Machinery Lubrication

Machinery Lubrication Sept Oct 2015

Machinery Lubrication magazine published by Noria Corporation

Issue link:

Contents of this Issue


Page 14 of 71

10 | September - October 2015 | Grease is a complex material that can be manufactured using dramatically different base oil viscosities and thickener types. Variations in soap content and composition can be expected as grease batches are made. Grease testing is primarily performed to support quality assurance and marketing of new grease products. Cone penetration is considered the most important of the labo- ratory-performed tests. While this ASTM test method provides a measure of grease consistency or stiffness, it is not well-suited for used grease, as it requires a large sample, which precludes its use for in-ser- vice testing. Alternative tests to cone penetration have been developed in which touch is utilized to characterize grease stiff- ness, but these test methods typically are crude and do not lend themselves to accu- rate results or trend analysis. However, other options that involve the use of stress rheometers have proven to be not only acceptable but preferred for monitoring the consistency of new and in-service grease. Problems with Cone Penetration The cone penetration method employs a weighted cone that is dropped into a fixed- size volume of grease for a defined time period. The depth that the cone is able to penetrate the grease is used to rate the grease's consistency with a scale developed by the National Lubricating Grease Insti- tute (NLGI). This test utilizes three different cup and cone sizes. The cups vary from a large (full scale) size of about 290 milliliters (ml) to a small size of 3.8 ml (one-quarter scale). The cup size determines the amount of grease required to conduct a test. Test samples obtained from field sources are generally much smaller than would be required for a cone penetration test. Many sumps in field-lubricated applica- tions contain less total grease than the cup volume of 290 ml, which is the minimum quantity needed for the full-scale test. Even a volume of 3.8 ml (one-quarter scale) is still greater than the majority of samples obtained from the field. Since more grease is needed to conduct a penetration test COVER STORY By Bryan Johnson, arizona PuBlic service A Better Way to Test Grease Consistency

Articles in this issue

Links on this page

Archives of this issue

view archives of Machinery Lubrication - Machinery Lubrication Sept Oct 2015