OR METAL ALLOY WIRE, STRAND, STRING, WIRE ROD OR STRIP

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority from Italian patent application no. 102018000004548 filed on 16/04/2018, the entire disclosure of which is incorporated herein by reference .

TECHNICAL FIELD

The present invention relates to a resistance annealing furnace to anneal at least one metal or metal alloy wire (2), strand, string, wire rod or strip.

In particular, the present invention finds advantageous, but not exclusive, application in in-line resistance annealing, i.e. directly at the output of a machine for the simultaneous production of one or more wires or one or more wire rods of an electric conductor (generally, copper or aluminium or their alloys), for example a wire drawing machine, to which the following description will explicitly refer without thereby losing generality.

A direct current resistance annealing furnace designed to be arranged in line, i.e. downstream of a wire drawing machine, usually comprises at least two, and in particular three, electric axes, which are provided with respective electric contact rings and are motorized to drag the metal or metal alloy wire or a plurality of wires in case the wire drawing machine is a multi-wire machine, a plurality of idle or motorized return rollers and a motorized output drawing ring.

The return rollers and the output drawing ring are arranged so as to define a specific path for the metal wire, which starts around the contact ring of a first electric axis, turns around the contact rings of the other two electric axes and the return rollers and ends around the output drawing ring.

BACKGROUND ART

As already known, the annealing furnace comprises an electric apparatus for generating a direct current voltage that is applied between the second electric axis and the other two electric axes, i.e., for example, the positive potential of the electric voltage is applied to the second electric axis and the negative potential of the electric voltage is applied to both the first and the third electric axes. Each electric axis comprises a shaft on which the respective electric contact ring is mounted and a coaxial cylindrical manifold integral with the shaft. Each electric axis receives a direct current from the electric equipment via sliding contacts consisting of electric brushes that slide over the manifold.

The annealing process takes place through a Joule effect due to the passage of current in the wire sections between the second electric axis and the other two (first and third) electric axes.

Usually, the path of the wire is divided into a first preheating section, which goes from the first electric contact ring to the second electric contact ring, a second actual annealing section, which goes from the second electric contact ring to the third electric contact ring, and a third cooling section, which goes from the third electric contact ring to the output drawing ring.

Usually, the first preheating section is longer than the second annealing section so that the temperature gradient of the wire in the first preheating section is lower than that of the wire in the second annealing section.

The electric voltage applied between the electric axes and the corresponding electric current circulating in the wire are commonly known as annealing voltage and annealing current and generally depend on the length of the preheating and annealing sections, on the wire advancing speed along the path and on the material and section of the wire .

The electric contact rings of the electric axes are made of metallic material, e.g. steel, to allow a maximum conduction of electric current during their contact with the wire to be annealed. An example of a current resistance annealing furnace is described and shown in the Italian patent application no. 102016000033186 in the name of the same Applicant.

The first electric contact ring of the first preheating section can have different functions depending on the conditions upstream of the annealing furnace:

1) if, for example, the annealing furnace is combined with a wire drawing machine having a final drawing capstan, the first electric contact ring of the annealing furnace has only the function of transferring the electric current to the wire for its annealing;

2) if, on the other hand, the annealing furnace is combined with a drawing machine lacking the final drawing capstan, the function of said final drawing capstan is transferred to the first electric contact ring of the annealing furnace. This function which can be materially carried out by the same ring (as, for example, in the "multi-wire solutions") or this function can be carried out by two physically (electrically) separated but mechanically connected rings mounted on the same axis (solution e.g. adopted on the roughing machines);

3) if, on the other hand, the annealing furnace is combined with a simple reel (and, therefore, not with a wire drawing machine) , the first electric contact ring can perform both functions, namely being only a wire current supplier if there is an external device which supplies the wire(s) to the reel and then transfers it to the annealing furnace, or being a drawing capstan if it extracts the wire(s) from the reel .

The solution in which the mechanical drawing function and the electric annealing function are concentrated in a single first axis is known. The advantages of this solution are the following:

a) no need for a mechanical connection system (belt or other) to transfer the motion from the final drawing capstan of a wire drawing machine, which would avoid a difference between the peripheral speeds of the two rings (final drawing capstan and first electric contact ring) with consequent damage to both the wire and the rings;

b) reduction of the space occupied by the line;

c) simpler maintenance thanks to greater constructive simplicity and reduced components;

d) reduction of overall costs.

However, there are situations in which the wire produced by the line must not undergo annealing and therefore an annealing voltage is not applied between the electric axes. If the first electric axis also has the mechanical drawing function or is mechanically connected to the final drawing capstan, for example by means of a non-releasable drive belt, and cannot be excluded from the wire path, then the relative electric brushes slide on the manifold in the absence of current flow, causing premature wear and damage to the manifold, the brushes and the axis.

In other situations in which the wire is annealed but by a reduced current, due to various factors, for example a reduced diameter of the wire or a reduced number of wires in the case of multi-wire lines or a reduced advancing speed of the wire, then the current density on the electric brushes could be reduced to values lower than those recommended by the manufacturer. Even these situations show an increase in wear and therefore an early damage to the electric brushes and the relative manifold.

The aforesaid problems also occur on the other electric axes (second and third) in case they are mechanically connected to the first electric axis and to the final drawing capstan of the wire drawing machine, for example by means of a non-releasable belt transmission.

DISCLOSURE OF INVENTION

The main object of the present invention is to provide a resistance annealing furnace to anneal a wire made of metal material, wherein said furnace is free from the drawbacks described above and, at the same time, is easy and inexpensive to manufacture. The annealing furnace can be either of the direct current type or of the alternating current type. According to the present invention, it is provided a resistance annealing furnace to anneal at least one metal or metal alloy wire, strand, string, wire rod or strip, as defined in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the annexed drawings showing a non-limiting embodiment, in which:

- Figure 1 schematically shows a first part of a direct current resistance annealing furnace made according to the present invention;

Figure 2 shows (with parts removed to facilitate the reading of the drawing) a second part (rear part) of the annealing furnace of Figure 1;

- Figure 3 shows a first electric axis of the annealing furnace of Figures 1 and 2, this first electric axis being motorized and provided with two raisable/lowerable brush holding assemblies, in which the upper brush-holding assembly is in a raised configuration (I);

- Figure 4 shows the first electric axis of Figure 3, in which the upper brush-holding assembly is in a lowered configuration (II);

- Figure 5 shows a side view of the first electric axis of Figure 4;

- Figure 6 shows a longitudinal section A-A of the first electric axis of Figures 4 and 5;

Figure 7 shows an axonometric view of a raisable/lowerable brush-holding assembly of the first electric axis of Figures 3 and 4;

- Figure 8 shows a perspective view of two brush-holding devices of the raisable/lowerable brush-holding assembly of Figure 7; and

- Figure 9 shows some exploded details of the brush-holding device of Figure 8.

BEST MODE FOR CARRYING OUT THE INVENTION

In Figure 1, 1000 indicates as a whole a direct current resistance annealing furnace to anneal a metal wire, this latter indicated with 2, and in particular an aluminium wire or a copper wire or a metal alloy based on aluminium or copper.

In particular, Figure 1 schematically shows the front part 600 of the annealing furnace 1000.

The annealing furnace 1000 is of the type designed to work preferably, but not necessarily, in line, i.e. arranged between the output of a wire drawing machine, of a known and therefore not shown type, and the input of a winder, also known and therefore not shown.

In a further embodiment not shown, the annealing furnace 1000 is coupled to a simple reel, which dispenses one or more metal wires. With reference to Figure 1, the wire 2 exits the wire drawing machine and enters the annealing furnace 1000 advancing in the direction 3, then leaving the annealing furnace 1000 in the direction 4.

Still with reference to Figure 1, the annealing furnace 1000 comprises three electric axes 5, 6 and 7, which are provided with respective electric contact rings 8, 9 and

10, at least two return rollers 11 and 12, which are idle or motorized and are arranged between the first two electric axes 5 and 6, and a possibly motorized output ring 13.

In other words, the annealing furnace 1000 comprises:

- a first electric axis 5;

- a second electric axis 6; and

- a third electric axis 7.

In the present invention, the first electric axis 5 is also a motorized drawing axis, as better seen in the remainder of the present description.

The return rollers 11 and 12 and the output ring 13 are arranged so as to define a determined path for the wire 2, which starts around the electric contact ring 8, turns around the return rollers 11 and 12 and the two electric contact rings 9 and 10 and ends around the output ring 13. The wire 2 runs along this path dragged by the motor drive associated with the first electric axis 5. Advantageously, but not necessarily, also the other electric axes 6 and 7 and the output ring 13 are independently motorized to help drag the wire 2. Alternatively, the electric axes 6 and 7 and the output ring 13 are connected to the electric axis 5 with a transmission system of a known and not shown type.

In a known manner, the annealing furnace 1000 comprises a voltage generator DC 14, which can be supplied by an AC voltage and in particular by the three-phase voltage Uac supplied by a three-phase electric network 15, to generate a DC voltage, the so-called annealing voltage, indicated with Uann in Figure 1, which is applied between the second electric axis 6 and the other two electric axes 5 and 7. The annealing process takes place through a Joule effect due to the passage of electric current in the wire sections between the second electric axis 6, and therefore the relative electric contact ring 9, and the other two electric axes 5 and 7, and therefore the relative electric contact rings 8 and 10.

As always shown in Figure 1, the path of the wire 2 is divided into:

- a first preheating section, which is indicated by 16 and extends from the electric contact ring 8 to the electric contact ring 9 passing through the return rollers 11 and - a second actual annealing section, which is indicated with 17 and goes from the electric contact ring 9 to the electric contact ring 10; and

- a third cooling section, which is indicated with 18 and goes from the electric contact ring 10 to the output ring 13.

Advantageously, but not necessarily, the cooling section 18 comprises a semicircular path section 18a around the electric contact ring 10.

In particular, the annealing furnace 1000 comprises a tank 19 full of cooling liquid and crossed by the cooling section 18 for an immersion cooling, and drying devices 20 to dry the wire 2 at the output of the tank 19. Alternatively, the tank 19 includes sprayers (not shown) for spraying the cooling liquid against the wire 2.

In the example shown in Figure 1, the positive potential of the voltage Uann is applied to the second electric axis 6, while the negative potential of the voltage Uann is applied to the first electric axis 5 and to the third electric axis 7.

This electric configuration is advantageous with respect to an inverted polarity (positive potential applied to the electric axes 5 and 7 and negative potential applied to the electric axis 6) because it avoids a draining of electric current towards the wire drawing machine that is arranged upstream of the annealing furnace 1000, and the winder that is arranged downstream of the annealing furnace 1000, and reduces the drainage of electric current in the cooling liquid .

Advantageously, the annealing section 17 passes through an annealing chamber 21. When the annealing furnace 1000 is in operation, i.e. when the electric contact rings 8-10 and the output ring 13 rotate to advance the wire 2, the cooling of the wire 2 starting from the semicircular path section 18a generates steam, which prevents the entry of air into the annealing chamber 21, thus protecting the wire 2 from surface oxidation.

Even more advantageously, the annealing chamber 21 has a pneumatic seal to contain nitrogen, which is mixed with the steam coming from the tank 19 so as to produce a protective gaseous mixture that prevents the oxidation of the wire 2. The protective gas mixture in the annealing chamber is particularly advantageous when the wire 2 is made of copper or of a copper-based alloy, since the copper oxidizes quickly at the annealing temperature, which is higher than 180°C. The surface oxidation of the wire 2 would cause an increase in the electric contact resistance between the wire 2 and the electric contact ring 10 and the formation of sparks.

In the specific example considered, in which the wire 2 is made of aluminium or copper or of a metal alloy based on aluminium or copper, the preheating section 16 has a length greater than the one of the annealing section 17 so that, with the same section of the wire 2, in the portion of wire 2 along the preheating section 16 there is a current Ipht that is lower than the current Iann that circulates in the portion of wire 2 along the annealing section 17.

In this way, the temperature gradient of the wire 2 in the preheating section 16 will be lower than the one of the wire 2 in the annealing section 17.

One or more of the electric contact rings 8, 9 and 10 can be made of a metallic electric conductive material or of a non-metallic electric conductive material, for example graphite, as e.g. described in the aforementioned Italian patent application no. 102016000033186. In this latter case, there can be no migration of metal by diffusion from the wire to the electric contact rings 8, 9 and 10. Advantageously, the graphite of the electric contact rings 8, 9 and 10 is an isotropic graphite, as described in the Italian patent application IT-102016000033186.

Figure 2 shows the rear part 500 of the annealing furnace 1000.

The rear part 500 comprises a cabinet 501 designed to contain the motor drives of at least one of the electric axes 5, 6, 7 and/or of at least one return roller 11 and 12 and/or of the output ring 13. For simplicity's sake, Figure 2 shows only the electric motor 85 of the first electric axis 5.

The rear part 500 and the front part 600 of the annealing furnace 1000 are separated by a wall 502 of the cabinet 501.

In this case, it is assumed that a wire 2 coming from the wire drawing machine enters the annealing furnace 1000 and starts to be wound around the first electric contact ring 8 (Figure 1) of the first electric axis 5 (Figures 1, 2, 3 and 4) . The wire 2 will then travel the path previously described with reference to Figure 1.

As shown in particular in Figure 6, the first electric contact ring 8 is fitted on a shaft 55 having a longitudinal symmetry axis XI and partially covered by a sleeve 78 fastened to the frame of the annealing furnace 1000.

The longitudinal symmetry axis XI, besides being the axis of the shaft 55, is also the longitudinal symmetry axis of the whole first electric axis 5.

Also the shaft 55 is made of an electrically conductive metallic material, such as for example a carbon steel.

With reference to Figures 3 and 4, the shaft 55 is set in rotation according to a direction of rotation indicated by R by the electric motor 85. It is known that the shaft 55 can be rotated directly by the electric motor 85, as shown in Figures 3-6, or can be dragged by a belt transmission or by a similar transmission .

While the first ring 8 is in the front part 600 of the annealing furnace 1000, the electric motor 85 and a brush holding assembly 100 are both located in the rear part 500 of the annealing furnace 1000.

It should be noted that the wall 502 has not been shown in Figures 3-6 to improve the reading of the drawings.

As shown in Figure 6, a metal manifold 66 is fitted on the metal shaft 55 and brings current to the first ring 8 through the aforementioned raisable/lowerable brush-holding assembly 100 (see below) .

Moreover, with particular reference to Figure 2, the electric motor 85 is fastened to the wall 502 by means of four bolts 85a.

As shown in Figures 3-6, the first electric axis 5 further comprises a fixed flange 67 provided with a peripheral notch 68 for reasons that will be explained further below. This fixed flange 67 is fastened by known and not shown means to the wall 502 and to the fixed protective sleeve 78 (Figure 6) .

In other words, like the fixed protective sleeve 78, the flange 67 is fixed with respect to the frame of the annealing furnace 1000, and is therefore not set in rotation by the electric motor 85.

As shown in more detail in Figures 7-9, the raisable/lowerable brush-holding assembly 100 comprises a fixed base plate 70 anchored to the wall 502 with known and not shown means. A shelf 71 projects from the fixed base 70. An actuator 72 provided with a stem 72a is fixed to said shelf 71.

The actuator 72 can be of the pneumatic type, as in the shown embodiment, or of the electric type, or of the hydraulic type.

The free end of the stem 72a is connected to a slide 73 by means of a joint 74. The slide 73 is slidably mounted on a guide 75 integral with the fixed base plate 70.

The slide 73, when actuated by the actuator 72 through its stem 72a, slides on the guide 75 from the top downwards, and vice versa, i.e. along a displacement direction indicated by F in Figures 3, 4 and 7.

A support pin 76 is fastened to the slide 73 and projects perpendicularly to the base plate 70 and to the slide 73.

In other words, while the stem 72a of the actuator 72 has a longitudinal symmetry axis Y, the support pin 76 has a longitudinal symmetry axis X2 perpendicular to the longitudinal symmetry axis Y.

The longitudinal symmetry axis X2 is also parallel to the aforementioned longitudinal symmetry axis XI of shaft 55 ( Figures 3 , 4 ) .

With particular reference to Figure 8, it should be noted that two brush-holding devices 80 are fitted side by side on the support pin 76.

It should also be noted that, as in the embodiment shown in Figures 3-5, the first electric axis 5 is provided with a further raisable/lowerable brush-holding assembly 100*, possibly identical to the already described brush-holding assembly 100, and symmetrically arranged on the opposite side (i.e. 180°) to this latter with respect to the longitudinal symmetry axis XI of the shaft 55.

In other words, the general shape of the brush-holding assembly 100* can be identical or similar or different from the one of the brush-holding assembly 100.

Obviously, the choice of the shape of the two brush-holding assemblies 100, 100* depends on various mechanical and electric factors, which will be considered each time by the technicians who will have to prepare the annealing furnace 1000 to carry out a specific treatment on electric wires having specific geometric and/or metallurgical characteristics .

Each brush-holding device 80 comprises a support 81 provided with a hole 82 in which the aforesaid support pin 76 is inserted. The support 81 is then fastened to the support pin 76 with known and not shown means.

Two brush-holding drawers 83, inclined at substantially 90° relative to each other, project from the support 81.

The initial inclination of each brush-holding drawer 83 with respect to the support 81 can be slightly adjusted before use by not shown adjustment means.

Each brush-holding drawer 83, in turn, provides a first compartment 84 (Figure 9) designed to receive a respective electric brush 89 provided with side pins 89a, which can slide in lateral notches 86 formed on two opposite walls of the first compartment 84. These side notches 86 act as limit elements of each electric brush 89 as it is consumed by sliding against the metal manifold 66 (Figure 6), and as it is pushed downwards by a respective spring 87.

It should also be noted that electric cables 89b electrically power each electric brush 89 (Figures 7 and 8) .

The respective spring 87 is used (Figure 9) to elastically compress downwards the electric brush 89, said spring comprising a first substantially V-shaped portion 87a from which a second curl-shaped portion 87b departs.

Obviously, any elastic system pushing downwards the electric brush 89 can be adopted instead of the spring 87. In use, the first portion 87a is housed in a second compartment 88 (Figure 9) and fastened to it with known and not shown systems, whereas the second portion 87b elastically presses on the upper surface of the relative electric brush 89.

As shown in Figure 8, the two compartments 84 and 88 are separated by a wall 88a.

Depending on the various types of annealing that the annealing furnace 1000 must carry out, each brush-holding assembly 100 and 100* mounts a number of brush-holding devices 80 that can be different from two. The brush holding devices 80 are easily mountable on and removable from the support pin 76.

The number of brush-holding devices 80 mounted on each brush-holding assembly 100, 100* depends on the maximum annealing current produced by the annealing furnace 1000 and by the maximum current density value in the electric brushes 89 set by the brush manufacturer. However, there is also a minimum current density value recommended by the brush manufacturer. When the annealing current is reduced, to prevent the current density from falling below the minimum value, the user raises one of the two brush-holding assemblies 100 and 100* by actuating the respective actuator 72.

Therefore, if required, the user can lower the brush holding assembly 100, thus actuating the actuator 72, namely it can bring the brush-holding assembly 100 from the raised configuration I of Figure 3 to the lowered configuration II of Figure 4, so that the support pin 76 is received by the peripheral notch 68 that, as already stated, is formed on the fixed flange 67. In other words, when the brush-holding assembly 100 is in the raised configuration I, the support pin 76 is in a corresponding raised position (Figure 3) in which the support pin 76 is outside the peripheral notch 68. On the other hand, when the brush-holding assembly 100 is in the lowered configuration II, the support pin 76 is in a corresponding lowered position (Figure 4), in which at least a portion of the support pin 76 is housed in the peripheral notch 68.

The fact that the support pin 76 is housed in the peripheral notch 68 of the brush-holding assembly 100 is of considerable importance if at least one electric brush 89 should melt, at least partially, due to the synergic effect of the friction between the electric brush 89 and the respective manifold 66 with the electric currents in the electric brush 89. In case of an at least partial melting of at least one electric brush 89, it would attach to the respective manifold 66 and if the support pin 76 were not received in the peripheral notch 68, the force exerted by the electric motor 75 on the shaft 55 would be discharged directly on the stem 72a of the actuator 72. In this case, the stem 72a could be even seriously damaged. On the other hand, if the support pin 76 is inserted in the peripheral notch 68 (lowered configuration II of Figure 4), the aforesaid force will be discharged on the fixed flange 67, and ultimately on the frame of the annealing furnace 1000, since, as already stated, the fixed flange 67 is integral with the frame.

Although the invention described above makes particular reference to a well-defined embodiment, it is not to be considered limited to this embodiment, since all variations, modifications or simplifications are within the scope of protection of the attached claims, such as for example :

- the use of more than two brush-holding devices 80 for each brush-holding assembly 100 and 100*;

- the use of more than two brush-holding assemblies, of the type indicated with the reference numbers 100 and 100*, angularly equidistant with respect to the longitudinal symmetry axis XI; and

- the possible use of brush-holding assemblies, of the type indicated with the reference numbers 100 and 100*, also on the second electric axis 6 and/or on the third electric axis 7.

Obviously, the annealing furnace 1000 described above is also suitable for the simultaneous annealing of more wires or more strands or more strings or more wire rods or more metal strips, after an appropriate axial sizing of the electric contact rings 8-10, of the return rollers 11 and

12 as well as of the output drawing ring 13 and of the related motor drives.

It should be further be noted that, although the description and the figures refer to a direct current annealing furnace, the present invention is applied, mutatis mutandis, to an alternating current annealing furnace .

The main advantages of the annealing furnace of the present invention are the following:

- when the first electric axis also acts as a drawing capstan or is connected to the drawing capstan by a mechanical transmission and the product wire is not subjected to the in-line heat treatment, the first brush holding assemblies 100 of this electric axis are brought into the raised configuration and therefore the electric brushes 89, not sliding on the relative metal manifold 66, do not wear out;

- when the annealing current is relatively low, a certain number of brush-holding assemblies are brought into the raised configuration to increase the current density in the electric brushes 89 in order to approach the minimum current density values recommended by the brush manufacturer; and - the lowering or raising of the brush-holding assemblies 100 and 100* can be automated during the setup of the annealing furnace 1000. In other words, the annealing furnace 1000 has a control system which, given the geometric characteristics of the annealing furnace 1000, the type and number of electric brushes 89 mounted and the production recipe (material, number, diameter of the wires, production speed and others), is able to calculate the annealing current typical for that production and therefore to define completely independently if it is necessary or not to raise or lower the brush-holding assemblies.