plastic for wear applications - guideline

Basic Summary of Plastic Materials for Wear Applications

(This is by no means a complete list.)

Polyamide (nylon)
Acetal (Delrin)
Polyimide (Dupont’s Vespel)
Polyamide-imide (Solvay’s Torlon)


Polyamides (nylon)

Polyamides, popularly know as nylon, are among the most versatile and durable of the plastics. They are primarily crystalline resins, but amorphous and semi-crystalline versions are available. Nylon has good strength, toughness, chemical resistance and a low coeficient of friction.

Polyamides are available in a variety of grades including general purpose, glass and/or mineral reinforced, or both reinforced and/or impact modified. There are also flame retardant grades and grades for medical devices.

Because of their strength, toughness and heat and chemical resistance, nylons have found uses in a wide variety of applications including bearings, gears, bushings, washers, guides, sprockets and sheaves. They are also used in electrical connectors, switches and housings.

One major downside is that nylon absorbs moisture. When nylon absorbs moisture, the tensile strength and hardness decline. However, the toughness increases.

Acetals (Delrin)

Acetals (or polyoxymethylene - POM) are highly crystalline thermoplastic engineering resins that offer high mechanical properties and resist many chemicals. More commonly know by Dupont’s brand Delrin, acetals are known for their high strength, fatigue and creep resistance, resilience, surface hardness, lubricity, toughness and excellent resistance to solvents, greases and petroleum-based fuels. Acetal copolymers are practically impervious to swelling when in contact with these substances, resulting in extremely high dimensional stability.

General uses for acetal include guides, gears, electrical components, slides and packaging equipment. While considered an “engineering resin”, it’s not as expensive as other materials used for wear applications (see below). Obviously this all depends on the specific grade.

The primary limitations for acetals are when using copolymer in hot water environments (boiling/steam), strong acidic or alkali environments, or in high operating temperatures.

Polyimides (Dupont’s Vespel)

Polyimides are processable by conventional thermoset transfer and compression molding, film casting and solution fiber techniques. Molding compounds filled with lubricating fillers or fibers produce parts with self-lubrication wear surfaces.

Thermoplastic polyimides can be filled with glass, boron or graphite fibers and can be molded into high-strength structural components with good flame resistance and electrical properties.

Polyimides have excellent high temperature mechanical performance, very high tensile and compressive strength, outstanding bearing and wear properties, and very good chemical resistance.

However, polyimides don’t do well in steam and other high temperature water applications. They’re also expensive.

Polyamide-imides (Solvay’s Torlon)

Polyamide-imides (PAI) are amorphous, high-temperature engineering thermoplastics. These materials possess superior mechanical properties up to 260oC/500oF , with good dimensional stability and creep, impact, and chemical resistance. Other strengths of PAIs include good radiation resistance and they are more stable than standard nylons under different humidity conditions.

Because of its intrinsic high temperature resistance, high dimensional stability and good machinability, PAI is very popular for precision parts in high-tech equipment. In addition, its good electrical insulating ability provides numerous possibilities in the field of electrical components.

PAIs can be processed by injection molding, but special screws are needed due to the reactivity of the polymer under molding conditions. At high temperatures, polyamide-imides can be affected by strong acids, bases and steam. They’re also expensive.

DISCLAIMER: All of what you just read is offered as a general guideline. While I did my best to collect this into something fairly easy to read, I’m not responsible for any errors or inaccuracies. Please do your own research before using, designing for or specifying ANY resin.

Hope this helps…

Warren

Also, for some more ideas on high-wear plastics. Take a look at what other companies use:

http://igus.bdol.com/iglide.asp

http://www.designnews.com/article/CA404433.html

http://www.slideways.com/plastic_bearings_d.html

Another good link:

http://www.machinedesign.com/BDE/mechanical/bdemech6/bdemech6_13.html

Cheers,

Warren

are any of those wear resistant plastics recyclable? most of them which have a high wear resistances have a glass filler/reinforcement

i’m doing a uni project and was wanting to replace the back aluminium shoe of a electric hand planer with a plastic with a high wear resistance - the aluminium is cheap > gets burs and scatches the timber . any thoughts

if you add a filler like graphite to nylon can it be re used - melted down and injection moulded agian?

my teacher wants the plastic to have a high wear resistance and be able to be reused/recycled

Wear is somewhat relative. You have to define how much were the product has to endure. A plastic bearing has to endure quite a bit, a rotomolded LLDPE kayak takes a lot of beating too, but that’s a different type of wear.

If you molded a handle out of recycled milk bottles (HDPE), you would have something that would be somewhat durable, but not indestructable. Plus dimensional stability and tolerances play a role and can become a problem for crystalline materials like PE and PP.

As for fillers, generally as soon as you add a filler package to a resin, like glass, recylcing becomes a problem. It can contaminate the rest of the batch. Any thermoplastic can be recycled (in production it’s called “regrind”), but there is a limit with respect to heat histories and logistics.

it’s to replace the back shoe of a electric hand planer - the back shoe only touches the newly cut timer - yet needs to withstand storage - misuse of a diy user etc scratching