GB2193130A - Producing an integral return bend in a metal tube - Google Patents

Abstract

In order that the return bend can be of relatively small radius despite the tube being of relatively large wall thickness, the method includes the steps of producing an initial return bend of a somewhat larger radius and of subsequently working the tube between a pair of jaws 24 to reduce the effective radius of the bend. The initial return bend is produced by moving grooved rollers about a grooved former. The grooving is such that the initial return bend cross-section is slightly elongate, the longer sides extending on either side of and in the direction of a plane containing the axes of the straight sections of tubing. <IMAGE>

Description

SPECIFICATION Bending of metal tube The invention relates to the bending of metal tube.

It is fairly commonplace to bend metal tube at a radius roughly equal to the outside diameter of the tube. However, there are instances where bends much smaller than this are required, for example in the cooling panels for electric arc furnaces where successive runs of steel tube extending across or around the panel are required to lie against each other, necessitating return bends at the opposite ends of the pipe run of radius D/2. The forming of what may be termed an integral bend of such small radius has been thought virtually impossible even when the tube has been raised to an elevated temperature to facilitate the plastic deformation of the metal. All previous attempts to do so have resulted in failure due to wrinking and tearing of the tube wall.

Indeed, the difficulty of forming a return bend of such a small radius in a steel tube has heretofore been such that it has become accepted practice, when producing cooling panels of the kind referred to, to assemble the runs of tube in overlying relation and to weld hollowed out end caps to the ends of adjacent pairs of tubes, the end caps each simulating a return bend of relatively small radius.

The forming of the cooling panels in this way has solved the difficulty involved in producing the required return bends at a radius as small as D/2 but has inevitably impaired the flow rate of cooling water through the panels because it has been impossible to maintain the streamline flow which is obtainable through an integrally formed bend.

The object of the invention is to provide a method of producing an integral bend in a metal tube, the bend being at a much smaller radius than previously thought possible to maintain a satisfactory wall thickness throughout the extent of the bend.

According to one aspect of the invention, there is provided a method of producing an integral return bend in a metal tube, the integral bend being of relatively small radius, the method including the steps of producing an initial return bend of a somewhat larger radius and of subsequently working the tube between a pair of jaws to reduce the effective radius of the bend to that required, the first mentioned step being carried out in such a way that the cross sectional shape of the tube in the region of the initial bend is slightly elongate with the longer length arranged about an axis located in a plane containing the axes of the adjoining staight lengths of tube.The step of producing an initial return bend in the metal tube and/or subsequent step of working the tube between the pair of jaws to reduce the effective radius of the bend, may be carried out after raising the tube to an elevated temperature. The required cross sectional shape of the initial return bend will preferably be brought about by the profiles of a former and of rollers forming a part of a bending machine used for the forming of the initial bend being shaped in a non-standard manner.

According to another aspect of the invention, there is provided a hydraulic bending machine in which a length of metal tube is to be formed with an initial return bend before being worked to reduce the radius of the bend to that required, the machine having a former and rollers of a particular profile to ensure that in the region of the initial bend in the workpiece the cross sectional shape of the tube is slightly elongate with the longer length arranged about an axis located in a plane containing the axes of the adjoining straight lengths of tube of the workpiece.

According to a still further aspect of the invention, there is provided a cooling panel for an electric arc furnace, the pipe runs of which are connected by integral return bends which have been formed by the inventive method.

In order that the invention may be fully understood and readily carried into effect, the same will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a side view of a hydraulic bending machine for producing bends in lengths of metal pipe, Figure 2 is a plan view thereof, Figure 3 is a side view of a hydraulic press which will be referred to, Figure 4 is a semi-diagrammatic plan view which shows a workpiece being worked between a pair of jaws forming part of the hydraulic press, and Figure 5 is a semi-diagrammatic section, on the line 5-5 in Figure 4, but drawn to a somewhat larger scale than Figure 4.

Referring now to the drawings, the hydraulic bending machine illustrated in Figures 1 and 2 is a generally conventional machine comprising a worktable 10, a mandrel 12 upstanding from the worktable at a radiused end of the machine, a generally cylindrical former 14 located on the mandrel, and a hydraulically powered forming head generally indicated 16.

The former 14 is provided around its periphery with an annular groove 18 of substantially semicircular cross sectional shape. The hydraulically powered forming head is provided with a pair of rollers 20,20 which have annular grooves 19 of similar shape to the groove 18. The length of pipe being formed in the machine can be acted upon between the periphery of the former 14 and the pair of rollers 20,20.

In the novel method embodying the invention of producing an integral bend in a metal tube, which will presently be described in greater detail, the hydraulic bending machine just described is used in normal manner to produce an initial return bend in the pipe at a radius in the region of D where D is the out side diameter of the tube.

In Figure 3 there is illustrated a hydraulic press in which the length of tube with the initial bend is acted upon to reduce the effec tive radius of the bend. The press includes a worktable 22, a pair of oppositely disposed jaws 24,24 controlled by respective horizon tally disposed hydraulic rams 26,26, and a centrally disposed pressure plate 28 controlled by a vertically disposed hydraulic ram 30.The arrangement is such that, when the length of pipe with the initial return bend has been posi tioned on the worktable 22, by the controlled operation of the pair of hydraulic rams 26,26 and the hydraulic ram 30 the bend can be gradually reduced until the effective radius of the bend is in the region of D/2. in other words the two straight lengths of pipe adjoin ing the initial return bend are gradually brought together by the jaws 24,24, as illustrated dia grammatically in Figure 4, and the resulting tendency of the tube to thicken in the region of the bend is countered by the pressure plate 28.

Reverting back now to Figures 1 and 2 and to the initial return bend produced in the tube being worked, although it has been said earlier that the hydraulic bending machine is used in normal manner to produce the initial return bend, and this is in fact true, the profiles of the annular groove 18 in the former 14 and the annular grooves lg of the rollers 20,20 are not exactly of conventional shape.They are of a profile such that the cross sectional shape of the tube in the region of the initial bend is slightly elongate with the longer length ar ranged about an axis located in a plane con taining the axes of the adjoining straight lengths of tube. (This is the reverse of what would normally be the case when bending a length of tube; there is normally a natural ten dency for the tube to deform in the region of the bend so that in cross section the longer length is arranged about an axis perpendicular to the plane containing the axes of the adjoin ing straight lengths of tube). It is this uncon ventional cross sectional shape of the initial return bend which enables the effective radius of the bend to be successfully reduced be tween the jaws of the hydraulic press.The cross sectional shape required in the region of the initial return bend is illustrated, although in a somewhat exagerated fashion, in Figure 5, where there is shown in chain-dotted lines the final cross sectional shape at the apex of the bend after its radius has been reduced be tween the jaws of the hydraulic press.

Various modifications may be made and it will be understood that there may well be ap plications where a return bend in a metal tube is required of greater radius than D/2 but nev ertheless of a radius so small as to be difficult to form by normal methods. It will be understood that the variations in the profiles of the former and of the rollers of the hydraulic bending machine in which the initial return bend is to be produced, to give the elongate cross sectional shape required, will soon be arrived at by a person skilled in the art, possibly after some trial and experiment. It will be understood that the step of producing an initial return bend in the metal tube and/or subsequent step of working the tube between the pair of jaws to reduce the effective radius of the bend, may be carried out after raising the tube to an elevated temperature. However, depending on requirements, it may be found that one or the other, or indeed both, of the steps referred to can be effected with the workpiece in cold condition.

Claims (6)

1. A method of producing an integral return bend in a metal tube, the integral bend being of relatively small radius, the method including the steps of producing an initial return bend of a somewhat larger radius and of subsequently working the tube between a pair of jaws to reduce the effective radius of the bend to that required, the first mentioned step being carried out in such a way that the cross sectional shape of the tube in the region of the initial bend is slightly elongate with the longer length arranged about an axis located in a plane containing the axes of the adjoining straight lengths of tube.

2. The method claimed in claim 1, in which the step of producing an initial return bend in the metal tube and/or the subsequent step of working the tube between the pair of jaws to reduce the effective radius of the bend, is carried out after raising the tube to an elevated temperature.

3. The method claimed in either one of the preceding claims, in which the required cross sectional shape of the initial return bend is brought about by the profiles of a former and of rollers forming a part of a bending machine used for the forming of the initial bend being shaped in a non-standard manner.

4. A hydraulic bending machine in which a length of metal tube is to be formed with an initial return bend before being worked to reduce the radius of the bend to that required, the machine having a former and rollers of a particular profile to ensure that in the region of the initial bend in the workpiece the cross sectional shape of the tube is slightly elongate with the longer length arranged about an axis located in a plane containing the axes of the adjoining straight lengths of tube of the workpiece.

5. A cooling panel for an electric arc furnace, the pipe runs of the cooling panel being connected by integral return bends which have been formed by the method claimed in any one of claims 1 to 3.

6. A method of producing an integral return bend in a metal tube, substantially as hereinbefore described.