| 摘要 |
<p>PURPOSE:To form continuous hardened layers to a large-sized rack over the entire tooth thereof by covering the non-hardening part of the large-sized rack with metallic blocks and heating the rack by high-frequency current, then injecting a cooling liquid to the non-heated part in the cooling liquid. CONSTITUTION:The blocks 15a, 15b which are made of thick metal plates and have an approximately L-shaped section are mounted on the top face 4 and bottom face 5 of the large-sized rack in tight contact therewith to cover the non-hardening part. The high-frequency current is supplied to a coil to preheat and heat the rack part 2 and to minimize the temp. difference between tips 2a and bottoms 2b. The large-sized rack 1 is then immersed into the cooling liquid 33 where the cooling liquid 33 is injected to the rack part 2 and a rear face part 3 from a front face cooling jacket 31 and a rear face cooling jacket 32. The strains such as deformation and bend of the rack 1 are thereby decreased and the tips 2, the bottoms 2b and the tooth faces are adequately heated and cooled, by which the uniform hardened layers are formed thereon.</p> |
