Technology

Plain bearings for mechanical engineering

General description

»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. Plain bearings have the task to support the relatively movable parts or to lead and the resulting forces to absorb and transfer . The sliding movement take place between the bearing body and the bearing parts.

In radial bearings moving the mobility of the sliding partners is ensured by the bearing clearance between the shaft and bearing body.

For axial bearings, the bearing clearance is only obtained when the bearing has two assigned via a common shaft axial faces. The sum of the opposed sliding surfaces distances yields the bearing clearance.

Modern designs always put greater demands on the sliding materials offered. In addition, a maintenance-free of the bearing is mostly expected, even in difficult operating conditions. Furthermore, an ever-increasing cost pressure will force a continued availability and use of plant and equipment used, with no restriction on their reliability can be accepted. In this context, can be optimal solutions in particular realize by plain bearing, which turn out to be operating safely and reliably over a long period.

Properties

Advantages

By mostly very different use characteristics of plain bearings, even the most difficult requirements can usually be optimally fulfills.

Some plain bearing are relatively insensitive to shock, vibration and shaking due to the material and the damping characteristic of the bearing surface.

Plain bearings run essentially noiseless, are robust and mostly also very resistant to dirt and need rarely additional seals. Bearing bushings are also available in segments, which can be advantageous in special constructions.

Disadvantaces

For some types of Plain bearings a higher starting torque can not be avoided. Non-maintenance-free bearings always require an adequate maintenance and lubricant supply. The efficiency of bearings can be considered in general as somewhat less than in rolling bearings.

PV-Value

A significant influence on the service life has the PV-value. He is the product of the specific bearing load (p) and speed (v).
The operating life decreases with increasing PV-value.

Friction

The coefficient of friction depends on the following factors:

  • Selection of the material pairing
  • Roughness of the counter surfaces
  • Specific bearing load
  • Sliding speed
  • Bearing temperature
  • Type of lubrication
Preferred use

For bearings with low rotational speeds: at swivel or axial movements; at impact stress and dirt contamination.

For bearings with universal claims: at agricultural machinery, construction equipment, vehicle construction etc..

For applications requiring a simple design and a low price.

For bearings with high or low temperatures and in particular corrosion resistance.

For bearings in the long-term area where long life is required, such as water and steam turbines, generators, centrifugal pumps, heavy marine shaft bearings etc., so where a wear-free operation is required, mostly in the field of fluid friction.

Factors for the operating life:

  • Specific bearing load
  • Sliding speed
  • PV value
  • Material and depth of roughness of the the sliding partner
  • Load zones distribution
  • Duty cycle
  • Temperature
  • Lubrication
  • Operating conditions (for example, dirt)

Delivery conditions

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

Storage

Bronze, stainless steel and plastic plain bearings are corrosion resistant and do not require special storage conditions. Steel plain bearings should be stored in dry areas with low humidity. It is advisable to unpack this type only just prior to installation.

Installation

At wrapped bushes, a certain ovality and an open butt joint can not be prevented technologically. Corresponding values were enshrined into the applicable standards.

The scope of such bushings is dimensioned that these, after installation in a housing bore, are round and have a sufficient interference fit.

The press fitting of bearings should always be done with a mounting mandrel. At wrapped bushes with a diameter greater than 50mm it is advisable to additionally use a mounting ring.

For an easier installation of Bearing bushings a chamfer of 15° – 30° is required on the housing. At flanged bushings should be provided an additional chamfer with about 1.0 x 45° (for larger bushings 1.5 to 2 x 45°), so that the waistband is flush with the housing surface. To ensure proper installation of the bolt, the shaft ends must also be chamfered or rounded. Sharp edges can damage the sliding surface during assembly and reduce the function of the camp.

Bonding

Bushes, thrust washers, strip and special parts, which are made of metal or plastics materials, can – in addition to screwing or pinning – also be fixed by gluing.

Specifically plastic bushings are very often additionally secured by gluing into the housing. This will be used when plastic bushings are subjected to high temperature variations.

Lubrication

  • Oil-lubrication

    The oil-lubrication can be used for low but preferably at high speeds and loads. The type of used lubricating oil is dependent of the particular application. Additions of molybdenum disulfide or graphite can improve the lubricating properties by increasing the adhesiveness and smoothing of the sliding surfaces

  • Grease-lubrication

    The grease lubrication is used mainly at low speeds, oscillating movements and impact loads, or when fluid lubrication can not be reached. For use, only high-quality bearing greases should be used. Lubricants which contain a solids-addition of more than 2% are not recommended because they can cause premature wear.
    For the lubrication of plastic plain bearings, no lubrication greases may be used which contain molybdenum sulfide. (for example: Molicote-fat)!

  • Dry-film lubricant

    Massive bronze bearing bushes guide with solid lubricant-insert in the sliding surface are also applicable as maintenance-free.

    All full-plastic plain bearings can be used to an increasing extent also for demanding dry-bearings and are usually a better solution than bronze or steel plain bushings.

    The application limits of these plastic plain bearings are mostly set by the thermal conductivity and thermal expansion. But for these applications are also specially developed plastics available.

    Dry lubricants such as molybdenum disulfide (MoS2) or graphite are in use at high temperatures or in emergency dry-running and at one-time-lubrication.

 

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

Installation notes

Bushings and flanged bushings are mounted normally with a mounting mandrel. In order to facilitate the installation it is advantageous to grease a little on the bearing seating surface. When installing of larger rolled bushings a mounting ring is recommended, whereby it is achieved that the bushing will be precentered and therefore a tilting will be prevented during pressing.

At rolled plain bearings which will be exposed to very high loads, the butt joint should be align with 90° relative to the load direction.

Running-in process

During running-in process, the lubricant or parts of the dry sliding layer is transferred to the counter surface. Thus, the surface roughness are filled up and unevenness compensated. This results in a sliding, which has a very low frictional resistance. Only after this operation, a positive sliding behavior can be developed with lower operating values.

 

 

Plain bearings for plant engineering

LHG – pre-finished and maintenance-free slide support bearings as floating bearings and fixed point bearings

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!

The following properties characterize the LHG slide support bearings:

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.

 

Delivery programm

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-Type: R812- 100/ 10
  LHG-Type: R812- 150/ 10
  LHG-Type: R812- 200/ 10
  L B t
Squared bearing plates LHG-Type: E812- 100x  100x 10
  LHG-Type: E812- 150x 100x 10
  LHG-Type: E812- 200x 100x 10
  LHG-Type: E812- 200x 200x 10
  LHG-Type: E812- 300x 100x 10
  LHG-Type: 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.