Lubricant functions and paint [partly illegible]

Reading: the question is cut off after "Describe"; I read it as "What are the functions of lubricants? What is paint? Describe its constituents."

Functions of lubricants

1. Reduces friction between moving surfaces by forming a thin film that separates them.
2. Reduces wear and tear, which increases the life of machine parts.
3. Acts as a coolant: carries away heat produced by friction.
4. Acts as a seal: prevents leakage of gases, e.g. between piston rings and cylinder.
5. Prevents corrosion by coating metal surfaces from air and moisture.
6. Cleans by washing away dirt, metal particles and carbon deposits.
7. Saves energy: smoother motion means less power loss and higher efficiency; also reduces noise and vibration.

Paint

Paint is a mechanical dispersion of pigment in a drying oil (vehicle) with thinner, drier and other additives, which dries to a thin protective and decorative film.

Constituents of paint

• Pigment: gives colour, opacity and strength (TiO₂, ZnO, iron oxide, white lead).
• Vehicle (drying oil): carrier that forms the film on oxidation (linseed oil).
• Thinner: reduces viscosity and evaporates after application (turpentine, mineral spirit).
• Drier: speeds up drying of the oil (Pb, Mn or Co linoleates).
• Extender (filler): barytes, gypsum, china clay; reduces cost and adds body.
• Plasticiser: prevents cracking of the film.