Solid Lubricants:

Solid lubricants are used in situation such as, 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 the machine is at high working temperature and pressure & hence under such conditions combustible lubricants are unsuitable.

Graphite:

• It is non-inflammable, soapy to touch, not oxidized in the presence of air below 3750C.

• It can be used up to much higher temp in the absence of air.

• It can be used in powdered forms or as suspension in oil or water.

• The suspension of graphite in oil is known as Oil Dag & is used in IC engines

• The suspension of graphite in water is known as Aqua Dag & is used to load processing industry.

• Graphite is also mixed with grease to form graphite greases.

Uses - in air compressors, lathes, and railway track joints, cast iron bearing, etc.

Diagram:

Molybdenum Disulphide:

• Molybdenum Disulphide has a sandwich like structure a layer of Mo atoms lies between two layers of S atoms. Poor interlaminar attraction is responsible for low shear strength in a direction parallel to the layers.
• It possesses very low coefficient of friction and is stable in air up to 4000C. Its fine powder may be sprinkled on surface sliding at high velocity, when it falls low spots in metal surfaces forming its film.

Diagram: