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Technology

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, 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.

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.

Disadvantages

For a few types of sliding bearings, a heavy starting torque is inevitable.
None-maintenance-free sliding bearings require constant and sufficient maintenance and lubricant supply.
The degree of the effectiveness of sliding bearings is generally lower than that of antifriction 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 surfaces
Specific bearing load
Sliding speed
Bearing temperature
Type of lubrication

Preferred use

For low rotational frequency, for pivoting and axial movement, for shock loading and dirt strain.
For all-purpose applications, for agricultural engines, construction machinery and vehicle construction.
For applications calling for simple design and low price level.
For high- or low-temperature environments and for special corrosion resistance.
For long-time applications requiring long durability, e.g. water and steam turbines, generators, rotary pumps, heavy journal bearings and the like, also for applications requiring wear-resistant running as is the case in the liquid friction sector.

The major features of the appropriate sliding bearings can be seen from our selection list.

Abrasion and length of use of sliding bearings depend on:

  • Specific bearing load
  • Sliding speed
  • Pv-value
  • Material and surface finish of sliding partners
  • Load zone allocation
  • Operation period
  • Temperature
  • Lubrication

Our bearings are mainly supplied in a pre-finished state. Versions for reworkability are possible for some types of bearings. Ask us!

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

For production reasons, wrapped bearings show a certain ovality and an open butt joint, as quoted in the valid standards.

The perimeter of those bearings is measured in such way that they show sufficient interference fit and roundness after mounting into a housing drill.

Basically, sliding bearings should be moulded with the help of a mandrel. Should a wrapped bearing’s perimeter exceed 50 mm, it is advisable to use an additional mounting ring.

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 of 1.0 x 45° (bigger bushings 1.5 to 2.0 x 45°) 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 affixed by bolting together, pinning or soldering but also by bonding. This does not apply to oil-soaked sinter bearings.

Lubrications

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

Besides press-fit assembly, our sliding bearings, thrust washers and strips can be fixed by means of screwing, pinning or glueing.

Especially our compound plastic bearings are often additionally secured by glueing into the housing. This is applicable if the bearing is confronted with high temperature variations.

Oil lubrication

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. By increasing the adhesion and smoothing of the sliding surfaces, additives of molybdenum sulfide or graphite can improve the lubrication properties.

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.

Dry-film lubrication

Dry-film lubricant like molybdenum sulfide (MoS2) or graphite come to use at high temperatures, dry-running operation or one-time lubrication.

Dry bearings without lubrication

These bearings mostly consist of compound material with PTFE or graphite bronze coating. Massive bronzed bushings with solid-lubricant pockets in their slide are as well maintenance-free. Full-plastic sliding bearings increasingly come to use in environments requiring high-class dry bearings. Limits of application of dry bearings are usually set by specific heat conductivity and heat strain.

Cylindrical and flanged bushings are normally mounted with a force-fitting mandrel.
To ease mounting, we recommend to lubricate the bearing carrier face with grease or oil.
When mounting bigger wrapped bushings, a mounting ring is recommended, whereby the bushing gets pre-centred. Thus, canting is prevented when force-fitting.

The butt joint at wrapped sliding bearings which are exposed to high strains has to be aligned 90° opposite to the working resistance direction.

In the running in process, lubricant or parts of the sliding layer are transferred to the counter surface. Thereby, surface roughness on the contact surface are filled and smoothed out. Herefrom results a sliding pairing, which shows a low friction resistance. Not until this procedure has been finished, can a positive sliding behavior then be developed.

Plain bearings for plant engineering

At piping, flue gas channels, boilers, heat exchangers, gas filters etc., thermodynamic expansion movements can occur due to temperature changes. This means, that in a simple steel/steel-bearings a not insignificant force can be been dammed. A mostly jerky “discharge” of these dammed forces, due to high friction values of the sliding partners, can result in a significant impairment of the bearing structure and the fixed points. In heavy cases, this even leads to deformation of the components until to cracks in the material.

For a simple, inexpensive and reliable construction-solution, is advisable the use of pre-finished slide support bearings and fixed-point bearings of the LHG.

Due to the excellent sliding- and load characteristics of the LHG sliding bearings, the aforementioned problems will counteracts effectively with PTFE-coated slide plates. Because the LHG-bearings additional prevent the well-known “stick-slip” effect, the respective construction can be used less complex and more cost-effective!

  • Optimal sliding pairing (stainless steel / PTFE) → Absolutely maintenance-free and resistant to aging
  • High load capacity in low overall height → Loads up to 2500 kN (standard), ≤ 10000 kN possible on request
  • Low friction coefficient → ca. 0,05 – 0,10
  • Prevention of edge pressure → For bearing types with calottes-body
  • Use even at high temperatures → Standard: -150°C to +250°C, high temperature: -150°C to +500°C
  • Corrosion protection → Galvanized or anticorrosion painting, (execution in stainless steel possible)
  • Optimal operating reliability → Use of the best materials
  • Well thought conception → Cost-effective, with a long lifetime

All types of the LHG sliding support bearings are fitted with a PTFE-coated bronze sliding plate. This sliding plate ensures, in conjunction with a mating surface of stainless steel 1.4301/1.4401 (roughness depth of <2µm), a very low dry-frictioncoefficient, without “stick-slip” effect and with the highest load capacity.

LHG – Calottes-slide support bearings

Calottes-slide support bearings are intended for demanding applications and equipped with the best possible use of properties!

The self-aligning, permanent parallelism of the sliding faces, avoids edge pressures and allows a consistently low coefficient of friction. The excellent gliding properties and small size of the bearing body helps to reduce manufacturing costs and this with absolute high reliability.

The LHG calottes slide support bearings are designed for loads of up to 500 kN, 1000 kN and 2500 kN.

In the standard version, with or without head plate, the bearings for the temperature range -150° are provided to +250°C. Special as high temperature bearings up to +500°C are available, as are high-load bearings up to kN = 10,000.

For all sizes, we also supply the pre-finished fixed bearing – LHG type Fix – in the matching height.

LHG – Flat-slide support bearings

The bearings are designed for simple requirements and a compact and low-cost Plain bearings solution!

The LHG Flat-slide support bearings are designed for loads of up to 500 kN, 1000 kN and 2500 kN.

In the standard version, with or without head plate, the bearings for the temperature range -150° are provided to +250°C. Special as high temperature bearings up to +500°C are available, as are high-load bearings up to kN = 10,000.
The installation heights are identical with the respective calottes-slide support bearings!

For all sizes, we also supply the pre-finished fixed bearing – LHG type Fix – in the matching height.

LHG – Slide plates for welding

These slide plates are provided for use simple bearings. The PTFE-coated steel plates offer by the high load capacity, depending on the type, a max. capacity of up to 3000 kN as well as versatile applications.

Standard Sizes:

D t
Round bearing plates LHG-Typ: R812- 100/ 10
LHG-Typ: R812-
LHG-Typ: R812-
L B t
Squared bearing plates LHG-Typ: E812- 100x 100x 10
LHG-Typ: E812- 150x 100x 10
LHG-Typ: E812- 200x 100x 10
LHG-Typ: E812- 200x 200x 10
LHG-Typ: E812- 300x 100x 10
LHG-Typ: E812- 300x 200x 10
Material steel (St37), one-sided PTFE- coated, stainless steel
Installation The LHG sliding plates can be mounted quickly and easily by spot welding.
Also available as a special design for screwing!

Legend: D – diameter, t – height, L – lenght, B – width

LHG – Customized designs

Apart from our standard delivery programme we are able to produce LHG – slide support bearings and LHG – bearing sliding plates in different shapes, sizes, strengths and load values.

On customers request, the production is also possible in special materials such as stainless steel, for applications in the food or chemical industry as well as specific medical industry applications.