Simple Solutions That Work! Issue 9

The Shell Sand process or “Croning” process was invented by Dr. Johannes Croning in Hamburg, Germany in 1944. This process is the oldest core and mold making technology that utilizes synthetic resins. Although many additional sand core and molding making technologies have since been introduced, the Shell Sand process is still a very effective core and molding process today. What is Shell Sand? Shell sand is a dry, pre-coated sand mix that is cured by heat. Sand is coated with a phenolic novolac resin along with a hexamethylene tetramine (hexa) cross-linker and other additives specific to the core or mold making process. The coated sand is a dry, flowable mix that is blown or gravity fed into a hot die. The heat initiates the cross-linker and cures the sand. The die temperature and investment time can be used to control how much sand is cured. Because heat is the catalyst, only an outside thickness is cured. If an open area is present, uncured sand can be emptied from the shape resulting in a sand core “shell.” Advantages of Shell Sand • Highest flowability of all chemically bonded systems • Highest hot strength organic binder system • Light weight cores and molds, especially for large shell cores • Low sand to metal ratio • Cured Cores/Molds are storage stable • Good dimensional stability • Resin coated sand is storage stable Based on the list of advantages and disadvantages, it is easy to see that shell sand is ideal for some applications. One of the key disadvantages is also the area in which Shell Sand has evolved: Emissions Shell Sand Emissions The primary source of emissions in shell sand core and mold making is the hexa component. Conventional formulas (HAI branding of Custom Coat) utilize a novolac resin with 12-20% hexa (based on resin) to cure the resin and create a strong core. This type of formula creates emissions of both ammonia and formaldehyde at core making. Although advanced have been made in reducing free phenol in the resins, the hexa remains as the key contributor to emissions. The first generation of low emissions sand, commercially known as CC E-Series, was developed. The novolac resin portion can be partially substituted by a heat curing phenolic resin. The hexa content can then be reduce as low as 5% based on resin. This is then combined with other emission reducing components. The results? A reduction of 70-80% in ammonia emissions, 80%-90% in formaldehyde emissions, and a large odor reduction! MITCH PATTERSON Product Manager Resin Coated Sand & Refractory Coating HA INTERNATIONAL ARTICLE TAKEAWAYS: • Comparison of Conventional, first generation low emission, & second generation low emission sand grades • Handling high humidity conditions EVOLUTIONOF FOUNDRY SHELL SAND FOR TODAY’S FOUNDRY 16