Solid lubricants

Solid lubricants consist of smallest lamella-like parts which slightly shift against each other and which are able to effectively separate metallic sliding surfaces from each other owing to their coating grid structure.

The bindings of these crystal structures are strong within the layers but substantially weaker between the layers.

Thus, these substances are easy to shift in the direction of the layers and can therefore take very high loads vertically to the layers. The good sliding effect and the high load capacity of the solid lubricants results from this.

The slip motion causes the solid lubricant lamellas to embed themselves into the surface roughnesses of the sliding materials where they form a dry lubricating film trough developing layers so that the sliding surfaces do not get into contact with each other.

The solid lubricant lamellas which are unsorted in the lubricating slit are straightened and pressed together parallel to the surface by forces affecting them from the vertical. Resulting from this a closed solid lubricant layer is formed which, due to its compressibility, partly absorbs any influencing pressure and spreads it on a bigger surface.

Parallel and accordingly high back pressures create a damping effect in the lubricating slit. The interaction prevents a hardening of the upper metal layers as well as a formation of hardening, deformity or bending zones, the so-called Clod build-up which occurs in zones close to the edge of the plain bearing.

Application area

Solid lubricants are used where a hydrodynamic lubrication cannot be achieved. Furthermore they are also used where conventional lubricating films would not withstand pulsating loads.

The combinational solid lubricants developed by SL Gleitlagertechnik meet these high demands in every respect.

In addition to 99,9% pure, chemically neutral, noncorroding graphite, standard anorganic lubricants like molybdenum disulphide (MoS2), tungsten disulphide (WS2), polytetrafluorethylene (PTFE) are used, as well.

The optimal effectivity of the lubricant is achieved by the combination of the components and their advantageous properties with the covering of the solid lubricant in the slip direction, which allow an equal distribution of the lubricant.

working temperature in air:

  • graphit (99,9%, pure) up to 430°C
  • graphit and PTFE up to 250°C

Additionally, special lubricants and special materials are available on request.

Although the plain bearings are self-lubricating and no additional lubricating agents are required, all solid lubricants can be used in combination with other lubricating agents ( oil, grease, etc. ) or lubricating systems as far as these do not contain any other solid lubricants or substances with abrasive properties.

In order to make sure that in such case no disadvantages arise due to interaction of the lubricants on each other, it is recommended to point this out by the inquiry.

Solid lubricants with crystalline flake structure

properties graphite (99,9% pure) molybdenum disulphide tungsten disulphide polytetrafluorethylene
working temperature (° C) − 120…600 − 100…400 − 180…600 − 200…260
frictional coefficient (μ) 0,1+…0,18 0,04…0,09 0,08…0,18 0,04…0,09
applicability in air very good / good very good very good good
–water very good good good
–vacuum not so good good very good very good
resistance against
–(sea) water very good not so good not so goot good
–chemical very good good good good
–radiation very good / good good good
crystalline structure hexagonal hexagonal hexagonal
colour greyish black greyish black greyish black transp. / white
oxidations–/ decomposition product CO, CO2 MoO3, SO2 WO3, SO2 C2F4

+) The frictional coefficient of pure grpahite could decrease in water (also sea water), other liquids, humid air, steam or under other ideal tribological conditions down to a value of 0,03.