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"Our supplier recently informed us about a new low-noise grease manufacturing process for motor greases. This appears to be an exercise in repackaging a product to sell it under a different name at a premium price. Does this new grease really offer extra value or should I continue with what I am currently using?"
Low-noise level greases are those greases that have been purified sufficiently so that there are no, or at least very few, large particles in the grease that could enter into the load zone and cause rotating elements to bump and grind, generating noise in the bearing.
These products were originally constructed for high-precision applications where the rise and fall of the bearing elements over contaminant particles entering the load zone through the grease could damage either the bearing or the driven component.
Let's take a look at a few issues surrounding this type of product. First, there are plenty of everyday applications where low-noise grease is highly desirable. The motors that control your stereo electronics, computer drives and other micro-motor applications would clearly benefit from low-noise or high-purity greases.
Second, bearing noise is eliminated by the removal of particles or contaminants that could cause the element to bump or impact the raceway. It makes sense that if there are contaminants that are large enough to interfere with the element's uniform movement through the load zone, that under the right loading conditions the contaminants could possibly have some effect on bearing longevity and motor reliability.
This concept is consistent with the idea that particles in fluid systems can enter load zones and compromise load distributions, race and element surfaces, and eventually component and machine lifecycles.
Also, there are several measures of grease quality. Grease cleanliness is characterized by the noise the grease produces in a bearing test cell. Standard off-the-shelf products are only visually checked for contaminants. The conscientious grease manufacturer would buy high-purity and high-quality materials from suppliers who demonstrate consistent quality.
However, without testing the raw materials and the final product for contaminants, it is impossible to determine just how much solid contaminant is in the final product.
There is a good argument that could be made for the use of low-noise grease in large grease-lubricated industrial motors from a reliability perspective. It is likely that the improvement in motor bearing life would cover the cost differential for the low-noise grease product, assuming that the thickener, oil viscosity and other properties of the grease were acceptable.