NTN Corporation has developed a “High Temperature Resin Pulley Unit” for engine auxiliary belts that is lighter in weight and has longer life compared with conventional steel pulleys.
In recent years there has been a mounting demand for greater fuel efficiency in automobiles, which has lead to lighter weight pulley units and the usage of resin materials. However, a disadvantage of the resin pulley is that the bearing temperature is higher due to poor heat dissipation and that results in reduction in life of the bearing grease. In addition, there is a risk that creep of the pulley against bearing outer ring may occur at high temperatures due to difference of coefficient of linear expansion of the resin and steel materials. The result of this creep phenomenon is that the bearing may separate from the pulley. Accordingly, solutions to these issues were required that increased the demands on the resin pulley units.
The resin pulley developed by NTN was able to reduce the temperature of the bearing by increasing the heat radiation area of the bearing outer ring compared with that of the conventional pulley unit. This change in conjunction with the newly developed long life grease resulted in the same or better life than a conventional steel pulley unit. The anti-creep performance of the outer ring against the pulley was improved by the use of a thermosetting resin* with its superior high temperature strength, along with an increase of resin volume at the insert location of the bearing outer ring, and an optimized configuration of the anti-creep groove.
NTN will market this product globally, as a contribution to improved automobile fuel economy.
*Thermosetting resin :
Resin hardened by chemical reaction at high temperature.
Thermosetting resin differs from thermoplastic resin in that with thermosetting the material gets harder at higher temperatures, where as thermoplastic resin gets softer as it's heated and hardens only when cooled. Therefore, the reduction of hardness for the thermosetting resin at high temperature is small.
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