Grease Characteristics

What type of Base Oil and Thickeners are used in Grease?

Base OIls

Diffferent base oils are used in grease for different applications. Food industry greases will use either white oils or vegetable oils, whilst industrial, automotive and other non food grade greases will use more common types such as refined mineral, Castor or synthetic based oils. Common Base Oils used in grease are -

Thickeners (Soaps)

Over 70% of grease used world wide uses a Lithium or Lithium Complex based soap as the thickener. Lithium based products have better water resistance properties compared to sodium soap greases, better high-temperature properties compared to calcium soap greases, and excellent mechanical properties (both resistance to shearing and good ability to be pumped). Lithium complex have a higher dropping point. Grease made with a lithium soap base adheres well to metal, is non-corrosive, may be used under heavy loads and exhibits good temperature properties.

Thickening agents used in grease can be as follows -

  • Clay (Organo Clay, i.e. Bentone).
  • Lithium.
  • Lithium Complex.
  • Lithium / Calcium Mixed Complex.
  • Calcium Complex.
  • Aluminium Complex.
  • Others (Calcium, Sodium, Polyurea).

What is Grease?

GREASE = BASE OIL + ADDITIVES + THICKENER

The ASTM (American Society for Testing and Materials) definition of grease is -

A lubricating grease is a firm to semi-fluid product obtained by the dispersion of 2 to 15%  of a thickening agent into a lube base oil.

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How does Grease work?

The thickeners in grease absorb lubricants and additives like a sponge and release them when under pressure. The lubricants prevent friction and create a barrier or film between moving parts.

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What are the properties of Grease?

Grease is developed with functional properties to protect and lubricate solid surfaces that come in contact with one another.

It also has other properties it must exhibit such as -

1) Act as a sealant - It fuctions as a sealant to minimise leakage and keep out contaminants and foreign materials. Due to its consistency it prevents leakage and keeps deteriorated seals more effective.

2) Containment - By its natual consitency, grease is easier to contain than oil and does not require such complex retention devices. Its rigidity keeps it more confined and easier to contain.

3) Suspend Solid Lubricants - Grease can hold solid lubricants in suspension such as Molybdenum Disulfide (Moly) and Graphite for extreme high pressure and high temperature applications.

4) Low maintenance - The lubricant levels of grease do not need to be monitored or controlled.

5) Provide corrosion protection for surfaces

6) Resist leakage, dripping and throw off

7) Resist change in structure or consistency during the service cycle

8) Maitain mobility under application conditions

9) Be suitable in a wide range of temperatures

10) Reduce friction and provide wear resistance

11) Resist water washout and and spray off.

12) Provide mechanical stability

13) Display excellent storage life

14) Be compatible with many different types of surfaces

 

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What does the colour of my Grease mean?

A grease’s colour is determined by base oil, thickener, additive and dye. A grease can be made to almost any colour to suit a particular environment, application or for identification purposes.

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What is an average shelf life of Grease?

The shelf life of any grease is affected by the type and amount of thickener used, consistency of the grease, manufacturing method employed and the formulation complexity. Generally, straight Lithium, Lithium Complex and Calcium Complex greases remain stable for a long time. Aluminium Complex greases tend to set and harden, but remain stable. Bentone and Barium greases tend to soften on aging. Based on these observations:

The shelf life of most Penrite greases is about 5 years. However, Steering Box Lubricant and Semi Fluid Grease only have a 2 year shelf life.