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Thread: porosity

  1. #1
    Join Date
    Mar 2006
    Location
    Waikerie SA
    Posts
    6

    Default porosity

    I have been making bells using traditional loam mould for some time I have made around 20 bells all with relative success. The last batch looked fantastic when cast but on fettling I discovered they are all riddled with porosity. Does anyone have any suggestions what I may have done wrong this time?
    Here is some pic of how I do the process https://www.stonevahestate.com/bells/

    bells6.jpgIMG_20211012_115150.jpg

  2. #2
    Join Date
    Apr 2018
    Location
    Drouin Vic
    Posts
    382

    Default

    Hi Vin, I was hoping someone with far more experience than me might reply to your post but having been doing some limited research in preparation for a little bit of yellow metal casting, it seems likely that the porosity is due to an oxidising condition in the melting process, i.e. a lean burn, resulting in gas absorption into the molten metal that is then released after pouring. Did you de-oxidise the molten metal before pouring?
    It would be great if you could post a thread describing how you did the swept molds, even if you used the same photos as your link but with some description attached.

  3. #3
    Join Date
    Mar 2006
    Location
    Waikerie SA
    Posts
    6

    Default Thank

    Thanks Pete, the melting has not changed, same fuel, same furnace, same pouring. I do think the problem has to be mould related, unfortunately I continually make small changes making the moulds which has definitely improved the surfaces and out comes till this batch. I feel that just maybe the pug that I seal the cope and mantle with was a little damper than normal. The other thing I have changed was an increase in the amount of horse hair and whether this allows the damp pug to wick moisture up into the mould causing the problem.
    I will post how the process is done in a day or two, just busy at the minute!

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