EP2562287A2 - Method and device for thermal spraying of coating materials - Google Patents

Abstract

The method comprises melting a coating material, which is present in the form of spray wire, and thermally spraying the coating material by an atomizing gas and/or combustion gas. The melted coating material is displaced by coupling of ultrasound in vibrations during melting. The ultrasound is directly coupled to the coating material in which: an ultrasonic generator (6) is brought in direct contact with the melted coating material; and an ultrasound is formed by a modulation or pulse-like variation of the current of the power supply. The method comprises melting a coating material, which is present in the form of spray wire, and thermally spraying the coating material by an atomizing gas and/or combustion gas. The melted coating material is displaced by coupling of ultrasound in vibrations during melting. The ultrasound is directly coupled to the coating material in which: an ultrasonic generator (6) is brought in direct contact with the melted coating material; and an ultrasound is formed by a modulation or pulse-like variation of the current of the power supply and by a modulation or pulse-like variation of an atomizing gas- and/or combustion gas-gas stream, where: the current changes its direction; the current direction change is carried out within ten seconds to pico seconds; and a current strength is 0.01-3000 Å . The ultrasound is indirectly coupled to the coating material in which: an ultrasonic generator is brought in contact with the melted coating material via a wire guide; and an ultrasonic generator is arranged in a gas stream of the atomizer- and/or combustion gas in a flow direction or a nozzle is designed as the ultrasonic generator, which couples the ultrasound indirectly via the gas stream into the melted coating material. The ultrasound is present in a frequency range of 15 kHz to 10 MHz. The thermal spraying step is carried out by a wire flame spraying and an electric arc. The atomizing gas is preheated to increase the temperature during arc spraying process. An independent claim is included for a device for thermal spraying of coating materials.

Description

Field of application and state of the art

The invention relates to a method and an apparatus for thermal spraying of coating materials.

Various coating devices are known which involve coating a substrate by means of atomized materials.

The DE 102 52 437 A1 describes an ultrasonic standing wave atomizer assembly for generating a paint spray for painting a workpiece. The ultrasonic standing wave atomizer assembly is designed to increase the sprayed paint quantity, ie the paint rate, during a painting process, while maintaining a selected range of droplet sizes. With the ultrasonic standing-wave atomizer arrangement, a stationary ultrasonic field with selected maxima is generated, wherein pipe sections for applying paint are provided in the region of the stationary ultrasonic field. Characteristic here is that a liquid present paint in the ultrasonic field in droplet form transferred, that is atomized. A disadvantage of this arrangement is the need for a complex control technique that controls and regulates the formation of the ultrasonic wave maxima. In addition, the frequencies or the frequency range for the formation of the maxima are limited at a given distance of the opposite sound surfaces.

The DE 37 35 787 A1 describes a method and apparatus for atomizing at least one jet of liquid, preferably molten metal, wherein the liquids are passed through the ultrasonic field within a compressed gaseous medium. The detected as disadvantageous low ultrasonic power is encountered with a compressed gaseous medium. With the compressed, that is under pressure medium, a higher energy transfer of the ultrasonic field is possible. The high density of the gas thus promotes the sound transmission, in particular because of better impedance matching. The ultrasonic oscillators are arranged perpendicular or transverse to the beam direction. It is also characteristic here that a jet of liquid material is atomized only by means of a downstream ultrasonic field. The gaseous, compressed medium merely increases the efficiency of the ultrasound transmission. A disadvantage of this arrangement is the need to use a compressed, so under pressure gaseous medium.

For the atomization of liquids, the literature discloses methods in which capillary waves are generated by the use of ultrasound on liquid surfaces, which finally leads to constriction and drop formation ( Günter Wozniak, atomization technique, chapter 5, Springer, Berlin Heidelberg 2003, ISBN 3-540-41170-4 ).

From the literature ( Modern Surface Technology, Edited by F.-W. Bach, A. Laarmann, T. Wenz, Wiley-VCH, Weinheim 2004, ISBN 3-527-31532-2 ), a number of methods for producing thermal spray coatings on the surface of a workpiece are known, for which the term "thermal spraying" is usually used.

When coating a workpiece by means of thermal spraying, the spray materials, usually metals or their alloys, but also ceramics, carbides or plastics / polymers, melted by the supply of thermal energy, melted or melted and accelerated by means of a gas jet.

The definition of thermal spraying according to DIN EN 657 is as follows: "Thermal spraying involves processes in which spray additives inside or outside spraying equipment are melted, melted or melted onto prepared surfaces and the surfaces are not melted." DIN EN 657 includes i.a. the following methods under the term "thermal spraying" together: arc spraying, plasma spraying, detonation spraying, laser spraying, induction spraying, molten bath spraying and (wire) flame spraying.

By melting the material liquefies, which is then atomized by the gas flow and simultaneously thrown on the surface to be sprayed. Some of the methods listed above, such as plasma spraying or detonation spraying (flame spraying is available with both powders and wires or rods) use powders that dictate particle size from the start. The particles formed by melting and atomization are the so-called spray particles, which reach the surface to be sprayed by the gas jet. In this case, the spray particles reach high speeds, depending on the method speeds between a few tens of meters per second up to 1500 meters per second (Lecture script "thermal spraying", E. Beyer, TU Dresden 2005) are achieved with which the materials finally on a Impact substrate. The impinging droplets or particles dig into the surface of the workpiece (mechanical stapling mechanism). In this process, the impinging, mostly still liquid coating material adapts to the contour of the surface to be coated, which on cooling to the formation of shrinkage stresses in the deposited layer can lead. Mechanical clamping is an essential adhesive mechanism, but not the only one, with no detailed reference to the different adhesive mechanisms, depending on the material.

The supply of thermal energy can take place, inter alia, in the form of electrical energy (arc spraying and plasma spraying) or chemical energy by burning liquid or gaseous fuels (for example wire flame spraying). In some cases, the energy is coupled in optically, inductively or capacitively. The spray material is already present in some processes as a powder or as a suspension and is supplied by means of a suitable conveying device (for example plasma spraying, flame spraying).

In many cases, however, is used on spraying materials in the form of wires, cored wires, rods or cords (collectively referred to as "spray wire"). In these cases, the spray material after melting must first be atomized by a suitable atomizing gas before it is accelerated by the most common gas and spun onto the surface of the workpiece. Depending on the process and requirements for the materials, compressed air, inert gases such as nitrogen, argon or helium, reactive or reducing gases (oxygen or hydrogen), gas mixtures or simply the combustion gases which also supply the thermal energy are used as atomizing gas.

Gas stream atomization is a stochastic, random process that results in a broad size distribution with particles of less than one micron up to more than 200 microns in diameter, which occur simultaneously (polydisperse). The known methods for producing thermal spray coatings on the surface of a workpiece have the disadvantage that very large particles in the gas jet are accelerated only insufficient, whereas small particles can already solidify before impact, which has a negative effect on the layer properties.

For influencing the particle size distribution during thermal spraying, the control variable is primarily the speed of the atomizing gas flow. On the gas flow can be influenced only to a limited extent by the choice of gas type, pressure, gas temperature or nozzle geometry, but the problem of a broad particle size distribution remains.

Task and solution

The object of the invention is to provide a method and a device for thermal spraying of coating materials, wherein the disadvantages known from the prior art are avoided and the droplet size distribution or the spray particle size distribution of the coating materials can be specifically influenced.

This object is achieved by a method for thermal spraying of coating materials, which are usually in the form of spray wires, wherein the material to be melted melted during melting by coupling of ultrasound into vibrations and by means of a Zerstäubergases or by means of the combustion gas (mixture from fuel gas and oxygen / compressed air) is atomized. For the purposes of this invention, thermal spraying is preferably understood to mean wire flame spraying and arc spraying, the latter being preferred. In wire flame spraying, the mixture of fuel gas and oxygen or compressed air (combustion gas) simultaneously serves as a means of melting and as a sputtering gas, in arc spraying, only a Zerstäubergas is used, since the melting takes place through the arc.

Combustion gas is synonymously understood as meaning the mixture of fuel gas or liquid fuel and oxygen or compressed air.

In a preferred embodiment of the method for thermal spraying of coating materials, the ultrasound is coupled directly into the coating material to be melted by exposing at least one ultrasonic generator directly to the coating material to be melted, i. the spray wire, is brought into contact.

In a further embodiment of the method for thermal spraying of coating materials, the ultrasound is indirectly coupled into the coating material to be melted by bringing the at least one ultrasound generator into contact with the meltable coating material via a contact-containing wire guide.

In a further embodiment of the method for thermal spraying of coating materials, the ultrasound is indirectly coupled into the coating material to be melted by arranging at least one ultrasound generator in the gas flow of the atomizer or the combustion gas or the gas nozzle or burner nozzle itself being designed as an ultrasound generator indirectly injects the ultrasound via the gas stream in the aufzuschmelzende coating material.

In a further embodiment of the method for thermal spraying of coating materials, the ultrasound is coupled directly into the coating material to be melted by forming the ultrasound by means of modulation or pulse-like variation of the current of the current supply, the current changing direction (polarity change), the current direction change within Tenth of a second to picoseconds occurs and the current is between 0.01 amps and 3000 amps. This is particularly applicable to arc spraying.

In a further embodiment of the method for thermal spraying of coating materials, the ultrasound is coupled directly into the coating material to be melted by forming the ultrasound by means of modulation or pulsed variation of the atomizing gas stream or of the combustion gas stream.

The ultrasound is in the frequency range from 15 kHz to 10 MHz.

The sprayed from the coating material spray particles are accelerated by means of atomizing gas or combustion gas at speeds of ten meters per second up to 1500 meters per second.

In a further embodiment of the method for the thermal spraying of coating materials, the atomizing gas or the combustion gas is preheated, preferably to temperatures above room temperature, more preferably to 100-1000 ° C., most preferably to 300-600 ° C. This preheating takes place exclusively during arc spraying.

In wire flame spraying, preheating is unnecessary since the temperature of the combustion gas is already well above the melting point of the spray wire (Flame Spraying Literature Data: Combustion Temperatures Typically 2660 ° C (Hydrogen), 2850 ° C (Propane) and 3160 ° C (Acetylene)) ,

The object is further achieved according to the invention by a device having at least one spray wire (1, 1 ') with aufzuschmelzendem wire end (2, 2') and at least one Drahtzuführvorrichtung (3, 3 '), which wire feed (4, 4') and contact-making wire guide (5, 5 '), wherein at least one ultrasonic generator (6, 6') on at least one spray wire (1, 1 ') is arranged.

As mentioned above, the two preferred variants of thermal spraying are wire flame spraying and arc spraying.

When wire flame spraying, the apparatus for performing the method, a burner nozzle (7), in which the melted end (2) of the at least one spray wire (1) is located. This burner nozzle (7) has entrances for fuel gas (8) and oxygen / compressed air (9), the mixture of which supplies the combustion gas. As fuel gases, the common process gases or flammable liquids are used, in particular acetylene, propane, ethene, methane, natural gas, hydrogen, acetylene being preferred.

In arc spraying, the apparatus for carrying out the method comprises a first and second spray wire (1, 1 ') with wire ends (2, 2') to be fused and two wire feeders (3, 3 '), each of which wire feed (4, 4') and contacting wire guide (5, 5 '), as well as electrical connections (10, 10') for the generation of the arc (11) between the fusible wire ends (2, 2 '). The at least one ultrasound generator is arranged either on the first or second spray wire (1, 1 ').

In a preferred embodiment, two ultrasonic transmitters (6, 6 ') are provided, one of which is arranged on the first and the other on the second spray wire (1, 1'). This preferred form with two ultrasonic transmitters applies both to direct and indirect coupling of the ultrasound into the spray wires (explained in more detail below).

The following explanations relate both to wire flame spraying and to arc spraying.

In one embodiment of the device, the at least one or the ultrasound transmitters (6, 6 ') are arranged directly on at least one or on the first and / or second spray wire (1, 1') and thus directly couple the ultrasound.

In a further embodiment of the device, the at least one or the ultrasound transmitters (6, 6 ') are arranged on the wire guide (5, 5') and thus couple the ultrasound into the at least one or the first and / or second spray wire (FIG. 1, 1 ') indirectly.

In a further embodiment of the device, at least one ultrasound generator (6) is arranged in the gas flow (12) in the flow direction, wherein the ultrasound generator (6) directs the ultrasound indirectly via the gas flow (12) of the atomizing or combustion gas into the at least one or the first and / or second spray wire (1, 1 ') coupled.

This is a method and a device for the thermal spraying of coating materials, preferably by means of wire flame or arc spraying, particularly preferably by means of an arc, wherein the ultrasound coupled into the coating material effects a favorable spray particle formation and separation. According to the invention, a narrow spray particle size distribution is achieved by means of ultrasound application, which in the ideal case is monodisperse, ie all particles have the same size. In practice, particle size distributions result in which at least 50 percent of the particles differ in diameter less than twenty percent from an average, preferably 70 percent of the particles in diameter deviate less than 15 percent from the mean, and most preferably more than 90 percent of the particles in diameter less than 10 percent of the mean value, whereby the mean value can be set by the frequency of the ultrasound. Because of the low dynamic viscosity at very high surface tension of liquid metals, the atomization by means of ultrasound for metals works particularly well in comparison to water or melted plastics.

The mean spray particle size depends on the frequency of the ultrasound. Possible sizes are between 200 microns to less than a micrometer. Favorable particle sizes are from a few microns to a few tens of microns, depending on material and application. Higher frequencies result in smaller particles and vice versa. A controlled adjustment of a defined size of the particles produced is desirable because different applications are to be realized. For example, where closed non-porous spray coatings are desired, smaller particles are produced, i. higher frequencies of ultrasound applied. When porous layers are desired, a lower frequency of ultrasound is used to produce larger particles which then form porous layers when applied to the substrate.

With decreasing spray particle size, the oxidation plays an increasingly important role, whereby the oxidation can be reduced or prevented with a shielding gas (relevant in arc spraying). Small spray particles can better follow the gas flow, which is advantageous for a controlled coating process.

Description of the figures

Fig. 1

eine Vorrichtung für das Drahtflammspritzen

Fig. 2

eine Vorrichtung zum Lichtbogenspritzen mit Ultraschallgebern an den Spritzdrähten

Fig. 3

eine Vorrichtung zum Lichtbogenspritzen mit im Gasstrom angeordneten Ultraschallgebern

The invention will be explained below with reference to drawings. It shows:

Fig. 1

a device for wire flame spraying

Fig. 2

a device for arc spraying with ultrasound transmitters on the spray wires

Fig. 3

a device for arc spraying with arranged in the gas flow ultrasonic generators

Fig. 1 shows a device for wire flame spraying, in which a spray wire 1 is held with a fusible wire end 2 of a wire feeder 3 or guided. This wire feed device 3 consists of a wire feed 4 and a wire guide 5, wherein the ultrasonic generator 6 is arranged directly on the latter. The spray wire 1 continues to pass through a burner nozzle 7, which has accesses for fuel gas 8 and accesses for oxygen / compressed air. The combustion gas, whose temperature is above the melting temperature of the spray wire 1, melts the spray wire 1 at the wire end 2 to be melted. In the melting zone 21, the spray stream 22, which contains spray particles 23, is formed by the gas stream 12. These form the sprayed layer 24 when it strikes the substrate 25.

In this embodiment, ultrasonic vibrations are introduced directly into the spray wire. This results in advantages that little control technology is required and a high efficiency compared to methods that are known from the prior art, is achieved.

Fig. 2 shows an apparatus for arc spraying with injection wires 1, 1 ', which have to be melted wire ends 2, 2'. The spray wires are guided by wire feeders 3, 3 'which consist of wire feeders 4, 4' and wire guides 5, 5 ', with the ultrasonic transmitters 6, 6' being arranged directly on the latter. Electrical connections 10, 10 'in conjunction with the power supply 14 are used to generate the arc 11. By the arc 11 to be melted wire ends 2, 2' of the spray wires 1, 1 'melted, resulting from the gas flow 12 in the molten zone 21 of the spray jet 22 is generated, which contains the spray particles 23. These are applied to the substrate 25 when impinging as a spray coating 24.

In this embodiment, ultrasonic vibrations are also introduced directly into the spray wire. This results in advantages that little control technology is required and a high efficiency compared to methods that are known from the prior art, is achieved.

Fig. 3 shows an embodiment of the arc spraying, wherein the ultrasonic vibrations indirectly in the spray wires 1, 1 'to be melted wire ends 2, 2' introduced become. The apparatus shown comprising wire feeders 3, 3 'with wire feeders 4, 4' and wire guides 5, 5 'corresponds to the one in FIG Fig. 2 shown. The ultrasound generator 6 is arranged here in the gas flow 12, so that the ultrasonic waves are transmitted to the atomizing gas and then to the wire ends 2, 2 'to be fused.

The ultrasonic vibrations are introduced in this embodiment in the gas stream 12 (impedance matching necessary), but not transversely to this, but in the flow direction, preferably before the gas stream 12, the arc 11 with the aufzuschmelzenden spray material (1,1 ', 2, 2') passes , Another advantage here is the simple integration into existing systems.

LIST OF REFERENCE NUMBERS

1, 1 '

spray wire

2, 2 '

to be melted wire end

3,3 '

wire feeder

4,4 '

wire feed

5.5 '

wire guide

6.6 '

ultrasonic generator

7

burner

8th

Access for fuel gas

9

Access for oxygen / compressed air

10, 10 '

electrical connections

11

Electric arc

12

gas flow

14

power supply

21

fusion zone

22

spray jet

23

spray particles

24

spray layer

25

substratum

Claims (16)

A method for thermal spraying of coating materials, wherein the coating material, which is in the form of at least one spray wire is melted and atomized by means of a Zerstäubergases or combustion gas, characterized in that the meltable coating material is set during the melting by coupling of ultrasound into vibrations. A method for thermal spraying of coating materials according to claim 1, characterized in that the ultrasound is coupled directly into the to be melted coating material by at least one ultrasonic generator is brought directly into contact with the meltable coating material. A method for thermal spraying of coating materials according to claim 1, characterized in that the ultrasound is indirectly coupled into the meltable coating material by the at least one ultrasonic transducer is brought via a contact-making wire guide with the melted coating material in contact. Method for the thermal spraying of coating materials according to Claim 1, characterized in that the ultrasound is indirectly coupled into the coating material to be melted by arranging at least one ultrasound generator in the gas flow of the atomizing or combustion gas in the flow direction or the nozzle itself being designed as an ultrasound generator, which indirectly couples the ultrasound via the gas flow into the meltable coating material. A method for thermal spraying of coating materials according to claim 1, characterized in that the ultrasound is coupled directly into the meltable coating material by the ultrasound is formed by modulation or pulse-like variation of the current of the power supply, the current changes its direction (polarity change) Change in current direction within tenths of a second to picoseconds and the current is between 0.01 amperes and 3000 amps. A method for thermal spraying of coating materials according to claim 1, characterized in that the ultrasound is coupled directly into the coating material to be melted by the ultrasound is formed by means of modulation or pulse-like variation of the Zerstäubergas- or combustion gas gas stream. Method for the thermal spraying of coating materials according to one or more of Claims 1 to 6, characterized in that the ultrasound lies in the frequency range from 15 kHz to 10 MHz. A method for thermal spraying of coating materials according to one or more of claims 1 to 7, characterized in that the thermal spraying is effected by means of an arc. Method for the thermal spraying of coating materials according to one or more of claims 1 to 7, characterized in that the thermal spraying is carried out by means of wire flame spraying. A method for thermal spraying of coating materials by means of an arc according to one or more of claims 1 to 8, characterized in that the atomizing gas is preheated during arc spraying to increase the temperature. Apparatus for carrying out the method according to one or more of Claims 1 to 10, having at least one spray wire (1, 1 ') with a wire end (2, 2') to be melted and at least one wire feed device (3, 3 '), which wire feed (4, 4 ') and contacting wire guide (5, 5'), characterized in that at least one ultrasonic generator (6, 6 ') on at least one spray wire (1, 1') is arranged. Device for carrying out the method according to claim 11 by means of wire flame spraying in which a burner nozzle (7) is present, in which the meltable end (2, 2 ') of the at least one spray wire (1, 1') is located, and which approaches for fuel gas ( 8) and oxygen / compressed air (9) (combustion gas). Apparatus for carrying out the method according to claim 11 by means of arc spraying with a first and second spray wire (1, 1 ') to be melted wire ends (2, 2') and two wire feeders (3, 3 '), which wire feed (4, 4') and contact wire guide (5,5 ') and electrical connections (10, 10') for the production an arc (11) between the fusible wire ends (2, 2 ') comprise, characterized in that at least one ultrasonic transducer (6, 6') on the first and / or second spray wire (1, 1 ') is arranged. Device according to one of claims 11 to 13, characterized in that the at least one ultrasound generator (6, 6 ') directly on at least one spray wire (1, 1') or on the first and / or second spray wire (1, 1 ') is and thus directly couples the ultrasound. Device for carrying out the method according to one or more of claims 1 to 14, characterized in that the at least one ultrasound generator (6, 6 ') on the at least one wire guide (5, 5') is arranged and thus the ultrasound in the at least one Spray wire (1, 1 ') indirectly coupled. Device for carrying out the method according to one or more of Claims 1 to 15, characterized in that at least one ultrasound generator (6) is arranged in the gas flow (12) in the direction of flow, the ultrasound transmitter (6) directing the ultrasound indirectly via the gas flow (12). the atomizer or combustion gas in the at least one spray wire (1, 1 ') couples.

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