Features
Maintenance-free plain bushes are used for rotary, oscillating and linear motion. These plain bearings are bearings for very small radial or axial design envelopes. These products are available as bushes and flanged bushes. The bushes are available in metric sizes and in inch sizes. They are rolled from a cut section of strip and have a butt joint over the entire width of the bearing.
The plain bushes are supplied with either steel backing or bronze backing. Bearings with a bronze backing have high corrosion resistance and very good thermal conductivity and are antimagnetic.
ACHTUNG
If the plain bushes are to be used in the aerospace sector or in the food or pharmaceuticals industry, please contact the Schaeffler engineering service.
Maintenance-free plain bearing material
For maintenance-free metal/polymer composite plain bearings from Schaeffler, the sliding material E40 and E40-B is used. The basis of the dry lubricant is polytetrafluoroethylene PTFE with embedded chemically non-reactive additives.
In the three-layered material, the steel or bronze backing has a sintered porous tin/bronze sliding layer whose pores are filled with the superimposed running-in layer, see table, ➤ Figure and ➤ Figure. The running-in layer is a plastic composite comprising PTFE and additives.
Sliding and running-in layer
E40, E40-B
Chemical element | Proportion of mass | Layer thickness |
---|
w |
---|
% | mm |
---|
Sliding layer | Running-in layer | Sliding layer | Running-in layer |
---|
Molybdenum disulphide MoS2 | ‒ | max. 8 | 0,2 – 0,4 | 0,01 – 0,05 |
Polytetrafluoroethylene PTFE | ‒ | 80 – 86 |
Fillers | max. 5,5 | max. 19 |
Tin Sn | 7 – 12 | ‒ |
Copper Cu | Balance | ‒ |
Resistance of the plain bearing material
The resistance of the material E40 depends on the chemical characteristics of the individual layers:
- The material E40 is resistant to water, alcohols, glycols and numerous mineral and synthetic oils.
- The tin-plated steel surface gives adequate protection against corrosion in most cases.
- In the case of the material E40-B, the bronze backing is additionally resistant to water vapour and seawater.
ACHTUNG
The material E40 is not resistant to acidic media (pH < 5) and alkaline media (pH > 9). The bronze backing of E40-B is not resistant to oxidising acids and gases such as free halides, ammonia or hydrogen sulphide, especially if these gases have a high moisture content.
Technical data for E40
The sliding layer E40 is maintenance-free. It can be used for rotary and oscillating motion as well as for short stroke linear motion.
The low-wear material has good sliding characteristics (no stick-slip), a low coefficient of friction and high resistance to chemicals. It does not absorb water (it is highly resistant to swelling), does not tend to weld to metal and is also suitable for hydrodynamic operation.
The maintenance-free plain bearing materials E40 and E40-B have the following mechanical and physical characteristics, see table.
Characteristics of E40 and E40-B
Characteristic | Loading |
---|
Maximum pv value for dry running | Continuous operation | pv | 1,8 N/mm2 · m/s |
For short periods | 3,6 N/mm2 · m/s |
Permissible specific bearing load | Static | pmax | 250 N/mm2 |
Rotary, oscillating | 140 N/mm2 |
Permissible sliding velocity | Dry running | vmax | 2,5 m/s |
Hydrodynamic operation | >2,5 m/s |
Permissible operating temperature | ϑ | –200 °C to +280 °C |
Coefficient of thermal expansion | Steel backing | αSt | 11 · 10–6 K–1 |
Bronze backing | αBz | 17 · 10–6 K–1 |
Coefficient of thermal conductivity | Steel backing | λSt | >42 Wm–1K–1 |
Bronze backing | λBz | >70 Wm–1K–1 |
Relative electrical resistance after running-in | Rrel min | >1 Ω · cm2 |
Sealing
The plain bearings are not sealed, but can be protected against the ingress of contamination and moisture by the use of external seals.
Lubrication
Plain bearings with the sliding layer E40 contain dry lubricants and do not therefore require lubrication.
Lubrication can be used to protect the mating surface against corrosion or simply to provide sealing against contamination. It should be checked in advance, however, whether it is more advantageous in such cases to use a corrosion-resistant material for the mating surface or a different means of sealing the bearing position.
In certain applications, the sliding layer E40 can be used in fluid media. In this case, the improved heat dissipation may considerably increase the operating life.
ACHTUNG
The compatibility of the media with the sliding layer E40 must be checked. Further advice should therefore be sought from the Schaeffler engineering service.
Lubricants
Oil and grease lubrication, even in very small quantities, impairs the transfer of material during the running-in phase.
Over time, grease and small quantities of oil mix with wear debris to form a paste that promotes wear. Solid lubricants such as zinc sulphide, molybdenum disulphide or similar grease additives are not permitted, since they promote this paste formation to an increased extent.
Relubrication
If it is not possible in exceptional cases to avoid the use of grease lubrication, the bearings must be relubricated periodically. During relubrication, old grease is replaced by fresh grease. At the same time, the grease flushes wear debris and contaminants out of the bearing.
ACHTUNG
If periodic relubrication is carried out, the formation of paste comprising debris and contaminants must be avoided.
Operating temperature
The permissible operating temperature for maintenance-free metal/polymer composite plain bearings is between –200 °C and +280 °C.
ACHTUNG
The running-in layer and sliding layer may undergo swelling in the presence of some mineral oils at temperatures above +100 °C. This could lead to jamming of the bearing.
This can be remedied by increasing the bearing clearance, since other characteristics of the sliding layer E40 are unaffected.
Suffixes
Suffixes for available designs: see table.
Available designs
Suffix | Description | Design |
---|
E40 | Maintenance-free sliding layer, with steel backing | Standard |
E40-B | Maintenance-free sliding layer, with bronze backing |
Design and safety guidelines
In addition to the design and safety guidelines described here, the following guidelines in the Technical principles must also be observed:
- theoretical bearing clearance of metal/polymer composite plain bushes
- design of bearing arrangements
- recommended mounting tolerances
- misalignment of plain bushes and edge loading of metal/polymer composite plain bushes
- pressing in of bushes.
ACHTUNG
Plain bushes should not be used for movement involving spatial motion. Any skewing of the shaft will reduce the operating life.
Friction
Sliding motion is free from stick-slip.
The friction in a plain bearing is influenced by:
- the roughness depth of the mating surface
- the mating surface material
- the specific bearing load
- the sliding velocity
- the operating temperature
- Up to approx. +100 °C, the coefficient of friction is slightly lower than the value at room temperature.
- Above +100 °C, the coefficient of friction may be up to 50% above the value at room temperature.
Friction behaviour
The coefficient of friction is lower under high specific bearing load and low sliding velocity. The coefficients of friction stated are valid for the condition after running-in, see table.
Coefficient of friction
for sliding layer E40
Specific bearing load | Sliding velocity | Coefficient of friction |
---|
p | v | μ |
---|
N/mm2 | m/s |
---|
250 | to | 140 | | ≦ | 0,001 | 0,03 | | |
140 | to | 60 | 0,001 | to | 0,005 | 0,04 | to | 0,07 |
60 | to | 10 | 0,005 | to | 0,05 | 0,07 | to | 0,1 |
10 | to | 1 | 0,05 | to | 0,5 | 0,1 | to | 0,15 |
| ≦ | 1 | 0,5 | to | 2 | 0,15 | to | 0,25 |
Bearing frictional torque
Calculation of the bearing frictional torque and the typical wear characteristics are given in the chapter Technical principles.
Running-in process
During the running-in process, part of the running-in layer is transferred to the mating surface, ➤ Figure:
- This compensates uneven areas.
- A mating surface with a low coefficient of friction is formed, which acts favourably on the operating behaviour.
- After running in, some of the porous bronze layer is visible on the sliding layer as individual areas of differing sizes, ➤ Figure. This shows that the bearing is running correctly.
Operating behaviour
After running-in, the wear of maintenance-free plain bearings proceeds in a linear manner, ➤ Figure.
Dimensioning and rating life
The dimensioning of plain bushes is summarised 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.
Operating conditions
Certain operating conditions may lead to a reduction or increase in the rating life, see table. If the plain bearings are to be used under such conditions, please contact the Schaeffler engineering service.
Guide values
Operating precondition | Rating life of E40 Lh |
---|
% |
---|
Dry running, intermittent | 200 |
Alternating between dry running and running in water | 20 |
Running in water | 200 |
Continuous operation in fluid lubricants | 300 |
Continuous operation in greases | 50 – 150 |
Calculation example for flanged bush EGF30260-E40
The rating life of the flanged bush is calculated on the basis of the sliding layer E40. For flanged bushes, the rating life must be checked for both the radial sliding surface and the axial sliding surface (flange).
Given data
The given data for calculation of the rating life are as follows:
- bearing arrangement for an extruder shaft
- shaft and axial running surface ground (unalloyed steel, roughness depth Rz 2)
- point load (rotating shaft, stationary bush).
Operating parameters
Bearing load | Fr | = | 14 000 N |
Fa | = | 3 000 N |
Operating speed | n | = | 25 min–1 |
Operating temperature | ϑ | = | +35 °C |
Bearing data
Flanged bush | = | EGF30260-E40 |
| Basic dynamic load rating | Cr | = | 92 400 N |
Ca | = | 35 200 N |
Inside diameter | Di | = | 30 mm |
Outside diameter of flange | Dfl | = | 42 mm |
Sliding material | E40 |
Required
- Bearing with the required rating life Lh ≧ 500 h.
Checking of permissible loads
For flanged bushes, the rating life must be checked for both the radial sliding surface and the axial sliding surface (flange).
ACHTUNG
The validity of the permissible loads and sliding velocities must be checked, since useful rating life calculation is only possible within this range.
Specific bearing load
The specific bearing load must be calculated with the aid of the specific load parameter K and checked for validity.
Radial component of flanged bushes:Axial component of flanged bushes:Sliding velocity in rotary motion
The sliding velocity must be calculated with the aid of the inside diameter Di or the flange diameter Dfl and checked for validity.
Radial sliding surface:Axial sliding surface:Specific frictional energy pv
The specific frictional energy pv must be checked for validity.
Radial component of flanged bushes:Axial component of flanged bushes: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 E40 must be selected from the matrix and used to correct the rating life equation appropriately.
Series | Sliding layer | Motion | Correction factors |
---|
fp | fv | fpv | fpv* | fϑ | fR | fW | fA | fB | fL | fα | fβ | fHz |
---|
EGF | E40 | Rotary | ■ | ■ | ■ | ‒ | ■ | ■ | ■ | ■ | ‒ | ‒ | ‒ | ‒ | ‒ |
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 = 1 000.
Correction factors
Correction factor | Value |
---|
Sliding surface |
---|
Radial | Axial |
---|
Load fp | 1 | 1 |
Sliding velocity fv | 1 | 1 |
Frictional energy fpv | 0,96 | 0,98 |
Temperature fϑ | 1 | 1 |
Roughness depth fR | 0,97 | 0,97 |
Material fW | 0,5 | 0,5 |
Condition of rotation fA | 1 | 1 |
Rating life Lh
The rating life for the radial sliding surface is calculated as follows:The rating life for the axial sliding surface is calculated as follows:Result
The basic rating life is determined by the radial sliding surface. The total rating life is therefore 560 h. The selected flanged bush fulfils the required rating life Lh ≧ 500 h.
Hydrodynamic operation
Metal/polymer composite plain bearings with the sliding layer E40 can be operated under hydrodynamic conditions. Higher circumferential speeds are permissible than with dry running.
Once the transition speed is reached, pure fluid friction is present. This allows wear-free operation.
At speeds below the transition speed, mixed friction is present and the self-lubricating effect of the sliding layer is utilised.
ACHTUNG
For hydrodynamic operation with the sliding layer E40, the roughness Rz of the mating surface should be less than the smallest lubricant film thickness in fluid friction.
Schaeffler offers the calculation of hydrodynamic conditions for plain bearings as a service.
Calculation
For the calculation of hydrodynamic conditions, the following data are necessary:
- load
- speed
- diameter of the housing bore dG with tolerance
- diameter of the shaft dW with tolerance
- bush width B
- viscosity of the fluid at operating temperature.
Design of mating surfaces
The shaft and mating surface of the bearing arrangement must be produced in accordance with the following specifications.
The shafts or parts of the mating surfaces should be chamfered and all sharp edges should be rounded. This allows easier mounting and prevents damage to the sliding layer.
Measures
The mating surface should always be wider than the bearing to prevent the formation of steps in the sliding layer.
The optimum operating life will be achieved with a roughness depth of the mating surface of Rz 2 to Rz 3:
- with dry running of the sliding layer E40.
ACHTUNG
Very small roughness values do not have a beneficial effect on the operating life, but larger roughness values reduce it considerably.
Surface quality
Ground or drawn surfaces are preferable as a mating surface. Surfaces that have been precision turned or rolled by precision turning, even with Rz 2 to Rz 3, can cause greater wear since helical manufacturing grooves are created by precision turning.
Spheroidal graphite cast iron GGG has an open surface structure and should therefore be ground to Rz 2 or better.
The direction of rotation of cast shafts in the application should be the same as that of the grinding wheel during machining, since increased wear should be anticipated if rotation is in the opposing direction, ➤ Figure.
Heat dissipation
Correct and sufficient heat dissipation must be ensured:
- If hydrodynamic operation is present, the heat is dissipated predominantly via the fluid lubricant.
- In the case of maintenance-free plain bearings, the heat is dissipated via the housing and shaft.
Protection against corrosion
Corrosion of the mating surface is prevented by sealing or the use of corrosion-resistant steel. Alternatively, suitable surface treatments may be carried out.
Fretting corrosion
Due to the tin coating applied as standard, fretting corrosion between the steel backing of the plain bearing material and the housing occurs only rarely. In such cases, electroplated protective coatings can be used to achieve a delaying effect.
Electrochemical contact corrosion
In unfavourable conditions, electrical cells (local elements) can be formed that reduce the operating life through corrosion of the steel. This should be checked at the design stage and clarified by means of tests. In case of doubt, please consult the Schaeffler engineering service.
Machining of plain bearings
Metal/polymer composite plain bearings can be machined by either cutting or non-cutting methods, such as shortening, drilling or bending.
The procedure is as follows:
- Separate the plain bearings starting from the sliding layer side, since the burr formed in cutting will impair the running surface
- Clean the bearing elements thoroughly.
- Protect any bright steel surfaces such as cut edges against corrosion by means of oil or electroplated protective coatings.
ACHTUNG
In electroplating with high current densities or or long coating times, the sliding layers should be masked to prevent deposits.
The machining temperature must not exceed +280 °C in the case of the sliding layer E40, otherwise there may be a health risk.
Alternative joining methods
If the press fit of the bush is not sufficient, the bush can be secured by additional adhesive bonding.
ACHTUNG
The running-in or sliding surface must always be kept free of adhesive.
If adhesive is used, the adhesive manufacturer must always be consulted, particularly on the selection of adhesives, preparation of the surface, hardening, strength, temperature range and elongation behaviour.
Electrical conductivity
The electrical conductivity of new bearings may be lower because the running-in layer is still present. The bronze layer is partially exposed after the running-in process, thus improving the electrical conductivity, ➤ Figure.
The electrical resistance is dependent on the size of the contact surface.
Setting the bearing clearance
Metal/polymer composite plain bearings are supplied ready for mounting. In order to set the tolerance of the bearing clearance, measures should be selected at the predimensioning stage that will not shorten the life of the bearings, such as closer tolerances of the housing bore or the shaft.
In a further possibility for setting the bearing clearance, the bushes are sized, ➤ Figure and table. This should only be carried out if there is no other way to achieve a reduced tolerance of the bearing clearance.
ACHTUNG
Sizing leads to a significant reduction in the rating life Lh of metal/polymer composite plain bearings with the sliding layer E40, see table. Precise values for the reduction in rating life can only be determined by means of tests.
Guide values for diameter of the sizing arbor and reduction in the rating life
Required inside diameter of bush after pressing in | Diameter of sizing arbor** | Rating life** |
---|
dK | Lh |
---|
% |
---|
DiE | ‒ | 100 |
DiE+0,02 | DiE+0,06 | 80 |
DiE+0,03 | DiE+0,08 | 60 |
DiE+0,04 | DiE+0,10 | 30 |
**Guide value, related to steel housing.
**Guide value for dry running.
Tables of deviations and wall thicknesses
The deviations for the bushes are defined in ISO 3547.
Deviations
of outside diameter
The deviations for the outside diameter Do conform to ISO 3547-1, Table 7, see table.
Deviations
Tolerances in mm
Do | E40 | E40-B |
---|
Deviation |
---|
mm | upper | lower | upper | lower |
---|
| Do ≦ | 10 | +0,055 | +0,025 | +0,075 | +0,045 |
10 | < | Do ≦ | 18 | +0,065 | +0,030 | +0,080 | +0,050 |
18 | < | Do ≦ | 30 | +0,075 | +0,035 | +0,095 | +0,055 |
30 | < | Do ≦ | 50 | +0,085 | +0,045 | +0,110 | +0,065 |
50 | < | Do ≦ | 80 | +0,100 | +0,055 | +0,125 | +0,075 |
80 | < | Do ≦ | 120 | +0,120 | +0,070 | +0,140 | +0,090 |
120 | < | Do ≦ | 180 | +0,170 | +0,100 | +0,190 | +0,120 |
180 | < | Do ≦ | 305 | +0,255 | +0,125 | +0,245 | +0,145 |
Wall thickness
for sliding layer E40
The nominal dimensions and limiting deviations for the wall thickness s3 of bushes and flanged bushes with the sliding layer E40 conform to ISO 3547-1, Table 5, Series B, see table.
Wall thickness
Tolerances in mm
Di | s3 | E40 | E40-B |
---|
Deviation |
---|
mm | mm | upper | lower | upper | lower |
---|
| Di < | 5 | 0,75 | 0,000 | –0,020 | ‒ | ‒ |
1 | ‒ | ‒ | +0,005 | –0,020 |
5 | ≦ | Di < | 20 | 1 | +0,005 | –0,020 | +0,005 | –0,020 |
20 | ≦ | Di < | 28 | 1,5 | +0,005 | –0,025 | +0,005 | –0,025 |
28 | ≦ | Di < | 45 | 2 | +0,005 | –0,030 | +0,005 | –0,030 |
45 | ≦ | Di < | 80 | 2,5 | +0,005 | –0,040 | +0,005 | –0,040 |
80 | ≦ | Di < | 120 | 2,5 | –0,010 | –0,060 | –0,010 | –0,060 |
120 | ≦ | Di | 2,5 | –0,035 | –0,085 | –0,035 | –0,085 |
Chamfers and chamfer tolerances
The tolerances and dimensions of the outer chamfer f and the inner edge break Fi for bushes of metric sizes conform to ISO 3547-1. For plain bushes of inch sizes, corresponding values apply.
Chamfer deformation due to round bending is permissible.