapped parallel or at a 90-degree angle to the tube‘s axis. Paper tubes have thinner walls and are widely used as containers or packaging for products with paper packaging machine. A paper core is essentially a heavy-walled paper tube. The much thicker wall of paper cores enables their use in winding webs or sheets of flexible material into rolls in converting operations. Paper machines produce extremely large rolls (also known as machine, jumbo, tambour or mother rolls), which are rotary slit or converted into many narrower smaller rolls on a winder with a paperboard core. Similar jumbo rolls are converted in plastic film, foil, textile and coated abrasive plants. You will be surprised that not all paper tubes are geared toward packaging applications. Paper cores can be machine elements. Paper cores used for winding large rolls in a paper mill or plastic film production plant are machine elements and require extremely high strength paper cores, which are often convoluted. Paper cores for retail or small diameter width rolls of adhesive tape, label, foil, paper, tissue or plastic film are a packaging and dispensing product, which can consist of a thinner, spiral wound core. The paper tube material is rotary or saw cut into paper cans or composite cans, shipping tubes, push tubes, pyrotechnic tubes, display poles, converting cores, concrete piling forms, and other paper tube products. Large fiber or composite drums and even paper straws are manufactured in a similar winding process. Convolute winders are typically used to make composite drums, which are a more eco-friendly alternative to steel drums. Paper straws are spiral wound at very high speeds. Paper Tube Shapes You will find that most paper tubes have a cylindrical shape or round cross-section, but paper tubes can be made with square, oval, hexagonal, triangular, and other custom shapes by using a square, oval and custom shaped winding mandrel. Custom shapes are useful for fitting the tube specifically to a part or product shape while elim Tapered paper tubes or paper cones are wound with a cone-shaped mandrel. Paper cones are used as yarn carriers in the textile industry. For certain applications, you may want your paper tubes slit or cut along their length to make half-shells such as facilitates covering large rolls for protection. They can be reconnected with tape or h-profiles. You will find covering a paper roll or coiled steel roll easier with half-shells compared to sliding a roll into a large protective paper tube. III. How Are Paper Tubes Made? Paper Tube and Core Manufacturing Paper tube and core manufacturing is a paper converting process combining web slitting, web winding and lamination or adhesive bonding steps. Through multiple wraps or revolutions of one or more paper webs or ribbons around a steel mandrel, several layers or plies of paper or paperboard are laminated together around a steel mandrel to form rigid, high strength tubes or fiber cores with paper core making machine. In my experience, plies are usually around 2 to 10 inches (50 to 250 mm) wide, but in some plies are as wide as 20 inches (500 mm). Ply thicknesses are typically around 0.008 to 0.050 (0.2 to 1.3 mm). The number of plies ranges from 1 to 50 or more, but paper cores with 3 to 30 plies are more common. We find that the strength of paper core is a function of the paperboard ply bond strength, ply thickness, bond area or overlap and adhesive bond strength. What I find interesting is that paperboards are made in a single thicker papermaking process or by bonding or laminating several plies together, so some paper tubes can consist of laminations or laminated plies! To me, a review of related patents and technology definitions in the USPTO website can help provide a greater understanding and in-depth details on the paper tube making process. Subclass B31C provides the United States Patent and Trademark Office (USPTO) cooperative patent classification (CPC) and technology definitions for paper or wound tube manufacturing processes. B31C 9/00 is defined as "Simultaneous forming of cylindrical and conical shapes by winding separate webs, e.g. forming bottles". The paper tube making process can include winding, folding and bending depending on the specific shape (round, square, conical, etc.) desired in the finished end product. Spiral Paper Tube or Core Manufacturing In the spiral paper tube or core manufacturing process with paper core machine, jumbo rolls of paper, paperboard, and lining materials are converted in a rotary slitting operation with paper slitting machine into narrower width ribbons. The paper ribbons are rewound into narrow rolls on rewinding stands. The narrow paper ribbon rolls are stacked in what looks to me like giant stacks of "poker chips". The "poker chip" stacks or rolls of paper ribbon are transported and loaded into the tube manufacturing machine. Narrow paper webs or ribbons from several different rolls are passed through guides and attached, adhered or taped to a steel mandrel in an overlapping fashion or with spacing between leading edges of the paper ribbons. The festooning or spacing allows the ribbons to feed without interference between ribbons. You will see that by attaching the leading edge or end of the ribbon obliquely or at an angle less than 90 degrees to the axis of the mandrel, the result is the formation of spiral during winding. The outer diameter of the steel mandrel determines the inner diameter of the finished paper tube. The wall thickness of the tube is a function of the thickness of the paper or paperboard ribbons, the adhesive thickness and the number of ribbons used in the process. Adhesive or glue is applied to each paper ribbon or ply before being wound onto the steel mandrel. In my experience coating webs of paper, cloth, vulcanized fibre and plastic film, a variety of web coaters can apply the adhesive to the plies such as: Roll coaters Reverse roll coaters Slot die coaters Extrusion coaters Curtain coaters Brush coaters Spray coaters Blade coaters Metering bar coaters Dip coaters What‘s fascinating is how the paper tube belt twists around in a helical shape to continuously form and bond the paper tube plies together. The flexible belt wraps around and applies pressure to the paper layers, which assures the proper formation of adhesive bonds between the paper ribbons. The fabric reinforced rubber belt also advances the tube forward along the mandrel. I have to imagine that the stresses and performance requirements on the paper tube forming belt are enormous. These belts are endless or seamless and prevent marking. They have high tensile strength and high friction to grab and move the tube along and easy to clean. Nitta, Passaic, Rainbow are some of the suppliers of tube forming belts. Next, we see that as additional paper plies are added at one end of the paper tube forming mandrel, the formed or laminated paper tube slides off the other end of the mandrel and is cut to length using rotary blade slicing or offline sawing operations. Additional deburring of the tube end edge may be performed depending on the end-use. Another interesting aspect of the paper tube manufacturing process to me is the ability to make an enormous amount of highly customized paper tube product or materials combinations by using different material plies. Liner or lining layers are used on the inner diameter (first ribbon) or outer diameter (last ribbon) of the tube to improve water resistance, moisture resistance or grease resistance. Liners can consist of metal sheet, foil, coated paper (wax, silicone, or plastic), plastic film and other protective materials. If your current application is not satisfied with existing paper tubes, you can well imagine a custom paper tube manufacturer can engineer a new combination of liners, plies and wraps to meet the needs of your specialized application. As long as the order volume is sufficient. One great ability I find in paper tube manufacturing is the ability to provide branding through labeling or print to enhance marketing inside and out. If printed or decorative graphics are required on the inside or outside of the paper tube, then the printed paper ribbons or ribbons made of printable material can be used on the first and last ribbons. A white paper or paperboard could be used on the outer layer with stronger brown kraft paper used on the inner layers. Convolute Paper Tube or Core Manufacturing In the parallel or convolute paper tube or core manufacturing process, jumbo rolls of paper, paperboard, and lining materials are converted in a slitting operation, but not into the very narrow width ribbons used in spiral tube manufacturing. In the convolute paper tube or core manufacturing process, the leading edge of the ribbon is parallel to the axis of the paper tube mandrel, so a single seam or flap along the length of the paper tube results. An external metal roll can apply pressure instead of a belt, which squeezes out any voids or air pockets providing better contact of the adhesive and therefore a stronger adhesive bond between paper plies. Since the paper web is wider, higher pressures and tension can be applied in the convolute winding process. The higher pressures and tensions in convolute paper tube manufacturing result in tubes with higher strength compared to the spiral wound tubes.
Дата Публикации: 07-12-21
What are the benefits of propolis?
Описание: What are the benefits of propolis? Propolis is a resin that bees create. It contains a mixture of bee saliva, beeswax which can be used into beeswax candles, and substances from plants and trees. Propolis may have some health benefits for humans, but more large-scale studies are necessary. Bees use propolis, or “bee glue,” as a sealant. Historically, humans have used it topically or as an oral supplement. However, it may not be suitable for everyone. This article will look at what propolis is, what the research says about its potential benefits, and how to use it. What is propolis? Propolis is a resinous, waxy substance that bees create by mixing their saliva with beeswax, along with compounds from various plants and trees. Bees use it to seal gaps in the hive to keep out intruders. Propolis also has antimicrobial properties and may protect bees from pathogens. The substances that make up propolis can be complex. Scientists have identified more than 300 separate compoundsTrusted Source in propolis. The exact composition can depend on the location of the beehive. As a rough guideline, propolis typically consists of: tree and vegetable resins: 50% beeswax: 30% pollen: 5% essential and aromatic oils: 10% Propolis also contains polyphenols, such as flavonoids, which are a type of antioxidant. Medicinal properties One 2019 review suggests that people have used bee propolis as a medicine since the year 300 BCTrusted Source. Ancient Egyptians used propolis for embalming, and some doctors used it during World War II to help with wound healing. The same 2019 review suggests that it may have the following properties: antibacterial antiprotozoal, which means that it works against parasitic illnesses, such as giardiasis anti-inflammatory antioxidant Some of the substances present in propolis may also have anticancer properties. However, although laboratory and animal studies into the properties of propolis and its components are promising, few high quality studies have proven its effectiveness as a treatment for specific conditions in humans. Potential uses Modern research suggests that propolis may be useful for: minor wounds oral hygiene inflammation cold sores The following sections will look at some of this research in more detail. Wound healing One 2015 reviewTrusted Source suggests that propolis may aid wound healing. An animal study in rats with diabetes showed that propolis helped the skin grow new cells in order to repair itself. Because people with diabetes can experience slow wound healing, this suggests that propolis could be beneficial for helping the skin heal more quickly. As propolis also kills some types of bacteria, it may also help prevent infection. Oral health According to the same 2015 reviewTrusted Source, propolis also appears to prevent the formation of calcium phosphate, which is the main component of dental plaque. Propolis and honey are also antibacterial, which may make them useful as ingredients in dental care products. According to one small study in the review, propolis significantly decreased the amount of bacteria in the saliva of people with periodontitis. Inflammation The antioxidants in propolis may work to reduce inflammation, such as the inflammation that arthritis causes. Animal studiesTrusted Source have tested propolis as an anti-inflammatory agent in rats and mice with arthritis. In both studies, the propolis inhibited swelling and appeared to have an impact on how the inflammation developed. Scientists believe that propolis may regulate inflammatory substances in the body, such as prostaglandins. Herpes A systematic review in the journal Complementary Therapies in Medicine suggests that propolis may work as an alternative treatment for genital or oral herpes. Herpes is caused by the herpes simplex virus (HSV). HSV-1 typically causes oral herpes, which can result in cold sores. HSV-2 is sexually transmitted, and it causes an infection that can result in painful blisters on the genitals. In the review, researchers analyzed several trials into honey and propolis, comparing their effects with those of acyclovir, which is a common HSV medication. In 4 out of 6 trials, propolis was more effective than acyclovir for treating HSV skin lesions — particularly cold sores. However, the researchers did not include a large number of trials in this review. Insufficient evidence Although people have used propolis for many health conditions in the past, there is not strong scientific evidence to support all of them. The following sections will look at some of these health conditions in more detail. Diabetes According to the 2015 reviewTrusted Source, one older study in rats found that propolis was associated with lower blood sugar levels. However, this is not enough e Cancer Laboratory studiesTrusted Source suggest that the compounds in propolis may inhibit cancer cell growth or induce cell death in cancer cells. Some in vivo tests have shown that flavonoids from propolis can inhibit the development of oral cancer, lung cancer, skin cancer, breast cancer, and more. However, much of the research in this field has involved isolated cells or animal models. COVID-19 One 2020 study in the journal Phytotherapy ResearchTrusted Source argues that propolis’s antiviral properties may mean that it works against SARS-CoV-2. This is the coronavirus that causes COVID-19. Previous laboratory studies have shown that propolis exhibits antiviral activity against other types of virus, including: espiratory syncytial virus Propolis also appears to help stimulate the immune system. For these reasons, the researchers suggest that propolis may help with preventing SARS-CoV-2 infection. However, while clinical trials on propolis’s ability to prevent COVID-19 are underway, there is currently no evidence to suggest that it is effective for this purpose. Allergies One study in the journal Oxidative Medicine and Cellular LongevityTrusted Source notes that propolis contains compounds that may have an anti-allergy effect in the body. Some people may feel a benefit from using propolis for this purpose. However, there is not much scientific evidence to prove that propolis can help reduce allergy symptoms. Safety Propolis appears to be safeTrusted Source for humans to use, at reasonable doses, both on the skin and internally. Reports of allergic reactions are rare, and there are no recorded cases of toxicity. However, because propolis can contain a wide variety of compounds depending on where it came from, it is not always possible to be sure of its contents. When looking for propolis products, check that the manufacturer has carried out third party testing to verify that the propolis is pure and safe to use. Always speak with a doctor before trying new supplements. How to use propolis People can use propolis in several ways, including: as an oral supplement diluted in water as a mouthwash topically on the skin Before using propolis, it is best to seek the advice of a doctor to check that it will be safe for an individual to use. Then, the person should patch test some propolis to make sure that they do not have an allergy to it. For use on the skin, apply pure propolis or a skin product that contains propolis as an active ingredient. For use in the mouth, dilute a small amount of propolis in water. Rinse the mouth or gargle the mixture for a while before spitting it out. Many premade products contain propolis as an active ingredient. In these cases, use the product as instructed on the label. Summary Research suggests that propolis has a number of properties that could benefit human health. People can use it on the skin, as a mouthwash, and as a supplement for a variety of minor health concerns. It can also be produced into bee jacket, bee suit, bee gloves, etc. However, there is not much high quality evidence to suggest that propolis is an effective treatment for specific conditions in humans. As a result, anyone with persistent symptoms should speak with a doctor about the best treatment options.
Дата Публикации: 07-12-21
7 BIG ADVANTAGES OF LED STADIUM LIGHTS
Описание: 7 BIG ADVANTAGES OF LED STADIUM LIGHTS The largest stadium in the United States, Michigan Stadium, holds over 100,000 people. While Michigan Stadium is the largest, almost every town has a stadium or baseball field that requires stadium lights. These stadiums are where a majority of high school athletes and collegiate athletes play. Lighting for these stadiums is very important; games are often held after dark or during cloudy days. Without proper lighting, it could be difficult to see the action for players and fans alike. This increases the chances of injuries and reduces the interest of fans in showing up and supporting their local teams. When deciding which kind of lighting you want for your stadium, there are a lot of choices. Older styles of lighting, including sodium-based and halogen-based lights, dominated the market for decades. Modern lighting solutions, however, are growing in popularity and present many advantages. There are a lot of variables to consider when planning for your stadium lighting. The size of the stadium, the number of lights, and how powerful they need to be are all concerns. Here are seven significant advantages of using an LED system for stadium lighting. 1. They Save Power and Are Cheaper to Operate LED lights use up to 75% less energy than older styles of lighting. This means that every minute you operate your stadium lights, you are saving money. Depending on what your stadium, baseball field, or even tennis court is used for, this can equal a lot of savings. If a game is played after dark, lights must be on all the time. In most places, lighting can equal up to hundreds or thousands of dollars a month in associated utility bills. This can put a strain on budgets for collegiate and municipal stadiums. While you may think that switching to LED stadium lights is an expensive proposition, here is where the savings start to counteract the price of updating. It is not the only way in which LEDs will save you money, but the direct impact on the reduction of power used is one you will notice right away. More than just saving money, this reduction in power allows your stadium to operate in a way that is more environmentally safe. Reducing the strain on power plants lowers the amount of carbon that is emitted. This helps to improve air quality and relieve environmental pressure. 2. They Last Longer One of the great advantages of LED lights is that they last for an incredible number of hours. Each LED light you install could last 25x longer than traditional bulbs. This doesn’t just save you on replacement lights, but also upon the manpower to change the lighting. In many stadiums, it can be difficult and dangerous to change the lights. It requires the use of safety equipment and even in some cases, having a bucket truck on site. This can, in turn, cause damage to the field, which will require even more labor to repair. The cost of replacing bulbs has to be factored here as well. While updating to an LED system may seem expensive, the reality is that you won’t be changing light bulbs very often. The light-emitting diodes of the LED pole light system can last longer than 25,000 hours in some cases. All of this will make your stadium cheaper to operate, but also more enjoyable to go to. Blown lights can scare children, cause delays, or reduce the ability of fans and players to see. If any of those things happen, your stadium will not be performing as well as it could have, had you used LED lights. 3. You Get Lighting Control When you are trying to illuminate a game, LED sport lights give you greater control over the amount of light generated. In some systems, you can also control the color of that light. There are a lot of options when it comes to LED lights. Using programmable light systems allows you to tailor responses to the game with your lights. This can help build excitement, celebrate your team, or even help to intimidate your opponents. Fans will delight if, during a touchdown, the lights sparkle with the color of your team. This control is also good for focusing lights or reducing the lighting over the crowd. This can make the action on the field much easier to see. The attendants at your stadium will appreciate not having the glare of lights ruining their view because you will be in control of where it glares and how. This also allows you to set up a system that slowly increases in brightness as the daylight fades. This helps to further control the energy use and cost of operating the system. LED lights are, therefore, a great way to take control of the performance or product you are offering to fans. 4. You Get Versatility of Use LED stadium lights are a great way to diversify what you can do with your stadium. If you wish to have concerts, then LED lights are strong and clear enough; you won’t need any additional lighting. You can also illuminate celebrations, such as those held during holidays and firework events. Increasing the number of uses of your stadium will help to increase revenue. The more income you can generate with your stadium, the more successful it will be. Providing your community with a venue for a variety of events also makes the stadium more valuable to the people who live near it. In the old days, stadiums were the centerpiece of most communities and college experiences. Using LED lights will help you maintain that dominance or regain it from other venues. LED stadium lights can help you provide a place that will draw in more attention than ever before. 5. They’re Better for Presentation and Broadcast If your stadium operates where a local news station is active, they will be drawn to the events there, as it is easy to televise with LED area lights. The crisp, clearness of the LED light will make their broadcast look more professional. The intensity of LED lights makes it easier for television cameras or digital devices to capture the contrast of events. This means that the ball will stand out more, the players will seem clearer, and the fans won’t look like a faceless blob. Other events that are recorded will also look better. This can include firework displays, community events like graduations, and anything that people will want to remember. By having a high-quality LED lighting system, you will draw those wanting to hold such events to your stadium. LED lights are directional, which gives great clarity. Unlike other bulbs, they don’t project light 360 degrees around the bulb, requiring reflectors. In the case of LEDs, any reflective surface in the light only intensifies this light more, by capturing what little shines around the diode itself. 6. They Don’t Make Heat LEDs don’t generate much heat. In fact, an LED can be touched by a bare hand while it is still in operation. Not only does this make them safer to work with, but it also helps to preserve the quality of the fixtures they are set in. Heat can cause warping to plastic and metal, and that isn’t a problem with LEDs. 7. LEDs Are Easier to Find in Stock It is also a fact that as the LED revolution continues to change, other forms of lighting non-LED high bay light systems become harder to replace. The availability of extra bulbs for older systems will continue to diminish. Those same bulbs will continue to increase in cost as fewer and fewer are needed on the market. The Power Is in Your Hands With Stadium Lights All of the reasons that are highlighted represent a chance to increase attendance and decrease cost. As you already know, if you’re operating a stadium, this is the goal of any adjustment or update to a public venue. Increased attendance and decreased cost of operation drives profits from running a stadium up or reduces the budget deficit it creates. If you’re operating a stadium or a public venue, you want to provide service and quality. Having a place where a high school athlete can remember their performance builds community. Memories developed in the stadiums across America are among the most cherished by fans and players alike. The stadium lights you choose to use will have a direct impact on the lives of others. Give them the crisp, clear beauty of LED street lights, and they will remember your venue as one to return to. Help your community build memories and a collective place to enjoy celebrations and sporting events. If you can do those things while saving money at every step of the process, there’s no reason not to. While it is true that a dollar doesn’t go as far as it used to, you will find that in some areas that’s the reverse. A dollar spent on an LED stadium lighting solution will go further than a dollar spent at any other time. If you found this article helpful, take a moment to look around the site for other useful reads.
Дата Публикации: 07-12-21
An Introduction to Metal Recycling
Описание: An Introduction to Metal Recycling Metals can be recycled repeatedly without altering their properties. According to the American Iron and Steel Institute (AISI), steel is the most recycled material on the planet. The other highly recycled metals include aluminum, copper, silver, brass, and gold. Why Do We Recycle Metals? Metals are valuable materials that can be recycled again and again without degrading their properties. Scrap metal has value, which motivates people to collect it for sale to recycling operations. In addition to a financial incentive, there is also an environmental imperative. The recycling of metals enables us to preserve natural resources while requiring less energy to process than the manufacture of new products using virgin raw materials. Recycling emits less carbon dioxide and other harmful gasses. More importantly, it saves money and allows manufacturing businesses to reduce their production cost. Scrap cable wire recycle machine also creates jobs. Quick Metal Recycling Facts Although almost every kind of metal can be recycled again and again without degradation of properties, in 2018, only 34% of metal in U.S. municipal waste facilities was recycled. Below are some additional facts: In 2019, 490.98 million (32%) of the the 1,532.51 million metric tons of crude steel produced worldwide was made using recycled materials with scrap motor wrecker. Around 69% of crude steel in the United States in 2019 was made of recycled materials. In the United States alone, around 2.2 million tons of steel cans and other steel packaging waste were generated in 2018. Steel and iron are the most recycled materials in the world due in part to the opportunity to recover large structures as well as the ease of reprocessing. The use of magnets in the sorting process enables recyclers to easily separate them from the mixed waste stream. Currently, the single most recycled container in the world is the aluminum can. Recycling a single aluminum can save enough energy to power 100-watt light bulb for nearly four hours. Types of Metals Recycled Metals can be classified as ferrous, or non-ferrous. Ferrous metals are combinations of iron with carbon. Some common ferrous metals include carbon steel, alloy steel, wrought iron, and cast iron. On the other hand, non-ferrous metals include aluminum, copper, lead, zinc, and tin. Precious metals are non-ferrous. The most common precious metals include gold, platinum, silver, iridium, and palladium. The Metal Recycling Process The main stages of the metal recycling process are as follows: 1. Collection The collection process for metals differs than that for other materials because of higher scrap value. As such, it is more likely to be sold to scrap yards than sent to the landfill. The largest source of scrap ferrous metal in the U.S. is from scrap vehicles.6 Other sources include large steel structures, railroad tracks, ships, farm equipment, and of course, consumer scrap. Prompt scrap, which is created in the course of new product manufacturing, accounts for one-half of ferrous scrap supply. 2. Sorting Sorting involves separating metals from the mixed scrap metal stream or the mixed multi-material waste stream. In automated recycling operations, magnets and sensors are used to aid in material separation. There are machines as electrostatic separators. At the entrepreneurial level, scrappers may employ a magnet, as well as to observe the material color or weight to help determine the metal type. For example, aluminum will be silver and light. Other important colors to look for are copper, yellow (for brass) and red, for red brass. Scrappers will improve the value of their material by segregating clean metal from the dirty material. 3. Processing To allow further processing, metals are shredded. Shredding is done to promote the melting process as small shredded metals have a large surface to volume ratio. There are metal crushing machine, hydraulic metal processing machine, recycle accessory machine. As a result, they can be melted using comparatively less energy. Normally, aluminum is converted into small sheets, and steel is changed into steel blocks. 4. Melting Scrap metal is melted in a large furnace. Each metal is taken to a specific furnace designed to melt that particular metal. A considerable amount of energy is used in this step. Still, as mentioned above, the energy required to melt and recycle metals is much less than the energy that is needed to produce metals using virgin raw materials. Based on the size of the furnace, the degree of heat of the furnace and volume of metal, melting can take from just a few minutes to hours. 5. Purification Purification is done to ensure the final product is of high quality and free of contaminants. One of the most common methods used for purification is Electrolysis. 6. Solidifying After purification, melted metals are carried by the conveyor belt to cool and solidify the metals. In this stage, scrap metals are formed into specific shapes such as bars that can be easily used for the production of various metal products. 7. Transportation of the Metal Bars Once the metals are cooled and solidified, they are ready to use. They are then transported to various factories where they are used as raw material for the production of brand new products. When the products made of these metal bars come to the end of their useful life, the metal recycling process cycles again. Challenges for the Metal Recycling Industry The current overall metal recycling rate of around 34% is not acceptable, given the recyclability of almost every kind of metal, and challenges remain with respect how to recapture more material for recycling. The expansion of community recycling programs and public awareness help in this regard. Another important reason for the low recycling rate has to do with the design of various metal products. The growing complexity of various modern products and their material mix makes recycling increasingly difficult. For instance, a smartphone can contain more than 70 different elements. So, extracting every kind of materials from a mobile phone and reusing them in the production of new products makes it difficult. Metal Recycling Technologies Modern recycling technologies can effectively identify many different kinds of metals, though there is still the need for even more effective recycling technologies to separate non-ferrous metals. Separating ferrous metals from non-ferrous metals is one of the most important steps in the sorting process. As ferrous metals contain iron, they are attracted by magnets and easily pulled out of the mixed waste stream. In scrap yards, cranes fitted with an electromagnet can remove larger pieces of ferrous scrap. When sorting metals from a mixed stream of recyclable material, the paper is removed first, leaving only plastics and metals. Then, electric currents are induced across the stream where only metals get affected. This process is called eddy current separation. Although aluminum is not magnetic, this technology can levitate it and allow plastics to drop out of the process. Recovering precious metals such as palladium, platinum, gold and other valuable metals such as copper, lead, and silver from electronic waste becomes economically viable only if enough scrap is collected. Such separation takes more technologically advanced and sophisticated recycling equipment. These days, in large recycling facilities, the use of sensors to identify metals through infrared scanning and x-ray has become popular. Three common categories of metal sensing processes include biotechnology, hydrometallurgy, and pyrometallurgy. The use of these technologies can effectively improve metal recovery rates. Business Opportunities in Metal Recycling Traditionally, metal recycling has been regarded as a profitable business opportunity. In recent years, however, depressed prices have proved to be challenging. At an entrepreneurial level, a common entry point into the metal recycling business is through starting scrap metal collection business or becoming a scrap metal vendor. Metal Recycling Laws and Legislation If you are looking to set up a metal recycling-related business in the U.S., you should know relevant recycling laws in your state. This interactive map allows you to find metal recycling laws pertinent to every jurisdiction. Metal Recycling Trade Associations ISRI (Institute of Scrap Recycling Industries Inc): ISRI is the largest trade association for businesses related to recycling. It represents over 1,300 for-profit companies from 40 different countries worldwide. BMRA (British Metals Recycling Association): BMRA represents over 270 scrap metal recyclers of UK and is the leading trade association in the UK. AMRIA: AMRIA refers to Australian Metal Recycling Industry Association. CARI: CARI stands for Canadian Associations of Recycling Industries. It has over 200 member companies. Being a member of trade associations in the recycling industry enables a new recycling business to know and understand the trends in the industry and maintain a good relationship with other businesses in the industry.
Дата Публикации: 07-12-21
Servo Motors Explained and Why They’re Useful in Robotics
Описание: Servo Motors Explained and Why They’re Useful in Robotics Servo motors are used for robotic applications that require precision positioning. Before diving too deeply into the ways servos are used in robotics, it’s helpful to first learn about the basic function and form of these critical components of motion control. What Is A Servo? At its most elemental, a servo is a precise and powerful way of converting rotational motion into linear motion. A servo (or servo motor, as it’s sometimes known) consists of: The Electronic Assembly, which consists of an AC or DC electric motor, a controller board, and a potentiometer. The Case, which is the plastic housing for the motor and other components. The Drive Gears, which reduce the motor’s high-speed output to a lower speed, higher torque servo output. The Output Spline, which is attached to the output shaft and is the final interaction point between the servo and object of the motion it is creating. A good example is a servo in a remote-controlled airplane. The output spline of the servo might be attached via a control rod to a control surface such as an aileron or rudder. The motion of the servo would, therefore, cause an equivalent movement of the airplane itself. How Does A Servo Work? The servo receives a signal from a motion controller. Depending on the pulse width modulation (PWM) of the input signal, the servo will rotate a certain amount. At rest, the output spline of a servo is usually at 0°. Based on an expected pulse frequency of 20 milliseconds (ms), a pulse width of 1.5ms will make the output spline rotate 90° in one direction. A pulse width of 2ms will make the output spline continue rotating 90° further to the 180° position. A pulse width of 1ms will make the output spline rotate 180° backward to the 0° starting position. The potentiometer constantly monitors the position of the output spline. When the output spline reaches the desired position, the power to the motor is cut and the servo robot will hold that position until it receives a signal not to. While stopped in a given position, a servo motor will actively try to hold that position. A key feature of servos is proportional operation. A servo motor will operate only as fast as it needs in order to rotate from its current position to its desired position. If a servo is stopped at the 180° position but needs to be at the 0° position, the motor will rotate very quickly to get there. If stopped at a position that is already closer to 0°, the motor will rotate much more slowly to get there. How Are Servos Useful In Robotics? Servo motors provide numerous benefits in I.M.M robotic applications. They are small, powerful, easily programmable, and accurate. Most importantly, though, they allow for near perfect repeatability of motion. They are used in robotic applications such as: Robotic Welding: Servo motors are mounted in every joint of a robotic welding arm, actuating movement and adding dexterity. Robotic Vehicles: Servos are used in the steering systems of the autonomous vehicles used to disarm and dispose of bombs. The RC Servo or Hobby Servo has been used to move the control surfaces of Radio-Control (RC) model aircraft for many years. It has since become very popular for driving the limb joints of small humanoid robots, and when converted for continuous rotation, the wheels of mobile robots. However, some features optimal for aircraft control are less than ideal for industrial robots. First, let’s get the terminology straight: The term Servo is short for Servomechanism, a device that uses internal feedback to ensure that its mechanical output follows an input control setting. That’s what I’m talking about here. A servo motor is the source of motion in a servomechanism, in this case, a small PMDC motor. A Servomotor is usually a PMDC motor optimised for use in a servomechanism, perhaps featuring rapid acceleration and built-in feedback sensors. They tend to cost a lot of money are definitely not found in hobby servos! These definitions are important, particularly when searching for suitable devices on the Internet. Use the search term ‘rc servo’. Position-Control Servo This type of servo has a rotary output, but the shaft can only rotate a maximum of half a turn or 180°. With a lever called a ‘horn’ attached to the output shaft it can provide a linear push-pull action, hence its original purpose as an actuator for the flight controls of a model aircraft. Outwardly, all ‘standard’ size hobby servos look the same: a rectangular black plastic or alloy box with two sets of fixing lugs, a 3-wire flat cable connection with 0.1in pitch socket header, and a splined output shaft protruding from one side. The original standard size, for example (781-3058) designed for fairly large radio-control model aircraft with IC engines, now sits alongside more compact versions termed ‘Mini’, ‘Micro’ and ‘Sub-Micro’. For really heavy applications there are sizes even larger than the standard. All analogue servos are controlled in the same way: angular position is encoded in a constant repetition rate (50Hz) pulse train where the width of a pulse carries the information. A pulse width of 1ms corresponds to maximum anticlockwise while 2ms turns the servo to the maximum clockwise position. It’s often assumed that a servo will turn through 180° with these numbers, but that is usually not the case (see later). The Motor This is usually incredibly weedy and cheap-looking because it has to fit into the case with a whole lot of other components. Fortunately, the gearbox which is necessary to reduce its rotational speed from about 6000rpm to an output in the region of 30rpm, also multiplies the torque available by the same factor. The Geartrain A lot of gears have to be crammed in to achieve a reduction factor of about 180:1. Of course, the output shaft cannot rotate more than half a turn, so datasheets normally describe servo speed in terms of how long it takes to turn by 60°. For example, a typical figure might be 0.15 secs/60°. That rapid movement could be a problem when using servos to drive the joints of a legged 4 axis robot, 5 axis robot, or 6 axis robot. It does tend to make it lurch about like a mechanical toy but is easily solved by ensuring that movement from one angle to another doesn’t take place in one go. Instead, incremental changes in the PWM signal are made, each separated by a short delay until the target angle is reached. Torque All RC servos will deliver an impressive amount of torque thanks to the gears - even the Minis and Micros. A standard ‘power’ servo can have a torque figure of around 170N.cm measured at a distance of 1cm along the servo horn. That means, in theory, the servo can hold a weight of over 17kg hanging 1cm away from the output shaft. In practice, a basic low-cost servo with nylon gears and no proper shaft bearings is unlikely to last very long if asked repeatedly to apply its theoretical maximum torque. Load up a servo too heavily and you will soon hear the crunching sound of stripping gear teeth. For robust applications, servo manufacturers make more expensive versions of their products with metal (brass) gears and ball-bearings on the output shaft. Metal gears certainly won’t break easily, but they will wear, ultimately rendering the servo inaccurate due to all the ‘slop’ in the geartrain. They also add to the overall weight, and the increase in geartrain inertia slows the servo’s response to a change. Nylon gears might break if mistreated, but wear is negligible. Servos with gears made from an enhanced plastic formulation called Karbonite are now available offering light-weight, high-strength and long-life – at a price. For a robot project, it’s very important to select servos with a good margin of torque. I have a toy/educational robot arm driven by mini-servos that’s prone to emitting loud buzzing noises and thrashing about wildly. I’m pretty sure the motors are not up to the task, load-wise. The Electronics It’s the electronics that turns a motor-gearbox set into a servomechanism with an operating principle based on feedback control. A potentiometer turned by the output shaft sets the pulse duration of a monostable triggered by the input control pulse. The two pulses are compared and the difference in duration between them provides an error signal to the motor driver circuit. The longer the error pulse, the faster the motor turns, slowing down as the error shrinks until it stops when the error reaches zero. Actually, the motor drive is cut off when a certain minimum error pulse width is achieved, introducing a short ‘deadband’ zone around the target position. The deadband stops the motor jittering once it has stopped, assuming any load has been removed. It must be remembered that with this type of servo, there is no ‘holding force’ applied once the target angle is reached. It means they are not very good for lifting weights and holding position against the force of gravity. They work best with horizontal applications, for example, moving a locking bolt backwards and forwards to unlock and lock a house door. Residual load will cause the motor to keep starting and stopping as it moves in and out of the deadband trying to hold position. This has two consequences: an annoying buzzing sound/vibration, and ultimately the motor windings burning out due to the high stall current flowing. It’s something to be borne in mind when designing a legged robot: make sure the servos are not under heavy load when it’s stationary. Until recently, the circuits in an RC servo were always analogue; digital servos are available now with a microcontroller doing most of the processing. Going digital improves speed and accuracy by working with a higher PWM frequency: 300Hz, up from the original 50Hz. Digital servos are also faster to react because the microcontroller can drive the motor at high-speed right to the target angle, rather than ramping down to a stop. The downside is a potential drop in reliability by siting a complex digital chip right next to a major source of electrical interference: a PMDC motor! Servo Interface The format of the control signal which determines the servo position is shown in Fig.2. It may seem over-complicated; why not after all, just use a variable voltage? What we have here is a method of encoding data called Pulse Width Modulation (PWM) used to modulate a Radio Frequency (RF) carrier for a wireless communications link. It all comes back to the original application for the hobby servo – radio-controlled model aircraft. Perhaps confusingly, PMDC motors can be driven directly by a PWM format signal with the pulse-width determining the motor speed. See my article ‘Spinning the Wheels’ for more information. Earlier I suggested that the output shaft of an RC servo will turn through 180°, but as you can see from Fig.2, the standard pulse width limits of 1 and 2ms only give you about 120°. This seems to be the rule with all the servos I’ve tested and while it may be OK for moving a model aircraft control surface, it could be a handicap for a humanoid robot. Fortunately, by reducing the minimum pulse width to 0.6ms and increasing the maximum to 2.4ms, we can get the full half-turn. This usually works, but no doubt it won’t with some products, so check before purchase. Some of the new digital servos on the market can be programmed for either range. Hardware Most microcontroller chips contain hardware ‘count-capture’ modules that can be programmed to generate PWM signals with no processor overhead. Or there are expansion boards available such as the Kitronik 16-channel module (204-8219) for the BBC Micro:Bit and the MikroElektronika 16-channel Click module (184-0942) for anything with a MikroBus socket. Both these modules generate the PWM on-board and communicate with the host microcontroller via an I2C serial bus link. The Pmod CON3 (134-6446) is a simple 4-channel adapter that needs to be connected to host-generated PWM signals. Connections Nearly all RC servos use a 3-wire flat cable terminated with a plug that fits over a 3-pin 0.1in PCB header. The three signals are Control input, DC power and Ground (Fig.2); wire colours vary between manufacturers, but the format is the same: the power supply +V is always in the middle. There is no polarising key so no matter which way it’s plugged in, +V is correctly connected! Power supply RC servo datasheets often quote values for torque and speed at two different power supply voltages. These are usually +4.8 and +6.0 volts corresponding to the power packs found in model aircraft containing four or five 1.2 volt NiCd rechargeable batteries. The +5 volt logic supply of a robot application will normally be adequate for one or two servos, but a separate supply will be needed for any more. When a servo is holding position under load, its DC motor is drawing a stall current of perhaps 500mA or more, and digital chips sharing the supply are vulnerable to glitches caused by sudden current surges.
Дата Публикации: 07-12-21