EP0098658A1 - Method for the production of metallic wire, wire obtained by this method and device for carrying out this method - Google Patents

Abstract

The wire-cross-section is first reduced down to an intermediate cross-section by subjecting the wire to a cold-rolling in a rolling-section with a plurality of stands which is part of a manufacturing unit. The cross-section is continuously further reduced down to the required cross-section in a wire-drawing section forming also part of the manufacturing unit. The first step in the reducing in the wire-drawing section is performed in a roller die, the other steps being performed in normal dies. The lubricating oil circuit for the roller die is completely isolated from the lubricating oil circuit for the other dies. After wire-drawing the wire is coiled on a coiling-machine.

Description

The present invention relates to a method for manufacturing metallic wire of reduced cross-section from wire of larger cross-section, according to which the cross-section of the wire is reduced by cold rolling in several steps.

In such a known method, the section reduction is carried out exclusively by rolling.

This method has certain advantages over another known method of reducing the cross-section of a wire, a method according to which the reduction of cross-section is carried out exclusively by drawing in several steps.

First of all, the introduction of a new wire into a rolling unit is very simple. Just introduce the wire in the first cage and it will be automatically introduced in the following cages. The unit can therefore be started quickly.

The introduction or reintroduction of a wire in a drawing unit is however more difficult. The multi-step drawing unit used must have a relatively large number of dies and, since the introduction of the drawing wire into the dies is very time consuming, this results in a considerable loss of time each time a new wire to be drawn must be introduced into the drawing unit or if the wire breaks. This is particularly the case for wires made of an aluminum alloy with a fairly large diameter, these wires being fairly rigid.

Second, the risk of wire breakage during rolling is much lower than when drawing.

With wire drawing, the risk of wire breakage is quite high, especially since the number of successive reductions is quite high and the degree of overall reduction is quite significant. The wire can be easily overloaded, especially when it is made of aluminum alloy.

Indeed, during the reduction in a wire drawing pitch, too high axial tensile tensions can be created in the wire and structural damage can arise in this wire. However, it is impossible to avoid the creation of axial tensile tensions in the wire, given the friction, the angle of the die and the return tension of the wire. These axial tensions give rise to hollows at the place of small imperfections of the wire material. These hollows grow in successive steps and can take on such dimensions that the effective cross-section of the wire is greatly reduced. The wire can then be easily overloaded and break in these places.

In addition, the surface area of the wire is subjected to sliding stresses, which can cause surface damage, especially in combination with imperfections in the material and / or friction and / or eccentricity of the wire in the die.

Rolling causes much less sliding stress on the surface of the wire and the risk of damage to the surface of the wire is much lower than during drawing.

Third, rolling creates a much lower temperature rise than wire drawing.

The energy used to draw is broken down 45% homogeneous deformation energy, 10% excessive deformation energy and 45% friction energy. The homogeneous deformation energy is transformed for 90% into heat and the friction energy is completely transformed into heat. As a result, each step of the drawing causes an increase in the temperature of the wire. As between the various steps, the cooling of the wire is limited, the temperature of the wire increases step by step, this increase being all the greater the higher the speed of the wire. This is particularly the case when a sliding wire drawing unit is / is used. Too much warming would result in a rupture of the layer surrounding ^it lubrifian wire which could cause surface faults.

In rolling, on the other hand, the friction energy is much less important; generally not more than 15% of the deformation energy. As a result, the warming at each rolling step is much less. In addition, the heat generated can easily dissipate in the cylinders, so that cooling is more important. As a result, there is practically no heat accumulation in the wire during the different rolling steps.

As the technical characteristics / of the wire obtained, such as the breaking load, the elongation and the resistivity, depend on the temperature of the wire, the cumulative heating during a wire drawing limits the speed of the wire for a unit of wire drawing and for specific technical characteristics of the wire.

The technical characteristics of the wire indeed depend on the cellular structure which develops during the treatment. The finer this structure, the higher the breaking load and the resistivity and the elongation is reduced. A higher temperature causes a restoration of the cell structure. By cooling between two channels, we control this restoration.

The absence of such accumulated heating during rolling has the advantage that the technical characteristics of the wire are independent of the speed of the wire and that higher speeds of the wire can be used.

This independence of the technical characteristics of the speed is however at the same time a drawback since during a rolling it is not possible to control or modify the technical characteristics for a given reduction in section using the speed some thread.

Besides this, rolling has other disadvantages compared to drawing.

Indeed, the surface of the wire obtained by rolling is of a significantly worse quality than that of a wire obtained by drawing.

In addition, it is not possible to obtain by rolling the dimensions and a shape as precise as the final section of the wire as by drawing.

Replacing the rolls in the rolling stands is very time consuming.

The object of the invention is to remedy these drawbacks and to provide a method of manufacturing metal wire which makes it possible to obtain a wire of good quality and with the desired technical characteristics with increased productivity compared to known methods.

For this purpose, the section of the wire is first reduced to an intermediate section by subjecting it to this cold rolling in a rolling part with several stands, forming part of a production unit comprising also a multi-pitched drawing part, and then continues continuously, in the drawing part of this production unit, the section reduction by drawing to the desired section.

The combination of cold rolling and wire drawing not only makes it possible to obtain the advantages of these two processes without their disadvantages but also makes it possible to increase the productivity of wire having the desired technical characteristics.

In a particular embodiment of the invention, the wire is subjected to cold rolling in a rolling part with several cages with reduction of fixed section.

In an advantageous embodiment of the invention, the section is reduced by drawing in a drawing part with constant elongation in steps.

In one preferred embodiment, the wire is wound up after the drawing by means of a winder.

In a particularly effective embodiment of the invention, an aluminum alloy wire is used as the metal wire.

Preferably, an aluminum alloy wire comprising magnesium and silicon is used.

The invention also relates to the yarn obtained by the process mentioned above as well as a production unit obviously intended to apply this process. Such a unit is characterized by the fact that it comprises a cold rolling part and a drawing part.

• La figure 1 est une représentation schématique d'une unité de production utilisée pour réaliser le procédé de fabrication de fil métallique selon l'invention.
• La figure 2 est une représentation graphique de la charge de rupture d'un fil en fonction de sa vitesse de sortie de l'unité de production, lorsque ce fil est obtenu respectivement par le procédé selon l'invention, exclusivement par laminage et exclusivement par tréfilage.
• La figure 3 est une représentation graphique analogue à celle de la figure 2 mais représentant l'allongement du fil obtenu en fonction de sa vitesse de sortie.
• La figure 4 est une représentation graphique analogue à celle des figures 2 et 3 mais représentant la résistivité du fil obtenu en fonction de sa vitesse de sortie.

Other particularities and advantages of the invention will emerge from the description of a process for manufacturing metal wire, a metal wire as well obtained and a production unit used to apply this process, according to the invention; this description is given below only by way of nonlimiting example and with reference to the accompanying drawings.

• Figure 1 is a schematic representation of a production unit used to carry out the method of manufacturing metal wire according to the invention.
• FIG. 2 is a graphic representation of the breaking load of a wire as a function of its output speed from the production unit, when this wire is obtained respectively by the process according to the invention, exclusively by rolling and exclusively by wire drawing.
• Figure 3 is a graphical representation similar to that of Figure 2 but showing the elongation of the wire obtained as a function of its output speed.
• Figure 4 is a graphical representation similar to that of Figures 2 and 3 but showing the resistivity of the wire obtained as a function of its output speed.

A wire 1 of aluminum or an aluminum alloy, manufactured in a known manner in a hot rolling mill, is continuously stretched to the desired diameter in two main steps in the same production unit.

In a first main step, the wire 1 is extended to an intermediate diameter in a cold rolling part, generally designated by the reference numeral 2 in FIG. 1.

This rolling part is a rolling unit of the type with several stands 3, with constant reduction or fixed by stand.

Such rolling units are known per se and are therefore not described in detail below. Such a unit which is particularly suitable is described in the article "Microrolling: cold rolling wires of unusual diameters" by G. Properzi in "Wire journal" of December 1979 and such a unit is marketed by the company Continuus SPA of Milan and designated as "Micro Rolling Mill".

The number of cages 3 of the laminating unit 2 depends on the diameter of the wire 1 supplying the unit and on the diameter of the wire 1 leaving the unit.

The rolling unit can moreover easily be adapted to other standard diameters of the wire 1 by removing or adding one or more pairs of cages 3 at the inlet end of the unit 2. When another diameter wire 1 coming out of the unit is desired, just remove or add one or more cages 3 to the outlet end of unit 2.

The standard wire diameters from hot rolling are 15, 12 and 9.5 mm. The rolling unit 2 is preferably constructed in such a way that, to go from a diameter of 15 mm to a diameter of 12 mm of the wire 1 or to go from a diameter of 12 mm to a diameter of 9.5 mm of the wire, it suffices to remove each time two cages 3 at the entry end of the rolling unit 2.

This rolling unit 2 can for example be made up of eight cages, the reduction in cross section of the wire being 20% per cage in the first four cages and 30% per cage in the other cages. With the diameters of the above-mentioned wire 1, and with eight, six and four cages 3 respectively, the diameter of the laminated wire is 4.75 mm. By removing the last and penultimate cages 3, a wire 1 with a diameter of 6.75 mm is obtained.

The cylinders of the various cages 3 are preferably driven by a mechanical chain using a single DC motor.

In certain cases, the section of the wire 1 can also be modified in shape during a rolling operation in a stand 3, but preferably the wire 1 leaving the part 2 has a round section.

In a second step, the cross section of the wire 1 leaving the cold rolling part 2 is reduced to the desired final diameter in a drawing part generally designated by the reference numeral 4 in FIG. 1.

A possibility of accumulation of the wire 1 is provided between the rolling part 2 and the drawing part 4 in the case where the speed of exit of the wire 1 from the rolling part 2 is greater than the speed of feeding of the wire to the drawing part 4. A production unit is used for this purpose comprising between the rolling part 2 and the drawing part 4 an accumulator 5. This accumulator is of known construction and is therefore not described in detail below.

The drawing part 4 is a unit of the sliding type and with different steps with a constant elongation at each step. This extension depends solely on the construction and in particular on the sector.

The drawing part 4 is preferably driven using a DC motor.

In a known manner, the drawing unit comprises a number of successive dies 6 or 7 each followed by a capstan 8. The first die 6 located at the entrance to the unit is not like the other dies 7 a normal die but a roller die also called "Roller-die".

The drawing part 4 can therefore be formed by a known drawing unit with normal dies, of which the first die is replaced by a roller die, also known per se. Neither this roller die nor this drawing unit will therefore be described in detail below.

The following units placed on the market are particularly suitable for applying the method according to the invention after the first normal die 7 has been replaced by a roller die 6: the drawing unit type H 750 from the company Machinenabrik Herborn, the unit of type 8-DXT-550 from Hi-Draw Machinery Limited, and the machine of type KDA from Bekaert.

The use of a roller die 6 for the first wire drawing instead of a normal die has the reason that in the rolling part 2 the wire is lubricated with an aqueous suspension as is normally the case in the rolling units, while in the drawing part 4, the wire 1 is lubricated and cooled with oil as will be described below. However, this oil is incompatible with the water in the suspension. The combination of rolling and wire drawing therefore poses the problem of eliminating all traces of suspension of the wire 1 between the rolling part 2 and the wire drawing part 4 or at least the normal dies 7 of this part of wire drawing 4.

Most of the suspension of the wire 1 is removed using a jet of compressed air which is directed onto the wire 1 by a head 9 mounted between the rolling part 2 and the pneumator 5.

After passing the head 9, the wire 1 may still have traces of suspension. These traces are removed by the oil with which the roller die 6 is lubricated. This oil is circulated in a closed circuit. We pump this oil from a tank 10 through line 11. This oil returns to the reservoir 10 through the return line 12. This closed circuit is completely independent of the oil used to lubricate the other dies 7. The slightest trace of water in this latter oil could effect disturbing the drawing by the dies 7. A roller die is on the other hand less sensitive to traces of water in the lubricating oil and it is for this reason that the first die 6 must preferably be a roller die.

Both the dies 7 and the capstans 8 are lubricated and cooled by oil which is pumped from a reservoir 13. This oil is supplied by lines supplied 14 to the dies 7 and by lines 15 on the capstans 8. Each pipe 15 is provided with a valve 16 which can be controlled remotely. All the oil is collected on the bottom of the wire drawing unit and returned to the reservoir 13 via the return line 17.

The oil returning to the reservoir 13 has been reheated. The oil in the reservoir 13 is continuously cooled by returning it in a closed circuit through a heat exchanger 18.

You can adjust the amount of oil that sprinkles each capstan 8, and therefore the cooling of the wire 1 at each step, using the valve 16 in the corresponding line 15. It is thus possible to act on the overall heating of the wire 1 in the drawing part 4.

It is obviously and also above all possible to act on the heating by acting on the speed of the wire 1 since the heating of the wire in the drawing part 4 is proportional to the speed of the wire 1.

The use of a DC motor to drive both the rolling part 2 and the rolling part drawing 4 makes it possible to easily and precisely control the speed ratio of the wire in these two units. It is thus easy to adapt the reduction in the section of the wire 1 during the first step in the drawing part 4 to the desired final diameter of the wire.

After the drawing, the wire 1 is wound using a winder 19, with automatic reel change. This winder 19 is also driven using a DC motor. Such winders are known per se and are therefore not described in detail below.

Between the drawing part 4 and the winding machine 19 there is provided an accumulator 20 with the help of which a possible difference is compensated for between the speed of exit of the wire 1 from the drawing part 4 and the speed of winding of the wire 1 by the winder 19.

The rolling part 2, the accumulator 5, the drawing part 4, the accumulator 20 and the winder 19 are mounted in line in the production unit.

The process described above is particularly suitable for aluminum or aluminum alloy wires. Among others, the following wires, indicated according to the specification of the Aluminum Association, are particularly suitable for the application of the method according to the invention: 1.100, 1.199, 1.350, 1.370, 2.011, 2.017, 2.024, 2.117, 4.043, 5.005, 5.052 , 5.056, 5.356, 6.053, 6.061, 6.110, 6.201 and 6.262.

The process described above has significant advantages over a process consisting only of cold rolling or wire drawing.

The process described above requires fewer dies than when the reduction in the cross-section of the wire is obtained exclusively by drawing. This has the consequence that the introduction of a new wire into the device for carrying out the process can be carried out in a fairly quickly and without too much difficulty.

The reduction in cross-section of the wire by drawing is also less. The result is a reduction in wire overload, both on the surface and inside. There is therefore less risk of wire breakage and less risk of surface / wire faults. There is less increase in wire temperature during the process so that the wire drawing speeds can be higher. The rise in temperature during cold rolling is much less than during drawing. In addition, the wire can be cooled, if necessary, between the rolling unit 2 and the drawing unit 4.

Compared to a process comprising only cold rolling, the process described above has the advantage of better quality of the wire obtained. The surface of the wire is much more perfect and one can obtain a wire of very precise dimensions and shape.

The combination of a cold rolling step and a drawing step further results in increased flexibility of use, and above all a higher productivity of wire having the desired technical characteristics. One can indeed easily act on the temperature of the wire as is the case in the methods comprising exclusively a drawing, but the speeds of the wire can be higher than with the known methods mentioned.

It has been found that these additional advantages are especially important when using a wire of an aluminum alloy comprising magnesium and silicon, in particular such an alloy used to manufacture electrical conductors. These advantages are important when, for example, a wire from one of the alloys is used. following, indicated according to the specification of the Aluminum Association: 6.053, 6.061, 6.110, 6.201 and 6.262. The method according to the invention and more particularly advantageous for the wire 6.201 as shown in the comparative example given below.

Example:

A wire rod, with a diameter of 9.5 mm, made of aluminum-magnesium-silicon alloy no. 6.201 according to the specification of the Aluminum Association, has been reduced to 3.15 mm. In diameter. The chemical composition of the alloy has been determined:

The other elements are normal impurities in Al-Mg-Si alloys used for the manufacture of electrical conductors.

The wire rod was produced by continuous casting and rolling of the Properzi type (Properzi rolling mill no. 7 of Continuus SPA), according to the process described in Luxembourg patent no. 80,656.

The wire was reduced in section by three different methods. In each case, the temperature of the wire on the spool of the winder at the output end of the production unit, and the breaking load, ^the elongation and the resistivity of the wire obtained were measured for different speeds of the wire. .

1. By a known process comprising exclusively a wire drawing:

the wire drawing was carried out in a Niehoff M 85 unit with a set of dies giving an elongation of approximately 32.5% except in the last pass, where the elongation was approximately 27%.

2. By a known process comprising exclusively rolling.

The rolling was carried out on a reduction machine of constant section.

3. By the process according to the invention.

In a first step, the wire rod was reduced in section from 9.5 mm to 4.75 mm in four steps in a unit of the Micro-Rolling Mill type from the company Continuus SPA of Milan. In a second step, the wire was reduced to the final diameter in a drawing unit with constant elongation per die, but the first die of which was replaced by a roller die. The wire drawing was carried out in four passes with constant elongation, that is to say an elongation of 27.5%. The following dimensions were used: 4.50 mm, 4.01 mm, 3.56 mm and 3.15 mm.

In order to allow an easy comparison of the mechanical and electrical characteristics of the wire obtained according to these three processes, the results obtained have been plotted in Figures 2, 3 and 4. In these figures, the breaking load, the elongation and the resistivity have been shown as a function of speed for the three processes. In each of the figures, curve 1 corresponds to the known method comprising exclusively a drawing, curve 2 corresponds to the method comprising exclusively a rolling and curve 3 corresponds to the method according to the invention.

It emerges from the results that the method according to the invention makes it easy to optimize the breaking load-resistivity couple.

It should be understood that the invention is in no way limited to the embodiment described above and that many modifications can be made thereto without departing from the scope of the present invention.

In particular, the method is not limited to wires made of an aluminum alloy.

Both rolling and drawing do not necessarily have to be carried out in parts with constant reduction in section at each step. The section reduction can vary with each step or part of the steps.

The wire drawing part does not necessarily have to consist of a roller die and normal dies. This part can comprise none or more than one roller die or even consist solely of such roller die.

The drawing part does not necessarily have to be constituted by a sliding drawing unit. Each coil can for example be driven separately by a motor without significant slip.

Claims (16)

1. Method for manufacturing metallic wire (1) of reduced section from wire (1) of larger section, according to which the section of the wire (1) is reduced by cold rolling in several steps, characterized in that first reducing the section of the wire (1) to an intermediate section by subjecting it to this cold rolling in a rolling part (2) to several cages (3) forming part of a production unit (2 , 4,5,19,20) also comprising a drawing part (4) with several steps and which is then continued continuously, in the drawing part (4) of this production unit (2,4,5, 19,20), reducing the section by drawing to the desired section. 2. Method according to the preceding claim, characterized in that the wire (1) is subjected to cold rolling in a rolling part (2) to several cages (3) with reduction of fixed section. 3. Method according to any one of the preceding claims, characterized in that the section is reduced by drawing in a drawing part (4) with constant elongation in steps. 4. Method according to the preceding claim, characterized in that the section is reduced by drawing in a sliding drawing unit (4). 5. Method according to any one of the preceding claims, characterized in that the wire is wound (1) after the drawing by means of a winder (19). 6. Method according to any one of the preceding claims, characterized in that an aqueous suspension is used as a lubricant in the rolling part (2), and that remnants of suspension of the wire (1) are removed using a compressed air jet between the rolling part (2) and the drawing part (4). 7. Method according to any one of the preceding claims, characterized in that the first step of the reduction by drawing is carried out using a roller die (6), called "roller-die". 8. Method according to the preceding claim, characterized in that the wire is lubricated during the first step of reduction by drawing with oil which is circulated in a circuit (10 to 12) completely independent of the circuits of oil (13 to 18) which is used to lubricate the wire (1) in the other wire drawing steps. 9. Method according to any one of the preceding claims, characterized in that the wire (1) is cooled in the drawing part (4) in a controllable manner. 10. Method according to any one of the preceding claims, characterized in that aluminum wire is used as the metal wire (1). 11. Method according to any one of claims 1 to 9, characterized in that a metal alloy wire is used as the metallic wire (1). 12. Method according to the preceding claim, characterized in that a wire of an aluminum alloy comprising magnesium and silicon is used. 13. Method according to the preceding claim, characterized in that a wire (1) of the alloy 6.201 according to the specification of the Aluminum Association is used. 14. Metal wire (1) obtained by the process according to either of the preceding claims. 15. Production unit (2,4,5,19,20) for applying the method according to either of claims 1 to 13, characterized in that it comprises a cold rolling part (2) and a drawing part (4). 16. Production unit according to the preceding claim, characterized in that the first die (6) of the drawing part (4) is a roller die, the lubricating oil circuit (10 to 12) for this die (6) being completely separate from the lubricating oil circuits (13 to 18) for the other dies (7) and the capstans (8).

Images