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NAB casting

NAB casting

NAB casting

(OP)
We are casting valve bodies in ASTM B95500 and C 95200. We are getting a peculiar problem especially in large risers. The metal is showing no gas at test sample and small casting from the same heat. But larger risers in large castings 4-8” Rise 20-30 minutes after pouring. Would appreciate any help

RE: NAB casting

What mold system?
What is the weight of the casting?
How are you de-gassing the melt?

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P.E. Metallurgy, consulting work welcomed

RE: NAB casting

What is your sleeve material being used (Exothermic/Insulating)? There are lighter sleeves with reduced wall thickness, giving higher thermal efficiency. Have you tried them?

Is it sufficiently well heated to remove any traces of moisture?

Large open type sleeves liquid metal remains exposed to the atmosphere for a longer period of time. Have you made any attempt to shroud the surface, to avoid any contact with the atmosphere?

Hope, you will find your answer soon.

RE: NAB casting

And are any of the gas issues actually in the castings or just the large risers?

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P.E. Metallurgy, consulting work welcomed

RE: NAB casting

What mold system is the most pertinent question and if sand molding is being used then you need to hire an experienced guy who can help you get over the problem.

Are you using chills?

DHURJATI SEN
Kolkata, India

RE: NAB casting

(OP)
We are using Silicate process. The castings vary from 100kg liquid to 450kg liquid. We are using insulating sleeves and to avoid the problem we also used sand risers We agg Foseco feedol and ferrux to hot top the casting. The gas in the risers causes the casting to have shrinkage under the risers. We degass when with Foseco E3 tubes. We use chills and sleeves to get the directional solidification. The same castings were poured a few months ago without any trouble. The problem started as soon as the humidity increased.I hope I answered all the questions

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