“One of the most critical steps is when the casting engineer meets with the customer. This is when you find the balance between what the designer thinks he needs and what he can actually make.”

Cores need patterns just as molds need patterns. These patterns are used in conjunction with coreboxes to produce a core. Core production can be performed manually or through automation, but the logistics remain the same. In low volume operations, core sand is fed into a corebox from a mixer. Sand also may be blown in when the cores are smaller, with high production rates. In the case of a coldbox core, time is then given for the core mix to cure. In the case of shell, hotbox or warmbox cores, the sand mixture in the box is heated to set the core. Once it is set, the core is removed from the corebox. 

Some factors of core production should be considered in core design. Because coreboxes are made in two halves that are clamped together, they will have a parting line, particularly if the sand is blown in. If this parting line is not sealed when the corebox is closed, coresand may blow out of the box to create fins on the cores. This will require more time in production to file the fins off the cores.

Sand is mixed with high pressure air when it is blown into the corebox for compaction. Sometimes, the air already in the corebox does not have enough time to escape, resulting in poor sand distribution and poor compaction. To prevent this problem, patternmakers use blow tubes and vents to keep air from being trapped in the corebox. However, the tubes and vents will leave marks on the surface of the core, and these will transfer onto the surface of the corehole or passageway in the metal casting. Metalcasters can dip or paint the core with a coating to remove the marks if they will cause a problem in the final application of the component.

Cores in Action

The use of cores will add to the final cost of your casting, and a casting design that fails to accommodate core design will be felt in the project’s budget. But the advantages of cores to casting design are major money savers, lending design freedom to manufacturing a component. A well-thought-out core package can create intricate passageways that either save money, reduce weight or improve functionality. For instance, a hydraulic valve body gray iron casting made at the green sand facility of Grede Foundries Inc. – Iron Mountain Div., Kingsford, Mich., incorporated two components into one to reduce weight by 11.3% (Fig. 1).

Fig. 1. This hydraulic valve body gray iron casting incorporated two components into one to reduce weight by 11.3%.