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Whether you are a beginner maintenance technician or if you do not replace the ball bearings regularly, this article will remind you of the tips for preloading ball bearings.
What is preload or preload?
Preload means the removal of a clearance. We speak of preload when the inner cage of a bearing is compressed axially against the outer cage of said bearing. In this case we speak of negative play. Another case is only possible if an axial force is present (compression). It is carried out during assembly. This kind of preload or preload is adjusted by means of a nut or wedging in the receiver housing. The preload can be radial or axial depending on the type of bearing.
What is a preload for and how do I apply it?
Correct preloading prevents premature wear of the bearings, reduces noise during operation, more efficient guiding of the shaft and compensation for wear and compaction. In general, preload is applied by measuring a force, sometimes a displacement over a distance or a path or by measuring the friction torque during assembly. Empirical preload values can be obtained from proven fixtures and applied to similar designs. For new designs, it is recommended to calculate the appropriate preload range using an online calculation simulator made available by different bearing manufacturers (e.g. SKF Simpro Quick ), then check it by testing in the app.
What bearings are to be preloaded?
What are the types of preloads?
There are three types of preload: adjustment preload, rigid preload and elastic preload.
- rigid or (fixed) preload: rigid preload is carried out by axially pressing two internal bearing rings mounted back-to-back or face-to-face for the external rings in order to eliminate play. An effort is therefore made internal axial compression during assembly, effort which will remain in place after assembly.
- Elastic preload: preload device comprising a bearing surface and an elastic ring enclosing the two outer rings brought into contact and comprising a set of clamping screws configured to impose a stress on the elastic ring. The linear actuator comprises an elastic preloading device capable of exerting a stress between the two outer rings spaced from each other. Rotational guidance is provided by two rows of angular contact ball bearings mounted at "O". The threaded rings of the roller screw mechanism constitute the inner rings of the ball bearings.
What conditions for a good bearing assembly?
The work station must be clean (free of impurities such as filings, humidity, etc.).
The technician must know the types of adjustment and bearings to be used and have at his disposal all means of measurement and control (caliper, micrometer, calibers, rings and calibration wedges ...) and degreasing. The shafts, axes and housings must not have any scratches or shocks and even less machining burrs. He must also have sufficient greasing and lubrication equipment.
What tools are necessary for adjusting the prestressing and mounting the bearings?
There are different tools for carrying out preloads, such as the load cell which is a dynamometer when it is mechanical , the spanner wrenches, the slot sockets , the torque wrench and its socket box , a game for hunting pins , the bearing heater induction , a cold mounting kit for bearings, hook spanner for bearing, impact wrench and a comparator.
Now, you are now able, thanks to this little digest which is not exhaustive, to carry out basic preloads if however your new bearings are not already preloaded. Other articles will complement this one in the near future.