[modeleng] Re: Lubricating oils

TEL,

Unlucky I would say...... <GRIN>

I've come across quite a few. Why did they put the sintered bushes in when 
they could have put a readily available sealed ball race in, beats me. 
Thinking about it, the engines that I have found them in everytime, was in 
Landrovers. And in both (really old) bedford trucks that I changed the 
clutches on for my uncle, after my cousins learnt to drive....... I couldn't 
tell you if the sintered bushes were original on the Bedfords, but they are 
on the Landrovers (Series 2A & 3, Discovery/defender until the end of the 
300 series engine). A few others were mix and match.

Straight PB works great, as long as it gets a good bit of grease on 
assembly. They don't last as long as the Sintered bushes though. Only 
because they run out of lubricant sooner. The "new" standard Landrover 
fitting proceedure is to soak in clean engine oil until the oil has soaked 
through. Remove form oil, and wipe clean with a rag. Push it into place, and 
then insert the removal tool (eg spare spigot shaft) all the way in and push 
it to one side, and roll it around the bush once or twice while keeping the 
pressure on as you roll. This expands the ends of the bush to lock it into 
place. (Unfortunately, it also ruins the porosity at the ends in the process 
and increases the diameter on the ends. An alternative could be to locktite 
it in place and then oil it.) Grease the bush before fitting the shaft. The 
oil in the sintered bush will keep the grease alive for many years. Why the 
"NEW" fitting proceedure? Because the bushes aren't made to have the same 
interferance fit any more, and this prevents it form coming loose.


Cheers,

Phill.

----- Original Message ----- 
From: "TEL" <tel47@xxxxxxxxxxx>
To: <modeleng@xxxxxxxxxxxxx>
Sent: Friday, June 05, 2009 5:49 PM
Subject: [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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