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Petrobond moulding sand

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hermetic:
If you look on youtube at some of the small foundries in India, you will see them adding waste oil to sand!

smiffy:
Today I went to a small foundry in Stourbridge as I wanted some castings made that are too large for my equipment.
It is owned by a very enthusiastic chap who gave me lots of advice regarding using petrobond sand.
Contrary to lots of you tube advice using engine oil is a complete no . They remix with a very small amount of molasses and have been using the same sand for a long time . The more you muller it the better the surface finish and it improves every time it is reused . J winter foundry supplies sell petrobond snake oil but he thought that molasses was just as good and much cheaper,
 Would certainly recommend him as very happy to do one off castings in cast iron, aluminium brass bronze etc.
  Mike

awemawson:
Mike that’s interesting. Did he give you any idea of proportions? And molasses is quite variable in its runnyness

smiffy:
He did not give any amounts as there are too many variables .  He was mixing about 60 kgs at a time and adding molasses in
very small quantities until he was happy with the feel of the  sand .He also said that it needed mullering for 10 minuets or more before you can tell if it is correct and the sand stands up well to multiple uses before it need more molasses added
  He said that you could also use linseed oil but the used sand needed much more mullering to recondition it  in between uses .
  I will start with about a egg cup full for every 20 kgs of sand  but first I need to make a proper muller   Mike

vtsteam:
Interesting. Both molasses and linseed oil are traditionally used in making baked sand cores (I haven't seen them used together -- separate recipes). They both burn out during the pour to allow the core to collapse.

Actually it's generally diluted molasses, called "molasses water". I've used molasses water for baked sand cores (mixed with a little wheat paste or flour) for aluminum molding. They burn out black to loose sand.

Baked sand core w/molasses water/wheatpaste before closing up the mold for a tailstock:

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