GB2140338A - Flexible tube bending mandrel - Google Patents

Abstract

The mandrel includes a non-flexible main body portion (2) and a flexible portion (9) including a elongate core (10) comprising a length of cable attachable to the body portion to extend in prolongation thereof. The cable carries a number of shells 13 each having spherical portions adapted to co-operate with a complementary shaped surface (14, 17, 5, 21) of an adjacent shell or with the end of the body portion, and retaining means (25, 26) securable to the cable for engagement with a toroidal element (20) forming the end deforming element of the flexible portion (9) to hold the parts of the flexible portion in firm endwise engagement with the body portion without inhibiting the flexibility of the body portion. The cables are readily replaceable. <IMAGE>

Description

SPECIFICATION Tube bending mandrel construction This invention relates to a tube bending man drel construction.

In many activities of and fields of engineer ing it is necessary to be able to bend tubes of various metal materials through predeter mined angles of bend without excessive crinkling or other deformation of the tube undergoing the bending operation. Such deformation commonly occuring on the inside of the bend, whereby the through bore area at the bend is reduced.

It is known to effect tube bending by insert ing into the tube to be bent a flexible mandrel in the form of a closely coiled spring or the like which serves to support the interior of the tube during the bending operation. In the use of such a mandrel it is always possible that the mandrel itself becomes deformed by reason of damage to coils of the mandrel so that it then becomes very difficult to remove the mandrel after completion of the bending operation.

It is also known to bend tubes by providing an assembly of spherical balls which are connected into end-to-end relation ships by linkages. In use the balls are inserted into the tube at the location at which it is desired to form the bend to provide the requisite support. In practice, it has been found that such a mandrel construction is very expensive to manufacture and is also subject to failure without warning accompanied by ensuing difficulties in extracting the broken mandrel and in effecting any subsequent repairs.

According to the present invention there is provided a flexible mandrel for use with a tube bending machine, the mandrel comprising a non-flexible body portion adapted at one end for attachment to the machine, a flexible portion including an elongate support means for at least ring member or shell connectable to the other end of the body portion to extend in prolongation thereof, each said ring member or shell having a spherical portion adapted to co-operate with a complementary spherically shaped surface provided at said other end of the body portion, and retaining means securable to the support means for engagement with the ring member or shell most remote from the body portion for holding the ring members or shells in firm endwise engagement with the body portion without inhibiting the flexibility of the flexible portion.

Preferably, each said ring member or shell has a spherically convex outside and spherically concave inside surface portions whereby the ring members or shells can engage in overlapping relationship for vertebral displacement on the flexible support means.

Preferably, the retaining means includes a further ring member which has a spherical surface portion that is complementary to the adjacent surface portion of the adjacent ring member or shell.

Conveniently, the support means comprises a length of cable having one end adapted for connection to the body portion and its other end adapted for co-operation with the retaining means.

For a better understanding of the invention and to show how the same may be carried into effect reference will now be made to the accompanying drawing in which there is shown a cross sectional view of a mandrel construction incorporating the features of the invention.

Referring now to the drawing the mandrel shown therein includes a main body 1 having a cylindrical outer surface 2. The main body has a plain end 3 in which is provided an axial bore 4 which is threaded to enable the mounting of the main body to a suitable support bar which is not shown.

A hemispherical recess 5 is provided in the other end 6 of the main body 1. The formation of the recess 5 is such that the end 6 essentially becomes a very narrow annulus. A second axially directed bore 7 is formed in the main body 2 this second bore 7 extending from the spherical recess 5 to a location adjacent to the inner end of the bore 4. This arrangement of the bores 4 and 7 produces a wall region 8. A further axial bore 8A is formed in the wall region.

The selectively deformable section 9 of the mandrel includes a core 10 which is formed by a steel cable which can be a multistranded arrangement comprising a 6 X 36 steel core of 1 3mm outside diameter. In practice the cables are intended to be generally capable of accommodating some 10,800 kgf.

A terminal unit 11 is provided at each end of the core 10. The terminal units may be of the same or different lengths and in the Figure the lengths are shown to be different.

The terminal units are swaged or otherwise secured to the actual core. It will be understood that the nature of the fitting of the terminal units needs to be able to accommodate any tension forces likely to arise in use.

The terminal units 11 are externally threaded. In addition, the end of the unit 11 located, as seen in the drawing, adjacent to the wall region 8 is adapted for engagement in the bore 8A. If desired the bore 8A and the end of the terminal unit engageable in the bore 8A may be suitably threaded.

The terminal unit 11 at the other end of the core 10 is provided with suitable flats 12 for receiving a spanner or the like.

The section 9 incorporates at least one part spherical shell 13. As will be seen each such shell 13 comprises an annulus whose outer wall defines the part spherical surface 14.

Each shell 13 has an annular end face 15 and an inner wall 16 defined by a second part spherical surface 17, and a cylindrical portion 18 which is coaxial with a line containing the centres of curvature of the two part spherical surfaces 14 and 17. it will be noted that the radii of curvature of the surfaces 14 and 17 are essentially identical and that the centres of curvature are so displaced relative to each other that the two surfaces effectively intersect to define a circular edge region 19 whose plane is parallel to that of the end face 15 and thus perpendicular to the line joining the centres. In addition the radii of curvature of the surfaces 14 and 17 are each identical to that of the main body surface 5.

With this arrangement each shell 13 is able to nest into the spherically recessed end of the main body and also one into the other in the manner shown in the drawing.

A torroidally shaped element 20 includes a part spherical surface 21 having a radius of curvature identical (for practical purposes) to the radii of curvature of the surfaces 5, 14 and 17, and two annular end faces 22 and 23. In addition, the element 20 has a cylindrical internal surface 24 having a diameter equal to the diameter of the cylindrical portion 18 of the shells 13.

The shells 13 and the torroidal element are mounted to the core in the following manner.

One of the terminal units 11 is screwed into the bore 7 of the main body 1. This is readilly effected by using a suitable spanner or the like on the flats 12 provided upon the other unit 11. After having secured the terminal 11 in place and thus the core 10 the requisite number of the shells 13 are mounted to the core is is clearly shown in the Figure. It will be understood that the the overall length of the core 10 will be related to the number of shells to be fitted and that in practice, a range of core lengths may be provided.

Following the mounting of the shells the torroidal element is mounted to the core 10.

The element 20 is held in place by a washer 25 providing a seating for the element 20.

The shells 13, the torroidal element 20 and the washer 25 are cramped towards each other and thus towards the surface 5 by means of a retaining nut 26 which engages with the threaded section of the unit 11.

The degree of tightness produced is such as to provide for a very firm engagement between the various part spherical surfaces whilst at the same time allowing for-a universal joint like relative movement when in use.

It will be apparent that the mode of deformation of the flexible portion is similar to the relative movements of the bones of a spine and can thus be regarded as a vertebral movement. Furthermore, it is convenient to regard the outer spherical portions 14 of the shells as being spherically convex and the inner spherical portions as being spherically concave.

During the flexing of the portion 9 in order to bend a pipe (not shown) the pipe will be deformed about a line of bend indicated by the chain dashed lines 27, the centre of curvature of the line of bend being shown at 28.

Although a mandrel is shown in the Figure as having two shells 13 it will be understood that one or more than two shells could be used according to requirements.

An advantage of the above discussed mandrel construction is that if the mandrel should be over stressed during use the cable will defrom, that is distort, thereby providing a visual indication that over stressing has taken place. The situation can be readily corrected by replacing the cable 10 by a replacement cable by removing the nut 26, and the torroidal element and shells; and then unscrewing the cable from the main body 1. A new cable 10 is screwed into place and the shells, torroidal element, washer and nut are replaced. The nut is tightened such that the torroidal element, the shells 13, and the body portion are held in firm endwise engagement without inhibiting the flexibility of the flexible portion 9. In practice, the internal cylindrical bores of the shells 13 and the element 20 are the same and are such that during flexure of the mandrel they do not contact the cable 10.

so that jamming or binding of the shells or element with the core 10 is avoided.

In use the body section 2 is mounted from a suitable support arm or the like. The mandrel is then inserted into the tube to be bent, the latter having an internal bore compatible with the overall diameter of the mandrel, by engaging the tube over the mandrel deforma ble section 9 and as much of the remainder of the mandrel and support arm or the like as is necessary to bring the required region of the tube that is to be deformed into co-operation with the deformable section 9. After this the tube is deformed by bending the tube relative to the axial direction of the support arm and main body to the extent desired. After this the tube is withdrawn from the mandrel and support arm or the like. The flexibility of the deformable section 9 will enable the latter to return to its initial rectilinear position, as shown in the Figure during the removal of the deformed tube.

It will be noted that the construction of the above discussed mandrel makes possible multiplane bending using the same machine.

Claims (8)

1. A flexible mandred for use with a tube bending machine, the mandrel comprising a non4lexible body portion adapted at one end foraftachment to the machine, a flexible portion including an elongate support means for at least a ring member or shell connectable to the other end of the body portion to extend in prolongation thereof, each said ring member or shell having a spherical portion adapted to co-operate with a complementary spherically shaped surface of an adjacent ring member or shell or with a complementary shaped surface provided at the other end of the body portion, and retaining means securable to the support means for engagement with the ring member or shell most remote from the body portion for holding the ring members or shells in firm endwise engagement with the body portion without inhibiting the flexibility of the flexible portion.

2. A flexible mandrel as claimed in claim 1, and in which each said ring member or shell has a spherically convex outside and a spherically concave inside surface portions disposed in overlapping relationship on the support means., the arrangement being such that the ring members or shells are able to undergo vertebral displacement during the flexing of the flexible portion of the mandrel.

3. A flexible mandrel as claimed in claim 1 or 2, wherein the support means comprises a cable having a sleeve-like mounting unit at one end thereof adapted for connection to the body portion, and a second sleeve-like part forming part of the retaining means at the other end of the cable.

4. A flexible mandrel as claimed in claim 3, and wherein said other end of the cable is adapted to provide means for co-operating with means for facilitating the connection of the cable with the body portion.

5. A flexible mandrel as claimed in any one of claims 1 to 4, and wherein the retaining means includes a torroidal element having a spherical surface portion complementary to a spherical surface portion of an adjacent ring member or shell, and means for enabling selective adjustment of the firmness of contact between contacting surfaces of the members or shells provided upon the support means.

6. A flexible mandrel as claimed in any one of claims 1 to 5, and wherein each said ring member or shell has a cylindrical internal surface defining a bore of a diameter greater than that of the corresponding dimension of the support means, the arrangement being such that the internal bores of the ring members or shells remain out of contact with the support means.

7. A flexible mandrel as claimed in claim 6 as appendent to claim 5, and wherein the torroidal element has an internal cylindrical surface having a diameter corresponding to that of the cylindrical internal surfaces of the ring members or shells.

8. A Flexible mandrel constructed and arranged to operate substantially as hereinbefore described with reference to the accompanying drawing.