| 摘要 |
PURPOSE:To form a wear resistant double pipe easily and at a low-cost without generation of cracks by supperposing and fastening an outer pipe of low yield point and high toughness on an annealed high hardness inner pipe of high yield point at hardened condition, then hardening both pipes to subject to auto- frettage. CONSTITUTION:The inner pipe 2 of high-carbon steel, etc. having high yield point and high-hardness at hardened condition is inserted into the outer pipe 1 of low-carbon steel, etc. having low yield point and high toughness and passed through a die 3 in an arrow direction. In this way, both the pipes 1, 2 are contracted and the difference R1 of these radii is made nearly zero to obtain a blank double pipe 4 fastened both the pipe 1, 2. Then the inner pipe 2 of the blank pipe 4 is hardened by the high-frequency induction heating from the inside. In this way, the inner pipe 2 is given high-hardness, increased the yield point and expanded its radius to auto-fret the both pipes 1, 2, and then the wear resistant double pipe having enough toughness and fastened with high grade of fitting allowance is obtained.
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