Hydraulics and Pneumatic Machines – JSS2 Basic Technology Lesson Note (Third Term)

Lubrication is the process of applying a lubricant, such as oil or grease, to an engine or its moving parts to reduce friction and allow smooth movement.

Behavioural objectives

By the end of the lesson, students should be able to:

1. define lubrication and lubricant;
2. list examples of lubricants;
3. state the functions of lubricants;
4. list the properties of a good lubricant;
5. explain how lubrication reduces friction between meshing gears;
6. state the difference between hydraulic and pneumatic machines.

What is lubrication?

Lubrication is the process of applying a lubricant to an engine or its components to reduce friction and allow smooth movement.

• Lubricant: a substance, such as oil or grease, that reduces friction between moving parts.
• Friction: the force that opposes movement when two surfaces rub together.
• Application: lubricants are applied as a surface coating to moving parts.
• Effect: the coating prevents wear, protects against corrosion, controls temperature and reduces friction between meshing gears.

What are examples of lubricants?

Four common examples of effective lubricants are grease, oils, penetrating lubricant and dry lubricant.

What are the functions of lubricants?

A lubricant has seven main functions in a machine.

1. Reduces friction: a thin film keeps moving surfaces from rubbing directly.
2. Prevents wear: less rubbing means the parts last longer.
3. Protects against corrosion: the coating keeps air and water away from the metal.
4. Controls temperature: it carries heat away from the parts (dissipates heat).
5. Controls contamination: it carries dirt and particles to a filter or sump.
6. Transmits power: in hydraulic systems, the oil carries force from one part to another.
7. Provides a fluid seal: it fills small gaps, for example between a piston and its cylinder.

What are the properties of a good lubricant?

A good lubricant has high viscosity index, thermal stability, hydraulic stability, demulsibility and corrosion prevention.

• High viscosity index: the oil does not become too thin when hot or too thick when cold.
• Thermal stability: the oil does not break down when it is heated.
• Hydraulic stability: the oil keeps its properties when used under pressure in hydraulic systems.
• Demulsibility: the oil separates quickly from water instead of mixing with it.
• Corrosion prevention: the oil protects metal parts from rust.

How does lubrication reduce friction between meshing gears?

Gear oil forms a thin film between the teeth of meshing gears, so the teeth slide over one another with little rubbing.

What happens when gear teeth mesh without lubrication?

1. The teeth rub directly against each other as the gears turn.
2. The friction generates heat.
3. The heat and rubbing wear away the surface of the teeth.
4. Power is lost in transmission.

How does lubrication solve the problem?

1. Suitable gear oil is applied to the gears.
2. The oil coats the teeth and separates the metal surfaces.
3. Friction between the meshing teeth falls, so less heat and wear occur.

What are the functions of lubricants in gears?

• Reduce friction: less rubbing between moving parts.
• Prevent heat build-up: the oil carries heat away.
• Protect moving surfaces: the film guards the teeth from damage.
• Trap harmful substances: the oil helps remove and trap harmful chemicals in the engine.
• Deaden sound: the oil film makes the gears run more quietly.
• Prevent corrosion: the oil keeps rust off the metal.
• Prolong gear life: the gears last longer.

What are hydraulic and pneumatic machines?

Hydraulic machines use a liquid under pressure, usually oil, to transmit force, while pneumatic machines use compressed air.

• Hydraulic machine: a machine in which pressure on an enclosed liquid is passed on to move a load.
• Pneumatic machine: a machine that uses the force of compressed air to do work.
• Link to lubricants: hydraulic oil also lubricates the moving parts and transmits power.

Evaluation

1. Define lubrication and lubricant.
2. List four examples of lubricants.
3. State five functions of lubricants.
4. Explain why meshing gears must be lubricated.
5. State two differences between a hydraulic machine and a pneumatic machine.

Assignment

State four functions of lubricants in gears and describe what happens when two gear teeth mesh without lubrication.