Abstract

Bimetallic castings are widely used in the mining industries as construction material for crushers which have to perform high abrasive resistance at the outer side and excellent machinability at the inner side. To manufacture bimetallic casting goods cconsecutive centrifugal and gravity casting methods are commonly applied. Centrifugal and consecutive casting come up with geometrical constraints at the parting line of both materials. This research dealed with the manufacturing of tapered grinding roll by applying gravity casting method. The possibilities of casting the white cast iron outer ring in the preheated ductile cast iron of the inner ring were investigated. The inner ring was first heated up by casting liquid metal around the inner side, which prevented the inner ring from cracking due to rapid expansion during the casting process and to provide adequyate shrinkage of inner ring during solidification. After achieving the desired temperature of the inner ring, the liquid metal of white cast iron was then poured into the cavity to form the outer ring. The preheating temperature of the inner ring was mainly derived from the linear thermal expansion of both quasi isotrophic material and the diffusion at the parting line. This preheating temperature has to facilitate the formation of metallurgical bonding and avoid cracks due to the difference of shrinkage value between inner and outer ring. The preheating temperature was set up in the range of 500°C -1000 °C and the flushing time was fixed for 7 seconds. Studies on the microstructure of sample material have revealed a formation of metallurgical bonding at all of the preheating temperature. The width of the diffusion at the interface area varied between 291 μm at 500 oC preheating temperature, 301 μm at 625 oC, 834,8 μm at 750 °C, 909,1 μm at 875 °C and 1027,7 μm at 1000 °C. By preheating temperature of higher than 750°C fusion occured at the interface area between inner and outer material. This research concludes that the casting of bimetallic by applying gravity casting method can be done by preheating the inner ring to 625 oC, interface temperature of 1150 oC, flushing time of 7 seconds and pouring the white cast iron outer ring at the temperature of 1430 oC

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