GB1564229A

GB1564229A - Feeding devices for plasma torches and the like

Info

Publication number: GB1564229A
Application number: GB49650/76A
Authority: GB
Original assignee: Alusuisse Holdings AG; Schweizerische Aluminium AG
Current assignee: Alcan Holdings Switzerland AG
Priority date: 1975-12-01
Filing date: 1976-11-29
Publication date: 1980-04-02
Also published as: DE2651779A1; JPS5268035A; SE7613413L; FR2333579A1; CH597925A5

Description

(54) FEEDING DEVICES FOR PLASMA TORCHES AND THE LIKE (71) We, SWISS ALUMINIUM LTD., a Company organised under the laws of switzerland, of Chippis, (Caton of Valais), Switzerland do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement:.

The invention presented here concerns feeding devices for equipment such as a plasma torch or the like to which granular or powdery material is fed, and by which this material is first melted and then sprayed at high speed onto a substrate or workpiece and on impacting is bonded onto it.

The known, commercially available plasma spraying systems have a maximum power of 50 kW. In practice however it has been found that the performance of these commercially available plasma units is inadequate for the coating of relatively large surface areas, and it is very difficult with these units to achieve and maintain a pre-selected, uniform thickness of coating over the whole surface of a workpiece which has a large surface area. Furthermore the known feeding devices of the plasma generating units exhibit a relatively low degree of efficiency on spraying or coating.

The object of the invention presented here is to provide a plasma generating system for a plasma torch, which the coating of workpieces can be achieved more economically than previously and with which the previously described difficulties associated with the known plasma systems are avoided.

This object is achieved by way of the invention in that the device for feeding the granular or powdery material to a plasma torch or the like comprises a distributor in a housing with means for symmetrical division of the material into two streams, which are emitted without pulsation from two gaspowered injector nozzles pointing to a predetermined fixed spot.

The accompanying drawings show one example of an embodiment of the invention, in a simplified schematic representation, viz: Figure 1: Side view of a plasma torch including components of the feeding device.

Figure 2: A circuit diagram for the feeding device of the plasma torch.

Figure 3: Front view, somewhat enlarged, of the plasma torch shown in Figure 1.

Figure 4: A section through the distributor housing of a two stage injector along the line IV-IV in Figure 3, but shown here on a larger scale.

Figure 5: A section through the distributor housing shown in Figure 4 and along the line V-V in that Figure.

As shown in Figures 1 to 5 the device for feeding granular or powdery material comprises a supply device 1 which supplies uniformly to a plasma torch 2 at a predetermed rate a mixture of granular or powdery material and gas. The material contained in a silo 3 (Figure 2) is fed by means of a feeding screw 5 in a pipe 4 to a pressure tank 6 which is connected via a pipe 7, a multi-way valve 8 and a reduction valve 9 to a compressed air main 9a, supplied by a compressor which is not shown here. In the pipe 7 there is provided a manometer 10.

Opposite the outlet orifice 11 of the pipe 4 and lying concentrically facing the orifice 11 there is provided on the wall of the tank 6 a working cylinder 12 in which a ram 13 can be moved back and forward. At the outer end of the ram 13 there is a valve disc 14, which is preferably conical in shape and with which the outlet orifice 11 of the pipe 4 can be closed. The pneumatically operated working cylinder 12 is connected to the air main 9a via a first pipeline 15, an electromagnetically operated multi-way valve 16, a pipe 20, and a reduction valve 17, and is also connected to the magnetic valve 16 via a second pipeline 18 and a reduction, non return valve 19.

Level gauges 25 and 26 are provided in the upper and lower regions of the pressure tank 6. The upper gauge 25 serves basically to prevent the pressure tank 6 from filling up to the region in which the ram 13 moves and above the region of the feeding screw 5.

The lower gauge 26 serves to give a signal and switch off the whole equipment when the contents of the pressure tank falls below the level of the lower gauge 26, e.g. when no further material is fed into the pressure tank 6 via the feeding screw 5. Below the outlet orifice 27 of the tank 6 there is provided a mixing chamber 28 which is connected to the air main 9a via a pipe 29, an in-line flowmeter 30, an on-off valve 31 and a reduction valve 32. In addition, in the pipe 29 there is provided a manometer 33 which allows the pressure in the pipe 29 to be read.

Two injection nozzles 35 and 36, which are connected via flexible feeding lines 37 and 38 to respective cyclones 39 and 40, are fixed on the side-wall 34 of the mixing chamber 28. Both flexible lines 37 and 38 are connected, at positions close to the mixing chamber 28, to the air main 9a via a pneumatic pipeline 41, an in-line flowmeter 42, a reduction valve 43 and an on-off valve 44.

The cyclones 39 and 40 are securely fixed to a cover plate 45 of a container 46.

Provided in the cover plate 45 are ports 47 and 48 through which the material can fow from the cyclones 39 and 40 into the container 46. In each of the upper lids 49 and 50 of the cyclones there is provided at least one opening 51 and 52 respectively, through which the spent air can escape. On two facing side-walls 53 and 54 of the upper region of the container 46 there is an ultrasonic unit comprising an emitter 55 and a receiver 56, which are connected by a electrical circuit to the multi-way valve 16, controlling the pnematically operated working cylinder 12.

The lower end of the container 46 is provided with a flange 57 which rests on a resilient element 58 which forms the connection between the container 46 and a funnel 59, which is in turn connected to the lid 60 of a distributor housing 61. The container 46 and the cyclones 39 and 40 are vibrated by means of a vibrator 75. In the funnel 59 there is a stirring device 62 which prevents the powdery or granular material from compacting, which would hinder flow.

In the lid 60 of the distributor housing 61 there is an opening 63 which connects the interior of the funnel 59 to a oval space 65 in which feeding screws 66 and 67 are sited.

The space 65 communicates with a second space 68 (Figure 4) to which the powdery or granular material is delivered by means of the feeding screws 66 and 67. As shown in Figures 4 and 5 the compacting space 68 posses two funnel-shaped exit chambers 69 and 70, each of which at its upper, wider part is connected to the open air by means of holes 71 and 72 respectively, which pass through the wall of the distributor housing 61. During operation, air is sucked in through the holes 71, 72 in order to impart better flow properties to the powdery or granular material. In order to adjust to the amount of air required which is basically dependent on the flow properties of the material used, the size of the openings 71, 72 can be changed by means of screws 73, 74, if this is considered useful.

In the distributor housing 61 there are two cylindrical holes 77 and 78, in each of which a two-stage injector 79, 80 is sited. Each two-stage injector comprises a cylindrical sleeve 81 which has a hole part 82 accommodating a injector nozzle 83, the said hole part 82 being cylindrical and having a shoulder which acts as a stop. Each of the two injector nozzles 83 in the distributor housing is connected to the air main 9a via a pneumatic pipeline 85 (Figure 2), a in-line flowmeter 87, an electro-magnetically operated on-off valve 89 and a reduction valve 91. The first hole part 82 in the sleeve 81 merges in the direction of flow of the material into a second conical-shaped hole part 92; the continuation of this hole part 92 is a third cylindrical part 93 which has a circular groove 94 round the circumference to accommodate a sealing ring; and the final part of the hole in the sleeve 81 is a cylindrical part 95 which has a larger diameter than the adjacent part 93. In this fourth part 95 of the hole in the sleeve 81 there is a thread 96. The funnel-shaped exit chambers 69/70 of the compacting space 68 open into the conical shaped part 92 of the hole in the respective sleeves 81.

The third part 93 of the hole in the sleeve 81 accommodates a venturi-nozzle 97 which is a press fit into the hole part 93. Another hole 111 runs from the fourth part 95 of the hole in the sleeve 81, out through the wall of the sleeve 81 and through the distributor housing 61. At the lower end of the sleeve 81 a tubular shaped connecting piece 98, for connection the two-stage injector 79, 80 with a pipeline 99, 100, is screwed into the thread 96. The connecting piece has a central hole which has two sections viz., in the upper part a section 101 which tapers down to a smaller diameter as viewed in the direction of flow of the material, and a lower section 102 which is cylindrical in shape. Between the outer wall 103 of the venturi-nozzle 97 and the walls of the cylindrical hole 95 in the sleeve 81 and the conical shaped hole 101 of the connecting piece 98 there is an annular gap 104 which narrows in the direction of flow of the material. The two holes 111 in the distributor housing 61 are connected to the air main 9a via a pipeline 84, an in-line flowmeter 86, on-off valve 88 and pressure reduction valve 90.

Each of the pipelines 99 and 100 connects an injector nozzle 105, 106 to the distributor housing 61. The injector nozzles 105 and 106 are fixed to the walls of the feeding device in such a way that the streams 108, 109 of material/gas mixture intersect, at a predetermined spot 110, in the plasma stream emitted from the housing 107, as shown in Figure 3. The manner of operation of the feeding device of the plasma torch is as follows: When the container 46 (Figure 2) is full, a signal from the ultrasonic unit 55/66 causes graular or powdery material. such as a metallic oxide for example. to be fed by the feeding screw 5 from the silo 3 into the closed pressure tank 6 through the outlet orifice ll of the pipe 4, which can be closed by the valve disc 14. until the tank 6 is filled up to the level of the upper level gauge 25.

An impulse from the gauge 25 then stops the feeding screw 5. On spraying, the level of material in container 46 sinks, and then the ultrasonic unit 5515h gives an impulse to the magnetic valve 16 which is connected to the working cylinder 12 and which activates the cylinder 12 moving the ram 13 and the valve disc 14 towards the outlet orifice 11 of the pipe 4 and closing the said orifice 11. After this orifice 11 has been closed, the electromagnetic multi-way valve 8 is opened and the interior of the tank 6 subjected to an increased pneumatic pressure. Simultaneously, the mixing chamber 28, into which the material flows through the opening 27 in the tank 6 under the force given by the pneumatic pressure, is subjected to a pneumatic pressure via the pipeline 29 and the open valve 31. The material which is mixed with air in the mixing chamber 28 is then transported further via the injector nozzles 35 and 36 and the flexible feeding lines 37 and 38 to the cyclones 39 and 40 where it is separated from the air used to transport it. In order to improve the flow properties of the material and to clear the flexible lines 37 and 38, air is passed through the pipe 41 at high pressure.

From the cyclones 39 and 40 the material passes to the funnel shaped container 59 via the openings 47 and 48 and past the ultrasonic unit 55, 56. In order to prevent the material from compacting together, it is loosened up by means of the vibrator 75 and the stirring device 62. When the container 46 has been filled with material above the level of the ultrasonic unit 55, 56. the supply of the material to the cyclones 39 and 40 is halted by closing the valve 31 in the pipe 29 to the mixing chamber 28, and the air pressure in the pressure tank 6 is released via the multi-way valve 8. As the same time the feeding screw 5 is put into operation and the outlet orifice 11 from the supply pipe 4 is opened by means of the valve disc 14. The flow of material delivered by the feeding screw 5 is halted when the level in the tank 6 reaches the level gauge 25. On the other hand at this stage of operation the valve 44 in the pressure pipeline 41 remains open whereby the residual material in the feeding lines 37, 38 is transported to the cyclones 39 and 40 and then the lines 37, 38 are subjected to a blast of air, so that the material cannot stick in the lines 37, 38.

The material is fed uniformly from the oval space 65 to the compacting space 68 by means of the two feeding screws 66 and 67.

The air streaming from the two nozzles 83 produce a reduced pressure in the two funnel-shaped chambers 69 and 70. The material is sucked into the conical spaces 92 and transported further by the air from the nozzles 83.

In order to improve the flow properties, air is allowed to infiltrate through the holes 71 and 72. The material which is fed in equal amounts to the two conical spaces 92 of the two stage injectors 79 and 80 is passed on to each venturi-nozzle 87 with the air of the nozzle 83. with simultaneously induced turbulence. Gas, the amount of which is adjusted to suit the nature of the material being sprayed, is passed through the annular gap 104 to the pipelines 99 and 100 and from there is directed out through the injector nozzles 105 and 106 in the form of jet streams 108 and 109 into the plasma stream emitted from the housing 107, to a predetermined fixed spot 110. Thereupon the particles of the material are melted and sprayed at high velocity onto a substrate or workpiece where on impacting they are effectively bonded onto it.

The feeding device is fitted with a device which is not shown here and which is for the electronic regulation of the rate of rotation (to an accuracy of + 0.1%) of the feeding screws 66 and 67 which are situated in the oval space 65 and are connected to a motor drive. The rate of rotation of the two feeding screws is to be adjusted or varied in accordance with the requirements. Further advantages of the feeding device are that it is suitable for granular or powdery materials which flow well or badly, and that the screws 66 and 67 do not cause any pulsed feeding of the material, with the result that the production of a layer with a uniform surface is ensured.

WHAT WE CLAIM IS: 1. A device for feeding granular or powdery material to a plasma torch or the like, comprising a distributor in a housing with means for symmetrical division of the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. material. The two holes 111 in the distributor housing 61 are connected to the air main 9a via a pipeline 84, an in-line flowmeter 86, on-off valve 88 and pressure reduction valve 90. Each of the pipelines 99 and 100 connects an injector nozzle 105, 106 to the distributor housing 61. The injector nozzles 105 and 106 are fixed to the walls of the feeding device in such a way that the streams 108, 109 of material/gas mixture intersect, at a predetermined spot 110, in the plasma stream emitted from the housing 107, as shown in Figure 3. The manner of operation of the feeding device of the plasma torch is as follows: When the container 46 (Figure 2) is full, a signal from the ultrasonic unit 55/66 causes graular or powdery material. such as a metallic oxide for example. to be fed by the feeding screw 5 from the silo 3 into the closed pressure tank 6 through the outlet orifice ll of the pipe 4, which can be closed by the valve disc 14. until the tank 6 is filled up to the level of the upper level gauge 25. An impulse from the gauge 25 then stops the feeding screw 5. On spraying, the level of material in container 46 sinks, and then the ultrasonic unit 5515h gives an impulse to the magnetic valve 16 which is connected to the working cylinder 12 and which activates the cylinder 12 moving the ram 13 and the valve disc 14 towards the outlet orifice 11 of the pipe 4 and closing the said orifice 11. After this orifice 11 has been closed, the electromagnetic multi-way valve 8 is opened and the interior of the tank 6 subjected to an increased pneumatic pressure. Simultaneously, the mixing chamber 28, into which the material flows through the opening 27 in the tank 6 under the force given by the pneumatic pressure, is subjected to a pneumatic pressure via the pipeline 29 and the open valve 31. The material which is mixed with air in the mixing chamber 28 is then transported further via the injector nozzles 35 and 36 and the flexible feeding lines 37 and 38 to the cyclones 39 and 40 where it is separated from the air used to transport it. In order to improve the flow properties of the material and to clear the flexible lines 37 and 38, air is passed through the pipe 41 at high pressure. From the cyclones 39 and 40 the material passes to the funnel shaped container 59 via the openings 47 and 48 and past the ultrasonic unit 55, 56. In order to prevent the material from compacting together, it is loosened up by means of the vibrator 75 and the stirring device 62. When the container 46 has been filled with material above the level of the ultrasonic unit 55, 56. the supply of the material to the cyclones 39 and 40 is halted by closing the valve 31 in the pipe 29 to the mixing chamber 28, and the air pressure in the pressure tank 6 is released via the multi-way valve 8. As the same time the feeding screw 5 is put into operation and the outlet orifice 11 from the supply pipe 4 is opened by means of the valve disc 14. The flow of material delivered by the feeding screw 5 is halted when the level in the tank 6 reaches the level gauge 25. On the other hand at this stage of operation the valve 44 in the pressure pipeline 41 remains open whereby the residual material in the feeding lines 37, 38 is transported to the cyclones 39 and 40 and then the lines 37, 38 are subjected to a blast of air, so that the material cannot stick in the lines 37, 38. The material is fed uniformly from the oval space 65 to the compacting space 68 by means of the two feeding screws 66 and 67. The air streaming from the two nozzles 83 produce a reduced pressure in the two funnel-shaped chambers 69 and 70. The material is sucked into the conical spaces 92 and transported further by the air from the nozzles 83. In order to improve the flow properties, air is allowed to infiltrate through the holes 71 and 72. The material which is fed in equal amounts to the two conical spaces 92 of the two stage injectors 79 and 80 is passed on to each venturi-nozzle 87 with the air of the nozzle 83. with simultaneously induced turbulence. Gas, the amount of which is adjusted to suit the nature of the material being sprayed, is passed through the annular gap 104 to the pipelines 99 and 100 and from there is directed out through the injector nozzles 105 and 106 in the form of jet streams 108 and 109 into the plasma stream emitted from the housing 107, to a predetermined fixed spot 110. Thereupon the particles of the material are melted and sprayed at high velocity onto a substrate or workpiece where on impacting they are effectively bonded onto it. The feeding device is fitted with a device which is not shown here and which is for the electronic regulation of the rate of rotation (to an accuracy of + 0.1%) of the feeding screws 66 and 67 which are situated in the oval space 65 and are connected to a motor drive. The rate of rotation of the two feeding screws is to be adjusted or varied in accordance with the requirements. Further advantages of the feeding device are that it is suitable for granular or powdery materials which flow well or badly, and that the screws 66 and 67 do not cause any pulsed feeding of the material, with the result that the production of a layer with a uniform surface is ensured. WHAT WE CLAIM IS:

1. A device for feeding granular or powdery material to a plasma torch or the like, comprising a distributor in a housing with means for symmetrical division of the

material into two streams, which are emitted without pulsation from two gas-powered injector nozzles pointing to a predetermined fixed spot.

2. A feeding device according to claim 1, in which there are two injector nozzles facing each other and pointing at the predetermined fixed spot.

3. A feeding device according to claim 1 or claim 2, in which the distributor is arranged to receive the material from supply means including a pressure tank which can be subjected to compressed air and which has an inlet opening which can be closed.

4. A feeding device according to claim 3, in which the pressure tank has a device for automatically closing the inlet opening.

5. A feeding device according to claim 4, in which the closing device comprises a working cylinder with a ram which can move backwards or forwards, and which has a valve disc at its outer end.

6. A feeding device according to any of claims 3 to 5, including a level gauge in the upper region of the pressure tank and another level gauge in the lower region of the pressure tank.

7. A feeding device according to any of claims 3 to 6, including, beneath the floor of the pressure tank, a mixing chamber which is connected to the pressure tank by an opening.

8. A feeding device according to claim 7, in which the mixing chamber is connected to receive compressed air from a compressed air supply.

9. A feeding device according to claim 7 or claim 8, in which the mixing chamber is connected to deliver material to two cyclones via respective pneumatic feeding lines.

10. A feeding device according to claim 9, in which the feeding lines are connected, close to the mixing chamber. to a pneumatic pipeline which is in turn connected to a supply of compressed air.

A feeding device according to claim 10, including openings in the lids of the cyclones to allow spent air to escape.

12. A feeding device according to claim 11. in which the cyclones are connected at their downstream ends to a container via ports in a cover plate through which the material can pass from the cyclones into the container.

13. A feeding device according to claims 5 to 12, including, on the side walls of the container, an ultrasonic unit comprising a emitter and a receiver, which is connected electrically to a multi-way valve controlling the working cylinder and ram.

14. A feeding device according to claim 12 or claim 13,in which the container rests on a resilient element and there is a vibrator on the container.

15. A feeding device according to claim 14, in which the resilient element forms the connection between the container and a funnel which is fixed securely in place downstream of the container.

16. A feeding device according to claim 15, including a stirring device in the funnel.

17. A feeding device according to claim 15 or claim 16, in which the funnel is fixed securely to the distributor housing, and there is an opening which connects the interior of the funnel with a space in the distributor housing.

18. A feeding device according to claim 17, including two feeding screws in the space, for feeding the material to two outlets from the space, connected to the two injector nozzles.

19. A feeding device according to claim 18, including a second space following on from the first-mentioned space, as seen in the direction in which the material is advanced by the screws.

20. A feeding device according to claim 19, in which the second space has two funnel-shaped outlet chambers, each of which is connected to the open air in its upper region by a hole which passes through the wall of the distributor housing.

21. A feeding device according to claim 20, including adjustment screws for changing the size of opening of the holes.

22. A feeding device according to claim 20 or claim 21, in which the funnel-shaped chambers join up with a conical part of the hole in the first stage of a two-stage injector set into a cylindrical hole in the distributor housing.

23. A feeding device according to claim 22, in which the two-stage injector is connected to a compressed air supply via a gas pipeline, an in-line flowmeter, an electromagnetically operated on-off valve and a reduction valve.

24. A feeding device according to claim 22 or claim 23, in which the two-stage injector comprises a cylindrical sleeve set into the hole in the distributor housing, and an injector nozzle and a venturi-nozzle in the sleeve.

25. A feeding device according to claim 24, in which on the lower end of the sleeve a tubular-shaped connection piece is screwed into place and defines a conical part of a hole which tapers down to a smaller diameter as viewed in the direction of flow of the material being sprayed, and following on from the conical part of the hole there is a cylindrical part of the hole, and there is an annular gap between the outer wall of the venturi-nozzle and the wall of the cylindrical hole part in the sleeve and also between the conical shaped part of the hole in the connecting piece and the outer wall of the venturi-nozzle.

26. A feeding device according to claim 25, in which the annular gap is connected to a compressed air supply via a hole which passes through the wall of the sleeve and the wall of the distributor housing.

27. A feeding device according to any of claims 22 to 26, in which each two-stage injector is connected via a pipeline to a respective injector nozzle in a holder.

28. A feeding device according to claim 1, substantially as described with reference to Figures 3, 4 and 5 of the accompanying drawings.