Q What are the factors to consider to determine the optimum binder formulation for our foundry green sand system?

Background: There are many different green sand binders and binder formulations available on the market, each utilizing a wide variety of materials or additives for specific castings and metals. For any foundry, a composite binder formulation must meet some basic needs, including:

* give the foundry sand the necessary characteristics to flow and mold around the pattern;

* develop sufficient strength in order to hold up to metal weight and metal flow;

* create a reducing atmosphere so sand and metal do not merge;

* fall away from the casting during shakeout.

Acheiving a sand system to meet all of these needs is not always simple. There ate many factors that should be taken into consideration when determining what composite mix formulation should be used:

Metal specifications--type of metal cast, casting type and size of casting (average weight and dimension);

Melt equipment--furnace type, manufacturer, and production rate (this is a determining factor in the 'turn-over' of the system sand);

Muller equipment and specifications--muller (manufacturer, model, production-rate, cycle times, batch size), bond addition system, water source and muller to molding distance;

Molding equipment--type, manufacturer, model and production rate;

Green sand handling system--shakeout system, sand cooler (return sand temperature) and return sand storage capacity;

Green sand binder--present formulation and additive percentages, packaging (bagged or bulk), usage (lb per ton of metal poured) and bond storage capacity;

Sand specifications--base sand type (supplier, AFS GFN and sieve distribution), usage in tons per year, new sand additions measured in lb per ton of metal poured, and sand-to-metal ratios and/or ranges;

Core sand--AFS GFN, type of core process, core sand per ton of metal poured, and binder level and type;

Sand laboratory--tests preformed and ranges of typical results. Results should be charted and statistical methods applied.

Recommendations: Once the information above has been defined, the proper bond formulation can be determined by monitoring sand system issues such as mold quality, shakeout, casting defect types and overall composite binder consumption. A review of data generated from standard sand tests can help a foundry gauge the impact of these factors and will determine whether of not the appropriate blended binder is being used. This information also will help sand system specialists make a recommendation as to the types of materials and formulation percentages needed.

Information was supplied by the AFS Molding Div. Foundry Sand Additives Committee (4-H).