Method for reduction and sizing of welded pipes and mill for effecting same

DETAILED DESCRIPTION OF THE INVENTION According to the invention, the reduction and sizing mill comprises a bed 1 (FIG.
1) which carries alternating vertical reducing stands 2 and 3 and horizontal reducing stands 4 with rolls 5, and a sizing stand 6 with rolls 7.
There may be more reducing and sizing stands mounted on the bed 1.
The reduction and sizing mill is combined with a forming and welding unit comprising a forming stand 8 with rolls 9 and a welding stand 10 with weld rolls 11.
In the plane of their axes of rotation, the working surfaces of the rolls 5, 7, 9 and 11 form passes.
The passes may be single-radius round (FIG.
2) and single-radius oval (FIG.
3), three-radius (FIG.
4) and two-radius (FIG.
5).
The single-radius round pass of the rolls (FIG.
2) is described by a single radius R drawn from the pass center O.
The single-radius oval pass (FIG.
3) is described by a single radius R' drawn from the center O' which is displaced in relation to the pass center O along the y-axis by a value .
DELTA.
.
X-axis is one of the pass disjunction.
The three-radius pass (FIG.
4) is defined by arcs of three radii described by a radius R.
sub.
1 of the apex, drawn from the center O.
sub.
1 found on the axis y.
sub.
1, a radius R.
sub.
3 of the taper, drawn from the center O.
sub.
3 found on the axis x, and a conjugate radius R.
sub.
2, drawn from the center O.
sub.
2 found at the intersection of the radii R.
sub.
1 and R.
sub.
3 drawn to points of conjugation "a" and "b".
The radius R.
sub.
1, drawn to the conjugation point "a", is at an angle .
alpha.
to the y axis.
The radius R.
sub.
3, drawn to the conjugation point "b", is at an angle .
beta.
to the x axis.
The two-radius pass (FIG.
5) is defined by arcs of two radii, i.
e.
the apex radius R.
sub.
1 ' drawn from the center O.
sub.
1 ' found on the minor axis y and the taper radius R.
sub.
2 ' drawn from the center O.
sub.
2 found on the major axis x.
The arcs of the two radii conjugate at point "a'" found on a straight line drawn through the centers O.
sub.
1 ' and O.
sub.
2 ' at an angle