EP0135826A1 - Apparatus for thermally spraying coating plasma - Google Patents

Abstract

PCT No. PCT/DE84/00173 Sec. 371 Date Apr. 24, 1985 Sec. 102(e) Date Apr. 24, 1985 PCT Filed Aug. 27, 1984 PCT Pub. No. WO85/00991 PCT Pub. Date Mar. 14, 1985.A spray gun comprises a nozzle defining an elongated, axially extending spray channel, a coaxial inlet leading thereto and having a flow-accelerating contour, and a coaxial combustion chamber leading to the inlet, the combustion chamber having a diameter larger than that of the spray channel. A nozzle head is displaceably mounted in the combustion chamber and is axially adjustable with respect to the inlet, the nozzle head feeding the fusible material into the combustion chamber and carrying a burner nozzle and respective conduits feeding a combustion gas and a spray channel flushing gas into the combustion chamber. An ignition electrode projects into the combustion chamber and is arranged for adjustment with respect to the burner nozzle in a direction transverse to the axis, and a control circuit comprises a switching element for supplying electric current to the ignition electrode whereby a spark is formed between the ignition electrode and the burner nozzle for igniting the combustion gas in the combustion chamber, and respective controllers for feeding the combustion gas and the flushing gas through the respective conduits, the control circuit sequentially operating the controller for feeding the flushing gas, the switching element for supplying electric current to the ignition electrode and the controller for feeding the combustion gas.

Description

The invention relates to a device for the thermal spraying of build-up welding materials, consisting of a coolable beam bundling nozzle with a space on the feed side to accommodate devices for controllable supply of the operating components, namely operating gases and build-up welding material.

Devices of the type mentioned are known for thermal spraying for applying powders according to DAS 1 089 614. The further prior art is represented by the European application 812 01061.9 and by the magazine "Metall" issue 3/83, page 238, Fig. Lb. In the latter device, nitrogen is used as the conveying gas, the flame (fuel gas being a mixture of methylacetylene propadiene and oxygen) being formed in the water-cooled jet nozzle. The process according to European application 812 01061.9 requires a complex dosing system with electronic control and regulation, i.e. the associated system is very expensive and its purchase and use are only worthwhile for certain applications, although with such a system (the equipment components are based on the constant pressure principle merged) spraying qualities can be achieved which can easily withstand a comparison with the spraying qualities achievable in plasma and flame shock spraying, ie are of very high quality. Since these systems cannot be operated using pure acetylene and, as mentioned, are very expensive, their use is forbidden for, as it were, normal spray application cases, ie for such cases it was possible to do so with simpler means, using such a method and such a jet nozzle (Pinch nozzle) associated advantages, namely avoiding or reducing spray losses, better particle melting and higher particle acceleration, have not been exploited to date.

In the device according to the DAS mentioned at the outset, there is no combustion chamber, but the mouth of the carrier gas powder outlet channel is arranged directly in the region of the junction into the jet bundling channel of the bundling nozzle, the expanded space around the nozzle only serving for the oxygen supply, which through an annular gap Carrier gas powder stream is added. Apart from the risk of reignition in the carrier gas powder supply channel, the nozzle is not designed to be adjustable, so that there are no possibilities for adaptation to different powders. In addition, the entire device must be ignited from the front, which is also not without danger.

The invention is therefore based on the object to provide a device with comparatively low spray losses, which, working according to the so-called differential pressure principle, on the one hand does not require or does not require much more than previously required for flame spraying in terms of apparatus expenditure, but on the other hand with adapted variability the combustion chamber allows the use of all combustible gases, but in particular also acetylene and different wettable powders and with which, in particular, the ignition or start-up process should also be able to be controlled safely.

This object is achieved with a device of the type mentioned at the outset according to the invention in that the expanded space is designed as a combustion chamber with a flow-accelerating transition contour for the confluence of the bundling nozzle det and an axially adjustable, differential pressure-charged burner nozzle or a nozzle holder with a nozzle is arranged in the combustion chamber with respect to the mouth of the beam bundling nozzle and that an ignition electrode which can be set on the nozzle is also arranged in the wall of the combustion chamber and this with an electrode after the flushing the bundling nozzle and before the supply of the fuel gas switching element is provided. Advantageous further developments of this solution result from subclaims 2 to 14.

The solution given is easiest to implement by combining the jet nozzle with a flame spray gun in such a way that the variability of the combustion chamber volume is retained. However, one remains dependent on the performance data of the spray gun used in each case. If you do not want to be able to process wire as a spray additive in addition to powder, the nozzle holder is designed as a correspondingly adapted nozzle assembly while maintaining the basic principle.

The solution according to the invention results in the following advantages with regard to the application layers: With high-melting materials (oxides, cermets, high-melting metals, etc.), it has been shown that a significantly better layer quality can be achieved. The tightness in the application layer is significantly increased compared to conventional flame spray applications. The adhesive strength is also significantly improved due to the higher kinetic energy of the spray particles, and there is also no impairment of the sprayed-on layer by powder particles which have baked in the beam bundling channel and which sooner or later become detached again. Through the Bün the spray jet, the otherwise unavoidable spray losses for targeted applications are significantly reduced.

Up to now, filler materials that cannot be sprayed alone can also be used with a flame spray gun. Furthermore, the requirement for the usability of all the combustion gases customary in this work area, in particular of acetylene, is also fulfilled by setting the combustion chamber volume in a correspondingly optimal manner, and finally the operation of such a device does not require complex electronic control, but only a simple electrical circuit and regulation for the guarantee the logical steps to ignite. For reliable ignition during commissioning and thus for the usability of the device in general, it is essential that it is carried out in the following steps in order to reduce the combustible gas-oxygen mixture to a minimum for the start-up phase: purging with pure oxygen, making it effective the ignition device and only then supply of the fuel gas. If this sequence was not followed, an ignition directly in front of the nozzle of the flame spray gun could lead to an explosion, possibly with extinguishing the flame, or ignition at the mouth of the beam focusing nozzle, as in the previous one. Direction according to which DAS is the case, to re-ignite into the nozzle and to extinguish the flame. This sequence, which is essential for the start-up phase, could be manipulated by hand on the flame spray gun for the gas supply, including switching on the ignition device on the device according to the invention, but this would be too cumbersome and too unsafe.

With regard to the ignition device equipped with an electrode, it has also proven essential for the device's long-term operability to be able to withdraw the electrode from the combustion chamber after it has been ignited, in order not to disturb the flow in the combustion chamber on the one hand and on the other to not to hinder the adaptation of the combustion chamber volume to the respective circumstances. In practice, this means that the nozzle and the electrode are moved to the ignition position and that, depending on the requirements, the optimum combustion chamber volume can then be set unhindered by the electrode.

A largely controlled combustion of the mixed gases takes place in the combustion chamber, the size of which must also be variable in the case of the flame spray guns / beam bundling nozzle combination, which can possibly lead to temperatures at which even metal evaporation occurs. For this reason, the combustion chamber wall is also designed to be coolable.

Since in the device according to the invention the combustion chamber volume is variable due to the adjustability of the nozzle or the nozzle stock, the residence time of the powder particles in the combustion chamber can be influenced thereby, ie the powder is preheated in an adapted manner or brought to the desired temperature in a targeted manner and even before it reaches the jet nozzle at high speed. In this context, it is essential that a flow-accelerating transition contour is present between the combustion chamber and the confluence with the beam bundling channel, advantageously with respect to the device axis with a convex shape, which is of particular importance in the present case insofar as otherwise, since the pulse at least melted particles emerge from the combustion chamber, the powder particles can already start in the junction area of the beam focusing channel. If this area does not fully grow when the flow is unfavorable, such approaches lead to the risk of tearing off and if such tearing particles get into the application layer, this does not lead to optimal coating results.

By changing the size of the combustion chamber, but possibly also changing the length of the jet bundling nozzle, both high-melting and low-melting spray additives can be sprayed, and finally there is the possibility of supplying atomizing or additional gases, which make it possible to influence the operation of the device in a targeted manner.

With regard to the length adjustment to the spray material to be processed, the beam bundling nozzle is therefore advantageously designed in several parts, which will be explained in more detail.

When the device is designed with a nozzle assembly, powder conveyance is carried out by an external powder conveying system during powder spraying, so that uniform powder conveyance is made possible. In the case of processing wire as a spray additive, the wire is also fed via an external feed device of known type for the wire.

In particular for a longer period of use of the device, this also applies to both variants, it has proven to be advantageous to ensure the formation of a jacket flow in the inner channel of the jet bundling nozzle conditions that are easy to implement in terms of equipment. Such a jacket flow can prevent the melted particles from caking on the walls of the inner channel, which is essential for a longer operating time.

Depending on the length of the jet bundling nozzle, additional devices for forming such a jacket flow can then also be made in the half on the confluence, preferably in the area before the confluence, which can also be generated, for example, by supplying inert gas. In addition, however, it is also possible to form at least part of the wall of the beam bundling channel from porous material (for example ceramic) and to surround this shaped body with a cavity which can be filled with compressed gas. The injected gas, which may also be a fuel gas, then forms a cladding layer in the channel, and baking of molten particles is practically no longer possible.

For the rest, the inner channel of the jet bundling nozzle does not have to be cylindrical, but can also be designed to widen conically towards the nozzle mouth.

Apart from the practical embodiments, which will be explained in more detail below, and the advantageous developments, the solution according to the invention creates a device which is conceivably simple in its construction, part of which can even be a conventional flame spray gun, which can be adapted to all by simple adaptability of the combustion chamber volume this area is accessible to conventional fuel gases or fuel gas mixtures and the. ensures a safe ignition process.

It is therefore essential for the device according to the invention the formation of a combustion chamber in which the outlet nozzle for the fuel gases and the carrier gas stream is arranged in the longitudinal direction. The size of the combustion chamber is therefore variable and only the gases burned out in the combustion chamber reach the beam bundle channel under acceleration. Since the powder particles thus also only get into the combustion chamber, they are melted or melted there in an adapted manner and in this state reach the bundling channel. Furthermore, the arrangement of a retractable ignition electrode in the combustion chamber is essential in order to ensure the ignition of only a relatively small mixture of fuel gas in the combustion chamber when the device is started up.

The device according to the invention is explained in more detail below with reference to the drawing of exemplary embodiments.

• Fig.1 im Schnitt die Vorrichtung einer Flammspritzpistolen/Strahlbündelungsdüsenkombination;
• Fig.2 im Schnitt die Vorrichtung in Form einer Düsenstock/Strahlbündelungsdüsenkombination;
• Fig. 3 eine besondere Ausführungsform der Strahlbünde- _lungsdüse;
• Fig. 4 eine weitere besondere Ausführungsform der Strahlenbündelungsdüse zur Ausbildung einer Mantelströmung;
• Fig..5 eine bevorzugte Ausführungsform der Elektrodenausbildung;
• Fig. 6 ein Schaltschema für die Vorrichtung;
• Fig. 7 ein Funktionsdiagramm und
• Fig. 8 einen Schnitt durch einen Teil der Vorrichtung in einer weiteren Ausführungsform.

It shows schematically

• 1 shows in section the device of a flame spray gun / beam nozzle combination;
• 2 shows the device in section in the form of a nozzle assembly / jet bundling nozzle combination;
• Fig. Ngsdüse a particular embodiment of Strahlbünde- _lu 3;
• 4 shows a further special embodiment of the beam focusing nozzle for forming a jacket flow;
• 5 shows a preferred embodiment of the electrode formation;
• Fig. 6 is a circuit diagram for the device;
• Fig. 7 is a functional diagram and
• Fig. 8 shows a section through part of the device in a further embodiment.

According to FIG. 1, the essential parts of the device are the flame spray gun 6 ″, which is only indicated by dashed lines, an adapter 3 containing the combustion chamber 2, the beam focusing nozzle 1 and the ignition device with electrode 7. The flame spray gun 6 ″ requires no further explanation, as is known per se . The adapter 3 must of course be dimensioned with respect to its receiving bore so that the head 6 'of the flame spray gun 6 ", in which the burner nozzle 5 is seated, can be used in the adapter 3, specifically with suitable elements in different positions to fix the To be able to adapt combustion chamber 2 to the respective requirements The ignition device with the ignition electrode 7 is also arranged so that it can be adjusted with respect to its longitudinal axis, so that the suitable ignition distance to the nozzle 5 can be set and an ignition arc or ignition spark can briefly occur for ignition.

In the present context, the ignition device according to FIG. 5 is designed as follows: The electrode 7 forms the armature of a magnetic coil 11 which, when excited, brings the electrode 7 to the nozzle 5 against the action of a return spring 12 in the ignition position (dashed line). In this position, the ignition current is switched on by a limit switch 13 (FIG. 6). After ignition, coupled with current cutoff of the coil 11, the electrode 7 is reset from the combustion chamber 2 by the spring 12. It is essential for the ignition process that the ignition does not take place only when the combustion chamber 2 is filled, but immediately at the beginning of the inflow of an ignitable gas mixture into the combustion chamber.

As can be seen in FIG. 1, the jet bundling nozzle 1 including the adapter 3 is water-cooled, wherein the cooling channels 14, 15 are connected to a connecting line 16. The coolant inflow connection 17 for both cooling channels 14, 15 is arranged in the attachment area of the jet bundling nozzle 18 to the adapter 3, and a common coolant outflow connection 19 is provided for both channels 14, 15.

3 (this applies both to the embodiment according to FIG. 1 and for that according to FIG. 2), the beam bundling nozzle 1 can be formed from individual parts 22 which can be connected to one another and which are connected to one another with regard to the passage of coolant by bypass lines 23, provided that not every individual part 22 is provided with separate inflow and outflow connections.

In order to form the aforementioned jacket flow within the jet bundling nozzle 1, one or more gas supply openings 21 are provided at the end on the adapter side, as shown schematically in FIG. 4. Furthermore, such openings 21 'can additionally be provided in the region of the mouth-side half of the steel bundling nozzle 1, for example in the flow shadow of a gradation 24 (on the right in FIG. 4). These embodiments can also be used in the device according to FIG. 2.

For the flawless, reliable commissioning and thus for the functionality of the entire device, also valid for both exemplary embodiments (FIGS. 1, -2), it is essential that the fuel gas supply regulator 8 and the oxygen or compressed air supply regulator 9 of the flame spray gun 5 "on the one hand and the switch-on element 10 for the ignition device are coupled to one another and arranged such that flushing the beam bundling nozzle with oxygen or compressed air, switching on the ignition device and inflow of the fuel gas can inevitably be effected one after the other. Suitable regulating and control elements are readily available for this.

The part which is movable or adjustable with respect to the combustion chamber 2 (flame spray gun 6 "or nozzle holder 6 according to FIG. 2) is advantageously provided with a marking or with an adjustable stop in order to ensure that the part in question with its for the ignition process Nozzle 5 is brought into the correct ignition distance from electrode 7.

The ignition device or the electrode 7 is expediently arranged in the plug-in region 3 'of the adapter 3 containing the combustion chamber 2, so that the access opening in the adapter wall for the electrode 7 is covered even when the volume of the combustion chamber 2 is set to the greatest extent, which is in consideration of the high temperatures in the combustion chamber 2 is advantageous.

The embodiment according to FIG. 2 differs from that described in FIG. 1 practically only in that instead of the spray gun a correspondingly adapted nozzle assembly or nozzle holder 6 is provided and one is therefore no longer bound to the performance data of the flame spray gun 6 " 2, the conveying elements for the wire-shaped spray material are not shown for the flame spray gun and the nozzle holder according to FIG. 2, since such elements are generally known. The nozzle holder 6 according to FIG of course, also be equipped with a connection for a powder storage container or for a powder supply line. Corresponding parts of this embodiment according to FIG. 2 are therefore designated with corresponding reference numerals which are provided with a dash index.

8, the flame spray gun or the nozzle assembly, the electrode and corresponding connecting lines are not shown. The convex design of the transition contour 4 ′ from the combustion chamber 2 into the beam bundling channel 25 can be seen particularly clearly here, which widens somewhat conically toward the mouth 26. Such an extension can also be provided in the embodiments according to FIGS. 1, 2. In addition, in the embodiment according to FIG. 8, the wall of the beam focusing channel 25 is formed as a molded body 27 made of porous, gas-permeable material. The porous molded body 27 is with a _; Compressed gas feedable cavity 28 to which the compressed gas is fed through a compressed gas feed connection 29. It is advantageous, as shown, to provide the cavity 28 with a decreasing cavity volume from the feed connection 29 in order to ensure the most uniform possible distribution of pressure gas outlet through the porous material of the molded body 27 over its entire length. The molded body 27 is formed, for example, from sintered A1 ₂ 0 ₃ or zr03 or mixed forms thereof. Since the molded body 27 is gas-permeable over its entire surface, a constantly renewing gas cushion is formed in the sense of the aforementioned jacket flow, it being entirely possible to additionally arrange openings 21 in the immediate vicinity of the overflow contour 4 '. The pressure gas supplied through the connection 29 can also be a combustion gas. act gas for an additional acceleration of the entire flow in the beam focusing channel 25 provides.

In the circuit diagram according to FIG. 6, only the large reference numerals 5, 7, 8, 9, 10, 11, 13 and X, Y have direct reference to corresponding reference numerals in FIGS. 1-5. Only the circuitry belonging to the device belongs to this device Elements 5, 7, 8, 9, 11, ie those that are below the dash-dotted line in the right part of the circuit diagram.

Corresponding relays K ₆ , K ₂ , K ₃ , K4 and corresponding circuit elements delayed on and off delay ensure the necessary functional sequence according to FIG. 7 on the device, t _{3 representing} the actual operating phase. The curves shown are of course only of qualitative importance. E.g. illustrates the ignition curve that the ignition current only flows in the time interval t ₂ , in which the fuel gas only begins to flow in. The electrode curve shows that the electrode is withdrawn immediately after the interval t ₂ . In the interval t ₄ , ie after the control unit has been switched off at S ₃ , the fuel gas supply drops immediately, but the oxygen supply can continue to run a little for purging purposes.

Claims (14)

1. Device for the thermal spraying of build-up welding materials, consisting of a coolable beam bundling nozzle with a space on the feed side to accommodate equipment for controllable supply of the operating components, namely operating gases and build-up welding material, characterized in that the expanded space as a combustion chamber (2) with a flow-accelerating transition contour ( 4 ') for the mouth of the bundling nozzle and in the combustion chamber (2) with respect to the mouth (4) of the jet bundling nozzle (1) an axially adjustable, differential pressure-fed burner nozzle (5) or a nozzle holder (6) with a nozzle is arranged and that Furthermore, an ignition electrode (7) which can be set on the nozzle (5) is arranged in the wall of the combustion chamber (2) and this with a switching element (10) which switches on the electrode (7) after flushing the bundling nozzle (1) and before supplying the fuel gas. is provided. 2. Device according to claim 1, characterized in that the flow-accelerating transition contour (4 ') from the combustion chamber (2) to the mouth (4) of the jet nozzle (1) is convex with respect to the longitudinal axis of the device. 3. Apparatus according to claim 1, characterized in that the nozzle holder (6) in the form of a known flame spray gun (6 ") is arranged adjustable in the bore of an adapter (3) of the beam focusing nozzle (1). 4. The device according to claim 1, characterized in that the adjustable ignition electrode (7) is designed as an armature of a magnetic coil (11), is provided with a return spring (12) and with ignition current switching contact (13). 5. The device according to claim 1, characterized in that the ignition electrode (7) in the plug-in area (3 ') of the adapter (3) of the beam focusing nozzle (1) is arranged. 6. The device according to claim 1, characterized in that the wall of the combustion chamber (2) is provided with a cooling channel (14) and this is connected to the cooling channel (15) of the jet nozzle (1). 7. The device according to claim 6, characterized in that the coolant inflow connection (17) for both cooling channels (14, 15) in the attachment region (18) of the jet nozzle (1) to the combustion chamber (2) and arranged for both channels (14, 15) common coolant outflow connection (19) is provided. 8. The device according to claim 1, characterized in that in the jet bundling nozzle (1), extending over its entire inner length, a nozzle tube (20) is interchangeably arranged. 9. The device according to claim 1, characterized in that at the adapter-side end of the jet nozzle (1) one or more gas feed openings (21) for forming a jacket flow are arranged along the inner wall of the nozzle (1). lO. Apparatus according to claim 1, characterized in that one or more gas supply openings (21 ') for forming a jacket flow along the inner wall of the nozzle (1) are arranged in the mouth-side half of the beam focusing nozzle (1). ll. Apparatus according to claim 1, characterized in that the jet bundling nozzle (1) is formed from a plurality of individual parts (22) which can be connected to one another. 12. The apparatus according to claim 1, characterized in that the inner wall of the jet bundling nozzle (1) from a tubular, inserted into the nozzle body formed body (27) made of porous, gas-permeable material and this is surrounded by a cavity (28) which can be filled with compressed gas. 13.The device according to claim 12, characterized in that the cavity (28) from the pressurized gas supply connection (29) is provided with a decreasing cavity volume. 14. The apparatus according to claim 1, characterized in that the switching element (10) for the electrode (7) and the fuel gas supply (8) - and oxygen or compressed air supply controller (9) of the device are coupled to one another and arranged such that the purging the beam focusing nozzle (1), the ignition current is switched on and the fuel gas flows in one after the other.

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