Methods of Steel Casting

Steel casting is a specialized form of casting involving various types of steel. Steel castings are used when cast irons cannot deliver enough strength or shock resistance. Examples of items that are steel castings include: hydroelectric turbine wheels, forging presses, gears, railroad car frames, bodies for valves and pumps, machinery used in mining, marine equipment, and engine casings. Steel castings are categorized into two general groups: carbon steel and alloy steel.

The methods of casting steel: The Szekely method consists of employing metal molds, one of the chief points being to coat the molds with chalk and paraffin. Shaw also employs metal molds. Slavianoff's electric casting method appears to be simply a method of melting steel by connecting it to one terminal of a strong electric circuit, the crucible in which it is to be melted, or the plate on which it is to be cast being attached to the other.

In the so-called sand core process, a sand core is cast in the ingot which is afterward worked down as usual; it was claimed that the sand did not injure the material, but this, as well as any advantage, is extremely doubtful. In Norton's fluid rolling process, fluid steel was to be worked direct into sheets by pouring it through revolving rolls properly adjusted, with the idea of preventing blowholes, and reducing the usual amount of scale.

Bessemer's method for making continuous sheets consisted in running molten steel between two water-cooled steel rolls, separated a suitable distance; the speed of the rolls was regulated according to the thickness of the sheet. In Whiteley's process for the production of plates, molten steel was run into a revolving cylinder and formed a shell which was taken out, cut open by a saw, and then rolled down. Pielsticker and Mueller's process was devised for producing bars, rods, and similar material direct from fluid steel by first passing it through dies, and then finishing the resultant material in a rolling mill or under a hammer.

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 (http://www.generalsteelcorporation.com/) 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.