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Metal Casting Technologies : March 2007
up and actual continuous ESR process. Figure 12a shows the smaller water cooled copper mould. Figure 12b shows the continuous square shaped ESR ingot being withdrawn. Figure 13 shows the ESR ingot along with the slag cap. Previously ESR process was restricted to the manufacture of only solid ingots. The solid ingots were then processed to the final shape of the component. This increases the cost of the component as secondary processes like forging/rolling/machining are needed. It was thought to produce the ingot into the final casting shape by using moulds of the same shape of the component. This is called Electroslag casting (ESC). The water cooled mould is made into the shape of the required casting in one or more parts and the metal is electroslag melted inside this mould to give the required casting. By using this lesser machining is required as near net-shape components are produced. ESC is a single step process for producing finished products, which can offer advantages to industry. ESC can produce large and complex castings, such as nuclear valves and tube fittings, crankshafts, gears and rolls, tools, dies, and die blocks. The application of ESR to produce hollow ingots was realized by Hopkins22. Russian workers Latash23 et al. developed the process. The hollow ingot is produced by using a central water cooled mandrel. The hollow ESR ingots exhibit comparable properties as that of standard ESR process. Addition of inoculants elements such as titanium, niobium to steel during ESR gives grain refinement and reduced segregation24. HAZARDS ESR is safe process provided that no water comes in contact with the molten metal or slag. If water is trapped below molten metal then it is dangerous. Mould should not get punctured. Moulds and base plates are the sources of water. Moulds should be checked always before ESR operation is started. Moulds can get mechanically or electrically damaged. Figure 14 shows a stuck ingot in the mould tube. The ingot couldn't be removed easily. Hence final option i.e. using METAL Casting Technologies March 2007 35