The influence of grease composition and properties on mechanical losses of deep groove ball bearings applied to electric motors

Carolina Croceta Bombazar

Value for the audience

This presentation will address the influence of grease components in the bearing mechanical losses, considering the results of several tests performed with deep groove ball bearings lubricated with different greases. You will understand how the grease can impact an electric motor performance (mostly in the start-up phase) and why it is important to know your electric motor lubricant.

Summary

The technological evolution of electric motors is guided by the increasingly higher levels of energy efficiency achieved day after day. The factors that can reduce the energy efficiency of electric motors, in a simplified way, can be divided into losses of electrical origin and losses of mechanical origin. The mechanical losses group can be divided into ventilation losses and friction losses, the last being mostly determined by bearing and lubrication. Although bearing design and variants can also impact in the mechanical losses, the lubricant still plays the main role in this process. The most common type of lubrication in electric motors that use rolling bearings is grease lubrication and this combination is going to be the subject of this paper. The possibilities for grease composition are almost limitless. The base oil can be mineral or synthetic, the thickener can be a metallic soap, an organic material or inorganic matters as bentonite, and the additives will depend on the application's needs. Each combination of these main components will behave differently. The thickener impacts the most in the motor start-up, when the lubricant film tends to be thicker due to the presence of thickener particles, resulting in friction and, consequently, high power losses and temperature rise. As for the oil, depending on its chemical structure and bonds, as well as its viscosity, it will present different physical properties that will affect its friction behavior. Finally, yet important, the additives can also be important aspects on the resulting mechanical losses of the motor, as these can either increase or decrease friction, depending on the additive type and the application's speed, load and temperature. This paper will address the influence of grease components in the bearing mechanical losses, considering the motor start-up phase (power and temperature peaks), and the stabilization phase (power and temperature stabilized).

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