Bronze casting

Discussion in 'Metals' started by MattMaie, May 19, 2018.

Help Support HMEM by donating:

  1. May 19, 2018 #1

    MattMaie

    MattMaie

    MattMaie

    Well-Known Member

    Joined:
    Nov 16, 2012
    Messages:
    47
    Likes Received:
    4
    What are the general characteristics of bronze? I am interested in using bronze for foundry work in making my own castings for models. Particularly steam engines. I do know that bronze is softer than cast iron, which would mean that it would wear faster. Given that a model would not likely be under any significant load, I figure this would not be a problem. I am also to understand that bronze alloys expand under heat at different rates from cast iron. I look forward to your input.
     
  2. May 30, 2018 #2

    jimsshop1

    jimsshop1

    jimsshop1

    Steamman70

    Joined:
    Nov 23, 2016
    Messages:
    112
    Likes Received:
    25
    Matt,

    I have not cast Bronze but have cast a brass ring for a flywheel for the Atkinson Differential Engine I am building. I also cast some aluminum parts for same. The melting temp. of the brass was around 1750 degrees and was very scary when pouring into the mould. That is so much hotter than the ali I poured and I would rather melt ali any day than the brass. Be very careful when you do this. It was my first time casting and I advise you to read a lot if you have never done this before. There are a lot of good tips in the casting section.

    Jim
     
  3. May 30, 2018 #3

    abby

    abby

    abby

    Well-Known Member

    Joined:
    Apr 14, 2009
    Messages:
    399
    Likes Received:
    111
    Some mis-conceptions here , firstly the idea that bronze will wear more quickly than cast iron !
    In what context are you comparing the two ? phosphor bronze is used as bearing material because it has good wear properties.
    You use the term bronze but what do you mean ?Starting with a simple alloy of copper and tin as developed in the bronze age there are dozens of copper alloys that may be classed as bronze and each has it's own set of properties.
    By far the most common "bronze" alloy used for steam work is 85:5:5:5 , this being 5% each of zinc, lead and tin with the remainder copper , there are variations of this formula depending upon where you live.
    In the USA this "bronze" is called red brass , in the UK it is known as gun-metal.
    Gun-metal casts at around 1100°C depending upon the thickness of section , I have cast it at over 1150°C for casting of under 2 mm thick.
    A flux of borax , potash and powdered charcoal will help a clean , close grained melt and plunging a phosphorus-copper de-oxidising tube just before pouring will remove entrained oxides.
    Unlike brass gun-metal does not lose zinc due to contact with wet steam (de-zincification) , it doesn't have much anyway , which is why it is good for steam stuff.
    Gun-metal castings are a joy to machine , HSS tools honed with diamond lap will give a beautiful finish.
    Aluminium Bronze is hard and resistant to corrosion but it is difficult cast as it oxidises very rapidly.
    It needs to be bottom poured to avoid entraining oxide , extra care is required with patterns because it will contract greatly , and it needs very sharp tools for working.
    It doesn't silver solder very well either.
    Silicon bronze , which most modern sculptures are made from is very clean , it does not fume and requires no flux or chemical treatment , it runs like water and has a tensile strength comparable to steel and can be readily TIg welded but it also requires brand new tools for machining.
    This is just a tiny bit of information re:bronze.
    Steam engines do not run at very high temperatures so expansion is not an issue.
    You should bear in mind that most models are rarely run after the initial novelty has worn off so in reality wear is a secondary consideration.
    Dan.
     
    Jack3M, Henry, goldstar31 and 3 others like this.
  4. Jun 1, 2018 #4

    jimsshop1

    jimsshop1

    jimsshop1

    Steamman70

    Joined:
    Nov 23, 2016
    Messages:
    112
    Likes Received:
    25
    Very educating explanation, thank you.

    Jim
     
  5. Jun 20, 2018 #5

    Wizard69

    Wizard69

    Wizard69

    Well-Known Member

    Joined:
    Mar 9, 2013
    Messages:
    1,337
    Likes Received:
    266
    While already covered just realize that "bronze" covers a lot of different materials/alloys. Some of these alloys are extremely difficult to machine.

    The difficult to machine part i learned the hard way soon out of high school. I was working machine repair in a plant that had a bearing for a slide shear off its mounting bolts. The engineer at the time snickered when i said no problem we can just drill new holes in the bronze part and drill and tap the frame for new mounting screws. I was literally shocked at just how difficult that bearing material was to machine.

    The point here is to avoid assuming that an alloy like the many bronzes out there is soft, easy to machine or has the other commonly associated features. Bronze materials can have a wide array of mechanical features.
     

Share This Page