Rolling bearings are high-precision machine elements that are produced using the latest high-technology equipment, machined to close tolerances of a few microns. To guarantee the optimum function of a bearing arrangement, a few basic rules concerning mounting should be followed.
Preparation: Prior to mounting, some careful preparation is necessary. When dealing with rolling bearings, maximum cleanliness is the paramount basic requirement. Especially when dealing with repairs, all contacting surfaces of seals, including all adjacent machine parts and components, should be carefully checked for their condition.
An inspection of the alignment of the bearing may be necessary with the field installation of large machines or in plants. Before bearing mounting commences, one should study all available documentation, such as drawings, maintenance manuals and notices. The bearing should only be unpacked immediately prior to mounting in order keep it protected from contamination.
Selection of the mounting method: Rolling bearings are generally mounted to their adjacent parts by means of either sliding or interference fits. The decision about whether a bearing should be mounted either in warm or cold conditions depends mainly on the bearing type, its size and the individual fits that are used for each application.
In any case, never apply mounting forces via the bearing rolling elements and never hit the bearing surface directly with any hardened tools such as hammers, cotter pin drivers, etc.
In the majority of applications, the bearing inner ring is located by a tighter fit than the outer ring. For this reason, rolling bearing outer rings are usually pressed into the housing bore in a cold condition. To mount bearing inner rings on to their shaft seats, there are many more possibilities, including cold or warm mounting, adapter or withdrawal sleeves, or mounting with hydraulic devices.
Mounting of bearings in a cold condition: Small- and medium-sized bearings are usually mounted in a cold condition as they normally do not have tight fits. The bearings are mounted using either presses or by hammer strikes.
Also, impact sleeves and impact bushes have been proven to be satisfactory tools. These are sets of discs and rings made from a special impact-proof plastic and lengths of aluminium tubes that fit to them. Impact bushes provide a quick and simple method of mounting small bearings, even when mounting a large volume of bearings.
Press mounting of bearings: The mounting of small- and medium-sized rolling bearings may be completed quickly and simply by using either mechanical or hydraulic presses, even when volume mounting. The bearing seats of the shaft and housing should be lightly oiled.
To avoid applying forces via the rolling elements, suitable auxiliary sleeves, washers or mounting bushes should be used for pressing (Fig. 1). When hydraulic presses are used, the setting of a certain pressure relief is recommended in order to avoid choking caused by defects in the bearing or in the housing.
Mounting bearings by using the oil-injection method: Larger and very large rolling bearings may be mounted in a much simpler way by using the oil-injection method. To fit bearings by the oil-injection method, hydraulic nuts are used. When mounting or dismounting bearings using oil injection, huge pressures are applied. The operating and safety instructions provided by the supplier of the hydraulic equipment must be followed carefully.
Mounting of bearings by heating: In cases where mounting of bearings in cold conditions is not possible or practical, heating of the bearing or even individual bearing rings may be of advantage.
When heated, the bearing rings expand, which enables easier bearing mounting. Suitable heating methods are oil baths, hot plates and boxes, thermo rings and induction heating (see Fig. 2). Never heat rolling bearings directly by means of open flames (see Fig. 3).
Practical training for mounting rolling bearings: Professional mounting of rolling bearings is the basic requirement for the optimum performance of bearings. Leading manufacturers of bearings provide theoretical as well as practical training programs (Fig. 4). MRO
The article was prepared by NKE Austria GmbH, a bearing manufacturer headquartered in Steyr, Austria. In Canada, NKE products are distributed through Global Bear Inc., Dorval, QC. For more information, visit www.globalbear.ca or www.nke.at.
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