Choosing the correct lubricants can be a difficult task, but it need not be complicated. The purpose of a lubricant is to reduce the friction on the moving parts of machinery, thus improving its performance and longevity. Lubricants come in two basic categories, oil and grease. Each has their strengths and weaknesses and which you choose depends on your application. A debate still goes on as to which is better.
Oil is typically 95% mineral based with 5% additives. Synthetics exist as well and one must also consider the grade of viscosity when choosing a lubricant, but it does tend to be more liquid than grease. Grease, on the other hand is basically oil thickened with soap. It is used typically in applications where fluid lubricants are too difficult or cannot be retained. In choosing an appropriate lubricant one must look at the pros and cons of each.
The advantages of grease is that it has a better start up performance because it doesn’t drain into the sump, it acts as a sealant and is less prone to leakage. Grease uses solid additives such as graphite, zinc oxide or molybdenum disulphide which may settle or become filtered in many oils. Oil, on the other hand, flows freely, enabling it to carry away unwanted heat. Oil doesn’t use thickeners, thus eliminating the danger of clashing incompatible thickeners, causing a change in consistency.
Contaminants in oil such as water or dirt are suspended briefly before being transported to filters and settling zones whereas grease can retain contaminants indefinitely. Oil is easier to change than grease as the machine does not have to be dismantled to do so. Removal of grease requires a complete purge. Disposing of oil is much more environmentally friendly than grease which is a total-loss proposition. There is no environmentally friendly way to dispose of grease.
Oil lubricants tend to have a higher rating than grease and are the typically the preferred industrial solution. However, each has its own merits. Grease is preferred because it is stable, suitable for any housing orientation, easy to transport, can withstand higher rotational forces and performs better at slow speeds. Oil is preferred because it is widely available, has excellent flow properties, even temperature gradients, and allows wear particles to settle so the lube is “fresh” during operation. A qualified dealer will be able to provide complete information on the best product to choose for your operation.