Delrin
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Delrin is the brand name for an acetal resin engineering plastic invented and sold by DuPont. Often marketed and used as a metal substitute, Delrin is a lightweight, low-friction, and wear-resistant plastic capable of operating in temperatures in excess of 90 degrees celsius (approx 200 degrees Fahrenheit).
Other names for this compound include: polyoxymethylene (POM), acetal resin, polytrioxane and polyformaldehyde.
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[edit] Uses
The Food and Drug Administration has approved Delrin for use in the food industry. Delrin was used by Mattel from 1968 to 1972 to produce the low-friction wheel bearings found on redline Hot Wheels. Delrin is made from acetal homopolymer resin & when extruded into large basic shapes (i.e.- sheets, rods & tubes) tends to be subject to porosity problems. These porosity problems can make the product less reliable in certain applications. Acetal copolymer (Acetron GP) is often used as a replacement for Delrin (acetal homopolymer) when porosity risk is a factor in material selection.
It is also used extensively in paintball markers, where it is used to make bolts, pump handles and many other parts. Its low cost, adequate strength, light weight and self lubricating properties make it ideal for markers. Its competition in this area, Nylatron, while slightly lighter is more prone to swelling. A swelled part can make the mechanism impossible to operate and sometimes even damages the marker. Nylon-based products such as Nylatron have better wear-resistance than Delrin, but do not have good moisture-resistance, and therefore not suitable to high-humidity or underwater appplications.
Delrin's resistance to liquids and low coefficient of friction have also made it useful as a bearing-replacement in casters and wheels, to be selected in cases where corrosive environments make a traditional roller or ball bearing impractical.
Another recent use for Delrin is in the manufacturing of Irish flutes (traditionally made of wood) and tin whistles (traditionally made of metal). Delrin flutes sound similar or identical to wooden flutes but have none of the shrinkage or cracking issues usually associated with wooden instruments in hot, cold, or dry environments. Builders such as Des Seery, Michael Cronnolly of M&E Flutes, and Tony Dixon all build Delrin flutes.
Delrin has become an increasingly popular material in the fabrication of guitar picks. It has excellent durability; it is much more resistant to wear than nylon at the point of string contact, especially on round wound strings. Delrin does not crack or break like celluloid or polyvinyl chloride (PVC), provides a solid, slip-free grip, and develops a "memory" over time—that is, it gradually develops a slight curvature that conforms to the user's grip.
Delrin is also much treasured by many makers and players of harpsichords, being used for the plectra which pluck the strings when a key is pressed. Delrin has been found to provide a tonal quality very similar to the bird-quill used in the heyday of the instrument, while being far more durable and consistent.
Delrin is used to make the combination wheels in most high security safe locks. Using delrin in the wheels makes the lock resistant to decoding by x-raying because of delrin's low density. However, neutron bombardment techniques may still be used to decode delrin combination wheels. Delrin also increases the locks resistance to wear.
It is also used to make frame sliders and knee pucks for motorcycle riders/racers.
Delrin is gaining popularity for the manufacture of diving equipment, due to its light weight and its low porosity to gas under pressure. Some other plastics can absorb gas under pressure, and swell or deform.
[edit] Bonding
Acetal polymers are typically very difficult to bond. Special processes and treatments have been developed to improve bonding of acetal. Typically these processes involve surface etching, flame treatment or mechanical abrasion. Typical etching processes involve chromic acid at elevated temperatures. Dupont has a patented process for treating acetal homopolymer called satinizing which created anchor points on the surface which give that adhesive something to grab. There are also processes involving oxygen plasma and corona discharge[1].
Once the surface is prepared a number of adhesives can be used for bonding. These include epoxies, polyurethanes, and cyanoacrylates. Epoxies have shown 150-500 psi shear strength on mechanically abraded surfaces and 500-1000 psi on chemically treated surfaces (500psi approx 3,4MPa). Cyanoacrylates are useful for bonding to metal, leather, rubber and other plastics.
Solvent welding is typically unsuccessful on acetal polymers due to the excellent solvent resistance of acetal. Thermal welding through various methods have been used successfully on both homopolymer and copolymer.
[edit] History
Delrin was first synthesized by DuPont's research chemists around 1952. The company filed for patent protection of the material in 1956 and completed construction of plant to produce the material at Parkersburg, West Virginia in 1960.
[edit] Notes
- ^ Snogren, R. C. (1974). Handbook of Surface Preparation. New York: Palmerton Publishing Co..
