FIELD: metal rolling.
SUBSTANCE: invention relates to screw piercing. Initial workpiece is heated, centred, the workpiece is pierced into the sleeve and its subsequent second piercing in the same stand or another mill and rolling at the helical rolling mill. At the first piercing one obtains sleeves with the diameter to wall thickness ratio which is less than or equal to 10, the total drawing at piercing makes up to 83 % of the total drawing at the specified mill, and the drawing coefficient at the first piercing is determined from the expression:
where: μ - total drawing coefficient for first and second piercings, μp is drawing coefficient in first piercing, n is number of rolls in stand.
EFFECT: higher quality and accuracy of pipe geometrical dimensions.
1 cl, 1 ex
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