Tension leveler

Abstract

A tension leveler includes a work roll coming into contact with a metal sheet and a pair of backup rolls coming into contact with the work roll. A hardening layer harder than the inside of the backup rolls is formed on the surfaces of the backup rolls. The Shore hardness inside the backup rolls is lower than the Shore hardness in the surfaces of the backup rolls by HS23 to HS36.

What is claimed is: 
     
         1 . A tension leveler comprising:
 a work roll coming into contact with a metal sheet; and   a backup roll coming into contact with the work roll,   wherein a hardening layer harder than the inside of the backup roll is formed on the surface of the backup roll, and   wherein the Shore hardness inside the backup roll is lower than the Shore hardness in the surface of the backup roll by HS23 to HS36.   
     
     
         2 . The tension leveler according to  claim 1 ,
 wherein the Shore hardness in the surface of the backup roll is HS70 to HS75, and the Shore hardness inside the backup roll is HS39 to HS47.   
     
     
         3 . The tension leveler according to  claim 1 ,
 wherein the backup roll is made of hypoeutectoid steel whose carbon content is equal to or lower than 0.8%.   
     
     
         4 . The tension leveler according to  claim 1 ,
 wherein the Shore hardness in the surface of the backup roll is lower than the Shore hardness in the surface of the work roll by HS8 to HS22.   
     
     
         5 . The tension leveler according to  claim 1 , wherein the Shore hardness in the surface of the work roll is HS83 to HS92.