Solid lubricants are used for certain system where oil and grease are either undesirable or inadequate.
Solid lubricants are generally used in the following cases-
When heavy machinery is to be operated at high speed and moderate load or at very high load and low speed.
When the machine parts are not easily accessible.
When machines are at high working temperature and pressure.
They are used in the form of powder or a suspension in water or oil.
The co-efficient of friction lies on range of 0.005 to 0.01. They separate two moving surfaces under boundary conditions.
They are economical, non-toxic, easy to apply, chemically inert, thermally stable and are resistant to radiations.
The substances most commonly used as solid lubricants are graphite, molybdenum-di-sulphide, mica, Teflon, chalk, soap stone etc.