casting
Casting History
During the Stone Age, metal could only be cut, split and chipped, forming crudely shaped objects. This changed upon the discovery that metals could be smelted if heated to the proper temperature. The discovery was especially significant because the metal would become fluid when heated, then hard again when cooled. This meant entirely new forms in an unlimited variety could be created from the liquid metal, provided the metal could be contained until it cooled. Containing the metal became possible with the invention of the mold in which the entire process of casting is derived from.
Metal casting began around the 4th Millennium, BC. The process of extracting the metal from ore began with copper. Later, lead, gold, silver and bronze were also extracted. Over the years, casting techniques evolved as well. Casting moved from the simple one-piece open mold to the two-part closed mold. Then the process of casting advanced further by creating a replica using an expendable material and mold. This method is the cornerstone of the "lost wax casting" process used to this very day. In fact, all of these ancient processes are still used today. Some are still practiced in the same primitive manners, while other techniques have been refined into highly technical processes utilizing various methods and materials to help satisfy increased demand, accuracy, efficiency and reproduction.
Mold Types & Material
Molds basically fall into two major categories: reusable and expendable. Reusable molds can make several castings from a single mold. Expendable molds can only be used once. These categories can then be broken down into sub-categories including one-faced and two-faced molds. One-faced molds are devised of one mold half containing a pattern cavity, while the other half is flat. The flat part is used to apply pressure on the metal forcing it into all parts of the pattern cavity. Two-faced molds utilize two mold half's, each containing a pattern cavity that must be properly aligned then filled. This produces a two-sided, three-dimensional casting. Expendable mold types are usually made out of clay or plaster. These materials are good due to their plasticity which allows very complex objects and patterns to be cast from them with great accuracy.
