DE102012107076A1 - Method and device for thermal spraying of coating materials - Google Patents

Abstract

The present invention relates to 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 nebulizer gas or combustion gas, characterized in that the to be melted coating material during melting by coupling of ultrasound into vibrations is offset. Likewise, the invention relates to a device for carrying out the method.

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 is after DIN EN 657 : "Thermal spraying involves processes where spray additives are sprayed on, melted or melted inside or outside spray equipment and spin-coated onto prepared surfaces. The surfaces are not melted. "DIN EN 657 summarizes the following processes under the term" thermal spraying ": 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 incident fits, usually still liquid coating material to the contour of the surface to be coated, which can lead to the formation of shrinkage stresses in the deposited layer on cooling. 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.

To influence the particle size distribution during thermal spraying, the controlled variable is primarily the velocity of the atomizing gas stream. 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 atomizing or combustion gas in the flow direction or the gas nozzle or burner nozzle itself Ultrasonic transducer is formed, which couples the ultrasound indirectly via the gas flow 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 with at least one spray wire ( 1 . 1' ) with the wire end to be melted ( 2 . 2 ' ) and at least one wire feed device ( 3 . 3 ' ), which wire feed ( 4 . 4 ' ) and contact wire guide ( 5 . 5 ' ), wherein at least one ultrasound 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.

In wire flame spraying, the device for carrying out the method has 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 ( 8th ) 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 device for carrying out the method has a first and second spray wire ( 1 . 1' ) with wire ends to be melted ( 2 . 2 ' ) and two wire feeders ( 3 . 3 ' ), which each wire feed ( 4 . 4 ' ) and contact wire guide ( 5 . 5 ' ), as well as electrical connections ( 10 . 10 ' ) for the generation of the arc ( 11 ) between the ends of the wire to be melted ( 2 . 2 ' ). The at least one ultrasound generator is either on the first or second spray wire ( 1 . 1' ) arranged.

In a preferred embodiment, two ultrasonic transmitters ( 6 . 6 ' ), one of which at the first and the other at the second spray wire ( 1 . 1' ) is arranged. 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 ' ) directly on at least one or on the first and / or second spray wire ( 1 . 1' ) and thus couple the ultrasound directly.

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

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

This is a method and a device for thermal spraying of coating materials, preferably by means of wire flame or arc spraying, more preferably by means of an arc, wherein the ultrasound coupled into the coating material effects a favorable spraying particle formation and separation. According to the invention, a narrow spray particle size distribution is achieved by means of ultrasound application, which is ideally monodisperse, i. all particles are 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

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

1 a device for wire flame spraying

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

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

1 shows a device for wire flame spraying, in which a spray wire 1 with a wire end to be melted 2 from a wire feeder 3 is held or led. This wire feeder 3 consists of a wire feed 4 and a wire guide 5 , wherein at the latter the ultrasonic generator 6 is arranged directly. The spray wire 1 continues through a burner nozzle 7 which accesses for fuel gas 8th and accesses for oxygen / compressed air. The combustion gas whose temperature is above the melting temperature of the spray wire 1 lies, melts the spray wire 1 at the wire end to be melted 2 on. In the melting zone 21 forms through the gas flow 12 the spray jet 22 , which spray particles 23 contains. These form the sprayed layer 24 when hitting 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.

2 shows a device for arc spraying with spray wires 1 . 1' , which ends of the wire to be melted 2 . 2 ' exhibit. The spray wires are from wire feeders 3 . 3 ' guided, which from wire feeds 4 . 4 ' and wire guides 5 . 5 ' exist, with the latter directly the ultrasonic transducer 6 . 6 ' are arranged. Electrical connections 10 . 10 ' in connection with the power supply 14 are used to generate the arc 11 , Through the arc 11 become the wire ends to be melted 2 . 2 ' the spray wires 1 . 1' melted, resulting from the gas flow 12 in the melting zone 21 the spray jet 22 is generated, the spray particles 23 contains. These are when impact as a spray coat 24 on the substrate 25 applied.

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.

3 shows an embodiment of the arc spraying, in which the ultrasonic vibrations indirectly in the spray wires 1 . 1' with wire ends to be melted 2 . 2 ' be initiated. The device shown comprises wire feeders 3 . 3 ' with wire feeds 4 . 4 ' and wire guides 5 . 5 ' corresponds to the in 2 shown. Of the

ultrasonic generator 6 is here in the gas stream 12 arranged so that the ultrasonic waves on the atomizing gas and then on the wire ends to be melted 2 . 2 ' be transmitted.

The ultrasonic vibrations are in this embodiment in the gas stream 12 initiated (impedance matching necessary), but not across this, but in the flow direction, preferably before the gas flow 12 the arc 11 with the sprayable material to be melted ( 1 . 1' . 2 . 2 ' ) happens. 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

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10252437 A1 [0003]
• DE 3735787 A1 [0004]

Cited non-patent literature

• Günter Wozniak, atomization technique, chapter 5, Springer, Berlin Heidelberg 2003, ISBN 3-540-41170-4 [0005]
• Modern Surface Technology, Edited by F.-W. Bach, A. Laarmann, T. Wenz, Wiley-VCH, Weinheim 2004, ISBN 3-527-31532-2 [0006]
• DIN EN 657 [0008]

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 melted 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. Device for carrying out the method according to one or more of claims 1 to 10 with at least one spray wire ( 1 . 1' ) with the wire end to be melted ( 2 . 2 ' ) and at least one wire feed device ( 3 . 3 ' ), which wire feed ( 4 . 4 ' ) and contact wire guide ( 5 . 5 ' ), characterized in that at least one ultrasound generator ( 6 . 6 ' ) on at least one spray wire ( 1 . 1' ) is arranged. Apparatus 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 melted end ( 2 . 2 ' ) of the at least one spray wire ( 1 . 1' ), and which fuel gas ( 8th ) and oxygen / compressed air ( 9 ) (Combustion gas). Apparatus for carrying out the method according to claim 11 by arc spraying with a first and second spray wire ( 1 . 1' ) with wire ends to be melted ( 2 . 2 ' ) and two wire feeders ( 3 . 3 ' ), which wire feed ( 4 . 4 ' ) and contact wire guide ( 5 . 5 ' ) as well as electrical connections ( 10 . 10 ' ) for the generation of an arc ( 11 ) between the ends of the wire to be melted ( 2 . 2 ' ), characterized in that at least one ultrasound generator ( 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 arranged and thus couples the ultrasound directly. 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 ' ) and thus the ultrasound in the at least one spray wire ( 1 . 1' ) indirectly. Device for carrying out the method according to one or more of claims 1 to 15, characterized in that in the gas stream ( 12 ) in the flow direction at least one ultrasonic generator ( 6 ), wherein the ultrasound generator ( 6 ) the ultrasound indirectly via the gas flow ( 12 ) of the atomizer or combustion gas into the at least one spray wire ( 1 . 1' ).

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