Click here to read the article with all figures in the October digital edition.

A recent survey by the AFS Green Sand Division asking foundries about their new sand addition practices revealed what was once considered a common practice was not so definitive for every plant. While 300 lbs. of new sand per 1 ton of iron poured has been an industry baseline, discussions with many sand foundries showed that for some, the practice of adding new sand had been eschewed for using their core sand as “new” molding sand.

In the survey of 47 sand foundries, 10 were not adding new sand, other than the core sand input. One of those foundries was AFS Corporate Member Cadillac Casting. While presenting at the virtual 2020 Sand Casting and Additive Manufacturing Conference last month, Travis Hepfner, quality engineer at Cadillac Casting, shared the foundry’s path to eliminating new sand additions. Digital passes can still be purchased to access the full conference agenda of recorded sessions at 
www.afsinc.org/sandam2020-schedule. 

Cadillac Casting (Cadillac, Michigan) is a ductile iron foundry that runs high production volumes on its 32x32 horizontal molding line, consuming about 127 tons of sand per day. It uses two 100B batch mullers to feed sand to the cope and drag machines. A premixer feeds the majority of the bond to the sand before it enters the storage bin leading to the mullers. 

Like most sand foundries, Cadillac Casting was adding new sand regularly to its system, but a key change to the product mix led the company to reconsider its process.

From the middle of 2018 into 2019, the iron foundry transitioned from high-volume, no-core knuckles (in quantities of millions per year) to high volumes of carrier castings, which required heavy cores weighing 30-40 lbs. each. This change in product mix meant a significant increase in core sand additions to the sand system. Cadillac Casting went from returning all the sand it could to maintain its levels while also adding new sand, to ending each day with a surplus of 10-20 gons of sand.

Rather than continue to throw out an abundance of sand each day, Cadillac Casting stopped adding new sand, relying solely on the core sand additions to maintain the appropriate level of sand in the system. 

As expected, that change in sand system additions had an affect on certain properties. The core sand is coarser than the previous new sand being added. Not surprising, this led to a change in the GFN, from 60 to 54. Alarmingly, it also caused an increase in the sand’s friability, which unfortunately led to an increase in inclusion scrap and an overall scrap increase of 2%. An adjustment needed to be made.

It was noticed that as friability was going up, the moisture levels were decreasing in the sand system. To combat the loss of moisture, the foundry began adding 1% cereal to the premix. The cereal helped maintain the moisture, lower the friability and ultimately reduce the scrap by 3%. As jobs continue to use heavier cores, Cadillac Casting is also starting to add more bond in the premix for better coating of the sand grains.

Overall, the transition to using core sand as new sand addition has been successful at Cadillac Casting, and the foundry has been able to reduce new sand costs as well as sand disposal costs.