Consequences of Grease Viscosity on Start-Up TQ

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At start-up, how pronounced are the differences in resistance to motion between a grease with the following viscosities (cSt @ 40ºC)? The values are all from NLGI #1 greases.
  • 150 cSt
  • 220 cSt
  • 313 cSt
To a layperson, it appears as though the first grease requires considerably less start-up torque than the third grease. .
 
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I'm not an expert on this but I believe as a "rule of thumb" you are correct. However, the type of and content % of the thickener will also come into play. A thinner base oil will generally require more thickener to get the grease to the same NGLI #, so there can be some offset in the benefit to the thinner base oil. The thicker base oil will also tend to protect better under high load conditions. Maybe one of the real pros will chime in.
 

Slalom4me

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Thanks. Is the Viscosity reported by ASTM D 445 indicative of the viscosity of the final grease product (ie: w/ additives)? Or is it describing the viscosity of the base stock? .
 

Slalom4me

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 Originally Posted By: salesrep
Base oil properties.
Thanks, salesrep. Would three NLGI #1 greases formulated from base oil with the varying cSt Viscosities above (post #1) appear to have a similar thickness/consistency when dispensed? That is to say, do the additives bring the final product to a standard level, despite the differences in the base oil viscosity? .
 

Slalom4me

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The information about grease on the following link is informative Grease Analysis - Monitoring Grease Servicability and Bearing Condition By Bill Herguth, Herguth Laboratories Viscosity of Grease "The viscosity of grease is often misunderstood. The viscosity typically listed on a new oil data sheet is usually the kinematic viscosity of the oil used in blending the grease measured, using the standard ASTM D445 method. The kinematic viscosity of the base oil is important in ensuring the correct grease, containing the correct grade of oil is used for lubrication purposes. However, we can also measure the viscosity of the grease itself. Since a grease is non-Newtonian, we can only measure the apparent viscosity because the viscosity of a non-Newtonian fluid changes with shear stress see “Understanding Absolute and Kinematic Viscosity” by Drew Troyer). The apparent viscosity of a grease is determined using ASTM D1092. This test measures the force required to force the grease through an orifice under pressure. As such, this test is an ideal way of determining the flow characteristics of grease through pipes, lines, dispensing equipment as well as its pumpability." "Rheology measurements of grease may soon replace both the cone penetration and the apparent viscosity measurements. Rheology is the study of the deformation and/or flow of matter when it is subjected to strain, temperature and time. A rheometer only requires a few grams of sample to perform the analysis, yielding much more information than the cone penetration or the apparent viscosity measurements. This makes the rheology measurement an ideal test for small amounts of used grease."
 

Slalom4me

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 Originally Posted By: Slalom4me
 Originally Posted By: salesrep
Base oil properties.
Thanks, salesrep. Would three NLGI #1 greases formulated from base oil with the varying cSt Viscosities above (post #1) appear to have a similar thickness/consistency when dispensed? That is to say, do the additives bring the final product to a standard level, despite the differences in the base oil viscosity? .
The answer to my question appears in Mr Herguth's article Grease Analysis - Monitoring Grease Servicability and Bearing Condition By Bill Herguth, Herguth Laboratories Changes in Grease Consistency "Grease is made up of base oil, a gelling agent or soap thickener (sometimes called filler) and additives, which perform in much the same way as oil additives. The consistency of grease is controlled by the type and ratio of the gelling agent to the oil and its viscosity ... " " ... worked penetration of new greases is the property upon which the NLGI (National Lubricating Grease Institute) grease consistency classification system is based ... " .
 
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Look for ASTM D1478 Low Temperature Torque of Ball Bearing Greases or ASTM D4693 Low Temperature Torque of Grease Lubricated Wheel Bearings in the specs on the greases. A few high quality greases list one of these. Lower is better.
 

Slalom4me

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Thank you. AFAIR, neither D 1478 nor D 4693 values have been published in the marketing information viewed to this point. Perhaps the technical service people can provide information about these results on request - I will inquire. With the understanding gained during the course of the thread, my current opinion is that the answer to the original question is that Viscosity of Oil (D 445) has less influence on start-up torque than Penetration (D 217) &/or Apparent Viscosity (D 1092). This statement is based on the belief that the latter two values represent viscosity of the final product after thickener(s) have been added. .
 
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