Method for forcedly cooling a heated metal plate

In a method for forcedly cooling a heated metal plate uniformly in the longitudinal direction of the metal plate, which comprises:

• moving a heated metal plate horizontally in the longitudinal direction thereof at a prescribed speed through a cooling apparatus comprising a plurality of rows of nozzles arranged at prescribed intervals in the width direction of said metal plate above and below said metal plate;
• and, spraying a cooling liquid from said nozzles onto the upper and the lower surfaces of said metal plate during moving of said metal plate through said cooling apparatus to cool said metal plate to a prescribed temperature;
• the improvement comprising:
• starting said spraying of said cooling liquid from said nozzles when a prescribed length of the trailing end portion of said metal plate during moving of said metal plate still remains outside of said cooling apparatus;
• discontinuing said spraying of said cooling liquid from said nozzles when a given length of the leading end portion of said metal plate during moving of said metal plate projects outside of said cooling apparatus by an amount such that said given length equals said prescribed length;
• said prescribed length of the trailing end portion of said metal plate being determined by the following equation:
• x=S.tau..sub.c (1-K)
• where,
• x:
• said prescribed length;
• S:
• moving speed of said metal plate in said cooling apparatus;
• .tau..sub.c :
• forced cooling period of time for the portion of said metal plate other than said trailing end portion of said metal plate which remains outside of said cooling apparatus by said prescribed length and said leading end portion of said metal plate which projects outside of said cooling apparatus by said given length which equals said prescribed length;
• and
• K:
• constant dependent on the material and the size of said metal plate;
• whereby said metal plate is cooled uniformly in the longitudinal direction thereof.