Grease Thickeners

[Robertmet]

Lubricants are not my field but I came across a list of thickeners for grease.One of them was silica.Maybe I'm missing something but how can you use silica,very abrasive , in a lubricant ??

 

[electricpete]

Beats me. Here is a description of silicone grease, uses silicon oil as base lubricant and thickener based on "fumed silica"

http://en.wikipedia.org/wiki/Silicone_grease

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[electricpete]

... if you follow think link for silica fume above you see

Silica fume consists of very fine vitreous particles

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[unclesyd]

Here is the basic information on grease.

http://www.reliabilityweb.com/art04/understanding_grease.htm

 

[Robertmet]

Thanks. The magic term is then 'silica fume' which is very fine amorphous [non-crystalline ] SiO2 .That should have little abrasive action.

 

[rmw]

I read the link Unclesyd gave. While well written and informative, I think he left out one important thing. Greases should never be mixed. Mixing can and most often does cause the lubricants to separate from the soaps causing lubrication failure.

rmw

 

[romke]

all "lubricating greases" can technically be called a "gel" - a lubricating fluid with a colloidal suspension of a thickener in it that gives the grease its structure. the thickener can be a metal soap (as in the most common greases) but it is also possible to make a grease with more exotic thickeners, eg silica or "claybased" compounds. in the case of silica it is not just ordinary "sand" but a very specific compound with very small dimensions without sharp (and abrasive) edges. the amount used is usually about 5-10 %, the rest of the grease is nearly all base oil or another type of fluid that can be used as a lubricant, often some extra additives (antioxidant, antiwear) are included. the type of thickener has a large influence on the behaviour of the grease - depending on the type used you may end up with a very "thick" grease or a semifluid grease. due to the colloidal structure greases usually have a nonnewtonian character. of course when you add a lot more "thickener" into less fluid the mixture can be very abrasive, as you can see for example in the dredging industry where sand dissolved in water (also a "gel") is pumped through pipes. usually the impellorblades in the centrifugal pumps that are used, only last for about a week and then need to be reconditioned over the weekend...

 

[coatingengineer]

Hi.

For greases to work, as you're aware, there are a number of rheological requirements to be met.

Parameters include: adherence, retention of properties under both shear & temperature, and some degree of fluidity. (More viscous materials risk more "work", especially in start-up.)

What kind of grease are you using? Generally, heavier duty greases integrate bases like ISO 460 (SAE 140). Thickeners can include: soaps of lithium, sodium, calcium (hydrated and anhydrous, polyurea and clay.

For more information, I'd look to The National Lubricating Grease Institute (NLGI):

http://www.nlgi.com.

Good luck!



William Gunnar

http://www.IndustrialCoatingsWorld.com

 

[davidtb]

Interestingly enough, there's much more concern about mixing greases than mixing oil viscosities.