Recorded February 7, 2011
Presented by Tom Schell, RTP Company
Does the world of wear resistant or internally lubricated plastic compounds seem more complex than it should be? Then join Tom Schell, senior product development engineer for wear resistant materials at custom compounder RTP Company, as he explains the fundamentals that will allow you to clearly understand the features and benefits of these unique plastics.
Questions and Answers
Q: What are the constarints from processing perspective particulaly for carbon fiber and Aramid fiber mdified compounds.
A: Carbon and aramid fiber filled products should process the same as glass fiber filled materials. From a compounding standpoint we can add up to ~ 50% by weight carbon fiber and up to ~ 20% by weight aramid fiber.
Q: I quite often am looking for a high CoF such as with clampsany thoughts
A: The addition of reinforcements like glass fiber and some minerals can improve wear resistance and actually increase CoF.
Q: by adding the additives to the resin if i want to paint the molded parts i.e. clear UV coating what is the adhesion compare to a normal resin?
A: The majority of wear modifying additive should not greatly affect adhesion of paint or coatings. Silicone is the one major exception to this; paints, inks, coatings will not adhere to silicone filled compounds.
Q: Is there wear performence difference between long-fiber or short fiber-reinforced polymer?
A: In general there shouldn’t be a big difference between short and long fiber reinforced materials in terms of wear. Wear performance in fiber reinforced products will depend a lot on part geometry and tool (mold) design. These factors affect fiber alignment in the final part and can lead to changes in overall wear performance.
Q: With “break in” what sort of thickness needs to be worn away?
A: The amount of material that needs to be worn is usually fairly thin, probably less than 100 microns in most cases. Tool steel temperature affects how thick the “resin-rich” surface of a molded part will be.
Q. “How does PP compare to POM in terms of Wear and Friction?”
A. Semi-crystalline thermoplastics usually outperform amorphous thermoplastics in terms of wear and friction. However, not all semi-crystalline polymers are created equal. Polypropylene is much softer than POM and does not provide wear performance as good as that of POM. Due to its inherently poor wear resistance our wear product portfolio does not contain a lot of compounds based on PP.
Q. “How does temperature resistance of a resin affect the wear rate or resistance to wear?
A. Part failures due to wear are usually thermal failures; as frictional heat is builds up it often causes “melting” of the surface. Therefore, resins with high temperature resistance generally provide the best wear resistance.
Q. “Is the dynamic coefficient of friction of semi-crystalline thermoplastics usually lower than amorphous thermoplastics”?
A. Yes, generally the smooth, more wear resistant surface of a semi-crystalline material will also have a lower coefficient of friction.
Q. “How long is the break-in period for the ASTM D-3702 test?”
A. For this test the break in period is 1500 min (25 hours) and the normal test length is 6000 min (100 hours.
Q. “Is there a change in surface finish when going from a natural resin to a resin filled with PTFE?”
A. Not usually, but sometimes. It depends on the loading, but for the most part you shouldn’t see much of a difference at all.
Q. “Can you test against plastic or other materials instead of steel for the ASTM D-3702 test?”
A. Yes! We often replace the steel thrust washer with a plastic one to obtain plastic vs. plastic testing. We also test against a variety of metals like brass, aluminum and stainless steel.
Q. “Can you use PFPE and PTFE together?”
A. Yes. In fact we have found that a combination of PTFE and PFPE often provides the best possible combination of wear and friction performance.
Q. “Do you need to change your mold design when going from a natural resin to a PTFE filled resin?”
A. No. The typical loading levels that we use in our compounds do not significantly affect the way the material is molded to a point where you need to change your mold design.
Q. “Does the PTFE film that builds up on the contact surface wash away when used in the presence of a liquid?”
A. No. Sometimes if the liquid environment is highly abrasive then that can wear things away. However, other additives like graphite do really well in aqueous environments.
Q. “Do you have additive combinations for high load applications?”
A. Yes. Please attend our “Ultra Wear” webinar in March 2012 as we review RTP Company’s research on wear resistant thermoplastic compounds that experience highly demanding applications.
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