PURPOSE:To save fuel and improve productivity by continuously supplying the pipe right after centrifugal casting while held put in metallic flasks to an annealing process and passing heating gas from the metallic flask of the front row to the metallic flask of the rear row. CONSTITUTION:Metallic flasks 3 containing a ductile cast iron pipe right after centrifugal casting are parallelly placed on a platen 4 of a heat treatment process via a carriage 8. A heat insulating carriage 15 is made to approach to the metallic flasks 3, and the end faces of the metallic flasks 3 are covered with heat-resistant heat insulating covers 18; at the same time, the respective metallic flasks 3 are communicated via ducts 20. The cast iron pipe in the respective metallic flask 3 is heated by oil burners 19 with the prescribed temp. gradients and are cooled slowly. At every fixed time, the carriage 8 and heat insulating carriage 15 are suitably operated to transfer the preceding metallic flasks 3 successively on the wheel base 1 on the lower stream side; at the same time, the succeeding metallic flasks 3 are put into the annealing process, whereby the centrifugally casting ductile cast iron is continuously heat treated.
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