Choosing a High-Speed Grease

Posted on Wed, Aug 12th, 2015 in: Bearing Maintenance

Most industrial facilities have bearings that rotate faster than normal processing equipment. When it comes to lubricating these pieces of equipment, not all lubricants behave the same way. It is decidedly important that these facilities select the appropriate high-speed grease for their needs. There are six primary factors in selecting a high-speed grease:

Base Oil Viscosity – Ensure the viscosity adequately provides the lubricating film but is not too thick to cause excessive heat and drag.

Dropping Point – The dropping point of the grease should exceed the operating temperature by a wide margin to avoid excessive bleed and possible bearing failure.

Thickener Type – Choose a thickener that can provide the proper dropping point, channeling and bleed characteristics. Also, if you use multiple greases, check the thickener types for compatibility in case of accidental mixing.

Channeling Characteristics – The grease should be able to channel so excess heat isn't generated from grease churning.

NLGI Grade – The consistency of the grease will have an impact on the bleed characteristics and channeling properties of the finished 
lubricating grease.

Additive Load – Most applications require additives to help the oil lubricate. For greases, a wide variety of chemical and solid additives can be blended to aid in film strength and reduce friction and wear.

Choosing a High-Speed GreaseThe Speed Factor And Viscosity Are Important

The speed factor is a term that helps define the relationship of the speed at which a bearing rotates with the size of the bearing. There are two main ways to calculate this factor. The first is known as the DN value, which uses the bearing inner diameter multiplied by the speed at which it rotates. The second method is known as the NDm value. This uses the bearing's median size, also known as the pitch diameter, and the rotation speed to calculate the speed factor.

The speed factor can help you determine a variety of lubricant properties, which you can then utilize to select the proper lubricant. Among these properties would be the viscosity of the oil and the National Lubricating Grease Institute (NLGI) grade of the grease for the application.

The Speed Factor (NDM) of a multi-purpose grease is 100,000 – 200,000 NDm's. High-speed, high-temperature, long-life grease is 600,000 NDm's whereas high-speed, long-life grease is 1,000,000 or greater NDm's.

The most important physical property of a lubricant is the viscosity. Viscosity is what determines how thick or thin the lubricating film will be based upon the load, speed and surfaces in contact. This must be matched to the needs of the bearing. Most general-purpose greases have a base oil viscosity of around 220 centistokes. While this type of grease may work fine for moderate speeds and loads, when the bearing speed increases, the viscosity must be reduced accordingly.

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