Investigation of Wear Mechanism in Ball Bearings Lubricated by a Bio-Lubricant

Due to increased environmental sensitivity, renewable-based lubricants, and food grade lubricants are being considered potential alternatives to petroleum-based lubricants. Understanding of bio-lubricant in relation to abrasive wear is essential for using ball bearings in industrial implementation. This study focused on wear mechanism on ball bearings lubricated by bio-lubricants. Palm oil and coconut oils were used in this study. Coconut oils were made by two processes, namely dry and wet processing, resulting in three types of oil (virgin coconut oil [VCO], refined coconut oil [RCO], and hydrogenated coconut oil [HCO]). Full-scale bearing life tests were conducted with 300 N load with 2,840 rpm for 6 hours. Method of lubrication was circulating oil by using pump injection to the self-aligning ball bearings. The results show that the main wear mechanism, which impacted on the surfaces of inner race, outer race, and ball for different bio-lubricants, were abrasive and adhesive wear. It found that the abrasion rate was the least severe for VCO. The discrepancies of worn surfaces are thought to be as a result of the physical and chemical properties of bio-lubricants.

Abrasive wear; Ball bearing; Bio-lubricant; Coconut oils; Palm oil

During the operation, rolling contact wear and rolling contact fatigue were occurred on ball bearing. After 6 hours operation with 2850 rpm of shaft rotations and 300 N radial load, the wear formation on the surface of inner race, outer race, and ball was varied with different bio-lubricants. The mechanisms of wear on the bearing were abrasive and adhesive wear. In the ball, the adhesive wear mechanism was very dominant. The wear phenomena for different bio-lubricants on ball bearings were complicated, because lubrication regime in the ball bearings is EHL where viscosity of lubricant is very important, the palm oil is not sufficiently viscose in the case. Thefore, the wear that occurred on the surface of the inner race, outer race, and ball bearing was influenced not only by the physical properties of the lubricant but also by its chemical properties. The important chemical property of the bio-lubricant is fatty acids, which account for lower abrasion. The abrasion rate is smaller for VCO than the other lubricants tested, as it has a high lauric acid (C12:0) content.

From the experiment results, the vegetable oil lubricants were good lubricity compared with the grease lubricant. The worn surface resulting from using the grease lubricant was very severe. It is caused that the starvation phenomenon was occurred on ball bearing because film thickness was reduced in thickness.

The authors are grateful for the financial supported by Directorate of Higher Education of Republic of Indonesia through the Fundamental Research Scheme with contract No. 14/H.16/FUNDAMENTAL/LPPM/2015 and No. 31/UN.16/FD/LPPM/2016 and Research Scheme of Mechanical Engineering Department Andalas University 2017.

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