16: Lubricants and Cutting Fluids

LUBRICANTS

Machines are lubricated to reduce friction between moving parts. The oil film prevents metal to metal contact. Grease is used on moving parts usually where there is not too much heat and where, sometimes, the bearing is sealed, but generally oil is the more widely used. Moving parts under heavy pressure are often lubricated with E.P. (Extreme Pressure) oil.

CUTTING FLUIDS

Cutting fluids should:

remove heat rapidly and thus reduce distortion,
wet the metal efficiently so that cooling may be effective,
have good lubricating properties thus reducing power, consumption,
reduce welding of chip to tool improve surface finish reduce tool wear,
protect workpiece and machine from corrosion,
permit increased speeds of production ,
wash away chips and swarf.

Cutting oils can be classified as follows:

1. Aqueous Cutting Fluids
water
aqueous solutions

2. Neat Cutting Oils
mineral oils
mineral/lard (compounded) oils
fatty oils
extreme pressure (E.P.) oils

3. Aqueous Emulsions of Soluble Cutting Oils

Water on its own has very good cooling powers but it has two disadvantages: 1. it rapidly rusts steel, 2. it does not wet metal efficiently. Modern soluble oils (10% emulsifiable oil, 90% water) overcome these disadvantages and they also give a measure of lubrication. Thus the greater the oil content of a soluble oil emulsion the better it will lubricate but the less it will cool, and vice versa.