RU2361964C2 - Method of economy plasmatic ultrasonic spatter of high-density powder coatings and plasmatron for its implementation (versions) - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: plasmatron for economical plasma spraying is outfitted by attachment or elongated anodic nozzle. Cooling of attachment or elongated anodic nozzle can be as separately as collateral. According to declared method powder is fed into anodic nozzle, is accelerated and heated in attachment channel or in elongated anodic nozzle. Adhering is removed by means of selection of process-dependent parametres, herewith length of attachment channel or elongated anodic nozzle must be not more than 15 diametres, channel diametre can be changed in the same direction as powder flow not more than 1.1÷1.2 times.

EFFECT: decreasing of required arc power, increasing of material utilisation.

7 cl, 5 dwg, 1 tbl

Description

The invention relates to a plasma-arc technique and powder metallurgy and is intended for spraying high-density coatings using a supersonic plasma jet.

A known method of supersonic plasma gas-air spraying of high-density coatings [1], based on the use of high costs of the gas-air mixture and, accordingly, an elongated plasma jet flowing into the flooded space. The power spent on generating such a jet reaches 180 kW with high performance; the authors recommend shortening the length of the anode nozzle [1, p.164] to increase the thermal efficiency of the plasma torch. In this case, the powder is supplied under the nozzle exit or into the anode nozzle and, basically, accelerates and heats up in a flooded supersonic plasma jet.

The disadvantage of this method is the need to use large capacities, and accordingly, the complexity of the designs of the plasmatrons due to the increased thermal load on the details of the plasmatrons and the low coefficient of use of powder discharge energy.

There is also a known method [2, pp. 35-38] of supersonic plasma spraying, based on the use of a nozzle up to 150 mm long attached to an air plasmatron. At the entrance to the forming channel of the nozzle, two openings are made for introducing a carrier gas - air. At a power of 50 kW, the flow rate of carrier air is 8 times greater than the plasma-forming, with an internal diameter of the nozzle 10 mm. It is obvious that the temperature of the de-energized jet will not be enough for melting refractory compounds and oxides, according to the author’s calculations, it is 2000 K, therefore this method is suitable for metals and their alloys with a melting point up to 2000 K. There is no data on the adhesion of powders on the walls of the nozzle channel.

The technical result of the invention consists in eliminating the above disadvantages - it is proposed, for example, a gas-air high-flow plasmatron with a cathode assembly, an interelectrode insert, an anode assembly with a cylindrical channel after the arc attachment zone, the powder is introduced after the arc attachment zone, heats up and accelerates in the cylindrical nozzle channel or anode nozzle with a channel length of not more than 15 diameters before flowing into the flooded space, while to eliminate the sticking of powder on the channel walls, the length it is determined in accordance with the power of the arc, the flow rate of the gas mixture and powder, but not less than 2-3 channel diameters.

As a result of compression of a de-energized plasma jet with powder in the cooled nozzle channel or in the anode nozzle with a channel length of no more than 15 diameters, the temperature and acceleration of the powder increase and supersonic spraying is performed at a power 25–35% less than when the powder is fed into the anode at a distance of 0 , 5 ÷ 1 diameter from the nozzle exit. To reduce the effect of gas-dynamic locking and eliminate sticking, the diameter of the nozzle channel should be equal to or greater than 1.2 of the diameter of the anode nozzle. Despite the decrease in the thermal efficiency of the plasma torch, due to the removal of energy by water cooling the anode and the nozzle, the efficiency of energy use by the powder increases.

The plasma-gas high-voltage plasmatron with an interelectrode insert [3] and the low-voltage gas-air plasma torch with a self-stabilizing arc length [4], which stably operate at high flow rates of plasma-forming gases, were selected as analogs of plasmatrons for economical plasma supersonic spraying.

The high-voltage gas-air plasma torch consists of four nodes - cathode, intermediate with interelectrode insert (MEV), anode and added nozzle, or anode with an elongated nozzle (figure 1)

The cathode assembly consists of a housing 1, into which the thermochemical cathode 2 is screwed, resting against the gasket 3. The cathode assembly is placed inside the insulator 4, in which there are grooves or holes cut along the tangent to the insulator housing, and a ring 5 with retaining rings is placed on the upper part of the insulator 4 with screws 6. The insulator abuts against the end of the MEW 7, which enters the housing 8. The sealing of the space for cooling the MEW is carried out by gaskets 9 and 10. The housing 8 has a thread on the upper part for a clamping nut 11, and a thread on the bottom the anode casing 12 is screwed through a ring 13 with threads inside and outside, isolated from the MEW casing, the washer 14 isolates the MEC from the anode casing 12. Anode nozzle 15 with gaskets 16 and 17 for sealing is placed in the anode casing 12. The nozzle housing 18 is screwed onto the anode housing 12. The nipples for feeding the powder 19 enter through the threads in the nozzle housing 18 and the anode housing 12 and are buried in the body of the anode nozzle 15. The nozzle 20, the gaskets 21 and 22 are placed in the nozzle body 18, and in the lower part the sealing nut 23 is screwed. Nipples 24 are connected to the housing 18 for cooling.

The plasma torch for economical plasma supersonic spraying with an anode of the nozzle with a channel length of not more than 15 diameters differs from the plasmatron with the nozzle by the design of the anode assembly and the cooling system. Figure 2 and figure 3 shows the cooling system of the shank of the anode, separately from the cooling of the anode, figure 4 shows co-cooling.

Figure 2. shows the shank of the anode 25, on which is wound a spiral from a copper tube 26, on which a coating of aluminum or copper is sprayed. The lower clamping nut 27 is put on the shank of the anode before installing the spiral. The nipples for supplying powder 28 are included on the thread in the lower clamping nut 27. Figure 3 shows an elongated anode, on the shank of which a sleeve 29 with a cooling cavity is mounted and sealed, water is supplied through the nipples 30. Figure 4 shows an anode with joint cooling anode and shaft. Holes are drilled in the anode 31 from the water nozzles 90 degrees from the powder inlet points, a sleeve with a cavity 32 is soldered to the shank. Water, when entering the anode nozzle, washes the anode shank through the water hole.

A plasma torch for economical plasma supersonic spraying of high-density powder coatings and a plasma torch for its implementation (options) with a nozzle or an elongated anode channel works as follows.

After turning on the cooling system, a plasma-forming gas - air - is supplied to the annular groove of the housing 9 through tangential grooves or holes in the insulator 4, the air swirls at the entrance to the MEA, then at the entrance to the anode nozzle the air flow is anti-swirl through the washer 14. The air flow is set according to the technology , simultaneously with the plasma-forming air, air is supplied from the dispenser through the powder supply nipples. The rectifier turns on, voltage is supplied to the cathode - MEW circuit, after the oscillator is turned on, a standby arc flashes, which turns off after the plasma closes the cathode - anode circuit, and the set current and voltage values are set. If necessary, propane-butane or natural gas is supplied with the air arc turned on, while the voltage increases. After reaching the required values of current, voltage, gas flow, the powder is fed into the nipples 19, which accelerates and heats up in the nozzle channel or in the elongated anode channel. The maximum length of the channel, at which there is no sticking, is determined experimentally and depends on the ratio of technological and design parameters.

A low-voltage gas-air plasma torch with a nozzle is shown in Fig. 5. The plasma torch case is made detachable from two parts - the upper 33 and the lower 34. The cathode assembly 35 with the insulator - swirl 36 is placed in the upper part, and the anode 37 is in the bottom, and the anode arc chamber consists of two cylindrical channels - input and output, between which snap surface of the anode spot in the form of a truncated cone. An insert 38 is placed in the outlet channel. A nozzle 39 is provided for powder supply. A nozzle housing 40 with water cooling nipples is screwed onto the lower part 34, into which the nozzle 41 is placed, the inner diameter of the nozzle being equal to the inner diameter of the insert 38. The gaskets 42 and 43 are sealed. The lower nut 44 is screwed onto the nozzle body 40 and abuts against the nozzle 41.

Low-voltage gas-air plasma torch with nozzle works as follows. After turning on the cooling of the electrodes of the plasma torch, plasma-forming gas - air is supplied into the annular groove of the upper part of the housing 33 and twisted through the grooves of the insulator 36 and, washing the cathode 35, expires through the channels of the anode 37, insert 38 and nozzle 41 into the flooded space. The rectifier is turned on, voltage is supplied from the oscillator between the cathode and anode, after which an arc flashes between the cathode and anode, and the anode spot rotates along the conical surface. If necessary, propane-butane or natural gas is supplied, while the voltage on the arc increases. The selection of all parameters and the geometry of the anode ensures the absence of shunting in the input cylindrical channel of the anode. The absence of powder sticking is ensured by the selection of the optimal length of the nozzle channel depending on the ratio of technological parameters.

The most important technological parameter - material utilization coefficient (CMM) at the same power and other parameters increases significantly when using a nozzle or anode with an elongated channel.

The table shows the experimental data on the effect of the nozzle or anode with an elongated channel on the CMM.

Device type Voltage U, B Current I, A Powder consumption Q _p , kg / h Air consumption Q _in , m ³ / hour Air pressure in dispenser P,
kg / cm ² The utilization of the material KIM,% Without nozzle 280 200 5 6 0.5 fifteen With a nozzle or anode nozzle with a channel length of not more than 15 diameters 280 200 5 6 0.5 70

Alumina (electrocorundum) was sprayed on the M50 fraction (average powder size 40 μm). A plasma torch with an MEA [3] was connected to a rectifier with an open circuit voltage of 500 V. The propane-butane consumption was 10% of the air consumption, a coating 1 mm thick was sprayed onto a St3 plate at a distance of 250 mm. The ratio of the nozzle channel length to the diameter of the anode nozzle is 5. To increase the CMM without the nozzle up to 60-70%, it was necessary to increase the current to 250 A or reduce air consumption by 30%, which led to a decrease in the powder velocity, decrease in adhesion and increase the porosity of the coating .

Despite the increase in thermal efficiency of the plasma torch due to energy removal during cooling of the nozzle or anode with an elongated channel, the energy use coefficient of the powder increases by 20–40%.

Literature

1.S.V. Petrov, I.N. Karp. Airborne plasma spraying. Kiev. Naukova Dumka, 1993. Academy of Ukraine, Institute of Gas.

2. V.S. Klubnikin. Supersonic plasma spraying of high-density and durable coatings. Proceedings of the 5th International Conference “Films and Coatings 98”. September 23-25, 1998 Edited by V.S. Klubnikin. St. Petersburg 1998, p. 35-38.

3. Shestakov A.I., Belenov A.S. High-voltage gas-air plasma torch. RF patent №2113775 from 11/05/1996

4. Shestakov A.I., Belenov A.S. Plasmatron gas-air low voltage. RF patent No. 2216133 dated July 16, 2002.

Claims (7)

1. A plasma torch for plasma supersonic spraying of high-density powder coatings containing a cathode assembly, an interelectrode insert, an anode assembly consisting of an anode body and an anode nozzle, nipples for supplying powder and two nipples for supplying water, characterized in that it is provided with a nozzle in the form of a housing with a nozzle placed in it and two sealing gaskets and a sealing nut screwed onto the lower part of the nozzle body, the nozzle body is screwed onto the anode body and abuts against the anode nozzle, and nipples for feeding powder buried in the body of the anode nozzle through a thread made in the nozzle body and the anode body. 2. A plasma torch for plasma supersonic spraying of high-density powder coatings containing a cathode assembly, an interelectrode insert, an anode assembly consisting of an anode body and an anode nozzle, nipples for supplying powder and for supplying water, characterized in that the anode nozzle is made with a channel length of not more than its 15 diameters, a clamping nut is put on the anode nozzle, in which nipples for feeding powder are fixed on the thread, and a spiral from a copper tube with a sprayed heat-conductive coating is put on the anode nozzle, in which nipples for supplying water are repaired, or a sleeve with an internal cooling cavity is soldered to the anode nozzle, in which nipples for supplying water are fixed. 3. The plasma torch according to claim 2, characterized in that a sleeve with an internal cavity for cooling is soldered to the elongated anode nozzle, while holes in the anode body are made with a diameter of 2 ÷ 3 mm from the side of the water inlet and outlet nipples, and the holes are 90 ° shifted regarding powder inlet nipples. 4. Plasma torch for plasma supersonic spraying of high-density powder coatings, comprising a detachable housing consisting of lower and upper parts, a cathode assembly, an insulator-swirler, nipples for supplying powder and an anode with an arc chamber made in the form of a truncated cone with an input cylindrical channel and output a cylindrical channel of a larger diameter into which the forming insert is placed, while the cathode assembly is made included in the anode, characterized in that a nozzle made with can scrap and abutting in mounted forming insert, the nozzle inner diameter equal to the inner diameter of the forming inserts, which nipples are screwed through the nozzle for supplying powder, and a nozzle pin has two cooling-water supply. 5. The plasma torch according to claim 4, characterized in that it comprises a lower sealing nut screwed onto the nozzle body, a thrust and sliding gasket, which is pressed by the sealing nut. 6. The method of plasma supersonic spraying of high-density powder coatings, characterized in that the spraying is carried out using a plasma torch according to any one of claims 1, 4, 5, while the length of the nozzle of the plasma torch nozzle is selected depending on the properties of the powders, arc power, flow rate of plasma-forming gases - air or air with hydrocarbons, one above which powder sticks, but no more than 15 channel diameters, counting from the arc attachment point, or spraying is carried out using a plasma torch according to claim 2 or 3, while y anode nozzle is selected depending on the properties of the powders, arc power, plasma gases flow - air or air with hydrocarbons such above which the powder adhesion, but not more than 15 channel diameters, starting from the point of attachment of the arc. 7. The method according to claim 6, characterized in that the diameter of the nozzle channel or the elongated anode nozzle is selected equal to or greater than the output diameter of the anode nozzle 1.1 to 1.2 times.

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