UPSETTING LUBRICATION METHOD

PURPOSE:To reduce the depth of the wrinkle and to improve the yield by mixing lubricant containing graphite as the main component with a specified rate of oxidation inhibitor in the lubrication method of an upsetting stage. CONSTITUTION:At a lubricating device 4 provided with nozzles 3 at an interval on a header 2, a range of an upsetting length L is coated uniformly with lubricant in the peripheral length, the upsetting part is heated by a tube end heating furnace 5 as it is rolled. An aligning stopper 6 aligns the tube ends when the tubes are sent to the upsetter 7. The tube 1 is clamped by an upsetting upper die 7A and an upsetting lower die 7C and the tube end part is pushed in by a mandrel 7B. The heated upsetting part is upset by the upsetting die to obtain a prescribed upset dimension. The upset part is oxidized by heating to form a scale layer, to generate a wrinkle 10 and end burrs 8 are generated in a bad lubricating state. When the oxidation inhibitor is mixed at the rate of 30-70% with the lubricant, the wrinkle can be reduced and the yild be improved.