Machines are here to stay. If you are familiar with the way machines are built and how they function, you will realize that “friction” is an inevitable factor in this segment. While in day to day activities, friction is a very beneficial thing to have, in the case of machines, not so much. This is where the world of Lubricants comes into the picture. Industrial machinery operates under intense, fluctuating conditions such as extreme temperatures, pressures and speeds for extended durations. Greases are used to increase the machine’s lifespan by ensuring minimal friction and wear. The grease withstands difficult conditions for the machine’s smooth running such as water exposure, dust entry, thermal radiation, contact with corrosive and acidic mediums etc.
What are Lubricating Greases?
The American Society for Testing and Materials (ASTM) defines lubricating grease as: “A solid to semifluid product of dispersion of a thickening agent in a liquid lubricant. Other ingredients imparting special properties may be included” (ASTM D 288, Standard Definitions of Terms Relating to Petroleum).
Lubricating greases are crucial to industrial applications in reducing mechanical friction and wear.
Grease formulation is a complex process that takes into account the multiple interactions between base oils, thickeners and the different types of additives. The properties of the final product depend not only on the formulation but also the manufacturing process and its storage conditions.
Greases are mixtures consisting of: (approximately)
- 75% lubricating oil
- 15% thickener
- 10% additives
The additives are added to enhance performance. For example, extreme pressure additives enhance the load-carrying capacity of the grease, corrosion inhibitors prevent metal from corroding, thus protecting and increasing the life of the machine.
Greases have applications in multiple industries like Food & Pharma, Iron & Steel, Mining, Oil & gas etc.
The base oil performs the actual lubrication. A few commonly used base oils are mineral oil, synthetic oil, or biobased oil. Majority of greases in the market are composed of mineral oil blended with a soap thickener. However, synthetic and biobased greases are growing in popularity nowadays. Selecting the right base oil viscosity is extremely critical. It depends on your application as well as the design and mode of operation of your machine.
High viscosity base oils are used for slow speeds and heavy loads, whereas low viscosity oils are used for high-speed applications.
Synthetic oils such as PAO and Esters have greater thermal stability and low-temperature performance than mineral oils.
The thickening agent is a material that, in combination with the base fluid, gives a solid to a semifluid structure to your lubricating grease. The most important feature of grease is its consistency. A grease that is too stiff may not get pumped into areas requiring lubrication, while a grease that is too fluid may leak out. Grease consistency depends on the type and amount of thickener used and the viscosity of its base oil. The primary type of thickeners typically used in grease is metallic soaps. These soaps include lithium, aluminium, clay, polyurea, sodium, and calcium variables. Different thickeners have different performance characteristics, therefore, temperature, load, water ingress etc. are some of the factors to be taken into account while choosing the right thickener for a grease.
Additives can play several roles in the formulation of lubricating greases. Primarily, they are used to enhance the existing desirable properties and suppress the undesirable ones. They are also used to introduce new properties. Although they are present in seemingly low quantities, they can be extremely crucial in changing the properties of grease.
The most commonly used additives are oxidation and rust inhibitors, extreme pressure, antiwear, and friction-reducing agents.
Additives enhance performance, protect the grease and the lubricated surfaces.