IE54227B1 - A process and a device for the rapid continuous annealing of a travelling metal wire - Google Patents

Abstract

1. A process for the rapid continuous annealing of a travelling metal wire, in which the wire to be annealed is passed into the groove of a pulley, this wire being annealed by heating with an induced current, the annealed wire being then passed into the same groove of the same pulley, above the wire to be annealed so as to constitute a closed loop in which the induced current circulates, the annealed wire being cooled before it passes into the groove of the pulley, characterized in that the wire rests on the sides of the groove via a plurality of point contacts, leaving free spaces between them.

Description

The present invention relates to a process and a device for the continuous annealing of metal wires based, in particular, on aluminium or copper.

It is known to anneal metal wires continuously by 5 the Joule effect. The annealing current in the wire is usually an alternating current produced by induction.

The inductor is generally toric shaped with the wire passing through the centre of the torus. The induced current circulates along the axis of the wire, providing that the wire is arranged in a loop which is closed in on itself, via an electrical contact at the exterior of the inductor, thus constituting a short circuit turn forming the secondary winding of a transformer of which the inductor represents the primary winding.

It is known, in particular, from GB-A Patent No. 969 192 (Somerset Wire Company Limited) electrically to close the secondary loop foimed hy the wire by making the wire pass over electrically interconnected pulleys. These pulleys can he coaxial or non-coaxial.

When annealing aluminium wires, this process has the disadvantage of causing rapid deterioration of the pulley contact strips.

' It is known that this disadvantage can be avoided hy producing the direct electrical contact between the wire to he annealed, that is the cold-worked wire, before 4 2 2 7 i l,s admission into the indue tor, and the annealed wire leaving the inductor. In this case, the cold wire to be annealed passes over the hot annealed wire. Such a device has been described in US-A-Patent No. 2 459 507 (Western Electric, inventor Κ. H. Denham).

A first disadvantage of this process results from the fact that the annealed wire, which is hot, is lengthened by thermal expansion and is wound on the bottom of the pulley groove, while the wire to he annealed, which is cold and unexpanded has to he wound on the annealed wire, therefore over a greater radius, imposing a higher linear speed. It is therefore necessary to allow for relative sliding between the two wires, which is effected hy limiting the winding arc of the wire to be annealed. However, this reduces the length of the electrical contact, which is a serious disadvantage owing to the strong intensity of the current flowing through the wire. Moreover, the relative sliding damages the surface of the wire.

A second disadvantage of this process originates from the fact that after the annealing operation the wire exhibits a high temperature which is sometimes close to its melting point. Under these circumstances, any local over-heating resulting from the passage of the current from one wire to another through the single contact generator leads to the formation of sparks and melting craters which impair the surface state of the wire in an unacceptable manner.

In our FR-A-Patent No. 2 288 152 (=US-A-Patent No. 118 613), we solved this problem by causing the wire to he annealed, to pass over the bottom of the pulley groove, annealing this wire hy induction heating, then causing the annealed wire to pass in the same groove of the same pulley above the wire to he annealed so as to form a closed loop in which the annealing current circulates.

The annealed wire is cooled before it passes in the groove of the pulley.

The device comprises an inductor, a pulley with a deep groove and a cooler. The wire to he annealed passes in the bottom of the pulley groove then in the inductor which generates the current needed for the annealing operation. It then returns in the annealed state to the groove of the pulley above the wire to be annealed so as to form a closed loop forming the secondary winding of an electricaltransformer of which the inductor is the primary winding. The cooler is placed between the outlet of the inductor and the pulley.

The device forming the subject of our FR-A-Patent No. 2 288 152 (=US-A-Patent No. 4 118 617) is illustrated in Figures 1 and 2. It comprises a pulley 1, having a deep groove 2, a first return pulley 3, a second return pulley 4, an inductor 5 provided with a tube 6 for protection hy water vapour, which is used in the case of copper, a cooler 7, a compressed air type dryer 8 and a third return pulley 9. 4 2 2 7 The section of the groove 2 oi the pulley 1 has the shape illustrated in Figure 2. The bottom 10 is constituted by an arc of a circle of radius r followed, over a height equal to 2.5 r, by two tangents 11 and 12 forming an angle of 5 11' with the axis 13 of the section. At the top of the groove, these two tangents are taken over hy two straight segments 14 and 13 forming an angle of 36° with the same axis 13 and opening to the exterior. The groove acting as a guide for the wire and not as an electric current supply can he produced from a material of low conductivity such as stainless steel, carbides, ceramic materials.

This form of groove allows the treatment of a wire having a radius of between 0.6 r and r. Wires of widely varying diameters can he treated with the same apparatus hy replacing the deep groove, either if the pulley has several grooves of different radius or if the groove or the pulley itself are easily detachable.

The protective tube 6 is made of electrically insulated material. When annealing copper wire it is traversed by a stream of water vapour.

The cooler 7 comprises a pulley 16 enclosed in a casing 17 in which a coolant, generally water, circulates. For the sake of clarity, the wire bears two different reference numerals in Figures 1 and 2 depending on whether it is in the cold-worked state before annealing 18 or in the annealed state 19. It reaches the coldworked state 18 from the die, passes into the bottom of the groove 2 oi the pulley 1 over a large arc of the order of 270°, then on to the return pulleys 3 and 4. It then enters the inductor 3 which it leaves in the annealed state 19, passes successively into the cooler 7 on the pulley 16 where it is cooled then into the dryer 8 where it is dried. Finally, after passing over the return pulley 9, it passes hack into the groove 2 of the pulley 1 over approximately 180°, above the wire in the coldworked state 18, then it leaves the apparatus.

The wires 18 and 19 touch each other over a large arc ensuring excellent electrical contact owing to the large diameter of the pulley and hence the absence of sparks and local beating. Furthermore, since the wires 18 and 19 are cold and are at the same temperature, the linear speed of the annealed wire 19 hardly differs from that of the wire to be annealed 18, which is not translated by relative sliding of the wires but by a slight elongation of the wire in the annealing zone, which is favourable for its good mechanical strength and improves the electrical contact with the wire 18.

This device gives results which are quite satisfactory for the continuous annealing of wires of small diameter, for example in the range of 0.2 to 2 millimetres, at a speed which can attain 1,800 metres per minute, the main pulley 1 having a diameter of 200 millimetres.

However, if wires of large diameter are to be annealed continuously, for example brass wires, of which the diameter may be between 2 and 5.5 millimetres, serious difficulties are encountered owing to the brittleness of the brass in the region where the temperature rises and to the excessive heat exchange between the pulleys and the wire to be annealed which, owing to its greater diameter, has to travel at a substantially reduced speed which may be, for example, of the order of 5 to 120 metres per minute instead of several hundreds up to approximately 2,000 metres per minute in the case of fine wire. This results in an inadequate level of annealing.

The invention relates to an improvement to the device forming the subject of our FR-A-Patent No. 288 152 (=US-A-Patent No. 4 118 617) which overcomes these disadvantages and permits the continuous annealing Of metal wires of relatively large diameter, capable of attaining 5 or 6 millimetres, depending on the type of metal or alloy, without this value constituting an absolute limit. The invention is characterised in that the main pulley, and preferably also the return pulley, comprise a groove of which the sides are provided with a plurality of inserts made of a material having a high melting point, low thermal and electrical conductivity such as alumina, which is resistant to wear and to abrasion, and makes point contact with the metal wire circulating in the groove. We have surprisingly found that these point contacts pennit the wire to be supported without damaging it or marking it undesirably and that all these successive point contacts, separated, by gaps in which the wire is not supported, constituted the equivalent of a virtual continuous groove. The sides oi this virtual groove preferably form an angle of 90°.

This arrangement allows not only round wires hut wires of square or hexagonal or other cross-section to he treated.

The device also comprises a wire cooling means arranged at the outlet of the return pulley situated at the outlet of the inductor and before the return of the wire on to the groove of the main pulley.

The solution involving coating the entire groove with a ceramic material has not been adopted, in fact, it has two disadvantages: the thermal conductivity of dense and hard ceramic materials such as alumina is far from negligible and the desired aim would not have been achieved in the case of a wire-groove contact over the arc of a circle of 180°. Furthermore, the production of a continuous ceramic groove would have constituted a very serious problem on an industrial scale and its cost would have been prohibitive, Figures 1 and 2 relate to our French Patent No. 2 288 152, Figures 3 to 5 illustrate the implementation of the invention, Figure 3 shows the general diagram of a continuous annealing device according to the invention.

Figure A shows the groove of the main pulley in 4 2 2 7 section (4A) and in elevation (4b), Figure 4C shows how the wire is placed in the groove of the main pulley when it is of square or hexagonal cross-section.

Figure 5 is a section through the groove along the axis.

The cold-worked wire to he annealed 20 is directed towards the main pulley 21. To assist understanding of the travel of the wire, it has been shown outside the pulleys but, in reality, it circulates well in the grooves of the various pulleys.

The rim 22 of this pulley comprises a groove 23 of which the sides 24 form an angle of approximately 90°. It also comprises over its entire periphery two rows of cavities 25 of which the axes form between them an angle of approximately 90° which is equal to the angle formed hy the sides 24 of the groove 23. These cavities open at the lateral faces 26 of the rim. The other end can be closed or can open on to the internal edges 27 of the rim.

In the latter case, which is the one shown in Figure 3, the cavities 25 comprise two portions, a front portion A and a rear portion 25B of which the diameter is less than the diameter of the portion 25A. In all cases, the front portion 25A must extend at least up to the vicinity of the groove 23. Moreover, the diameter of the front portion 25A is such that the cavity opens at the corresponding side of the groove.

Some ceramic heads 28 of which the external diameter is approximately equal to the internal diameter of the cavities 25A have heen introduced and fixed, for example hy adhesion with an organic adhesive or a mineral cement, in the front portion of the cavities 25A. These heads are preferably hollow so that a continuous duct is formed with the narrowed portion 25B of the cavities, ensuring, if necessary, certain cooling of the heads hy forced circulation of air and preventing excessive heating thereof. The arrows in Figure 4A show how the cooling air stream can he directed.

Since a portion of each head projects into the sides of the groove, the wire 20 rests at points on the heads, alternately on each side of the virtual groove thus formed, hut does not make contact with the sides 24 of the metal groove 23.

The heads are sufficiently close to prevent the wire from having a tendency to assume an undulated shape, particularly if it is of large diameter (from 2 to 6 mm for example). In practice, the gap between the axis of the beads on each side can attain 3 to 10 times, and even up to 20 times the diameter of the wire to be annealed When round wire is annealed, the entering wire 20 rests on the bottom of this groove, and the annealed wire 29 passes into the same groove in a superimposed relation25 ship with the entering wire, in accordance with the invention. When annealing wire of square or hexagonal cross-section, the positioning and the superimposition of 4 2 2 7 the entering wire 20 and the annealed wire 29 in the groove take place without difficulty (Figure 4C) (which would not have been the case in the form of groove claimed in our French Patfent·2:ώβδ 1152) thus permitting excellent electrical contact.

After passage over the main pulley 21, the wire (20) passes through the inductor 30, then over the large return pulley 31 which is constituted hy a pulley with two parallel separate grooves, one of the grooves serving for the passage of the wire leaving the inductor and being equipped with the same ceramic bead device as the pulley 21, and the other being a simple metal groove shaped in the rim of the pulley and of approximately the same diameter as the parallel groove formed by the ceramic beads. To clarify the drawing, the travel of the annealed wire taking place in the metal groove has been drawn in broken lines. The annealed wire 29 then passes through a cooling device with a film of water 32 like the one foraing the subject of French Patent No. 2 442 418 (Trefimetaux) and which is capable of evacuating a heat flow of the order of 50 Mw/m2, for example, over a 5 mm diameter brass wire brought to 650° by the inductor and circulating at 5 metres per second.

The cold annealed wire again passes over the main pulley 21 above the cold-worked wire 20 then over the small return pulley 33, then in the metal groove of the large return pulley 31 (shown in broken lines) and leaves the annealing device in the direction, for example, of a winding device Embodiment An annealing device was constructed in accordance with the present invention, intended particularly for the annealing of 2 to 5.5 mm diameter brass wires. The main pulley 21 has a diameter over the groove bottom of 750 millimetres. The groove is constituted by two halves which are symmetrical about a plane passing through its rotational axis. The division appears at CC’ in Figures 4b and 5· The two halves are assembled by electrically insulating parts and are held 1 to 2 millimetres apart so as to avoid any risk of looping of the voltage induced by the annealing current in the pulley 21 which is metallic and mounted on an insulating hub 3¾.

On each of its sides, the groove has 72 alumina beads having an external diameter of 10 mm, an internal diameter of 4 mm and a length of 30 mm. The distance between beads is 35 mm between axes on each side.

The inductor 30 induces in the wire 20 a current capable of attaining 6,000 amperes under 70 volts, permitting, for example, a 5·5 mm diameter brass wire to be annealed at a speed of 5 metres per second.

The issuing wire has a particularly noteworthy surface state which is free from scoring or traces of electrical discharges. Furthermore, the rapid annealing thus achieved is particularly advantageous when treating -3227 lead brasses (cut-away brasses capable of containing 3 or (tjC of lead), as it prevents tbe coalescence of the lead particles which inevitably takes place during static annealing in a fixed furnace and which is translated during the cutting operation hy long fine shavings which are only slightly brittle and become entangled and tend to block automatic lathes.

Claims (12)

1. A process for the rapid continuous annealing of a travelling metal wire, in which a wiri^to^fie annealed is passed into the groove of a pulley, this wir^/telng annealed hy heating with an induced current, the annealed wire/being then passed into the same groove of the same pulley, above a^y^wlre/to^^e^ annealed so as to constitute a closed loop in which the induced current circulates, the annealed wire/Eelng cooled before it passes into the groove of the pulley, wherein the wir^rest nS on the sides of the groove via a plurality of point contacts, leaving free spaces between them. 10

2. A device for the rapid continuous annealing of a travelling metal wire, comprising a main pulley, at least one return pulley, an inductor, a cooler, wherein the main pulley comprises a groove in which the sides are equipped with a plurality of inserts made of a material of low thermal and electrical conductivity, which is resistant to wear and to abrasion, which lb make point contact with the metal wire circulating in the groove.

3. A device according to Claim 2, wherein on each side of the groove the successive point contacts are situated at a distance of between 3 and 20 times the diameter of the wire to be annealed.

4. A device according to Claim 2 or 3, wherein all the successive points 20 of contact of the travelling metal wire on the Inserts arranged on the sides of the groove constitute the equivalent of a continuous virtual groove, the sides of which form an angle of 90°.

5. A device according to one of Claims 2 to 4, wherein the Inserts are constituted hy cylindrical beads made of alumina-based ceramic material. 25

6. A device according to Claim 5, wherein the heads are hollow and are traversed by a coolant.

7. A device according to one of Claims 2 to 6, wherein the return pulley situated at the outlet of the Inductor comprises two grooves of approximately equal diameter one of which is equipped, on its sides, with 30 inserts of the same type as those in the main pulley. 0. A device according to one of Claims 2 to 7, wherein it comprises a means for cooling the wire arranged at the outlet of the return pulley situated at the outlet of the inductor and before the return of the wire on the groove of the main pulley.

8. 9. A device according to one of Claims 2 to 8, wherein the groove on the 5 main pulley is formed hy two portions which are symmetrical about a plane passing through the axis of rotation, and the two halves are assembled by electrically Insulating connection means which maintain between them a space which is electrically insulating towards the voltage Induced in the pulley by the current circulating in the wire being annealed.

9. 10 10. A process for the rapid continuous annealing of a travelling metal wire substantially as described herein with reference to Figures 3 to 5 of the accompanying drawings.

10. 11. Wire annealed by a process according to claim 1 or 10.

11.

12. A device for the rapid continuous annealing of a travelling metal and as shown in „ wire, substantially as described herein with reference to/Figures 3 to 5 of lb the accompanying drawings.