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Metal Casting Technologies : March 2011
Foundry Investment Diecasting Offices: www.synchro32.com email@example.com +61 (0) 845 370 3232 ERP Cast Metal Specific April 5th - 8th Booth#300 50% Reduction on New Installation and Training *ENDS MARCH / APRIL June 28th- July 2nd Booth#12G04 115th is given by the resistance of the slag to the passage of an electric current through it. The ingot builds up in the mould and the slag is displaced in the upward direction. As the molten slag meets fresh surface of mould, a thin layer of slag adjacent to the surface solidifies to form a shell. The thin layer of solidified slag between the metal and mould wall produces a good ingot surface. The consumable electrode is thus changed into an ingot of refined metal with superior properties. A clean sound ingot is obtained as the inclusions are removed in the ESR process. The important parts in an ESR unit consist of mould and the base plate; electrode feed arrangement, the power source. The ESR moulds are made of copper or steel. Steel moulds have a lesser life compared to the copper mould. The shape of the mould is decided by the shape of the ingot desired and can be square, rectangular or circular, etc. Static and moving type moulds can be employed in the ESR process. The moving type mould can produce a longer ingot. Both alternating and direct current can be used for the process. Usually AC is used as the equipment is cheaper and AC helps in stirring the slag metal interface due to electrocapillary action and creates better refining action. The main problem in the ESR process is about the starting. Arcing, exothermic mixtures, solid conducting slags have been used. Arcing for a long time should be avoided. Premelted molten slag addition gives a smooth start for the ESR process. There is no arcing in molten slag addition. The molten slag has to be added rapidly at the base of the mould to prevent any loss of temperature. The electrode chemistry should be near to the desired ingot composition. Some elements have a tendency to oxidize and the loss can be compensated in the ESR process. The slag cover eliminates atmospheric contamination of the molten metal. ESR process removes defects like inclusions, porosities and segregation. The set up consists of a vertical screw rotated by a dc motor through a reduction gear moves the electrode holder up and down between two vertical guides. Metallic mould and base plate are both water cooled in the ESR process. A fume extractor is fixed above the mould to drive off the fumes generated. Tapered mild steel moulds can be used in the ESR process to reduce the costs of a copper mould. The main variables in the ESR process are the slag composition, current and voltage. The slag chemistry is of the greatest importance as it is the main refining part. The liquidus temperature of the slag should be below than that of the metal to be refined. Since the melting point of aluminium is 6600 C, the slag used should have a lower melting point below this.