Choosing the right grease

It’s not easy to choose the right type of grease because there are so many varieties on the market. Many things are to be considered: type of use, load, speed, temperature, etc.  So what do we have to know in order to make the right decision?  

Manufacturing

Greases are composed of approximately:

•      70% to 90% liquid lubricant : mineral or synthetic  oil

•      10% to 30% oil insoluble thickener: soap

•      0% to 10% additives to increase performance

Types of thickener

Thickener, also called soap, is composed of interlaced fibers, like a sponge.  His main purpose is to retain oil just like a sponge retains water.  

Many types of soap can be used in the manufacturing of greases

•      Lithium

•      Aluminum complex

•      Lithium complex

•      Calcium sulfonate

•      Bentonite

•      Polyurea

 
During the last few centuries, the most popular thickener was lithium complex which offers good results in different types of applications. Today, considering applications are more and more severe and that companies want to limit the number of products in inventory, greases based on calcium sulfonate are widespread and have become very popular because they offer versatility and exceptional results on all levels.  Contrary to other types of thickeners which will perform on a limited number of properties, calcium sulfonate greases are high quality products and perform very well in all types of environments and applications.

Base oil viscosity:

Grease being composed of 70% to 90% oil, oil viscosity has a major influence on those characteristics.

Usually, we prefer using a low viscosity grease for higher RPM and lighter loads, whereas high viscosity will be used for lower RPM which are submitted to higher loads.

Knowing the viscosity of the oil used in the making of the grease is not all.  We have to know the grease viscosity in different temperatures. For example, a 220 cSt grease can be excellent at a 40 °C operating temperature, but be extremely ordinary at 100 °C. Before choosing, it’s essential to properly measure the operating temperature. The following chart gives a good indication of preferred viscosities according to temperatures.

*To determine the bearing interior temperature, add 10 °C to the exterior temperature
(Ex: 70 °C externally equals 80 °C internally)

Grease consistency (NLGI grade)  

The NLGI grade of a grease represents its consistency.  It can vary between 000 (the most liquid) and 6 (the thickest).  For exterior applications, temperature will affect the choice of NLGI grade. Usually, we use a grade 2 grease inside or during summer, whereas we use a grade 0 or 1 during winter because it’s easier to pump into systems. The following chart gives an idea of greases consistencies according to their NLGI grade.

To know more about grease or for advice on choosing lubrication products, don’t hesitate to contact one of our SINTO lubrication experts.

Daniel Laflamme,
SINTO lubrication expert chemical engineer