Contamination is expelled from composite bearing journals due to the modulus of elasticity difference between the pin and journal. The composite bearing has a modulus, in the radial direction, of 0.97 Msi. Compared with steel as 30 Msi, the bearing will elastically deform at a much higher rate in the presence of a point load generated by rolling small particles of contamination between the bearing and the steel pin.
For steel bearings, the modulus is the same for the bearing and the pin. Both materials deform, leading to scoring on both surfaces. Over time, the surfaces of both materials are effectively threaded and begin interlocking causing higher torques to actuate the joint until the equipment becomes locked.
Let's look at the life of contaminants in working PolyLube bearing:
- The contaminating particle enters the bearing journal.
- The oscillating motion of the machinery will cause the particle to move in a circular pattern.
- This motion will drive the particle to the unloaded side of the joint.
- As the load distribution of the bearing changes, the particles are driven out of the bearing.
- The presence of small angles of misalignment aid in the migration of the particles.
No Grease Flushing Required
The contamination particles will migrate to the unloaded side of the bearing and ultimately out of the joint. This can be thought of as an extremely slow version of the pumping action that occurs in hydrodynamic bearings.
Grease Attracts Contamination
Since there is no need for grease flushing with PolyLube, there is also no exterior grease present to act as a trap for new contamination. This avoids the high solid content grease from acting as a grinding or lapping compound. The result is decreased exposure to contamination and a cleaner piece of equipment.
Break-in and Film Transfer
The secret to PolyLube’s high load greaseless operation is the use of uniquely woven PTFE super-filaments in the bearing liner. They exhibit tensile strengths twenty times greater than PTFE resins and are not subject to cold flow under high load. No secondary lubrication is necessary due to the film transfer process, even during start-up.
As the bearing begins service, the liner’s PTFE undergoes a phase change and disburses over the mating pin surface, transferring from the inner diameter to the pin's wear surface and smoothing out any macroscopic surface imperfections. Essentially, a small amount of the liner is worn away and sacrificed to coat the pin with a low friction PTFE film. This wear is often negligible, usually less than 0.001”.
This allows the bearing to have a very low coefficient of friction with minimal long-term wear, under high loading conditions. Following the break-in period, the wear rate stabilizes, remaining relatively constant for the bearings’ life. Testing of the PolyLube MRP bearing at 22,500 pounds, with 50° oscillation angle, resulted in stable wear under 0.005” at over 1.5 million cycles.
The elapsed time for break-in is PV (Pressure and Velocity) dependent. The equilibrium wear rate varies from operation to operation, due to a number of factors including: loads, speeds, pin hardness, material, and pin surface finish. For more specific guidance on the break-in period to anticipate given your specific application, please contact a PolyLube application engineer.
PolyLube MRP bearings are designed to minimize wear; however, the bearing wear is dependent on general operating conditions, such as speed, sliding distance and load. With intermittent rotation or oscillation, radial wear should be negligible over thousands of hours. Hard chrome plating gives excellent wear performance and protects the pin from corrosion. Coatings such as chrome, electroless nickel, YZD or nitro carbonizing are all common treatments for pin materials used with PolyLube bearings. Some customers have even experienced great results using standard 1018 pin material.
Any ratings are typical for design purposes. Your design parameters may affect final ratings. Consult with a Polygon sales engineer for guidance. Final testing and approval is the customer's responsibility for their application. This information is derived from our testing and published data. There is no assurance of these properties, or warranty provided that these products are suitable for any particular purpose or operational situation.
Polygon certifies that their product will be free from material defect. Polygon will not accept any liability for loss, damages, or costs from use or misuse of our products.
Specifications are subject to change, and may be affected by our continual process of improvement. Changes may be made without prior announcement.