- Technical knowledge center
- Principles of selecting bearing fits
- Hole tolerance fields H7-H11
- Typical fits of bearing nodes
- Reconditioning tolerances of holes for pins and bushings
- DIN 471 / DIN 472 circlips
- Slide bushings – types and selection
- Installation and removal of bearings – technical principles
High rotational speeds, significant loads, small contact areas between rolling elements and raceways, and the relatively small length of the ring seating surface in relation to its diameter mean that bearing fits require certain dimensional and geometric parameters.
The correct selection of the fit and the quality of the manufacturing of the bearing surfaces determine the durability of the bearing node, the stability of operation and the safety of operation.
Requirements for tolerance fields and fits are specified in ISO 286-2.
The accuracy of bearings is specified in ISO 492.
These standards define:
– tolerance fields of shafts and holes,
– requirements for roughness of bearing surfaces,
– permissible deviations of shape and position,
– values of permissible angles of ring misalignment,
– recommendations for mounting of rolling bearings.
The scope of application includes bearing nodes of machinery and equipment in which:
– shafts are solid or thick-walled tubular,
– bodies are rigid structures (steel, cast iron),
– the nominal diameter of the bearing bore does not exceed 2500 mm,
– the operating temperature of the bearing does not exceed 100°C.
Selection of fit
The fit should be selected individually for a particular node by the designer, taking into account the actual operating conditions.
The strength of the connection must be sufficient so that the immobilized bearing rings do not move in relation to the bearing surfaces.
The heavier the working conditions – heavier loads, greater load variation, higher dynamics and impact – the greater the pressure should be.
Press fit prevents:
– rotation of rings,
– fretting phenomenon,
– seat knockout,
– damage to the settling surface.
Requirements for settlement surfaces
It is only possible to meet the requirements of the fit if the right fit is maintained:
– dimensional accuracy,
– shape accuracy,
– concentricity,
– surface roughness.
The limiting deviations of the diameters of the shaft and body bore must correspond to the selected tolerance field.
Settling surfaces and thrust surfaces (backstops) should be precision-machined to prevent the crushing of micro-roughness during assembly and the formation of friction corrosion.
The low height of the micro-roughnesses reduces their deformation during assembly and increases the accuracy of diameter measurements with contact instruments.
Deviations in shape (ovality, conicity) and deviations in position (misalignment) must be within the limits specified by ISO 1101 geometric tolerance standards.
Construction requirements
Settling surfaces should have insertion chamfers with a small taper angle to ensure smooth installation and reduce edge damage.
The design of the node should allow proper installation and removal of the bearing.
The height of the backstops must be less than the thickness of the bearing ring at the periphery.
Grooves should be provided for shaft mounting to allow the use of a puller.
Removal holes should be provided in the housings for the outer rings.
The mounting holes should be made without unnecessary steps that impede installation.
