"The U.S. Bureau of Mines developed a system for casting unique, slotted steel armor by modifying the conventional expendable pattern casting (epc) process that is normally used for making aluminum castings. Three innovations were added to the epc process to make the successful adaptation: (1) vacuum was applied to sand molds, (2) continuous narrow-necked feeding systems were used to permit the casting of thin walls, and (3) fixtures were designed to prevent pattern damage and to hold critical casting tolerances." - NIOSTHTIC-2 NIOSHTIC no. 10011544

National Institute for Occupational Safety and Health