Maintenance Technology May 2015 - (Page 32)

BEARING SECRETS MODIFICATION CATEGORY OPERATING ENVIRONMENT/CONDITION Housing temperature Ft Below 150 F (65 C) 1.0 150 to 175 F (65 to 80 C) 0.5 176 to 200 F (80 to 93 C) 0.2 Over 200 F (93 C) 0.1 Light nonabrasive dust 1.0 Heavy nonabrasive dust 0.7 Light abrasive dust 0.4 Heavy abrasive dust 0.2 Humidity almost always below 80% 1.0 Humidity usually between 80 and 90% 0.7 Occasional condensation 0.4 Occasional water on housing 0.1 Less than 0.2 ips (5mm/sec) peak velocity 1.0 0.2 to 0.4 ips ( 5 to 10 mm/sec) 0.6 Above 0.4 ips (10 mm/sec) 0.3 Horizontal bore centerline 1.0 Bore centerline at 450 to horizon 0.5 Vertical centerline 0.3 Ball - radial, angular contact, and thrust 1.0 Cylindrical, needle roller 0.5 Tapered and spherical roller 0.1 Contamination Fc Moisture Fm Vibration Fv Position Fp Bearing type Fb FACTOR Fig. 3. Modifying factors for recommended re-greasing intervals of ball and roller bearings based on operating conditions rounded off to once per month. (Note: This approach does not apply to very-slow-speed bearings.) 3. OIL-LUBRICATED PLAIN BEARINGS The procedure needed to select the correct lubricant for higher-speed plain bearing applications (over 100 rpm) is beyond the scope of this article. As mentioned in Part 1, and in Ken Bannister's article this month on the path to bearing reliability, if the oil supply to the bearing exceeds the leakage, the bearing will develop its film. Complicating the situation is the fact that the leakage rate will depend on the clearance, ambient temperature, oil ISO grade and the load, and the correct lube specification requires a long and detailed calculation. Remember that bearings with babbitt contact faces are far more tolerant of contamination than those with bronze or aluminum contact faces. (Note: Bronze and aluminum lack the embedability of babbitt, and any contamination with solid particles approaching the film thickness can lead to upset conditions.) 4. GREASE-LUBRICATED PLAIN BEARINGS The key to successful lubrication of grease-lubricated plain bear- 32 LUBRICATION TECHNOLOGY MAY 2015 LubricationTechnologyOnline.com ings is the additive package in the grease. Decades ago, it was common to find lead in bronze bearings because the lead would liquefy and provide a lubricant film under high pressures. Today's environmental concerns have virtually eliminated lead as a lubricant component. Science replaced it with various chemicals, including molybdenum disulfide, sulfurized isobutylene compounds and potassium-boron compounds. These formulations have led to outstanding results. Still, there can be a huge difference in performance from one formulation to the next. When it comes to setting up a re-lubrication schedule for grease-lubricated plain bearings, it is imperative to consult with- and heed the advice of-an experienced lubrication professional and/or your lubricant supplier. The same is true for other important decisions in your lubrication program. LT Neville Sachs has extensive experience in machinery reliability and lubrication. The author of two books on failure analysis and a contributor of sections to other books, he has also written more than 40 articles. A Professional Engineer, Sachs holds STLE's CLS certification, among others. Contact him at sachscracks@att.net. Special Section http://www.LubricationTechnologyOnline.com

Maintenance Technology May 2015

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