This article focuses on the nobake process and when it would be appropriate for use.
An MCDP Staff Report
Click here to see this story as it appears in the January/February 2018 edition of Metal Casting Design & Purchasing
Dozens of chemically bonded sand molding methods exist, but they can be divided into three main categories: coldbox, heat-activated and nobake. The basic principle is that a binder and catalyst are mixed with the sand to help form the mold into a “brick-like” product when cured. The differences in the process focus on the sand resin binder and catalyst used and how the mold or core is cured.
Coldbox—with this method, sand is coated with one of several binders, such as liquid sodium silicate or phenolic urethane, and catalyzed by a gas (such as carbon dioxide or sulfur dioxide) passing through the sand. This causes the resin binder to harden (cure) and lock the sand grains in place to maintain a solid mold wall.
Heat-Activated/Shell (also called hotbox and warmbox)—heat is used as the curing means in shell molding. Plastic resin-coated sand is compacted around a pattern and allowed to rest until a “shell” forms. The mold then is heated to temperatures higher than 500F (260C) to cure the mold.
Nobake (also called airset, dry sand and precision sand)—like coldbox, several binders are optional. However, a liquid catalyst is used. The sand is processed in a continuous mixer and then formed around the pattern until it is fully cured.
Mold coatings are applied to more than 75% of noble molds. The coatings help prevent defects and improve surface finish.Read More