SKF's Innovative Approach to Self-Aligning Bearings
SKF’s innovative self-aligning bearings solve vibration, friction, and operating temperature problems.
Many general industrial applications use some type of self-aligning bearing to maintain the alignment between a shaft and housing. Physical placement, a flexing shaft, or thermal expansion of the shaft causes misalignment. To solve misalignment, bearing manufacturers have relied on two self-aligning bearings to correct the problem. In this configuration, one self-aligning bearing fastens to the housing as a locating bearing and shaft while the other self-aligning bearing has the freedom to travel axially on a seat located in the housing. The second bearing functions as the non-locating bearing.
CARB Toroidal Bearings
One important drawback to the traditional self-aligning configuration occurs because of the friction and vibration generated as the non-locating bearing moves. In turn, the bearing system may deteriorate due to heat caused by friction and axial forces. SKF uses a unique approach to overcome these problems by placing a CARB ® toroidal roller bearing as the non-locating bearing. SKF’s CARB toroidal bearing relies on an inner ring that moves independently of the outer ring. The separate movement of the inner and outer rings eliminates possible axial distortion and allows the shaft and bearing structure to thermally expand and contract.1
The Latest SKF Innovation
Originally introduced during 1999, the SKF Explorer® performance class of self-aligning bearings offered higher load carrying capacity, low friction and increased service life. SKF accomplished these improvements through the application of a unique heat treatment process to clean and homogenous bearing steel. The current use of hardened and tempered NitroMax steel provides enhanced corrosion resistance and fatigue strength.
SKF Bearing Steel
SKF uses an extremely clean, through-hardening carbon chromium steel for all standard bearings. With a variety of heat treatments, the steel gains a hardness ranging between 58 and 65 HRC and higher strength. SKF super precision bearings receive additional heat stabilization.
SKF uses NitroMax steel for super precision bearings intended for high speed applications. The high-nitrogen stainless steel has enhanced wear resistance under poor lubrication conditions, high fracture toughness, and increased resistance to corrosion. Each of those characteristics results in extended bearing service life.2
The final tempering stages of the heat treatment yield increased hardness, dimensional stability, and high impact toughness for self-aligning bearings that work in less-than-desirable environmental conditions. With the use of NitroMax steel, the bearings have less sensitivity to the temperature differences that occur between the outer and inner rings. Moreover, the bearings have lower frictional losses and operating temperatures.
An Upgraded Heat Treatment Increases Reliability
Bearings exhibit wear because of contamination, poor lubrication or misalignment. Because of the need to enhance bearing performance for industries such as mining, mineral processing, industrial transmission, and wind generation, SKF has improved bearing wear resistance by upgrading the heat treatment for bearing steel. Improving wear resistance allows self-aligning bearings to operate longer at high speeds under all lubricant conditions.
This upgraded heat process also increases bearing hardness and fracture toughness. As a result, the chance of inner ring fracture caused by operating stresses that occur at very high speeds is diminished. Improving the fracture toughness allows more time to identify the initial signs of damage and to prepare for repairs. The combination of increased bearing hardness and fracture toughness nearly eliminates unplanned downtime.
Looking at the Results
The upgraded SKF Explorer self-aligning bearings3 have greater wear resistance and improved service life when compared to the original Explorer performance class. Tests show that the upgraded bearings have a longer time between spalling and through-fracture. Upgraded SKF bearings continue to operate longer even after the detection of damage.
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