The invention relates to a method for producing a bent pipe comprising at least one desired curvature, wherein a substantially straight pipe is divided into a number of segments and zones present between two successive segments.

The invention also relates to a device suitable for carrying out such a method
and comprising a number of pivotally interconnected parts. Such a device is for example disclosed in GB-A-1081597.

With such a method, which is known from US patent US-B2-7,222,512, outwardly extending bulges are formed in zones in a substantially straight pipe, whilst segments located on either side of a zone are present in parts which are pivotable relative to each other. The bulges form a beginning of a crease to be formed in the zone. After the bulges have been formed, the segments are pivoted relative to each other by means of the aforesaid parts, as a result of which bending of the pipe takes place. Since the dimension in axial direction of a bulge formed on an inside bend of the bent pipe to be formed is larger than that of the bulge on an outside bend of the bent pipe, it is possible to compensate for the difference in length in the inside bend and the outside bend of the bent pipe, or, in other words, the difference in radius between the inside bend and the outside bend of the bent pipe.

A drawback of the known method is that the bulges formed in the zones form creases which extend along the entire circumference of the pipe. In addition, the segments located between the zones are substantially identical in shape both in the original, substantially straight pipe and in the bent pipe that is eventually formed. As a result, walls including an angle with each other are obtained in the interior of the pipe, so that an even flow is not obtained in the bent pipe when the pipe is used as a flow channel.

The object of the invention is to provide a method by means of which a pipe can be given practically any curvature, whilst an even transition between the segments is obtained.

This object is accomplished with the method according to the features of claim 1 and a device according to the features of claim 11.

Starting from a desired curvature in a pipe, the local curvatures in the pipe wall are determined for every segment of the bent pipe, along the entire circumference of said pipe.

Then a substantially straight pipe is theoretically divided into said segments, and the walls of said segments are given the local curvatures. Since the segments form part of a curvature, for example a circular arc or a differently configured bend, zones will be present between the segments, at least on inside bend of the curvature to be formed, when a substantially straight pipe is divided into said segments. When the substantially straight pipe is bent to form the bent pipe, the segments are moved towards each other, with the local curvatures of the adjoining segments becoming aligned and the, preferably contiguous, local curvatures forming a continuous curvature in the bent pipe.

In this way it is possible to form practically any curvature or bend in a pipe, whilst a smooth surface can be realised at least on an outside bend of the curvature.

The term "pipe" as used herein is understood to mean a tubular section having a circular or other cross-section, which may be constant or change in the longitudinal direction of the pipe.

It is noted that from US 1,958,447 a method for forming a bent pipe is known wherein part of the pipe is bent relative to the remaining straight part of the pipe and provided with creases. Then a part of the pipe between the bent part of the pipe and the remaining part of the pipe is bent and provided with creases. This process is repeated until the pipe has obtained the desired curvature. The device used for carrying out the method comprises a single part which is pivotable relative to a part in which the remaining pipe part is clamped down.

With the pipe according to the present invention, all the segments in the substantially straight pipe are provided with a local curvature. Only then are the segments moved relative to each other so as to form the curved pipe. The device that is used for this purpose comprises a number of pivotally interconnected parts, which number preferably corresponds to the number of segments of which the curved pipe is formed.

One embodiment of the method according to the invention is characterised in that the local curvature of a segment of the substantially straight pipe has a smaller radius on an inside bend of the curvature to be formed than on an outside bend of the curvature to be formed.

In this way both the inside bend and the outside bend will have obtained the radius associated with the respective inside bend and outside bend after the substantially straight pipe has been bent to form the bent pipe.

Another embodiment of the method according to the invention is characterised in that the internal wall on the outside bend of the curvature of the bent pipe is substantially smooth.

By providing each segment of the original straight pipe with a local curvature, at least on the outside bend of the curvature to be formed, which curvature corresponds to the eventually desired curvature of the bent pipe, the outside bend part of the bent pipe that is eventually formed will be substantially completely smooth. The interior of the pipe will be substantially completely smooth as well, thus enabling a smooth flow through the bent pipe.

Yet another embodiment of the method according to the invention is characterised in that a segment of the substantially straight pipe tapers off from an inside bend of the curvature to be formed to an outside bend of the curvature to be formed.

As a result, a bent pipe will be obtained when the sides of the segments facing the inner side are moved together, in which bent pipe the segments are substantially contiguous.

Another embodiment of the method according to the invention is characterised in that a zone comprises a part of the straight pipe that can be creased between two successive segments, each zone in the bent pipe being folded into a crease.

As a result of the zones being folded into a crease, the segments are moved together. The crease is larger near the inside bend than near the outside bend, and gradually decreases in size in the circumferential direction of the pipe. Creases need not be formed near the outside bend, since the segments can directly join one another at that location. As a result of the presence of the aforesaid creases, hardly any stretch will occur when the material is being bent. As a result, also materials having a low plastic deformation capability, to be expressed in elongation at break, for example, can be used for producing bent pipes. Think in this connection of materials such as steel, aluminium and other metals or plastics.

Yet another embodiment of the method according to the invention is characterised in that a beginning of a crease is formed in each zone of the substantially straight pipe.

In this way each zone will be creased to the desired configuration when the substantially straight pipe is bent to form the bent pipe.

Instead of forming creases, it is also possible to remove the zone that is present between two successive segments from a substantially straight pipe, wherein, after the straight pipe has been bent to form the bent pipe, sides of adjacent segments of the bent pipe will at least substantially abut against each other. Preferably, said abutting sides are connected together. Said removal of the zones present between two successive segments can take place prior to the formation of the local curvature in the segments; preferably, however, it will take place after the formation of the local curvatures in the segments.

In this way a more precise formation of the segments is ensured.

Yet another embodiment of the method according to the invention is characterised in that the substantially straight pipe is positioned in a number of pivotally interconnected parts, each part comprising at least one curvature to be locally provided of a segment positioned therein, whereupon the pipe is deformed, during which deformation each segment is pressed against the wall of the associated part, as a result of which the segment is provided with the local curvature, and the parts are subsequently pivoted relative to each other, thus forming the desired curvature in the pipe.

In this way a controlled formation of the local curves in the segments is realised, wherein, once the local curvatures have been formed, the substantially straight pipe is bent to formed the bent pipe by pivoting the parts relative to each other.

Creases may be formed in the zones between the parts, if desired.

The invention will now be explained in more detail with reference to the drawings, in which:

• Figure 1 shows a theoretical model of a bent pipe;
• Figure 2 shows the bent pipe of figure 1, divided into segments;
• Figure 3 shows the bent pipe of figure 2 developed along a line;
• Figure 4A shows a theoretical model of the substantially straight pipes comprising removed zones that is to be formed;
• Figure 4B shows a detail of the substantially straight pipe shown in figure 4A;
• Figure 5 shows a theoretical model of the substantially straight pipe comprising removed zones that is to be formed, in which zones to be creased are present between the segments;
• Figures 6A-6L and figures 7A-7E show various views of the forming of a bent pipe from a substantially straight pipe;
• Figures 8A-8C show a perspective front view, a perspective top plan view and perspective side view, respectively, of another bent pipe according to the invention;
• Figure 9 shows a perspective front view, a perspective top plan view and perspective side view, respectively, of yet another bent pipe according to the invention;
• Figure 10 shows a perspective front view, a perspective top plan view and perspective side view, respectively, of yet another bent pipe according to the invention;
• Figures 11A and 11B show a perspective view and a top plan view, respectively, of a device according to the invention;
• Figures 12A and 12B show top plan views of a device according to the invention with a substantially straight pipe and a bent pipe formed by means of the device, respectively, present therein.

Like parts are indicated by the same numerals in the figures.

• Figure 1 shows a theoretical model of a bent pipe 1 which extends along an axis 2. The bent pipe 1 has a circular cross-section. The bent pipe 1 has an inside bend 3 with a radius R_i as well as an outside bend 4 with a radius R_o" wherein R_o > R_i.
• Figure 2 shows the bent pipe 1 of figure 1, in which the bent pipe 1 is divided into segments S₁, S₂...S_n formed by lines 5 which extend from the centre M of the radii R_i and R_o. Each segment S₁, S₂...S_n extends through the same angle α. Each segment S₁, S₂...S_n has an inside radius R_i1, R_i2 ...... R_in and an outside radius R_o1 R_o2..R_on which, in this theoretical model, are the same as the radii R_i and R_o, respectively, of the bent pipe 1. Segment S₁ is bounded by the angular points a_o and a₁ on the outside of the bend and angular points b_o and b₁ on the inside of the bend. Segment S₂ is bounded by the angular points a₁, a₂, b₁, b₂. The angular point a₁ thus forms an angular point both of the segment S₁ and of the segment S₂. Similarly, the angular point b₁ forms an angular point of the segments S₁ and S₂.
• Figure 3 shows the bent pipe 1 shown in figure 2, in which the segments S₁ - S₄ have been pivoted away from each other, such that the angular points a_o, a₁, a₂, a₃, a₄ lie on a straight line L. The opposite longitudinal sides 7, 8 of adjacent segments S₁, S₂ include the angle α with each other.

As is clearly shown in figure 3, each segment S₁, S₂ .... S_n has an inside radius R_i1, R_i2 ...... R_in and an outside radius R_o1 R_o2..R_on. Because the segments S₁, S₂ have been pivoted away from each other, the angular point b₁ is no longer a common angular point, but it is now formed by two angular points b₁.

Figure 4A shows the bent pipe 1 fully developed into a substantially straight pipe 10, in which all the angular points a₁, a₂ ..... a_s lie on the line L. Zones Z₁, Z₂ .... Z_n are present between the adjacent segments S₁, S₂ .... S_n, which zones are not filled in the substantially straight pipe 10 that is shown in figure 4.

Figure 4B shows a larger-scale detail of segment S₃, in which the outside radius R_o3 can be clearly distinguished.

Figure 5 shows a substantially straight pipe 11, which is different from the straight pipe 10 shown in figure 4A in that, in contrast to figure 4, the zones Z₁, Z₂ ..... Z_n-1 present between the segments S₁, S₂ ..... S_n are filled.

When the substantially straight pipe 10 shown in figure 4A is being bent, with the segments S₁, S₂ ..... S_n being moved together, the bent pipe shown in figure 1 is obtained again. By interconnecting the sides 7, 8 of the segments S₁, S₂ ..... S_n, a pipe 1 having a fully closed wall is obtained again. It is also possible, of course, not to interconnect the longitudinal sides 7, 8 if the intended use of the pipe 1 allows this.

With the substantially straight pipe 11 shown in figure 5, the zones Z₁, Z₂ ..... Z_n-1 will need to be folded to form a crease when the pipe 11 is bent to obtain the pipe 1 shown in figure 1, so as to ensure that the sides 7, 8 of adjacent segments can be positioned substantially opposite each other.

The theory of determining the local curvatures in the segments of a substantially straight pipe as well as the subsequent formation of a bent pipe from a substantially straight pipe comprising segments and zones present therebetween has been explained with reference to figures 1-5.

Now various practical examples will be explained with reference to figures 6A-11B.

Figures 6A-7E show the deformation of a cylindrical pipe 21 having a constant diameter over its entire length, via a substantially straight pipe 22 that is divided into segments and zones present therebetween, into a bent pipe 23. In addition to the deformation of the straight pipe 21 into the bent pipe 23, also the cross-sectional shape of the pipe 21 is changed from a cylindrical cross-section with a constant diameter to a cross-sectional shape that changes along the length of the pipe from triangular into cylindrical.

Figure 6A shows a longitudinal section of the substantially straight pipe 22, which has been divided into a number of segments S₁, S₂ ..... S_n and zones Z₁, Z₂ ..... Z_n-1 present therebetween in the above-described manner, on the basis of the desired curvatures in the bent pipe to be formed. As figure 6A clearly shows, zone Z₁ extends less far towards the wall 24 that is to form the outside bend than the zone Z_n-1. The segments S₁, S₂ ..... S_n have a curvature with a radius R_o1, R_o2 ..... R_on at the wall 24. If all the radii are identical, the outside bend of bent pipe to be formed will be circular in shape. It is also possible for the radii to change gradually, to that the final bent pipe 23 will have a curvature different from a circular arc. The same applies, of course, with regard to the wall 25 of the substantially straight pipe 22 that is to form the inside bend.

Seen in the circumferential direction of the substantially straight pipe 22, the curvature of a segment S₁, S₂ ..... S_n changes gradually from the curvature with radius R_i1, R_i2 ...... R_in near the wall 25 that is to form the inside bend to the curvature with radius R_o1, R_o2 ..... R_on at the wall 24. Each zone Z₁, Z₂ ..... Z_n-1 has an outwardly projecting bulge 26 in the wall thereof, whose degree of bulging varies along the circumference of the substantially straight pipe 22.

The substantially straight pipe 22 with the segments S₁, S₂ ..... S_n formed therein and the zones Z₁, Z₂ ..... Z_n-1 present therebetween can be formed by means of a hydroforming technique. With this technique, which is known per se, the cylindrical pipe 21 is placed in a space present in a device. Said space is bounded by walls comprising a profile corresponding to the profile to be formed in the substantially straight pipe 22 that is to be produced. Then a fluid, such as oil, is introduced into the pipe 21 under pressure, whilst simultaneously forces are exerted on the pipe 21, in axial direction. As a result, the pipe 21 is deformed to obtain the substantially straight pipe 22 comprising the segments, the zones and the curvatures and bulges formed therein. The straight axis of the pipe 21 is substantially identical to the axis of the substantially straight pipe 22 with the local curvatures formed in the segments.

Once the substantially straight pipe 22 has been formed, the pipe 22 is bent to form the bent pipe 23. Said bending comprises moving the segments S₁, S₂ ..... S_n towards each other on a side facing the wall 25, causing the zones Z₁, Z₂ ..... Z_n-1 to be folded together, resulting in the formation of a crease 27 (see figure 6E). The wall 25 that forms the inside bend comprises the substantially contiguous segments S₁, S₂ ..... S_n, with the local curvature with radii R_i1, R_i2 ..... R_in forming a substantially continuous internal wall 28, which is interrupted only by the creases 27.

Since the zones Z₁, Z₂ ...., Z_n-1 do not extend to the wall 24 that forms the outside bend, the segments S₁, S₂ ..... S_n join one another in a perfectly contiguous manner at the wall 24, so that a substantially completely smooth inner wall is obtained. Thus a good flow is obtained in the bent pipe 23 when the pent pipe 23 is used as a flow channel. The central axis of the bent pipe 23 has a curvature with the same centre of curvature as the outside bend of the bent pipe 23.

Figure 6E1 and figure 6E2 show the same view of the bent pipe 23 but with different details VID, VIE and VIH, VIL, VIK, respectively.

As appears from the cross-sections VIH-VIH, VIL-VIL and VIK-VIK shown in figure 6H, figure 6K, figure 6L, the cross-sectional shape of the bent pipe 23 gradually changes from circular to triangular.

This also appears from figure 6F and figure 6G, which show a side view of the substantially straight pipe 22 and the bent pipe 23 formed therefrom, respectively.

As figures 7D, 7E clearly show, the creases 27 formed by zone Z₁, Z₂ ..... Z_n-1 do not extend along the entire circumference of the bent pipe 23. Moreover, each crease 27 decreases in size, seen in circumferential direction from the inside bend to the outside bend.

Figures 8A-8C show another bent pipe 31 formed by using the method according to the invention, which pipe is provided with identical cylindrical openings 32, 33 at both ends and which comprises a part 34 having a triangular cross-section near the centre. The bent pipe 31 comprises a first bent part 35, which extends between the circular passage 32 to the part 34 with the triangular cross-section, and a second bent part 36, which extends from the part 34 with the triangular cross-section to the circular passage. Such a pipe 31 is for example obtained by providing inter alia the segments and zones desired for the bent parts 35, 36 in a straight pipe. Then the substantially straight pipe thus formed is bent in a number of steps to obtain the desired bent pipe.

Figures 9A-9C show another embodiment of a bent pipe 41 which is different from the bent pipe 31 shown the in figure 8A-8C in that the circular passages 42, 43 at the ends of the bent pipe 41 are different in diameter.

Figures 10A-10C show yet another embodiment of a bent pipe 51 according to the invention, which comprises two bent parts 52, 53 and a part 54 with a triangular cross-section, which extends therebetween. A cylindrical pipe 55, which has a larger diameter near the end 56 than near the bent part 53 and the other end 57, joins the bent part 53.

Figures 11A and 11B show a perspective view and top plan view, respectively, of a device 61 according to the invention, which is suitable for producing the bent pipe 23, for example. The device 61 comprises two parts 62, 63 to be positioned opposite each other, which are each provided with parts 65 interconnected via pivot arms 64. Mating parts 65 of the lower part 63 and the part 62 positioned thereabove jointly define a passage 66, whose wall 67 is provided with local curvatures which correspond to curvatures to be formed in a segment S₁, S₂ ..... S_n.

The operation of the device 61 is as follows. The upper part 62 is removed from the lower part 63, whereupon a pipe 21 is placed in the passages 66. Then the upper part 62 is positioned over the straight pipe 21. Subsequently, fluid pressure is applied in the pipe 21, whilst at the same time axial forces are exerted on the ends of the pipe 21. As a result, the wall of the pipe 21 is deformed, and the curvatures are formed in the segments S₁, S₂ ..... S_n by the walls 67 of the passages 66. As is shown in figure 11A, free spaces 68 are present between the passages of adjacent parts 65. The pipe 21 will slightly move out at the location of the free space 68, as a result of which the bulges 26 are formed in the zones Z₁, Z₂ .... Z_n-1. Thus, the substantially straight pipe 22 is obtained.

Figures 12A-12B show a similar device 71 according to the invention, which is provided with supports 72, 73 at both ends. After the pipe 21 has been deformed by means of the device 61 or 71 into the substantially straight pipe 22 with segments S₁, S₂ ..... S_n formed therein and zones Z₁, Z₂ .... Z_n-1 present therebetween, the parts 65 are pivoted relative to each other in the directions indicated by the double arrow, as a result of which the substantially straight pipe 22 is bent to obtain the bent pipe 23. Since the segments S₁, S₂ ..... S_n firmly abut against the walls 67 of the passages 66 during said bending, the segments S₁, S₂ ..... S_n will not deform. The hydraulic pressure applied by the fluid may or may not be maintained during the bending of the substantially straight pipe to form the bent pipe.

The zones Z₁, Z₂ ..... Z_n-1 present between the segments S₁, S₂ ..... S_n are deformed further outwards upon forming the bent pipe 23, resulting in the formation of the creases 27. Walls of each crease 27 are pressed firmly together by the ends 69 of the parts 65 during this process.

It is also possible to carry out the bending of the substantially straight pipe provided with the segments and the zones to obtain the bent pipe by means of a separate device.

In the theoretical model shown in figure 1-5, the angle α is the same for all the segments S₁, S₂ ..... S_n. It is also possible, however, to have the segments S₁, S₂ ..... S_n extend through different angles α₁, α₂ ..... α_n.

The forming of the segments and zones in the pipe can take place not only by hydroforming but also by means of explosion transformation, rubber pressing, hot forming, etc.