METHOD AND APPARATUS FOR FORMING ONE PIECE DUCT SECTIONS

Abstract: The invention provides that a curved duct section is formed by coiling a strip of metal, the strip being cyclically profiled so that as coiling takes place coils which are narrow at one side and broad at the other side are formed and the narrow sides lie to one edge of the duct and the broad sides lie at the other edge of the duct so that a curved duct is formed. The strip is coiled about a vertical axis so that the duct grows upwardly. A machine for producing the duct is also disclosed.

Description: Method and Apparatus for Forming One Piece Duct Sections The present invention relates to a method of and apparatus for forming curved sections of ducting from a single strip of material. The invention is particularly concerned with the formation of ducting having a circular cross section although it could also be applied to ducting of other cross sectional shapes. There are many ways of making straight sections of ducting and among the most common of these is the spiral wound method in which a coil of strip metal is fed at an angle to a rolling mechanism which winds it to form a straight duct of circular cross section and of any required length. However / in most systems in which ducts are used, it is necessary for the ducts to change direction and therefore the curved sections of duct commonly called bends or elbows must be provided. For duct diameters of up to 300 mm the bends are usually manufactured as two identical pressed halves which are seam welded together, but for ducts with a diameter of above 300 mm this method is prohibitively expensive and therefore the bends are usually manufactured by joining together several bend segment rings and finishing each end of the bend with a half segment ring. This method of forming a bend is time consuming and some part of the work must be done manually. In a first aspect of the present invention there is provided a method of forming a curved duct section / said method comprising coiling a strip and joining the edges of adjacent coils, wherein at least one and preferably each of several adjacent coils being narrower at one side than at the other to cause the duct section to curve as it is formed. Preferably said strip is coiled about a vertical axis so that said duct section grows upwardly, the new coils being added at the lower end of the growing duct section. In a second aspect of the invention there is provided a strip for forming a curved duct section, characterised in that said strip is profiled about its centre line so that its width varies cyclically to enable the strip to be coiled as aforesaid. The edges of said strip may be folded to form seams when the strip is coiled into a duct section. The strip may be of a metal such as steel. In a third aspect of the invention there is provided a method of producing a strip for forming a curved duct section comprising feeding an uncut strip to cutters which trim the edges of said strip, characterised in that the cutters oscillate in the plane of said strip so as to produce a trimmed strip which is profiled at least over a length to define at least one coil when the strip coiled in accordance with the method as aforesaid. Preferably the edges of said strip are folded by folding means immediately after trimming so that seams can be formed when the strip is coiled. Preferably, said folding means oscillate in the plane of said strip so as to follow the line of the trimmed edges of said strip. There may be provided means for the automatic control of the movement of said cutters and said folding means in accordance with one or both of the feed rate of the strip and the required radius of the bend. The control means may comprise a computer. In a fourth aspect of the invention there is provided strip coiling apparatus comprising seam forming means and a plurality of strip guide means characterised in that said seam forming means is in a fixed position and said seam forming means and said guide means are positioned on the circumference of a circle, said guide means being mounted for position adjustment so that the radius of said circle can be varied. Preferably said seam forming means comprise powered rollers which also act as strip feeding means. Preferably, said guide means are movable along threaded rods lying so as to radiate from said seam forming means. There may be means intergearing said threaded rods to ensure that said guide means remain circularly disposed when they are adjusted in position. Said guide means may comprise pairs of idler rollers, each pair defining a nip through which the strip passes. There may also be provided cutter means for cutting the end or ends of the duct formed from the coiled strip to square same relative to the duct axis. The invention will now be described in greater detail with reference to the accompanying diagrammatic drawings wherein:- Fig. 1 is a perspective view of a conventionally formed spirally wound staight duct section; Fig. 2 is a side view of a conventionally formed duct bend; Fig. 3 is an end view of a conventionally formed duct bend; Fig. 4 is a plan view of a duct forming apparatus of the invention; Fig. 5 is a side elevation of the duct forming apparatus of the invention; Fig. 5A is an enlarged perspective view of the edge cutting and forming section of the apparatus shown in Fig. 5; Fig. 5B is a side view of of one of the stations of the section of Fig. 5A; Fig. 6 is a enlarged plan view of the strip winding mechanism; Fig. 6A is an enlarged sectional view of the drive station of the mechanism shown in Fig. 6; Fig. 6B is a portion showing the cutting drive of the drive section of Fig. 6A; Fig. 7 is a schematic representation of the formation of the first coil; Fig. 8 is a side view of a duct bend according to and formed according to the present invention; Fig. 9 is a schematic representation of the first coil after it has been cut; Fig. 10 is a sectional side view of the strip showing the folded edges before the seam is clinched; and Fig. 11 is a sectional side view of the strip showing the folded edges after the seam is clinched. Fig. 1 shows a conventionally formed straight duct section 10 having a circular cross section and being spirally wound from a single metal strip 12. This spiral winding method has previously only been applied to straight duct sections and conventionally, the duct bends or elbows 14 (Figs. 2 and 3) have been formed from several hollow metallic segment rings 16 each of which has a narrow side and a broader side, the narrow sides being grouped together to form the throat of the bend and the broader sides being grouped together to form the back of the bend. At each end of the bend 14 there is a half section 18 which is added so that the end of the bend will be circular in cross section and can easily be connected to a straight duct section. The coils of the straight duct may be connected by folding and clinching the adjacent strip edges, whilst the rings 16, 18 will tend to be welded together. It is highly desirable that such duct bends can be made from a single strip of metal since this would reduce the manufacturing cost and would decrease the amount of manual control needed in the process. Figs. 4, 5, 5A and 5B show an apparatus by means of which it is possible to form a curved section of duct from a single strip of material. A strip 20 of a etai such as steel is drawn on its edge from a coil 22 and passed in sequence through cutters 24, an edge folding mechanism 26 and a winding mechanism 28. The cutters 24 trim the edges from the strip and form them into a wave like pattern as shown in Fig. 5, so that the edges are profiled about the centre line of the strip so that the width varies cyclically to enable the strip to be coiled into the configuration of a curved duct. The strip after trimming thus has wide portions 30 which will eventually form the back of the bend and narrow portions 32 which will eventually form the throat of the bend. After trimming, the strip then passes to an edge folding mechanism 26 which folds the top edge 34 and the lower edge 36 of the strip to the respective cross sectional shapes shown in Fig. 10. This process is the same as that used for conventional straight spirally wound duct sections and may require there to be several sets of rollers 38. The rollers 38 are powered and act as the feeding mechanism for or contribute to the feeding of the metal strip 20. Because both edges of the strip 20 are trimmed into a wave formation, it is necessary for both the cutters 24 and the rollers 38 comprising the edge folding mechanism 26 to be moveable back and forth and in the case of Figs. 4 and 5, in a vertical plane, and the mechanism is now described in more detail with reference to Figs. 5A and 5B. Referring specifically to Figs. 5A and 5B, the strip 20 is shown at the right hand side of Fig. 5A as travelling in the direction of arrow 2OX. The strip lies in a vertical plane, and as can be seen strip 20 travels through a number of units or stations until it emerges as shown at 22X with the formations 36 and 34 on the lower and upper edges thereof. The first station in fact forms the cutter station 24 whilst the four following stations 24X, 26X, 28X and 3OX are for the progressive formation of the upper and lower edges of the strip to provide the seam formations 34 and 36. Each of the stations is of similar construction, and therefore only one will be described. The difference between the first station and the following stations is that the first station is cutting station 24, whereas the following stations are forming stations. Each station comprises a pair of floating blocks 32X and 34X which are mounted by pivot pins 36X and 38X on bearing guides 4OX and in particular in bearing blocks 42X and 44X. The bearing blocks 42X and 44X slide vertically in block 40X so that the blocks 32X and 34X as well as being able to pivot about the pins 36X and 38X, can also move together and apart at least to the extent dictated by the physical limits of block 40X. It will be appreciated that there are two blocks 40X for each pair of blocks 32X and 34X. The blocks 42X and 44X may be free floating within block 40X, or may be under the control of power cylinders such as cylinder 46X. When cylinder 46X is utilised, it is powered to move the blocks 42X and 44X in accordance with the profiling required on the strip 20X. As shown in Fig. 5B, each of the blocks 32X and 34X carries a pair of parallel shafts 48X, 50X in the case of block 32X and 52X and 54X in the case of block 34X. These shafts carr rollers 56X, 58X in the case of block 32X and 60X and 62X in the case of block 34X. The roller pairs 56X and 58X on the one hand and 6OX and 62X on the other hand and in the case of station 24 will be simple cutting rollers which profile the strip 20, but in the case of the following stations will be forming rollers for forming and folding the edges of the strip. Operation of the arrangmeent of Figs. 5A and 5B will be understood but will be described briefly. As the strip 20 travels through the stations 12, so it is trimmed as indicated at station 24, and the scrap is wound on a pair of take-up rollers 64X which are power driven. The blocks 32X and 34X are moved cyclically together and apart so that the profiling of the strip as indicated in Fig. 5 takes place. The blocks 32X and 34X of the subsequent stations are also oscillated in sympathy with the profiling of the strip so as to form the edge formations 34 and 36. It will be appreciated therefore that the control of the operation of the cylinders 46X of the respective stations must be synchronised and controlled as the respective roller pairs 56X, 58X and 60X, 62X will be in different positions for the respective stations at any one time. By arranging for the blocks 32X, 34X to be able to pivot about pins 36X and 38X, so the rollers 56X to 62X can tilt to follow the inclination of the profiled edge of the strip 20, engaged thereby, and the particularly effective cuting profiling arrangement results. It will be noted from Fig. 5B that the shaft pairs 48X, 5OX are inter-geared by gears 66X, 68X, and 7OX, 72X so that the rollers of each pair will rotate in synchronism and in opposite directions. One pair of rollers, for example 60X and 62X is power driven by means of a motor 74X. Both pairs can be driven if required. The trimming and profiling arrangement described in itself constitutes a patentable novelty. After the edges of the strip 20 have been trimmed and folded, the strip passes to the winding mechanism 28. This mechanism consists generally (Fig. 6) of several pairs of idler rollers 40, each pair defining a nip 42 through which the strip 20 passes. The rollers 40 are arranged around the circumference of a circular path 44 and each pair of rollers is moveable along a fixed screw threaded rod 46. The rods 46 are arranged chordwise of the circular path 44 so that if they were extended inwardly somewhat, their paths would converge at a single point 48 on the circumference of the circular path 44. At the convergence point 48 is positioned a further pair of rollers 50 which clinch the lower edge 36 of one turn of the metal strip to the upper edge 34 of the succeeding turn of the strip and thus forms a seam. The clinching rollers 50 are driven and therefore act as further driving means for the strip 20. There is also an inter gearing mechanism (not shown) for the rods 46 which ensures that when the rollers 40 are moved along the threaded rods 46 they will always remain disposed in a circular path 44 and therefore the distances moved by different rollers from an original position to a new position will differ. The method of winding the strip using mechanism 28 is now described in more detail with reference to Figs. 6A and 6B. Figs. 6A and 6B illustrate diagrammatically how the leadin and trailing ends of the duct shown in Fig. 8 are cut, so that such ends will be squared off relative to the duct axis. In Fig. 8 the ends are indicated by 53 and 55, and referring to Fig. 8 it will be seen that the coiled strip 20 defines a somewhat complex helical shape insofar as the strip is coiled in the nature of a helix, but because the stip is profiled as shown in Fig. 5, so the resulting duct forms the elbow or bend shown in Fig. 8. In order that the clinching and cutting mechanism shown in Fig. 6 can operate effectively, it is desirable that at least the roller pair 50 should be capable of being raised and lowered in synchronism with the widening and narrowing of the strip as it is fed through the roller pair 50, and therefore as shown diagrammatically in Fig. 6, the roller pair 50 is carried by a pair of sleeves 20Y and 22Y which are in turn supported for rotation on a bearing block 24Y. The sleeves 20Y and 22Y are inter-geared by means gears 26Y, and 28Y, and a drive gear 30Y meshing with gear 28Y effects driving in the opposite directions but in synchronism of the sleeves 20Y and 22Y and therefore the roller pair 50. Gear 30Y is driven via a shaft 32Y which is supported in bearings in the block 24Y, and the power unit for driving shaft 32Y is a motor and gearbox unit 34Y as shown in Fig. 6A. The block 24Y is mounted for vertical sliding movement on a slide 36Y, so that a block 24Y and therefore the gearbox and motor 34Y, the gears 26Y, 28Y and 30Y, the sleeves 20Y and 22Y and the clinching rollers 50 can be raised and lowered as indicated by arrow 38Y in Fig. 6A. The rollers 50 can therefore follow the profile of the strip as it is fed therebetween to ensure the most effective clinching of the edges of adjacent coils to form the duct shown in Fig. 8. To effect the squaring of the ends of the duct shown in Fig. 8 however requires a still further motion of the cutters relative to the rollers 50 as will be understood clearly from consideration of Fig. 8. The squared ends 53 and 55 do not lie on the natural helical join between the coils of the duct, and therefore some relative movement between the cutters and the rollers 50 must take place if the ends are to be effectively squared off. This relative movement is achieved by the arrangement diagrammatically illustrated in Fig. 6A. Inside the sleeves 20Y and 22Y are cutter shafts 40Y and 42Y on the top ends of which are mounted a pair of cutter discs 44Y and 46Y which act as shown in Fig. 6A like a pair of scissors in order to slice through the material. The discs 44Y and 46Y are not in themsleves driven but because they act in the nature of 11 scissors, and because the strip is forced by the rollers 50Y through the winding mechanism, the cutters 44Y and 46Y will effect the cut as the progression of the strip takes place. The shafts 40Y and 42Y are intergeared by means of gears 48 and 50Y which are drivingly connected to a stepping motor, the purpose of which is to rotate the shafts 40Y and 42 between two positions which are angularly offset by 180°. This is so because the discs 44Y, 46Y are as shown in Fig. 6 eccentrically mounted on the shafts 40Y and 42Y by means of eccentric discs 52Y and 54Y. By so rotating the shafts 40 and 42Y, the discs 44Y and 46Y can be moved into cuttin engagement as shown in Fig. 16, or out of such engagement as shown in full lines in Fig. 6B. Cutting can be and is i fact selective, as obviously the duct is cut only at th beginning of formation of same, to form the leading end 53, and at the end of formation of same, in order to form th trailing end 55. The rotation of the shafts 40Y and 42 between respective positions will of course be sequenced an controlled with the rest of the operation of the machine. Additionally, shafts 40Y and 42Y are provided wit circumferential rack teeth which are engaged by pinions 56 and 58Y which are intergeared so as to rotate in synchronis and in opposite directions by a motor not shown, in order t raise and lower the shafts 40Y, 42Y during the cuttin movement to ensure that squared off ends 53 and 55 will b formed. The raising and lowering motion of the shafts 40 and 42Y as indicated by arrow 60Y. When the block 24Y is raised and lowered, the whole assembl illustrated in Fig. 6B is raised and lowered, and when th pinions 56Y and 58Y are rotated, the raising and lowerin motion of the cutters 44Y and 46Y is superimposed upon th raising and lowering movement of the block. It is preferred that, referring to Figs. 6A and 6B in conjunction with Fig. 6, in addition to the roller pair 50 being provided with cutters 44Y and 46Y, also the roller pairs indicated by 40Z should similarly be provided with cutters. The roller pair 50 and the two roller pairs 40Z are located at 120° relative angular positions having regard to circumference 44, so that during cutting of an end 53 or 55 of the curved duct three cuts are made simultaneously, and these cuts will join end to end so that the cut duct, when the trailing end is being formed will not become unstable on the machine, as it might do if only a single cutter pair 44Y/46Y were used. The raising and lowering of the block 24Y and/or the raising and lowering of the shaft pair 44Y/42Y, may be effected by power driven screw and nut arrangements, and the movement of the cutter discs 44Y and 46Y between the cutting and open positions may be by means of a transmission involving a clutch suitably controlled by the control system of the machine. Thus, in order to form a curved duct section, the edges of the strip 20 will be trimmed and folded and the strip will then be passed through the rollers 50 and around the circular path 44 through each of the nips 42 in the guide rollers 40. When the strip 20 has completed a full turn, it will continue around the path 44 beneath the first turn. As a new length of strip 20 is added to the duct section, the rollers 50 will clinch the seams to the position shown in Fig 11. The first turn 52 (Fig. 7) of the forming duct section will have a step 54 defined by the leading end of the metal strip 20. As the first turn is completed. The cutters as described hereinbefore move from a non-cutting position 57 to the cutting position as shown in Fig. 6B. The cutters cut the growing duct section 60 so that the step 54 is removed and the duct section 60 once formed will have am end 33 of circular cross section which is squared to the duct axis as shown in Figs. 8 and 9. When the duct section is completed, there will be a similar cutting step at the end and the cutters can be used to square the other end 55 of the duct. The cutters move up and down in synchronism with the rotation of the duct section in order to ensure that squared ends 53, 55 to the duct section 57 as shown in Fig. 5, are achieved. As new turns 58 are added to the lower end of the growing duct section 60, the duct section 60 will rotate as shown by the dotted lines in Fig. 5. It has been found that this upright position is the most stable position in which a curved duct section 60 can be formed since there will be no effect due to gravity on the out of balance centrifugal force which arises as a result of the rotation of the duct section. The strip 20 can be fed from the coil 22 at a range of angles as shown by the arrow 64 in Fig. 5. The angle chosen will depend on the required radius of the duct section. The rate of vertical movement of the cutters 24 and the edge folding mechanism 26 will depend on the diameter of duct section required and also on the feed rate of the strip 20 from the coil 22. It is therefore desirable to provide some sort of control means (not shown) to control the movement of the cutters 24 and the rollers 38 of the folding mechanism 26. The positioning of the guide rollers 40 on the threaded rods 46 is also dependent on the required radius of the duct section 60 to be formed and therefore it is possible to control the movement of the rollers 40 by computer. Using the apparatus of the invention, it would be possible to input into the computer the required diameter, length and radius of curvature of the duct section 60 and the computer would then calculate the necessary feed rate and angle of the strip 20 from the coil 22 and would control the vertical movement of the cutters 24 and the folding rollers 38. The guide rollers 40 would be moved to their correct positions on the threaded rods 46 under the control of the computer and the computer would also control the movement of end cutters. Using the method and apparatus of the invention it is therefore possible to provide curved duct sections which form a single strip of metal and the method represents a considerable reduction in the time and cost required to make a duct bend. Modifications of the invention may be made. Thus, the strip may be profiled only in sections, interspaced with straight sided sections so that duct length comprising curved sections and straight sections can be produced by the method and apparatus according to the invention.

Claims: CLAIMS 1. A method of forming a curved duct section, comprising coiling a strip and forming the edges of adjacent coils, at least one of said coils being narrower at one side than at the other to cause the duct section to curve as it is formed. 2. A method according to Claim 1, wherein several consecutive coils are narrower at one side than the other, the narrow sides of the coils being adjacent. 3. A method according to Claim 1 or 2, wherein the strip is coiled about a vertical axis so that the duct section grows upwardly, the new coils being added at the lower end of the growing section. 4. A method according to any preceding claim, wherein the adjacent coils are formed by clinching adjacent coil edges together. 5. A method according to any preceding claim, wherein the strip is of metal. 6. A method of forming a curved duct section, according to any preceding claim, wherein the strip is driven through forming rolls to form said coils. 7. A method according to any preceding claim, wherein the strip is cut to shape to define said coil or coils which is or are narrower at one side, or the other before it is coiled. 8. A method according to any preceding claim wherein the edges of the strip are provided before coiling with formations to enable the coils to be joined together during coiling. 9. A method according to any preceding claim, including the steps of trimming the leading and/or trailing end of the duct section to square it off relative to the duct axis. 10. A method according to Claim 9, wherein the leading end and/or trailing end of the duct section and is trimmed whilst coiling is taking place. 11. A method according to claim 9 wherein the leading and/or trailing end of the duct is cut by means of three equiangularly spaced cutters. 12. A method of forming a curved duct section substantially as hereinbefore described with reference to the accompanying drawings. 13. A strip of rigid but coilable material for forming a curved duct section, wherein the strip is edge profiled so that its width varies cyclically at least over a length to define at least one coil when the strip is coiled in accordance with the method as claimed in any of Claims 1 to 11. 14. A strip according to Claim 13, wherein the material of the strip is metal. 15. A strip according to Claim 13 or 14, wherein the edges of the strip and folded to form seams when the strip is coiled. 16. A strip of rigid but coilable material substantially as hereinbefore described with reference to the accompanying drawings. 17. A method of producing a strip for forming a curved duct section comprising feeding an uncut strip to cutters which trim the edges of the strip, and wherein the cutters oscillate in the plane of said strip so as to produce a trimmed strip which is edge profiled at least over a length to define at least one coil when the strip is coiled in accordance with the method as claimed in any of Claims 1 to 11. 18. A method according to Claim 17, wherein the merement of the cutters is controlled in accordance with the required radius of the bend of the duct section to be produced from the strip. 19. A method of producing a strip substantially as hereinbefore described with reference to the accompanyin drawings. 20. Strip coiling apparatus comprising seam forming means and a plurality of strip guide means, wherein said sea forming means is in fixed position and said seam formin means and said guide means are positioned on th circumference of a circle, said guide means being mounted fo position adjustment so that the radius of said circle can b varied. 21. Apparatus for producing curved duct sections comprisin means for feeding rigid but coilable strip material, cuttin means for profiling the edges of the strip so that its widt varies cyclically, means for coiling the profiled strip s that narrow portions of the strip but adjacent in the coile strip so that a curved duct section is formed, and means fo forming adjacent coils. 22. Strip coiling apparatus substantially as hereinbefor described with reference to the accompanying drawings.

Inventors: FIRTH COLIN, FIRTH, COLIN
Applicants: FIRMAC LTD, FIRMAC LIMITED
Application year: 1991
Main classification: B21C37
IPC codes: B21C37