Patent ID: 7469565

Claim:
A method of manufacturing a seamless tube comprising: a) a step of applying a lubricant to a mandrel bar, b) a step of inserting the lubricated mandrel bar into a mother tube, c) a step of carrying out elongation rolling of the mother tube with a mandrel mill, d) a step of stripping a seamless pipe from the mandrel bar, e) a step of cooling the mandrel bar, and f) repeating steps (a-e) a number of times using the same mandrel bar characterized by comprising a step of washing at least a portion of a conveyor installed in a conveying step of the mandrel bar which is situated from a lubricant applying device to the entrance of a mandrel mill, a step of washing, on the upstream side of the lubricant applying device, the mandrel bar which is used for repeated elongation rolling, and a step of applying a lubricant to the mandrel bar by the lubricant applying device, wherein applying a non-graphite-lubricant organic binder-containing lubricant to the mandrel bar and washing of the conveyor and the mandrel bar are carried out such that the amount of graphite C2 (g/m 2 ) deposited on the surface of the mandrel bar before it is supplied to elongation rolling and the amount of carbon C1 (g/m 2 ) contained in an organic binder of the applied non-graphite-based organic binder-containing lubricant satisfies the following Equation 1 and Equation 2: 0.08 ×C 1+0.05 ×C 2≦3 (1), and 3 ≦C 1 +C 2≦50 (2).