RU2113775C1 - Gas-air high-voltage plasma generator - Google Patents

Abstract

FIELD: powder metallurgy, plasma equipment, in particular, for coating deposition. SUBSTANCE: swirl generator of device is designed as sleeve which is made from insulating material and has tangential side slots. Cathode unit which is located inside sleeve has blunt-nosed cathode which runs inside inter-electrode insertion. Angle at vertex of input cone of inter-electrode insertion is in range of 120-130 degrees. Double gas screen prevents break-down between anode and inter-electrode insertion. EFFECT: increased arc voltage with respect to short inter-electrode insertion and decreased current values. 14 cl, 3 dwg , 1 tbl

Description

 The invention relates to the field of powder metallurgy, in particular spraying coatings and plasma technology.

 One of the promising directions for the development of modern arc plasma torches for spraying is characterized by an increase in power and the use of gas-air mixtures to generate high-speed plasma jets.

 An increase in discharge power is achieved by increasing the length of the arc and the voltage on it.

 To simplify the design and increase the reliability and maintainability of plasma torches with increased arc voltage, a circuit with a single or double interelectrode insert (MEM) and a swirl of a plasma-forming gas-air mixture is promising [1].

 The disadvantages of a single MEA include the danger of breakdown between the MEA and the anode, an increase in losses with a long MEA (more than 10d, where d is the diameter of the arc channel).

 To prevent breakdown, a gas curtain is usually provided between the MEA and the anti-spin anode against the main stream, but there is not enough information about the device of this unit.

 The aim of the invention is the creation of a plasma torch with a relatively short MEW (length shorter than 10 d) and at the same time a sufficiently high voltage across the arc, which allows to reduce the working current and increase the reliability of the electrodes, to eliminate the risk of breakdown between the MEW and the anode. This goal is achieved by new designs of a near-cathode swirling apparatus, a system for supplying a gas curtain to the MEA – anode gap, and a design for interfacing anode housings for MEW.

To increase the arc voltage due to the increased cathode voltage, the swirl is made in the form of a bushing from an insulator with tangential side grooves, inside of which there is a cathode assembly with a blunt thermochemical cathode inside the interelectrode insert, while the angle at the top of the input cone of the interelectrode insert is within 120 -130 ^o .

 Structurally, the casing of the anode assembly is screwed onto the intermediate casing with the MEA, sealing its cooling cavity, and the insulator between it and the anode assembly has grooves dividing the countercurrent gas flow into two; one is washed by the MEA, the other is the input cone of the anode, and the cone of the insulator coincides with the cone of the anode, which eliminates the risk of breakdown and the effect of radiation on the insulator.

 In FIG. 1 shows the design of the inventive plasmatron.

 The simplification of the plasmatron design was achieved by taking the prototype of the plasmatron configuration without MEE, in which all water and gas communications were moved outside the enclosure [2].

 The inventive plasmatron consists of three main nodes: the cathode, intermediate with the MEW and the anode.

 The cathode assembly consists of a housing 1, to the upper part of which a fitting 2 is welded to connect the cathode cable-hose (cable with water entering the cathode assembly), a nipple 3 and an inner rod 4 that separates the water stream. The lower part of the housing has a thread on which a nut 5 is screwed, pressing the thermochemical cathode 6 to the rubber gasket 7.

 The cathode assembly is placed inside two caprolon bushings 8 and 9, between which there is a rubber gasket 10. Sleeve 9 has tangential grooves (Fig. 2), sleeve 8 has holes in the upper part with M6 thread, into which the locking bolts 11 are screwed.

 The cathode assembly with the bushings is placed in the intermediate housing 12, the bush 9 being abutted end-to-end with the slots in the MEW, the bush 8 is pressed against the nut 13. The thermochemical cathode 6 enters the cylindrical upper part of the MEW.

 The space for cooling the MEA is sealed with two gaskets - one in the inner bore of the intermediate housing 14, the other 15 in the lower part of the MEA. A thread is provided on the outside of the lower part of the housing on which the anode assembly is screwed through an insulating caprolon ring 16 with threads inside and out.

 The body of the anode assembly 17 is equipped with two fittings 18 for connecting the anode cable hose and water outlet, and a nipple 19 for supplying a gas-air mixture. The anode 20 is pressed with a special washer 21 with holes for supplying powder. In the upper part of the anode assembly, a washer-insulator 22 with grooves is placed.

 The operation of the plasma torch is as follows.

In the spraying chamber, where the plasmatron is located, ventilation, water, and air are turned on. Air is supplied through a tee into the intermediate casing and the anode casing (separate gas supply is possible). In the intermediate casing there is an internal annular bore into which air enters and then, through the lateral tangential grooves of the sleeve, the swirling stream, washing the thermochemical cathode, rushes through the annular gap of 1.5 - 1.7 mm into the central hole of the MEW through the inlet cone having an angle at top 100 ^o - 180 ^o .

 At the MEE outlet, the central air stream meets the air stream passing through the side groove of the anode casing and twisting through the grooves in the washer insulator 22 against the direction of rotation of the central stream, and thanks to the grooves on both sides of the washer-insulator (Fig. 3), the air stream is divided two: one washes the surface of the MEA, the other the input cone of the anode.

 Structurally, the MEA with its lower cone enters the cone of the anode so that the gap between them is 3-4 mm. To eliminate the effects of arc radiation on the insulator washer, the latter has a conical bore.

 When the rectifier is turned on, the oscillator first triggers, the on-duty arc between the cathode and MEW flashes, and the plasma jet closes the cathode and anode as a conductor, after which the main arc starts to burn, the on-duty one is switched off.

 After the main arc is turned on in air, propane-butane (or natural gas) is fed through a special mixer valve, powder is supplied to a de-energized plasma stream under the nozzle or the anode and the coating process begins.

 After working for one year in the bus fleet No. 9 in Moscow on the restoration of parts for the Ikarus bus, the claimed plasmatron withstood more than 500 inclusions for one cathode, spent more than 600 hours in total, after which the anode erosion was within acceptable limits. During this period there have never been any water leaks, caprolon parts and asbestos cement washer - the insulator was not exposed to arc radiation.

 When working on a PUN-1 serial plasmatron, the Kiev-7 installation (also with MEW) had to change the gaskets after 1 - 2 days, the electrodes changed after 10 - 20 hours.

 The table shows some indicators of these tests.

 Comparative tests of the plasmatron PUN-1 and the claimed showed a significant advantage of the latter.

The plasma torches operated on a single Kiev-7 facility, the rotational speed of a part with a diameter of 80 mm was 1.7 s ^-1 , and the plasma torch speed was 30 mm / s. A powder mixture of PRN70X-17 and PTYu10N (30%) was sprayed, the nozzle diameter in both plasmatrons was 8 mm, and the powders were fed under the nozzle exit.

The thickness of the sprayed coatings in both cases is 1.5 mm. The coatings sprayed by the inventive plasmatron showed less porosity, especially when increasing the air supply to 11 - 13 m ³ / h.

 The arc voltage in both plasmatrons depends on their design and the concentration of propane-butane in the gas mixture.

If the inventive plasmatron has an input cone in the MEW equal to 120 ^o , when working in air, the voltage on the arc was more than 280 V and then the installation was turned off, since the open-circuit voltage of BEP-80 was 300 V.

 To ensure comparable results, the inventive plasmatron had to bore the second cone in the MEW (see the dotted lines on the MEW drawing), the voltage in the air dropped to 200 V, then with the addition of 10% propane-butane the voltage rose to 280 V.

If necessary, reduce the amount of propane-butane to maintain the highest voltage on the arc (280 V at an open-circuit voltage of 300 V), increase the input MEA cone to 100 ^o or more, in the absence of propane-butane, as we have already shown, the angle should be within 120 ^o - 130 ^o .

The optimality of the chosen geometry of the discharge space in the inventive plasmatron confirms the possibility of sufficient heating of such an amount of gas-air mixture (13 m ³ / h), in which supersonic plasma jet with a relatively small power on the arc is realized - less than 50 kW and reduced current. When fed to the lower part of the anode, aluminum oxide was sprayed at a spraying distance of up to 450 - 500 mm, with a utilization rate of up to 50%.

 Literature.

 1. Petrov S.V., Karp N.N. Plasma gas-air spraying. Kiev, "The Science of Dumka", 1993, p. 100, p. 164 - 167.

 2. Fridland M.G., Pershin V.A. Plasma torch with a continuously renewed cathode for coating. Automatic Welding, 1985, N 1, p. 58 - 61.

Claims (2)

1. High-voltage gas-air plasma torch, including a cathode assembly, an intermediate housing with an interelectrode insert and anode assembly, a swirler at the entrance to the interelectrode insert and an anti-swirl between it and the anode, the nodes being structurally independent and separately cooled, characterized in that the swirl is made in the form of a sleeve of an insulator with tangential lateral grooves, inside of which there is a cathode assembly with a blunt thermochemical cathode entering the interelectrode insert, the angle at the apex of the input cone and the interelectrode insert is in the range of 120 - 130 ^o C.  2. The plasma torch according to claim 1, characterized in that the casing of the anode assembly, screwed onto the intermediate casing with the interelectrode insert, seals its cooling cavity, and the insulator between it and the anode assembly has grooves that divide the anti-swirl gas flow into two - one washes the interelectrode insert and the other is the input case of the anode, and the cone of the insulator coincides with the cone of the anode.

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