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This one won’t work — the operating environment is too hot. And this one won’t work because it’s too expensive. But this one, the higher operating temperature UHMW-PE, is just right.
Until recently, options for elevated temperature applications were limited to high operating temperature (300°F and higher) that were very expensive or typical engineering polymers that degraded quickly at elevated temperatures, leading users to ask, “Is it worth the additional cost and trade-off in terms of wear/surface characteristics to use a polymer material designed for a higher temperature environment than needed?” With the recent introduction of a higher operating temperature UHMW-PE product into the marketplace, the answer to that question is an emphatic “NO.” Now, just like the fairy tale, there is a “just right” solution: a polymer designed to excel in chemical and thermo-cycling environments up to 275ºF, with no loss in wear and surface characteristics ... and at an affordable price.
Even in manufacturing environments with temperatures under 200ºF, there are a number of benefits to choosing polymer, particularly UHMW-PE, components. By eliminating metal on metal, noise levels are greatly reduced. In addition, polymer components weigh less than steel, reducing operating power requirements. Finally, UHMW-PE components exhibit superior release characteristics and resist abrasion, corrosion, chemicals and moisture. These benefits, however, don’t hang around very long when the material is in a manufacturing environment where temperatures range up to 275°F. In fact, at these higher temperatures, standard UHMW-PE is subject to an increased oxidation rate, causing rapid material degradation.
Higher operating temperature UHMW-PE, on the other hand, is specifically formulated to combat the oxidation rate of the material at higher temperatures, thereby slowing material degradation and extending wear-life in chemical, elevated temperature and thermo-cycling environments.
This article was written by Ron Denoo, Quadrant Engineering Plastic Products.
|In This Issue:
temperature UHMW-PE is no fairy tale
Finally an affordable material for elevated temperatures.
UHMW-PE: the titan of polymers
UHMW-PE: the “ultra” material
Test Your Knowledge
The International Association of Plastics Distribution, founded in 1956, is an international trade association comprised of companies engaged in the distribution and manufacture of plastics materials.
Members include plastics distributors, processors, manufacturers, resin manufacturers, manufacturers’ representatives and associated products and services, all of whom are dedicated to the distribution channel.
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The first question that’s top-of-mind for most plastics distributors when a purchasing decision arises is not “How much will it cost?” or “How quickly will I get my delivery?” or “I wonder if they’ll give me that trip to Disney World for placing this order?” Instead, the single most important question for today’s distributor is “Of all the different products now available, which one will provide the perfect solution?” Increasingly, ultra high molecular weight polyethylene, or UHMW-PE, is the correct answer.
Simply put, UHMW-PE has a “rare DNA.” While every thermoplastic stands out with one or two key benefits, UHMW-PE possesses several. When compared to traditional polymers, it’s the only thermoplastic that has the industry’s highest resistance to abrasion and chemical erosion, while at the same time maintaining product integrity under higher impact-stress situations.
Additionally, UHMW-PE’s self-lubricating character yields a non-stick surface comparable to PTFE. Put all of those benefits together with its low moisture absorption character and its low coefficient of friction, and you have the strongest, most durable plastic available anywhere — ready to go into service just about anywhere.
Uses of ultra high molecular weight polyethylene cover a diverse spectrum of applications including bulk material handling, food processing and beverage machinery, chemical, mining and mineral processing equipment, sport and leisure industry and transportation-related applications.
UHMW-PE is odorless, nontoxic and tasteless. Made up of unusually long chains with a molecular weight numbering between 3 and 6 million, these chains serve to transfer load more effectively to the polymer backbone by strengthening intermolecular interactions. This results in one of the strongest and most durable thermoplastics on the market.
UHMW-PE is produced in powder form, generally ranging from 100 to 200 microns in diameter. Because this is an extremely high viscosity polymer, compression molding and ram extrusion are the preferred processes used to generate the high pressures required to manufacture stock shapes or custom profiles where subsequent tailoring may be required.
While natural and reprocessed grades are still the most common, specialty and premium grades are becoming more popular as they allow the core UHMW-PE product to be modified by way of additives and/or fillers that enhance a desired property needed for a specific application.
This article was written by Birgit Karen Moecks, Röchling Engineering Plastics.
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Ultra high molecular weight polyethylene, or UHMW-PE as it is most commonly referred to, is the most versatile polyethylene for industrial needs on the market today. This low-cost material outperforms many of the other plastics materials being offered.
UHMW-PE is used in a wide variety of applications, ranging from something as sensitive as joint replacements in humans to a product as crucial as radiation shielding in nuclear submarines. Dewatering elements on paper-making machines and chute liners are also commonly used applications of UHMW-PE and show the versatility of the product’s application.
UHMW-PE is a very light-weight material that can be easily handled and has practically zero water absorption. Because of its light-weight nature, installation is trouble-free. The ease with which UHMW-PE is machined makes it a perfect material to mill, plane, saw, drill and rout into a variety of fabricated parts.
UHMW-PE is a high viscosity polymer, and because of its extremely low melt-flow index and very high molecular weight, it cannot be processed by the common methods used in ordinary thermoplastics. Compression molding (or press sintering) and ram extrusion processes are used to generate the high pressures needed to produce this material into various shapes and sizes.
UHMW-PE is commonly manufactured in sheet, rod, tube and profile. Ultra high molecular weight polyethylene has a molecular weight ranging from 3 to 6 million g/mol. This extremely high molecular weight gives UHMW-PE the unique properties of high abrasion resistance and high impact strength. These characteristics when combined with its intrinsic properties of low coefficient of friction and chemical resistivity, enables UHMW-PE to have many widespread applications.
This article was written by Rohit Saigal and Deborah Wright, Polymer Industries.
UHMW-PE is defined as polyethylene whose molecular weight is 3.1 million or higher. When making this determination, it was found that physical properties increased rapidly as lower MW values increased, and then leveled off at the 3,100,000 value. As with most high-performance polymers, processing of UHMW-PE is not easy. Because of its high melt viscosity, conventional molding and extrusion processes would break the long molecular chains that give the material its excellent properties. Current manufacturing methods include compression molding, ram extrusion and warm forging of extruded slugs.
UHMW-PE has outstanding abrasion resistance and an extremely low coefficient of friction. Impact strength is high and chemical resistance is excellent. The material does not break in impact strength tests using standard notched specimens; double-notched specimens break at 20 ft-lb/in (42.1 kJ/m2).
UHMW-PE has a crystalline melting point of 267°F (131°C). Recommended maximum service is about 200°F (93°C). Care should be taken when fastening UHMW-PE, as its large thermal expansion can cause the material to buckle between fasteners if they are too far apart.
For more information on UHMW-PE and other plastic materials, IAPD’s Introduction to Plastics is an invaluable training manual. Information about it and other IAPD educational resources is available online at www.iapd.org.
What do you know about UHMW-PE? Answers are at www.iapd.org/popquiz.html.
1. Please sort the following materials from those with the most water absorption to the least.
2. UHMW-PE has good chemical properties. However, which of these chemicals will affect UHMW-PE negatively?
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.