Gas Entrapment 1

[chakraguy]

Hi guy, at my investment casting company facing a new type of defect .

Can anyone suggest any solution for this defect ?
Clearly , it's not cause by mis-run defect.

Casting Process: investment casting
Ceramic material : Alumina silicate
Casting temperature: 1500ºC
Mold Temperature : 1150ºC
Casting Material : KHR12C
Fiber wool cover: Yes
Defect type: Gas entrapment lookalike , Round shape hole ,
Material composition : Scrap material (SCH 13Nb) 30% and new material 70%
Casting Weight : Around 50 Kg

 

[arunmrao]

Need more details, about the type of mould, alloy, casting weight pouring temperature , melt treatment etc. More information that you provide, better will be the response.

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[EdStainless]

So this is a modified HH.
Has this casting ever worked correctly?

Are they doing any de-gassing?
What about deoxidizers?
One concern may be how fast they are filling the molds.
They could be filling faster than the venting will handle.

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P.E. Metallurgy, Plymouth Tube

 

[arunmrao]

Grade HH is rarely found to be gassy. 1500C is a good temperature. Just check your ladle and mould conditions. Hope, your charge material was clean .You may try adding some FeSiZr and CaSi to the melt before pouring.

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[MagBen]

Given the size of defects (comparable to the part!), it is hard to imagine the gas was from the melt material itself. Maybe those were not gas entrapped issue.
The solidus temperature of this alloy is about 1350C, if you postponed the casting process, or, it took too long time to cast, you could lost temperature. Could increase pouring temp work?

 

[Compositepro]

This looks like gas injected into the metal from the mold wall, which could be due to out-gassing or just a negative pressure in the mold drawing air in though the mold. If this section of the part were last to solidify it could be due to shrinkage in the whole mold showing up in this one location. That could be due to uneven mold temperature due to oven non-uniformity, or due to hot metal flowing though this section to fill other sections, meanwhile heating this section to a higher temperature.

It could also be a large amount of air trapped at the bottom that then rose. But, the fact that many voids are at the mold wall tends to indicate that the gas came through the wall.

 

[chakraguy]

Yes , It have worked correctly , Some mold didn't have this defect ,and some did.
Thanks for advice.
But have anyone ever encountered this kind of defect?