Manufacture of especially thin-walled stainless pipes
In the manufacture of stainless pipes, cold rolling, some of the metal is lost.
Grind stainless steel pipes by a continuous method on centreless-grinding or belt-grinding machines or by local grinding in defective places. Since the depth of grinding depends on the localization and the depth of occurrence of defects in individual areas, then when grinding the preforms of a stainless steel pipe, the waste averages 2.5% of the initial mass of the billet. When turning and boring, more metal is lost - this depends on the depth of the layer being removed.
When etching stainless pipes, metal loss is 0.5% per etching. As for one rolling of a stainless steel pipe , there may be 3 to 4 etchings and one clarification, the losses will reach 1.5% of the initial mass of the pipe coming in for processing.
When annealing, the loss to scale is about 0.75%, and when quenched, 1%.
If the stainless pipes are heated before annealing and quenching in furnaces with an inert atmosphere, the losses with scale are reduced to 0.1% (depending on the integrity of the furnace, the purity of the inert gas, the pipe is cooled in an oven or outside it
When rolling stainless pipes , marriage is possible for a number of reasons. When rolling the calculated "rate" of marriage is 1%. With the excellent work of the personnel, a technological marriage can be completely ruled out.
Stainless steel pipes entering the cold rolling mill are cut by the technology perpendicular to the axis of the pipe and must have unbleached ends. Therefore, after the heat treatment, the ends of the stainless steel pipes going to secondary rolling are cut off. The size of the trimming is 20 - 100 mm. With the length of stainless pipes to 5 m in the mill, when cutting the ends of stainless pipes before rolling, about 1% is lost.
If the pipes are ordered with a measured length, the length of the cut ends will be of the order of 500 mm, and for the non-dimensional lengths - 350 mm. The proportion of waste to the scrap depends directly on the length of the stainless pipes after the last rolling and is 2.5-1.75% with a pipe length of 20 m. If the pipe is 7 m long, the waste will increase to 7%.
When the stainless steel pipe is delivered, it is possible to not eliminate the defects in the form of captivity, shells, sunsets, cracks, waviness