[modeleng] Re: Lubricating oils

As I am sure our resident ME Phill knows, oil will drain from a stationary 
bearing or at least that is what my 1921 Audel's manual says.

Phill, did you ever get the entire 8 books in that Audel's series you found 
on ebay?  If you are only missing #8, don't worry as it deals with 
electricity and not steam.

Jesse in rainy Troy, TN USA

> Ron,
>
> With really small bearings, you can take advantage of the excess 15W40. 
> The
> basic rule is, the bigger the bearing (diameter) the thicker the oil. The
> smaller the bearing the thinner the oil. This is because the surface 
> speeds
> are generally in the same range, but the clearances are shrinking as the
> bearing decreases in size. As the clearances decrease, and the RPM 
> increases
> to maintain the surface speed, the shear stress of the oil becomes 
> greater,
> and hence the pwer being absorbed also increases. This is counteracted to
> some degree by the heat generated by this process, which thins the oil, 
> but
> not enough unless it is over heated. If the bearing is turning slowly, 
> then
> you are often better of using a thicker oil. Very few 3.5" and 5" gauge
> loco's are driven at scale RPM. This is partly due to the scale effect of
> miniaturization. Basically, properties don't change, just the quantities.
> Therefore, things like the expansion rate of steam is the same, regardless
> of the size of the engine. THEORETICALLY, a miniature staem loco, can go
> just as fast as the prototype. Unfortunately, they can't due to ballancing
> dynamics, mass stability, etc. etc. They just fly of the track, before 
> they
> come anywhere near reaching thier potential. Which brings us back to the 
> RPM
> of operation. At 3/4" scale, the scale opperating speed is 1/16 of the 
> full
> size. So assuming you are racing around the track at 5 mile an hour, which
> is pretty typical for what I have seen, then you are doing a scale speed 
> of
> 90 miles an hour..... Hmmmm..... I doubt whether many full sized shunting
> engines did that speed...... Full size speed here, was 50 miles per hour 
> for
> goods services. That makes a scale speed of 3.125 miles per hour. That's a
> pretty slow walking speed.... If you are operating at full size RPM,
> approximately 300 RPM, then you are better of using a thicker oil than a
> thin one. The boundry film pressures are lower at 300 RPM than at 600 RPM.
> and hence the thinner oil used for 600 RPM will not generate enough 
> pressure
> in the boundary layer to keep the 2 components apart. That's when wear
> starts.....
>
> Slideway oil is good stuff, on your machinery. But, not always for
> everything else. Take the tacking agent for example. It "tacks" the oil,
> only after it has stood still for a while. It has no useful effect while 
> the
> bearings are moving. If you let it sit and "tack off" and then start 
> moving
> the bearing again, it imeadiately reverts to it's normal liquid nature 
> until
> it stand still for a while again. So the tacking agent can make clean-up
> after running harder. But the other aditives are excellent, for our use, 
> as
> long as they don't get to hot. I know that most of the tacking agent don't
> like heat.
>
> I hope that gives you all more food for thought.
>
>
> Cheers,
>
> Phill.
>
>
> ----- Original Message ----- 
> From: "Ron Head" <ronald.head@xxxxxxxxxxxxxx>
> To: <modeleng@xxxxxxxxxxxxx>
> Sent: Thursday, June 04, 2009 1:32 AM
> Subject: [modeleng] Re: Lubricating oils
>
>
>> Some interesting replies so far!
>> The preference seems to lean towards heavier oils, perhaps with a
>> tackiness additive.  I was surprised to hear that some folk use steam oil
>> for everything!
>>
>> I've always been reluctant to use motor oil in anything other than a car
>> engine, as I don't know what effect the detergents have on bronzes etc.
>> Mind you, my current car is a diesel which uses the most expensive
>> synthetic oil imaginable, so I've got plenty of surplus 15W40 doing
>> nothing!
>>
>> I also have some Mobil Febis K68 slideway oil in my shop, which I use on
>> my lathe bed.  This has a tackiness additive, so it might be suitable for
>> motion....who knows?  Anybody tried it?
>>
>> Regards
>> Ron
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