Design of bearing arrangements
Adjacent construction of spherical plain bearings
The chamfers, radii, edge breaks and surface quality required for the shaft and housing bore are defined as follows.
Chamfers, radii and chamfer dimensions
Spherical plain bearings have a convex transition between the outside surface and the bore to the end faces. This gives easier mounting.
The bearing rings must be in contact with the shaft and housing shoulders. The largest radius of the shaft and housing locating face must therefore not be larger than the smallest chamfer dimension r1 min, r2 min of the bearing.
In the case of spherical plain bearings, the shaft and housing bore of the adjacent construction should have a lead chamfer of between 10° and 20°, ➤ Figure. Any burrs must be removed.
Chamfer dimensions
Lead chamfers
Surface of the shaft and housing bore
The seating surfaces for the bearings must be designed such that the forces introduced via the bearings do not cause impermissible changes to the geometry of the shaft and housing and do not cause permanent deformations of the spherical plain bearing.
ACHTUNG
Where spherical plain bearings are subjected to high loads of p ≧ 80 N/mm2, the shaft and housing must be checked.
If it is possible that a preload and an associated frictional torque in the bearing is present, this must be taken into consideration in the design of the bearing arrangement. The accuracy of the adjacent construction must therefore be checked with Schaeffler.
Roughness of bearing seats
Recommended values apply to the roughness of the bearing seats, see table.
Roughness values
Bearing seating surface | Roughness |
---|---|
μm | |
Housing bore | ≦ Rz 16 |
Shaft | ≦ Rz 10 |
Geometrical and positional tolerances of bearing seating surfaces
The geometrical accuracy of seating surfaces is dependent on the application of the spherical plain bearings and the operating conditions. In order to achieve the required fit, the bearing seats on the shaft and housing bore must conform to certain tolerances, ➤ Figure and table.
The tolerances for the bores and shafts correspond to the fundamental tolerances in accordance with ISO 286-2.
Guide values for geometrical and positional tolerances
Accuracy of bearing seating surfaces
The degree of accuracy for the bearing seat tolerances on the shaft and in the housing correspond to the fundamental tolerances in accordance with ISO 286-1, see table.
ACHTUNG
When using the fits in accordance with ISO 286-1, the envelope requirement Ⓔ always applies.
Geometrical and positional tolerances of bearing seating surfaces
Bearing seating surface | Fundamental tolerance grades** | |||
---|---|---|---|---|
Roundness tolerance | Parallelism tolerance | Axial runout tolerance | Straightness tolerance | |
t1 | t2 | t3 | t4 | |
Shaft | IT6/2 | IT6 | IT10/2 | IT6/2 |
Housing | IT6/2 | IT6 | IT10/2 | IT6/2 |
**ISO fundamental tolerances (IT grades) in accordance with ISO 286.
Adjacent construction of plain bushes
In the design of the adjacent construction of plain bushes, a distinction is made in relation to the bearing type. The guidelines on ELGOGLIDE plain bushes and ELGOTEX filament wound bushes are similar and have been combined.
ELGOGLIDE plain bushes and ELGOTEX filament wound bushes
The shaft and housing bore should be produced as specified, ➤ Figure. For the shaft, a roughness Rz 1 is recommended. A higher roughness will reduce the operating life of plain bushes. A roughness higher than Rz 4 must be avoided.
Design of adjacent components
ELGOGLIDE plain bushes
For optimum conditions, the shaft should be hardened and have a hard chromium coating or should be made from corrosion-resistant steel. For increased loads, the hardness of the steel should be at least 55 HRC. Lower hardness values may lead to a reduced rating life.
ELGOTEX filament wound bushes
For optimum conditions, the shaft should be hardened. For increased loads, the hardness of the steel should be at least 55 HRC. Lower hardness values may lead to a reduced rating life.
If the full volume of the sliding layer is to be used, the raceway on the shaft must be hard, smooth and resistant to corrosion.
Metal/polymer composite plain bushes
Shafts should be chamfered and all sharp edges rounded. For easier pressing in, the chamfer should be produced to fG × 20° ±5°, see table and ➤ Figure.
The recommended mounting tolerances for the shaft and housing bore must be observed, see table.
For the housing bore, a roughness depth Rz 10 is recommended. The optimum operating life in dry running of the sliding layer E40 is achieved with a roughness depth of the shaft of Rz 2 to Rz 3.
ACHTUNG
Very small roughness depths will not increase the operating life, but larger roughness depths will lead to a significant reduction.
Chamfer width
Bore diameter dG | Chamfer width fG | |
---|---|---|
mm | mm | |
dG ≦ 30 | 0,8±0,3 | |
30 < | dG ≦ 80 | 1,2±0,4 |
80 < | dG ≦ 180 | 1,8±0,8 |
180 < | dG | 2,5±1 |
Chamfer on housing bore
Flanged bushes
In flanged bushes, the radius at the transition from the radial to the axial component must be taken into consideration.
The flanged bush must not be in contact in the area of the radius and, where axial loads are present, an adequate level of additional support must be provided for the flange. Chamfer width for the housing bore, see table and ➤ Figure.
Chamfer width
Bore diameter dG | Chamfer width fG | |
---|---|---|
mm | mm | |
dG ≦ 20 | 1,2±0,2 | |
20 < | dG ≦ 28 | 1,7±0,2 |
28 < | dG ≦ 45 | 2,2±0,2 |
45 < | dG | 2,7±0,2 |
Chamfer on housing bore
Axial location of spherical plain bearings
Spherical plain bearings under high loads undergo elastic deformation. This leads to relative micromovements in the fits. As a result, the bearing rings can creep in an axial direction despite a tight fit.
ACHTUNG
In order to prevent axial displacement, the bearing rings must always be located axially.
Retaining ring or spacer ring
Suitable means of locating the bearing rings are as follows, ➤ Figure and ➤ Figure:
- retaining rings. These allow easy mounting and dismounting of the bearings.
- spacer rings between the bearing ring and adjacent component if weakening of the shaft by annular slots is unacceptable or the bearings are to be preloaded.
Preload prevents rotary motion between the bearing ring and adjacent construction, even with a loose fit.
Location by snap rings
Location by snap rings and spacer rings
Spacer sleeve, end washer and cover
Spherical plain bearings can also be located with the aid of a spacer sleeve or end washer and a cover, ➤ Figure and ➤ Figure.
Location by means of spacer sleeves and covers
Location by means of end washer and cover
Location of thrust washers and strips
Concentric seating of thrust washers is ensured by means of recesses in the housing.
Undesirable rotation of the thrust washers must be prevented by means of a dowel pin or countersunk head screw. The screw head or dowel pin must be recessed relative to the running surface by at least 0,25 mm.
If it is not possible to make a recess in the housing, the plain bearings must be secured by means of several dowel pins or screws. It is also possible to use other cost-effective joining techniques such as laser welding, soft soldering or adhesive bonding.
It is not always necessary to provide security against rotation. In some cases, the adhesive friction between the backing of the plain bearing and the housing will be sufficient.
ACHTUNG
Strips can be located in the same way as thrust washers.
Prevention of rotation
by dowel pin
Prevention of rotation
by countersunk head screw
Recommended mounting tolerances for spherical plain bearings
Spherical plain bearings are radially located by means of fits.
The recommended values for shaft and housing fits are dependent on the adjacent construction, see tables.
Application as locating bearings
Tight fits prevent damage to the adjacent construction. The shaft and bore fits must therefore be selected such that no sliding motion occurs on the shaft or in the housing bore.
When using tight fits, the following must be noted:
- Interference between the housing and outer ring causes contraction of the outer ring.
- Interference between the shaft and bearing bore causes expansion of the inner ring.
ACHTUNG
These elastic deformations of the bearing rings reduce the internal clearance of the spherical plain bearing. If a tight fit is not possible, the bearing rings must be secured against axial sliding motion on the shaft or in the housing, see link.
Application as non-locating bearings
The axial displacement should occur between the shaft and bearing bore:
- The length/diameter ratio of the guidance is more favourable at this point than on the outer ring of the bearing.
- The axially split outer ring expands under axial load and can therefore jam in the bearing location.
- No wear should occur in the housing bore.
ACHTUNG
The surface of the shaft must be produced so that it is resistant to wear. The surface hardness must be ≧ 55 HRC. Maintenance-free spherical plain bearings can have a lining of ELGOGLIDE in the bearing bore, suffix W7 or W8.
When used as non-locating bearings, spherical plain bearings requiring maintenance should only be lubricated via the shaft.
In the case of a non-locating bearing arrangement, the shaft fit g6 is recommended.
Maintenance-free spherical plain bearings
In comparison with spherical plain bearings requiring maintenance, looser fits may be used with maintenance-free bearings. The bearing friction is lower in this case due to the hard chromium/PTFE sliding contact surface.
ACHTUNG
Tighter fits may be necessary for applications with pulsating or alternating loads or where circumferential loads are present. Since maintenance-free spherical plain bearings have only a very small internal clearance, preload may occur in the bearing once in the fitted condition.
Shaft and housing fits for maintenance-free spherical plain bearings
Type | Bore | Material in adjacent construction | |
---|---|---|---|
d | Housing/shaft** | Housing/shaft** | |
mm | Steel/steel | Light metal/steel | |
≦ 300 | K7/j6** | M7/j6** | |
> 300 | J7/j6 | ‒ | |
Angular contact spherical plain bearings | ‒ | M7/m6 | ‒ |
Axial spherical plain bearings | ‒ | M7/m6 | ‒ |
**The envelope condition Ⓔ applies here.
**In the case of alternating load, M7/m6 is recommended.
**For radial spherical plain bearings with a lined bore (suffix W7 or W8), the shaft tolerance f7 should be selected.
**GE..-PW: for shaft m6.
Spherical plain bearings requiring maintenance
The operating life of spherical plain bearings requiring maintenance is reduced by preloading of the sliding surfaces and excessively small load-bearing areas of the sliding surfaces as a result of an impermissibly high internal clearance. The recommended values for shaft and housing fits are dependent on the adjacent construction, see table.
ACHTUNG
If tighter fits are necessary, for example where high, impact type loads occur, the operating clearance must be checked by means of calculation.
If it is possible that a preload and an associated frictional torque in the bearing is present, this must be taken into consideration in the design of the bearing arrangement. The accuracy of the adjacent construction must therefore be checked with Schaeffler.
Shaft and housing fits for spherical plain bearings requiring maintenance
Type | Radial internal clearance | Material of adjacent construction | |
---|---|---|---|
Housing/shaft** | Housing/shaft** | ||
Steel/steel | Light metal/steel | ||
Radial spherical | Group 2 (C2) | K7/j6 | M7/j6 |
Group N (CN) | M7/m6➤ | N7/m6➤ | |
Group 3 (C3) | M7/m6 | N7/m6 | |
Angular contact spherical plain bearings | ‒ | M7/n6 | ‒ |
Axial spherical | ‒ | M7/n6 | ‒ |
**The envelope condition Ⓔ applies here.
**GE..-LO: for shaft r6.
**GE..-PB: for housing/shaft K7/m6.
Recommended mounting tolerances for plain bushes
The plain bearing bushes are pressed into the housing. This provides axial and radial location. No additional means of location are required.
Recommended mounting tolerances, see tables.
ACHTUNG
If shafts with the tolerance class h Ⓔ are used, the bearing clearance must be checked in accordance with the equations for Δsmax and Δsmin.
For aluminium housings, mounting tolerances to M7 Ⓔ are recommended.
Mounting tolerances for metal/polymer composite plain bushes
Diameter range | Sliding layer** | ||||||
---|---|---|---|---|---|---|---|
mm | E40 | E40-B | E50 | ||||
Shaft | |||||||
| |||||||
| dW < | 5 | h6 | f7 | ‒ | ||
5 | ≦ | dW < | 80 | f7 | f7 | h8 | |
80 | ≦ | dW | h8 | h8 | h8 | ||
Housing bore | |||||||
| |||||||
| dG ≦ | 5,5 | H6 | ‒ | ‒ | ||
5,5 | < | dG | H7 | H7 | H7 |
**The envelope condition Ⓔ applies here.
Mounting tolerances for plain bushes with ELGOGLIDE or ELGOTEX
Adjacent component | Sliding layer** | |
---|---|---|
ELGOGLIDE | ELGOTEX | |
Shaft | f7 | h7 |
Housing bore | H7 | H7 |
**The envelope condition Ⓔ applies here.
Misalignment of plain bushes
Precise alignment is important for plain bushes. This is particularly valid for maintenance-free plain bushes, in which load cannot be distributed by means of a lubricant film.
The misalignment across the entire bush width should be ≦ 0,02 mm, ➤ Figure. This also applies across the entire width of bushes arranged in pairs as well as to thrust washers.
ACHTUNG
Plain bushes should not be used for movement involving spatial motion. Any skewing of the shaft will reduce the operating life.
Permissible misalignment of bushes
Edge loading of metal/polymer composite plain bushes
In the case of metal/polymer composite plain bushes, the high edge loads should be reduced by means of chamfers, larger bore diameters in the vicinity of the edge or wide bushes that protrude beyond the edge of the bore, ➤ Figure.
Where bushes are arranged in series, they should be of the same width and the butt joints should be in alignment.
Reduction of peak stresses at edges
Angular contact spherical plain bearings in O or X arrangement
If angular contact spherical plain bearings are to transmit axial and radial loads, the bearings can be installed in pairs in an O or X arrangement under preload, ➤ Figure and ➤ Figure.
The precondition for angular contact spherical plain bearings requiring maintenance is:
- axial clearance per bearing of 0,1±0,05 mm.
Angular contact spherical plain bearings in O arrangement
Angular contact spherical plain bearings in X arrangement
Combination of axial and radial spherical plain bearings
If axial spherical plain bearings are combined with radial spherical plain bearings of dimension series E to DIN ISO 12240-1 in order to support radial forces, the axial and radial load must be distributed over both bearings. The pin in the shaft locating washer must have a radial release of approx. 1 mm or the pin must only be in contact with the large end face of the shaft locating washer, ➤ Figure.
ACHTUNG
For a bore diameter of d ≧ 160 mm or larger in the case of maintenance-free radial spherical plain bearings, the bearing must be fitted in a closed housing. The diameter D of the axial bearing corresponds to the inside diameter of the housing.