Voice of the Industry.

QUESTION: Sometimes re-examining sand conditioning processes and implementing small changes can reap large benefits in terms of fewer sand-related defects. What changes in sand conditioning and preparation have made the biggest positive impact on casting quality in your experience?

"Hot molding sands are responsible for many foundry casting problems. Hot sands are brittle, sticky, cause increased sand inclusion problems, deteriorated casting finish and higher scrap rates. The use of sand-cooling devices has had a profound effect on casting quality. With the ever-increasing speed of molding lines, the sand is recycled so rapidly that the heat of the casting operation cannot dissipate before it returns to be mixed or mulled. Hot sands require more moisture and more clay to produce the physical properties required for good molding. Cool sands require less clay and additives, less mulling or mixing time, and produce a more consistent prepared sand. The muller or mixer is not meant to do extensive sand-cooling or lump-breaking."

Matt Granlund, consultant, Foundry Systems Control, St. Joseph, Minnesota 

"One of the most effective ways of facilitating casting operations and minimizing operational problems, including sand-related defects, is to try to work toward a 'robust' sand system. This does not imply special equipment or increased testing. Rather, it includes all aspects that help minimize fluctuations in the sand system. For nearly all test parameters, the absolute value (LOI, ADV, AFS clay, temperature, etc.) of a measured characteristic is not as important as maintaining a narrow range for this parameter. For example, it would be beneficial to have a fairly consistent influx of core sand into a green sand system rather than switching from a coreless job to one with an extreme core load, such as 1000 lb/ton of metal poured. It would help to hold as constant a sand-to-metal ratio as possible, instead of going from a 3:1 ratio to 15:1 and back, or to keep sand temperature at a constant value. We still are too obsessed with absolute values and frequently convince ourselves with 'good' average values, ins tead of examining the full range of values. Any influence we have to minimize variations in operations will positively affect results. Consistency of operation is more important than any single aspect."

Dieter S. Leidel, consultant, Tanoak, Inc., Barrie, Ontario, Canada

"Many ridiculed a paper titled 'Compactibility Testing, A New Approach in Sand Research' by F. Hofman introduced at the 1996 AFS Casting Congress, but many others realized this probably was the first lab test directly related to sand properties at the molding station. This test soon became the base control for many muller controllers. CE. Wenninger added compactibility to his chart relating moisture and green strength, and to simplify this chart, Brillion Iron Works (BIW) redrew the data into two charts. The first chart related green strength to compactibility for determining the working bond for process control. The other chart related green strength to moisture for the available bond value, indicating the level of moisture-absorbing materials in the sand. BIW has added hoppers for dust collector fines to help control this number. Also, work closely with your suppliers. BIW traced casting problems to the lack of screen control of new sand for both core- and moldmaking. It worked closely with suppliers to re place the AFS GFN with the statistic '[Chi.sup.2]' to correct this problem. Specifications had to be agreed upon for each of the major screens. BIW's sand suppliers now furnish the [Chi.sup.2] value with the screen cert for every truckload. This has improved finish and reduced scrap and binder requirements. In addition, because of variations in wet tensile strength and soluble calcium values in the sodium bentonite, in 1985 BIW started using chemically treated calcium bentonite in place of a blend of bentonites. Since then, the remaining sand systems have been converted. The company has found control of the system to be improved and sand-related scrap reduced. Since 1995, BIW also has been working with one supplier to reduce benzene emissions for one sand system, and two more systems have been converted with good results."

Alan Volkmar, retired, Brillion Iron Works, Brillion, Wisconsin 

"I am a technical service person who addresses complaints and solve production problems on a daily basis. At times, I hear complaints that a product doesn't perform well. The lot in question may start off well and develop a problem later. What has changed? The answer I hear usually is 'nothing.' If the sand is a resin-coated material 'shell sand,' the consumer should have a job card with all the necessary information to run the pattern the way it last ran best. You must document air and gas requirements as well as temperature and proper pattern-mounting. In addition, I recommend taking a 5-gal sample of optimal sand for future comparison testing. If you can give your supplier a sample of the sand that ran well and a sample that didn't, you together can decide which sand will suit your needs and whether the sand is in specification, on the high side or on the low side for your needs. My best suggestion is to talk to your operators. The person on the line knows the machine better then anyone, regardless of the system. That person knows what is needed and can save you a lot of scrap and money. Make him part of a team solution to any problems. On several audits, when I questioned an operator on problems with his machine, I was told, 'No one cares what I need to produce a good core--just get the production out.' Put confidence in your people and involve them. Your greatest asset is an involved employee who takes pride in a job well-done."

Dave Phipps, senior technical service representative for foundry and industrial products, Borden Chemical Co., Aurora, Illinois