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Grease Thickeners

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Robertmet

Materials
Aug 5, 2007
153
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 ??
 
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... if you follow think link for silica fume above you see
Silica fume consists of very fine vitreous particles


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



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