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Malleable or cast-iron castings are sometimes united by heating in contact to a high temperature; this is termed "bumming" together. It is sometimes necessary to make an addition to a casting to complete or to replace a portion which has been broken off. For this purpose the casting already made is placed in a mold of the proper shape and molten metal poured in.

The solid metal must be heated up to a sufficiently high temperature, and there are two methods which are usually distinguished as (a) casting on, where the solid metal is heated with a flame, and (b) burning on, where the molten metal is first caused to run into and out of the mold until the solid portion has been sufficiently heated, when the outlet hole is closed, and the mold allowed to fill up.

Wm. Chalk's method for uniting a sleeve or boss of cast iron, etc., on a wrought- iron shaft consists in heating the shaft to a welding temperature, putting it in a suitable mold, and pouring around it the molten metal.

Falk's method is somewhat similar, and is intended for uniting the ends of rails; an iron mold is placed around the ends, and extremely hot metal is then poured around them until they are partially fused and will unite readily. Permanent mold casting (typically for non-ferrous metals) requires a set-up time on the order of weeks to prepare a steel tool, after which production rates of 5-50 pieces/hr-mold are achieved with an upper mass limit of 9 kg per iron alloy item (cf., up to 135 kg for many nonferrous metal parts) and a lower limit of about 0.1 kg.

General steel cavities are coated with a refractory wash of acetylene soot before processing to allow easy removal of the work piece and promote longer tool life. Permanent molds have a limited life before wearing out. Worn molds require either refinishing or replacement. Cast parts from a permanent mold generally show 20% increase in tensile strength and 30% increase in elongation as compared to the products of sand casting. The only necessary input is the coating applied regularly.

Typically, permanent mold casting is used in forming iron, aluminum, magnesium, and copper based alloys. In the modern era, the process is highly automated with the use of robotic equipment and computers.The news come from http://www.bossgoo.com/