Herron Casting Services

SYSTEMS DISCUSSION

by David J. Herron, B.S. MTE.

HERRON HYBRID GATING: A cost-cutting, HORIZONTAL GATING system exclusive to HERRON CASTING SERVICES that combines the best features of traditional pressurized and non-pressurized systems (i.e., high slag retention as well as high sand retention, high shrink control, low metal turbulence, and low velocity cavity entry). Yield is comparable to non-pressurized systems. HERRON HYBRID GATING is a very advanced application of fluid dynamics and thermodynamics yet is very readily utilized by our custom software and is easily built by reputable pattern shops. This is our usual recommendation.

PRECISION HYBRID GATING: This system is recommended when using VERTICAL MOLDING or the IN-MOLD ductile iron process, particularly when castings are tall or exceed 250 pounds. This system has all the advantages of HERRON HYBRID GATING, being an adaptation of it for VERTICAL GATING. It also includes the most advanced reaction chamber we know of for IN-MOLD ductile. We believe this chamber design is essential to repeatable success with IN-MOLD DUCTILE and COMPACTED GRAPHITIC IRONS. PRECISION HYBRID GATING is exclusive to HERRON CASTING SERVICES! This technique is essential in VERTICAL MOLDING and pays dividends in HORIZONTAL MOLDING also.

NON-PRESSURIZED/ESH: This is a popular system in the foundry industry due to its many approximations and simplifications, most notably being the use of the Effective Sprue Height (ESH). With the proper ratio of choke to runner to ingate, this system will provide high slag retention and low velocity cavity entry. That ratio varies from one foundry to another and from one size mold to another. Here-in lies the unpredictability of the system and the mixed results reported among foundrymen. We do not recommend this system, in-spite of wide spread use by others. Often taught in gating seminars, it is only an intro to scientific gating.

PRESSURIZED/ESH: As with non-pressure systems, this is popular for its simplification using the ESH (Effective Sprue Height) and also for its high yield. It also provides relatively high sand retention since runners are in the cope. The ratio of sprue/runner/choke is simply a descending order so it is not as critical as in non-pressure systems. The problem here is low slag retention and exceedingly high velocity cavity entry. We rarely recommend this system.

FILTER SYSTEMS: Filters can be used with any of the above methods. They CANNOT replace good gating design. Good gating design, however, can often eliminate filters and their high cost. Filters have become widely popular because there is a dearth of true expertise in gating and true understanding of metallic fluid flow. We often design systems that incorporate filtering as an OPTION. There will be a modest improvement by the use of the filter, but often, not enough of a difference to justify the expense! We try to help you eliminate filters as often as possible, particularly in non-cored work, where the filter slows the production rate.

THE MOST-FORGIVING GATING: If the metal and sand were perfect and the molder and pour-off were perfect you might pour castings with only a sprue. If these are less than perfect but not really bad, then a pressure system with its high yield might do. But if losses nail you to the wall on random days then you have probably settled on non-pressure systems with frequent regates attempting to improve. Stop changing so often! Select HERRON HYBRID GATING or PRECISION HYBRID GATING as… your most forgiving gating.

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DHerron@HerronCasting.com

E-mail: DHerron@HerronCasting.com

312-261-0229