Maintenance Technology May 2015 - (Page 30)

BEARING SECRETS PART 2 The Inner Life of Bearings: Lubricant Selection And Application Frequencies T his overview of bearing geometries and operating conditions will help simplify the sometimes difficult process of choosing the right lubricant. Part 1 of this series (Lubrication Technology, February 2015 issue) explored the three types of common industrial bearings. This concluding installment offers quick tips from the real world on how to select the correct lubricants for these bearings and their recommended frequency of application. The approaches vary. 1. OIL-LUBRICATED BALL AND ROLLER BEARINGS Lubricating ball and roller bearing isn't difficult. Assuming the lubricant is clean and contains no water, its most critical aspect is viscosity. The three heavy horizontal lines in Fig. 1 show a general guide to the minimum recommended viscosities for ball, roller and roller thrust bearings. The figure shows that for a tapered roller bearing running at 140 F (40 C), an ISO 46 is the minimum recommended. (Note: This chart is not applicable for slow-speed applications-those below approximately 50 rpm-and is drawn for oil with a viscosity index of 95.) Ball, radial roller and roller thrust bearings have different geometries, which necessitate different lubricant viscosities: ■ As a ball bearing rolls, it only has point contact and, thus, tolerates variations around its path. ■ A plain roller or tapered roller bearing has a line of contact, which requires a greater film thickness to prevent damage. ■ In an operating thrust bearing, the roller describes an arc with a tremendous difference in surface speed between the innermost and outermost contact points, which means it requires an even thicker film to prevent skidding damage. The typical lubricating oil for rolling-element bearings will be clean, free of water, and contain the correct additives for the bearing's ambient working conditions. For example, in water-contaminated applications, it is good for the oil to incorporate additives that reduce the chance of corrosion, but extreme-pressure (EP) additives are only helpful in very-lowspeed applications. 2. GREASE-LUBRICATED BALL AND ROLLER BEARINGS A typical grease is roughly 80% oil, 5% additives and 15% thickener. The role of the thickener is to act as a reservoir for the oil, allowing it to slowly separate as the temperature rises and flow into the bearing; the viscosities shown in Fig. 1 are still critical. But because heat tends to deteriorate a thickener over time and BY NEVILLE SACHS, P.E. 30 LUBRICATION TECHNOLOGY MAY 2015 LubricationTechnologyOnline.com Special Section http://www.LubricationTechnologyOnline.com

Maintenance Technology May 2015

Table of Contents for the Digital Edition of Maintenance Technology May 2015

Maintenance Technology May 2015 - Cover1
Maintenance Technology May 2015 - Cover2
Maintenance Technology May 2015 - 1
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Maintenance Technology May 2015 - Cover3
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