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- Создано: 14-02-22
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The Safe Use of Extension Cords in the Lab
Описание: The Safe Use of Extension Cords in the Lab Essential to modern life and a familiar part of our surroundings, yet often not treated with deserved respect. Run over, walked on, crimped in windows and doors, left out in sun and storm alike, strung together, bent, yanked, and strung across rooms and under carpets, strewn across wet grass and through holes in walls, taped up and snarled in tangles that would give a sailor nightmares. Used in the office, in the lab, and in the field, taken for granted until you need one. What are we talking about? American UL power cords, one of the most indispensable tools we use today, but too often with little consideration. And, sometimes used in a fashion that could have disastrous results. In 1997, more than 12,000 people were treated for electrical shocks and burns; about 2,500 of them were treated for injuries stemming from extension cords.1 In addition, each year about 4,000 injuries associated with electric extension cords are treated in hospital emergency rooms. Half of these injuries involve fractures, lacerations, contusions, or sprains from people tripping over extension cords. Roughly 3,300 home fires originate in extension cords each year, killing 50 people and injuring about 270 more.2 However, with a little care and some precautions, these conveyors of power can be used safely. We must caution up front, that if you have more than a few Europe VDE Power Cords powering equipment in your lab, it is probably time to either call an electrician to install additional strategically placed outlets, or to rearrange equipment. Likewise, if you have any cords running through walls, up through the ceiling and down somewhere else, an electrician is definitely required. Extension cords should only be used when necessary and only for temporary use. You should always plug equipment directly into a permanent outlet when possible. Where this is not possible, however, you should begin by selecting the right cord for the job. Indoors or outdoors, the use of extension cords serve different needs and should be selected accordingly. Regardless of location, always use the three-prong type of cord approved for either indoor or outdoor use. In addition, the cord should have a certification label from an independent testing lab such as UL (Underwriters Laboratories) or ETL (Electrical Testing Laboratories) on the package and attached to the cord near the plug. The amount of current a cord can handle will depend on the diameter of the conductors (copper wire part of the cord). Cords that contain more copper can safely handle more power. The wire size is measured by the gauge of the wire. You will usually find numbers like 16, 14, or 12 gauge on an extension cord package and the cord itself. Now, this is one of those confusing issues. You would think that a 16-gauge wire is bigger than a 12-gauge wire, but it’s not! As the number gets smaller, the thickness of the conductor gets bigger. A 12-gauge wire can safely carry much more power than a 16-gauge wire. Compare the capacity on the label to the intended load. Always use the shortest extension cord possible, to minimize risk of damage to the cord and reduce electrical resistance across the length of the cord. Extension cords, by the nature of their length and conditions of use, are much more prone to damage than other types of wiring. It is important to check the total length of the cord for damage before putting it into use. One should start by looking at the ends of the cords. The male end—the end with the three prongs that fit into an electrical outlet—is the one that is most prone to damage. The two flat power-conducting prongs are subject to bending, while the round prong (often called the ground pin), can be broken off. Without the ground pin there is no path to ground through the wires—potentially a very dangerous situation. Outdoor use extension cords, and many equipment cords, have a tough outer layer designed to protect the inner wires. If the outer jacket is damaged, the softer inner insulation around the wires can easily become damaged as well. Does this mean you should whip out the tape to repair it? No, damage to an extension cord jacket, or any cord for that matter, should never be fixed by wrapping it with tape. Even electrical tape does not have sufficient strength or abrasion resistance to make a permanent repair as required by OSHA. A taped-up extension or power cord to a piece of equipment is an easy OSHA citation. So, what to do if you have a damaged cord? If the damage is extensive, cut off the plug and throw it out. Replace it with a new cord. Alternatively, the cord can be cut at the point of damage and a new plug installed. Too many times, especially if the female end is damaged, we see outlet boxes intended for structural use installed on the extension cord. These are not permitted if the box is designed to be surface mounted. The clues to easy identification are indentations (knockouts) on the side about the size of a nickel and small holes on the back. Instead, use hard-walled outlet boxes that are approved for use on a flexible cord. Next, where to plug it in? If you are outside, or in a wet or damp location, or near water, look for outlets protected by Ground Fault Circuit Interrupters (GFCIs). A GFCI is a fast-acting device that detects small current leakage from electrical equipment. In other words, it senses electricity traveling to ground via something other than the wires, such as yourself. It shuts off the electricity within 1/40th of a second if sufficient current leakage is detected. It provides effective protection against shocks and electrocution. GFCI pigtails—very short cords with a GFCI built in—can be used with plug and cord equipment in areas without protected outlets. Although GFCI outlets are required by building codes for bathrooms, kitchens, rooftops, and garages, they are not always required near laboratory sinks. This requirement varies by locale and code enforcement authority. We think, however, it is a good idea, and almost always recommend them on outlets within six feet of laboratory sinks. Special cases, such as in pits, tanks, or near certain manufacturing processes where flammable materials are used, require special electrical equipment designed such that they will not be possible ignition sources. This equipment carries the designation “intrinsically safe.” Only intrinsically safe equipment may be used in these potentially explosive areas. A tertiary care 1000 bedded hospital contains more than 10,000 pieces of equipment worth approximately 41 million USD, while the Australia SAA Power Cords supplied along with the imported equipment do not comply with country-specific norms. Moreover, the local vendors procure power cords with type D/M plug to complete installation and also on-site electrical safety test is not performed. Hence, this project was undertaken to evaluate the electrical safety of all life-saving equipment purchased in the year 2013, referring to the guidelines of International Electrotechnical Commission 62353, the Association for the Advancement of Medical Instrumentation (AAMI) and National Fire Protection Association (NFPA)-99 hospital standard for the analysis of protective earth resistance and chassis leakage current. This study was done with a measuring device namely electrical safety analyser 612 model from Fluke Biomedical. The power source for all equipment is alternating current (AC) with frequency - 50Hz; unfortunately, humans are most sensitive to this frequency. Some of the effects are tissue injury, burns, and fibrillation of the heart. The main cause for these effects are leakage current which occurs naturally in all the electrically operated equipment due to stray capacitance between two wires or wire and metal chassis. This can be eliminated by generating a low resistance path from equipment to ground, ideally at zero potential. Though the equipment is designed with the highest degree of protection, safety is attained only when there is a proper connection between the equipment and hospital earth by a component called power cord. If the protective earth resistance (PER) is not as per the International Electrotechnical Commission (IEC) norms, the safety of equipment is violated. Therefore, during installation of medical equipment, electrical safety test is highly required to conform various safety parameters described by IEC 62353. The initial tested data serves as a reference guide for recurrent test throughout the working lifetime of each equipment. In future, on the recurrent test, the deviations of ground integrity and leakage current can be monitored for necessary corrective actions. It is now clear that all the life-saving equipment must undergo electrical safety test on recurrent intervals to ensure safe operation. The purpose of this project was to find out the root cause and influence of environmental factors for equipment failures during the first year of purchase. In addition, implementing electrical safety checks on recurrent intervals to guarantee safe usage of equipment on the patient are discussed. We conducted electrical safety study on 200 life-saving equipment purchased in the year 2012–2013 in Jawaharlal Institute of Postgraduate Medical Education and Research, Pondicherry . They belonged to Class I category with detachable Swiss SEV Power Cords of power consumption
Дата Публикации: 14-02-22
Choosing Pots and Pans to Improve Your Cooking
Описание: Choosing Pots and Pans to Improve Your Cooking As a Fine Cooking editor, I’ve had the chance to observe lots of great cooks at work. From them, I’ve learned plenty—including the fact that good-quality pots and pans made of the right materials really can improve your cooking. Rather than having a rack filled with stock pot and pans of all shapes and sizes, owning a few well-chosen pieces will give you the flexibility to cook whatever you want and the performance you need to cook it better. I polled some of our authors to find out which pans were the most valuable to them and why. I then came up with six pieces, starting with two indispensables: an anodized-aluminum stockpot to handle stocks, soups, stews, some sauces, blanching, boiling, and steaming; and a high-sided stainless-steel/aluminum sauce pan with a lid for frying, deglazing sauces, braising small items like vegetables, making sautés and fricassées, cooking rice pilafs and risottos, and a whole lot more. The other four pieces I picked make for even more cooking agility and add up to half a dozen ready-for-action pots and pans that you’ll really use (see For every pot, there’s a purpose…). All good pans share common traits In a well-stocked kitchen store, you’ll see lots of first-rate pots and deep fry pan. They may look different, but they all share essential qualities you should look for. Look for heavy-gauge materials. Thinner-gauge materials spread and hold heat unevenly, and their bottoms are more likely to dent and warp. This means that food can scorch. Absolutely flat bottoms are particularly important if your stovetop element is electric. Heavy-gauge pans deliver heat more evenly (see “Good pans are worth their price…,” below). To decide if a pan is heavy enough, lift it, look at the thickness of the walls and base, and rap it with your knuckles—do you hear a light ping or a dull thud? A thud is good in this case. Good pans are worth their price because they manage heat better “Good conductor” and “heavy gauge” are the key features of good cookware. Here’s how these characteristics affect cooking. You get responsive heat. Good heat conductors, such as copper and aluminum, are responsive to temperature changes. They’ll do what the heat source tells them to do—heat up, cool down—almost instantly. You get fast heat flow. Heat flows more easily through a good heat conductor, assuring a quick equalizing of temperature on the cooking surface. You get even heat diffusion. A thicker pan has more distance between the cooking surface and the heat source. By the time the heat flows to the cooking surface, it will have spread out evenly, because heat diffuses as it flows. You get more heat. Mass holds heat (heat is vibrating mass, so the more mass there is to vibrate, the more heat there will be). The more grill pan there is to heat, the more heat the pan can hold, so there’s more constant heat for better browning, faster reducing, and hotter frying. You’ll want handles and a lid that are sturdy, heatproof, and secure. Handles come welded, riveted, or screwed. Some cooks advise against welded handles because they can break off. But Gayle Novacek, cookware buyer for Sur La Table, has seen few such cases. As long as handles are welded in several spots, they can be preferable to riveted ones because residue is apt to collect around a rivet. Many pans have metal handles that stay relatively cool when the pan is on the stove because the handle is made of a metal that’s a poor heat conductor and retainer, such as stainless steel. Plastic and wooden handles stay cool, too, but they’re not ovenproof. Heat- or ovenproof handles mean that dishes started on the stovetop can be finished in the oven. All lids should fit tightly to keep in moisture. The lid, too, should have a heatproof handle. Glass lids, which you’ll find on certain brands, are usually ovensafe only up to 350°F. A pan should feel comfortable. “When you’re at the store, pantomime the way you’d use a pot or pan to find out if it’s right for you,” advises Fine Cooking contributing editor and chef Molly Stevens. If you find a pan you love but you aren’t completely comfortable with the handle, you can buy a rubber gripper to slip over the handle. Just remember that grippers aren’t ovenproof. Some pans need special talents Depending on what you’ll be cooking in the pan, you may also need to look for other attributes. For sautéing and other cooking that calls for quick temperature changes, a pan should be responsive. This means that the fry pan is doing what the heat source tells it to, and pronto. For example, if you sauté garlic just until fragrant and then turn down the flame, the pan should cool down quickly so the garlic doesn’t burn. Responsiveness isn’t as crucial for boiling, steaming, or the long, slow cooking that stocks and stews undergo. For sautéing and oven roasts, it helps if the pan heats evenly up the sides. When you’ve got a pan full of chicken breasts nestling against the pan sides, you want them all to cook quickly and evenly, so heat coming from the sides of the pan is important. Even heat up the sides of a pot is important for pot roasting, too. Paul Bertolli, Fine Cooking contributing editor and chef of Oliveto restaurant in Oakland, California, counts on his enameled cast-iron oval casserole by Le Creuset for braising meat because “it’s a snug, closed cooking chamber with even heat radiating off the sides for really good browning.” Bertolli finds that meat fits especially well into the oval shape. For cooking acidic foods, such as tomato sauces, wine sauces, and fruit fillings, a pan’s lining should be nonreactive. Stainless steel, enamel, and anodized aluminum won’t react no matter what they touch, while plain aluminum can discolor white sauces and foods that are acidic, sulfurous, or alkaline. It can even make those foods taste metallic. Eggs, vegetables in the cabbage family, and baking soda are some of the other foods vulnerable to aluminum’s graying effect. In the past, there was concern about aluminum and Alzheimer’s, but evidence has been far from conclusive. Interview yourself to help you choose the right pans There’s nothing wrong with matching cookware in principle. Packaged starter sets are attractively priced, and a whole lineup of matching pans can be attractive, too. But a single material isn’t suited for every kitchen task—with sets, you’re often stuck with pans you don’t need. That enameled cast-iron casserole is just right for the cassoulet you’ll move from stovetop to oven. But its matching saucepan overcooked your last caramel because the pan was too heavy to heft quickly once the sugar turned color. You’ll get more use out of pieces that you hand-pick yourself. You may already own a matched set (the red Le Creuset ensemble I got years ago as a housewarming present is still hanging in my kitchen), but as you add new pieces to your collection, you’ll have a chance to branch out to different materials (see “Materials that make the pot”). To decide what you need, ask yourself questions like the ones that follow. Materials that make the pot The letters identifying the materials key to the photo below. A. Stainless steel is a poor conductor of heat all by itself, but it’s a peerless surface metal: easy to clean, durable, shiny for good visibility, and completely nonreactive. B. Copper is a superb heat conductor and radiates visual warmth, too, if you keep it polished. All alone, copper is highly reactive with food, so the pans must be lined. It’s often used as a bottom layer for better heat conduction. C. Aluminum is a top-notch heat conductor and is lightweight and easy to handle, but it reacts with acidic, sulfurous, and alkaline foods. Aluminum is often used as a core or bottom layer for better heat conduction. D. Cast iron is an excellent retainer of heat and great for high temperatures. It’s relatively slow to heat up and cool down, and needs thorough drying and oiling. E. Nonstick coatings have greatly improved to withstand high heat and abrasion. F. Anodized aluminum is aluminum that’s been electrochemically sealed, making for a nonreactive, hard surface. The dark interior, though, makes it difficult to see color change in pan juices and translucent sauces. G. Enameled cast iron’s coating solves the maintenance problems of cast iron, but the heating benefits remain. The enamel coating can chip with wear and abrasion. Are you more likely to make saucy dishes like fricassées and sautés than delicate foods like omelets and crêpes? A bigger sauté or frying pan with high sides and a lid may be a better choice than a shallower, slope-sided omelet pan without one. “At home, I make a lot of dishes where the pasta gets thrown in with the other ingredients for the last few minutes, and my anodized-aluminum sauté pan is the one I always grab,” says Molly Stevens of her favorite Calphalon pan. “It’s responsive, I know the food won’t scorch, and I love the handle.” She adds that its anodized surface is easy to clean. Do you cook lots of soup on weekends to freeze for meals during the week? A heavy stockpot may be essential. “I always choose heavy-gauge for anything that stays on the stove a long time,” says Larry Forgione, chef/owner of the New York City restaurant An American Place, who says food burns and sticks whenever he uses a thin stockpot. Abby Dodge, Fine Cooking’s recipe tester, agrees. “With soups and stocks, a heavy bottom comes first,” she insists. “And if your budget allows it, go for the best.” Do you make pasta several times a week? Don’t toss that big, thinner-gauge pasta pot if you already have one; it’s fine for boiling and steaming — and lighter is better when you’re carting a boiling pot from stove to sink. But if you don’t have a big pot yet, think about doubling up your pasta-boiling with stock- and soup-making by using a heavy stockpot. Do you like making sauces? “When I’m browning or deglazing, I need to see what the pan juices are doing,” says Jim Peterson, Fine Cooking contributing editor and chef. For such jobs, he avoids pans with a darker interior, such as anodized aluminum, and prefers a shiny stainless-steel lining. Nancy Silverton, baker, pastry chef, and co-owner of La Brea Bakery and Campanile in Los Angeles, agrees. “I love the steady heat and surface of seasoned cast iron, but seeing color change is crucial, so I need a pan that’s bright inside, like stainless,” she says. Silverton cautions that tin- and aluminum-lined pans affect the taste of acidic foods, such as compotes and fruit fillings. Both Peterson and Silverton love the visual warmth of copper but agree that top-notch stainless with an aluminum core, like All-Clad, works just as well. Do you often serve stews, pot roasts, or braised meat dishes? Paul Bertolli loves the way Le Creuset enameled cast iron handles such dishes. “I can start dishes on the stove, transfer them to the oven, and all the juices will be ready to deglaze in the same pot.” He adds that one-pot cooking makes for swift cleanup, too. And Scott Peacock, a southern chef, loves enameled cast iron because “you can put on a lid, set the pot at the back of the stove, and it will hold the food at a good serving temperature a long while.” Do you like cooking chops, steaks, or thick fish fillets? Cast iron may be heavy, but chef and writer Regina Schrambling says that “for searing fish at intense heat and finishing it in the oven, I trust it.” Scott Peacock likes it, too, especially for making golden-crusted cornbread, but cautions that unless cast iron is well seasoned, it can make acidic foods taste metallic, and that metal utensils themselves are apt to scrape off seasoning. Are you trying to cook with less fat? Nonstick may be a good choice, and happily, nonstick technology has come a long way in the past few years. With the old-style, lighter-weight nonstick pans, it was hard to get the pan hot enough to sauté properly. Nonstick pans are now being made of harder, high-heat-tolerant metals, such as anodized aluminum and stainless steel, and the coatings themselves can withstand more heat and abrasion — no more nonstick flakes in your food. Another potential disadvantage of sautéing in nonstick is the difficulty in deglazing. The nonstick surface can be so effective that you never get any good brown bits in the bottom of the pan. With Circulon, which has a finely ridged nonstick interior, browning takes place more like in a conventional pan, and Circulon’s Commercial line is super heavy duty. The Chinese iron pan can function as a nonstick pan even without a polytetrafluoroethylene (PTFE) coating after a “Kitchen God blessing” seasoning process. We simulate this process and disclose the science behind the “Kitchen God blessing,” finding that through repeated oil-coating and heating, the reversible insertion and extraction of oxygen atoms split the surface of the iron pan, gradually producing Fe3O4 nanoballs. These balls give the iron pan a conditional hydrophobicity property, meaning the pan would be hydrophilic when the ingredients contain much water and hydrophobic when they contain less water. The former enables heat to be transferred rapidly through the nanoballs while the latter slows down the heat transference and prevents the pan from sticking. This discovery provides an approach of generating nanoballs on the surface of the metal and also discloses the secret of the fantastic taste produced by cooking with a Chinese iron pan. “Kung-Pao Chicken,” one of the most famous Chinese dishes, is difficult to cook in Western kitchens. The secret behind the successful creation of this dish is the Chinese iron pan. Nonstick pans are produced by coating them with polytetrafluoroethylene (PTFE) materials to construct a superhydrophobic surface . Besides the environmental and safe concerns about the PTFE coating, the PTFE's low surface energy , although it creates a nonstick pan, is detrimental to the taste of the cooked food. Because of the oleophobic/hydrophobic quality of the PTFE materials, the fat serving as the heating medium aggregates into clusters instead of dispersing homogeneously, hindering the even transference of heat to the ingredients, adversely affecting the taste of the final product. In contradistinction to this, there is an ancient saying in China that the Kitchen God will bless a pan and endow it with the oleophilic/hydrophobic quality and a stainless surface after a special seasoning process. The seasoning process, or “the pan's inauguration”, is somewhat religious in nature, but the result, in actuality, is based on science. At the very beginning, the Kitchen God, a native Chinese spirit, is invited through incense-burning. Then, the inner surface of a fresh pan is coated with animal fat (in this work we chose beef tallow). Next, the pan is placed on a stovetop and heated with a low flame for several minutes. This process is repeated several times until the Kitchen God's blessing is received. After seasoning, the pan, made of cast iron, will remain bright for several years. In reality, seasoning ends when the pan has made the proper contact angles with the water and oil, which is determined by the chef, rather than by the Kitchen God (Fig. 1(a, b and c)). The oil acts as the reaction medium in the cooking process, making an oleophilic surface essential for the food to have a good taste. Ingredients are always watery, so a hydrophobic surface is vital for a nonstick pan. For this reason, almost every chef in a Chinese restaurant treats their oleophilic/hydrophobic iron pans as priceless treasures. As they generally don't know how to season their pans properly, most Westerners find it difficult to replicate the taste of Kung-Pao Chicken or other delicious stir-fried Chinese food. Now the secret behind the seasoning of the Chinese iron pan will be revealed. We investigated the seasoning process with burner temperatures ranging from 375○C to 600○C. The morphologies of these experiments are shown in Fig. 2(a). The samples were named Fe-temperature-cycle number, e.g., Fe-450-3 refers to the sample seasoned three times at 450○C. The surface of the pan turned black after seasoning at 375○C and 450○C and rusted at 600○C. As shown in Fig. 1(b), after five cycles of seasoning at different temperatures, Fe-450-5 exhibited a hydrophobic surface with a contact angle of 117.6○ with water droplets. All the samples had oleophilic surfaces, which guarantee uniform heat transfer from the pan to the food (Fig. 1(c)). The hydrophobicity of the Fe-450-5 surface was attributed to the formation of Fe3O4 nanoballs after seasoning. The volume expansion during the seasoning cycles is reversible. The diagrams and SEM images in Fig. 3(d–e) show the vertical formation and growth of Fe3O4 nanoballs. We can clearly determine that when an iron pan is seasoned at 450 °C, the smooth surface of the iron pan gradually becomes coarse during the first two cycles, and nanoballs begin to appear. Interestingly, the nanoballs shrink after the 3rd seasoning cycle (Fig. 3(d) and Fig. S2). For each seasoning cycle, the beef tallow first provides a low Po2 and then evaporates to provide a high Po2. During this process, the coordinate number of the surface iron atoms repeatedly changes between six and four. The formed Fe3O4 repeatedly shrinks and expands and finally large particles crack into small nanoballs.
Дата Публикации: 14-02-22
Christmas crafts for adults to try this festive season
Описание: Christmas crafts for adults to try this festive season Christmas crafting is one of the best ways to spend Christmas 2021. Pick a project from our easy, step-by-step guides to start making fabulous Christmas arts and crafts, decorations and handmade Christmas gifts that your friends and family will love. Christmas is here, so shops are reeling us in with their Christmas adverts, sparkling lights and ornate, festive displays. Despite the fact we can all enjoy a spot of Christmas shopping, nothing sums up the spirit of the season more than lovingly-gifted handmade gifts, decorations and treats. Not only is embarking on a daily craft decorations project a cosy way to spend a winter evening; handmade Christmas gifts are also a more sustainable way to tell your friends and family you love them and to decorate your home as the festivities get underway. After last year’s damp squib of a festive season, handmade gifts are also a heartfelt and meaningful way to tell your friends and family how much they mean to you as we’re (hopefully) reunited this Christmas. Whether you’re looking to craft your own Christmas wreath, make your own Christmas candles to place on a sparkling Christmas table or make personal, handmade gifts for your loved ones, there are plenty of Christmas arts and crafts to keep you busy this festive season. Take a look at our list of daily use decorations ideas you can easily try your hand at – from decorations for your home and Christmas food and drinks to fun gift ideas. Rest assured, you won’t be making any old stocking fillers. All our guides will show you how to make trending and useful crafts, from stylish dried flower wreaths and Instagram-approved painted candles to collaged Christmas cards and festive sloe berry gin. Whether you’re a crafting fanatic looking for new ideas or a beginner searching for easy to make arts and crafts that will still look slick and professional, you’ve come to the right place. Merry Christmas and happy crafting. Give a truly heartfelt Christmas present this year by making your very own gifts by hand. Not only will your loved ones appreciate them so much more, it also means you can make your presents as eco-friendly as possible (there’ll be no excess cardboard or shrink-wrap on these bespoke gifts). Whether you want to make traditional festive favourites to spread some cheer this season, or you’d prefer to home craft decoration fun items that your friends and family will be able to keep forever, there’s a craft on our list for you. Christmas is a time to wine and dine. But, instead of automatically going to the Christmas means decking your halls with soft twinkling lights and bright, colourful decorations. Whether you’re looking to level up your Christmas tablescaping game this year with handmade candles and lovingly crafted placemats or you’re after some stunning floral arrangements to bring the festive vibes, there’s a crafting guide here for you. With winter break upon us and Christmas just around the corner, it’s time to embrace the festive spirit of the season. Escape the chilly weather by staying indoors and crafting with your kids. Christmas crafts are a great way to entertain your little ones while letting them release their creativity. We have 50 easy Christmas crafts for kids at every skill level. Need to decorate your Christmas tree? There are fun Christmas tree ornament ideas that your kids will be excited to hang up. Looking for a personalized Christmas gift you can give to family? Try creating a snow globe or themed treat. Once you decide on a craft to make, pair it with light up Christmas decorations to give your home the complete cozy Christmas feel. The festive season is the perfect time for some do-it-yourself fun with the kids, who love cutting paper and using glue to create magical shapes. Get creative making stars, ornaments to decorate the tree. Children will get a sense of pride and achievement seeing the handmade decorations on the festive tree. Here, we show how you can make a paper tree and decorations. Make cones out of all the papers. You will require about six to seven sheets of each colour. Now, stick the cones together, starting from the bottom with the largest cone and ending with the smallest on top. After sticking all the cones now make a star and stick it. You can attach a ribbon, so that you can use it to hang on the tree. From making your fireplace more festive to crafting one-of-a-kind ornaments and trimming your Christmas craft decorations, our holiday craft projects will help you creatively take your home from ho-hum to ho-ho-ho! Get crafting to deck out every area with DIY Christmas decorations that perfectly showcase your personal seasonal style. For many, it (wrongly) contained connotations of amateurism, appearing homespun and deeply unfashionable. Scroll forward to the present and things look very different. Tom Daley made headlines at the Olympics, not only for winning medals but also for knitting a commemorative cardigan while supporting Team GB in the stands. Our TV schedules are overrun with shows devoted to sewing, repair, pottery and jewellery making. And brands from Loewe to Kettle Chips have celebrated craft (with different degrees of credibility) through awards and marketing campaigns. What changed? I would posit that the craft revival started in 2008, with the combination of the banking crisis and the publication of a hugely influential book, The Craftsman by Richard Sennett. Historically, craft does well in recession, when people pay more attention to the value of things and are more willing to entertain the idea of repairing possessions rather than simply binning them. So the field of craft has garnered some (long-overdue) kudos. But what’s next? And who are the people taking it forward? According to Annie Warburton, CEO of Cockpit Arts, London’s leading studios for contemporary crafts, ‘Craft is advancing on several different fronts.’ And one of those fronts is the collectibles market. Last year, for instance, studio ceramics auction house Maak sold a piece by Magdalene Odundo for ￡240,000, a record for a living ceramic artist. In June, Design Centre Chelsea Harbour launched Artefact, a new fair devoted to high-end craft, while craft galleries such as Adrian Sassoon and Sarah Myerscough have become staples at international art and design shows like Masterpiece and PAD. As Warburton points out, compared to the fine art world, there are potential bargains to be had: ‘People are realising that, at the moment, the field is seriously undervalued in terms of price. Canny collectors are getting in on collectable craft.’ Makers themselves are also expanding craft’s horizons through a combination of technology and material experimentation. Gareth Neal is a designer and maker, whose work in wood has ranged from investigating the traditional Orkney chair to working with cutting-edge CNC (computer numerical control) processes to create ‘Ves-el’ vases, in collaboration with the late Zaha Hadid. Most recently, he has been experimenting with 3D-printing sand (in a process called binder jetting) to create a huge, ribbed vessel that’s a little under two-metres tall. I see technology as another tool,’ he says. ‘It’s just that nowadays tools are no longer something you carry about in a box on the back of a cart. They’ve outgrown the traditional workshop.’ Interestingly, Neal shies away from describing himself as a craftsman preferring the term, ‘craft explorer’. ‘I’m someone who is trying to find new territory and uncover different areas to play in,’ he says. While Neal is using technology to challenge established notions of craft, James Shaw is fascinated by how we place value on materials. He has eschewed current fashion and has become an advocate for plastic. I was quite interested in the hierarchy of materials, where plastic comes way down at the bottom,’ he explains. ‘I thought maybe there was some connection between that and the silly things we do with it, like using it for a few seconds and throwing it away. I figured if I applied the skills, understanding and time that easter craft decorations, it might unpack some other aspects of the material.’ For his ‘Plastic Baroque’ series, Shaw takes high-density polyethylene pellets (recycled from packaging), which are heated, extruded through a kind of homemade gun, and then rapidly manipulated before the gooey substance cools down, to create objects that are subsequently sold on the collectibles market. He is by no means alone in working with materials more often thought of as waste. Emma Witter is a maker and artist who uses animal bone to create wonderfully delicate sculptures. She began working with the material for practical reasons. ‘It was about having no money and working with what was around me,’ she explains. ‘If I wanted to use metal, for example, I’d have to go to a foundry, which is expensive. So I was collecting things that were to hand and free.’ She picked up her first bones from her own meals and at dinner parties. ‘On the odd occasion we went to restaurants, I’d put them aside,’ she tells me, with a hint of a giggle. Importantly, too, there has been a collective realisation in the craft world that it needs to expand its base and appeal to a more diverse cross-section of the population. Over the past 18 months, for example, it has been fascinating to watch the rise of Chris Day, a mixed-heritage glass artist, who graduated from Wolverhampton University in 2019. Since then, his extraordinary work, which focuses on the Black experience in the UK and US, juxtaposing glass and copper piping and wire, has been shown at London’s SoShiro and Vessel Gallery. He currently has a genuinely moving installation at All Saints Church at Harewood House, just outside Leeds. The beauty of craft is that it is light on its feet. Makers are playing with new techniques and materials that could inform all our futures. And it has something to say on a range of topics, too, from sustainability to discrimination. In short, craft is not to be underestimated.
Дата Публикации: 14-02-22
Impacts of food contact chemicals on human health
Описание: Impacts of food contact chemicals on human health Research on Chemical Intermediates publishes current research articles and concise dynamic reviews on the properties, structures and reactivities of intermediate species in all the various domains of chemistry. The journal also contains articles in related disciplines such as spectroscopy, molecular biology and biochemistry, atmospheric and environmental sciences, catalysis, photochemistry and photophysics. In addition, special issues dedicated to specific topics in the field are regularly published. Food packaging is of high societal value because it conserves and protects food, makes food transportable and conveys information to consumers. It is also relevant for marketing, which is of economic significance. Other types of food contact articles, such as storage containers, processing equipment and filling lines, are also important for food production and food supply. Food contact articles are made up of one or multiple different food contact materials and consist of APIs and Intermediates. However, food contact chemicals transfer from all types of food contact materials and articles into food and, consequently, are taken up by humans. Here we highlight topics of concern based on scientific findings showing that food contact materials and articles are a relevant exposure pathway for known hazardous substances as well as for a plethora of toxicologically uncharacterized chemicals, both intentionally and non-intentionally added. We describe areas of certainty, like the fact that chemicals migrate from food contact articles into food, and uncertainty, for example unidentified chemicals migrating into food. Current safety assessment of food contact chemicals is ineffective at protecting human health. In addition, society is striving for waste reduction with a focus on food packaging. As a result, solutions are being developed toward reuse, recycling or alternative (non-plastic) materials. However, the critical aspect of chemical safety is often ignored. Developing solutions for improving the safety of food contact chemicals and for tackling the circular economy must include current scientific knowledge. This cannot be done in isolation but must include all relevant experts and stakeholders. Therefore, we provide an overview of areas of concern and related activities that will improve the safety of food contact articles and support a circular economy. Our aim is to initiate a broader discussion involving scientists with relevant expertise but not currently working on food contact materials, and decision makers and influencers addressing single-use food packaging due to environmental concerns. Ultimately, we aim to support science-based decision making in the interest of improving public health. Notably, reducing exposure to hazardous food contact chemicals contributes to the prevention of associated chronic diseases in the human population. We, as scientists working on developmental biology, endocrinology, epidemiology, toxicology, and environmental and public health, are concerned that public health is currently insufficiently protected from harmful exposures to food contact chemicals (FCCs). Importantly, exposures to harmful FCCs are avoidable. Therefore, we consider it our responsibility to bring this issue to the attention of fellow scientists with relevant expertise, but currently not engaged in the area of FCMs, as well as decision makers and influencers in government, industry and civil society dealing with environmental and health-related aspects of food packaging. We propose that a broader, multi-stakeholder dialogue is initiated on this topic and that the issue of chemical safety of food packaging becomes a central aspect in the discussions on sustainable packaging. Food contact chemicals (FCCs) are the chemical constituents of food contact materials and finished food contact articles, including food packaging, food storage containers, food processing equipment, and kitchen- and tableware . We define FCCs as all the chemical species present in food contact articles, regardless of whether they are intentionally added or present for other reasons. It is clearly established by empirical data that FCCs can migrate from food contact materials and articles into food, indicating a high probability that a large majority of the human population is exposed to some or many of coenzymes and nucleotides series . Indeed, for some FCCs there is evidence for human exposure from biomonitoring , although some FCCs may have multiple uses and also non-food contact exposure pathways. When food contact material regulations were first developed, it had been generally assumed that low-level chemical exposures, i.e. exposures below the toxicologically established no-effect level, pose negligible risks to consumers, except for carcinogens . However, more recent scientific information demonstrates that this assumption is not generally valid, with the available evidence showing that exposure to low levels of endocrine disrupting chemicals can contribute to adverse health effects . In addition, chemical mixtures can play a role in the development of adverse effects , and human exposure to chemical mixtures is the norm but currently not considered when assessing health impacts of FCCs . The timing of exposures during fetal and child development is another critical aspect for understanding development of chronic disease . Currently, these new and important insights are still insufficiently considered in the risk assessment of chemicals in general, and of FCCs in particular . We have previously published an in-depth analysis of the scientific shortcomings of the current chemical risk assessment for food contact materials in Europe and the US . For example, in the European Union (EU) the regulation EU 10/2011 includes a list of authorized substances for the manufacture of plastic materials and articles in contact with food and, for some of the fine chemicals, their permitted maximum concentration, either in the plastic food contact article or in food (i.e. specific migration limit) . However, there are still many substances that are present in plastics and other materials as non-intentionally added substances (NIAS). Even though the EU regulations 10/2011 explicitly and EU 1935/2004 generally require a risk assessment of NIAS, there are many difficulties: first, identification of NIAS is very demanding and, secondly, studying the effects on human health is often not possible because for example the chemicals are not available as pure substances or testing would be too expensive . What is more, there is no regulatory requirement to assess toxic effects of the chemical mixtures migrating from food contact articles . To summarize, we are concerned that current chemical risk assessment for food contact chemicals does not sufficiently protect public health. Therefore, we would like to bring the following statement to the attention of policy makers and stakeholders, especially those currently working on the issue of packaging waste but not focusing on the chemical safety of food contact articles (Table 1). By mapping the challenges (Table 2), we aim to initiate a broader debate that also involves scientists with different expertise of relevance to the issue. Importantly, chemical safety must be addressed in two ways: e.g. (i) a discussion of how chemical safety is ensured, based on the current scientific understanding and e.g. (ii) a debate of the chemical safety of food packaging in the circular economy, which aims at minimizing waste, energy and resources use . Therefore, we provide an overview of the most pressing challenges based on current scientific understanding. Ultimately, the public is to be protected from exposures to hazardous FCCs while at the same time the aims of the circular economy need to be achieved. To reach these goals, we think that there is a need to better inform decision making on future food packaging research and policy. Chemicals can transfer from food contact materials and articles into food. This phenomenon is known as migration and has been studied since the 1950s . All types of food contact materials may exhibit chemical migration, but the types of migrating Sitagliptin Phosphate Monohydrate CAS 654671-77-9 and their levels differ significantly. Analysis of FCC lists issued by legislatures, industry, and NGOs worldwide indicates that almost 12,000 distinct chemicals may be used in the manufacture of food contact materials and articles . For example, European Union (EU) and EU Member State regulations list a total of 8030 substances for use in different types of food contact articles . In the United States (US), 10,787 substances are allowed as direct or indirect food additives, and roughly half of these are FCCs . Many additional FCCs may be used in the US under the assumption of being generally recognized as safe (GRAS), but they are not notified to the US Food and Drug Administration (FDA) and therefore no public record on their use is available . In general, information on the actual use of a chemical in food contact materials (and its levels) is difficult to obtain . All migrating FCCs have inherent toxicity properties that can cause different effects at different doses and are related to the timing of exposure, mode of action, and other aspects. At the same time, levels of FCCs that humans are exposed to reflect their use (or presence) in a food contact article and are associated with its concentration in food. To evaluate the risk of a given chemical to human health, information on its inherent toxicity (i.e., its hazard) and the actual levels of exposure is needed. Many of the chemicals that are intentionally used in the manufacture of food contact articles have not been tested for hazard properties at all, or the available toxicity data are limited . Moreover, endocrine disruption, as a specific hazard of concern, is not routinely assessed for 2,4,5-Trifluorophenyl Acetic Acid CAS 209995-38-0 migrating from food contact articles, although some chemical migrants are known endocrine disruptors . Exposure data are commonly based on assumptions or estimates – for example derived from dietary assessments or unpublished (proprietary) data of an intentionally used FCC’s concentration in a food contact article . Thus, there is significant uncertainty associated with these data. In short, decisions on the use of a chemical in food contact materials are commonly made in data-poor situations.
Дата Публикации: 14-02-22
Stainless steel in construction
Описание: Stainless steel in construction Stainless steel has unique properties which can be taken advantage of in a wide variety of applications in the construction industry. This paper reviews how research activities over the last 20 years have impacted the use of stainless steel in construction. Significant technological advances in materials processing have led to the development of duplex stainless steel pipe with excellent mechanical properties; important progress has also been made in the improvement of surface finishes for architectural applications Structural research programmes across the world have laid the ground for the development of national and international specifications, codes and standards spanning both the design, fabrication and erection processes. Recommendations are made on research activities aimed at overcoming obstacles to the wider use of stainless steel in construction. New opportunities for stainless steel arising from the shift towards sustainable development are reviewed, including its use in nuclear containment structures, thin-walled cladding and composite floor systems. Stainless steel has many desirable characteristics which can be exploited in a wide range of construction applications. It is corrosion-resistant and long-lasting, making thinner and more durable structures possible. It presents architects with many possibilities of shape, colour and form, whilst at the same time being tough, hygienic, adaptable and recyclable. The annual consumption of stainless steel has increased at a compound growth rate of 5% over the last 20 years, surpassing the growth rate of other materials. The rate of growth of stainless steel used in construction has been even faster, not least due to rapid development in China. It is estimated that in 2006, approximately 4 million tones of stainless steel went into construction applications worldwide, 14% of the total quantity consumed. Stainless steel has traditionally been used for facades and roofing since the 1920s. There are also early examples of it being used structurally, for example in 1925 a reinforcing chain was installed to stabilize the dome of St Paul’s Cathedral, London. Nowadays, stainless steel is used in a very wide range of structural and architectural elements, from small but intricate glazing castings to load-bearing girders and arches in bridges. This paper seeks to summarise the recent technological advances in the stainless steel sheet which have had an impact on usage of stainless steel in construction. New applications which have emerged over the last 20 years are described. Areas of research needed to respond to current market and procurement challenges are discussed. Finally, new opportunities arising from the shift towards sustainable development are described. Stainless steel producers are continually developing their manufacturing processes with the aim of reducing costs, lowering emissions, shortening lead times and improving quality. These improvements have helped to control the cost of stainless steels, within the constraints set by the dependence on raw materials. Perhaps the most significant recent advance impacting the construction sector has been the use of duplex grades for structural applications, which offer a combination of higher strength than the austenitics (and also the great majority of carbon steels) with similar or superior corrosion resistance. Table 1 compares the composition and mechanical properties of the two widely used austenitic stainless steel coil, 1.4301 and 1.4401, with those of three duplex stainless steels. (The ferritics in the table are discussed in Sections 3 Expansion of construction applications over the last 20 years, 4 Research in response to market and procurement challenges.) Duplexes have tremendous potential for expanding future structural design possibilities, enabling a reduction in section sizes leading to lighter structures. It is worth noting that although they have good ductility, their higher strength results in more restricted formability compared to the austenitics. The corrosion resistance of duplex grade 1.4362 is similar to that of 1.4401. The more highly alloyed 1.4462 displays superior corrosion resistance, especially to stress corrosion cracking. High nickel prices have more recently led to a demand for lean duplexes with low nickel content, such as grade 1.4162 shown in the table. The corrosion resistance of grade 1.4162 lies between that of 1.4301 and 1.4401; it currently costs slightly less than grade 1.4301. Although usually used internally in buildings, some ferritic grades have been developed which are suitable for building envelope and structural products. For example, over the last 10 years, grade 1.4510 has been used widely in France in a tin-coated roofing system. This tin-coated finish weathers over time, gradually developing into a matt-grey patina. Over the last 20 years, significant developments have occurred in materials processing and finishing technology, often driven by exacting architectural requirements for specific projects. The range in surface finishes has extended, ranging from matt to shiny, smooth to very rough, with combinations possible by juxtaposing finishes, adding colour etc. More finishes have become available—involving metallic and organic coatings, electrolytic and PVD (Physical Vapour Deposition) coating processes or skin passing operations. They have improved the competitive position of stainless steel compared to other high volume metallic roofing materials such as zinc, aluminium, copper and even carbon steel. The performance of the stainless finishes has also been improved in order to meet strict hygiene and cleaning requirements. Improved manufacturing processes have resulted in greater consistency of surface finish, both across a sheet and from batch to batch. Products are also now able to meet tighter dimensional tolerances. Traditionally stainless steel welded tubes were produced by tungsten inert gas (TIG) welding. However, with the advent of reliable, high-power laser power sources, the laser beam welding (LBW) process has moved quickly into the production of stainless steel longitudinally welded tubes. The energy concentration reached in the focused spot of a laser beam is very intense and is capable of producing deep penetration welds in thick section stainless steel, with minimal component distortion. The process originally employed high capital cost equipment and its use was reserved for mass production manufacturing. However, now that more compact equipment has been developed, the use of laser welding is becoming more widespread. In addition to hollow sections, laser welded stainless steel I sections, angles and other shapes are now available (Fig. 2). In recent years there has also been a dramatic increase in the use of stainless steel profiles in which a focused laser beam is used to melt material in a localised area. A co-axial gas jet is used to eject the molten material from the cut and leave a clean edge with a continuous cut produced by moving the laser beam or workpiece under CNC control. There is no tooling cost, prototyping is rapid and turn around quick. The improvements in accuracy, edge squareness and heat input control mean that other profiling techniques such as plasma cutting and oxy-fuel cutting are being replaced by 2.2. Design The development of codes, standards and specifications for stainless steel as a result of research studies carried out by industry and academics has played a significant role in enabling the wider use of stainless steel in construction. The structural performance of stainless steel differs from that of carbon steel because stainless steel has no definite yield point and shows an early departure from linear elastic behaviour with strong strain hardening. There can also be significant differences between the stress–strain curves for tension and compression. This has implications on the buckling behaviour of members and the deflection of beams. Designers require guidance on grade selection and the use of stainless steel in contact with other materials (e.g. carbon steel, reinforced concrete, masonry, timber and aluminium) in order to avoid corrosion between the dissimilar materials. Methods of connection also require specific guidance, particularly where welding is concerned, to maintain surface finish and corrosion resistance. Prior to the development of design standards for structural stainless steel, designers were forced to conduct their own investigations or abandon stainless steel in favour of alternative materials which have proven track records and design guidance. They were required to work from first principles with an unfamiliar and costly material with unusual mechanical properties. This was an unsatisfactory situation; at best it was wasteful of the designer’s time, at worst it led to misconceived design practice, misuse and either unserviceability or failure. The Gateway Arch in St Louis, Missouri, inspired a great amount of research into the structural performance of stainless steel in the US in the early 1960s. The first American specification dealing with the design of structural stainless steel members was published in 1968 by the AISI . Following an extensive research project at Cornell University, in 1974 the specification was revised and published as the Specification for the Design of Stainless Steel Cold-Formed Structural Members, and this has subsequently been extended and updated in 1991 and 2002. Australia, New Zealand and South Africa have published approximately equivalent standards largely based on the American standard 3., 4.. In 1995, the Design and Construction Standards of Stainless Steel Buildings were published by the Stainless Steel Building Association of Japan . These specifications cover the design of welded, fabricated sections from relatively thick plate. A recent Japanese research programme studied the behaviour of lightweight stainless steel members and the Design Manual of Light-Weight Stainless Steel Structures was subsequently published in 2005 . Between 1989 and 1992, SCI carried out a research project to develop European guidance in the areas of material selection, design, fabrication and maintenance to ensure the safe and proper application of steel in construction. The project included forming a properties database, materials tests, member and connections tests, analysis of results, design recommendations and worked examples. The resulting guidance was published by Euro Inox in 1994 as the Design Manual for Structural Stainless Steel. Subsequently the draft pre-standard Eurocode 3 Part 1.4, giving rules for the design of structural stainless steel pipe fittings, was published in 1996, closely based on the Design Manual. A European research project between 1997 and 2000 carried out a further programme of tests and analyses into the performance of structural stainless steel . The results of the project were incorporated into the Second Edition of the Design Manual, published in 2002, with an extended scope including circular hollow sections and fire resistant design. A further European research project studied the behaviour of high strength structural members made from cold worked stainless steel through further tests and analyses between 2000 and 2003 . The results were included in the Third Edition of the Design Manual, published in 2006. The same year, Eurocode 3: Part 1.4 (EN 1993-1-4) was issued as a full European Standard . Its contents are aligned with the Design Manual, with the exception of the guidance on fire resistance where the Design Manual presents a less conservative approach. A Commentary to the Design Manual has also been prepared as a separate document which explains the basis of the recommendations and presents the results of relevant test programmes . In a fire, austenitic stainless steel columns and beams generally retain their load-carrying capacity for a longer time than carbon steel structural members. This is due to their superior strength and stiffness retention characteristics at temperatures above 500 °C (Fig. 3). SCI has coordinated a year research project studying the behaviour in fire of a range of structural stainless steel solutions through testing and numerical studies. The project included fire tests on stainless steel and concrete composite columns and beams, separating structures and load-bearing systems designed to retard the temperature rise. Slender hollow sections were also studied. The final report is due to be published in 2008 .
Дата Публикации: 14-02-22
History and Manufacturing of Glass
Описание: History and Manufacturing of Glass The word glass comes from the Teutonic term “Glaza”, which means amber. Although the origin of glass production line is still uncertain, the Mesopotamians from the 5th century BC discovered an ash by chance when they fire to melt clay vessel to use for glazing ceramics or when copper was smelted. In Egypt, greenish glass beads were excavated in some of the Pharaohs’’ burial chambers dating from the early 4th century BC, and this has been referred to as intentional glass manufacture. From the second century BC, the production of rings and small figures by using core-wound techniques began to appear. The oldest blueprint for glass was made on clay tablets in 669-627 BC, which read: “Take 60 parts sand, 180 parts ash from marine plants, and 5 parts chalk”. This blueprint is now held in the great library of the Assyrian king, Ashurbanipal, in Nineveh. The invention of the Syrian blowing iron around 200 BC by Syrian craftsmen enabled the production of thin-walled hollow vessels in a wide variety of shapes. Excavations have revealed that in the Roman era glass was used for the first time as part of the building envelope of public baths in Herculaneum and Pompeii. These panes could have been installed in a bronze or wood surround or without a frame. In the middle ages, this technique spread to the northern Alpine regions, and utensils like drinking horns, claw beakers, and mastos vessels started to be produced; in addition, the use of glass increased in the building of churches and monasteries. Blown cylinder sheet glass and crown glass were invented in the 1st century AD and the 4th century AD respectively. In both, a blob of molten glass was drawn off with a blowing iron, performed into a round shape, and then blown into a balloon. Blown cylinder sheet glass and crown glass remained two of the most important production techniques for producing glass furnace until the early 20th century. From the 17th century, glass usage was not only limited to churches and monasteries but it also started to be used for glazing palaces. High demand motivated glass-makers to develop new methods, and in 1687 the process of casting glass was invented by the Frenchman Bernard Perrot, in which the glass melt was poured onto a smooth preheated copper table and pressed onto a pane with a water-cooled metal roller. In this way, a glass pane of up to 1.20 x 2 m could be produced. Although this method made it possible to produce glass at a cheaper price, the use of glass windows was still expensive. Considerable improvement was made after industrialisation in the 19th century. In 1839, the Chance brothers succeeded in adapting the gridding, cutting and polishing of blown cylinder glass in order to reduce breakages and improve the surface finish. In the 1850’s, it became possible to produce a massive amount of glass panes required for the construction of a crystal palace. Machine-made glass panes were not produced until 1905, when Emile Fourcault succeeded in drawing these directly out of glass melt. In 1919, Max Bicheroux made a vital discovery in the production of glass by concentrating several stages of the procedure into a continuous rolling mill; the glass melt left the crucible in portions and passed through two cooled roller to form a glass ribbon. In this way, a glass pane with the dimensions of 3 x 6m could be produced. In the 1950s, the Englishman Alastair Pilkington developed the hot end glass equipment, wherein viscous glass melt was passed over a bath of molten tin floating on the surface. Tin was used because of the high temperature range of its liquid physical state (232 to 2270°C) and having a much higher density then glass. Floating is currently the most popular process, representing over 90% of all flat glass production worldwide. Float glass is made in large manufacturing plants which operate 24 hours a day, 365 days a year. In this process, raw materials are melted at 1550°C, and the molten glass is poured continuously at 1000°C onto a shallow pool of tin. The glass float on the tin forms a smooth flat surface of almost equal thickness (depending on the speed of the rollers), which then starts to cool to 600°C; after this, it enters the annealing Lehr oven and slowly cools down to 100°C to prevent any residual stress. The typical size of glass panes are 6 x 3.20 m, and hard coating can be applied during the manufacture. In this process, the two sides of the glass pane are slightly different. On the tin side, some diffusion of tin atoms onto the glass surface occurs, causing a lower glass strength on this side due to the surface flaws occurring during production. The tin side can be easily detected by ultraviolet radiation. Another process for the production of flat glass is the cast process. In this process, cold end glass equipment is poured continuously between metal rollers to produce glass with the required thickness. The rollers can be engraved to give the required surface design or texture and produce patterned glass. The glass can be given two smooth surfaces, one smooth and one textured, or two textured sides, depending on the design. In addition, a steel wired mesh can be sandwiched between two separate ribbons of glass to produce wired glass. Wired glass can keep most of glass pieces together after breakage, and it is therefore usually used as fire protection glass. Viscosity constantly increases during the cooling of liquid glass, until solidification occurs at about 1014 Pas. The temperature at solidification, called the glass transition temperature, is about 530°C for SLSG. The glass actually freezes, and no crystallization takes place. The extremely cooled liquid nature of glass means that, unlike most solids, the electrons cannot absorb energy to move to another energy level and are strictly confined to a particular energy level. Therefore, the molecules will not absorb enough energy to dissipate energy in ultra violet, infrared or visible bandwidths. However due to some impurities in SLSG, the glass could be greenish or brownish due to Fe2+ and Fe3+ respectively. Extra clear glass, called low iron glass, which has a reduced amount of iron oxides, is commercially available. The physical properties of glass mainly depend on the glass type. At room temperature, the dynamic viscosity of glass is about 1020 dPas, a very high amount bearing in mind that water is 1 dPas and honey is 105 dPas. With this high viscosity at room temperature, it could take more than an earth age for flow effects to be visible to the naked eye. Although some observation have shown that in old churches glass panes are thicker at the bottom than at the top, and have referred to this as flow, it is actually because of the glass manufacturing process at the time which was reliant on centripetal force relaxing (crown glass process), making the centre much thinner than the outer parts; in addition, when being installed, the thinner part was usually placed at the top for better visual sparkle and stability. Toughened glass is a kind of safety glass, which has a higher strength due to its residual stresses. It cannot be worked on any further (such as cutting or drilling) after the toughening process has been done . Toughened glass is becoming more and more important as its range of applications grow. The main application of thermally toughened glass production processing line, automotive glass and some domestic glasses like Pyrex, while the main uses of chemically strengthened glass are as laboratory and aeronautical glass. Toughened glass (also known as Fully Tempered Glass - FTG) begins with annealed glass. It is heated to 620°C - 675°C (90-140°C above the transition temperature) and rapidly cooled with jets of cold air. This causes the outer surface of the glass to solidify before the inner part. As the interior cools, it tries to shrink, but the solidified outer surface resists this force and goes into compression (usually between 90 and 150 N/mm2) and the interior goes into tension. The temperature distribution is usually parabolic, with a colder surface and a hotter interior. To get the best results with maximum temper stress, the surface should be solidified exactly at the point when the highest temperature difference occurs and the initial tensile stress is released. In this type of glass, surface flaws do not propagate under compressive stress, and so toughened glass can sustain higher stresses than annealed glass. Glass with low thermal expansion, such as BSG, is more difficult to be toughened. EN 12150 parts 1 and 2, the fragmentation count and the maximum fragment size are specified as standard requirements, although American standards (ASTM C 1048-04) take 10000psi (~69 MPa) surface compression or 9710 psi (~67Mpa) as the minimum standard requirements. Different manufacturing methods can produce glass with widely different properties, and this could be due to the jet geometry, thermal expansion coefficient of the glass, air temperature, roller influence, glass thickness, air pressure, heat transfer coefficient between air and glass, etc. Toughening can have a great effect on the stress to the surface and interior of glass. Chemical toughening (tempering) is an alternative process to thermal toughening. Cutting and drilling is possible, but the cut or drilled parts will have the strength of annealed glass. The use of chemical tempering is very uncommon; it is used in conditions where the extreme angle or geometry causes thermal tempering to be not as effective as it should be. The toughening process is based on ionic exchange (sodium ions in glass exchange with potassium); to do this, the glass is immersed in hot molten salt, which leads to compressive stress at the surface. However, the strengthened zone is shallow to about 20μm in 24 hrs . The shortcoming of this type of glass is that if surface flaws are deeper than the compression zone, sub-critical crack growth can occur without an external load. This phenomenon, which can cause spontaneous failure, is called self-fatigue. The fracture behaviour of this type of glass is like float glass.
Дата Публикации: 14-02-22
How felt is made
Описание: How felt is made Most fabrics are woven, meaning they are constructed on a loom and have interlocking warp (the thread or fiber that is strung lengthwise on the loom) and weft (the thread that cuts across the warp fiber and interlocks with it) fibers that create a flat piece of fabric. Felt is a dense, non-woven fabric and without any warp or weft. Instead, felted fabric is made from matted and compressed fibers or fur with no apparent system of threads. Felt is produced as these fibers and/or fur are pressed together using heat, moisture, and pressure. Felt is generally composed of wool that is mixed with a synthetic in order to create sturdy, insulating felt for craft or industrial use. However, some felt is made wholly from synthetic fibers. Felt may vary in width, length, color, or thickness depending on its intended application. This matted material is particularly useful for padding and lining as it is dense and can be very thick. Furthermore, since the fabric is not woven the edges may be cut without fear of threads becoming loose and the fiber unraveling. Felted fibers generally take dye well and craft felt is available in a multitude of colors while industrial-grade felt is generally left in its natural state. In fact, felt is used in a wide variety of applications both within the residential and industrial contexts. Felt is used in air fresheners, children's bulletin boards, craft kits, holiday costumes and decorations, stamp pads, within appliances, gaskets, as a clothing stiffener or liner, and it can be used as a cushion, to provide pads for polishing apparatus, or as a sealant in industrial machinery. Felt may be the oldest fabric known to man, and there are many references to felt in ancient writings. Since felt is not woven and does not require a loom for its production, ancient man made it rather easily. Some of the earliest felt remains were found in the frozen tombs of nomadic horsemen in the Siberian Tlai mountains and date to around 700 B.C. These tribes made clothing, saddles, and tents from felt because it was strong and resistant to wet and snowy weather. Legend has it that during the Middle Ages St. Clement, who was to become the fourth bishop of Rome, was a wandering monk who happened upon the process of making felt by accident. It is said he stuffed his sandals with tow (short flax or linen fibers) in order to make them more comfortable. St. Clement discovered that the combination of moisture from perspiration and ground dampness coupled with pressure from his feet matted these tow fibers together and produced a cloth. After becoming bishop he set up groups of workers to develop felting operations. St. Clement became the patron saint for hatmakers, who extensively utilize felt to this day. Today, hats are associated with felt, but it is generally presumed that all felt is made of wool. Originally, early shockproof felt was produced using animal fur (generally beaver fur). The fur was matted with other fibers—including wool—using heat, pressure, and moisture. The finest hats were of beaver, and men's fine hats were often referred to as beavers. Beaver felt hats were made in the late Middle Ages and were much coveted. However, by the end of the fourteenth century many hatmakers produced them in the Low Countries thus driving down the price. The North American continent was home to many of the beaver skins used in European hatmakers' creations in the eighteenth and nineteenth centuries. North American Indians' second-hand skins, replete with perspiration, felted most successfully and were in extraordinary demand for hatmaking in both the New and Old Worlds. The beaver hat was surpassed in popularity in the second half of the nineteenth century by the black silk hat, sometimes finished to resemble beaver and referred to as beaver-finished silk. The steps included in making felt have changed little over time. Felted fabric is produced using heat, moisture, and pressure to mat and interlock the fibers. In the Middle Ages the hatmaker separated the fur from the hide by hand and applied pressure and warm water to the fabric to shrink it manually. While machinery is used today to accomplish many of these tasks, the processing requirements remain unchanged. One exception is that until the late nineteenth century mercury was used in the processing of felt for hatmaking. Mercury was discovered to have debilitating effects on the hatter causing a type of poisoning that led to tremors, hallucinations, and other psychotic symptoms. The term mad hatter is associated with the hatmaker because of the psychosis that stemmed from the mercury poisoning. Hats of wool felt remain quite popular and are primarily worn in the winter months. The use of felt has enlarged over the past century. Crafts enthusiasts use it for all types of projects. Many teachers find it to be an easy fabric for children to handle because once it is cut the edges do not unravel as do woven fabrics. Industrial applications for felt have burgeoned, and felt is found in cars as well as production machinery. Felt is produced from wool, which grips and mats easily, and a synthetic fiber that gives the felt some resilience and longevity. Typical fiber combinations for felt include wool and polyester or wool and nylon. Synthetics cannot be turned into felt by themselves but can be felted if they combine with wool. Other raw materials used in the production of wool include steam, utilized during the stage in which the material is reduced in width and length and made thicker. Also, a weak sulfuric acid mixture is used in the thickening process. Soda ash (sodium chloride) is utilized to neutralize the sulfuric acid. Quality control begins with the arrival of the materials. Materials are checked for quality and weight. Some companies purchase wool that has been scoured and baled; the purity of the bales is examined upon entry. Other important quality control checks include continuous monitoring of the carded webs, since the web sizes are important first steps in producing the desired length and width of the felt. Once the batts are shrunk in width and length, the company checks the weight, density, width, length, and evenness of the batts. When production is complete, visual checks may reveal that the surface of a batt is slightly uneven and additional pressing may occur to even out the surface. The acid baths are also very carefully monitored. The amount of time the fabric is in the acid bath is precisely calculated by weight and length of yard good, lest the piece is ruined. Finally, the company producing industrial felt has to check its goods against a governmental standard for the product. The government has determined that 16 lb (7.3 kg) density felt must be 1 in (2.5 cm) thick, 36 in (91.4 cm) wide, 36 in (91.4 cm) long, and weigh 16 lb (7.3 kg). If the felt weighs less than this, the fabric is not dense enough and does not meet government expectations for that grade of felt. I discovered something wonderful over in Germany! Schnitzel! – kidding… No, I found heavy-weight industrial felt in a fabric store and was instantly in love! It is grey wool and 3mm thick, which makes a wonderful media for a variety of ‘making’ such as bags and purses, containers, footwear etc… I immediately put it to the test. Working and making with industrial felt is actually quite easy compared to usual sewing practices. But first, what is felt? Felt is the short word for a variety of material that is made by the combining of fibres without knitting or weaving. The fibres are matted by some method of twisting or vibrating until they become so entangled with each other that they hold strong. It’s really the same as how one turns their hair to dreadlocks. Original machine parts felt dates back to as much as 6,500 BC. It can be hand made, manufactured or even made by having huge rolls dragged behind horses to matt the fibres. Depending on the fibres and thickness it can even be used for furnishings. I just love how versatile it can be. See here for some very innovative work by Freya Sewell. There are interesting stories of mongolians pulling rolls of felting behind horses til strong and thick. That thick felt provides the protection on the walls of the yurt. Felt is breathable, warm, strong, but also tends to be light for it’s size. As you can see, the fibres are very densely matted and have no direction. For that reason, it can be cut and will not unravel or fray. That makes less work of finishing edges! Another designer’s dream! I used a rotary cutter as well as a matt knife with straight edge. It allows for perfect edges. Using a cutting matt keeps it square and easily measured and protects your table. Another of the major advantages of felt is that even though it is strong AND thick, it can usually still be sewn with a machine. That is one of the frustrating problems of leather; it is tough to sew on a regular sewing machine. My felt was 3mm and I had no problem sewing 2 thicknesses as the needle does not have a problem getting through. My other felt (polyester, I suspect) was thinner but denser and was still easy to sew. Due to it’s density and stiffness it was sewn on the ‘right sides’. That gives it an industrial charm. Pop rivets come in a variety of lengths and sizes. They are unique as they work by pulling the material together from the right side. The rivet is inserted through the holes in the material thicknesses, a backup washer is inserted on the inside, and then the rivet gun pulls the shaft from the outside (the bulbous end is pulled through the end which anchors it) and the shaft breaks with a ‘pop’ and then comes out. Hand-made felt is irregular and sometimes looks like thick skin because of its pleats. It does not go under a press so it is not flattened. This feature added to its extraordinary thickness gives felt a primitive aspect. It is a beautiful material that I love but with which I do not work. It can be found in many different thicknesses from 2mm to 2cm. It is resistant over time and has a minimal aspect. That is why I have chosen to work with it. Both types of sealing pad felt are nonwoven textiles and can both be clean-cut without fraying. That is why they do not need finishings such as hemming.
Дата Публикации: 14-02-22