Posted by Michael Gilligan on 18/01/2017 10:41:53:
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A very encouraging start, Michael
… Please keep us informed.
MichaelG.
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P.S. … Your practical results are obviously what matters … but I was pleased to find this:
**LINK**
Obviously: I have only skimmed through it, but it does appear to be worth reading.
Edited By Michael Gilligan on 18/01/2017 11:06:37
Thanks Michael, If I do keep reporting on the build, I may move the information over to a dedicated thread which I can link here if I need to.
Wow that's a little lengthy, definitely the academic type wrote this! But pleasingly, it does appear to offer some documented scientific backing for the "casting skin" effect.
Although the only suggested method I can see for beating it is shot blasting, probably because It erodes away the non carburized layer.
He suggests that the cause is due to "metal to mould interaction". The difference in temperature, surface quality of the sand (and subsequent ingress of sand into a casting, possibly caused by the degree of roughness present on the mould surface). This might be the glossy layer I was referring to, it does seem to "trap" and encase the sand beneath it. I can't seem to find a notable mention of how annealing it helps, but it has definitely changed the surface quality of my own casting.
No doubt, some chemical or abrasive methods may work as well.
Michael W