Grease is a solid or semisolid lubricant that is used to lubricate the machinery when two parts are moving in relative motion. Lubrication helps to reduce friction and wear and this improves the life of the machinery. Grease is made up of a base oil, a thicker and additives. The percentage of these in grease can vary and grease is made up of 65 -95% base oil, 5 – 35% thickener and 0-15% of additives.
For hot equipment lubrication, you will have to use grease designed to withstand high temperatures. Normal grease can break down at elevated temperatures limiting the lubricating life of grease. For high-temperature operation conditions, high-temperature grease has to be used.
High-temperature grease should have properties like high dropping point, shear stability, adhesive properties, good thermal and oxidation resistance, water resistance and good resistance against heavy loads. Several compounds can withstand high temperatures and maintain their tribological properties as well.
In steel mills, the bearings operate at elevated temperatures of 120° C – 150° C. The grease to be used in this case needs to function well at high temperatures and also should have load-carrying capability. In this case, you will have to use high-temperature grease with EP. The EP stands for ‘Extreme pressure’ which means the grease can work under high load-carrying conditions. Additives like nanoparticles can be used to enhance the EP properties of grease.
Grease for high-temperature and EP
In grease, the thicker holds together the base oil and the additives. This gives grease a certain consistency which gives it advantages over lubricating fluids. Grease offers ease of use, low
friction and protection against corrosion.
- The base oil forms the largest portion of grease and it can be a mineral oil or synthetic oil. Most of the greases are made from mineral oil. Next is synthetic oil and PAO (polyalphaolefin) followed by silicones. The base oil does the lubrication of the moving parts. For high-temperature applications, the PAO and PFPE (perfluoropolyether) base oils offer high stability and lubricity.
- For high-temperature and EP applications lithium complexes or calcium sulfonate thickeners are used. These thickeners offer better thermal stability and load-carrying capacity. Lithium complex greases have good high-temperature properties, stability and water resistance. Calcium sulfonate grease provides excellent water resistance properties.
- Additives are added to improve the properties of grease like oxidation stability, corrosion resistance, wear resistance, water resistance and more. The additive used should be able to function along with the thicker and the base oil. The final mixture formed must be a stable mixture of the distinct components.
Selecting the right grease
You should select a high-temperature EP grease depending on your application. The grease that suits your operating conditions the best should be used. The factors you should check for are as follows:
- You can begin by first seeing the temperature range of your application and what can cause the grease to degrade. The dropping point at which the grease breaks down should be more than the operating temperature of the application.
- If your application requires high load carrying capacity then you should select grease with the right additives. Some of the additives for high loads are sulfur, phosphorus, molybdenum and more.
- At high temperatures, grease can get oxidized and break down therefore select greases that offer a good resistance to oxidation.
- You should also check that the grease you intend to use is compatible with the materials used in your machinery and seals.
Process of applying grease
While lubricating you should apply grease as recommended by the manufacturer for quantity and frequency. Over-greasing can lead to excess heat generation and waste. Before applying grease to the machinery the old grease and contaminants should be removed. The grease point should be cleaned well.
You should ensure that the machinery has proper seals and gaskets to prevent the grease from escaping. You should monitor your machinery to assess the lubrication and the performance of the machinery. You can check for oxidation and degradation of grease and take preventive action immediately.
When in use the grease is subjected to mechanical stress and its consistency will change. The softening of grease will lead to it leaking from the housing. This will require that you lubricate your machinery frequently to avoid failure of the machinery due to lack of lubrication. To avoid such problems you should select a grease with the right thickener.
The grease you select should help to maintain the life of your machinery and even extend it. It will also help your machinery to function at its full potential.