HOW FITS THE BEARING TO HOUSING
For rolling bearings, inner and outer rings are fixed on the shaft or in the housing so that relative movement does not occur between fitted surfaces during operation or under load. This relative movement (referred to as "creep") between the fitted surfaces of the bearing and the shaft or housing can occur in a radial direction, an axial direction, or in the direction of rotation. To help prevent this creeping movement, bearing rings and the shaft or housing are installed with one of three interference fits, a "tight fit" (also called shrink fit), "transition fit," or "loose fit" (also called clearance fit), and the degree of interference between their fitted surfaces varies.
The most effective way to fix the fitted surfaces between a bearing's raceway and shaft or housing is to apply a "tight fit." The advantage of this tight fit for thin walled bearing is that it provides uniform load support over the entire ring circumference without any loss of load carrying capacity. However, with a tight fit, ease of installation and disassembly is lost; and when using a non-separable bearing as the floating - side bearing, axial displacement is not possible . For this reason , a tight fit cannot be recommended in all cases.
1.1 The necessity of a proper fit
In some cases, improper fit may lead to damage and shorten its bearing life, therefore it is necessary to make a careful analysis in selecting a proper fit. Some of the negative conditions caused by improper fit are listed below.
Raceway cracking, early peeling and displacement of raceway
Raceway and shaft or housing abrasion caused by creeping and fretting corrosion Seizing caused by loss of internal clearances
Increased noise and lowered rotational accuracy due to raceway groove deformation
1.2 Fit selection
Selection of a proper fit is depend upon thorough analysis of bearing,s operating conditions,
including consideration of:
Shaft and housing materials, wall thickness, finished surface accuracy, etc.
Machinery operating conditions (nature and magnitude of load, rotational speed and temperature, etc.)
1.3.1 "Tight fit," "transition fit," or "loose fit"
For raceways under rotating loads, a tight fit is necessary.
(Refer to Table 1.1) "Raceways under rotating loads " refers to raceways receiving loads rotating relative to their radial direction. For raceways under static loads, on the other hand, a loose fit is sufficient. (Example) Rotating inner ring load the direction of the radial load on the inner ring is rotating relatively. For non-separable bearings, such as ball bearing, it is generally recommended that either the inner ring or outer ring be given a loose fit.