Selecting a grease is one of the most crucial decisions you make for your equipment. Your choice could make the difference between cost savings, reduced downtime, or equipment failure. There are several factors to consider when selecting the right one, but the main things to consider are the components of the grease itself: thickener type, base oil type, and base oil viscosity.
The thickener of the grease performs an important job—holding the lubricant in place. It’s essentially what makes grease, a grease, rather than an oil. A grease thickener impacts your grease’s operating temperature, load, speed, and material compatibility. A good thickener type will meet two criteria: it is compatible with the equipment manufacturer’s recommendations and will be suitable for the conditions it’s performing in. Thickeners can be many types of chemical compounds, but most are not compatible and should not be mixed. The most common thickeners are lithium, lithium complex, aluminum complex, and polyurea.
|Lithium||Cheaper than Lithium Complex and boasts low oil separation. Avoid using over 275° F.|
|Lithium Complex||Known to be the most versatile. Not H1 approved and cannot be used as food-grade grease. Tolerates up to 350° F.|
|Aluminum Complex||Great oxidation and water resistance. Most popular food grade thickener with H1 approval. Use up to 350° F.|
|Polyurea||Excellent oxidative resistance. Best choice for electric motors and sealed-for-life applications. Use up to 350° F.|
(H1 lubricants are for use in areas of incidental contact of food/ingredient manufacturing)
These greases function in a variety of machines, operations, and conditions. Some of the more popular uses of grease are for cables, plain bearings, rolling-element bearings, linear bearings, ball screws, slideways, and seals. All these components are in machines that may be operating in the extreme heat and dust of a desert in Egypt or subzero temperatures on a fishing trawler in the middle of the Atlantic Ocean.
As you can see, there are many different types of applications and environments and just as many types and brands of grease to go along with these machines and conditions. Therefore, a good grease will be the one that best works for your type of machinery and its environment.
Base Oil Type
Base oils make up 80 – 95% of your typical grease and will typically consist of synthetic or mineral oil. To determine the best base oil type, consider the conditions in which the grease will perform like temperature, load and pressure. In most applications, mineral oils provide the much-needed lubrication when combined with a suitable thickener and additives. While paraffinic base oils are used more often in greases than naphthenic (low paraffin content), some applications receive several benefits such as improved low-temperature flow from using a blend of the two.
When used in more demanding circumstances, synthetic base oils such as polyalphaolefin (PAO) base oils are often appropriate because of their wide temperature range in both hot and cold applications. The advantages of using synthetic base oils include:
- Wider temperature range by 10°C to 20°C than other base oils
- Less viscosity loss when hot
- Greater elastohydrodynamic lubrication (EHL) film thickness
- Reduced evaporation at high temperatures
Base Oil Viscosity
Viscosity is arguably the most important property of any lubricant. A common mistake when selecting a grease is to confuse the grease consistency with the base oil viscosity. Because the majority of grease-lubricated applications are rolling-element bearings, one should consider viscosity selection for those applications. There are several common methods for determining minimum and optimum viscosity requirements for element bearings, most of which use speed factors, commonly referred to as DN or NDm. Speed factors account for the surface speed of the bearing elements and are determined by the following formulas:
DN = rpm * (bearing bore)
NDm = rpm * ((bearing bore + outside diameter) / 2)
Selecting the right grease is only the start when it comes to taking care of your equipment. If you don’t establish the correct regrease intervals and dispense the correct amount of grease every time, you may be facing unplanned downtime before you know it.
When it comes to grease-lubricated rolling-element bearings, the UE Systems OnTrak can help you regrease at the right time, with the right amount, every time. By monitoring bearing friction, the OnTrak is able to detect the moment grease is needed and grease the bearings automatically with the operator’s permission.
This tech combined with proper grease selection and best practices sets the foundation for a lubrication program that gets real results including less downtime and cost-saving benefits.