[TheForge] OT - Grease/oil seals for a gear box

[Bruce Freeman]

Well, the size is smaller:  3/8" shaft.  But also I am not familiar
with these seals, since I don't work on trucks.  From a Google search
they seem to be very simple ring seals, but I can't tell for sure.
What can you tell me about them?

On Fri, Jul 10, 2009 at 2:00 AM, Peter Fels & Phoebe
Palmer<artgawk at thegrid.net> wrote:
> Bruce;
>  Is there a reason not to use the sort of seals found on automobile and
> truck rear axles?
>
> Bruce Freeman wrote:
>> Well, I am surprised!  I always thought of packing seals for plumbing
>> applications like valve stems, where the rotating rate is about once
>> per day!  I've looked up a little and find some of them are good for
>> "high speed" applications, but I don't have enough info yet to
>> determine what RPM that means.
>>
>> Does anyone know what considerations go into selecting design criteria
>> and packing material for an application with speeds upwards of 2000
>> RPM?  (I'm shooting for 10kRPM, but doubt I'll get there with this
>> prototype, for reasons other than the packing seals.)
>>
>> It happens I might be able to modify my apparatus to incorporate
>> packing seals, depending upon the requisite design parameters.
>>
>> So I have some questions I'm hoping some of you can field:
>> 1) I presume that I want to box in the packing material with
>> close-fitting "washers".  Does it matter >how< close-fitting?  Or is
>> it OK if the packing can swell into  a gap between shaft and "washer"?
>> 2) Likewise, does the packing need to be completely contained, or is
>> it OK to compress it with actual (close-fitting) washers, rather than
>> the more elaborate "box" used in plumbing fixtures.  (Washers would
>> allow the packing to swell outwards from the shaft.)
>> 3) What kind of material would be appropriate?  (If you can reference
>> the McMaster webpage, all the better:
>> http://www.mcmaster.com/#packing-seals/=2ofm9j )  The shafts are
>> steel.  The housing is aluminum.
>> 4) The packing will be adjacent to a ball bearing in every case.  I
>> presume I'll need a "washer" to isolate packing from bearing?  (Lest
>> there be friction between inner race of bearing and packing.)
>>
>> Again, your advice will be appreciated.
>>
>> On Thu, Jul 9, 2009 at 1:57 PM, Peter Fels & Phoebe
>> Palmer<artgawk at thegrid.net> wrote:
>>> Bruce..there should be a huge selection of standard oil/grease seals
>>> available if your shafting is standard sizes.
>>> Alternately, you could take some teflon packing cord and fake up a
>>> compression seal that ought to do fine. A home made O ring seal isn't
>>> all that hard but will have a shorter life, depending on the finish of
>>> the shaft.
>>>
>>> Bruce Freeman wrote:
>>>> I'm constructing a simple gearbox for a mechanism I'm playing with.
>>>> The gearbox itself is of no importance except as to provide power to
>>>> the mechanism, and the nature of the gearbox is such that I cannot
>>>> simply buy a commercial unit.
>>>>
>>>> Perhaps naively, I simply mounted sealed ball bearings into
>>>> appropriate recesses in the housingn, counting on the small clearance
>>>> between bearings, shafts and housing to  seal against oil leakage.  No
>>>> go.  The oil leaks right out pretty quickly.  Grease works better, but
>>>> also leaks.  Loss of grease is not a problem - the potential for
>>>> contamination of the driven device is the problem.
>>>>
>>>> Next I tried sealing between bearings and shafts or housing with a
>>>> medium-strength "lock-tight" product.  No go.  Oil leaks right out
>>>> when gearbox is run.
>>>>
>>>> I could go to a product like RTV rubber, but I'd probably never be
>>>> able to change out the bearings again if I did that.  Still I may
>>>> consider it.
>>>>
>>>> I'm looking for other ideas.  I'd prefer not to remanufacture the
>>>> housings, but  could do that if necessary.  For example, I'd have to
>>>> do something like that if I went to O-ring seals.  However, I'm not
>>>> convinced O-rings would do a better job, so am not ready to take that
>>>> particular step.
>>>>
>>>> How is this done in commercial mechanisms?
>>>>
>>>> Any suggestions would be appreciated.
>>>>
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>>
>>
>>
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-- 
Bruce
NJ

The total lack of evidence is the surest sign that the conspiracy is working.