RU2324023C2 - Device for continuous high-temperature processing of carbon yarn - Google Patents

Abstract

FIELD: chemistry; production of high-modulus carbon fibers.

SUBSTANCE: device comprises heating element, which is superhigh frequency field source, and tube to run carbon yarn through it. Heating element comprises superhigh frequency cell, which consists of waveguide-to-coaxial adapters with common coaxial leg. On waveguide-to-coaxial adapters, rectangular waveguides are installed. They are located in parallel planes and rolled out equiangularly to each other. Cross-field generators installed at opposite ends of each waveguide are used as superhigh frequency field source. Phase-shifting devices provide for periodic operation of each pair of generators. Between superhigh frequency cell and cross-field generator, a decoupler (isolator or circulator) may be installed. Cross-field generators may be optionally provided with heat coils.

EFFECT: increase of carbon yarn processing temperature.

3 cl, 2 dwg

Description

The invention relates to the production of high modulus fibers and is intended for high temperature processing of carbon fiber materials.

A known installation for high-temperature processing of fibrous materials [USSR author's certificate N 506145, IPC Н05В 3/00, published 05.03.1976], containing a water-cooled housing with a non-oxidizing medium, current leads made in the form of rotary cams and a conveying device in the form of a pulling mechanism.

The disadvantages of this device are the large energy consumption per unit of output, burnout of graphite cams, a change in processing temperature during the process itself, associated with a change in cam resistance and voltage drops in the network, which leads to heterogeneous characteristics of the processed bundle.

A camera device is known for heat treatment of moving threads (tows) [USSR author's certificate N 199322, IPC D01d, class. 29a, 6/06, publ. 07/13/1967], comprising a cooled case with a metal tube inside it that is included in the electric circuit for passing the thread and thermal insulation, devices for supplying and removing inert gas, supply and reception rolls.

The disadvantage of this furnace, as in the previous case, is the high energy consumption and rapid burnout of the main node of the furnace during processing - a tubular heater. An increase in the volume of products in this furnace is possible only by increasing the size of the furnace itself, which leads to an increase in the shortcomings described above.

Closest to the proposed is a device for high-temperature processing of fibrous materials [GB patent No. 2053629, Cl. D02J 13/00, 1981], comprising a heating element in the form of a microwave field source and a tube for passing a carbon tow.

The disadvantage of the prototype device is the low limit temperature of the processing of the bundle, equal to the melting temperature of the quartz tube (about 1300 ° C). Another disadvantage of the device is the use of a resonant method for supplying an electromagnetic field of an ultrahigh frequency to a carbon tow. With intense absorption of energy by a bundle, the quality factor of the resonator decreases, which makes the indicated method of supplying microwave energy ineffective. Given the final coupling coefficient of the microwave generator with the resonator, we will have a low efficiency of the specified device. The absence in the device of the “grounding” elements of the driving harness leads to a large loss of microwave energy through the harness due to intense radiation outside the resonator.

The objective is to create a device that provides an increase in the temperature of processing a carbon tow to 2500-3000 ° C with high efficiency and with a design that allows the use of inexpensive household microwave generators (magnetrons).

The problem is achieved due to the fact that in the device for continuous high-temperature processing of carbon tows containing a heating element in the form of a microwave field source and a tube for passing a carbon bundle, the heating element includes a microwave cell made in the form of waveguide-coaxial transitions with a common coaxial arm on which rectangular waveguides are installed, located in parallel planes, and are deployed relative to each other at equal angles, p In this case, microwave sources are used as a microwave field source, installed at the opposite ends of each waveguide and equipped with phase-shifting devices that ensure periodic operation of each pair of generators.

In addition, a decoupling device in the form of an insulator or circulator can be installed in the device between the microwave cell and the microwave generator, and the microwave generators can be additionally equipped with thermal fuses.

The invention is illustrated by drawings: figure 1 shows a section aa of the device for continuous processing of harnesses, figure 2 is a top view.

The device comprises a tube 1 for passing carbon tows, which is made of beryllium oxide and is installed along the general axis of symmetry of the microwave cell, made in the form of three waveguide-coaxial transitions 2, on which six rectangular waveguides 3 are installed, designed to work with wave H ₁₀ , located in parallel planes and deployed relative to each other at angles of 120 °. On the opposite sides of each of the waveguides 3, by means of flanges 4, magnetron generators 5 are connected with a waveguide output, operating in a pulsed mode with a duty cycle of two and alternating operating intervals. For this purpose, industrial magnetron generators are used, which are installed in microwave ovens, with additional phase-shifting devices (not shown in FIG.) In the power supply circuit of magnetron generators 5, which ensure their alternating operation. As a result, to the heated bundle 6 located in the central part of the tube 1, the microwave field energy will be supplied “quasi-continuously”: in the first half of the working cycle from the left magnetron, in the second - from the right magnetron. A peculiar mode of adding the output powers of two incoherent microwave generators to a common load is implemented, the functions of which are performed by a carbon tow 6, which is the central conductor of the above-mentioned symmetric waveguide-coaxial transition.

The beryllium tube 1 has a device for supplying 7 and discharging 8 of inert gas (for example, argon) and a water cooling system 9, the supply of tow 6 is carried out using rollers 10.

The device operates as follows.

The processed bundle 6 is fed into the microwave cell 2 (stretched through a tube 1 of beryllium oxide) by feed rollers 10, which also perform the role of grounding. Power is supplied to the magnetrons 5 and they begin to alternately generate a microwave field propagating in the form of waves along the waveguide to the load, the functions of which are the above-mentioned symmetric waveguide-coaxial transition 2 with a carbon bundle 6 in its coaxial arm. The inert gas supply 7 and 8 exhaust devices create a neutral medium in the tube 1 of beryllium oxide passing through the coaxial shoulders of the working cells. To cool the tube 1 during operation, water cooling is provided 9. When pulling the bundle 1 through the coaxial shoulders of three microwave cells 2, it is heated by the microwave field to a predetermined temperature sufficient for heat treatment. Reception of the bundle 1 leaving the furnace is carried out by rollers 10. During operation of this furnace, the uniformity and efficiency of heat treatment of a fibrous long carbon material are increased.

The design of the microwave cell is designed in such a way that it allows a symmetric mode of power addition from two identical magnetron-type microwave generators operating in a pulsed mode with a duty cycle of two and alternating operating intervals in one waveguide. Such generators are used in microwave ovens, reliable in operation, mass-produced by the electronics industry and sold at affordable prices.

When treating a carbon tow in a microwave cell with a longitudinal electric field, it is heated by microwave currents to a temperature of T≈3000 ° C in a neutral atmosphere (argon, nitrogen) at a pressure equal to the air pressure outside the cell. Under these conditions, microwave plasma arises around the bundle. The cause of the plasma is the inevitable thermionic emission from the heated surface of the bundle in the presence of an intense microwave field.

The electron cloud is localized in close proximity to the surface of the bundle and helps to equalize its temperature and virtually eliminates the presence of oxygen there. This is an important technological condition in the process of high-temperature processing of a carbon tow. The electron cloud is a quasi-equilibrium formation due to the continuous influx of electrons from the side of the heated surface of the bundle and their continuous return. The equilibrium density of the electron cloud is determined by the temperature of the emitting surface.

A quantitative assessment of the intensity of electron emission from the surface of a carbon tow can be made using the well-known Richardson-Deshman law. For a carbon surface heated to an extreme temperature of 3273 ° K, we obtain a value equal to

n _e ≈2.58 · 10 ²⁴ m ^-2 · s ^-1 = 2.58 · 10 ¹⁸ mm ^-2 · s ^-1 .

This value is so large that the appearance of a microwave plasma around a bundle heated to such a temperature in argon at normal pressure will be inevitable. The microwave plasma is clearly localized in the space around the bundle and moves along its surface with the speed of pulling the bundle through the working region of the microwave heating.

The considered method of supplying microwave energy to carbon tows can be called “waveguide”. He was tested on the layout and proved to be very effective.

Compared with the prototype, this method has significant advantages:

- a significant reduction in energy consumption per unit of output,

- reducing the cost of consumables (heating elements),

- improving the ecology of production,

- reduction of inert gas costs,

- the use of a cheap source of microwave fields (serial magnetrons produced by industry for microwave microwave ovens).

Claims (3)

1. Device for continuous high-temperature processing of carbon bundles, containing a heating element in the form of a microwave field source and a tube for passing a carbon bundle, characterized in that the heating element includes a microwave cell made in the form of waveguide-coaxial junctions with a common coaxial arm, on which mounted rectangular waveguides located in parallel planes and deployed relative to each other at equal angles, while as a source field of microwave frequency used magnetron ultrahigh frequency generators mounted on the opposite ends of each waveguide and provided with a phase shifter, providing a periodic operation of each pair of generators. 2. The device according to claim 1, characterized in that a decoupling device in the form of an insulator or circulator is installed between the microwave cell and the microwave generator. 3. The device according to claim 1, characterized in that the microwave generators are additionally equipped with thermal fuses.

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