(Thanks to the Simpson Technologies Corporation for the opportunity to review this research paper they authored, "The Fundamentals of Green Sand Preparation and Control." We've shared a few of the most important sentences of the report. Photos from Modern Casting, American Foundry Society.)
By Scott Strobl, Vice President of Technology
Understanding the raw materials, tests and equipment to reduce sand variations will optimize your green sand process for a more profitable molding operation.
A basic understanding of the materials that constitute a green sand system and the equipment required to prepare and maintain the integrity of the system are extremely important to assure quality castings.
The intent of this article is to briefly summarize a generic sand preparation system.
Testing and Control
The test results quantify important sand properties and characteristics to benchmark the system and ultimately help to reduce variation of the sand and incoming raw materials. Moisture is an extremely critical sand additive that can greatly impact casting quality and the operation od a sand system.
The size and distribution of the sand grains are extremely important in controlling the surface finish of the casting. A green sand mold must withstand the pouring temperature of the molten alloy. It is more important to understand that if the silica content of system sand is reduced to a critical level, the surface finish of castings from alloys with high pouring temperatures may deteriorate due to the loss of refractory. Any large deviations in surface area could have profound effects in the physical characteristics of the molding sand. Obviously, as the size of the sand decreases, its surface area increases.
Clay is the adhesive that maintains the mold shape at both ambient and elevated temperatures. The addition of water is required to activate the clay. The moisture content of system sand is extremely critical and can effect nearly all the physical properties that are measured in a foundry. There are two naturally occurring clays - sodium and calcium bentonite - that are utilized in a majority of metalcasting operations. Calcium benonites are better known for the ability to quickly develop green properties. They offer better flow that sodium bentonite (which tends to be more plastic) and lower deformation at equal moisture percentages. Therefore, they have a greater ability to flow freely through the sand system and into deep and/or tight pockets on a pattern.
Carbon additives are generally added to cast iron sand systems to help reduce the occurrence of metal penetration and improve surface finish.
Mulling is one of the most important aspects in green and control. A thorough understanding of the mulling cycle sequence must be maintained to help minimize cycle time and optimize the effectiveness of the muller.
Maintaining the System
Maintaining a sand system involves the reduction of fluctuations and variations. In other words, additions of new clay must be made ot offset losses to thermal destruction, dust collection, etc.
Controlling a green sand system requires a detailed understanding of the raw materials, laboratory test results and production equipment. A basic understanding of sand control will optimize your green sand process for a more profitable molding operation. The intent of this article is to provide an introduction to many of these key points. To maximize the potential of a particular sand system requires a complete understanding of the raw materials and interrelationships between these components and the equipment making up the preparation system must be attained.
About Simpson Technologies
Simpson Technologies was founded by the Scottish foundryman Peter L. Simpson in 1912 and is now an over one hundred year old, five generation family business specializing in the design and production of advanced process technologies and services for the global metal casting and chemical process industries. Our primary products include batch and continuous high intensity mixing equipment, molding sand coolers, on-line mixer control & automation systems, core sand preparation systems, foundry sand reclamation systems and sand laboratory instrumentation.
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