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BR Standard class 6 No. 72010 'Hengist' and Clan Discussion Thread

Discussion in 'Steam Traction' started by Bulleid Pacific, Nov 23, 2009.

  1. Flying Phil

    Flying Phil Part of the furniture

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    Stress relieving after casting or welding is very important. When I started my engineering career I expressed surprise at the number of castings just left outside the main works - some had clearly been there for years before going in for machining. It was explained that they needed to "settle". When I moved to the welding shop a big welded fabrication had to be put under a "top hat" oven and cooked for two days at about 500 degrees C before being allowed to slowly cool and then go for machining.
    These days I suspect sometimes that the cost is regarded as a luxury by the accountant...and fought to be retained by the engineers!
     
  2. W.Williams

    W.Williams Well-Known Member

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    Would this not be a contradiction in terms?

    Dimensional instability in cast and welded parts or structures arises due to residual stresses inside the component that are left over from manufacture. In short, stresses that are competing against one another and when viewed across the structure are unresolved.

    So a part is either dimensionally stable or it is not. This is often a result of the residual stresses being heat-treated out or not. Castings are often left for years as above to resolve themselves, however welded steel structures are different.

    If there has not been a heat treat the part of structure may well continue to deform, and when you machine it it will deform further due to the loss of material on a given surface/plane.

    In large structures this is less concerning as tolerances are higher, however in smaller structures with tight tolerance requirements, one would argue the only way to ensure good geometric conformity over the long run it to bake it in an oven for a specified time. Particularly if there is a lot of weldment in the part.


    As for luxury v necessity, if welding codes are not followed, and structural parts fail, it is advisable suitable fallback/indemnity is in place. By not removing residual stresses in welded structures, you are practically inviting stress cracking in the future. When will depend largely on cyclic loading, but this too is a calculation and cracking may occur before a predicted outcome. Much of this of course depends on the loading. Frame stretchers will be seeing significant loads.
     
    Last edited: Jun 9, 2021
  3. ianh1

    ianh1 Member

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    All castings are being heat treated. There is a photo in the build diary that shows the bogie wheels being heat treated

    https://www.theclanproject.org/build/Clan_BuildDiaryMonth.php?buildyear=2018&buildmonth=03

    This week we're concentrating on the fit of the front firebox support stretcher and the dragbox. A lot of metal has to come together at the rear of the main frames.
    Capture.JPG

    This partly exploded view attempt to show how the red main frame plates and the blue frame extensions have to sit on the grey "wing" plates of the front firebox support stretcher. Bolted to the bottom of the wing plates are the rear spring hanger brackets for the trailing driving wheel. Work is in progress to make sure that the frame plates are sitting tightly on the wing plates.

    We've also removed the dragbox from the frame extensions as we need to ensure that the dragbox sits tightly against the rear face of the frame extensions. Some fettling is required here.
     
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  4. Flying Phil

    Flying Phil Part of the furniture

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    Thanks Ianh, this is obviously a well engineered project and the way in which the various problems over the years have been resolved is fantastic - well done to the whole build team and supporters.
     
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  5. class8mikado

    class8mikado Well-Known Member

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    doesnt it make you want to grab a spanner !
     
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  6. northernsteam

    northernsteam New Member

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    ..yeah!!
    Just imagine having to undo and redo all those bolts to make sure it all fits together properly! That's where these projects get expensive and the facilities available at CTL make it so much easier than a draughty shed at a railway somewhere.
     
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  7. northernsteam

    northernsteam New Member

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    (Deleted in favour of direct correspondence)
     
  8. MellishR

    MellishR Part of the furniture Friend

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    Apologies if the question has been asked and answered earlier, but why do the frame extensions exist? Was that as designed by BR? Was it not possible in the 1950s to roll the frames in one piece each?
     
  9. LMS2968

    LMS2968 Part of the furniture

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    The trailing frames extensions are of shallower section to allow the ashpan to fit above them. To retain structural strength they have to be made of thicker material, so cannot be rolled as part of the frame plates.
     
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  10. 30854

    30854 Resident of Nat Pres

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    Reading that, my thoughts straight away turned to cast frames. That tech, from near the end of steam's reign (I think developed over the pond) was employed by Beyer Peacock, for their export market, but never seems to have found much favour here. Perhaps it just came too late in the day.
     
  11. class8mikado

    class8mikado Well-Known Member

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    Even the 'Jump' to bar frames was considered too much...
     
  12. 242A1

    242A1 Member

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    The cast steel bed complete with cylinders included appear to have been produced in 1929. Before this cast steel sides were produced with cast steel stretchers bolted into place as were the cylinder castings.
    For UK locomotive builders the cast steel bed was used for the export market, the NBLC built Class 25NC is one example.
    There was another way of achieving the advantages offered by these challenging castings which also delivered a substantial weight saving. The SNCF considered three types of frame. The first was developed by Etablissements Corpet-Louvet and was a welded H section, simple in construction and very rigid in the horizontal plane due to the bracing at horn gap level. The second was a monobloc type but using smaller castings welded together. The third was a tubular type of welded construction and this can be seen in the prototype SNCF Class 152P.
    Cast beds had to be imported but welding did provide a solution and the tubular section construction does offer further advantages. The Standards had to be built with the workshops that BR had. I wonder if any group will come into being determined to build a "Standard" as it should have been built as opposed to being dated and compromised from the start?
     
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  13. huochemi

    huochemi Well-Known Member Friend

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    It has been asked before. The problem is that the trailing frames (a) have to be shallower in depth to fit under the firebox but (b) cannot be very well stayed, to keep the area below the ashpan etc clear. This means that the frame plates for that section either have to be thicker or additional frame plates added. The LNER and the LMS used the latter, rather inelegant, method by having an additional frame plate outside the main frames although on the LNER (judging by images of the P2) the main frame plate is actually of full length. On the LMS Pacifics, there was a "three-ply" effect at the stretcher at the front end of the firebox where the main frame plate and the two trailing frame plates joined - see attached drawing of a Princess' frames. Bulleid introduced the globally standard concept of narrow bar frames for the trailing frames into the UK which was then adopted on the last two Duchesses and the BR Standard Pacifics. Even on locos with fabricated bar frames throughout, separate trailing frames were often (usually?) used. To cite an arbitrary example where I have the dimensions to hand), on the Chinese QJ 2-10-2s, the main bar frames are 140mm thick and the trailing frames are rather thinner at 77mm.
     

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  14. Hermod

    Hermod Member

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    Standard steam locomotives is good growing egoes but not for railways.
    As I read Cox he was no believer in it himself,but honoured of course being their chosen designer.
    Cox explains that steam locomotives are intended to be used an awfull lot of years and can never be built at such a rate and series that automobile efficiency can be applied.
    Optimun serie size is seven identical locomotives and a spare boiler.Boilers takes two times so long to repair as chassis and about 14 % of locomotives are under repair.

    UK railways after WW1 did not pay dividends and migth as well have been nationalised then.The ARLE locomotives proposal from NER (Q7 and B16 same boiler and cylinders) were something in that direction.
    In 1945 it could have been argued that driving wheels , boiler tube plates of one design and cylinders were the parts to be identical for all future locomotives until the next wave of ego tripers arives on scene.
    Let us say that five feet drivers and wide fireboxes over drivers was wish of the great leader and that Jarvis was mastermind.
     
    Last edited: Jun 11, 2021
  15. 242A1

    242A1 Member

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    The lessons of the French experience with the application of TIA were that boiler repairs became far less frequent so much so that it became possible to close many boiler repair facilities. Later it became clear that the boiler would seldom have to be removed from the locomotive in order for repairs to be carried out. This ties in with findings that a boiler and firebox need not be removed during the working life of the locomotive whilst also acting as a stress bearing member of the complete structure. Those that were uncertain of the effectiveness of their treatment protocols might want to make use of the "zip-on" boiler concept developed by Col. K. Cantlie which allowed for a boiler to be either removed or attached to a locomotive in around fifteen minutes.

    On the design front are we concerned with evaporation or specific steam consumption? If insufficient attention is paid to achieving the best SSC figures then you need a larger heavier boiler to deliver the steam you require to produce the power output you are required to achieve. And what power outputs are expected to be achieved and delivered for service? What are the traffic demands? The designers of the standards appear to have seriously misjudged the power outputs that were going to be needed to serve what might be called a more modern era.

    The GWR is reported as paying ordinary shareholders a dividend of 4.17% between 1929 and 1934 and this reached 6.14% in 1946/7; we are looking at a complicated situation here.
     
  16. Hermod

    Hermod Member

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    If boiler and chassis are mated for life it means no narrow firebox down between plate frames.
    That was stated explicitly by mr Witte after WW2 in germany.
    The best economy steam engine within Stephenson format is a two-cylinder compound with reheat.
    Maximum manual coal firing rate is around 1400 kg/h for one hour or less than 1000kg per hour for a shift.
    Best steam economy on french compounds were 5.1kg of 20 bar steam per ihph.
    It takes ca 1kg of coal to make 7 kg og steam
    A small boiler will use more coal on the move but less when stationary.
    In germany the crew feeling was that ideal steam locomotives were 1000 horsepower machines.
    P8s 4-6-0 from 1911 and Baureihe 50/52 from 1938 were scrapped last.
    Very close in size and concept to B1 and clas 9fs.
    Hanomag put a wide firebox on some new P8s for Poland 1924.
    https://en.wikipedia.org/wiki/PKP_class_Ok22
    Witte considered the grate of the BR 50 to big after WW2 and had some tests made with part of the grate made inactive.It gave a small improvement but not enough to warrant more changed.
    With the wisdom of to day it can be seen that the power from a BR class 6 could have been got from less steel and coal if made as a 2-8-0 with five feet drivers,Zara truck up front and some kind of balance thing like on the Nord 2-8-2 tanks in Paris or the big pacific Garrats for Moroco.
    East Germany built two examples called BR 25 .
    Powerfull ,fast and frugal but to late as Stalin outlawed new building of steam locomotives in 1953.
     
    Last edited: Jun 12, 2021
  17. Jimc

    Jimc Part of the furniture

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    I think sometimes enthusiasts misunderstand standardisation. I submit that the most important parts to standardise are consumables that need to be held in stock at the sheds. If you can sufficiently standardise those parts then there's an enormous saving to be made in the amount of spares stock you have to carry. Parts that are only exchanged at the factory are a bit less critical, especially if your heavy repair is sufficiently centralised. Next probably comes anything that can be prefabricated/prepared before the locomotive comes in the shops and which will speed turnaround. Note that if it's a large assembly then too many different types will take up a lot of storage space in the works and again its large lumps of capital lying about. BTW Cook reckoned that with nine 4700s only using the Std 7 boiler they had to watch the shopping carefully so they didn't end up with two exchange boilers being required.

    Cook records that by careful attention to water quality on the GWR, softening plants, better water supplies etc they managed to increase boiler life from around 400,000 miles to sometimes over 1,000,000, and from two boilers over the life of an engine to about 1.25. No doubt more could be achieved, but the economics of French lines seem to be very different from GB ones. Its evident from GWR loco cttee minutes that the cost of water supplies was a significant concern, and one presumes TIA put the cost of water up significantly, so savings on maintenance had to be balanced against that.
     
  18. 242A1

    242A1 Member

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    Why be concerned about a narrow firebox and fitting it between the frames? If you are desperate to have a narrow box you can have one and have it accessible too, there is more than one way of designing a locomotive frame. But if the boiler is going to last the working life of the locomotive anyway and it is designed to be easily and speedily attached or removed if the eventuality should by chance arrive what is the problem?

    Porta addressed the two cylinder general purpose compound concept in the Manchester Paper read before the Manchester Centre of the Institution of Locomotive Engineers. The proposed design was that of a 2-8-0, a version with a maximum axle loading of 13 tons for gauges of 3 ft, to 3 ft. 6 ins. and a version with a maximum axle load of 18 tons for standard gauge and beyond. These designs owed some of their thinking to the Italian "624" class making use of inside cylinders with valves actuated by external valve gear. The inside cylinders reduced radiation losses and inertia forces when compared with an outside cylinder fitted variant and also offered a slight weight reduction. The aim was for a locomotive that could maintain a dbhp in the order of 1,800 between the speeds of 30 and 70 mph. I know that the paper was read after the standards were designed but Porta had been developing his ideas and proving his concepts since the 1940s.

    The fitting of stokers to locomotives was found not to have a significant impact on fuel economy particularly in France. So being concerned with manual firing rates is a bit of a distraction. Some railways used to select for physical suitability and train the firemen to keep the pressure on the mark. I find the figure of 1,400 kg perhaps understandable but cannot help but wonder what Marty ate for breakfast, he could shovel 4 tons an hour.

    When it comes to your boiler you have to consider unburnt fuel losses and you also tailor your design to suit the quality of fuel available to you. In North America a boiler with a grate area of 182 square feet was designed which had a boiler barrel diameter of 9 ft. 2 ins. It could burn 18 tons of fuel per hour and evaporate 55 tons of water in the same period. Another boiler with a grate area a little under 40.5 sq. ft. would burn 4.5 tons of fuel per hour and would evaporate 23.5 tons of water when doing so. The first boiler was designed to burn low grade lignite whereas the second boiler was French and though French coal was not the best quality this boiler would have been well catered for with bituminous product. A lower quality of fuel drives the weight of your locomotive upwards and it can be ruinous for your power to weight ratio. And the same can be said for not managing your unburnt losses.

    The Standard Class 6 weighed 88.5 tons and was first built in 1951. For that locomotive weight, in the light of the lessons of the 1920s and 30s when it came to locomotive design, what sustained power output should have been expected?
     
  19. Cosmo Bonsor

    Cosmo Bonsor Member

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    "I think sometimes enthusiasts misunderstand standardisation. I submit that the most important parts to standardise are consumables that need to be held in stock at the sheds. "
    This.
    A spokesman for a current loco builder said 'Locomotives are the only product you sell the prototype of of'. I suppose you can add ships.
    The standardised bits are always things like injectors, clacks (SECR ones are very good), brake ecjectors, brake blocks and so on.
    They often have many small parts that need servicing and replacement. This has a bit affect on inventory costs and the hidden cost of workshop knowledge.
    I have puzzled for a long time why companies standardised on components that anecdotally proved poor and persisted with them. Sunk costs?

    As for wheel size, coupled wheels around the 5' and a little more seemed fine for speeds up to about 70 mph given proper balancing, axlebox design and lubrication. It gives you good acceleration with a moderate top speed. It seems to be a solved problem if the French example above is anything to go by. I bet they were fun to be on the footplate too.
     
  20. Hermod

    Hermod Member

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    I would commit murder for reading that paper.Is there a link somewhere?

    My ideal 6P has a single low pressure cylinder between frames .
    Within UK loading gauge there can be a 20 inch outside high pressure cylinder going to driver 2 or 3 .
    If going to first driver it can be 24inch sitting between wheel and coupling rods.
    The mid inside low pressure piston can then be ca 30 to 36 inch diameter.
    On the other outside there is a conrod with a mass going forward and backwar suitably phased and eliminate a lot of unpleasant vibration. The SNCF 240 was 114 tons so 88 tons 6P can be made to give 70% of what the 240 Chapelon could give. A little more because a two cylinder compound is a little bit more efficient than a fourcylinder
     
    Last edited: Jun 12, 2021

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