This invention relates to a method of and apparatus for forming hollow generally cylindrical bodies from strip material.

Some common methods of forming such bodies involve passing the strip between opposed forming rolls which apply a bending moment to the strip in order to bend it into the required curvate shape. A problem with some methods of this kind is that it is difficult to avoid leaving a substantially unbent straight portion at one or both ends of the curved strip necessitating further corrective forming and/or machining steps in order to produce a substantially truly cylindrical body.

An object of the present invention is to provide a forming method and apparatus which enable the aforesaid problem to be alleviated or avoided.

According to the present invention, a method of forming a generally cylindrical body from strip material comprises introducing the strip material to a location with a first surface thereof facing an array of forming elements arranged along an arcuate path, effecting relative movement between the elements and an opposing cylindrical surface portion of a mandrel to engage the mandrel with a second surface of the strip opposed to the first and force the first strip surface into engagement with the array of elements, and effecting relative driving rotation between the mandrel and array to move the strip such that a bending moment is applied to the strip by interaction between the mandrel and elements to form the strip into a substantially cylindrical shape.

According to another aspect of the invention, apparatus for forming a generally cylindrical body from flat strip material comprises a forming tool incorporating an array of forming elements arranged along an arcuate path, a mandrel arranged with a generally cylindrical surface portion thereof in opposition to the array of elements, means operable to produce relative movement of the elements and mandrel towards one another, the arrangement being such that, prior to said relative movement, the mandrel and array are spaced apart to permit a substantially undeformed strip portion to be placed therebetween with the strip portion extending across the array, and rotary driving means being provided to drive the strip between the elements and mandrel for forming the strip into a cylindrical body.

Preferably, the forming elements are rollers carried, conveniently, in low- friction support means which may typically be V-blocks of low-friction material in which the rollers are freely rotatably supported, preferably over a substantial part of their lengths.

The invention will now be described, by way of example, with reference to the accompanying drawings in which:-

Figure 1 is an end view, partly in cross-section, of one form of the strip forming apparatus of the invention;

Figure 2 is a plan view of the apparatus of Figure 1 , with parts thereof omitted;

Figure 3 is an enlarged cross-section along the line Ill-Ill of Figure 1 ;

Figure 4 is an enlarged cross-section along the line IV-IV of Figure 2;

Figures 5 to 9 are schematic illustrations of the apparatus of Figures 1 to 4 in different operative states;

Figures 10 and 1 1 are schematic illustrations respectively in perspective and side elevation of an alternative form of the apparatus of the invention, and

Figures 12 and 13 are schematic illustrations respectively in perspective and end elevation of another alternative form of the apparatus of the invention.

The apparatus illustrated in Figures 1 to 4 of the drawings has a roller tool, indicated generally at 1 , carrying an array of forming elements, indicated generally at 2 in the form of rollers. A cylindrical rotatably driven main roll or mandrel 3 is mounted above and spaced from the array of forming rollers 2 and may be brought into cooperative relationship with the rollers 2 and a strip 4 to be formed, in the manner to be described hereafter.

The array of rollers 2 includes three equi-spaced relatively large diameter rollers 5, 6 and 7 mounted by way of respective low-friction bearing sleeves 8 on respective fixed shafts 9, of which the end portions are non- rotatably secured in end cheeks 10 (Figure 3). Each of the rollers 5, 6, 7 is provided with a pair of opposed flanges 5A, 6A, 7A at the respective ends thereof and between which the strip 4 to be formed is closely guided laterally. Between respective pairs of rollers 5, 6 and 6, 7, are arranged respective groups of relatively small diameter rollers 1 1. Each

group, in this embodiment, includes four such rollers 1 1 , all of these rollers, together with the rollers 9 being arranged so that their external rolling surfaces lie on an arc of a circle centred at A. The groups of rollers 1 1 are carried respectively on support blocks 12, each having a number of V-shaped grooves 1 3 extending axial ly of the rollers and within which the individual rollers 1 1 are mounted. As can be seen more clearly from Figure 4, each roller 1 1 is rotatably mounted on the tool 1 by way of fixed pivot pins 14, the rollers resting against the sides of the grooves 13 and being thereby afforded support. In order to minimise frictional rolling resistance at the support blocks 12, these may be made partially or wholly of low-friction material, such as suitable plastics. Alternatively, the surfaces of the supports contacted by the rollers may be coated with low-friction material.

The mandrel 3 is drivingly coupled to a rotary motive device, such as an hydraulic motor, to effect rotation thereof when required. The mandrel and/or roller tool 1 are connected to means, such as one or more hydraulic cylinders, illustrated schematically at 3A in Figure 5, to enable them to be forced towards each other at the commencement of a forming operation, for the purpose to be described.

A forming operation will now be described with reference to Figure 1 and also Figures 5 to 9, which latter illustrate successive steps in the forming method of the invention. At the commencement of the operation, the strip 4, which be may be fed from a continuous roll or be in the form of a discrete length as illustrated, is fed into the gap between the mandrel 3 and the various rollers 5, 6, 7 and 1 1 , until it bridges between the extreme rollers 5 and 7, as illustrated in Figures 1 and 5. The hydraulic cylinder device 3A is then actuated to produce relative

movement towards each other of the roller tool and mandrel. When the mandrel contacts the outer surface of the bridging part of the strip 4, it deforms this strip part downwardly into contact with the rollers 1 1 , so that the strip assumes an arcuate form following the path defined by the rollers of the roll tool and the outer surface of the mandrel 3. This condition is illustrated in Figure 6. Rotation of the mandrel is now commenced in the direction indicated by the arrows in Figures 1 and 7 to 9. The outer surface of the mandrel 3 provides a relatively high friction level between the mandrel and the engaging surface of the strip enabling the strip to be driven through the roller tool, over the freely rotatable rollers therein. During this movement it experiences a bending moment at each contact with one of the rollers 1 1 such that the strip is permanently bent into the desired curvate form. As can be seen from Figures 8 and 9, the formed strip passes around the mandrel 3 and the free ends of the strip are brought substantially together at a location adjacent the first roller 9. The mandrel 3 and roller tool 1 are then separated by the hydraulic cylinder device, 3A enabling the formed ring to be removed from the mandrel for transport, as for example by a conveyor, to another location where the adjacent ends of the formed strip may be permanently connected together, as for example by welding. Alternatively, the welding or other connection step may be performed prior to removal of the formed strip from the roller tool.

It is possible to use the method and apparatus of the invention to form hollow generally cylindrical bodies from strip material which is of non- rectangular cross-section, or to profile strip material of rectangular cross- section simultaneously with the cylinder-forming operation, or any appropriate combination of these techniques.

Figures 10 and 1 1 illustrate schematically the formation of a generally cylindrical body from laterally flanged strip material of mainly rectangular cross-section. The mandrel 30 is provided with grooves 31 of rectangular cross-section spaced so as to receive therein the lateral flanges 32 of strip material 33. As can be seen from Figure 1 1 , the roller tool 34 carries, as previously, an array 35 of forming rollers which, in this case, includes relatively large diameter end rollers 36 and a plurality of relatively small diameter rollers 37 arranged between the end rollers. All of these rollers are freely rotatable and are arranged so that their external rolling surfaces lie on a circular arc as before. The method of the invention is carried out in the manner previously described, including the steps of placing the strip material between the spaced apart mandrel and forming rollers, bring the mandrel and rollers together in a linear movement to perform an initial arcuate forming operation and subsequently driving the strip between the rollers and mandrel for final cylindrical forming. The flanges 32 engage within the mandrel grooves 31 during the arcuate forming step and remain so engaged during the cylindrical forming step. It may be unnecessary, in this embodiment, for the rollers 36 to be flanged since lateral guidance for the strip during forming is provided by the interengaged flanges 32 and grooves 31.

An alternative possibility is illustrated in Figures 12 and 13. This involves the use of strip 33 of entirely rectangular cross-section which is profiled, during cylindrical forming, by a mandrel 30 having a grooved or corrugated outer surface 31 cooperating with freely rotatable rollers of complementary surface shape forming part of a roller tool 35, one of the rollers 36 being visible in Figure 13 and forming part of an arcuate array of forming rollers similar to that shown in Figure 1 1. It will be seen that carrying out the method of the invention in the manner previously

described will result in a cylindrical body having a corrugated major surface, as can be seen clearly from Figure 12.

The use of several forming rollers of relatively small diameter enables bending moments to be applied to the strip at closely adjacent locations, which minimises or eliminates the tendency of the strip to flatten at the locations between these forming rollers. The three larger diameter rollers 5, 6 and 7 are provided in order to sustain the very substantial bending forces involved, although these may be replaced by further smaller diameter rollers when forming is performed, for example, on relatively thin gauge material requiring smaller bending forces. In an alternative arrangement, at least the middle one of the rollers 5, 6, 7, may be replaced by a non-rotatable shoe over which the strip slides rather than rolls. In general, combinations of rollers and shoes may be used in any convenient numbers, or an array consisting entirely of shoes or other non-rotatable elements may be employed.

It will be understood that the numbers of forming elements 1 1 may be varied according to requirements and the numbers of elements contained in the respective groups may differ. Moreover, although the illustrated mandrel has a completely cylindrical outer surface, it would be possible to use a mandrel of part-cylindrical form of which the arcuate working surface is of sufficient circumferential extent to permit its adequate forming cooperation with the roller array. The initially deformed strip may be driven between the mandrel and forming elements by driving the mandrel, the forming elements, or both. The initial deformation step may be performed by moving the mandrel, the forming tool, or both.

The invention can be seen to provide a simple and effective method and apparatus for bending strip into substantially circular formations and the accuracy of the formed articles may be such that they may be used as components in larger assemblies with little or no corrective shaping.