There are many typical indicators when looking for a good electric motor grease, including viscosity, consistency, thermo-oxidative resistance, antiwear, dropping point and shear stability.
Our primary recommendations for electric motor grease are Mobil Polyrex™ EM & EM 103* greases, which are specially designed for electric motors applications, enabling high temperature operation, long life and low noise applications.
Our secondary recommendation for electric motor grease is Mobilith SHC™ 100 – a high protection multipurpose grease. This is recommended particularly for electric motors exposed to harsh environments such as ambient temperatures below -20°C, or subject to a high level of vibrations or load.
Other recommendations for specific equipment builder applications include UNIREX™ N2 & N3 greases, which are recommend only when required to meet specific OEM approvals** (e.g., Siemens, ABB EU).
*Mobil Polyrex EM 103 grease mainly for vertical installed electric motors.
**Review EMEBS online for specific approvals.
Greases are manufactured by combining three essential components: base oil, thickener and additives.
Base oils are the liquid portion of any grease and may be mineral, synthetic, or any fluid that contains lubricating properties.
Thickeners may be any material that, in combination with the base oil, produces the solid to semi-fluid structure.
As in lubricating oil additives, grease additives and modifiers impart special properties or modify existing ones.
Mixing different types of greases can sometimes lead to incompatibility problems. Grease incompatibility results from chemical interactions between the thickener or additive systems of the dissimilar greases. In some cases, grease incompatibility can lead to equipment failure or damage of the lubricated components.
Mixtures of incompatible greases will exhibit either excessive hardening or softening relative to the consistency of the individual pure greases. The hardening or softening tendencies of the mixture will generally become more pronounced as the operating temperature increases or as the rate of shearing on the grease mixture increases.
Incompatible greases may also exhibit excessive oil separation or “bleeding” tendencies at higher temperatures.For more information please consult the Technical Topic titled "Grease compatibility."
Mixing different greases, even those with similar thickener types, can sometimes lead to ineffective lubrication resulting in damage of the lubricated components. If not spotted soon enough this may lead to equipment failure. These situations occur due to chemical or structural interaction between the thickener or additive systems of the different greases which would be classified as “incompatible.”
Symptoms of incompatibility come in various forms. Most frequently grease mixtures will exhibit a change in consistency relative to that of the individual pure greases. This tendency will be more pronounced as the operating temperature or the rate of shearing of the grease mixture increases. Incompatible greases may also exhibit abnormal oil separation or “bleeding” at higher temperatures. If greases that are incompatible are mixed in application it could lead to grease or oil leakage, premature aging or insufficient oil bleed in the contacting zones. Although less probable but not unknown, the greases’ performance additives may act antagonistically, adversely affecting the lubrication performance such as protection against friction, wear, rust or corrosion.
For more information please consult the Technical Topic titled "Grease compatibility."
If you have ever opened a grease container and found a puddle of free oil, you almost certainly may have wondered whether the grease is still fit for use. The phenomenon described is called static oil bleed. Some in-depth review of grease fundamentals is needed to comprehend it is inherent to greases.
There are several reasons to lubricate plain bearings with grease:
- As a result of the lower end leakage, the amount of lubricant required for the bearing is lower.
- When a grease-lubricated bearing is stopped for any period of time – with the flow of lubricant shut off – the high apparent viscosity of the static grease reduces end leakage sufficiently so the grease usually does not completely drain or squeeze out.
- Some grease remains on the bearing surfaces so that a fluid film can be established almost immediately upon startup. As a result, torque and wear during the starting phase may be greatly reduced.
- During shutdown periods, retained grease also acts as a seal to prevent the entry of dirt, dust, water, water vapor and other environmental contaminants and, thus, protects the bearing surfaces against rust and corrosion.