<VV> lube oil contamination

[Jay Maechtlen]

Hi, Bob-
It was contained in one of the replies to "Setting part cleanliness 
specifications for gears"
It's the last couple of lines in romke's response on 9 sept.

Helpful Member! romke 
<http://www.eng-tips.com/userinfo.cfm?member=romke> (Automotive) 	
9 Sep 14 3:46

i think it will be very hard to come up with a usable specification that 
not interferes with normal assembly and operating practice. in the past 
there have been indications that when reducing 
<http://www.eng-tips.com/viewthread.cfm?qid=371258#> the particle count 
of the lubricant, wear on roller bearings could be reduced quite a bit. 
however, trying to carry this out in standard assembly was shown to be 
incompatible with normal production requirements. if you want to reduce 
the particle count you will need to assemble in a "clean room" and use 
"superclean" lubricant that is filled into the gearbox through a 
suitable filter. as soon as the gears start to operate however they will 
start generating lots of debris initially and still quite a bit after 
properly run in.

in theory these wear debris could be taken out by a suitable filter - 
the problem being that you need a large capacity filter with suitable 
filter size characteristics. since gears (unlike a properly designed 
hydraulic system <http://www.eng-tips.com/viewthread.cfm?qid=371258#> 
that can be made clean with suitable filtering and can stay clean 
afterwards) gears will continue to add wear debris in a rate that a 
suitable equilibrium can not be achieved.

a better way to protect 
<http://www.eng-tips.com/viewthread.cfm?qid=371258#> gears and bearings 
would imo be to include a magnetic plug to collect most of the metallic 
wear debris to keep them away from bearings and gears once "caught"

you should also be aware of the fact that both in gears and in roller 
bearings the lubrication is of the elastohydrodynamic variety - meaning 
that the lubricant film may be as thin as 0.1 micron at high loads. that 
means that minute sized debris still can do a lot of damage, so small 
that filtering them out with normal filtering equipment is impossible.

perhaps the best way to assure long gear and bearing life is to make 
sure that the gears are run in properly, which may call for the 
temporary use of a specialized running in lubricant. one other thing to 
consider is that since lubrication is of the EHD variety, complete 
separation of mating surfaces will never be possible at all speeds and 
loads and thus gears or bearings will fail eventually due to surface 
fatigue and the wear debris that result from it.

just one more remark: life of gears and bearings can be shortened 
exponentially when small amounts of water are present in the lubricant - 
even 0.1% can reduce the lifespan quite considerably.

On 9/13/2014 9:57 AM, BobHelt at aol.com wrote:
> Jay,
> Not to question the comment, but I was unable to locate the source. 
> could you be more specific as to just where this comment was made. I 
> couldn't find it.
> Bob Helt
> In a message dated 9/12/2014 9:04:56 P.M. US Mountain Standard Time, 
> virtualvairs at corvair.org writes:
>
>     On an engineering forum (eng-tips - Transmission, Driveline, Hybrid
>     Drive engineering Forum
>     <http://www.eng-tips.com/threadminder.cfm?pid=78&page=1>), I saw the
>     following:
>
>     " life of gears and bearings can be shortened exponentially when
>     small
>     amounts of water are present in the lubricant - even 0.1% can
>     reduce the
>     lifespan quite considerably. "
>
>       interesting...
>
>     -- 
>     Jay Maechtlen SoCal '61 2-dr modified w/fiberglass skin,
>     transverse 3.8
>     Buick V6 TH440T4 trans
>


-- 
Jay Maechtlen SoCal '61 2-dr modified w/fiberglass skin, transverse 3.8 
Buick V6 TH440T4 trans


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