[modeleng] Re: Lubricating oils

Geez Phil, with all the engines I've pulled down over the years, and 
that's considerably more than a few, I've never come across a sintered 
spigot bush. Just lucky? I've made plenty of replacement bushes with 
plain old bearing store PB tho', and with a light greasing on assembly 
they last for years.
Phill Smith wrote:
> G'Day Jesse,
>
> I'm glad that at least one person enjoyed my rant on bearings. I hope all 
> will forgive my typo's and misspelt words, as my spell checker in Outlook 
> Express has died again, and this time I'm not going to waste my time trying 
> to fix it.
>
> As for being refered to as "Dr Phill".... I think I have seen a couple of 
> minutes of that show, and don't know if it is a complement or not.... 
> <LAUGH>
>
> Ok, lets answer your questions...
>
> Sintered bronze bearings came about as a solution to an age old problem. The 
> problem is, lubricating bearings that are damn near imposible to get to, and 
> are imposible to set up remote oiling for. One of the most obvious 
> situations is for the spigot bearing mounted in the flywheel of your car's 
> engine. The sucess of the sintered bronze bearing is because it is porous. 
> It is made by granulating bronze to a small size, then putting it into a 
> former and heating it only just enough to melt the surfaces of the granuels. 
> This enables them to bond together and still retain it's porous nature. The 
> porousity enables the bearing to retain oil for lubrication, for very long 
> periods of time. Ten to fifteen years is not not unusual an unusual life for 
> a sintered bronze bush. The porous nature of the sintered structure also 
> permits the foreign bodies to be lodged out of the way from being in contact 
> with the shaft.
> The problems with sintered bronze are as large as the benefits. It is very 
> soft, so is easily deformed, when compared to a normal plain bronze bush. 
> Once they start to compress, the access for the lubricant is restricted, and 
> they start to wear dramatically due to both lack of lubrication, and, the 
> embedded foreign bodies are no longer tucked away, but are now protruding. 
> The softness of these bearings limits the loads that can be placed upon them 
> to less than a 1/3 of that permisible with a standard plain bearing. The 
> other problem with sintered metals, is that the surface of every granual has 
> an oxide layer. This layer, in the harder sintered bronze materials, can 
> cause bluntening of your tooling if you try to machine it. They also require 
> hardened steel pins/shafts to be used, otherwise the oxides will wear the 
> shaft.
> Sintered metals are not designed to be machined. This is because the forces 
> involved in machining cause compression of the grain structure and smearing 
> of the grains across the pores. If you must machine it, use very sharp 
> tooling with a positive rake with light cuts and fine feeds, as this will 
> help reduce the problems caused by machining.
>
> Next question..... Anyone? <GRIN>
>
>
> Cheers,
>
> Phill.
>
>
> ----- Original Message ----- 
> From: "Jesse Livingston" <fernj1@xxxxxxxxxxx>
> To: <modeleng@xxxxxxxxxxxxx>
> Sent: Friday, June 05, 2009 2:09 AM
> Subject: [modeleng] Re: Lubricating oils
>
>
>   
>> Blimey Dr.Phill,
>>
>> That was a good lecture on bearing materials and I enjoyed and was
>> intellectualized by it .  I assume that by PB you mean phosphor bronze and
>> not powdered bronze like "Oilite®".  Sometimes I worry about the powdered
>> "sintered" bronze bushes I have used as the material seems to dull HSS 
>> tool
>> bits for some reason.  I know it holds oil well , but still I wonder if it
>> is not abrasive to some extent.  You left that material out of your 
>> lecture
>> professor so would you mind elaborating on the subject?
>>
>> Oh, congratulations on having the entire set of Audel's Mechanics and
>> Engineers Guide from 1921.  My set shows considerable wear as my father
>> probably used them when he was attending Mississippi State A & M college,
>> plus I use them extensively when designing new projects for magazine
>> articles.  The covers are in pretty fair shape, but the index pages are
>> loose in some volumes.
>>
>> Jesse in still drizzly Troy, TN USA
>>
>> Jesse,
>>
>> I picked up all 8 books as a set when I purchased them on Ebay, and in
>> perfect condition. I did notice later, that they showed up on ebay as
>> individuals, but would have been expensive to buy like that.
>>
>> As for oil draining from stationary bearings...... Yes you, and Audel, are
>> absolutely correct. But the drainage rate is dependant on 3 factors.
>> Temperature of the oil, size of the drainage oriface, and, time. In our
>> close tollerance bearings, compared with a 6" bearing with a free running
>> fit giving (for heavy loads) of 10 thou' clearance, drainage is very slow
>> and is unlikely to lose enough oil to stop boundary film lubrication in 
>> the
>> time it takes to refuel, unload passengers, take on water, chat up the
>> passenger kid's aunty etc. Yes, I was terrible when I was single. I had a
>> built in compass the would point me at every single woman within 100
>> yards.....
>>
>> As most of you will know (from reading this lists postings) that I am
>> getting ready to build a Juliet as a teaching instrument for my eldest son
>> as he builds one. Going through the original articles in the ME magazine,
>> has shown several areas of poor engineering. This is in the area of 
>> bearing
>> surfaces and materials. LBSC wrote the articles for the complete novice, 
>> so
>> I was not expecting high tech bearings. Or was I? Perhaps I was, as why 
>> else
>> am I going to change them. Things like crank pins, eccentrics, cross head
>> guides, expansion links, die blocks, and valve gear pins, will now be
>> hardened and polished high tensile steel. Modern hardening steels are
>> relatively inexpensive (compared to LBSC's time), easily obtainable, and
>> easily heat treated at home. The advantages of making these small changes,
>> show up over the long term as they will wear (as will their matching
>> componants) at around 10%, or less, of those materials originally 
>> selected.
>> This works because the difference in the materials becomes greater. Look 
>> at
>> the bearings in your cars engine. They are really soft compared to the 
>> crank
>> shaft. An even better example is the cam shaft and it's bearings. Hardened
>> steel on (what is essentially) white metal bearings. Your camshaft wears 
>> at
>> a much lower rate than the crank shaft, and not just because it is turning
>> slower, but because the difference between the dissimilar metals is 
>> greater.
>> The use of a bronze bush, is to be able to carry a larger load on the
>> bearing than a softer material can accomodate without deformation, at the
>> same size. The softer material will give you a better bearing, but must be
>> much larger to take the same load without going out of round. GM will work
>> Ok on polished mild steel pins/shafts etc, just.... PB is designed for
>> polished hardened steel pins ONLY. It will destroy a mild steel pin at the
>> same time as wearing itself. But when used on a really hard material, will
>> last a very long time. GM also prefers hardened steel pins.
>>
>> Bearing wear occurs due to 2 main factors.
>> 1) bearing being overloaded and deforming. This happens to the softer of 
>> the
>> 2 materials first. The case 2 takes over.
>> 2) foreign bodies. Foreign bodies can be any thing from dirt, soot, dust, 
>> to
>> bearing material particals. These items behave in 2 ways. Firstly, if they
>> are small and/or sharp enough (dust, soot, and bearing fragments) they
>> become embedded in the softer material of the bearing and then act as a 
>> lap
>> on the harder surface. This then accellorates the process as it removes 
>> more
>> of the harder material, which in turn also becomes embedded in the softer
>> material and hence wears away the pin/shaft. Secondly, if they are large
>> and/or blunt they act as grinding paste and wear away the softer material 
>> at
>> a faster rate than they do the hard material.
>>
>> This is why really hard pins/shafts with PB bushes is favoured as a plain
>> bearing. The PB is hard and strong enough to withstand high loads and some
>> abbrasion. While the really hard pin/shaft is highly resistant to lapping
>> when polished. If unpolished, small pieces will be torn from the surface 
>> of
>> the pin/shaft and be embedded into the PB to ask as a lap.
>>
>> There is one last factor for the selection of bronze on hardened steel....
>> Coefficient of friction. Bronze has a very low coefficient of friction, 
>> and
>> so has hardened and polished steel.
>>
>>
>> Oh dear..... It looks like I digressed a bit here..... Sorry Gents. I seem
>> to have digressed to giving the lecture "bearings 102", so I'll leave it
>> there.
>>
>>
>> Cheers,
>>
>> Phill.
>>
>>
>>
>>
>> ----- Original Message ----- From: "Jesse Livingston" <fernj1@xxxxxxxxxxx>
>> To: <modeleng@xxxxxxxxxxxxx> Sent: Thursday, June 04, 2009 9:27 PM 
>> Subject:
>> [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.
>>
>>
>> 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
>>
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>>
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