An Introduction to Self-Aligning Plain Bearings
What makes a bearing self-aligning and what to think about during part selection.
In this article, we will define self-aligning plain bearings, cover how they came to be, go through their material makeup, design, and applications, then conclude with some things to think about during part selection. Additional resources will be included for further research.
What makes a bearing plain and self-aligning?
Bearings can mediate friction in two main ways: through mechanical parts like balls that roll, such as in ball bearings, or through non-mechanical parts like plastic, which can contain materials such as solid lubricants that eliminate the need of external grease and deter damage to its part. The latter mechanism, which is non-mechanical, is what is referred to as a plain bearing.
Self-aligning refers to the fact that the bearing can handle various types of motion, such as tilting, oscillating and linear motion, not just axial in the case of a rotating shaft. The key here is that something needs to be kept in some kind of horizontal, vertical or planed alignment. If that alignment or angle is not kept perfectly consistent, the bearing structure will compensate for that movement, excess friction will be avoided and the machine can continue to function without failure.
Therefore, a self-aligning plain bearing is a bearing with no mechanical parts that compensates for misalignment in a bearing system.
Self-aligning bearings are made of two pieces. First, they have an inner spherical ball. The shaft or spindle goes through the inside of that spherical ball. The latter piece is fitted in a larger piece called a housing, which can be in various designs. Some inner pieces are removable and some are fixed.
In order to suit different applications, self-aligning plain bearings come in a variety of designs, including rod ends (pictured above), clevis joints, two and four-bolt flange bearings (pictured below), and pillow block bearings. They are all united by the fact that they all compensate for misalignment in some way. They differ in shapes of their inner piece and housing.
Their two component parts can be made of different materials, usually either plastic or metal. The parts can both be plastic, as seen in the photos above, or they can both be metal or a combination of both for either the inner piece or the housing. Sometimes a metal or plastic liner will be included to reinforce the strength or flexibility of a larger design.
Plastic self-aligning plain bearings can have a number of advantages over their metal counterparts. Read more to learn about these key benefits.
Application areas are varied, including the food industry, packaging, heavy duty, automotive, renewable energy and automation.
Where did self-aligning bearings come from?
Self-aligning plain bearings come from their metal counterparts (simply called self-aligning bearings) invented in 1838 by James Nasmyth. The inventor noticed that rotating shafts would end up unevenly placed inside the supporting bearings on each end. Uneven placement would take place due to accidental “change in the level of supports of the bearings,” situation in dark places or difficulty accessing the parts. The latter two would lead to uneven installation (In modern times, it is also acknowledged that even bending shafts can be to blame). In these situations, increased friction, heat and even fires would occur.
To resolve this issue, James Nasmyth therefore invented a self-aligning metal bearing. If and when the system encounters misalignment, the bearing compensates for this error by allowing a give in the directions the motion occurs without breaking the housing or gaining excess friction. Motion compensated for would include oscillating (side to side, up and down) and linear (front to back) motion in these systems.
Self-aligning bearings have come a long way since 1838 as more material and design options are now available, including high-performance plastic spherical balls and housings that are self-lubricating, corrosion resistant, lightweight and maintenance-free.
Would plastic components benefit your application? Contact us at 1-800-965-2496 to find out. We’d be happy to help you choose the right solution.