Steel Castings

It could be any number of things....best thing to do is run down the check list and see what jumps out at you as a possibility....

http://en.wikipedia.org/wiki/Casting_defect

http://ebookuniverse.net/international+atlas+of+casting+defects

Thank You.

/!\ beaware of my replies coz of non-specialit's
perhaps::
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Electrical potential differences between risers and the "ground"? May be very low level.... Before pouring, use a sensitive voltmeter.....make sure that you check using both AC & DC settings.....

Best of luck.

PS. A ground strap may be all that is needed. Maybe the problem ONLY happens when the pour is doe, some electrolytically produced reaction for example.....

Abhijit I believe from your posting that you are using exothermic sleeves as feeders and these are very susceptible to moisture pick up and seem to be your problem.Please ensure that your stocking of sleeves is free from moisture. Moreover I suggest to switch over to insulating sleeves which will behave better and the problem as described by you will be overcome.

Hello. But will the insulating sleeve feed the casting ?. What is the maximum insulating riser size that can be used to feed the casting ?

Are your molds really dry? Have they been sitting long after bake-out?

Accumulated moisture in the mold will be driven towards the exits(risers), and will condense around the opening producing hydrogen when hit by the molten metal. Hydrogen is soluble in molten steel.

Just a thought.

I worked for a company that manufactured fifth wheels and other thin section castings. The problem you mentioned can just drive you nuts. There has been some good advise from the group here, but like always we can not see the issues, only guess from the description provided. I would suggest calling on your sleeve, mold wash supplier and to your pattern makers for help. They can put thier eyes on the issue and better solve this with out a lot of guessing.