GB2205260A

GB2205260A - Method of end device for bending pipes

Info

Publication number: GB2205260A
Application number: GB08811181A
Authority: GB
Inventors: Yasuji Hatano; Hideaki Shinmyo
Original assignee: Nihon Radiator Co Ltd
Current assignee: Marelli Corp
Priority date: 1987-05-25
Filing date: 1988-05-11
Publication date: 1988-12-07
Also published as: DE3816940A1; GB8811181D0

Description

1 2205260

TITLE OF THE INVENTION

Method of and Device for Bending Pipes BACKGROUND OF THE INVENTION

This invention relates to a method of and a device for bending pipes, and particularly relates to a method of and a device for bending pipes which make it possible to bend a pipe to achieve a bend radius no greater than the diameter thereof.

An example of a conventional pipe bending device is described in Japanese Patent Publication No. 38045/1984.

Fig. 5 shows a conventional pipe bending device. In this device, one end section of a pipe 2 to be bent is held in a lateral groove la of a rotatably supported U-shaped bending roll 1 by means of a clamper 3. The other end section (the one on the side of the portion to be bent) of the pipe 2 is engaged with a groove 4a of a pedestal 4.. In this condition, the bending roll 1 is rotated in the direction indicated by the arrow, thereby bending the pipe 2 in such a manner as to impart to it a bend radius corresponding to the circular section lb of the bending roll 1.

Generally, in a pipe bending operation, the inner portion of the pipe section which is being'bent is subjected to compressive force, whereas the outer portion thereof is subjected to tensile f"orce. The difference between these two L forces depends on the difference between the peripheral lengths of these two portions. The smaller the bend radius is, the greater is the difference in the peripheral lengths. The elongation of the pipe material and the compression ratio also become larger, resulting in susceptibility to formation of cracks and wrinkles.

In the example shown in Fig. 6,-a 1D bending, i.e. a bending in which the bend radius R is equal to the pipe diameter D, is being performed on the pipe 2. In this case, the compression/elongation ratio at the bend portion 2a can be obtained as follows:

Suppose the pipe center is the neutral axis, Inner pipe periphery = 2 x-R x J'C Pipe center = 2 x R x outer pipe periphery = 2 x 1.5R x fE When the neutral axis is 1, the ratio between the three is 0.5: I 1 1.5. Consequently, the outer periphery of the pipe bend section 2a undergoes an elongation of 50%, and the inner periphery of the same a compression of 50%. One can conclude from this that theoretically, a 1D bending cannot be performed without using a material with an elongation ratio of 50% or more.

In the case of the conventional bending method shown in Fig. 5, a bending operation can only be performed with a bend radius of 1D or more even when a core bar is inserted into 1 t the pipe 2 to be bent.

Japanese Patent Publication No. 9888/1982 discloses a method of and a device for forming an elbow on a short pipe. According to this publication, a compressive bending is first performed on a short pipe, then a stretch bending is performed on the same to form an elbow.

Since the bending process in this example consists of two separate stages, the pipe undergoes elongation during the second stage, which hinders bending operations employing a small bend radius because it may give rise to cracks in the pipe. Bending operations with small bend angles such as 10' or 20 are especially difficult to perform. Further, this example involves a large-scale piece of equipment, which is rather impractical. Moreover, whilst it permits bending of end portions, it is not suited to bending of longer pipe lengths as a compressive bending process is involved.

The present invention is.directed to solving the above-mentioned problems and providing a method of and a device for bending pipes capable of bending a pipe with a bend radius no greater than 1D even when the material is one with a small elongation ratio. SUMMARY OF THE INVENTION

In accordance with the present invention, while a bending roll is being rotated in the pipe bending direction, a pipe bend portion held between a pressure die and a block 4 member is bent around the circular portion of the bending roll as it emerges from between these members, and the outer peripheral portion of the pipe which is being subjected to the compressive force of a pressing means is changed in such a manner that its elongation ratio is restrained, whilst at the same time the inner peripheral portion thereof is changed in such a manner that wrinkle generation is prevented under the elongating tensile force of a block member and a core bar. Accordingly, the present invention makes it possible to bend a pipe with a bend radius of 1D or less even when the pipe material is one having a small elongation ratio.

Further, this invention can be put into practice simply by modifyng the pressurizing means employed in a conventional pipe bending machine, so that no large scale equipment is needed. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a side elevational view of a pipe bending device in accordance with the present invention; Fig. 2 is a side elevational view illustrating the operational condition after bending; Fig. 3 is a side elevational view of a pipe which has been bent; Fig. 4 is a side elevational view of the.essential part of another embodiment of the pipe pressing mechanism in accordance with the present invention; a 1 Fig. 5 is a side elevational view of a conventional pipe bending device; and Fig. 6 is a schematic view illustrating a pipe. DESCRIPTION OF THE PREFERRED EMBODIMENT

Figs. 1 and 2 show an example of the pipe bending device in accordance with the present invention. A U-shaped bending roll 10 is so mounted that it can rotate around the center 0 of the circular portion thereof. On its circumferential surface is formed a semi-circular groove 10a which conforms with the outer diameter of the pipe 11 to be bent. The pipe 11 has a bevel end surface llb on the side of a bend portion lla thereof. A clamping member 12. arranged in opposition to one side of the pipe bending roll.10 presents a semi-circular groove 12a with which the pipe 11 is engaged. This clamping member 12 permits one end section of the pipe 11 to be held onto the bending roll 10.

A pressure die 13 holds the other end section, i.e.-the section on the bend portion lla side, of the pipe 11. This pressure die 13 is arranged in the vicinity of the bending roll 11 in such a manner that it can move vertically, and presents a semi-circular groove 13a with which the lower half (corresponding to the outer bend periphery) of the section of the pipe 11 which is on the side of the bend portion llais engaged. A block member 14 presents a semi-circular groove 14a for holding the upper half (corresponding to the inner bend periphery) of the section of the pipe 11 which is on the side of the bend portion Ila. One end of this block member 14 holds the section of the pipe 11 on the bend portion Ila side that it is engaged with the groove 10a of the bending roll 10.

A boost cylinder 15, arranged on the same axis as the pipe 11, presents a piston rod 15a, to the end of which is connected a cylindrical pipe pusher 16 which can be inserted into the grooves 13a and 14a of the pressure die 13 and the block member 14, respectively. The tip of the pipe pusher 16 presents a bevel end surface 16a, symmetrical with the bevel end surface llb of the pipe 11 on the bend portion Ila side, which exerts a pressurizing force,while the pipe 11 is being bent on the outer bend periphery side of the bevel end surface l1b, thereby restraining the elongation of the outer bend periphery of the pipe. A core bar 17, slidably engaged within said cylindrical pipe pusher 16, has a wrinkling checker 18 connected to one end thereof; the other end of the core bar 17, which engages with the pipe pusher 16, is connected to one end of an operation rod 19 which passes through the axial core of a piston rod 15a of a boost cylinder 15. The other end of the opeation rod 19 is connected to a hydraulic cylinder (not shown). In some cases, the bevel surface 16amay not be in symmetry with the bevel surface llb.

1 7 The process of bending the pipe 11 by means of a device with the above- mentioned construction will now be exp1ained.

First, the clamping member 12 is opened and the pressure die 13 is displaced in the direction of the arrow A2 in Fig. 1. Then one end section of the pipe 11 to be bent s engaged with the lateral groove 10a of the bending roll 10, and the clamping member 12 is operated to fix the pipe 11 to the bending roll 10. In doing so, the bevel end surface llb of the pipe 11 is set in the position shown in Fig. 1. After that, the pressure die 13 is displaced in the direction indicated by the arrow Al in Fig. 1, whereby the entire pipe bend portion lla is sandwiched from below and above by the pressure die 13 and the block member 14, respectively. Then, the core bar 17 and the wrinkling checker 18 are inserted into the pipe 11 at the opening on the side of the bend portion Ila, and the boost cylinder 15 is advanced to bring the tip of the bevel end surface 16a of the pipe pusher 16 into engagement with that of the bevel surface llb of the pipe 11, thus exerting compressive force on the latter.

When in this condition the bending roll 10 is rotated in the direction indicated by the arrow B in Fig. 1, the bend: portion Ila of the pipe 11 is bent along-the circular portion 10b of the bending roll 10, resulting in the state shown inFig. 2. During this process, the bend portion lla of the pipe 11 is bent along the groove in the circular portion of 1 ig the bending roll 10 as it emerges from the respective grooves 13a and 14a of the pressure die 13 and the block member 14. At the same time, the pipe pusher 16, advancing faster than the above emerging movement, exerts compressive force by a pressing action onto the outer bend periphery side.of the pipe bend section lla in order to restrain the tendency for extensive elongation of the outer bend periphery section which would otherwise be dominant, thereby preventing the outer bend periphery section from growing thinner to an excessive degree.

On the other hand, the inner peripheral wall of the inner bend periphery side of the pipe bend portion lla is held by the core bar 17, the wrinkling checker 18 and the block member 14, so that the inner peripheral wall starts to be stroked as the above emerging movement of the pipe bend portion lla takes place. This means the wall is subjected to a tensile force acting in such a manner that the compression thereof is reduced. As a result, generation of cracks and wrinkles on the bend portion lla of the pipe 11 can be avoided, thus making it possible to bend a pipe with a bend radius of 1D or less even when the pipe material is one with a small elongation ratio.

The following are some results obtained by actually bending a pipe in accordance with the method of thisinvention:

c- 1 C By bending a pipe having a diameter of 48.6 and a thickness of 2.Omm and made of NSS442M3 (with an elongation ratio of 30%), to an angle of 900with a bend radius of R35, it was confirmed that a thickness reduction of ca. 25% took place on the outer bend periphery section. This rdeans that a pipe can be easily bent with a bend radius no greater than the diameter thereof without generating cracks or wrinkles thereon.

When the bending operaion of the pipe 11 has been completed, the clamping member 12, which is then in the state shown in Fig. 2, is released, and the pressure die 13 is displaced in the direction indicated by the arrow A2, in order to allow the pipe which has been bent to be taken out. Fig. 3 shows a product thus obtained.

At this stage, the pipe 11 presents an uneven end surface llc on the side of the bend portion lla, which may be rendered smooth by a secondary processing.

In the above example, the end surface of the pipe 11 on the bend portion lla side was formed as a bevel surface. However, the pipe 11 may be bent with the end surface left straight. In that case, the end surface would present a more complicated configuration than the one shown in Fig. 3.

Fig. 4 shows another embodiment of.a pipe bend,portion pressurizing mechanism in accordance with the present invention.

h /0 In this embodiment, the pressure die 13 is mounted on a base 20 in such a- manner that it is slidable in the longitudinal direction of the pipe 11. The pressure die 13 can be made to move bac and forth by the boost cylinder 15 mounted on the base 20, and a stage 21 is formed in the pipe engagement groove 13a of the pressure die 13, which stage 21 is engaged with the tip of the bevel end surface llb of the pipe 11 to provide axial compressive force to be exerted on the outer pipe bend periphery portion when the pipe is being bent.

This embodiment gives an effect similar to that obtained by the foregoing emobidment.

1 0 1 1.

Claims

WHAT IS CLAIMED IS:

1, A method of bending pipes, comprising the steps of: clamping one end section of a pipe to be bent onto a bending roll, holding in a sandwiched state the other end section of the pipe which is on the bend portion side thereof-by means of a pressure die and a block member, inserting a core bar into the bend portion of the pipe, and bending the pipe by rotating said bending roll, with the outer bend periphery section being pressed in such a manner that it is compressed by means of a pressurizing means.

2. A device for bending pipes, comprising a bending roll with a circular section for bending pipes, a clamping member for clamping one end section of a pipe to be bent to one side of said bending roll, a pressure die arranged in the vicinity of said bending roll and adapted to hold the bend portion which is on the other end section of said pipe to be bent at its outer bend periphery section, a block member arranged in the vicinity of said bending roll and adapted to hold the bend portion of said pipe to be bent at its inner bend periphery section and to exert tensile force thereon, a core bar member inserted into the bend portion-on the other end section of said pipe to be bent, and a pressurizing means which is engaged with the edge portion of the outer bend periphery section on the other end section of said pipe to be bent in order to press said outer bend periphery section in Q -F such a manner that it is compressed.

3. A method of bending pipes substantially as hereinbefore described with reference to the accompanying drawings.

4. A device for bending pipes substantially as hereinbefore described with reference to the accompanying drawings.

14 Published 1988 at The Patent Office, State House, 66171 High Holbora, London WCIR 4TP. Further copies may be obtained from The Patent OffIce, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent. Con. 1/87.