VERKTYG VID ETT RORVALSVERK

The tool according to the invention in a tube rolling mill comprises a mandrel 1 and rolls 5, which are arranged across the lengthwise axis 0-0 of the mandrel 1 and separated by equal distance from same. In the side surfaces of the rolls 5 are accommodated roll grooves 6, in which a tube 4 is supposed to be machined during the rolling. The roll groove 6 has variable cross section surface along the length, along which are arranged a diameter reduction zone, a grooving zone, and a compression zone between them. The diameter reduction zone has a parabola-shaped cross section profile that is formed during the rolling at the bottom part of the roll groove 6 in the roll 5. One portion of the compression zone bordering the grooving zone also has a broadening of the cross section profile formed during the rolling at the bottom part of the roll groove 6 in the roll 5 in the form of a convex parabola at the lengthwise axis 0-0 of the mandrel 1. The generatrix of the mandrel 1 is parabola-shaped over the portion of its length corresponding to said portion of the compression zone 8. The other portion of the compression zone according to the invention has a broadening of the cross section profile formed during the rolling at the bottom part of the roll groove 6 in the roll 5 in the form of a parabola, whose convexity faces the direction away from the lengthwise axis 0-0 of the mandrel 1. The portion of the generatrix of the mandrel 1 corresponding to this other portion also has the shape of a convex parabola and borders a cylindrical portion of the generatrix of the mandrel 1, corresponding to the diameter reduction zone.