Bearing

Plastic used in bearings, as in gears, have many success stories because certain plastics have the required properties to meet different product application performances. Similarly to plastic gears, plastic bearings have a long history of successful performance. Small to large bearings are used in applications requiring light to heavy duty. Some TPs have inherent lubricating characteristics and additives such as molybdenum disulfide, polytetrafluoroethylene (PTFE), and others enhance other TPs as well as TSs. Other TPs, as well as TSs, by the addition of PTFE and/or molybdenum disulfide, become excellent candidates for bearing materials.

There are high performance laminated (RP) fabric, bonded with phenolic plastic incorporating antifriction ingredients. They have given excellent service when properly applied in various applications particularly in the past. This group of bearings has a low coefficient of friction, antiscoring properties, and adequate strength for use in steel mills and other heavy-duty applications.

PV Factor

Bearings are designed to keep their frictional heat at a low value and have conditions that lead to dissipation of such generated heat. Major heat contributors are the magnitude pressures P exerted on the projected area of the bearing and the velocity V or the speed of the rotating bearing. Experience has set limits on this PV value. Limits within PV factors have been developed for specific plastics that provide the industries with successful bearings. Other heat contributors are coefficient of friction of mating materials, lubrication, clearances between bearing and shaft, rusted shaft, surrounding temperature, surface finish, hardness of the mating materials, contaminants, and bearing wall thickness that relates to heat dissipation.

The basic rule is that neither the pressure or the velocity should exceed a value of 1000 (psi or ft/min). As an example with a PV limit for acetal of 3000, the PV factor could be 1000 ft/min times 3 pounds or 1000 pounds times 3 ft/min at the extreme, provided heat conditions resulted in uniform rate of wear. The coefficient of friction data, available from suppliers, can also provide guidelines to the efficiency in comparing the different materials.

The limit of the PV factor for each material or the internally lubricated materials for the constant wear of bearing is usually available from the supplier of the plastic. Lubrication whether incorporated in a plastic or provided by feeding the lubricant to the bearing will raise the PV limit 2.5 or more times over the dry system.

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