INDUCING BACK TENSION IN A MOVING STRIP VIA A DRAG PAD

Abstract: A method of inducing back tension in a longitudinally moving magnetiseable strip (6) comprising the steps of positioning a stationary electro-magnet (5) adjacent to one side of the strip (6), interposing a layer of fabric or other friction material (8) between the magnet (5) and the strip (6) and energising the magnet (5) to effect drag on the strip (6) due to pressure contact between the strip (6) and the layer (8). Also disclosed is a drag pad comprising an electro-magnet (5) providing an array of closely spaced, mutually parallel, elongate pole faces (19, 20) each of opposite polarity to its neighbouring face or faces and a layer of friction material (8) covering the array.

Description: TITLE* INDUCING BACK TENSION IN A M0VIN6 STRIP VIA A DRAG PAD TECHNICAL FIELD This invention relates to the treatment of steel or other magnetiβeable strip as it is being wound on to a bulk coil thereof. Typically, the invention may be applied to the slitting of a relatively broad strip into two or more narrower strips as part of the finishing operations at a steel mill. More particularly, the invention relates to devices for maintaining a back tension in the strip as it * is wound on to the coil so as to provide a suitably rigid coil. BACKGROUND ART Hitherto, a common expedient has been to use two drag pads each in the form of a wooden block wrapped in felt, carpet or other replaceable friction material which are pressed against opposite sides of the strip. A disadvantage of that known arrangement is that dirt particles accumulate on the pads and these sometimes cause scratch marks in the finished strip. This is especially disadvantageous because of the modern trend to provide material direct from the mill having a high quality ornamental finish, such as a coloured, bonded paint or enamel, on one side. Another known method of providing tension uses treaded bridle-rolls but this method also involves contact with both sides of the strip and can result in colour imprinting from one coil to the next. DISCLOSURE OF INVENTION The present invention was devised to overcome the above-indicated disability and does so by utilising a single pad embodying an electro-magnet to attract the strip against the pad and in that way provide the necessary pressure between the strip and pad to induce the required frictional resistance to the movement of the strip. Thus, in accordance with the invention, the drag pad contacts only one side of the strip which, in practice, is the rough-finished side on which surface imperfections are of little significance. Therefore, the invention consists in a method of inducing back tension in a longitudinally moving magnetiseable strip comprising the steps of positioning a stationary electro-magnet adjacent one side of the strip, interposing a layer of friction material between the magnet and the strip and energising the magnet to effect pressure contact between the strip and the layer. The invention also consists in a drag pad comprising an electro-magnet providing an array of closely spaced, mutually parallel, elongate pole faces each of opposite polarity to its neighbouring pole face or faces and a layer of friction material covering said array. BRIEF DESCRIPTION OF THE DRAWINGS By way of example, an embodiment of the above described invention is described in more detail hereinafter with reference to the accompanying drawings. Figure 1 is a diagrammatic side elevation of a drag pad according to the invention, shown as in use. Figure 2 is a diagrammatic perspective view of the drag pad of Fig. 1 with its layer of friction material omitted. Figure 3 is a perspective detail view of the internal components within the enclosure marked 3 in Fig. 2, drawn to a larger scale. Figure 4 is a detail sectional view taken on line 4-4 of Fig. 3 drawn to a still larger scale. DESCRIPTION OF EMBODIMENTS The illustrated drag pad comprises an electro-magnet 5 disposed beneath a steel strip or strips 6 issuing from pinch rolls 7 and being drawn therefrom to a wind-up coiler (not shown). At least the operative part of the surface of the magnet 5 in contact with the strip or strips is covered with a layer 8 (shown in Fig. 1) of cloth friction material. Preferably, the layer 8 (shown in Fig. 1) directly interposed between the magnet 5 and the strip 6 is part of a long web of cloth wound initially on an uncoiler roll 9 (seen only in Fig. 1) and advanced from time to time, as the in use portion becomes worn, to a coiler roll 10. For preference, the magnet 5 has smoothly curved upstream and downstream nosings 11 providing substantially tangential meeting and departure between the strip 6 and the layer 8.- The magnet 5 comprises a base plate 12, an outer angle-iron frame secured to the base plate 12, a bed 13 of electrical steel laminations 14 stacked side by side within the outer frame and an inner frame member 15 loaded by through-bolts 16 towards the opposite outer frame member to clamp the laminations 14 into a solid bed. That bed may be pierced by a plurality of tubes 17 for the passage of cooling water to carry off thermal losses generated by what is necessarily a compact but powerful electro-magnet. The bed of laminations defines a plurality of mutually parallel slots extending transversely of the direction of travel of the strip 6. Preferably each slot houses a solid copper strap conductor 18 which at their respective ends are brazed together to constitute single turn, low resistance coils. Alternatively, each slot can house a plurality of turns. The coils are connected in series so that the lamination teeth to each side of the coil slots present at their ends alternate north and south pole faces 19 and 20 respectively. The coils sides comprising the straps 18 are wrapped in insulation 21, held in place by wedges 22 and the slot mouths and the coil end connections are all encapsulated in an insulating, hard setting, synthetic resin 23. In other less preferred embodiments the operative layer of friction material may be part of a larger sheet wrapped about the magnet 5 in the same way as such sheets are conventionally wrapped about the wooden body of a conventional drag pad. Also, the friction material may be bonded to a very thin layer of steel and either wound on in the manner previously described and shown in Figure 1, or simply placed on the magnet surface as a sheet, and held in position by magnetic forces, each sheet being replaced when worn. As shown in the drawings it is preferred for the drag pad to be disposed in use so that the magnet pole faces extend transversely of the strip being processed, although other orientations are known to be effective. The length of each pole face is preferably at least equal to the width of the strip. For safety's sake it is preferred for the magnet to be energised from a low voltage power supply, hence the large strap conductors of the magnet coils. Becaus.e the polarity of the magnetic pole faces preferably alternates from one to the next and as the pole faces are quite close together there is very little net magnetic field at even quite short distances from the drag pad as a whole. Indeed, to ensure that a substantial proportion of the magnetic field extends within the strip being processed, it is preferable for the friction material to be somewhat thinner than is conventional, preferably less than 1.0 mm, thickness. Additionally it has been found that the necessary forces cannot be readily achieved without having a magnet at least 0.5 . long. If desired, to further reduce damage to the unfinished side of the strip which contacts the drag pad, the area of contact may be extended by comparison with that of conventional pads and a lesser pressure may be used. Also for preference the power supply to the magnet may include means to vary the magnet's energising current thereby to adjust the contact pressure to suit the nature of the strip being processed.

Claims: THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:- 1. A method of inducing back tension in a longitudinally moving magnetiseable strip comprising the steps of positioning a stationary electro-magnet adjacent to one side.of the strip, interposing a layer of friction material between the magnet and the strip and energising the magnet to effect pressure contact between the strip and the layer. 2. A method according to claim 1 wherein the step of interposing the layer between the magnet and the strip is effected by advancing a web of friction material extending from an uncoiler roll across the magnet to a coiler roll. 3. A method according to either claim 1 or claim 2 wherein said layer is bonded to a thin steel or other magnetisable lamina. 4. A method according to any one of the preceding claims comprising the further step of adjusting the magnet's energising current to adjust the pressure of contact between the strip and the layer. 5. A drag pad comprising an electro-magnet providing an array of closely spaced, mutually parallel, elongate pole faces each of opposite polarity to its neighbouring face or faces and a layer of friction material covering the array. 6. A drag pad according to claim 5 further comprising an uncoiler roll and a coiler roll for a web of friction material such that said layer may be replaced from time to time by advancing the web from one roll to the other. 7. A drag pad according to either claim 5 or claim 6 wherein said magnet is adapted to be energised from a low voltage power supply. 8. A drag pad according to any one of claims 4 to 6 further comprising means to adjust the energising current of the magnet. 9. A drag pad substantially as described herein with reference to the accompanying drawings.

Inventors: MORRISON BRUCE ROBERT, MORRISON, BRUCE, ROBERT
Applicants: LYSAGHT AUSTRALIA LTD, JOHN LYSAGHT (AUSTRALIA) LIMITED
Application year: 1985
Main classification: B21B39
IPC codes: B21B39, B21C47, B65H23