| 摘要 |
The heat treatment of a continuous band or sheet of metal as the same travels through a plurality of stages in a protective atmosphere, between conveying rollers, by applying direct-current electricity to the rollers for inclusion of the travelling sheet in the circuit therebetween. The charged rollers in the initial stage are spaced more widely from one another than those in the later stage, to compensate for the lower resistivity of the metal in the former, so that the Joule effect or I2R factor in the stages are substantially equalized. The protective atmosphere of oxidizing, reducing or inert gases which encompasses the sheet, is confined in chambers of galvanized iron sheeting and the like, the walls of which are in close proximity to the travelling sheet, so that lesser amounts of reacting gases are necessary. Furthermore, no indutive electric currents are generated in the walls of the chambers, as is the case when alternating currents are applied to the conveying rollers, with the consequent heat loss. The lack of any extraneous source of heat within the chambers through which the metal sheet passes, other than the direct-current energy, results in a system of low thermal inertia with the capability of a fine and rapid control of the heating to produce uniform physical and metallurgical properties across the entire width of the sheet up to the edges thereof. The heat treatment may be executed for the purpose of annealing or tempering the sheet or modifying its surface coating, either independently or preparatory to the coating thereof in a coating bath.
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