The Correct Use of Grease – Vital for Efficiency and Lower Costs
Grease is used in all types of applications, from bearings and gearboxes to gear wheels and forest machines. Grease reduces friction, protects against corrosion and seals against water. And of course there’s the unique aspect – the fact that it stays in places where oil would simply run off. Here are some rules for using lubricating grease correctly.
ABC OF GREASE
A lubricating grease comprises 80–90% base oil. The choice of oil affects the grease’s performance. Either mineral or synthetic base oils can be used. However, a synthetic oils can have grease properties that mineral oil cannot, such as a wider temperature range, greater chemical resistance or better electrical properties.
Grease is thickener and therefore holds the oil in place. In our industry we say that thickener grease gives body and character, for instance stability, water resistance, melting point and sealing ability. The additive hones and targets the performance. Additives can increase the grease’s resistance to oxidation, protect against corrosion, reduce friction or counteract seizing up.
STAYS WHERE IT IS
Lubricating grease should provide good lubrication, reduce friction and abrasion, and protect against corrosion. So far, grease and oil are similar. But grease has unique properties. It can act as a seal and keep dirt, water and contaminants out of the lubrication point. Grease stays where it is and reduces friction in places where oil would simply run off.
This is also why grease is used in different kinds of applications, such as ball, roller and slide bearings, gearboxes and open gear wheels. Nowadays lubricating grease is also increasingly used in forest machines for central lubrication of the chain and cutting bar.
GREASE OR OIL?
There are advantages to using lubricating grease instead of oil. Because of its consistency, as mentioned, grease stays put in the lubrication point. It has sealing properties, offers good corrosion protection and can withstand heavy loads. But it does have limitations. Unlike oil, grease cannot conduct heat away, for example, in an engine which needs cooling. Nor can lubricating grease be filtered to increase its purity. It is also difficult to separate water from grease.
CHOOSE THE RIGHT GREASE
Each application can be different and places particular demands on the lubricating grease. When choosing a product, it is important to consider water, dirt and chemicals to temperature, rpm and load. As with lubricating oils, the viscosity of the base oil is important. Low viscosity base oils tend to work better at low temperatures, while lubricating grease with high base-oil viscosity is used with higher loads and temperatures.
Also consider the speed/revs per minute in the application. Low speeds call for a high viscosity base oil, while low viscosity base oils are better in fast-moving applications.
BLEND WISELY – DEVASTATING CONSEQUENCES
When a new grease is being used in an application, it is important to know whether the new grease and the old one can be mixed. At best nothing happens, meaning that the greases are miscible. The grease mix may however harden, and this can have devastating consequences for a centralised lubrication system. On the other hand, the grease mix could soften, which can cause leakage and bearing failure. One suggestion is to always talk to your lubricant supplier, who can carry out miscibility tests ahead of a product switch.
WARNING – OVER-LUBRICATION
It is important to use the correct amount of grease, and to lubricate with the right frequency. More is not always better, and overdosing the grease can be a costly business. Over-lubrication of bearings can lead to higher temperature and oxidation of the grease, which will cause the grease to break down and age more quickly.
This can lead to increased wear and eventually result in bearing failure. Seals can also be damaged if bearings are over-lubricated. Too high a pressure from the grease gun when lubricating bearings can damage the seal. This could enable water and contaminants to seep into the bearing, leading to wear and corrosion.
To prevent this, be sure to review all lubrication points and draw up a maintenance schedule. The schedule will specify the right amount of lubricating grease and re-lubricating intervals.
By Tore Nilsen, FUCHS Lubricants