EP2468914A1 - Method and device for arc spraying - Google Patents

Abstract

Electric arc spraying comprises melting at least one wire-shaped spray material in an electric arc (30) by electrical current and atomizing gas stream (41) and applying on a work piece (6) by spraying in the form of a particle stream (5), where at least one wire-shaped spray material is preheated before melting in the electric arc. An independent claim is also included for a device for implementing method comprising arranging a preheating device (45) for preheating at least one wire-shaped spray material before melting in the electric arc.

Description

The present invention relates to a method for arc spraying, in which at least one wire-shaped spray additive is melted by means of electric current in an arc and atomized by means of a Zerstäubergasstrom and applied in the form of a particle stream on a workpiece, and a corresponding device.

State of the art

Arc spraying is a thermal spraying process in which a wire-shaped spray additive is melted by means of electrical current, which generates an arc. A corresponding device is z. B. in the US 2 982 845 A disclosed.

For this purpose, usually two electrically conductive, metallic wires are used, which are continuously melted off as electrodes, but so-called single-wire methods are also known. To the wires, which are guided by means of a feed device at an angle under continuously decreasing distance towards each other and are conductively connected to a current source, a voltage of usually 15 to 50 V is applied. At sufficiently small distance of the wire ends to each other ignites an arc. A nebulizer gas stream dissolves the melt from the wire ends and accelerates them in the form of a particle flow of very fine droplets on a workpiece to be coated. The size and shape of the droplets can be adjusted by selecting the respective atomization conditions. In general, high flow rates of the nebulizer gas used lead to fine particles, which naturally impinge on the workpiece at high speed.

The order rate achieved with conventional systems is about 8 to 20 kg / h, the particle speed about 150 m / s. The spray additive is melted with a thermal energy of about 4,000 ° C. Usually produced layers have a thickness of 0.2 to 20 mm. While wires with a diameter between 1.6 and 3.2 mm are used in conventional systems, they are used in high-performance systems Wires up to 4.8 mm diameter used. The temperature of the arc exceeds the melting temperature of the spray additive by far. The thus overheated droplets may undergo metallurgical reactions with the workpiece surface at the point of impact or lead to the formation of diffusion zones. In this way, especially when using larger droplets, a particularly good adhesion and cohesion of the layer can be achieved.

In this context, it is also known to heat the nebulizer gas stream used. So revealed the EP 0 386 427 A2 an arc spray system with two separately adjustable nozzles, each of which can produce supersonic flows. The atomizing gas used may be highly compressed air, inert gases, active gases and gas mixtures. The preheating serves to increase the flow velocity of the atomizing gas. It is preferably carried out by electrically heated heat exchanger. As a result, the expansion capability and thus the exit velocity of the nebulizer gas is increased as a result of the volume increase associated with the preheating and achieved a finer atomization. Accordingly, a considerable increase in the speed of the spray particles should be achieved even with very high electrical power consumption of the spray gun.

The direct use of electrical energy causes a particularly good efficiency of the arc spraying technique. Due to the process, the selection of the spray additive material is limited to electrically conductive materials that can be supplied as wire. However, this limitation can be partially overcome by the use of cored wires (tube wires). By way of example, carbidic and / or ceramic components can also be sprayed in order to produce hard material layers. Arc spraying is particularly suitable for coating large-area parts. The areas of application include, among others, the corrosion protection, the wear protection, the production or coating of plain bearings and the "rescue" of incorrectly machined machine parts.

During arc spraying, problems arise in that the melting and melting behavior of the two wires guided towards each other, which are each connected as anode and cathode, is different. This leads to a different, difficult to control droplet formation and thereby to a reduction in the quality of a corresponding coating.

There is therefore a need for improvements in arc spraying.

Disclosure of the invention

Against this background, the present invention proposes a method for arc spraying in which at least one wire-shaped spray additive is melted by means of electric current and atomized by means of a Zerstäubergasstrom and applied in the form of a particle stream on a workpiece, and a corresponding device having the features of the independent Claims. Preferred embodiments are subject of the dependent claims and the following description.

Advantages of the invention

According to the invention, a melting behavior of one or more spray additives during arc spraying is improved by preheating at least one of the wire-shaped spray additives in the arc prior to melting. As it has been found according to the invention, this preheating of the filler achieves an increased melting rate.

A pre-heated spray additive stabilizes a melting process, resulting in more reproducible arc spraying results. A molten by means of an arc spray additive can be better atomized and it can, for example due to changes in viscosity properties, an increase in the particle velocity can be effected. Moreover, the advantages achieved according to the invention include a significant saving of energy, and processing of higher melting materials of spray additives is made possible, since by preheating a larger amount of heat (namely, the preheating in addition to that of the arc) can be introduced. In particular, the formation of spatters can be reduced. With spritzers here larger wire detachments are meant, which are generated by short circuits and then uncontrolled, ie with non-adjustable speed, temperature and size, with splashes and then cause layer defects. Furthermore, the preheating can stabilize the overall melting process. More than with a known heating of a nebulizer gas flow, heating can be done individually for each wire. This is particularly advantageous in two-wire systems.

With particular advantage, in the context of the method according to the invention, at least one wire-shaped spray additive material is preheated to a temperature which is between room temperature and a solidus temperature of the spray additive material. In this way, the maximum heat can be introduced into a corresponding spray additive material and at the same time ensure that a corresponding wire-like material can be handled in a spraying device (for example by a feed device). In the context of the method according to the invention, the atomising gas stream is particularly preferably preheated to a temperature which is between room temperature and 1000.degree. This can bring the maximum heat.

Further advantages can be achieved if in addition the atomizing gas stream is preheated. This can, as already mentioned, increase its speed and / or increase the total amount of energy in the system on. The increased Geschwindikeit is particularly very advantageous if on the wire heating already one, in particular a wire-individual, influencing the corresponding material properties has been made. Heating of wire and atomizing gas flow thus possibly provides a disproportionate added value. It can also be done by means of the heating means mentioned below.

With particular advantage, at least one wire-shaped spray additive material and / or the atomizer gas stream is preheated to a temperature which is selected as a function of a material composition, a material quantity and / or a feed rate of the spray additive material. Due to such a procedure, for example, changing wire diameters or material compositions can be taken into account with particular advantage. Correspondingly, significant advantages can be achieved by preheating at least one wire-shaped filler material and / or the atomizer gas flow to a temperature that is selected as a function of a composition and / or a volume flow of the atomizer gas flow. As mentioned, by a speed of the atomizing gas flow in particular the Size of the forming droplets influenced. If a temperature is additionally set as a function of a nebulizer gas flow, a defined droplet size and / or velocity can thereby be achieved.

With particular advantage, at least one wire-shaped spray additive material and / or the atomizer gas stream by means of induction, by means of a plasma and / or by means of a flame, in particular by means of a fuel gas-oxygen flame preheated. The heating by means of a plasma offers in wire heating the particular advantage that in this case also the surface of the wires used by impurities, oxidation products and the like can be cleaned, so that reduced requirements must be placed on the purity of the wires and / or their storage conditions. The process is thereby simpler and cheaper.

A heating device which contains an electric heater, through which the wire-shaped material is guided or through which or flows past the atomizer gas flow, is also advantageous for preheating. The preheating of the wire-shaped filler material via the Zerstäubergasstrom, which in turn can be heated to suitable temperatures, is conceivable or preheating the Zerstäubergasstroms by a preheating device for a wire-shaped spray additive, which in turn can be preheated before melting in the arc. Wire-shaped spray additive material and atomizing gas can also be preheated independently of one another and / or via a common preheating device. The person skilled in the art is aware of processes known from the prior art which ensure a particularly efficient and defined introduction of heat into materials. With particular advantage, the process of the invention can be used when two wire-shaped spray additives are used in arc spraying. These two wire-shaped spray additives can be preheated to the same or different temperatures before melting in the arc, so that, for example, an identical melting rate of two different wire materials is achieved. However, as mentioned, the method according to the invention can also be used in other arc spraying techniques, for example single-wire, vacuum or vacuum single-wire arc spraying. With particular advantage, the method according to the invention can be used when in gaseous spraying Components composed nebulizer gas flow is used. these can For example, include nitrogen, argon, oxygen, hydrogen, helium and mixtures thereof in different proportions. As a result, for example, the thermal conductivity and / or the viscosity of the atomizing gas flow can be adjusted in a targeted manner. At least one of the components can then, if appropriate, be preheated and used to set a total heat.

With regard to the apparatus according to the invention for arc spraying, reference is expressly made to the features and advantages explained on the method side. In particular, such a device comprises at least one preheating device, which is provided for preheating at least one wire-shaped spray additive before melting in the arc and / or at least one preheating device, which is provided for preheating the Zerstäubergasstroms before sputtering of the spray additive. This can be advantageously designed as a burner for generating a burner flame. In particular, in this case, a fuel gas-oxygen burner, as it is known from the prior art, are used. With particular advantage, a preheating device can also be designed as induction heating with an inductor with induction loop or coil. A high frequency (HF) induction heating of known type can be used, for example, to heat one or both wires and / or to indirectly heat the atomizing gas flow, alone or in addition to a flame heating, are used. In such RF induction heaters, a single or multi-turn working coil (inductor) is provided, which is traversed by an alternating current of high frequency. In the vicinity of the coil thereby an electromagnetic alternating field is generated. If a conductor is introduced into this electromagnetic alternating field, a voltage is induced therein, which generates an alternating current. According to Joule's law, according to Q = 1 ² R t (I: current, R: resistance, t: time), heat is generated as a result in the current-carrying surface areas of the conductor. For cooling the coil, a cooling device, for example a water cooling, is advantageously provided. The HF induction heating is advantageously galvanically isolated from the other control components in order to ensure the greatest possible safety. It can be provided to provide interchangeable inductor elements, for example with different inner diameters, in order to ensure adaptability to different wire materials. Depending on the heat output to be introduced and the room requirements, a simple induction loop or a multi-turn inductor may be provided. In particular, a preheating device which is set up as a plasma source can also be provided. Plasma sources, such as plasma torches, are known from the prior art and ensure a particularly efficient introduction of a large amount of energy. In a simple advantageous embodiment, the preheating device comprises an electric heater and is designed such that the wire-shaped filler material can be passed through it for preheating or that nebulizer gas can flow through it or along it to be preheated. As mentioned, a plasma allows a cleaning of the surface of the filler material. In the event that a wire-shaped spray additive and the nebulizer gas is preheated, it makes sense to use one and the same preheater (for example, with electric heater) through which the wire and the gas are passed. Further advantages and embodiments of the invention will become apparent the description and the enclosed drawing.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

The invention is illustrated schematically with reference to an embodiment in the drawing and will be described in detail below with reference to the drawing.

figure description

FIG. 1

shows a schematic representation of an apparatus for arc spraying according to the prior art.

FIGS. 2 and 3

show a schematic representation of a respective device for arc spraying according to a particularly preferred embodiment of the invention.

FIG. 4

shows a partial sectional view of an apparatus for arc spraying according to the prior art.

FIG. 5

shows a partial sectional view of an apparatus for arc spraying according to a particularly preferred embodiment of the invention.

FIG. 6

shows a partial sectional view of an apparatus for arc spraying according to a particularly preferred embodiment of the invention.

In the figures, identical or comparable elements are given identical reference numerals and will not be explained repeatedly for the sake of clarity.

In FIG. 1 FIG. 1 schematically illustrates an apparatus 100 for arc spraying according to the prior art.

In the device 100, a first 1 and a second 2 wire-shaped spray additive are each guided through each other by a wire guide 11, 21. For advancing the wire-shaped spray additives 1, 2 toward each other, feed devices 12, 22 are provided in the form of rollers or rollers rotating in the direction of the arrow.

Furthermore, a current source 3 is provided, which is connected to the wire guides 11, 21 by means of electrical connections 31, 32 for loading the wire-shaped spray additives 1, 2. In an area in which the wire-shaped spray additives have a sufficiently small distance, an arc 30 is formed, through which the material of the wire-shaped spray additives 1, 2 is melted. A nebulizer gas nozzle 4 is provided, by means of which a nebulizer gas flow 41 is provided and guided. The atomizing gas flow 41 causes a sputtering of the wire additives 1, 2 melted in the arc 30 and a formation of a particle stream 5, which can be directed onto a workpiece 6. FIG. 2 shows a device 200 for arc spraying according to a particularly preferred embodiment of the invention in a schematic representation. The device 200 comprises the essential elements of the device 100 FIG. 1 on. In addition, however, preheating devices 10, 20 are provided for the wire-shaped spray additives 1, 2, which preferably surround the wire-shaped spray additives, for example in the form of a wire guide distal to the wire guides 11, 21. As mentioned, the preheating devices 10, 20 be designed as an electric heater, burner, inductors and / or plasma sources. The preheating devices 10, 20 may be configured the same or different and / or based on the same or different preheating principles. By the preheating devices 10, 20 of the wire-shaped spray additive 1, 2 is preheated before reaching the arc 30. It can also be provided to provide the preheating devices at a different position, which enables an effective preheating which is advantageously not in conflict with the application of current via current source 3. In particular, the preheating devices 10, 20 can be provided on the feed device side of the wire guides 11, 21.

FIG. 3 shows a further apparatus 200 for arc spraying according to a particularly preferred embodiment of the invention in a schematic representation. However, for the sake of clarity, the illustration of the preheating devices for the spray additives 1, 2 has been omitted. The device 110 comprises the essential elements of the device 100 FIG. 1 on. In addition, however, a pre-heater 45 is provided for the atomizing gas flow 41, which preferably coaxially surrounds a supply line for the atomizing gas flow 41. As mentioned, the preheater 45 may be configured as an electric heater, burner, inductor and / or plasma source. Several preheating devices 45 may be provided, configured the same or different and / or based on the same or different preheating principles. The preheating device 45 pre-heats the atomizing gas flow 41 before it reaches the arc 30. It can also be provided to provide the preheating device at a different position, which enables an effective preheating which is advantageously not in conflict with the application of current via the current source 3. In particular, the preheating device 45 may be provided proximal to a nebulizer gas nozzle 4.

FIG. 4 shows a device 100 for arc spraying according to the prior art in partial section. The device 100 has a housing 90, which is shown partially opened in a front region 91. Wire-shaped sprayed addition materials 1, 2 are guided through a respective wire guide 11, 21. A wire feed device (such as the wire feed devices 12, 22) is not shown here. To control the feed speed serve adjusting 13, which can be arranged for example on the housing 90 or at another position. A nebulizer gas nozzle 4 is provided, which via a Zerstäubergasanschluss 42 and is configured to form a nebulizer gas flow 41 and a particle stream 5 (both not shown). Between the wire-shaped spray additives 1, 2, an arc 30 forms.

In FIG. 5 a device according to a particularly preferred embodiment of the invention is shown in partial sectional view. The device 300 comprises the essential elements of the device 100 FIG. 4 on. In addition, in device 300, a preheating device is provided for each wire filler material 1, 2 in the form of an inductor 70 with an induction loop or coil 71. The inductors 70 are adapted to act on the induction loops 71 with radio frequency energy as previously explained. By means of a corresponding thermal loading of the wire filler materials 1, 2, these are preheated before reaching the arc 30. The heating can be regulated by means of regulating devices 72, which can be provided on the housing 90. In addition, a conduit 73 is provided for charging the respective inductors 70. ln FIG. 6 1, a device 400 for arc spraying according to a particularly preferred embodiment of the invention is shown in partial section. Like device 300, device 400 comprises the essential features of device 100 FIG. 4 on. In device 400 preheating devices are provided, each of which is designed as a burner 80 for generating a burner flame 81. As before, a preheat amount can be adjusted by the burners 80 by means of a controller 82. To feed the burner 80 supply lines for example, fuel gas and / or oxygen are provided.

Although in the above figures identical preheating devices were each shown in isolation for both wire addition materials 1, 2, it should be understood that in particular, it is also possible to provide different wire addition materials 1, 2 with different and / or multiple and / or common preheating devices 10, 20 to act on. For example, provision may be made for preheating by means of a burner 80 in a first step and preheating by means of an inductor 70 in a second step FIG. 7 a device according to a particularly preferred embodiment of the invention is shown in partial sectional view. The device 120 comprises the essential elements of the device 100 FIG. 4 on. However, for the sake of clarity, the illustration of the preheating devices for the spray additives 1, 2 has been omitted. In addition, in device 120, a preheating device 45 for the atomizing gas flow 41, which is provided via leads 47 via a nozzle 4, is provided. The heating can be regulated by means of a regulating device 46 which can be provided on the housing 90. Although in each case a single preheating device 45 was specified in connection with the preceding figures, it should be understood that in particular it can also be provided that several and / or or to provide different preheating devices 45 and / or to heat wire consumables 1, 2 with different and / or multiple and / or common preheating devices 45. For example, provision may be made for preheating by means of a burner in a first step and preheating by means of an inductor in a second step.

Claims (12)

Method for arc spraying, in which at least one wire-shaped spray additive (1, 2) is melted by means of electric current in an arc (30) and atomized by means of a nebulizer gas stream (41) and applied to a workpiece (6) in the form of a particle stream (5), characterized in that at least one wire-shaped spray filler material (1, 2) is preheated in the arc (30) before melting. The method of claim 1, wherein at least one wire-shaped spray additive (1, 2) is preheated to a temperature between room temperature and a solidus temperature of the spray additive (1, 2). The method of claim 1 or 2 further comprising preheating the nebulizer gas stream (41) prior to nebulizing the at least one wire-form spray additive. A method according to claim 3, wherein the atomizing gas flow (41) is preheated to a temperature between room temperature and 1000 ° C. Method according to one of claims 1 to 4, wherein at least one wire-shaped spray additive material (1, 2) is preheated to a temperature which is selected depending on a material composition, a material amount and / or a feed rate of the spray additive material (1, 2). Method according to one of claims 1 to 5, wherein at least one wire-shaped spray additive material (1, 2) is preheated to a temperature which is selected in dependence on a composition and / or a volume flow of the atomizing gas flow (41). Method according to one of claims 1 to 6, wherein at least one wire-shaped spray additive (1, 2) by means of induction, by means of an electric heater and / or by means of a plasma and / or by means of a flame (81), in particular by means of a fuel gas oxygen Flame, and / or preheated by means of a heated atomizing gas flow (41). Method according to one of the preceding claims, wherein at least two wire-shaped spray additives (1, 2) are used and preheated before melting in the arc (30) to the same or different temperatures. A method according to any one of the preceding claims, wherein a nebulizer gas stream (41) is used of gaseous components comprising nitrogen, argon, oxygen, hydrogen, helium and mixtures thereof in different proportions. The method of claim 9, wherein at least one of the gaseous components of the nebulizer gas stream (41) is preheated. Arc-spraying apparatus adapted to carry out a method according to any one of the preceding claims, comprising at least one preheating means (10, 20, 70, 80) for preheating at least one wire-shaped spray additive (1, 2) before melting in the arc ( 30) is provided. Apparatus according to claim 11, in which at least one preheating device (10, 20, 70, 80, 45) is designed as a burner (80) for producing a burner flame (81) or an inductor (70) with an induction loop and / or induction coil (71 ) or a plasma source or an electric heater.

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