Cutting Fluids
I. Lubricants selection and Application
A.Viscosity
Most important property of any lubricant is viscosity. 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 element bearings, one should consider viscosity selection for those applications. While most would not use an EP 220 gear oil for an oil-lubricated electric motor bearing, many people will use a grease containing that same oil for an identical grease-lubricated bearing. There are several common methods for determining minimum and optimum viscosity requirements for element bearings, most of which use speed factors, commonly denoted 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) and NDm = rpm * (( bearing bore + outside diameter) / 2)
The NDm value uses pitch diameter rather than bore diameter because not all bearings of a given bore have the same element diameter, and thus have different surface speeds. Knowing the speed factor value and likely operating temperature, the minimum viscosity requirement can be read directly from charts like Figure 1.
Figure 1. (Courtesy of ExxonMobil)
Figure 1 assumes the base oils’ viscosity index. To be more precise, one would need to use a chart that identifies the viscosity at operating temperature, then determine the viscosity grade from a viscosity/temperature chart for a given lubricant.
B. Right Additives
It’s time to consider additives. The additive and base oil types are other components of grease that should be selected in a fashion similar to that used for oil-lubricated applications. For instance, a lightly loaded high-speed element bearing does not require extreme pressure (EP) additives or tackifying agents, while a heavily loaded open gear set does.
Most performance-enhancing additives found in lubricating oils are also
A.Viscosity
Most important property of any lubricant is viscosity. 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 element bearings, one should consider viscosity selection for those applications. While most would not use an EP 220 gear oil for an oil-lubricated electric motor bearing, many people will use a grease containing that same oil for an identical grease-lubricated bearing. There are several common methods for determining minimum and optimum viscosity requirements for element bearings, most of which use speed factors, commonly denoted 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) and NDm = rpm * (( bearing bore + outside diameter) / 2)
The NDm value uses pitch diameter rather than bore diameter because not all bearings of a given bore have the same element diameter, and thus have different surface speeds. Knowing the speed factor value and likely operating temperature, the minimum viscosity requirement can be read directly from charts like Figure 1.
Figure 1. (Courtesy of ExxonMobil)
Figure 1 assumes the base oils’ viscosity index. To be more precise, one would need to use a chart that identifies the viscosity at operating temperature, then determine the viscosity grade from a viscosity/temperature chart for a given lubricant.
B. Right Additives
It’s time to consider additives. The additive and base oil types are other components of grease that should be selected in a fashion similar to that used for oil-lubricated applications. For instance, a lightly loaded high-speed element bearing does not require extreme pressure (EP) additives or tackifying agents, while a heavily loaded open gear set does.
Most performance-enhancing additives found in lubricating oils are also