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Correctly securing plain bearings
Causes of problems and solutions for perfect function
Plain bearings are crucial components in structures with moving elements. However, even small errors when securing bearings can have serious consequences: unwanted noise, excessive wear or even complete failure of the bearing point. In the following, we will show you the most common causes of these problems, then provide you with suggested solutions and show you how to optimally secure plain bearings.
What you will find on this page
Why plain bearings drift
So-called "drifting" is the reason why we secure plain bearings. But what does this term actually mean?
Drifting plain bearings lose their tight fit in the housing bore and move even though they are supposed to be fixed. This problem often occurs when the press fit - the mechanical tension that holds the bearing firmly in the hole - is insufficient. Causes for this can include:
High temperatures
The plain bearing material expands and is therefore no longer firmly seated in the housing bore.
Excessive surface pressure
High loads lead to deformation or creep of the material.
Inaccurate manufacturing tolerances
A housing bore that is too large or imprecise will not provide sufficient hold.
The consequences of drifting
Plain bearings that rotate together with the shaft in the hole cause wear in both the housing and themselves. This leads to unwanted noise or even total failure.
Preventing the drifting of plain bearings
- Ensure that the temperatures do not exceed the maximum recommended value for the plain bearing.
- Check the surface pressure to which the plain bearing is exposed.
- Ensure that the tolerances of the housing bore and shaft are correct. At least an h9 tolerance is recommended for the shafts. Their inner diameter is only set after they have been press-fit into the H7 housing bore. Further information is available here.
Temperatures at which securing our plain bearings is recommended
If the plain bearings are moved axially or the forces can have an axial effect on the bearing, there is a risk of the bearing moving out of the hole even earlier. In these cases, the bearings must be specially secured in addition to being press-fit. The adjacent table shows the temperature limit above which the plain bearings must be secured in the hole, even at low axial forces. The greater the forces, the more likely it is that such securing should be considered.
Locating spigot of plain bearings
If the press fit of the plain bearing is not sufficient, there are various options available for axially securing plain bearings.
The most tried and tested methods are listed below:
Bearing with undercut
The slotted design offers high installation flexibility and compensates for manufacturing tolerances in the hole. The bearing is pressed into place and then it fixes itself automatically. The two flanges ensure that it cannot slip out of the housing bore.
Area of application: Ideal for applications with variable tolerances and simple assembly.
Snap-on solutions
Snap-on bearings have undercuts or locking lugs that compress during assembly and automatically reset after installation to hold the plain bearing securely in the housing.
Application: Useful for manual assembly, as the plain bearings are assembled quickly and efficiently.
Flanging
In this process, the bearing is mechanically deformed after placement by a flat press so that it sits firmly in the hole.
Area of application: Particularly suitable for high quantities (e.g. automotive industry), as automation offers high precision and efficiency.
Screw connection
Holes in the bearing flange enable fixing with screws. This method ensures maximum holding force, but is complex to assembly.
Area of application: Applications where particularly high forces act or maximum safety is required.
Anti-rotation feature of plain bearings
In addition to the locating spigot, the anti-rotation feature is a common design issue. Plain bearings are designed to move through the shaft while the bearing itself is fixed in the housing.
Metal or PTFE plain bearings require a firm fixation, as their sliding properties depend on the liner on the inner diameter. Plastic bearings are more resistant here, as the homogeneous material itself has good sliding properties. Nevertheless, even with plastic bearings, spinning in the hole is undesirable, as housing bores are generally not optimised for friction.
Practical solutions for anti-rotation feature
Fixing holes
Additional holes in the flange allow screws to be fixed to hold the bearing securely in position. This solution offers maximum stability with low risk of failure, but is cost-intensive for large numbers.
Positive fit on the outer diameter
Offsets or undercuts on the outer diameter of the bearing engage in corresponding recesses in the hole. This method is comparatively cost-effective, as it requires almost no additional work during injection moulding.
Reworking the housing bore
In some cases, it may be advisable to insert the housing bore in a different way or to change the housing material to enable a better fit for the plain bearing.
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