GB2129720A - Cold working continuous lengths of metal - Google Patents

Abstract

A method of cold working continuous lengths of rod 11 by twisting includes the steps of clamping the rod etc., at spaced apart clamps 15 and 16 and then rotating a central part of the clamped length by means of a twisting head 17 incorporating a chuck for clamping to the rod. Between successive clamping and twisting operations the rod is advanced through the apparatus by feed rollers 14. Various twisting and untwisting patterns are possible. The chuck may be rotated in one direction and then in the opposite direction while a single length of rod remains clamped. Alternatively the chuck may be rotated in a first direction only. This twists section 111 of rod in one direction. This section of rod is then advanced to position 112 and subsequent rotation of chuck 17 in the same direction untwists the section at 112 whilst applying initial twist to the new section at 111. <IMAGE>

Description

SPECIFICATION Cold working continuous lengths of metal The invention relates to a process of and apparatus for cold working of continuous lengths of metal.

The invention is concerned primarily with material which is known as rod, namely material which has been reduced in diameter by rolling and is of such a diameter that it can conventionally be wound into coils for storage. However the invention could also be applied to material normally known as bar which has a greater diameter than rod and after manufacture is normally cut into straight lengths for storage and transportation. The invention could also be applied to wire, namely material which has been drawn through a die to reduce its diameter although there is little call for subsequent cold working of wire. The material may be of circular or other cross section.As the invention is concerned primarily with conventional rod material, the term rod will be used throughout the remainder of the specification as a generic term for rod, bar or wire, whether or not it has a circular cross section.

For many structural purposes such as concrete reinforcement, hot-rolled low-carbon steel rod does not have sufficient strength but would be an attractive material to use from the cost point of view.

Useful materials can be achieved at higher cost by a higher carbon content and/or alloying or by cold working. One established form of cold working involves cutting the rod to discrete lengths and twisting the material beyond its elastic limit while holding it under tension. The pitch of twist is normally between six and twenty diameters, de pending on the starting material and the required properties but pitches outside this range are not known and can provide useful results.

Carrying out the twisting in discrete lengths is a major disadvantage because even with careful plan ning it is normal to waste 4% or 5% of the material when it is cut into smaller lengths for use such as concrete reinforcement.

It has not in the past been practicable to cold work continuous lengths by twisting.

In accordance with one aspect of the invention there is provided a method of cold working continuous lengths of rod bytwisting including the steps of clamping the rod at three locations mutually spaced along its length, applying twist to the material beyond its elastic limit by rotating it about its axis at the central clamp relative to the outer clamps, unclamping, advancing the material axially relative to the clamps, and repeating the clamping, twisting and advancing operations continually, the distance of each advance being such that all of the continuous length of material is subjected to twist ing as it passes the clamping and twisting region.

Because there is no provision or requirement for twisting at spools or other devices between which the rod is passed, there should be no nett twisting of the rod. Thus, depending on the pattern of advance and the manner of the twisting, the rod may be twisted and subsequently untwisted throughout its length to give zero nett final twist for all sections of the rod or alternatively the resulting rod may be made up of sections with alternating directions of twist.

The central clamp may be rotated in one direction and then rotated back through the same number of turns to apply twisting followed by untwisting in the two sections between the central clamp and each outer clamp. The rod may then be advanced by almost the total distance between the two clamps.

However, as the central clamp must have a finite length, there is a tendency to leave a short untwisted portion at the region of the central clamp.

Preferably the central clamp is equidistant from the outer clamps and the material is advanced by a distance no grnaterthanthe distance between central and outer clamps. In this way, the material clamped during one twisting operation is always twisted during another twisting operation. With this arrangement it is preferable that the central clamp should always rotate in the same direction. In this way, twist applied to a length of material immediately before the central clamp by twisting its leading end in one sense is removed when that length is moved to a position adjacent the exit clamp to be untwisted by applying twist in the same sense to the trailing end of the length. The result with this arrangement is no nett twist in any section of rod.

The operation is essentially carried out in discrete steps but can be made compatible with continuously moving lengths of material either by providing buffer stores for the length of each advance or by using a "flying" twist in which the clamping and twisting equipment moves axially with the material during its twisting phase and moves backto meet the next length to be twisted.

The rod should preferably be retained under tension throughout the twisting operations.

According to a second aspect of the invention there is provided apparatus for cold working continuous lengths of rod comprising a clamping and twisting station incorporating an upstream clamp, a downstream clamp, a rotatable chuck between clamps, means for clamping and unclamping rod in the clamps and the chuck, means for rotating the chuck to twist the rod beyond its elastic limit and means to advance the rod through the clamping and twisting station when it is not clamped.

A bank of such apparatuses may be provided at the input of an apparatus for producing concrete reinforcing mesh. In such a case, one twisting apparatus is provided for each longitudinal rod being fed into the mesh forming apparatus. It is conventional to advance such a series of longitudinal rods in steps into the mesh forming apparatus and to weld one cross rod to all the longitudinal rods at a welding location between each advance of the rods.

The advance of the rods in the mesh forming apparatus can be synchronised to the advance of the same rods through the bank of twisting and clamping apparatuses.

An accumulator/pull through unit may be provided for each rod between its twisting apparatus and the mesh forming apparatus and may comprise a device for deflecting the rod from its axial path when clamped in the mesh forming apparatus but un clamped in the twisting apparatus in order to draw rod through the twisting apparatus. Subsequently, while the rod is clamped and being twisted in the twisting apparatus, the rod accumulated by deflection is drawn through the mesh forming apparatus.

An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a diagrammatic perspective view of a simple apparatus for carrying out the invention; Figure2 is a diagram in conjunction with which the degree of twist imparted to successive portions of the rod will be explained; Figure 3 is a diagrammatic plan view of a battery of twisting apparatuses installed in conjunction with a welded mesh forming apparatus; and Figure 4 is a side elevation of the apparatus shown in Figure 3.

Figure 1 illustrates an apparatus by which the method of the invention may be performed. A continuous length of rod 11 is fed from a conventional pay-off device 12 through a clamping and twisting section as indicated by arrow 13. A set of powered feed rollers 14 serves to pull the rod from the pay-off device.

The rod passes through an upstream clamp 15, a downstream clamp 16 and a rotatable twisting head 17 arranged centrally between the clamps 15 and 16.

The twisting head 17 incorporates a chuck (not shown separately) which can be caused to clamp the rod and in general terms can be considered to be a central clamping. Pu rely for the purposes of illustration, the twisting head 17 is shown as being rotatable by means of a rack 18 engaging teeth 19 around the periphery of the twisting head. A more practicable form of drive for a twisting head will be described subsequently with reference to Figure 3.

The clamps 15 and 16 and the chuck of the twisting head 17 may be engaged and disengaged as required by a control system which is not shown and this control system also causes the powered feed rollers 14 and the rotation of the twisting head to be operated as required. At least one of the clamps 15 and 16 should also be provided with means for maintaining tension in the section of rod between the clamps while the rod is in a clamped condition. If the twisting head can float axially, one tensioning device is sufficient.

The way in which the rod 11 is cold twisted as it passes through the apparatus will now be described.

Starting from the situation as shown, with a length of rod already installed in the apparatus, the passage of rod is stopped by disengaging the feed rolls 14, the clamps 15 and 16 are operated to clamp the rod against rotation and the twisting head is engaged with the rod. The twisting head is then rotated in one direction to cause the section of rod 111 between up-stream clamp 15 and twisting head 17 to be rotated in one direction and the section of rod 112 between twisting head and clamp 16 to be rotated in the opposite direction. Tension is maintained on the rod during the twisting. The amount of twist should normally be to give a pitch of between six and twenty diameters but ranges of twist outside these limits can still provide useful results.Whilst maintaining the clamped condition for both clamps 15 and 16 and twisting head, the twisting head is then reversed through the same number of turns as the original twisting whilst maintaining the tension.

This leaves the section of rod between clamps 15 and 16 in a finally untwisted state but the effect of twisting and subsequently untwisting, beyond the elastic limit of the material, has the effect of cold working and thus of increasing the tensile strength of the material. As is conventional with cold twisting, the pitch of the twist is selected to increase the yield strength and ultimate tensile strength of the rod to a required extent without making the rod excessively brittle.

The section of rod which was between clamps 15 and 16 can then be advanced through the apparatus by releasing both clamps and the twisting head chuck and engaging the feed rollers 14. When a new and untwisted section of the rod 11 comes between the clamps 15 and 16, the feed rolls are disengaged and the clamping, twisting and untwisting operation is repeated. Successive sections of the length of the rod are twisted in this way until the whole of the length of the rod has been twisted. It is of course necessary to ensure that the length which is fed through the apparatus during each cycle of operation is such that no portion of rod is left untwisted.

No problem is caused if a small part of a previously twisted section is again exposed to twisting because the previous cold working applied to this material increases ittorsional strength and ensures that the new cold working is applied to the previously untwisted parts of the rod.

A problem can arise however in connection with the short section of rod which is clamped by the twisted head. To ensure that this part is twisted, it is preferred to advance the rod at each cycle through a length of approximately half the distance between clamps 15 and 16 rather than approximately the whole distance between the clamps. Details of a particularly advantageous twisting cycle will be explained with reference to Figure 2. In Figure 2 the rod is shown as notionally divided up into successive sections of length X. The length X corresponds to the length by which the rod is advanced through the apparatus for each twisting cycle. This length X is notionally divided up into a main section M and a short clamping section C which is the portion which in a particular cycle becomes clamped in the twisting head 17. For convenience, successive sections C, M will be referred to as c1, ml and so on. It should be observed that the length of rod available for twisting between the clamp 15 and head 17 and that between head 17 and clamp 16 is c2 + m2 or m3 + c4 and thus is equal to X.

The twisting cycle will not be explained in relation to a notional length Xwhich is represented in the first cycle by cl, ml, in the second sycle by c2, m2 and so on. During the first cycle, the lengths at cl and ml remain untwisted because they are upstream of the clamp 15 apart from a small section of ml which is clamped within clamp 15. During the second cycle, the same length of material has progressed to be represented by sections c2 and m2. With the arrangement under consideration the twist ing head 17 is rotated in one direction only and through a fixed number of turns. The whole of the section c2, m2 is thus twisted in a direction which for convenience will be referred to as positive when this section lies between clamp 15 and twisting head 17.

During the next cycle of operation the length of rod under consideration has been advanced to be represented by sections c3 and m3. Section c3 is unaffected by the next twisting operation because it is clamped within the clamping length of the twisting head 17. Section m3, together with section c4 lies between the twisting head 17 and clamp 16 and is thus to be subjected to further twisting. Prior to this new twisting, the pitch of twist of section c4 corresponds to that of section m3 because section c4 will have been twisted along with section m4 between clamp 15 and head 17 in the cycle before m3 was twisted. c4 will have retained its twist while in the twisting head 17. Operation of the twisting head 17 rotates the trailing end of m3 in the same direction as its leading end was previously twisted and thus applies negative twist.The effect of this negative twist is of course to untwist section m3 and leave it with nett zero twist. For the next twisting operation, the section previously at c3 takes its position at c4 and is untwisted along with the succeeding m section. When the rod advances into or beyond clamp 16, no further twisting occurs.

It can be seen that with the arrangement described above, all sections of the rod are subjected to equal twisting followed by untwisting. To avoid the danger that very short sections might remain unworked by twisting if the apparatus goes out of adjustment it is desirable to ensure that the advance through the apparatus for each cycle is very slightly less than the spacing between twisting head and clamp. As previously explained, this short length of material would not be cold worked twice because after its initial cold working it would have greater strength than the unworked section of bar so that the new working would be concentrated in the unworked bar.

The application of several apparatuses in accordance with the invention at the input to an apparatus for forming welded mesh for concrete reinforcement will now be described with reference to Figures 3 and 4. Figure 3 shows six continuous lengths of rod 31 to 36 each of which runs through a composite up-stream clamp 37, a twisting head such as 38 and a composite down-stream clamp 39 with a tensioning facility. After clamp 39 each rod passes through a combined accumulator and pull-through unit 41 and from there leads in to a conventional mesh forming apparatus for concrete reinforcement mesh.

In a typical mesh more than six lengths of rod would be employed and the apparatus shown would have to be multiplied accordingly. For mesh manufacture, longitudinal rods 31 to 36 are fed through the machine in steps corresponding to the pitch of the mesh and after each feeding step a transverse rod is welded to all of the longitudinal rods at a welding station extending across all the rods. The longitudinal rods are then advanced by one more pitch and a new transverse rod is welded in position.

In this way, the mesh is in effect manufactured in continuous lengths, although it is normally cut to lengths of twelve metres immediately after manufacture to facilitate storage and transport.

Each twisting head such as 38 is driven by a gearbox 42 incorporating a worm reduction drive.

The gearboxes such as 42 are driven by a belt or chain drive 43 from a common shaft 44 which in turn is driven by an electric motor 45 through a clutch 46.

The combined twisting heads and gearboxes are arranged alternatively ahead of and behind the shaft 44 to enable adjacent units to have their axes sufficiently close together for the transverse spacing required for the longitudinal rods of reinforcement mesh. Because the twisting heads are thus staggered and have to be central between the up-stream and down-stream clamps on the rods, the actual clamping locations such as 47 and 48 are also staggered within the composite clamps. Figure 4 shows diagramatically a hydraulic cylinder 49 within the composite clamp 39 and this serves as a tensioning device.

Figure 4 also shows sufficient details of the accumulator/pull-through unit 41 to enable this to be understood. Immediately prior to pulling rod through the clamping and twisting station, the rods extend in a straight line from clamp 39 to the mesh forming apparatus as indicated in dashed lines at 51.

The unit 41 is comprised essentially of fixed guides 52 and 53 around which the rod can be curved within its elastic limit and a displacer 54. The displacer is movable between a position shown in dashed lines where it allows the rod to pass in a straight line from the clamp 39 to mesh forming apparatus and a position shown in full where it causes the rod to be deflected within its elastic limit around both the guides 52 and 53 and the displacer 54 itself. The displacer is pivoted on an arm 55 and has its movement controlled by a hydraulic cylinder 56.

In operation, with the longitudinal rods 31 to 36 clamped in the mesh forming apparatus and the rods lying along the straight path shown at 51, the clamps 37 and 39 and the twisting heads such as 38 are operated with the head 38 rotating in one direction only as described with reference to Figure 2. This effects cold working of the rod as previously described. The rod is then released from clamps 37 and 39 and from the twisting head 38 whilst remaining clamped in the mesh forming apparatus.

In this condition, the hydraulic cylinder 56 is operated to move the displacer 54 from the position shown in dashed outline to the position shown in full. This causes the rod to deviate to the position shown in full at 57 and thus draws rod through the twisting apparatus. The clamps 37 and 39 are then engaged for another twisting cycle. Displacer 54 is raised, leaving an accumulation of rod which is available to be taken in to the mesh forming apparatus to weld the next transverse rod to the longitudinal rods. The longitudinal rods are clamped in the mesh forming apparatus before the next twisting cycle has been completed and the clamps and twisting head released. At that stage another operation of the displacer pulls still more rod through the twisting apparatus.

In this way, low carbon steel which in itself is not sufficiently strong for use in concrete reinforcement mesh can be cold worked as it is fed from a continuous supply at the input to the mesh forming apparatus. Placing the twisting apparatus in the same line as the mesh forming apparatus saves the expense of additional handling operations associated with conventional twisting apparatus, saves the space required for twisting in long discrete lengths and prevents waste of material which can be associated with using difference lengths for the twisting and mesh forming activities.

With this arrangement, it is of course necessary to space the clamps 37 and 39 of the twisting apparatus so that the advance required during each cycle through the twisting apparatus corresponds with the pitch of the mesh.

The cold twisting effected by the invention is very effective in straightening the rod with the result that no separate straightener is required. Winding cold twisting rod into coil and then straightening it can adversely affect its properties. For this reason it is preferred to avoid coiling the rod after manufacture.

The absence of any coiling requirement in the arrangement of Figures 3 and 4 is thus particularly valuable.

Claims (15)

1. A method of cold working continuous lengths of rod by twisting including the steps of clamping the rod at three locations mutually spaced along its length, applying twist to the material beyond its elastic limit by rotating it about its axis at the central clamp relative to the outer clamps, unclamping, advancing the material axially relative to the clamps, and repeating the clamping, twisting and advancing operations continually, the distance of each advance being such that all of the continuous length of material is subjected to twisting as it passes the clamping and twisting region.

2. A method as claimed in claim 1 in which the central clamp is rotated in one direction and then rotated back through the same number of turns to apply twisting followed by untwisting in the two sections between the central clamp and each outer clamp.

3. A method as claimed in claim 2 in which the rod is advanced between twisting operations by almost the total distance between the two clamps.

4. A method as claimed in claim 1 or claim 2 in which the central clamp is equidistant from the outer clamps and the material is advanced by a distance no greater than the distance between central and outer clamps.

5. A method as claimed in claim 4 in which the central clamp always rotates in the same direction so that twist applied to a length of material immediately before the central clamp by twisting its leading end in one sense is removed when that length is moved to a position adjacent the exit clamp by applying twist in the same sense to the trailing end of the length.

6. A method as claimed in any one of the preceding claims in which the discrete steps of twisting are made compatible with continuously moving lengths of material by providing a buffer store for the length of each advance.

7. A method as claimed in any one of the preceding claims in which the rod is retained under tension throughout the twisting operations.

8. A method of cold working continuous lengths of rod by twisting substantially as described with reference to and as illustrated by Figure 1 or Figure 2 or Figures 3 and 4 of the accompanying drawings.

9. Apparatus for cold working continuous lengths of rod comprising a clamping and twisting station incorporating an upstream clamp, a downstream clamp, a rotatable chuck between the clamps, means for clamping and unclamping rod in the clamps and the chuck, means for rotating the chuckto twist the rod beyond its elastic limit and means to advance the rod through the clamping and twisting station when it is not clamped.

10. A bank of apparatuses as claimed in claim 9, provided at the input to an apparatus for producing concrete reinforcing mesh.

11. A bank of apparatuses as claimed in claim 10 wherein the advance rods in the mesh forming apparatus is synchronised to the advance of the same rods through the bank of twisting and clamping apparatuses.

12. A bank of apparatuses as claimed in claim 11 wherein an accumulator/pull through unit is provided for each rod between its twisting apparatus and the mesh forming apparatus.

13. A bank of apparatuses as claimed in claim 12 wherein each accumulator/pull through device comprises a device for deflecting the rod from its axial path when clamped in the mesh forming apparatus but unclamped in the twisting apparatus in order to draw rod through the twisting apparatus and subsequently while the rod is clamped and being twisted in the twisting apparatus allowing the rod accumulated by deflection to be drawn through the mesh forming apparatus.

14. Apparatus for cold working continuous lengths of rod substantially as described with reference to and as illustrated by Figure 1 or Figures 1 and 2 or Figures 3 and 4 of the accompanying drawings.

15. A bank of apparatuses for cold working several continuous lengths of rod prior to welding into mesh substantially as described with reference to and as illustrated by Figures 3 and 4 of the accompanying drawings.