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A key consideration for any engineer and machine designer must be the safety of the machine operator, as innovative form meets function and safety. While a machine or device may perform perfectly in its mechanical function, its design will fail to fulfill its most vital criterion if it operates at the expense of user safety.
Shielding and guards also create a protective barrier, preventing product or process contamination, pilferage, tampering, alteration and/or interruption. A shield can vary from the simplest sneeze guard to an extremely critical protective biological or radiological containment barrier. Historically, designing engineers relied on expensive and bulky fabricated metal and glass guards to prevent human contact with harmful and, often, lethal materials or environments. These include hot surfaces; moving devices; noise sources; and harmful dusts, liquids and gases in industrial environments.
Metal and glass
Safety and reinforced glass affords observation of a product or process, yet the hefty price and weight of glass are difficult to incorporate into a structural design plan. Glass also maintains a typically limited scope to flat glazing applications. Safety or reinforced glass may perform well initially; however, it will likely require replacement once it is penetrated, chipped, over-stressed, or impacted and subsequently damaged.
PETG copolyesters are uniquely suited for exposure to low temperature environments, such as food processing operations and food packaging machines operating in a sub-zero environment. While certain plastics dramatically forfeit impact resistance at lower temperatures, copolyesters retain their plaque impact resistance in even the most extreme environments.
Used for over 50 years, cellulosic plastics are manufactured from renewable, cellulose-based resources, such as wood or cotton fibers, and are truly a “green” industrial material. Cellulosic plastic sheet is employed in unusually difficult applications in which other types of plastic cannot perform. For example, for many years, cellulosic plastic shielding and machine guards have functioned well in brutal mining operations that utilize extremely harsh, chemically aggressive drilling oils, hydraulic oils, greases, fuels and other fluids.
Specialty plastics satisfy many important considerations, providing a comprehensive solution at an affordable price, when compared to competitive materials. Plastics are more easily manipulated and formed into unique shapes and complicated structures than metal or glass materials. Unlike some metals, plastic articles formed from copolyesters and cellulosics typically do not require continued repainting to reduce corrosion effects. Plastics also offer resistance to the common problems of metallic rusting and glass chipping and cracking. Copolyester and cellulosic plastic sheet are easy to heat bend and thermoform into unique shapes and forms. This allows the machine designer more design flexibility while creating attractive, safe and protective shielding.
This article was written by David Salyer, Eastman Chemical Company.
|In This Issue:
Selecting plastic materials for machine guards and safety shielding
PETG shields are lightweight and easy to fabricate
Creating animation with lenticular
Mechanical fastening that lasts with PETG sheet
Test your knowledge
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In today’s competitive market environment, capturing the attention of potential customers is extremely challenging. People are constantly confronted by advertisements from all directions. They come across printed media on a daily basis. But imagine a 3-D graphic showing a model striking different poses as a customer walks past or a product demonstration with stop action sequencing at a trade fair. Our eyes are instinctively attracted to movement — but the problem is how do you make still images “move?”
It can be done with lenticular technology. This is a high resolution imaging process developed for the purpose of creating multi-imaging visual effects such as 3-D or animation. Printed images that move, change shape, leap out in brilliant 3-D or even reproduce action video sequences are made possible by the use of lenticular sheet, extruded PETG (polyethyleneterephthalate glycol).
The specialized lenticular print process can show depth, motion or both. Lenticular sheet is made up of tiny ridges or lenses (hence the name “lenticular” printing). Multiple images are interlaced or woven together in a pre-press studio. When that woven image is printed to the back of a lenticular material, the lenses hide all but one image at a time and as the viewing angle changes, the image that is shown to your eye continuously moves to the next in the series. When a series of images are run before your eyes, it creates animation.
The most common method accounting for over 90 percent of the lenticular imaging in the world today is direct to the lens lithographic printing. From high-resolution films, plates can be exposed and positioned in precise register on a four-color process press. Most presses available in this category are in fact likely to be six-color, allowing white to be printed in the same pass. Usually more opaque white needs to be added later after the inks are dry. There are many methods of doing this (ink, silk screening, laminated cover stock or polypropylene film). The white layer is used as both a protection for the image and to provide “brightness.”
This article was written by Quinn Plastics.
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With the accelerating rate of new product launches every year, brand owners are faced with an increasingly competitive retail environment in which to market their products. To attract consumer interest in crowded stores, marketers and designers rely upon fabricators to create point-of-purchase (P-O-P) displays and in-store fixtures that are both eye-catching and durable enough to withstand frequent consumer handling. In addition, fabricators need to balance these aesthetic and performance requirements against their own needs for production and supply chain efficiency.
Mechanical fastening: an overview
Fabricators have a number of considerations to make when choosing between different types of mechanical fasteners for projects involving plastic sheet. Rivets are one popular option fabricators can use to easily attach pieces of plastic sheet. Holes are typically drilled slightly larger than the diameter of the fastener in order to allow for expansion and contractions caused by environmental conditions. This also helps to decrease stress on the part, which can reduce display breakage.
Due to their durability and unique functional properties, metal rivets are ideal for joining metal and plastic sheet. Since metal and plastic have different inherent attributes, this is a distinctive advantage for designs that call for the use of both materials. A drawback to using metal rivets, however, is that fabricators must take care not to over-tighten during the fastening process, as this could cause stress on the plastic sheet, increasing the risk of breakage.
If metal rivets are used, softer metals, such as aluminum, are preferred. Significantly less force is needed to attach aluminum rivets as compared to steel ones. Washers should also be used on both sides of the rivet to help distribute localized stress generated in the area around the rivet connection. Due to their ability to generate higher stress levels, steel rivets should never be used to attach plastic sheet pieces together.
Another viable and often used alternative is plastic rivets. As opposed to their metal counterparts, plastic rivets are lightweight and exert less stress around the fastened area. On the other hand, plastic rivets have less strength capability, which can limit options for designs that would benefit from combining plastic with another type of material, such as wood or metal.
The third mechanical fastening option is T-bolts, which may be used to fasten plastic sheet both to another plastic and to other materials. Although T-bolts are sometimes not as aesthetically pleasing as the other two options, they add strength and durability to the parts being fastened. Additionally, their flexibility allows parts to be shipped flat and assembled at the store with basic instructions, reducing production time. They also allow for easy display disassembly.
T-bolts are often used when display and fixture designs call for rotational movement around the fastened area. As with the use of rivets, care needs to be taken not to over-tighten T-bolts, and washers should be used on both sides where possible.
Mechanical fastening and
PETG sheet is ideal for a variety of bonding processes, including mechanical fastening. Unlike alternative materials, like acrylic, PETG’s high impact resistance reduces the potential for cracking or breakage during fabrication, shipping and ongoing consumer use or abuse. This durability is also a benefit for both the retailer and brand owner, helping them to create a safer in-store environment and convey a more premium image at point-of-purchase. PETG’s durability can also extend the lifespan of retail fixtures and displays, decreasing replacement needs and saving money.
PETG sheet offers the possibility of deep draws when thermoformed. It also allows complex die-cuts and precise molded details with minimal sacrifice of structural integrity. To help meet the needs of designers who require increased design flexibility, PETG sheet is able to bend and curve, according to realistic criteria, without breakage. This attribute offers the potential for more creative and complex shapes and aesthetics.
As in-store fixtures are commonly required to last for three to five years in high-traffic retail areas, displays need to be kept clean. Offering excellent chemical resistance, PETG sheet can withstand the harsh chemicals included in many common cleaning agents. PETG sheet’s durability also allows it to be downgauged without sacrificing structural integrity. This can create lighter, more cost-conscious fixtures for fabricators and brand owners.
Alternative fastening techniques
Bringing it all together
This article was written by Chad Alan Frazier and Gary Boone, Eastman Chemical Company.
PETG (glycol-modified polyethylene terephthalate) is a clear amorphous thermoplastic with higher impact strength than acrylic. PETG is available in clear and opaque formulations and comes in grades for injection molding and sheet extrusion. PETG sheet is easily die-cut and can be printed.
Often referred to as a “copolyester,” PETG is used in a variety of extrusion and molding processes and applications because of its clarity, toughness and ease of processing. These processes include:
The flexibility and durability of this thermoplastic enables a wide range of applications, such as store fixtures and shelves, food bins, decorative laminate films, profiles, indoor signs, lenticular imaging, packaging for medical equipment, general use packaging, food packaging, labels, cards, etc.
With a glass transition temperature (Tg) of approximately 80°C (176°F), PETG is readily vacuum and pressure-formed as well as heat bent at a low forming temperature. This results in faster processing times with less energy consumption than some other materials. Additionally, there is no need to pre-dry PETG sheet prior to thermoforming.
PETG offers the capability to produce complex shapes, precise details, deep draws and compound curves. It die-cuts and punches easily and can be bonded or fastened with adhesives, solvents, ultrasonic welding or rivets. In addition, PETG is easily decorated by painting, silk screening or hot stamping.Colors may be added during processing, using color concentrates, dry colors or liquid colorants. Most color concentrates are custom-made.
The property table for PETG is online at www.iapd.org/new/bookstore/free_resources.html. For more information on PETG and other plastic materials, IAPD’s Introduction to Plastics is an invaluable training manual. Details about it and other IAPD educational resources are available online at www.iapd.org.
What do you know about PETG? Answers are at www.iapd.org/popquiz.html.
1. PETG is a copolymer of:
2. The materials acrylic, polystyrene, ABS, PVC, PETG and CAB represent which product group?
Your IAPD Distributor is your choice in finding the right material for your application. Go to www.iapd.org to find a distributor in your area. You can search by company name, location or product category.
The IAPD Magazine web site at www.theiapdmagazine.com allows you to search by material, trade name and fabrication process. You can also search for fabrication capabilities.
Designing with Plastics is published by the International Association of Plastics Distribution. While every effort has been made to ensure accuracy, IAPD encourages you to verify information with a plastics distributor to ensure you select the correct plastic products to meet your needs.