Mumbai University > First Year Engineering > Sem1 > Applied Chemistry 1

Marks: 6M

Year: Dec 2014

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.

Uses of graphite:

1. The major use of graphite is in making lead pencils of different hardness, by mixing it with different proportions of clay. The weakly held layers of carbon atoms in graphite easily slide over each other and are left behind on paper as black marks.

2. Due to its slippery nature, graphite is used as a dry lubricant in machine parts.

3. Being resistant to chemicals and having a high melting point and also because it is a good conductor of heat, graphite is used to make crucibles.

4. The presence of free electrons makes graphite a good conductor of electricity and it is used to make electrodes.

5. Graphite has the ability to absorb fast-moving neutrons, thus, it is used in nuclear reactors to control the speed of the nuclear fission reaction.