| 摘要 |
PURPOSE:To operate a furnace while preventing yellowing and inter-layer exfoliation by circulating convectively and directly a combustion gas during heating up for preheating of the furnace inside and passing convectively the hot air subjected to a heat exchange with the combustion gas in the subsequent stage of carrying a material to be coated into the furnace. CONSTITUTION:A burner 6 and circulation fans 13, 17 are operated by shutting fully dampers 14, 15, opening slightly dampers 18, 19 and opening dampers 7, 8 and the suction air from a return duct 4 is heated to a high temp. by the combustion gas from the burner 6 and is supplied together with the combustion gas through a supply duct 5 to the furnace to constitute a direct hot wind circulation route N1 where the gas is heated up to the prescribed temp. during the heating up of the hot wind circulation type drying furnace for painting in order to preheat the furnace. An indirect route N2 is constituted by shutting fully the dampers 7, 8, branching the return duct 4 and the supply duct 5 in the mid-way to the two lines and opening the dampers 14, 15, 18, 19 to required opening degrees so that the hot air subjected to the heat exchange with the combustion gas is circulated convectively in the stage of carrying the material to be coated into the furnace. The formation of fatty material is thus prevented and the furnace is economically operated.
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