Greases & Gels

 

The word 'grease' originates from the Greek word 'crassus' meaning 'fat'. Animal fats were the first examples of lubricants and were used to lubricate the wheels of Chariots by the Egyptians  3500 years ago.

 

Nowadays a grease is made up of three main types of ingredient, a fluid or oil, thickener and additives.

 

Why use a grease?

 

Greases are generally used where oil systems are not appropriate or practical for example in a wheel bearing on a car. In some applications the grease can be sealed in the bearing and will provide lifetime lubrication, in others it is neccesary to rejuvenate the grease by adding some more periodically and purging the old grease.

 

What are the different types of grease?

 

Greases are generally divided by the type of thickener however also the base oil type and properties must be considered as well as the additives included within the grease. The properties of the greases vary according to their make up.

 

Thickeners such as Lithium, Calcium, Sodium, Barium, Aluminium and other metallic soaps are used along with non soap thickeners such as Bentone, Silica and Polyurea.

 

The type of base oils used include, mineral oils, vegetable oils, synthetic fluids, esters, silicones, polyglycols & fluorocarbons to name a few.

 

Additives are included top enhance the properties of the grease such as anti-oxidants, anti-wear, extreme pressure, anti-rust & solid lubricants (Molybdenum di-sulphide, Graphite, PTFE etc).

 

Greases are also classified according to their consistency which indicates the hardness or softness of the grease. This is measured by a penetrometer which consists of a cone of specific weight and size dropped into the grease for 5 seconds, the penetration is then measured and the grease classified. The system generally used is the ISO system or NLGI (National Lubricating Grease Institution) standard.The following table shows the NLGI classification and compares each grade with household products of similar consistency.

 

NLGI consistency numbers

 

NLGI number ASTM worked (60 strokes)

penetration at 25 °C

tenths of a millimetre Appearance Consistency food analogy

000 445-475 fluid cooking oil

00 400-430 semi-fluid applesauce

0 355-385 very soft brown mustard

1 310-340 soft tomato paste

2 265-295 "normal" grease peanut butter

3 220-250 firm vegetable shortening

4 175-205 very firm frozen yogurt

5 130-160 hard smooth pate

6 85-115 very hard cheddar cheese