GB2122521A - Apparatus and method for bending rod or tube - Google Patents

Abstract

Apparatus for bending rod or tube, particularly to produce lever handles or pull handles for doors, comprises a pair of pivotally mounted supports (24, 25) spaced longitudinally apart between a pair of parallel blocks (22, 23) to define a space towards and away from the centre of which a former (35) is movable. The supports have semi- circular grooves (26) in their upper surfaces to support a rod or tube laying across said space. The lower end of the former (35) is of V-shape with a pair of mutually inclined surfaces (36, 37) joined by a short arcuate surface (38). All these former surfaces have a semi-circular section groove (39) therein, so that, in use, as the former is lowered the tube or rod of corresponding circular section is received in the grooves (26, 39) in the supports and former, and bent as the supports pivot downwardly at said space as the former descends. By this method a bend with an internal radius substantially less than the generally accepted minimum can be obtained, as well as with minimum tool marking occurring. <IMAGE>

Description

SPECIFICATION Apparatus and method for bending rod or tube This invention relates to apparatus for bending rod or tube and to a method for such bending.

The techniques for bending tube are many, but it is generally accepted that to bend a tube to produce a radius inside the bend of 13 times the tube diameter cannot be achieved without excessive stretching on the outside and excessive compression on the inside. Beyond this limit distortion and buckling generally occurs and even bursting of the tube wall, particularly at the outside of the bend.

It is generally accepted, moreover, that to bend tube down to this limit is only possible if the interior of the tube is well supported over the region of the bend by a spring or other internal support.

The same considerations as to distortion are apparent for bending rod, though of course no internal support is appropriate.

In general, though there are many devices for bending tube, they are substantially all limited by these considerations. Almost all use the principle of holding one end of the tube or rod and bending the other end around a former which may be more or less shaped to correspond with the internal radius to be achieved.

In certain industries it is also desirable to produce a bend in tube or rod with minimum marking from the tools used.

It is the object of this invention to provide apparatus and a method to enable tube or rod to be bent to produce a bend with internal radius substantially less than the generally accepted minimum and also in which minimum tool marking occurs.

In accordance with the invention there is provided apparatus for bending tube or rod including two spaced supports on which, in use, the tube or rod rests at either side of the position at which the bend is to be made, and a former movable towards the centre of the space defined between two supports, the former being shaped to define an internal bend in a tube or rod and the supports both being pivotally mounted so as to move with portions of the tube or rod at opposite sides of the bend position as it is bent by movement of the former towards the space between said supports.

Preferably the supports and the former have grooves of a shape corresponding, in part, to the external profile of the cross-sectional shape of the tube or rod to the bent.

According to a further aspect, the invention relates to a method of bending tube or rod comprising placing a tube or rod to be bent onto two spaced supports for the tube or rod, moving a former towards the space between the supports, and the supports being pivotally mounted so that as the former is moved towards the said space, the tube or rod is bent therein and the supports move with the portions of the tube or rod at opposite sides of the bend position.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic sectional view of a pull handle formed from tube bent in accordance with the present invention; Figure 2 is a perspective view of part of the tube or rod bending apparatus constructed according to the present invention; Figure 3 is a cross-sectional view, on a larger scale, of the rod or tube bending apparatus; Figure 4 is a side view of the apparatus; and Figures 5 and 6 show how the spacing of a pair of supports of the apparatus is altered for different diameters of tube or rod.

Although this invention is applicable to the bending of tube or rod in general, it is particularly concerned with the bending of tube or rod to produce lever handles or pull handles for doors and the like.

Fig. 1 shows a pull handle 10 of conventional appearance, but which has a bend 11 with an internal radius substantially less than the generally accepted minimum of 1 + times the external diameter of the tube. In the example shown, the internal radius is only 0.5 times the diameter. As shown, the bend is through 90 , but this could be greater or less if required. The handle is free or substantially free of any tool markings and thus has an acceptable exterior surface finish.

Figs. 2 to 4 show apparatus for producing such a handle. The apparatus shown fits, in use, in a die set machine, with the top die being cut away for a purpose which will be described.

The apparatus comprises a generally rectangular base 12 at opposite corners of the longer rear side of which are disposed two cylindrical platforms 13, 14 carrying respective upright cylindrical columns 15, 16. These carry respective cylindrical collars 17, 18 thereon at their upper ends, the collars providing support for an upper die 19 (Figs. 3 and 4) extending between the columns. The die has a forwardly extending portion 20 which is parallel to the base 12 and extends to the front thereof. The die 19 is cut away at its left side to allow clearance for a bent tube, as will be described.

On a raised front portion 21 of the base 12 are disposed a pair of rectangular blocks 22, 23 which are linearly spaced apart, and are parallel to the longitudinal sides of the base 12. Between the two blocks are a pair of spaced supports 24, 25. Each support has a generally semi-circular section groove 26 in its upper surface, the bottom surface of the groove terminating in the radius 27 at the inward end thereof. The support itself has chamfered surfaces 28, 29 at the sides of the radius portion.

Each support is pivotable about a horizontal pin 30 passing through each block. Each pin has an enlarged circular head 31 with a partcylindrical cut-out 32, which receives a peg 33. The peg 33 prevents rotation of the pin 30.

In their respective normal positions however the supports are disposed with their grooves horizontal, as shown best in Figs. 2 and 3.

The support 25 has an end stop 34 engaged therewith at its outer end, the stop blocking the groove 26 to limit insertion of a pipe along the groove, in use.

Depending from the die portion 20 is a former 35, the lower end of which is of Vshape, being formed by a pair of surfaces 36, 37, which are joined by a short arcuate portion 38, the surfaces 36, 37 being generally at 90 to one another. In each surface is a generally semi-circular section groove 39, the grooves, like the surfaces, being joined by an arcuate part 40. The shapes of the grooves 26 and 39 together substantially form a cylindrical section to receive a tube or rod of similar size, in use. This can be best seen from Fig. 4.

The former 35 is disposed centrally over the space between the supports 24, 25 and is movable vertically between a fully raised position, in which the tube or rod to be bent can be inserted onto the supports 24, 25, and a fully lowered position, in which the tube is bent to the desired maximum angle, in this case 90'. Obviously the degree of bend is governed by the angle between the two grooves 39 and also the lowest point to which the former can be moved. Movement of the former can be controlled in a conventional manner, such as by hydraulic or pneumatic means.

In use, a straight rod or tube is placed on the supports so that it is disposed in the grooves 26, with one of its ends abuting the end stop 34. Naturally the sizes of the grooves 26 and 39 are chosen for a certain tube or rod diameter and can be replaced by different supports and former having matching larger or smaller grooves. The grooves could of course be other than semi-circular.

If a tube, rather than a rod, is to be bent, it must be internally supported. This can be carried out, for example, by filling the tube with a pre-formed aluminium rod as a sliding fit (tolerance 0.00762cm to 0.01524cm) or alternatively filling it with melted aluminium and allowing it to cool. Another filler could be a suitable resin. In either case the filler should have a lower melting point than the material of the tube, so that it can be melted out of the tube after the bending operation.

Once the tube or rod is in position, the former is lowered to engage it at a position centrally between the supports 24, 25. Continued downward movement of the former causes the supports to pivot about their respective pin 30 and the tube or rod to bend.

Figs. 5 and 6 show the end of the bending operation for two different sizes of tube.

When the desired degree of bend is reached, in this case 90 , the former automatically stops and can then be operatively raised to allow the tube or rod to be removed from the apparatus. If a pull handle is being formed, for example, the other, unbent end of the rod or tube is then placed against the end stop 34, with the bent end extending away from the support 24. The process is then repeated to complete the second bend of the pull handle, thereby giving it its U-shape. As this bending occurs, the bent end will be forced upwardly, and this is the reason that the lefthand top part of the die is cut away, namely to accommodate this upward movement of the previously bent end of the handle.

The distance between the pins 30 of the two supports must be varied with different diameters of rod or tube. Fig. 5 shows the position of maximum bend with a first diameter rod 41, and Fig. 6 shows the position with a larger diameter of rod 42. Thus as previously mentioned a different arrangement of blocks 22, 23, supports 24, 25, and former 35 is required for different rod or tube diameters.

Since the former 35 moves centrally between the two pins 30, it is possible to calculate geometrically the required horizontal spacing of the pins for a particular tube or rod diameter, by way of an isosceles triangle having its apices at the centres of the pins 30 and at the centre of curvature of the internal bend of the tube or rod. Figs. 5 and 6 both show such a triangle, drawn on this view of the former in its lowermost position forming a 90' bend in the tube or rod, the radius of the bend being 0.5 times the external diameter of the tube or rod.

If 'S' is a perpendicular distance from the centre of the pin 30 to the bottom of the groove 26 in a support 24 or 25, and 'D' is the external diameter of the tube or rod, then from Figs. 5 and 6 it can be seen that the two equal sides of the isosceles triangle are of length: S + D + 0.5D = S + 1.5D. Since the angles between each such side and the remaining side of the triangle is 45 , it is possible to write: COS 45'=(S+ 1.5D)---Y, where Y is the length of said remaining side, i.e. the required spacing between the centres of the pins 30.

As COS 45 = 1 i < 2, this spacing of the pins can be written as Y = < 2(S + 1.5D). For any particular support, distance S is fixed, and thus for any particular tube or rod diameter D, the spacing Y can be evaluated. For example for a tube diameter of 25mm, the spacing is o/2 [ 23-8 + (1.5 X 25) ] , where S = 23.8mm.

Accordingly Y = < 2 X 61.3 = 86.7mm. For a diameter of 30mm, this spacing increases to V2 [ 23.8 + (30 X 1.5) ] = 97.3mm.

The surfaces 27 of the grooves are radiussed to prevent them possibly digging into the rod or tube as the bending process begins, although as can be seen from Figs. 5 and 6 these surfaces are clear of contact with the tube or rod at the end of the bending process.

It has been found that by the use of the method and apparatus of this invention, it is possible to produce a bend down to 0.5 of the tube or rod diameter, with no necking or stretching and with minimum tool marking.

Accordingly a high quality finished product results. Moreover the apparatus is relatively simple to construct and operate, and relatively inexpensive to provide.

Claims (15)

1. Apparatus for bending tube or rod including two spaced supports on which, in use, the tube or rod rests at both sides of the position at which the bend is to be made, and a former movable towards the centre of the space defined between the two supports, the former being shaped to define a bend in the tube or rod, in use, and the supports both being pivotally mounted so as to move with portions of the tube or rod at opposite sides of the bend position as it is bent by movement of the former towards the space between said supports.

2. Apparatus as claimed in claim 1, wherein the supports and the former have grooves therein of respective shapes corresponding, in part, to the external profile of the cross-sectional shape of the tube or rod to be bent.

3. Apparatus as claimed in claim 2, wherein the groove in each of the supports has its end adjacent said space radiussed below the level of the remainder of the groove.

4. Apparatus as claimed in claim 2 or claim 3, wherein one of said supports has a stop engaged therewith at its end remote from said space to block said groove and thus limit insertion of said tube or rod along the groove, in use.

5. Apparatus as claimed in any one of the preceding claims, wherein said supports are spaced apart linearly between a pair of parallel blocks, the supports being pivotally mounted on said blocks by respective pivot pins fixed against rotation relative to said supports and extending transversely to said blocks so that, in use, said supports pivot in a plane parallel to said blocks.

6. Apparatus as claimed in any one of the preceding claims, wherein a lower end of said former which contacts the tube or rod to bend it, in use, is formed by a pair of mutually inclined surfaces joined by an arcuate portion.

7. Apparatus as claimed in claim 6, wherein a generally semi-circular section groove is formed in said surfaces of said lower end of the former.

8. Apparatus as claimed in any one of the preceding claims, wherein said former depends from a die portion supported on columns, part of said die portion being cut away to accommodate, in use, upward movement of a bent end of a rod or tube whilst its other end is also being bent.

9. A method of bending tube or rod comprising placing a tube or rod to be bent onto two spaced supports for the tube or rod, moving a former towards the space between the supports, and the supports being pivotally mounted so that as the former is moved towards the said space, the tube or rod is bent therein and the supports move with the portions of the tube or rod at opposite sides of the bend position.

10. A method as claimed in claim 9, wherein said tube or rod is placed on said supports so that one end of said tube or rod engages against a stop at an end of one of said supports remote from said space.

11. A method as claimed in claim 9 or claim 10, wherein said being process is terminated when part of the tube or rod is fully received in partly correspondingly shaped grooves at opposite sides of an end of the former.

12. A method as claimed in any one of the preceding claims, when a tube is to be bent, wherein it is internally supported.

13. A method as claimed in claim 12, wherein said tube is internally supported by filling it with a metal filler rod as a sliding fit or by filling it with a melted filler, the filler material having a lower melting point than the melting point of the material of the tube, and melting out said filler material after the bending process has been completed.

14. Apparatus for bending tube or rod substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

15. A method of bending tube or rod substantially as hereinbefore described with reference to and as shown in the accompanying drawings.