Diagonal rolling of hollow stock

Diagonal rolls for stretching hollows are of a truncated-cone-like configuration, each with two shoulders and a recess in between, for cooperation with a cylindrical mandrel rod in order to obtain a two-stages-in-one reduction in wall thickness; the shoulders merge in smoothing surfaces.

BACKGROUND OF THE INVENTION 
The present invention relates to rolling seamless hollow stock for purposes 
of making seamless tubes by means of diagonal rolling, using frustoconical 
rolls. 
German Pat. No. 174 372 disclosed a mill, using two or more obliquely 
oriented rolls of frustoconical or truncated-cone-like configuration. 
These rolls are arranged in a common plane of rolling, and they are 
oriented so that the thick end of each roll is located downstream as far 
as the movement of the rolled stock is concerned. The oblique orientation 
follows particular rules; its angle with reference to a first plane, that 
includes the axis of rolling; establishes the transport angle, while the 
angle relative to a second plane, which includes also the axis of rolling 
and is oriented orthogonally to the first plane, is the spreading angle, 
being approximately half the apex angle of the frustocone. The 
frustoconical surface of the roll can be subdivided into a concial feed or 
entrance portion, thicker and thinner portions (with reference to an ideal 
cone) and an exit or discharge portion at the thicker end of the cone. 
These rolls cooperate with a piercing mandrel. 
Pipes made in that manner are usually subsequently sized, also by diagonal 
rolls, and they are further stretched. Sizing and stretching is also used 
for making tubes from hollows which have been produced initially 
otherwise. The hollow blooms that are to be made are destined, e.g., for 
final wall thickness-to-diameter ratios of 1:15, or even thicker pipes, 
possibly being hollow blanks to be subsequently sized in pilger mills 
(reciporcating step rolling), or in a continuously working sizing mill, or 
stretching in a push-bank. 
It has been suggested to make thin-walled, seamless pipes by stretching 
hollows, e.g., by means of multipass or multistand rolling, using rather 
small stretch values per pass or per stand and using diagonal rolls, 
possibly with a sizing shoulder. All of these proposals have not been 
realized in practice. It is believed that the thermal conditions interfer 
technologically with the desired goal of stretching. See, for example, 
German Pat. No. 926 541 or German printed patent application No. 960 328. 
DESCRIPTION OF THE INVENTION 
It is an object of the present invention to improve seamless pipe-making 
technology, based upon the earlier proposals for thick-walled pipes, but 
improving them to permit the making of a thin-walled pipe (wall 
thickness-to-diameter ratio smaller than 1:15) in a simple process and in 
a single pass. 
It is a specific object of the present invention to provide a new and 
improved diagonal rolling mill for stretching hollows, using truncated 
cones as rolls, the rolls being obliquely oriented to the axis of rolling 
by the transport and spreading or twist angles; the smaller end of each 
truncated cone faces the oncoming hollow. 
In accordance with the preferred embodiment of the invention, it is 
suggested to provide each of the rolls with two annular shoulders, 
preferably of different height, and being separated by a recess which 
includes a conical run-up or feed surface to the second shoulder. 
Preferably, sizing surfaces are provided immediately downstream from each 
shoulder. These rolls cooperate with a cylindrical mandrel rod, i.e., a 
cylindrical, inside tool of which different portion but of the same 
diameter are located opposite the two shoulders of any of the rolls. 
These two shoulders establish two deformations of the hollow, in a single 
pass, and at such a short distance as between the deformation zones that 
there is interaction between them. This permits the making of thin-walled 
tubing, whereby particularly a larger reduction of the wall thickness is 
feasible as compared with the prior art methods. Shoulders in rolls are 
known per se, the inventive combination of two shoulders and the resulting 
two-step-in-one stretch operation permits the making of thinner tubes than 
was heretofore possible.

The FIGURE shows, in particular, a diagonal roll 1; the journal ends have 
been omitted. Also, mounting and drive of this roll are conventional and 
are, therefore, not shown. The mill is comprised of at least two such 
rolls which are disposed for rolling in a common plane transversely to the 
rolling axis 2. 
Reference numeral 3 refers to the axis of roll 1, being inclined by an 
angle 4 relative to axis 2. This angle 4 defines the spreading angle or 
angle of twist and is approximately half the cone angle of the overall 
surface contour or roll 1. The arrow 5 denotes the fact that the axis 3 is 
actually obliquely disposed. Thus, the angle 4 is actually the angle 
between a projection of axis 3 into a plane (the plane of the drawing) 
that includes the axis 2. Arrow 5 stands in representation of the 
transport angle. The roll 1 (as well as the second one of the mill) 
cooperates with a cylindrical mandrel rod 6. The mandrel rod extends in 
cantilever fashion from a thrust mount, either at the entrance side or at 
the exit side of a hollow 7 to be rolled into a thin-walled tube 8. 
Alternatively, the mandrel rod may float in the hollow. 
The rod 6 may turn on its own axis during rolling and be stationary 
axially, or it may move axially in the direction of rolling or oppositely 
thereto. It is important that this internal tool 6 has a uniform, circular 
contour wherever it faces working portions of the roll. During operation 
and rolling, the hollow 7 enters the mill, in the drawing from the left 
and moves toward the right. 
The roll 1 itself is of overall truncated-concial or frustoconical 
configuration. In detail, the small end of that truncated cone is 
comprised of an entrance or feed cone 9 (truncated) which engages the 
hollow 7 and any portion thereof initially. This cone pushes the material 
of hollow 7 against a first shoulder 10. Since the hollow undergoes a 
corkscrew or helical motor; a smoothing surface 11 is provided directly 
downstream from shoulder 10. This surface 11 on a ridge provides for an 
equalization of the now thinner wall of the hollow. 
As a consequence of the combined action of shoulder 10 and ridge surface 
11, the hollow is not only locally stretched, but also its diameter is 
increased. Accordingly, an annular recess portion 12 is provided in the 
roll so that the material can be displaced into that recess space, but in 
a controlled manner. A second entrance or feed cone 13 is provided as the 
downstream part of recess 12, which second cone forces the material 
against a second shoulder, 14. Again, a smoothing portion and annular 
ridge 15 is provided directly downstream from the shoulder 14. The working 
surface of roll 1 includes, finally, a rounding portion 16 which is 
conventional. This portion does not participate directly in the stretching 
of the tube, now tube 8, but equalizes the enlarged diameter thereof. 
In view of the deforming of the stock being rolled, one has to observe that 
the material is held back at the shoulders of the roll so that the 
stretching at the second shoulder 14 has to match the relative diameter 
increase of the roll from the first (10) to that second shoulder. It was 
found that the diameter increase of shoulder 14 with reference to the 
diameter of shoulder 10 should correspond at least to one-third of the 
desired relative length increase (stretching) of the hollow at and beyond 
the second shoulder 14. 
The final tube 7 has a thinner wall than is made possibly by conventional 
diagonal rolling mills; but it matches in quality all of the rather high 
demands. 
In the preferred form, the shoulder heights (of shoulders 10 and 14) should 
be about 2:1. The shoulders should have an angle of about 30.degree. 
relative to the axis of rolling (and of the hollow), and their dimensions 
are in the range of from approximately 3 mm to approximately 11 mm, there 
being correspondingly smooth transitions to the adjacent working surfaces. 
Shoulders of the type specified cause a relative large deformation over a 
relatively short length and the material is correspondingly heated. Since 
the two shoulders are axially rather closely spaced, relatively little 
heat is conducted away from the material into the roll and the mandrel 
rod, particularly in and from the range from the first shoulder 10 to the 
second shoulder 14. Thus, the technological treatment of the material of 
the hollow is quite favorable. Moreover, the mill is simpler as compared 
with known diagonal mills because one uses a cylindrical mandrel rod. Any 
particular adjustment of a particular portion of the mandrel relative to 
the rolls is not necessary. This facilitates the operation, particularly 
as far as subsequent adjustment during rolling is concerned. Also, the 
rod, having a uniform diameter can be longitudinally adjusted, 
repositioned, or even more freely in axial direction. 
The leading end of the pipe-hollow (7) runs against the first shoulder 
which does not present any problems even for rather thick hollows. As soon 
as the ground shoulder (14) engages the hollow, tension is exerted upon 
the hollow resulting from the relief recess 12 and the large rolling 
diameter at shoulder 14 (portion 15!) so that the wall thickness of the 
hollow is reduced thereat, and the hollow is prevented from deviating (too 
much) from a round cross sectional contour. Also, material will not be 
dislodged between the rolls and cause any breakdown. 
The discharge of the now thin wall of tube 7 fails likewise to cause any 
problems because the second shoulder stretches significantly less and, 
thus, deforms the material to a relatively small extent. This is 
accomplished by a smaller shoulder height, as was already mentioned 
earlier. The procedure contrasts favorably with rolling on prior-art 
mills, using but one shoulder. 
The two smoothing portions 11 and 15 should be provided and proportioned in 
order to offer a constant (radial) spacing relative to mandrel rod 6. 
Also, these shoulder extensions will grip the hollow more firmly and 
define definite radial spacing relatively to the uniform diameter mandrel 
rod. 
The invention is not limited to the embodiments described above, but all 
changes and modifications thereof not constituting departures from the 
spirit and scope of the invention are intended to be included.