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Brake Block Specification

Discussion in 'Steam Traction' started by David Withers, Jan 7, 2019.

  1. David Withers

    David Withers New Member

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    I hope you're all having a good start to the new year, and best wishes for the rest of 2019.

    I understand that a high phosphorus content in cast iron brake blocks improves braking, as well as giving a longer life as it increases the hardness.

    I need to learn if high-phos brake blocks are suitable for use with newly-turned (hence relatively soft) tyres. Or should low-phos iron be used for 'running in', to give the tyres time to work-harden?


    Any help very much appreciated, as always.
     
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  2. gwalkeriow

    gwalkeriow Well-Known Member

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    We have just had delivery of brake blocks for our LBSCR coaches they have a 3% phosphorous content. One of our LBSCR coaches has newly retyred wheelsets we just use our standard block on it.
    When I was with BR we would frequently have vehicles fresh off the wheel lathe they would always have the standard brake block fitted.
     
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  3. David Withers

    David Withers New Member

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    Thanks for your reply, Gary.

    I wonder if BR and/or IOW ever checked the tyre wear rate between different brake block compositions?

    Since asking the original question, I've learned that the shedmaster of a prominent heritage railway instructs grade 220 (the old grade 14) or softer, with no added phosphorus.

    Also, Pete Briddon supplies soft blocks for new tyres and hard blocks for work-hardened tyres.

    The important thing for me is that the blocks need to be the sacrificial element, especially on this loco as it is a difficult and expensive job to turn the tyres on the driving wheelset (drive pin/arm forgings need pressing out and in, which can damage them). So I think I'll specify grade 220 with low phosphorus and see how they wear for future reference.

    Thanks again for your input; it all adds to the knowledge base!
     
    Last edited: Feb 21, 2019
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  4. Steve

    Steve Part of the furniture Friend

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    I always go for grade 14 iron, whether going on newly turned or old tyres. However, in a previous life I was involved with investigation into braking on underground mining locomotives and the conclusion reached was that the hardness was significantly affected by where and how the newly cast blocks were placed to cool down. If they are cast on a cold day and left in a draught they will be significantly harder than if left in a warmer environment.
     
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  5. David Withers

    David Withers New Member

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    That's very useful information about chilling, Steve. It reminds me (from 50 years ago!) that the camshaft lobes and rocker lever pads of our internal combustion engines were chilled during the casting process so as to give them a hard surface.

    It's also helpful to know that you specify grade 14 iron even for running against old tyres. Do you know if the foundry casts the standard mix, or is the phosphorus content increased?

    In most cast irons, phosphorus needs keeping very low as it promotes porosity and brittleness. I'd never come across deliberately increasing phosphorus until this brake block saga.
     
  6. 30854

    30854 Part of the furniture

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    Do we know when railway braking crossed the line from 'suck it and see' to something closer to empirical science? Presumably it was some time after IKB's 'tolerably useless' comment.
     
  7. Chuffington

    Chuffington New Member

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    I am told by the foundry most preserved railways spec grade 14 (the odd exception), and most mainline engines spec grade 17 the way they material is cooled also affects hardness.
     

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