Understanding Plastic-to-Plastic Wear: Design Principles & Lubrication Strategies

Wear of Plastics Against Plastics

When designing plastic-to-plastic bearings, shafts, gears, or any other moving parts, the specific combination of polymers must be chosen with care. Even polymers that naturally lubricate well can behave very differently when paired with one another.

Plastics and the Laws of Nature

Unlike rigid metals, plastics do not follow the conventional friction equations. This non‑rigidity leads to unexpected results when plastics slide against metal or even against each other. For example, friction is not proportional to load; it typically rises with speed, and the static coefficient of friction is lower than the dynamic value.

Viscoelastic, Low‑Modulus Materials

When two viscoelastic, low‑modulus plastics interact, the wear behavior can be inconsistent. The most predictable pattern emerges when the same thermoplastic contacts itself—though this configuration produces a very high wear rate unless operating temperatures and pressures are kept exceptionally low. In all‑plastic systems, wear can be mitigated by using crystalline reinforcements or by pairing dissimilar polymers. If only a single compound is viable, incorporate an internal lubricant such as PTFE at 15–20 % by weight.

Wear on Moving Surfaces

Wear tends to increase when dissimilar neat resins mate. Similar trends appear when lubricated (unreinforced) resins contact either themselves or other lubricated resins. Adding reinforcing fibers usually raises wear against an unreinforced partner, but applying reinforcement to both surfaces can lower overall wear. Glass‑fiber composites generally exhibit lower wear factors than carbon‑fiber composites because glass fibers are harder than carbon fibers.

Lubrication of Composites with PTFE

Incorporating PTFE into composites dramatically reduces wear for both similar and dissimilar pairings. During the initial break‑in period, a thin PTFE film transfers to the mating surface, creating a PTFE‑to‑PTFE bearing condition that lowers wear on both moving and stationary parts. This approach also mitigates the wear impact of glass fibers on the opposing surface.

Silicone Fluid Added to Thermoplastics

Adding silicone fluid to thermoplastic composites yields compounds with lower wear factors than neat resin, though still higher than PTFE‑lubricated mixtures. In plastic‑on‑plastic applications, choosing pairs with comparable wear factors is preferable to pairs with large disparities, provided the total wear remains within acceptable limits.

Have questions about plastic‑to‑plastic wear? Call Craftech® Industries, Inc. at 518‑828‑5001 or email tech@craftech.com and let our engineering team help you solve your design challenges.