[GreenKeys] [External] Re: Lubricating a 15 printer

[Jones, Douglas W]

From: Richard Knoppow [1oldlens1 at ix.netcom.com]
> I want to address one thing: in this article he mentions that
> Shell oil warns about mixing greases with different thickeners.
> The question remains to me what did the original engineers
> want and what currently available material will serve the purpose.

All greases are oils of one kind or another thickened with something so that the oil doesn't get squeezed out of where it is needed.  In many cases, the nature of the thickening agent doesn't really matter to the function of the grease, just the mechanical and lubricating properties of the result.  There may be several different ways to formulate a grease that will do the job quite well.

What I recall from researching the grease issue is that there are two basic categories of thickeners:  Soaps and clays.  The challenge is that in some cases, when two different greases are combined, even though the greases may have identical lubricating properties when used in pure form, the combination can go bad.

A typical grease failure that can result from mixing greases is the separation of the thickening agent from the oil.  Either thickening agent, alone, will stay mixed uniformly with the oil, but when you mix the two greases, the thickening agents interact, binding to each other more strongly than either one of them binds to the oil.  The net result is that the grease separates into oil that drips and leaks out of the area needing lubrication, leaving behind a sludge of congealed thickening agents that makes a very bad lubricant.

         Doug Jones
         jones at cs.uiowa.edu