PROCESS AND APPARATUS FOR PRODUCING SPIRALLY-SEAMED METAL TUBING

Abstract: A process and an apparatus for producing spirally-seamed tubing from metal strip are disclosed. The edges (15) of the metal strip (12) are prepared and the metal strip is fed into a generally cylindrical forming head (13) to bring the prepared edges of the strip closely adjacent one another in overlapping relationship, and the overlapping edges are welded together by means of inner and outer electrode rollers (16, 17). A conducting strand (18) is fed round the rotary electrodes to pass between the rollers and the strip and so provide continuously fresh electrical contacts. The conducting strand (18) may comprise a copper wire which is fed from a supply coil (19), round one roller (16), through a cleaning device (24), round the other roller (17), and then to waste.

Description: PROCESS AND APPARATUS FOR PRODUCING SPIRALLY-SEAMED METAL TUBING The invention relates to the formation of spirally-seamed metal tubing. It is well-known to produce tubing from metal strip by feeding the strip into a forming head where the edges of the tube are joined together to form a spiral seam. The seam may be formed by clinching shaped edges of the strip, as in the SPIROMATIC lock-seam machines, or the edges may-be butt-welded together. Butt-welded tubing is relatively inconvenient to produce, and welded seams have tended to fracture, particularly when the strip material is sufficiently flexible to impart a degree of resilience to the tube. One disadvantage of lock-seam tubing is that it is not sufficiently fluid-tight for some purposes unless a continuous seal is applied to the seam. It is an object of the present invention to provide a method and a machine for producing spirally- seamed tubing from metal strip, in which the above dis¬ advantages are at least reduced. According to the invention,a process for producing spirally-seamed tubing from metal strip comprises: preparing the edges of the metal strip; feeding the metal strip into a generally cylindrical forming head to bring the prepared edges of the strip closely adjacent one another in overlapping relationship; welding the overlapping edges together by means of inner and outer electrode rollers; and feeding at least one conducting strand round the rotary electrodes to pass between the rollers and the strip and so provide continuously fresh electric contacts. Preferably, the conducting strand comprises a copper wire which is fed from a supply coil, round one roller, through a cleaning device, round the other roller, and then to waste. The invention also provides an apparatus for performing the process. An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a side elevation showing a machine, according to the invention, for producing spirally- seamed metal tubing; Figure 2 is a plan view corresponding to Fig. i; Figures 3 and 4 are detail views showing a guide for the metal strip, Fig. 4 being a section on the line IV-IV in Fig. 3; and, Figure 5 is a detail view showing electrode rollers. Referring to the drawings, the machine comprises a drive unit 10 having drive rollers 11 which draw metal strip 12 from a decoiler (not shown) and feed the strip into a forming head 13 where the strip is formed into a spirally-seamed metal tube 14. The operation of the drive unit 10 is similar to that of the SPIROMATIC tube-forming machine as des- scribed in, for example, British Patent No. 1034421, and the forming head 13 is of comparable construction. In the present machine, however, the strip is formed into tubing by welding rather than by clinching into a spiral lock-seam as in the earlier Patent. During passage through the drive unit 10, one of the side edges 15 of the strip 12 is deformed by slightly offsetting portion 15A, as shown in Fig. 4, and the strip, passing through one helix turn in the head 13, has its edges welded together by means of elect¬ rode rollers 16,17. The tubing so formed issues, rota¬ ting, laterally from the forming head. According to the invention, a clean copper wire 18 of about 2mm diameter is drawn upwardly from a supply drum 19, over idler rollers 20 and between drive rollers 21, to pass over further idler rollers 22 before reaching and passing round the lower electrode roller 16. The wire then passes over idler roller 23 and upwardly through a wire-brush cleaning device 24, before passing round idler rollers 25 and the upper electrode roller 17. The wire then continues round yet further idler rollers 25A before being fed by traction rollers 26 through a chute 27 to a suitable waste hopper (not shown) . Corr¬ ect tension in the wire 18 is ensured by correlated operation of the drive and traction rollers 21 and 26, and also by means of pneumatic piston and cylinder devices 28 which act to take up any slack in the wire and also incorporate control sensors for the drive and traction rollers . The drive unit 10 and the forming head 13 are mounted on a base 29, and the wire-feed mechanisms are mounted on a pivotal base 30 having a control panel 31. Referring particularly to Fig. 5, it will be noted that the copper wire 18 is interposed between the electrode rollers 16, 17 and the overlapping edges 15 of the metal strip 12. Welding is effected by current pulses passing from the rollers and through the copper wire, and it will be appreciated that the wire provides continuously clean electrical contact with the metal strip. This represents a great improvement over the conventional direct contact between electrode rollers and the metal being welded, which rapidly contaminates the surfaces of the rollers and necessitates frequent cleaning. Also, in the case of welding coated metal such as galvanised steel, the provision of the copper wire greatly reduces damage to the thin zinc coating. The copper wire 18, which leaves the bin 19 in a very clean state, becomes somewhat contaminated during its first run over roller 16 but it has been found satisfactory for the wire to have a second run over roller 17 after wire-brush cleaning in the device 24; it is then advisable to return the wire for re¬ cycling, rather than to attempt further cleaning. The preferred welding operation is stitch-welding, by which process a pulsing current through the electrodes produce a series of short welds (say, 2mm in length) separated by shorter gaps (say ^mm in length) , but the gaps are immediately sealed by welding action extending from the adjacent ends of the welded lengths. This results in, effectively, a seam weld, and the weld is completely fluid-tight. The arrangement of the generally Z-shapec guide bar 32, best shown in Figs. 3 and 4, is important in precisely positioning the overlapping edges 15 of the metal strip prior to welding, and the shaped upper member 33 of the guide bar is adjustable to produces optimum precision. It is also important that the contact areas at the welding points are correct and uniform, and accurate dimensioning is greatly assisted by maintain¬ ing an even tension on the copper wire, in addition to the usual provision for adjustment of the electrode roller positions. It has been found preferable to have the upper roller 17 mounted on a pivotal arm. 34, not: only for accurate adjustment but also to permit the roller 17 to be raised and so facilitate the start of each tube-forming operation. As indicated above, the invention is particularly suitable for use in welding galvanised steel, as the interposition of the copper wire minimises damage tc the zinc coating, but the machine can also be used for welding strips formed from other metals such as stainless steel. Although stitch-welding is particularly attractive in relation to the efficient supply of electric current, some metals such as stainless steel can be seam-welded using the present machine, and spot-welding could be employed if hermetic sealing were not required. The tubing formed by the present invention has a wide range of uses, including chimney linings, hermetically-sealed ventilating conduits and barrels, which may be formed with corrugations, and also smaller items such as cans for food etc. Particularly with the last-mentioned items which are conventionally produced in individual short lengths, the tubing produced by the present invention may be severed into lengths by a 'flying saw' as used in the lock-seam SPIROMATIC machines but preferably provided with a plurality of rotary saw blades 35 (Fig. 2 ) .

Claims: CLAIMS 1. A process for producing spirally-seamed tubing from metal strip, comprising: preparing the edges of the metal strip; feeding the metal strip into a generally cylindrical forming head to bring the prepared edges of the strip closely adjacent one another in overlapping relationship; welding the overlapping edges together by means of inner and outer electrode rollers; and, feeding at least one conducting strand round the rotary electrodes to pass between the rollers and the strip and so provide continuously fresh electric contacts. 2. A process as claimed in Claim 1, in which the conducting strand comprises a copper wire which is fed from a supply coil, round one roller, through a cleaning device, round the other roller, and then to waste. 3. A process as claimed in any preceding Claim, in which welding is effected by current pulses which produce a series of short welds separated by shorter gaps to be promptly sealed by welding action extending from adjacent ends of the welded lengths. 4. A process as claimed in any preceding Claim, in which one of the said edges of the metal strip is slightly offset to produce tubing with a generally unin¬ terrupted inner or outer surface. 5. A process as claimed in any preceding Claim, in which said electrode rollers are arranged one above the other, and the upper inner roller is vertically adjustable in position. 6. A process as claimed in any preceding Claim, in which the tension in said wire is continuously adjusted in relation to the means which feed the wire. 7. An apparatus for producing spirally-seamed tubing from metal strip, in which the metal strip is fed into a generally cylindrical forming head to bring the prepared edges of the strip closely adjacent one another in over¬ lapping relationship, the apparatus comprising inner and outer electrode rollers for welding together the overlapping edges, and having means for feeding at least one conducting strand round the rotary electrodes to pass between the rollers and the strip and so provide continuously fresh electric contacts. 8. An apparatus as claimed in Claim 7 , in which the conducting strand comprises a copper wire which is fed from a supply coil, round one roller, through a cleaning device, round the other roller, and then to waste. 9. An apparatus as claimed in Claim 7 or 8, in which adjustable guide means are provided to support one of the edges of the metal strip to produce tubing with a generally uninterrupted inner or outer surface. 10. An apparatus as claimed in any of Claims 7 to 9, in which said electrode rollers are arranged one above the other and the upper inner roller is vertically- adjustable.

Inventors: ROSENGREN STIG ERIK, ROSENGREN, STIG, ERIK
Applicants: DIXON DONALD COSSAR, SPIRO MACHINES SA, DIXON, DONALD, COSSAR, SPIRO MACHINES S.A.
Application year: 1988
Main classification: B21C37
IPC codes: B21C37, B23K11