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Riser insert sleeve breaker cores eliminate pock mark defects at Huron. (Case History).

Huron Casting, Inc., a 440-employee shell-molding steel foundry in Pigeon, Michigan, was experiencing a casting defect while using fiber-based riser insert sleeves and breaker cores (referred to as cookies). The foundry was using insertable riser sleeves with an attached cookie to improve the yield of its castings. The insert sleeves improve the thermal properties at the surface of the riser so that smaller, more efficient risers can be used and still will yield a solid casting.

The cookies aid this technique by reducing the contact area between the casting and the riser and by incorporating a notch into the riser neck that allows the riser to be easily broken off after shakeout and cooling. However, the use of the sleeves with cookies created gas holes and pock mark defects on the surface of the casting underneath the sand of the cookies.

Some of these pock mark surfaces were deep enough to require welding above the casting contour. A heat treat tempering operation also was added to relieve welding stresses, and then the area was snag or hand ground to customer specifications. These additional operations added costs, detracted from acceptable surface appearances, hindered ship dates and decreased customer satisfaction. Huron wanted to eliminate the rework operations to correct these defects.

The foundry worked with Ashland Specialty Chemical Co.'s Foundry Products Div., Dublin, Ohio, to find the optimal recipe for shell sand cookies for use with Ashland's Exactcast Riser Sleeves. Several recipes were tried. The final (and successful) recipe tested included a 3.5% low reactivity binder, fine clay and black iron oxide. Gas evolution testing showed there was 21% less gas generated from the new recipe.

The reformulated shell sand recipe resulted in a cookie that not only solved the pock mark defects but also contained a lower amount of nitrogen.

After June 2002, when new recipe cookies were put into production, pock marks under cookies were reduced or eliminated. A comparison to prior data showed that welding was reduced by 85% and hand grinding was reduced by 22%. These figures confirmed what had already been seen on the castings--a greatly improved surface appearance.

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Title Annotation:Huron Casting Inc.
Publication:Modern Casting
Date:Oct 1, 2002
Previous Article:Grinding cells reduce labor shortage problem, increase casting consistency, throughput in cleaning & finishing at Aarrowcast. (Case History).
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