Gear lubricant compositions

Gear lubricant compositions are classified by the American Petroleum Institute (API) using the so-called GL ratings (7,8). These classifications are subdivided into six classes. The lowest rating. 

The input speed to the gear train was varied from 1500 to 4500 rpm, the torque from 0.025 to 0.5 Nm, and the contact load on the idler gears from 0.5 to 30N. The peripheral speeds of the gears were up to 3.3 ms , the relative slip 1 ms and the maximum contact stress 900 MPa. The test temperature was varied between 20°C and 250 C, and the chamber pressure was 10 Torr. 24 lubricating gears containing different proportions of copper, silver and molybdenum disulphide were tested, and the best performance was given by a composite of 87% copper, 5% silver and 8% molybdenum disulphide. 

Polymers and polymer matrix composites are increasingly replacing metals in bearings, cams, gears, and other sliding components. Polytetrafluoroethylene (PTFE) is an example of a self-lubricating polymer that is widely used for its wear resistance. Fiber reinforcement of PTFE improves other mechanical properties without sacrificing the wear performance. 

This is a fruitful area for specially developed formulations which combine lubricity with good creep and temperature resistance. The Audi 80 gear shift mechanism is composed of two snap-fitted components in a nylon-based composite containing PTFE and silicone as well as glass fibre in another case an actuator tube in reinforced PPS moves in contact with the PEI housing for an automatic gear shift. (Both these examples feature formulations from the LNP Company.)... 

Thus, in addition to performing efficiently as gears, the PBT gears provided excellent frictional properties, with an inherent lubricity contributing to long-term wear resistance. Torque tests conducted on these gears in operation performed at levels ten times in excess of the normal operating values. In the next chapter we shall see how plastics and composites can be made to hold up well under environmental stresses. 

John E. Theberge. Properties of Internally Lubricated and Glass-Fortified Thermoplastic Resin for Gear and Bearing Applications , 25th Annual Technical Conference, Reinforced Plastics/Composites Division, The Society of the Plastics Industry, Inc., Washington, DC, 1970. 

Poljmier composites, especially those which are hybrid in nature, have good wear performance and such a class of materials is very suited for both low fidction (bearings, gears) and high friction (footwear, tires, brakes, and fidction drives) applications whilst keeping the wear rate to a minimum. Finally, polymer composites often do not work well in lubricated or water environments due to the problem of the weakening of the interface between the fillers and the matrix and removal of the transfer layer in the presence of a fluid. 

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