Q & A

"I've heard the term 'slumpability' used when referring to greases. Can you explain what this is and why it is important?"

Yes, the word 'slumpability' sounds strange and may conjure thoughts of your 3rd grade teachers repeated reminders to sit-up and quit 'slumping' in your desk.

The meaning of the word as it applies to greases is similar. The slumpability of a grease relates to how feedable it is, or its ability to be drawn into a pump. For example, if grease is pumped from the bottom of a supply tank through a pipe, it is essential for further grease to continually take its place for the pumping to be able to continue. Otherwise, the pump will lose its prime. The grease must be able to fall or 'slump' from the sides of the tank to the pumping zone.

Fibrous or stringy greases typically have better feedability or slumpability characteristics than greases that are buttery (not fibrous). However, these same greases on occasion can prove more difficult to push downstream of the pump through piping.

Currently there is no standard test for slumpability.

Today's Tip

• The main factor that limits the use of mineral oils in high temperature applications is their oxidation stability, rather than the viscosity thinning or thermal stability. In the presence of air, it is generally not advisable to use mineral oils in any application at temperatures above 200 degrees F (93 degrees C).

• Tomorrow (Aug 1) is the last day to save $100 with the Early Bird Discount when registering for Practicing Oil Analysis 2001! Register now at: http://www.noria.com/conference/

Each tip published will earn the sender $10. Send your tips to webmaster@noria.com or fax to 918-746-0925.

Book Bits

From the book "Proactive Maintenance for Mechanical Systems":

Lubricity Stability

Lubricity stability is a measure of a hydraulic or lubricating fluid’s resistance to the degradation of its lubricity during storage and service. Lubricity is a liquid’s ability to impart low friction when surface contact or boundary lubrication conditions exist. A fluid that forms a film of low shear strength between two contacting surfaces is one with good lubricity. This lubricity is directly related to the chemical structure and the chemical affinity of the fluid for metals.

When a full fluid film is present between moving elements of a hydraulic component, hydrodynamic lubrication exists. The fluid film between mating parts decreases in thickness whenever the following occurs:

• Load increases

• Fluid viscosity decreases

• Surface velocity decreases

The thickness of the fluid film decreases until eventually the laws of hydrodynamics no longer apply since the effects of boundary or surface forces are no longer negligible. As the separating film becomes still thinner, ultimately metal-to-metal contact of adjacent asperities occur.

For more information about the book "Proactive Maintenance for Mechanical Systems" go to:

http://www.noria.com/secure/product_detail.asp?catalogid=48

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Lube-Tips is published by Noria Corporation. Oil Analysis and Lubrication Experts