Bondable UHMW: Adhering
to the Plastics Industrys Needs
Over the last 20 years, UHMW-PE has become a staple product in a wide range of industries from conveying lines to replacement hips. Its low coefficient of friction rivals Teflon while possessing 30 times the abrasion resistance, making it an ideal material for sliding or release applications. Its impact strength also makes UHMW the perfect candidate for applications in colder, even cryogenic environments. USDA and FDA approvals for virgin grades make it ideal for use in the food processing industry.
The material is easily machined and offers good chemical and stress cracking resistance. In addition, it has good sound dampening properties, making it ideal for use in a wide variety of applications, such as materials handling equipment, food and beverage handling lines, agricultural product liners, drawer glides, recreational equipment, gaskets and washers, and vending machine components.
If there is such a thing as a drawback to UHMW, it is the fact that the material is difficult to produce, primarily because UHMW has no melt index. For this reason, UHMW is usually limited to thick sheets, ram extruded profiles or skived films.
UHMW is typically installed using fasteners or other joining methods. However, new products are available in todays marketplace that eliminate the added expense of external fastening systems.
The development of a bondable UHMW a thinner gauge, adhesive-backed material is enabling companies to save in material, time and labor.
Oxidation increases the surface energy of UHMW, allowing it to accept a pressure-sensitive adhesive. Since installation of UHMW is now simplified, many plant managers and maintenance supervisors are replacing mechanically fastened sheet with the new thinner-gauge, adhesive-backed UHMW tapes.
Cost savings are also realized with this type of product. For example, since countersinking usually requires a 3/16-inch space, a 1/4-inch sheet will only provide a 1/16-inch usable wear surface. This means that 75 percent of the sheet product does nothing but hold bolts its scrap. However, a 1/16-inch piece of bondable UHMW will provide the same fastening results. Also, bondable UHMW can be adhered in continuous coils up to 0.125 inch thick. Thus, catch points and seams are virtually eliminated, producing a much smoother and efficient operation of conveyor lines and sorting equipment.
In addition to being able to produce product in continuous length coils, other advantages of this process include tight thickness tolerances and low stress or flatter sheet. Companies such as Crown Plastics currently offer bondable UHMW in 18-inch wide maximum sizes, but a machine capable of producing 24-inch wide material should be in operation some time this year.
Two Adhesive Forms
Pressure sensitive adhesives are available in two forms: acrylic based and rubber based. Rubber based adhesive are very aggressive and work with a wide range of substrates. They are designed for general-purpose ambient temperature applications and provide an excellent bond to stainless and polished aluminum.
Acrylic adhesive systems provide good UV stability and resistance to chemicals and elevated temperatures. They are considered more stable than rubber adhesives but dont possess the high initial bond of the rubbers. Acrylics will maximize their bond after about 24 hours of a wetting out process.
For applications which require a higher or more permanent bond, a Treated-For-Bonding (TFB) UHMW is also available. Treated material is sanded on one side and oxidized making it suitable to be used with epoxy systems or contact cements. Adhesive selection needs to be based on the substrate and application requirements.
The above information was supplied by Crown Plastics. For more information, contact Crown Plastics at (800) 368-0238 or visit its Web site at www.crownplastics.com
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