Internal clearance and operating clearance

Internal clearance

Axial internal clearance
Radial internal clearance

As the internal clearance is called that measure by which the two rings (outer- and inner ring) of a bearing - which has not yet been installed - can be relocated from one final position into the respectively opposing one in the radial (radial internal clearance) or axial (axial internal clearance) direction without tension.

The internal clearance is of high importance regarding the undisturbed functionality of the ball bearing since it influences the performance capability of the bearing with regard to the operating life, the heat development, the concentricity and sounds.

Operating clearance

The internal clearance basically has to be differentiated from the operating clearance to which one refers in case of an installed bearing being still warm from operation. An intact operating clearance ultimately depends from the internal clearance of the uninstalled bearing and its alterations which arise from operational influences (temperature-, deformation and fit influences). The internal clearance has to be greater than the residual radial internal clearance in operation (operating clearance), as it is reduced by installation- and operation-related factors. An operational ball bearing ideally ought to have a preferably low clearance.

Normal internal clearance and suffix

Ball bearings having a normal internal clearance CN are designed for showing a functional operating clearance in case of ordinary operating conditions and the compliance with the usual shaft- and housing tolerances. Depending from the respective operating or installation conditions a radial internal clearance diverging from the normal internal clearance CN can nevertheless be necessary. Should it be the case that enormously high charges impact on the ball bearing with the installation and operation, for example, it is possible that the internal clearance is so immensely reduced that roller bearings have to be used with an internal clearance which is greater than the normal one. Bearings having an internal clearance which differs from CN are described with the suffixes C1, C2, C3, C4 and C5. Information about the importance of suffixes, operating conditions and typical applications can be learned by the following table.

suffix
importance
operating conditions
typical application
C1
internal clearance
  • in case of quiet, vibration-free running
  • small engines with particular specifications
  • precision bearings
C2
internal clearance
  • considerable alternate loads with swivel motion
  • in case of quiet, vibration-free running
  • low speeds
  • roller pivots for rolling mills
  • small engines with particular specifications
  • precision bearings
CN
normal internal clearance (mostly only indicated if followed by further letter, since the internal clearance is constricted or shifted, for example)
  • bearing in operation with ordinary temperature
  • no exceedance of the temperature-difference 10 K
  • usual fits
  • shaft and housing made of steel
  • suitable for various applications
C3
internal clearance > normal
  • large, considerably-loaded bearings
  • press fit of the rings leading to the reduction of the internal clearance
  • high temperature gradients between the rings
  • in case of fixed rings
  • transport castors in rolling mills
  • dryer sections in paper machines
  • vibratory sieves
C4
internal clearance > C3
  • large, considerably-loaded bearings
  • press fit of the rings leading to the reduction of the internal clearance
  • high temperature gradients between the rings
  • in case of fixed rings
  • transport castors in rolling mills
  • dryer sections in paper machines
  • traction engines for railways
  • vibration sieves
  • fluid coupling
  • gearboxes for tractors
C5
internal clearance > C4
  • large, considerably-loaded bearings
  • press fit of the rings leading to the reduction of the internal clearance
  • high temperature gradients between the rings
  • great shaft deformation
  • half-floating wheel bearing arrangements in automobiles

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