To summarise the invention, first, the rolls employed for the forming are configured from a plurality of vertical roll pairs and a plurality of horizontal roll pairs arranged alternately in the direction of travel of the cylindrical pipe. Furthermore, by way of example, the configuration which is adopted involves the division of the forming rolls into several groups and the incorporation thereof on a common support frame for each divided group, and the employment of a support position control mechanism which, using the support frame unit, varies the position of the rolls on the pipe.

The invention is characterized in that a support position control mechanism is employed to alter the roll position incorporated by the support frame and the roll gap in the vertical and horizontal direction, and the desired cylindrical pipe is sent forward to pass through the altered roll gap and is pushed or drawn wherein the desired deformation to the cylindrical pipe is applied to create the desired angular pipe. This invention, by virtue of this configuration, enables angular pipes of differing dimensions to be formed, as appropriate, with high productivity, from cylindrical pipes of differing dimensions with no changing of the forming rolls at all.

Background Art The process whereby, using a cylindrical pipe as the raw material, an angular pipe with a square cross section or rectangular cross section is formed is widely employed as a means for manufacturing an angular pipe.

This process of forming the cylindrical pipe, as shown in Figure 1, is one which involves the employment of a so-called 4-roll type forming roll configured from a driven, or non-driven, 4-piece roll group comprising an above/below pair of horizontal rolls 10a, lOb and a left/right pair of vertical rolls 20a, 20b arranged in such a way that the axial centres thereof lie along the same plane.

The method adopted involves the employment of a plurality of stands of forming stands in which the abovementioned 4-piece group forming rolls are enclosed-normally 3 to 6 stands are employed-wherein the left/right and above/below centre of the roll gap of the abovementioned vertical roll pair and abovementioned horizontal roll pair enclosed by the abovementioned stands are aligned and arranged to be on a horizontal single line, and while the cylindrical pipe, which constitutes the raw material pipe, is sent to the downstream side passing through the gap formed by the arranged abovementioned 4-piece group rolls of the abovementioned forming stands, the desired deformation is applied to the cylindrical pipe an angular pipes successively formed.

Figure 2 shows one example of the application thereof. In this example, a cylindrical pipe 60, which constitutes the raw material pipe, is held at the end parts thereof in a ram 40 of an oil pressure cylinder 30 by way of a tightening means such as a chuck, and by the pressure force of the abovementioned oil pressure cylinder 30, the pipe is sent into (in the direction of the arrow in Figure 2), for the purpose of forming, the roll gap of the abovementioned forming roll where it is subjected to forming processing.

In the example shown in Figure 2, the abovementioned forming stand row which is employed is configured from: enclosed rolls 50a and No. 1 forming roll stand for initiating the forming of the cylindrical pipe into a angular pipe; enclosed rolls 50b and No. 2 forming roll stand to advance the different form; and enclosed rolls 50c and No. 3 forming roll stand for finish- forming to an angular pipe 70 whose final cross-section is square or rectangular. The enclosed forming rolls in the case of, by way of example, the No. 1 moulder rolling stand, are configured from 4-piece group rolls comprising an above horizontal roll 10c, below horizontal roll 10d, and a pair of left/right vertical rolls 20c, 20d. The configuration of the forming rolls in the No. 2 and No. 3 forming roll stands is the same.

It will be noted that, in addition to this, in the case where a pitch roll stand is deployed for continuously sending the raw material pipe or product pipe to the upstream side or downstream side of the forming roll stand row, among 4-piece group rolls incorporated in the forming roll stands, a forming device which comprises a mechanism for driving the above/below horizontal rolls or left/right vertical rolls is widely employed.

Furthermore, there are many cases in the continuous manufacture of a raw material pipe in which the manufacturing line of a so-called electrically sewn pipe and the above-described pinch roll stand or forming roll stand are aligned and directly coupled, and the manufacture of a circular pipe and forming into an angular pipe is carried out completely continuously.

However, the following problems are inherent in a device of such prior art which is used for the forming of an angular pipe from a cylindrical pipe,: 1) Each time the dimensions of the product (angular pipe) change a changing of the rolls is required; 2) The raw material pipe (cylindrical pipe) undergoes sudden deformation at the region of entry of the rolls of each stand, the propulsive force in the required direction of forming is liable to increase, and slip is liable to occur between the raw material pipe and the forming roll due to a shortage of propulsion forces, and furthermore, accompanying this, problems of instability in the line forming speed are also likely to occur; 3) Because the deformation of the raw material pipe (cylindrical pipe) is concentrated in the areas just before and just after the roll, warp, which forms a shape defect in the edge part of the formed angular pipe cross- section, is liable to be generated, smoothness of the edge part is worsened, and the product quality is lowered.

4) There is a strong tendency for the deformation to be concentrated in the angular part (corner part) of the product (raw material pipe) cross-section, and there are faults in that significant residual strain or residual stress is liable to be generated in the angular part and cracks or the like are liable to be generated in the angular part inner surface or outer surface.

In particular, the problem described in 1) above is a particularly serious problem pertaining to the manufacture of angular pipes.

Accompanying the diversification of requirements in recent years, the need to manufacture a small volume of each of a diversified type of angular pipes of different dimensions has increased, and high productivity manufacturing technology which is able to deal with the production of many sizes in small lots has been demanded. In particular, there has been a strong demand for the adoption of common-use roll technology so as to reduce the roll costs and the downtime due to roll change which have increased markedly accompanying the alterations of the product dimensions.

In reality, tests with a view to the development of angular pipe manufacturing technology which is able to meet these demands has been carried out continuously but, to this point, no examples of success in the common-use of forming rolls which can deal with large changes in product dimensions has been found. Accordingly, although aware these were unsuitable, in addition to some forming rolls being forced into common-use.

In addition, in regard to the problem of 4) described above, as well as the bending strain during forming, a large compression strain in the cross- sectional circumferential direction is applied to the corner portion of the cross-section of the angular pipe, and a large residual stress which has its origins in this deformation is generated which may cause cracks at the corner portion and other defects. Heating has been tried in order to avoid the problems which have their origin in this residual stress but, conversely, there were many instances in which a reduction in the dimensional precision was invited due to the effect of heat, and a satisfactory solution to this problem has not been found.

Meanwhile, there are strict stipulations regarding the dimensional precision of the shape of the product (angular pipe), such as the radius of the corner portion of the cross-section as well as the flatness of the side portion. A range of work has been carried out to fulfil these stipulations, and the present situation is that, in order to achieve the objectives using the forming device of the prior art, a huge amount of work and effort is required.

Disclosure of Invention In the method for manufacturing an angular pipe, the objective of the invention is to provide a method for manufacturing an angular pipe, and the device therefor, wherein: a variety of sizes of angular pipe are able to be formed from a cylindrical pipe without changing the rolls; shape defect such as warp is not generated at the side portion and the deformation strain is minimal; and manufacture can be achieved with high productivity.

As a result of a range of investigations carried out into roll configurations able to effect the forming of various sizes of angular pipes from cylindrical pipes without changing the rolls, the inventors discovered that, by the adoption of a configuration in which pairs of left/right vertical rolls and pairs of above/below horizontal rolls are arranged alternately in the direction of travel of the raw material cylindrical pipe at multiple stages, the arrangement of a successively narrowing horizontal roll pair and vertical roll pair opposing gap at each stage is possible, and that the opposing gap of all the rolls can be altered easily in accordance with the size of the cylindrical pipe as well as the size of the angular pipe. In this way, it was discovered that, by the employment of one group of horizontal rolls and vertical rolls such as this, the cylindrical pipe can be moved forward and pushed or drawn through the predetermined roll gaps and an angular pipe, with a square cross-section or rectangular cross-section, can be continuously manufactured from a cylindrical pipe.

In addition, the inventors discovered that: by the division of the roll groups, in which the vertical roll pairs and horizontal roll pairs are alternately arranged at multiple stages, into a plurality of groups in the direction of travel of the raw material pipe; the provision of a mechanism which affords the alteration of the opposing gap of the roll pairs in each group as appropriate; and as the device, each group is able to be supported by a supporting frame and position control of the roll in each group is able to be performed. Size changes can be executed easily and swiftly, and manufacture with good shape precision and good productivity can be achieved.

In addition, the inventors discovered that, in a configuration in which it is possible to rotate all the vertical roll pairs and horizontal roll pairs along the axis of the cylindrical pipe, forming can be achieved in such a way that, the welding seam can be positioned at any portion of the cross-section of the angular pipe.

Brief Description of Drawings Figure 1 is a schematic diagram that shows the schematic configuration of the forming rolls in a device for forming an angular pipe of the prior art.

Figure 2 is a schematic diagram that shows the schematic configuration of a device for forming an angular pipe based on a method of push forming.

Figure 3 is a schematic diagram which shows the schematic configuration of a pair of vertical rolls and pair of horizontal rolls for forming which are enclosed in a roll forming device employed in the method of manufacturing an angular pipe based on the present invention.

Figure 4 is a schematic diagrams which shows a state in which 3 different types of angular pipe have been manufactured using the roll forming device based on the invention shown in Figure 3; Figure 4a shows a case in which a desired square-shaped angular pipe of comparatively large dimensions is manufactured from a cylindrical pipe; Figure 4b shows a case in which an oblong-shaped angular pipe is manufactured from a cylindrical pipe of the same diameter as that in Figure 4a; and Figure 4c shows a case in which a square-shaped angular pipe of comparatively small dimensions is manufactured from a cylindrical pipe of small diameter.

Best Mode for Carrying Out the Invention The roll forming device employed in the method for manufacturing the angular pipe based on the present invention, and more particularly, the configuration of the enclosed forming roll groups, is shown in the Figure 3 type diagram. As shown in the diagram, an above/below pair of horizontal rolls a, b and left/right pair of vertical rolls c, d are arranged alternately and at multiple stages 1 ~ n, m. Here, there is an alternate alignment of a plurality of horizontal roll pairs, in an odd number stage n, and a plurality of vertical roll pairs, in an even number stage m. It will be noted that the order of arrangement may be such that the vertical rolls are the first rolls.

The axial centre of the vertical rolls and the axial centre of the horizontal rolls belonging to the adjacent vertical rolls pairs c, d and horizontal roll pairs a, b are, unlike the 4-roll type forming roll of the prior art shown in Figure 1, not on the same planar surface, and are arranged in such a way that a distance between the surface which includes the axial centre of the abovementioned horizontal roll pairs, and the surface which includes the axial centre of the abovementioned vertical roll pairs, is maintained to the degree that they do not interfere with each other.

In the aforementioned roll line arrangement, group division can be performed at the appropriate number of stages as determined from the demands of control or formability such as, by way of example, group division in a constant number such as at 3-stages 4-stages or 5-stages, or group division at a range of different numbers of stages.

The abovementioned vertical roll groups and abovementioned horizontal roll groups are supported by joint supporting frames respectively.

The supporting frame comprises a roll supporting mechanism equipped with a set-position altering control means which affords the adjustment and change, in accordance with the product dimensions and cylindrical pipe dimensions of the raw material pipe, of the roll gap formed by the abovementioned vertical roll pairs and the abovementioned horizontal roll pairs.

In addition, conversely, the support frame itself may be moved by means of the set-position altering control means wherein, by way of example, a configuration may be adopted in which the gap between the aforementioned right vertical roll and aforementioned left vertical roll can be altered, as appropriate, by the employment of a set-position altering control mechanism, in which the abovementioned support frame is mounted in advance, to afford the movement in the left/right direction in respectively identical phases.

As a set-position altering control means for the roll pairs or support body, any well known mechanical mechanism and control means can be adopted.

Moreover, in the rollforming device based on this invention, from one edge towards the other edge of the arrangement of the abovementioned vertical roll groups which form the left/right pairs and horizontal roll groups which form the above/below pairs, that is to say, towards the downstream side from the upstream side when the cylindrical pipe 60 is moved forward, the roll profile is established in such a way that, its curvature is reduced step-wise. In addition, in the final stage, in both the abovementioned horizontal roll pairs and abovementioned vertical roll pairs, a roll is employed which has a profile of a very small curvature, that is to say, a roll which is almost equivalent to a flat roll.

Based on such a configuration, the desired cylindrical pipe, by way of the roll gap of the abovementioned vertical roll pairs and the abovementioned horizontal roll pairs arranged alternately in a row form, is moved forward and formed, by pushing or drawing while the desired deformation is applied, into the desired angular pipe which has either a square-shape or rectangular-shape cross-section.

In addition, in this roll forming device, a roll drive device can be introduced to drive all or a selected portion of the rolls as appropriate, so that the automatic forwarding of the pipe during forming is possible, and the function of the device of the present invention can be improved even further.

In this invention, the number of vertical roll groups which form the abovementioned left/right pairs and the number of horizontal roll groups which form the abovementioned above/below pairs can be selected, as appropriate, based on factors such as the diameter of the cylindrical pipe being formed, the wall thickness, material quality, and shape and dimension of the angular pipe which is required.

In addition, the diameter of the horizontal rolls and vertical rolls for the abovementioned forming is determined, as appropriate, by, for example, the dimensions and form of the angular pipe and the raw material pipe which constitutes the subject material. By way of example, in a case where a cylindrical pipe of 4 inch diameter is to be used as the raw material pipe, if only the deformation of the raw material pipe is considered, at most, the use of a forming roll of small diameter of about 50 to 60 mm is possible, The entire length of the forming device in this case would be in the region of 2.5 m to 3.0 m, which is much shorter by comparison to the forming device of the prior art, and a marked shortening of the length of the device is possible.

Because the method of forming based on the invention involves the forming using forming roll groups formed in a comparatively large number of pairs, it has a very small forming amount (forming strain) per roll compared to the 4-roll type forming method of the prior art. For that reason, the generation of cracks and other product defects can be prevented effectively Embodiments Embodiment 1 In Figure 4a, there are 15 vertical roll groups which form the abovementioned left/right pairs and 15 horizontal roll groups which form the abovementioned above/below pairs in a roll forming device for manufacturing a angular pipe based on the invention, making a total of 30 roll groups. This shows a case in which the roll gaps of the horizontal roll pairs and vertical roll pairs are set so as to be of a predetermined dimension, wherein an angular pipe is manufactured, which has a desired square cross- section of comparatively large dimensions, from a desired cylindrical pipe.

Embodiment 2 Figure 4b, in the same forming device as the case of embodiment 1, shows a case in which a mounted roll setting-position altering control mechanism is employed and the gaps of the horizontal rolls and vertical rolls are altered, wherein an angular pipe, which has an oblong cross-section, is manufactured from a cylindrical pipe which has an outer diameter the same as that used in embodiment 1.

Embodiment 3 Figure 4c shows a case in which, in a forming device the same as that of embodiment 1, a mounted roll setting-position altering control mechanism is employed and the gaps of the horizontal rolls and vertical rolls are altered, wherein an angular pipe is manufactured, which has a desired square cross-section of comparatively small dimension, from a cylindrical pipe.

In each of the embodiments described above, based on the method of this invention, a variety of angular pipes of differing dimensions can be manufactured, with precision and stability, from cylindrical pipes of various dimensions without changing rolls.

Industrial Applicability The forming device and roll forming method based on the invention, in a method for forming an cylindrical pipe into a angular pipe, affords the realization of the complete common-use of forming rolls which had been impossible in the prior art, and it affords the efficient manufacture of angular pipes of different dimensions without changing of the roll groups.

Accordingly, this invention is one in which, by a marked improvement in the productivity of the forming work and the gentle deformation applied to the raw material pipe, an angular pipe product of a high product quality standard, and with very high dimensional precision, can be manufactured easily and at low cost.

In a word, the invention has, by comparison to the device and method for forming an angular pipe from a cylindrical pipe of the prior art, the following advantages: 1) In a certain range of raw material pipe dimensions and product dimensions (by way of example, raw material pipe minimum diameter: raw material pipe maximum diameter = 1: 3, product cross-section aspect ratio 1: 1-1 : 3), because roll exchange is unnecessary, the productivity can be markedly increased.

2) Because the raw material pipe is deformed gently the raw material pipe passes easily into the roll gaps, and the required propulsion force for the pushing or drawing can be markedly reduced. In this way, a stabilized forming speed can be realized.

3) By virtue of the fact that the raw material pipe is deformed gently, the accumulation of strain is small whereby is possible to suppress defects such as cracks or the like during or following forming.

4) Because the sections of the cylindrical pipe are deformed smoothly, warp is unlikely to be generated at the side portion of the cross section of the angular pipe and an angular pipe of good flatness at the side portion can be produced.