Spherical plain bearings, maintenance‑free
Features
Spherical plain bearings allow spatial adjustment movements and, depending on the bearing type, can support radial, combined or axial loads.
Radial spherical plain bearings
Maintenance-free radial spherical plain bearings comprise inner rings, outer rings and maintenance-free sliding layers. The inner rings have a cylindrical bore with a curved outer slideway.
The outer rings have a cylindrical outside surface and a concave inner slideway.
Between the inner and outer ring is an ELGOGLIDE sliding surface. The sliding surface in the series GE..-UK and GE..-FW is PTFE composite , while the sliding surface in series GE..-PW is PTFE film . For a description of the sliding surfaces, see link.
The bearings are available in open and sealed designs.
Area of application
Radial spherical plain bearings are preferably used to support radial forces. GE..-UK-2RS(-2TS), GE..-FW-2RS(-2TS), GE..-DW and GE..-DW-2RS2 are also suitable for alternating loads up to a contact pressure of p = 150 N/mm2. The bearings are used where particular requirements for operating life apply in conjunction with maintenance-free operation or where, for reasons of lubrication, bearings with metallic sliding contact surfaces are not suitable, for example under unilateral load.
Large radial spherical plain bearings GE..-DW and GE..-DW-2RS2 of d ≧ 320 mm are X-life bearings and are indicated as such in the dimension tables.
These bearings have even higher performance materials, lower coefficients of friction and lower running-in wear than comparable bearings.
Split outer ring
In series GE..-UK-2RS(-2TS) up to a diameter d ≦ 140 mm, the outer ring is axially split at one point, while for diameters d ≧ 160 mm it is axially split at two points and held together by means of heavy-section retaining washers.
In the case of bearings GE..-FW-2RS(-2TS) up to a diameter d ≦ 120 mm, the outer ring is axially split at one point, while for diameters d ≧ 140 mm it is axially split at two points and held together by means of heavy-section retaining washers. In the case of GE..-DW and GE..-DW-2RS2, the outer ring is radially split. It is held together by means of screws and dowel pins.
Extended inner rings
GE..-FW-2RS(-2TS) and GE..-FW have extended inner rings. As a result, larger tilt angles are possible.
Series, sliding layer, standard
Radial spherical plain bearings are designed according to their specific series with different sliding layers, see table and section.
Series and design
Series | Sliding layer | DIN ISO | Dimension series | Shaft d | |
|---|---|---|---|---|---|
mm | |||||
over | incl. | ||||
GE..-UK-2RS | ELGOGLIDE | 12240-1 | E | 17 | 300 |
GE..-UK-2TS | ELGOGLIDE | 12240-1 | E | 30 | 300 |
GE..-FW-2RS | ELGOGLIDE | 12240-1 | G | 25 | 280 |
GE..-FW-2TS | ELGOGLIDE | 12240-1 | G | 25 | 280 |
GE..-DW | ELGOGLIDE (X-life) | 12240-1 | C | 320 | 1 000 |
GE..-DW-2RS2 | ELGOGLIDE (X-life) | 12240-1 | C | 320 | 1 000 |
GE..-UK | PTFE composite | 12240-1 | E | 6 | 30 |
GE..-FW | PTFE composite | 12240-1 | G | 6 | 25 |
GE..-PW | PTFE film | 12240-1 | K | 6 | 30 |
Angular contact spherical plain bearings
Angular contact spherical plain bearings GE..-SW correspond to DIN ISO 12240-2. They have inner rings with a curved outer slideway and outer rings with a concave inner slideway to which the sliding layer ELGOGLIDE is attached by adhesive.
The bearings are available for shaft diameters from 25 mm to 200 mm. Other sizes are available by agreement.
Area of application
The bearings can support radial and axial loads and are suitable for alternating dynamic loads. They can be used in paired arrangements as preloaded units.
Angular contact spherical plain bearings are used to support high loads occurring in conjunction with small motions. They are a good plain bearing alternative to tapered roller bearings 320..-X in accordance with ISO 355 and DIN 720, since they have the same mounting dimensions.
Axial spherical plain bearings
Axial spherical plain bearings GE..-AW correspond to DIN ISO 12240-3. In these units, the shaft locating washer is supported in the ball socket-shaped sliding zone of the housing locating washer.
The sliding material in the housing locating washer is ELGOGLIDE or, in the case of a nominal diameter d ≧ 220 mm, ELGOGLIDE in X-life.
The bearings are available for shaft diameters from 10 mm to 360 mm. Other sizes are available by agreement.
Area of application
The bearings are preferably used to support axial forces. They are suitable as support or base bearings and can also be combined with radial spherical plain bearings of dimension series E in accordance with DIN ISO 12240-1.
Axial spherical plain bearings GE..-AW of d ≧ 220 mm are X-life bearings and are indicated as such in the dimension tables.
These bearings have even higher performance materials, lower coefficients of friction and lower running-in wear than comparable bearings.
Sliding layers
Maintenance-free spherical plain bearings have special sliding layers based on polytetrafluorethylene PTFE in the outer ring.
In descending order of performance capability, these are:
- ELGOGLIDE, the highest performance sliding layer
- ELGOGLIDE-W11, the sliding layer for low friction
- PTFE film
- PTFE composite .
These materials form the slideway, transmit the forces occurring and perform the lubrication function.
ACHTUNG
Maintenance-free bearings must not be lubricated.
ELGOGLIDE
The sliding layer comprises a 0,5 mm thick layer of ELGOGLIDE, is embedded in synthetic resin and attached by a high strength bond to the support body, ➤ Figure.
The flow behaviour of the sliding layer is, in conjunction with the supporting body, almost negligible even under very high load. The adhesive bond is resistant to moisture and swelling.
ELGOGLIDE is a registered trademark and product of Schaeffler.
ELGOGLIDE, maintenance-free plain bearing material
ELGOGLIDE designs
For differing requirements, the following are available:
- ELGOGLIDE
the standard material for very high dynamic contact pressures from 25 N/mm2 to 300 N/mm2 and a long operating life - ELGOGLIDE-W11
the material for dynamic contact pressures from 1 N/mm2 to 150 N/mm2 and with low coefficients of friction even at low contact pressures. - The operating limits of the plain bearing materials must be observed.
PTFE film
The PTFE film (metal fabric material) is fixed to the outer ring curved surface, ➤ Figure.
The metal fabric is made from high strength bronze and acts as a stabiliser for the sintered PTFE composite.
PTFE film , cross-section
PTFE composite
PTFE composite comprises sheet steel with bronze attached by sintering and an embedded plastic composite made from PTFE, ➤ Figure.
The composite is embedded with form fit between the inner ring curved surface and the outer steel surface.
PTFE composite , cross-section
Bearing materials
Maintenance-free spherical plain bearings fulfil all the requirements in terms of fatigue and wear resistance, hardness, toughness and structural stability as well as maintenance-free operation.
The materials used for the inner and outer rings and the shaft and housing locating washers are generally hardened and ground rolling bearing steel, see table.
Materials and design
Series | Material | |
|---|---|---|
Inner ring or shaft locating washer | Outer ring or housing locating washer | |
GE..-UK-2RS | Hardened and ground rolling bearing steel, curved surface finished or polished (from d ≧ 240 mm) and Durotect CMT coated. | Axially split at one point in GE..-UK-2RS(-2TS) to d ≦ 140 mm and in GE..-FW-2RS(-2TS) to d ≦ 120 mm. In larger sizes, axially split at two points and held together by means of heavy-section retaining washers on the outside diameter. |
ELGOGLIDE fixed by adhesive in the outer ring curved surface. | ||
GE..-DW | Hardened rolling bearing steel, curved surface ground, polished and Durotect CMT coated. | 42CrMo4-TQ in accordance with DIN EN 10083-1, radially split and held together by means of screws and dowel pins arranged axially on one side. |
ELGOGLIDE fixed by adhesive in the outer ring curved surface. | ||
GE..-UK | Hardened rolling bearing steel, curved surface finished and Durotect CMT coated. | Formed around inner ring by special upset process from two bushes pushed into each other, outer steel surface subsequently precision machined. |
PTFE composite embedded with form contact between the inner ring curved surface and the outer steel surface. | ||
GE..-PW | Hardened and ground rolling bearing steel, curved surface finished. | Brass, formed about inner ring, outside surface subsequently precision machined. |
PTFE film fixed by adhesive in the outer ring curved surface. | ||
GE..-SW | Hardened rolling bearing steel, curved surface ground, polished and Durotect CMT coated. | Outer ring in GE..-SW and housing locating washer in GE..-AW made from hardened rolling bearing steel. Curved surface ground, in the case of GE..-AW ≧ 160 mm, housing locating washer made from unhardened steel. |
ELGOGLIDE fixed by adhesive in the outer ring or housing locating washer curved surface. | ||
Durotect CM, Durotect CMT
Microcracked hard chrome plating.
Coating process
- Electroplating method
- Subsequent heat treatment recommended for high strength materials (against hydrogen embrittlement).
Advantages, benefits
- Improved friction and wear behaviour under lubricant starvation
- Increased life due to hard surfaces as wear protection
- Good corrosion protection and high resistance to many chemicals with coating thicknesses greater than 30 μm
- Protection against tribocorrosion
- Protection against standstill marks (false brinelling)
- Low friction coefficient, good sliding characteristics
- Anti-adhesive characteristics.
Common applications
Applications with high wear load in automotive and industrial sectors:
- spherical plain bearings
- shafts
- bearing and engine components.
Characteristics
Feature | Coating | |
|---|---|---|
Composition | Hard chrome plating | |
Colour | Silver (lustrous) | |
Structure | Microcracked hard chromium layer, | |
Layer thickness | 0,1 μm – 500 μm (depending on application) | |
Hardness | 850 HV – 1 100 HV | |
Temperature resistance | Colour stable up to Hardness stable up to | +300 °C +700 °C |
Radial spherical plain bearing GE60-UK-2TS, maintenance-free
Application example with high wear load:
spherical plain bearings in excavator
Sealing
Sealed radial spherical plain bearings have the suffix 2RS, 2RS2 or 2TS. They are protected by lip seals on both sides against contaminants and water spray.
Large radial spherical plain bearings GE..-DW-2RS2 have seals with increased sealing action for very high requirements.
Radial spherical plain bearings GE..-UK-2TS and GE..-FW-2TS are sealed on both sides by integrated, triple lip high performance seals.
Angular contact and axial spherical plain bearings are not sealed but can be protected by means of an external seal.
Lubrication
Maintenance-free spherical plain bearings do not have relubrication facilities and must not be lubricated.
ACHTUNG
Maintenance-free spherical plain bearings must be subjected to dry running-in. Any lubricant will impair the smoothing effect necessary and will considerably reduce the operating life of the bearings.
Operating temperature
The permissible operating temperature is dependent on the sliding contact surface and the sealing arrangement, see table.
ACHTUNG
If the temperature exceeds the stated values, there will be a reduction in the operating life and the effect of the sealing arrangement.
Operating temperature
Series | Temperature | |
|---|---|---|
°C | ||
over | incl. | |
GE..-UK | –50 | +200 |
GE..-UK-2RS➤ | –30 | +130 |
GE..-UK-2TS➤ | –30 | +100 |
GE..-DW | –50 | +150 |
GE..-DW-2RS2➤ | –40 | +120 |
GE..-FW | –50 | +200 |
GE..-FW-2RS➤ | –30 | +130 |
GE..-FW-2TS➤ | –30 | +100 |
GE..-PW | –50 | +200 |
GE..-SW | –50 | +150 |
GE..-AW | –50 | +150 |
**Due to the different sliding layers in the series, see table, these bearings are suitable, if they are used without seals, for temperatures from –50 °C to +150 °C.
Temperature-resistant seals
If sealed bearings must be used at higher temperatures, an unsealed bearing with external, temperature-resistant seals can be used, ➤ Figure.
Open spherical plain bearing with external seals
Suffixes
Suffixes for available designs: see table.
Available designs
Suffix | Description | Design |
|---|---|---|
2RS | Standard lip seals on both sides | Standard |
2RS2 | Double lip seals with increased sealing action on both sides | |
2RS4 | Triple lip seals with increased sealing action on both sides | |
2TS | Triple lip high performance seals on both sides with steel reinforcement for applications with high contamination | |
W1 | Inner and outer ring made from corrosion-resistant steel | Special design, available by agreement only |
W3 | Inner ring made from corrosion-resistant steel | |
W7 | Inner ring bore with ELGOGLIDE lining; inside diameter d reduced by 1,08 mm (dNEW = d – 1,08) | |
W8 | Inner ring bore with ELGOGLIDE lining; inside diameter d remains in accordance with nominal diameter (dNEW = d) | |
W11 | For low contact pressures (starting as low as 1 N/mm2) and minimal friction | |
G8 | Outer ring with Corrotect ZN** coating, curved and end surfaces of inner ring with Durotect CMT coating |
**Other surface coatings are available by agreement.
Design and safety guidelines
The chapter Technical principles brings together the essential guidelines on the subjects of operating clearance, the adjacent construction and mounting and dismounting.
Friction
The friction behaviour is dependent on the sliding contact surface and changes during the operating life. Calculation of the bearing frictional torque and the typical wear characteristics are given in the chapter Technical principles.
Running-in phase
During the running-in phase, PTFE particles are transferred from the sliding layer to the opposing running surface. As a result, the small roughness features of the inner ring surface are filled in. It is only once this tribologically smooth surface is produced in conjunction with the detached PTFE particles that the bearings can achieve a long operating life.
ACHTUNG
Maintenance-free spherical plain bearings do not have relubrication facilities and must not be lubricated.
Any lubrication of maintenance-free spherical plain bearings after dry running-in will impair the smoothing effect necessary and will considerably reduce the operating life of the bearings.
Design of bearing arrangements
In the design of the adjacent construction, the guidelines in the chapter Technical principles must be observed.
The housing locating washer of an axial spherical plain bearing is exposed to an expansion force under load, which leads to tangential stresses and thus to an expansion of the diameter of the housing locating washer. This reduces the load carrying capacity of the bearing. An adequately dimensioned, closed adjacent construction partially counteracts this situation and enables full utilisation of the load carrying capacity of the axial spherical plain bearing. However, if this requirement is not met, the maximum static axial load must remain limited to 1,2 · C.
Predimensioning
In the case of maintenance-free spherical plain bearings, predimensioning can be carried out.
Dimensioning and rating life
The dimensioning of maintenance-free spherical plain bearings is brought together in the chapter Technical principles.
Depending on whether the bearing is subjected to dynamic or static load, the following must be checked:
- static load safety factor S0
- maximum permissible specific bearing load p
- maximum permissible sliding velocity v
- maximum specific frictional energy pv.
ACHTUNG
The rating life can be calculated if the range of validity is observed.
Interchangeability of bearing parts
In the case of maintenance-free spherical plain bearings, the inner ring and outer ring or respectively the shaft locating washer and housing locating washer of each bearing are matched to each other by means of the manufacturing technology used. As a result, these bearings must not be interchanged with each other.
Calculation example for radial spherical plain bearing GE50-UK-2TS
The rating life of the radial spherical plain bearing is calculated on the basis of the sliding layer ELGOGLIDE.
Given data
The given data for calculation of the rating life are as follows:
- pivot of a tiller steering axis
- axial and radial loads in the pulsating range.
Operating parameters
Bearing load | Fr min | = | 10 000 N |
Fr max | = | 70 000 N | |
Fa | = | 20 000 N | |
Swivel angle | β | = | 12° |
Tilt angle | α1, | = | 1,2° |
Swivel frequency | f | = | 30 min–1 |
Load frequency | PHz | = | 0,20 Hz |
Operating temperature | ϑmin | = | –20 °C |
ϑmax | = | +50 °C |
Bearing data
Radial spherical plain bearing | = | GE50-UK-2TS | ||
| Basic dynamic load rating | Cr | = | 444 000 N |
Sphere diameter | dK | = | 66 mm | |
Sliding material | ELGOGLIDE | |||
Required
- Bearing with the required rating life Lh ≧ 8 500 h.
Checking of permissible loads
ACHTUNG
The validity of the permissible loads and sliding velocities must be checked, since useful rating life calculation is only possible within this range.
Combined load
For calculation of the combined load, the factor X must be determined from the diagram for radial spherical plain bearings using the ratio Fa/Fr = 20 000 N / 70 000 N = 0,29:
Specific bearing load
The specific bearing load must be calculated with the aid of the specific load parameter K:
Combined swivel and tilt motion
The motion angle for combined motion must be calculated and checked for validity:
Sliding velocity in swivel motion
The sliding velocity must be calculated with the aid of the sphere diameter dK and the motion angle β1 for combined loads and checked for validity:
Specific frictional energy pv
The specific frictional energy pv must be checked for validity:
Determining the rating life equation
For calculation of the rating life, the valid rating life equation must be selected and then subjected to correction.
Selection of the valid rating life equation
For maintenance-free plain bearings, the following applies:
Correction factors, as a function of bearing type
The correction factors necessary for the plain bearing material ELGOGLIDE must be selected from the matrix and used to correct the rating life equation appropriately.
Series | Sliding layer | Correction factors | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Spherical | Rod end | fp | fv | fpv | fpv* | fϑ | fA | fα | fβ | fHz | |
GE..-UK | ‒ | ELGOGLIDE | ■ | ‒ | ‒ | ■ | ■ | ■ | ■ | ■ | ■ |
Rating life equation following correction
Calculation of rating life
The values for the correction factors in the corrected rating life equation must be taken from the diagrams. The specific plain bearing factor KL = 25 000.
Correction factors
Correction factor | Value |
|---|---|
Load fp | 0,7 |
Frictional energy fpv* | 0,78 |
| |
| |
Temperature fϑ | 0,6 |
Condition of rotation fA | 1 |
Tilt angle fα | 0,91 |
Swivel angle, oscillation angle fβ | 0,78 |
Variable load fHz | 0,6 |
Rating life Lh
The rating life is calculated as follows:
Result
The ratio Fa/Fr for radial spherical plain bearings is in the valid range ≦ 0,3, but calculation of the rating life does not fulfil the required rating life Lh ≧ 8 500 h. For this reason, an angular contact spherical plain bearing GE50-SW is selected and calculated, see link.
Calculation example for angular contact spherical plain bearing GE50-SW
The rating life of the angular contact spherical plain bearing is calculated on the basis of the sliding layer ELGOGLIDE.
Given data
- For calculation of the rating life, the application and the operating parameters in the preceding calculation example are used, link.
Bearing data
Angular contact spherical plain bearing | = | GE50-SW | ||
| Basic dynamic load rating | Cr | = | 355 000 N |
Sphere diameter | dK | = | 74 mm | |
Sliding material | ELGOGLIDE | |||
Required
- Bearing with the required rating life Lh ≧ 8 500 h.
Checking of permissible loads
ACHTUNG
The validity of the permissible loads and sliding velocities must be checked, since useful rating life calculation is only possible within this range.
Combined load
For calculation of the combined load, the factor X must be determined from the diagram for angular contact spherical plain bearings using the ratio Fa/Fr = 20 000 N / 70 000 N = 0,29:
Specific bearing load
The specific bearing load must be calculated with the aid of the specific load parameter K and checked for validity:
Combined swivel and tilt motion
The motion angle for combined motion must be calculated and checked for validity:Sliding velocity in swivel motion
The sliding velocity must be calculated with the aid of the sphere diameter 0,9 · dK and the motion angle β1 for combined loads and checked for validity:
Specific frictional energy pv
The specific frictional energy pv must be checked for validity:
Determining the rating life equation
For calculation of the rating life, the valid rating life equation must be selected and then subjected to correction.
Selection of the valid rating life equation
For maintenance-free plain bearings, the following applies:Correction factors, as a function of bearing type
The correction factors necessary for the plain bearing material ELGOGLIDE must be selected from the matrix and used to correct the rating life equation appropriately.
Series | Sliding layer | Correction factors | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Spherical | Rod end | fp | fv | fpv | fpv* | fϑ | fA | fα | fβ | fHz | |
GE..-SW | ‒ | ELGOGLIDE | ■ | ‒ | ‒ | ■ | ■ | ■ | ■ | ■ | ■ |
Rating life equation following correction
Calculation of rating life
The values for the correction factors in the corrected rating life equation must be taken from the diagrams. The specific plain bearing factor KL = 25 000.
Correction factors
Correction factor | Value |
|---|---|
Load fp | 0,94 |
Frictional energy fpv* | 0,84 |
| |
| |
Temperature fϑ | 0,6 |
Condition of rotation fA | 1 |
Tilt angle fα | 0,91 |
Swivel angle, oscillation angle fβ | 0,78 |
Variable load fHz | 0,7 |
Rating life Lh
The rating life is calculated as follows:
Result
The selected angular contact spherical plain bearing GE50-SW fulfils the requirement for a rating life Lh ≧ 8 500 h. Since angular contact spherical plain bearings are only supplied in an open design, external seals must be selected for sealing.
Accuracy
The main dimensions as well as the dimensional and geometrical accuracy of the inside and outside diameter are in accordance with DIN ISO 12240-1 to DIN ISO 12240-3.
The dimensional and tolerance values are arithmetic mean values and dimensional checking is carried out in accordance with ISO 8015.
Spherical plain bearings with axially split or radially split outer ring
Before surface treatment and axial splitting, the outside diameters are within the deviations given in the tables.
As a result of axial and radial splitting, the outer rings become slightly out of round. The roundness of the outer ring is restored once it is mounted in a locating bore produced in accordance with the specifications.
ACHTUNG
Measurements taken of the outside diameter of the unmounted bearing cannot be used as the original actual values for the outside diameter.
Deviation in roundness before mounting
