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Surface fines

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Tjark:
Is there someone who knows how to get a good surface fines when using a sand core made with a mix off sand and SS?
I having only this problem  with one balanced core as on the picture.
Maybe someone knows if there is some kind off coating to get a smother finish.
The casting temp is good and I have no gas inclusions, see picture off the base site, turned with a diamond tip.

ths:
Are you using baked cores, or CO2 setting cores? When I was doing foundry at tech, I always got great results with the CO2 process. Core sand was generally finer than the regular casting sand, but not as fine as facing sand.

How well was the core sand mixed with the binder? It looks from the photo that a bit has broken off, perhaps washed away during the pour.

Cheers, Hugh.

PS: I don't know what SS is.

tel:
sodium silicate I suspect

Tjark:
Ths, as Tell said SS is sodium silicate, this is the Co2 process as you mentioned.

The casting is a old type Amal carburetor what is not for seal anymore.
The inner core for the carb bore and slide I am quite satisfied with.
It could be a little better but so far its oke.

The bottom off the carb (here will fit the needle yet and main yet) is very rough.
I have used the same method for the carb bore and slide as for the bottom core.
Yet the bottom core was not oke, after casting.
Maybe I did not compressed the sandmix for the bottom core enough.
Will give it a next try when the whether is clearing up.

ths:
Yes, sodium silicate. That's what we used. Good luck with the next pour.

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