Technology

ENGINE CONSTRUCTION

General description

A sliding bearing or bushing identifies a component which supports and guides moving elements.
The acting forces are absorbed and transferred by the sliding bearing. The moving part – often a shaft, a trunnion or flat bar – slides directly on the intended sliding surface of the sliding bearing.
The lubrication is provided by embedded dry –lubricants or solid lubricant layer which are connected to a support shell. Conventional sliding materials such as bronze or hardened steel, depend on liquid lubrication, such as grease.
For radial movements, the sliding ability is provided by a clearance between shaft and sliding bearing.
Sliding bearings are available as bushings, thrust washers, sliding strips, spherical plain bearings and many other forms.
In comparison to ball-and roller bearings, sliding bearings are generally able to transfer higher loads, are ideal for slow and oscillating motions, deal better with dirt ingress, handle high and low temperatures and are in maintenance-free & corrosion- free versions available.

Mechanical designs of the Modern-day go further, they have to last longer and they have to perform better. Simultaneously this increases mechanical demand on sliding bearings. They have to be made more compact, stronger, maintenance-free and that often at a competitive rate.

 

 

Properties

Advantages

With our different types of bushing materials, even the most difficult requirements of a sliding bearing application can usually be optimally fulfilled.

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 rarely need additional seals. Bearing bushings are also available in segments, which can be advantageous in special constructions esp for large diameters of > 1.3m.

 

Disadvantaces

The starting torque for some plain bearing materials is higher and cannot be avoided. It is essential for maintenance-bound bearing materials to have a proper lubricant (oil or grease) supply and maintenance intervals. The efficiency of plain bearings can be considered in general less than in roller or ball bearings.

PV-Value

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

Friction

The following factors influence the coefficient of friction:

  • Choice of the pairing materials, eg bronze bushing and high tensile steel shaft
  • Roughness of the counter surfaces, high Rz (or Ra) value will not only increase the friction but also shorten the bearing life!
  • Specific bearing load, higher loads reduce the friction – but the loads still need to be in the limits
  • Sliding speed, after overcoming the “stick-slip” the friction generally reduces
  • Bearing temperature, cold or heat could change the bearing properties and influence the friction
  • Type of lubrication, every application is different and the right choice of grease is essential

 

Preferred use

Applications with low rotational speeds: for swivel or axial movements; for high impact loads, shock loads and dirty environments.

Generic and standard applications at agricultural machinery, construction equipment, vehicle construction etc..

Solutions demanding cost effectiveness and a simple design.

Applications with unusual temperatures (-/+) and corrosive environments.

For applications that require a long bearing life such as water turbines and off-shore applications in general.

Factors influencing the bearing 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

SBS delivers finished machined bushings, plates and components. We can supply some of our materials as raw materials or in a per-finished state for final machining on site. Ask us!

Storage

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

Installation

With wrapped bushes, a certain ovality and an open butt joint cannot 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. For 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. As 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 flushed 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,  in addition to screwing or pinning, can 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 speeds but preferably at high speeds and loads. The type of used lubricating oil is dependent on 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 cannot be reached. For use, only high-quality bearing greases should be applied. 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 as it contains 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 larger rolled bushings, a mounting ring is recommended, whereby it is achieved that the bushing will be pre-centered. Therefore, a tilting will be prevented during pressing.

As rolled plain bearings which will be exposed to very high loads, the butt joint should be aligned 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 being compensated. This results in sliding, which has a very low frictional resistance. Only after this operation, a positive sliding behaviour can be developed with lower operating values.

 

 

PLANT CONSTRUCTION

General description of support bearings

For our range of bridge and support bearings SBS works closely with LHG.
LHG pre-finished and maintenance-free slide support bearings as free-floating bearings and fixed 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.