轴承应用知识.ppt

Bearing Basics 1 - * Bearing Life Back to the coat hanger example: Both hangers will break after about the same number of bends. If we had 1000 wires and bent them all, some would fail earlier, some later. Statistics would give us a chart of average wire life. These calculations account for life under controlled conditions only. There is no adjustment in the basic life calculation for outside influences (Contamination, Poor Lubrication, Vibration, etc.) These external factors reduce actual bearing life below that predicted by the basic life equation. Bearing Basics 1 - * Bearing Basics 1 - * Bearing Basics 1 - * Bearing Life Calculation Basic life equation result is in millions of revolutions. Most folks don’t count revolutions, they count hours. Modified equation results in life in terms of operating hours See chart on page XX 4000 US catalog What happens if we double the Speed? Life reduced by 1/2 What happens if we double the load? Life reduced almost 90% A 20% increase in Load reduces Roller Bearing Life by 54% Increasing loads dramatically affects the life of the bearing. Speed changes life linearly. Bearing Basics 1 - * Bearing Life Calculation Chart is from page 33 BMIG “P” value for most applications is 5-10% of C value. Designers generally choose load ratios (C/P) in the “normal” range, between 8-20. This gives them the performance they need without applying more bearing than necessary to do the job. Bearing Basics 1 - * Bearing Basics 1 - * SKF New Life Method OPTIONAL SLIDE The older theory didn’t explain why some bearings didn’t fail as predicted. New life theory works in clean and dirty environments. Only clean bearings with loads within specified limits can reach infinite life. Factor aSKF can be obtained from charts following p. 35 of the 4000 US Catalog. Bearing Basics 1 - * Correct Fits Bearing manufacturers have – over many years of development and experience – established a range of shaft and housing fits that apply to the various be