The radial bearing clearances

Bearing clearance

Bearing clearance is defined as the distance that the bearing outer ring can be displaced relative to the inner ring, in the absence of load.
The offset in the radial direction is called a radial gap. (2)
The offset in the axial direction – an axial gap (1)


Why a bearing clearance?

A small gap is always necessary to avoid metal to metal contact in the bearing between the moving parts. Therefore, before choosing a bearing, you must carefully examine that surrounds it. Different clearance is necessary:

– An interference fit;
– Increase or decrease the shaft housing under the influence of temperature;
– Used as a shaft or housing of other materials, such as aluminum;
– Compensation for bearing nominal displacement relative to other parts.

As classified bearing clearance?

C1 – bearing clearance smaller than C2
C2 – bearing clearance smaller than normal
CN – normal clearance
C3 – bearing clearance larger than normal
C4 – bearing clearance greater than C3

According to the ISO standard, if the bearing designation none is specified – normal bearing clearance.

Conformity clearance signs on the Russian and international designation

bearing TypeEPK, RussiaSKF, SwedenFAG, Germany
Single row radial ball, d6C2C2
normalnormalC0 normal
Roller radial short cylindrical roller with interchangeable parts0C1C1NA
With a cylindrical (conical) hole, the normal (6) normal normal C0
Roller double row radial spherical with cylindrical (conical) hole1
normalnormalC0 normal

Under the clearance in the bearing understand the amount of movement, which is formed of one shear bearing rings relative to each other at a certain low load measurement in the radial direction (radial clearance) Oti axial (axial clearance) Oa.

There are three types of gaps: the initial, planting and working. Under the initial radial clearance understand the bearing clearance in the delivery condition. Measurements of radial clearance are carried out with the help of the device by displacing one of the bearing rings in its extreme position under a certain load, for some design groups of bearings radial clearance measurements performed by selecting the appropriate probe gap thickness. For different groups of radial bearings design have their own groups (rows) of the radial clearance. Each group is limited to minimum and maximum values of acceptable radial clearance and is designated number (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, normal). Marking is performed on the band gap and the bearing packing videostream left bearing seat coating grade accuracy. For example, the bearing type 205 accuracy class 5, group 8 radial clearance designated 85-205. The most common group of radial clearances called normal. It has no number and is not put in a conditional bearing designation. With such a gap is produced most of the radial ball and roller bearings, which provide for the majority of cases, the usual crop satisfactory operation of the bearing assembly.

By planting a radial clearance gap understand, set after mounting bearings. The reasons for changing it is elastic deformation of the rings caused by interference fit and form errors seats.

Workers called radial clearance bearing clearance at steady-state temperature and duty cycle of the machine. In this case because the temperature drop it may increase or decrease due to the fact some of the rings receives more heat. The approximate difference between the heating temperature outer and inner rings, which affects the change of the internal clearance can be calculated using the formula:

De = Dtx αx (d + D) / 2


α = 1,2 * 10-5 – linear expansion coefficient for steel;

d- the inner diameter of the bearing, mm;

D- bearing outside diameter, mm;

Dt – Temperature difference between shaft and housing, hail.

Thermal elongation of the shaft can be increased or decreased depending on the gap of the bearing structure and its installation scheme. The gap increases proportional to the load on the bearing. Considering these factors, it is necessary to choose the appropriate group of radial bearing clearance .. Is that the most favorable working clearance for radial ball bearings is an option when it is close to zero, and even tightness small value can be considered favorable. But if these bearings perceive only axial loads, they must have an increased gap, which allows to increase the working angle of contact and thus increase the axial load capacity.

Roller bearings with cylindrical, conical and spherical rollers should generally have a small working gap in units of general application. But in some cases they are mounted and preloaded such as roller bearings with cylindrical rollers in a precise machine spindles or tapered roller bearings in the main vehicle transmission. For satisfactory operation of roller spherical bearings should always have a positive working gap.

Bearing with a tapered bore has a slightly larger initial radial gap than with a cylindrical bearing bore. This is due to the specifics of creating a compulsory interference fit when mounting bearings on tapered shafts gang or on adapter and withdrawal sleeve.

Diameter ext. ringsС2С0С3С4С5