WO2018091248A1

WO2018091248A1 - Heating a continuously moving wire

Info

Publication number: WO2018091248A1
Application number: PCT/EP2017/077332
Authority: WO
Inventors: Cédric SAVIO
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2016-11-18
Filing date: 2017-10-25
Publication date: 2018-05-24
Also published as: FR3058914A1

Abstract

The invention relates to a method of executing a polymer deposition cycle including a process of heating a moving wire(50') having properties of an electrical conductor. The method includes a step of depositing a layer of a polymer solution on the surface of the wire(50'). The wire(50') is heated to raise the temperature of the wire(50') to a predetermined setpoint temperature. The temperature of the wire(50') is controlled at the predetermined setpoint temperature, to allow a solvent to evaporate before the polymerization of the polymer solution.

Description

HEATING A CONTINUOUSLY MOVING WIRE

TECHNICAL FIELD

The invention relates in a general way to a method of executing a polymer deposition cycle including a process of heating a moving wire having conductive properties.

CONTEXT

The coating of the surface of a wire with a material of a different kind to modify or improve some of its properties is known and widely used in industry. Depending on the nature and use of the wire, the coating may serve, for example, to improve corrosion resistance, to provide electrical insulation, to modify the tribo logical properties, to allow adhesion to another material, or simply for decoration. In some cases, the coating material is deposited in the liquid state and then undergoes a treatment or transformation intended to make it change to the solid state, for example a change in temperature, polymerization, evaporation of a solvent, or other process.

In the case of a treatment or transformation of the coating that requires a temperature increase, it is sometimes preferable to increase the temperature of the wire rather than the ambient temperature around the wire in order to increase the temperature of the coating deposited on the wire and thus cause polymerization. In this case, the problem to be resolved is that of transmitting the necessary energy to increase the temperature of a continuously moving wire that may, in some cases, be covered with a thin layer of material in a liquid state. For the invention described here, the term "wire" is applied to wires having properties of electrical conductors.

SUMMARY

The invention relates to a method of executing a polymer deposition cycle includin a process of heating a moving wire having properties of an electrical conductor. The method includes the following steps: depositing a layer of a polymer solution on the surface of the wire; heating the wire to raise the temperature of the wire to a predetermined setpoint temperature; and controlling the temperature of the wire at the predetermined setpoint temperature, to allow a solvent to evaporate before the polymerization of the polymer solution.

In some embodiments, the steps of heating the wire and controlling the temperature of the wire include the following steps: providing a heating circuit having an induction coil and a capacitor connected in parallel and forming a resonant circuit; supplying the heating circuit with a continuous supply voltage; measuring the current consumed by the power supply to the heating circuit;

calculating the power supplied by the heating circuit power supply; estimating the temperature of the wire; and establishing a control period in order to make the temperature of the wire dependent on the predetermined setpoint temperature. In some embodiments, this control period is established every 100 ms.

In some embodiments, the power corresponding to the measurement of the current consumed by the heating circuit power supply represents the electrical power consumed for heating the wire.

In some embodiments, the method also includes the step of varying a heating time which is calculated during the control period.

In some embodiments, the continuous supply voltage is split by transistors so as to form an alternating voltage at the terminals of the induction coil and the capacitor. The voltage applied to the induction coil is sinusoidal.

In some embodiments, the method also includes the step of driving the wire at a predetermined constant speed while passing the wire through the inside of the induction coil.

In some embodiments, the method also includes the step of performing a plasma surface treatment on the wire before the step of depositing a layer of the polymer solution on the surface of the wire.

In some embodiments, the method also includes the step of creating a partial vacuum during the step of heating the wire.

The invention also relates to a system for controlling the temperature of moving wires that executes a method as described. The system includes an impregnation installation that carries out a continuous process of uniform deposition of the polymer solution on the surface of the wire. The system also includes a heating installation that carries out a heating process including the heating of the wire and the control of its temperature.

In some embodiments, the system also includes an unwinding and adjustment installation that carries out processes of unwinding and adjusting the wire; a drive system that drives the wire at a given constant speed; and a rewinding and adjustment installation that carries out a process of rewinding and adjusting the tension of the wire.

In some embodiments, the system also includes a plasma treatment installation that carries out a plasma surface treatment on the wire.

The invention also relates to a wire formed by the system.

Other aspects of the present invention will become apparent from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

The nature and the various advantages of the present invention will be more readily understood from reading the following detailed description, together with the attached drawings, in which the same reference numerals denote identical parts throughout, and in which:

Figure 1 shows a schematic view of an embodiment of a system for heating a moving wire having properties of an electrical conductor.

Figure 2 shows an embodiment of an induction coil of the heating system of Figure 1.

Figure 3 shows an embodiment of a heating circuit that includes the induction coil of Figure 2 and a capacitor, and that is used to heat a wire and to measure its temperature.

Figure 4 shows a schematic view of an embodiment of a system having a series of installations that jointly define a polymer deposition cycle.

Figure 5 shows a perspective view and Figure 6 shows a side view of an example of integration of the induction coil of Figure 2 for heating a wire covered with a thin layer of a material in the liquid state.

DETAILED DESCRIPTION OF THE DRAWINGS

With reference now to the figures, in which the same numbers denote identical elements, Figure 1 shows an embodiment of a system 10 having a series of installations that can be used to heat a wire in continuous movement at constant speed (for example, in the direction of the arrow A of Figure 1) so that the wire has the desired properties at its exit from the installation. The wire could be moving in other systems that are not shown. The system 10 includes an unwinding and adjustment installation 100 that carries out processes of unwinding and adjusting a wire 50. The wire 50 includes a conductive material so that the wire is an element having properties of an electrical conductor. The wire 50 may be a metal wire having a small diameter (for example, a diameter of about 0.2 mm to 1 mm).

The wire 50 is supplied on a wire bobbin 110 at the installation 100. This wire may be round or of a simple shape (for example, square, oval, rectangular, etc.) to ensure that the heating is uniform. At the installation 100, a tension controller 120 controls a constant unwinding tension for the wire 50. The wire bobbin 110 and the tension controller 120 may be selected from various devices available on the market, and the unwinding and adjustment processes are known to those skilled in the art.

After leaving the unwinding and adjustment installation 100, the wire 50 is transported to a heating installation 400 that enables the temperature of the wire to be raised to an appropriate value for the desired properties of the wire upon leaving the installation. At the heating installation 400, the wire 50 travels at high speed, and is heated by induction heating.

With reference to Figures 2 and 3, the induction heating consists of an electronic control card supplying an induction coil 412 and a capacitor 411. The temperature of the wire 50 is increased by means of the induction coil 412 placed around the wire 50. The electrical conductivity and resistance of the material of the wire 50 depend on the temperature. The resistance of the material may be calculated from the electrical conductivity, given that resistance and conductivity are inversely proportional.

When the induction coil 412, through which the wire 50 to be heated passes, is supplied with an electric current, it creates a magnetic field. This magnetic field induces eddy currents in the metal wire 50. It is the Joule effect, due to the eddy currents, that is responsible for increasing the temperature of the object to be heated (that is to say the wire 50).

The electrical power consumed to heat an element that is a cylinder of material may be described thus:

P = π^■ d^■ h^■ H^{2 ■ ■} p^■ μ₀ ^■ μ_γ · f ^■ C^■ F where: d: Diameter of the cylinder [m]

h: Height of the cylinder [m]

H: Magnetic flux intensity [A/m]

p: Resistivity [Q.m] of the conductive material of the element

μο: Magnetic permeability of a vacuum (4π.10-7 H/m)

μτ: Relative permeability of the conductive material of the element

f: Frequency [Hz]

C: Coupling factor which decreases with the length of the inductance

F: Power transmission factor

It will be noted that the heating power depends on the resistance of the cross section of the element to be heated (that is to say the wire 50).

Figure 3 shows the electrical circuit diagram of the induction furnace represented by a heating circuit 402. The heating circuit 402 is supplied with a continuous supply voltage (Ubus). The continuous supply voltage is then split by transistors 408 so as to form an alternating voltage at the terminals of the coil 412 (that is to say an ideal inductor 404 and an inductor resistance 410) and the capacitor 411 (that is to say an ideal capacitor 406 and a capacitor resistance 407), and this voltage is measured by a voltage measurement (V) 414. Although the supply voltage of the heating circuit is continuous, that of the coil is alternating and has a frequency close to the resonance frequency.

The supply voltage of the induction furnace is controlled by the electronic card, and its amplitude is therefore known. The power supplied by the heating may therefore be ascertained by measuring the current flowing through the circuit, using a current sensor (see the current measurement (A) 413 in Figure 3) and multiplying this current by the amplitude of the supply voltage of the heating circuit. Setting a frequency close to the resonance frequency minimizes the power that is supplied.

This is because, primarily, the power supply of the induction furnace only has to compensate for the losses of the system. These losses are mainly eddy current losses in the element to be heated. Eddy current losses depend on the resistance of the wire to be heated, which increases with an increase in its temperature. When the temperature of the wire is increased, the losses, and consequently the power to be provided by the power supply, also increase. By measuring the power supplied by heating, we can therefore ascertain the temperature of the wire 50 by correspondence. By appropriate control, therefore, the temperature of the wire 50 can be regulated precisely, for example, to avoid degrading the mechanical properties of the wire.

The heating circuit 402 is constantly supplied with a continuous voltage

(Ubus). During a first heating phase, the coil (412) and the capacitor (411) are supplied, for a predetermined time, with a sinusoidal voltage obtained by splitting the continuous voltage by means of the transistors 408. This time is

predetermined by the heating controller, and depends, among other things, on the temperature error (between the setpoint and the measurement). During this phase, the current consumed by the heating circuit 402 is measured. Since the supply voltage (Ubus) of the heating circuit (412) is known, one can determine the power consumed by the heating circuit, from which the temperature of the wire 50 can thus be determined.

The power supply to the induction coil 412 and the capacitor 411 is then switched off. After this switch-off, the part of the heating circuit 402 that includes an inductance-capacitor circuit (412 and 411) continues to oscillate at the resonance frequency of the circuit. It is at this moment that the resonance frequency is measured by the voltage measurement 414, mainly for the purpose of process control.

Finally, when the temperature of the wire is known, a controller determines the heating time for a control period, in order to make the temperature of the wire 50 dependent on the setpoint temperature. In one embodiment, a control period is established every 100 ms. The value of the control period may be different;

additionally, in the case cited here, the heating time varies between 5 and 95 ms. In another embodiment, the control period is established every 250 ms, and the heating time varies between 5 and 245 ms. If a different control period is selected, the heating time will vary.

The temperature of the wire 50 is controlled by varying the heating time calculated by the controller during the control period (for example, the heating time calculated by the controller every 100 ms, every 250 ms, etc.). The wire 50 (or a portion of wire considered here) enters the coil 412 with a temperature equal to the ambient temperature. Each portion of wire considered here moves forwards into the coil 412, and each portion undergoes heating. At the exit 412b from the coil 412, the temperature of the wire 50 has reached the setpoint temperature.

The temperature is maintained over the whole length of the wire, or for the time required by the method. In all the control periods (every 100 ms, for example), the temperature controller calculates the heating time, which will be dependent on the temperature error. In some embodiments, the method passes through a plurality of control periods, with a different heating time and a decreasing temperature error on each occasion. Control takes place throughout, and the temperature is maintained throughout. A small amount of heating is provided if the temperature is close to the setpoint, and more heating is provided if the temperature is a long way from the setpoint.

The speed of travel must be constant to enable the temperature to be measured. The geometry of the wire 50 must also be constant; that is to say, the cross section of the wire must be constant along its length. The electrical resistivity and the magnetic permeability of the wire 50 must be stable for a given temperature.

With reference to Figure 1 again, a wire 50 is driven by a drive installation 500 that drives the wire 50 at a given constant speed. In some embodiments, the wire may move at a speed of about 5 m/min. In some embodiments, the deposition method enables deposition to take place at a speed of advance of the wire varying from several metres per minute up to 100 m/min. The drive installation 500 may be selected from a variety of devices available on the market.

The drive installation 500 transports the wire 50 from the heating installation 400 (where it passes through the induction coil 412 in the direction of the arrow A) to a rewinding and adjustment installation 600. The rewinding and adjustment installation 600 carries out a process of rewinding and adjusting the tension of the wire 50 which is fed to a receiving coil 610 of the installation 600. At the installation 600, a tension controller 620 controls a constant rewinding tension for the wire 50. The receiving coil 610 and the tension controller 620 may be selected from various devices available on the market. The rewinding and adjustment processes are known to those skilled in the art.

Since the deposition of a coating on the surface of elements such as the wire 50 is well known in the manufacture of various products, Figure 4 shows an embodiment of a system 10' having a series of installations for performing, in combination, a cycle of deposition of a polymer or of a polymer solution in a solvent. The system 10' includes an unwinding and adjustment installation 100, a heating installation 400, a drive installation 500 and a rewinding and adjustment installation 600 as described in relation to the system 10 of Figure 1. Each installation may be used for the execution of at least one process during the polymer deposition cycle for the production of elements with a thin layer of polymer, including elements having properties of electrical conductors.

A metal wire 50' is produced and guided in a continuous manner so that the resulting wire has the desired properties, these properties being variable and adaptable according to the product for which the wire is intended. The disclosed invention describes a continuous process, meaning that all the steps can be executed without interruption. Continuous methods eliminate the need for intermediate treatment steps during the process of forming the chosen coating on the selected wire. Continuous methods also make it possible to coat wires of greater length, instead of pieces of wire. When a system capable of continuously coating and producing very large lengths of wire is provided, it is possible to use wires in various industrial methods (such as incorporation into rubber for use in tyres). The overall method of coating deposition may be executed relatively more rapidly, with less variation in terms of thickness, uniformity and integrity of the coating.

The polymer deposition cycle includes the provision of a heating process, including the heating of the wire 50' and the control of its temperature, as described in relation to the system 10. The wire 50' must include a conductive material so that the wire is an element having properties of an electrical conductor, but it is to be understood that elements other than metal wires could be used.

The properties of the polymer are determined by the ingredients selected for a mixture of a polymer dissolved in a solvent (that is to say, a solution). The mixture of the polymer and solvent is adjusted to provide deposition conditions that enable a complete coating to be formed on the wire (to provide a desired degree of viscosity, for example). The wire 50' may have a polymer coating deposited from an aqueous, alcohol-based or organic solution which can be cross- linked with an elastomeric material to be reinforced (rubber, for example).

With reference to Figure 4 again, a wire 50' obtained from the unwinding and adjustment installation 100 is transported to a plasma treatment installation 200. The plasma treatment installation 200 is an optional installation for a polymer deposition cycle which carries out a surface treatment on the wire 50'. During this process, the plasma treatment modifies the surface properties of the wire 50' to improve the adhesion between the wire and the polymer. The installation may use any known plasma solutions, including solutions using air, flame and chemical products. Plasma treatments are known to those skilled in the art.

With reference to Figure 4 again and also to Figures 5 to 6, the wire 50' obtained from the plasma treatment installation 200 is transported to an impregnation installation 300 for the execution of a continuous process of uniform deposition of the polymer solution in liquid form on the surface of the wire 50'. The impregnation installation 300 is an installation for a polymer deposition cycle for the uniform deposition of a thin layer (about 10 μιη) of polymer solution on a metal wire having a small diameter (for example, a diameter of about 0.2 mm to 1 mm).

A uniform coating thickness is produced on the wire 50' by the combined effects of the surface tension and the viscosity of the polymer solution on the one hand, and the surface energy of the wire on the other hand. The thickness of the polymer layer measured on the wire 50', at the end of the polymer solution deposition process, depends mainly on the viscosity of the polymer solution and the speed of travel of the wire 50'. It is preferable for the thickness to be very small (about 10 μηι for example), but the thickness of the solution depends on the rubber formulation chosen for the tyre and the architecture of the tyre.

With reference to Figure 4 and Figures 5 to 6, a wire 50' obtained from the impregnation installation 300 is transported to the heating installation 400 for the execution of a heating process, including the heating of the wire 50' and the control of its temperature. At the heating installation 400, the solvent is evaporated by the combined action of an increase in the temperature of the wire 50' and a reduction of pressure in the space surrounding the wire. To evaporate the solvent from a wire 50' having a small diameter (about 0.2 to 1 mm, for example) that is travelling at high speed (at least 5 m/min, for example), the wire is heated by means of induction heating, as described in relation to the system 10. The heating installation 400 raises the temperature of the metal wire and therefore enables a sufficient temperature to be reached in order to evaporate a solvent and increase the viscosity of the polymer solution before it is polymerized.

This heating means enables the temperature of the wire 50 to be increased without any physical contact with it, which is important, particularly when the wire is, for example, covered with a material in the liquid state. This is why the induction heating principle was chosen.

With reference to Figure 4, in an example of the operation of the heating, the wire 50' is a 0.35 mm diameter steel wire, coated with a liquid solution containing a solvent and a polymer. In this example, the wire 50' has been coated with a layer of liquid polymer solution in an apparatus 300, and moves inside a glass tube 418 in which a partial vacuum has been created. The wire is heated to vaporize the solvent contained in the solution, so that only the polymer remains on the surface of the wire at the end of the process. The heating cycle is timed over a period of 100 ms. Within this period, heating may take place for 5% to 95% of the time. As the heating time increases, the energy injected into the wire also increases.

As soon as it leaves the induction coil 412, a given length of the wire 50' starts to cool, by radiation and by convection with the ambient atmosphere. The total length L412 of the induction coil is therefore proportional to the time required for the full evaporation of the solvent from the polymer layer deposited on the surface of the wire 50', and to its speed of advance. The speed of travel must be constant to enable the temperature to be measured. The geometry of the wire 50' must be constant; that is to say, the diameter of the wire 50' must be constant for a round section, or the geometry of the section must be identical for other shapes. The electrical resistivity and the magnetic permeability of the wire 50' must be stable for a given temperature.

The measurement of the temperature of the wire 50' is not affected by the coating, since this coating is neither electrically nor magnetically conductive.

The measurement of the resonance frequency, combined with the measurement of the resistance of the heat part, may provide information on the presence of the part to be heated, or of degradation of the resonant circuit. Overheating the capacitor causes the value of capacitance to vary. This variation is manifested in a variation of the resonance frequency; this variation may be detected to prevent a breakdown of the heating circuit.

One or more sensors and/or types of sensors may be used if necessary, including, but not limited to, environmental sensors (for detecting atmospheric conditions such as the temperature, pressure and/or humidity during the execution of the method, for example) and verification sensors (for detecting a deviation from a specified formulation, for example). Thus the invention makes it possible to treat a wide variety of wires according to the product to be manufactured.

At least some of the various techniques may be used in association with hardware or software, or with a combination of these where justified. As used here, the term "method" or "procedure" may cover one or more steps executed at least by an apparatus that is electronic or based on a computer having a processor with the function of carrying out instructions that execute the steps.

The terms "at least one" and "one or more" are used interchangeably. The ranges described as being located "between a and b" incorporate the values of "a" and "b".

Although particular embodiments of the disclosed apparatus have been illustrated and described, it is to be understood that various changes, additions and modifications may be made without departure from the spirit or scope of the present description. It follows that no limitation is to be placed on the scope of the invention described, except for those stated in the attached claims.

Claims

1. A method of executing a polymer deposition cycle comprising a process of heating a moving wire (50') having properties of an electrical conductor, wherein the method comprises the following steps:

depositing a layer of a polymer solution on the surface of the wire (50'); heating the wire (50') to raise the temperature of the wire (50') to a predetermined setpoint temperature; and

controlling the temperature of the wire (50') at the predetermined setpoint temperature, to allow a solvent to evaporate before the polymerization of the polymer solution.

2. A method according to claim 1, wherein the steps of heating the wire (50') and controlling the temperature of the wire (50') comprise the following steps: providing a heating circuit (402) comprising an induction coil (412) and a capacitor (411), connected in parallel and forming a resonant circuit;

supplying the heating circuit (402) with a continuous supply voltage

(Ubus);

measuring the current consumed by the power supply of the heating circuit (402);

calculating the power supplied by the power supply of the heating circuit

(402);

estimating the temperature of the wire (50'); and

establishing a control period in order to make the temperature of the wire (50) dependent on the predetermined setpoint temperature.

3. A method according to claim 2, wherein the control period is established every 100 ms. 4. A method according to claim 2 or claim 3, wherein the power

corresponding to the measurement of the current consumed by the power supply of the heating circuit (402) represents the electrical power consumed for heating the wire.

5. A method according to any of claims 2 to 4, further comprising the step of varying a heating time that is calculated during the control period.

6. A method according to any of claims 2 to 5, wherein the continuous supply voltage (Ubus) is split by transistors (408) so as to form an alternating voltage at the terminals of the induction coil (412) and the capacitor (411), and the voltage applied to the induction coil (412) is sinusoidal.

7. A method according to any of claims 2 to 6, further comprising the step of driving the wire at a predetermined constant speed while passing the wire through the inside of the induction coil (412).

8. A method according to any of claims 1 to 7, further comprising the step of performing a plasma surface treatment on the wire (50') before the step of depositing a layer of the polymer solution on the surface of the wire (50').

9. A method according to any of claims 1 to 8, further comprising the step of creating a partial vacuum during the step of heating the wire (50'). 10. A system (10') for controlling the temperature of moving wires which executes a method according to any of claims 1 to 9, wherein the system comprises:

an impregnation installation (300) that carries out a continuous process of uniform deposition of the polymer solution on the surface of the wire (50'); and a heating installation (400) that carries out a heating process comprising the heating of the wire (50') and the control of its temperature.

11. A system (10') according to claim 10, further comprising:

an unwinding and adjustment installation (100) that carries out processes of unwinding and adjusting the wire (50');

a drive system (500) that drives the wire (50') at a given constant speed; and

a rewinding and adjustment installation (600) that carries out a process of rewinding and adjusting the tension of the wire (50').

12. A system (10') according to claim 10 or claim 11, further comprising a plasma treatment installation (200) that carries out a plasma surface treatment on the wire (50').

A wire (50') formed by a system according to any of claims 10 to 12.