Technical information for engine construction sliding bearings
»Sliding bearing« identifies a bearing in which a movable component, generally a shaft, a shaft extension or a guide rail, slides on top of the surface - the »slide« - of a stationary bushing, a bearing seat or a sliding strip.
Sliding bearings are to support or to guide the parts movably opposed to each other as well as to absorb and transfer the occurring forces. The sliding movement takes place between the bearing box and the supported component. In relation to radially-moved bearings, the running smoothness of the sliding partners is ensured by the bearing free play between shaft and bearing box. In relation to axially-moved bearings, the bearing free play is determined by two axial areas assigned to each other by a mutually shared shaft. The sum of the opposed sliding area and distances determines the bearing free play.
State-of-the-art constructions place ever bigger demands on common sliding materials. Many customers expect a maintenance-free bearing, even if operating conditions are complicated. Furthermore, constantly rising pressure to maintain low production costs demands an enduring availability of our products, so as to ensure the allowance of the continuous use of the engines and plants deployed, as such, any compromise on the reliability of our products is unacceptable. In this regard, perfect solutions are possible in particular with sliding bearings which are fail-safe and reliable over a long period of time.

Mechanical properties

Advantages

As a result of the differing modes of utilizing sliding bearings, even the most complex aims can be achieved.
Due to their material and the damping effect of the hydrofoil, some sliding bearings are relatively insensitive to impacts, vibrations and shocks.
Sliding bearings run silently, are robust, and are to a great extent corrosion resistant and further, rarely need additional sealing.
Bushings are also available in split versions, which serve their requisite purpose in certain constructions. The price level of sliding bearings is generally lower than that of anti-friction ones.

Disadvantages

For a few types of sliding bearings, a heavy starting torque is inevitable. Maintenance-bound sliding bearings require constant and sufficient maintenance and lubricant supply. The degree of the effectiveness of sliding bearings is generally lower than that of anti-friction bearings.

PV - value

The pv-value has a substantial impact on the length of use.
The pv-value is the product of specific bearing load (p) and speed (v).
The length of use decreases with rising pv-value.

Friction

The friction-value depends on the following impacts:
Choice of material matching
Surface roughness of counter surface
Specific bearing load
Sliding speed
Bearing temperature
Type of lubrication

Factors to determine length of use

Specific bearing load
Sliding speed
Pv-value
Material and surface finish of sliding partners
Load zone allocation
Operation period
Temperature Lubrication
Operating conditions (e.g. contamination)

Preferred use

For low rotational frequency
For pivoting and axial motion
For shock loading and dirt strain
For all-purpose applications, for agricultural engines, construction machinery and vehicle construction.
For high- or low-temperature environments and for special corrosion resistance.

Delivery condition

Principally, we deliver our sliding bearings in pre-finished condition. As to a few types of bearings, specifications suitable for post-machining are possible. Ask us!

Storage

Bronzed, stainless steel and plastic sliding bearings are corrosion resistant. Steel and compound sliding bearings should be stored in dry rooms at low air humidity and should be taken out of package only immediately before mounting.

Mounting

Basically, sliding bearings should be moulded with the help of a mandrel.
To simplify the mounting of a sliding bearing, a bevel of 15∞ - 30∞ at the housing is essential. Flanged bushings should be provided with an additional bevel so as to make sure the flange bears completely and planar on the housing's surface.
To ensure proper mounting of the bolt, the shaft extensions must be bevelled and chamfered. While assembling the bearing, sharp angles can cause damage to the sliding surface and degrade the operation of the bearing.

Bonding

Metallic or plastic bushings, thrust washers, strips or special parts can not only be armed by bolting together, pinning or soldering but also by bonding. Especially plastic bearings are often additionally protected by bonding into the housing. This is often employed if plastic bushings are exposed to high variations in temperature.

Lubrication

To choose the ideal lubricant, it is advisable to talk to an adequate manufacturer. 

Lubrications

Oil-lubrications

Oil-lubrication is preferable for high rotational frequency and strains, but also applicable for low rotation speed. The type of lubrication oil depends on the particular application.

Grease lubrication

Grease lubrication is to be applied in case of low rotational frequency, pendulousness and impact loading, or if float friction is not within reach.
High-class sliding bearing fat should be used exclusively. Lubrications with solid additives exceeding a proportion of 2 % are not recommendable, as they are likely to cause wastage ahead of time. By no means grease may be used for lubrication of plastic bearings, which contains Molybdänsulfid (e.g. molicote grease).

Dry-film lubricant

Solid bronzed bushings with solid-lubricant pockets in their sliding surface are as well maintenance-free.
Full-plastic sliding bearings increasingly come to use in environments requiring high-class dry bearings and are often a better solution than bronze- or steel sliding bearings. Limits of application of dry bearings are usually set by specific heat conductivity and heat strain. Special plastics are available for those applications.