Grease is the most widely used lubricant in the various mechanical systems where bearings and gears are used. Grease is manufactured by combining a base oil, a thickener and an additive into a semi-fluid or solid mixture. The most important physical property of grease is its viscosity which drops on the application of shear to give an effect of an oil lubricated part.
Grease is from the early Roman or Egyptian eras and was prepared by combining lime with olive oil. This is how calcium grease was made. Now soaps are used as thickeners to oils. Grease is made from base oil (85%), a thickener (10%) and other additives that impart special properties. You can buy grease online depending on the application it will be used in.
The lubrication is actually done by the base oil and for this mineral oil, vegetable oil or synthetic oil can be used. Thickeners used are metal soaps like calcium and lithium, polyureas or clay. Additives help to enhance the performance of grease and help to protect the grease and the lubricating surface.
The lubricant viscosity to be used depends on the application, where high speed is required low-viscosity grease is used and where slow speed is required high-viscosity grease is used.
The main function of grease is to lubricate the moving surfaces and remain in contact without leaking under the centrifugal action. Grease should retain its properties even when shear is applied. It should be applied well using a Grease gun to cover all the parts of the lubricated machinery and it should be able to flow into the parts.
Properties of grease
- Grease is easier to contain than oil. When the machinery is shut down the grease remains in the components while the oil drains away.
- The viscosity of grease reduces under shear.
- It can be used as a sealant to minimise leakage and prevent contamination. The chances of contamination in pharmaceuticals or food products are reduced when grease is used due to its resistance to flow into the products.
- It can hold solid lubricants in suspension. The fluid level need not be measured or controlled.
- The dropping point of grease is the lowest temperature at which a drop of oil can be separated from it. This is used to determine the upper-temperature performance limit. Due to the use of additives, the Thermo oxidative stability of the base oil is used to determine the performance temperature of modern grease.
- It can be used in vertical and overhead applications due to its good drip resistance.
- It is useful in applications that are sealed permanently like bearing and remote gearboxes.
Uses of grease
- It is used in applications where oil cannot be confined. Greased machinery tends to use less power.
- It is used when relubrication is difficult or dangerous.
- During the high-speed or low-speed operating conditions it can be used to prevent wear.
- It can be used where noise reduction is important as grease reduces noise.
- It is used where less time is required for lubricating and the equipment is used intermittently.
- It can be used in extreme conditions like high temperature, shock loads and high pressure.
- It is used to inhibit the corrosion of metal parts in contact with the lubricants.
- It helps to reduce the friction between the moving parts by surface adsorption.
Types of grease
The two main types of grease are Soap-based and Non-soap-based. Grease is manufactured using the Batch process or the Continuous process.
The soap-based grease is manufactured using processes like saponification, dehydration, additives, filtration, milling and deaeration. The non-soap-based grease is manufactured using processes like polymerisation, additives and homogenise.
In soap-based grease, base oil, thickeners like metal soaps and additives are used. In non-soap-based grease base oil, thickeners like impure clay and polyureas and additives are used.
Grease has a unique ability to incorporate liquid as well as solid (in the form of powder) additives. It should have a desirable colour and odour therefore dyes and odorants are added to it. These do not affect the performance of grease but appeal to the senses.
Calcium-based soaps are the oldest and the simplest used thickeners in grease with a maximum operation temperature between 60° C – 70° C. Now different types of grease are manufactured that offer a higher operating temperature of 150° C like calcium sulfonate greases, aluminium complex grease, sodium complex greases, clay-based greases and polyurea greases.
Grease is a type of lubricant that does not flow but bleeds which means that it releases oil when squeezed between the contacting surfaces. Grease is sold in the market and you can easily buy grease online.