EP1999297B1 - Cold-gas spray gun - Google Patents

Description

The invention relates to a device for cold gas spraying. In particular, the invention relates to a cold gas spray gun and a device with such a cold gas spray gun and a method that uses a cold gas spray gun according to the invention.

In cold gas spraying or kinetic spraying, powder particles from 1 μm to 250 μm are accelerated in a gas stream to speeds of 200 m / s to 1600 m / s without melting or fusing, and sprayed onto the surface to be coated, the substrate. Only upon impact with the substrate does the temperature increase at the colliding interfaces due to plastic deformation under very high strain rates and leads to welding of the powder material to the substrate as well as to each other. For this, however, a minimum impact speed must be exceeded, the so-called critical speed. The mechanism and quality of welding are comparable to explosive welding. By heating the process gas, the sound velocity of the gas is increased, thereby increasing the flow velocity of the gas in the nozzle and thus also the particle velocity upon impact. The gas may e.g. in a Laval nozzle, i. an initially diverging up to a nozzle throat, then diverging nozzle to be accelerated to supersonic speed, wherein the powder material is injected before or after the nozzle throat in the gas jet and accelerated toward the substrate.

The particle temperature on impact increases with the process gas temperature. This leads to a thermal softening and ductilization of the powder material and lowers the critical velocity of the impacting particles. As the speed of sound also increases, raising the process gas temperature increases both particle velocity and particle temperature upon impact. Both have a positive effect on the order efficiency and coating quality. The process gas temperature always remains below the melting temperature of the Spraying used powder material. In the cold gas spraying method, therefore, a "colder" gas is used in comparison to other spraying methods in which the powder particles are melted by the gas. As with injection molding, where filler metals are melted by hot gas, the gas must be heated in cold gas spraying as well.

In order to be able to accelerate powder particles, in particular coarser particles between 25 and 100 μm, gas at high pressure is necessary. For this purpose, the components of a device for cold gas spraying must be designed to be pressure-resistant. Most systems for stationary operation are designed for 30 bar, whereby the individual modules are designed for the necessary pre-pressure of approx. 35 bar. Some plant types are even designed only for pressures up to 15 bar or for pressures up to 7 bar. If, as desired, the pressure is to be further increased and the high temperature can act directly on the material of the contact surfaces of the components, this leads to the fact that expensive and difficult to process high-temperature materials must be used or the component, in particular a spray gun, by his Size and the necessary wall thicknesses becomes relatively heavy. The heat removal via the contact surface also leads to losses and an undesirable drop in the gas temperature, in particular in front of the nozzle throat of the Laval nozzle.

From the US 6,623,796 B1 is a spray gun with a Laval nozzle known, consisting of an input cone and an output cone, which abut one another at a nozzle neck. The Laval nozzle is supplied with air under high pressure via an air heater and a mixing chamber in which an air powder is mixed. The powder is accelerated through the Laval nozzle as a supersonic nozzle and heated by the air heated in the air heater without it melts.

A disadvantage of this prior art is that the material strength and strength of the components of the spray gun must be designed very large in order to withstand the high pressure at high temperatures of the material can, as the material strength decreases sharply with temperature.

From the US 2002/033135 A1 is a spray gun with a nozzle, a mixing chamber and a decoupled from the mixing chamber high-pressure gas heater known. The gas is passed through a hose directly into the mixing chamber.

In the WO 2006/034777 A1 a spray gun with a nozzle and a mixing chamber is shown. The gas is heated in a separate preheater and passed by a hose to the spray gun, the preheater is thus arranged independently of the spray gun. On the spray gun, a reheater is arranged.

From the US 2007/0160769 A1 is a spray gun with a high-pressure gas heater which is arranged on the mixing chamber is known, but without a nozzle.

From the post-published DE 102005004116 is a cold gas spray gun with a nozzle for accelerating gas jet and particles known to be in one converges converging nozzle portion and a nozzle outlet, which merge into one another at the nozzle neck, and a powder injection tube which ends more than 40 mm in front of the nozzle throat.
From the post-published DE 102005004117 a device for cold gas spraying with a spray gun with a nozzle and a heater for gas heating is known, wherein the heating is divided into at least two heaters for gas heating and a post-heater is attached directly to the spray gun while a second, freestanding preheater via a line with the spray gun connected is.
From the post-published DE 102005053731 a device for high-pressure gas heating with a gas-flowed pressure vessel, a arranged in the pressure vessel heating element and insulation is known. The insulation is arranged on the inner wall of the pressure vessel and there are means for heat dissipation of the pressure vessel so that the pressure vessel has a lower temperature than the heated gas.
It is therefore an object of the invention to provide a device for cold gas spraying, in particular a spray gun, which can be operated with gas under high temperatures and pressures and yet has a low weight and has an easy-to-carry spray gun.
This object is achieved by a cold gas spray gun having the features of independent claim 1. Advantageous developments of the device are specified by the subclaims.
Advantageously, with the cold gas spray gun according to the invention, the usable process gas pressure can be raised to well above 35 bar without excessively increasing the weight of the cold gas spray gun due to large material and wall thicknesses. Due to the internal insulation of the high-pressure gas heater and / or mixing chamber and the Laval nozzle, the components under pressure can be operated at significantly lower temperatures and thus higher material strength. The insulation further avoids unnecessary thermal losses to the environment and creates less Cost of gas heating. Finally, there is also a lower inertia of the cold gas spray gun when commissioning, since not the relatively large masses of wall material must be heated, and increased durability, due to the lower temperature stress of the materials. Increasing the process gas pressure and thus increasing the gas density, together with an increase in the process gas temperature and the use of coarser particles, has a particularly advantageous effect on the quality of the coating and becomes possible only through the internal insulation. Also, despite high process gas pressure and process gas temperatures, a high efficiency of the injection can be achieved and the disadvantages of a low gas density and smaller cross sections are avoided. Without the insulation, these problems occur when reducing the cold gas spray gun. This reduction would be necessary to comply with weight limits at the same time required material thicknesses.
In a favorable embodiment, the pressure vessel of the high-pressure gas heater and / or the mixing chamber are lined with an insulation consisting of solid or flexible ceramic insulating material.

According to the apparatus of claim 1, the pressure vessel of the high pressure gasifier and / or the mixing chamber is isolated by a gas gap between an inner shell enclosing the gas and an outer shell.
Advantageously, high pressure gas heater, mixing chamber and Laval nozzle are linearly and concentrically aligned.
An angled gas guide in the available spray guns leads to an uneven thermal load, component distortion and thermally induced stresses, which would quickly lead to damage of the gun at the high gas temperatures required here. This is avoided by a straight gas flow.
The flow direction of the gas between high-pressure gas heater and mixing chamber can be deflected by an angle of up to 60 ° to each other.

If the flow guidance in the region of the two-phase flow of supplied particles is continuous and free of edges, this reduces the risk of particle deposits. Before the mixing chamber can be achieved by a deflection of up to 60 °, a more compact design of the cold gas spray gun.

In a favorable embodiment, the mixing chamber is at the same time the convergent section of the Laval nozzle.

Advantageously, the converging portion of the Laval nozzle has a length between 50 and 250 mm and has a conical or concave or convex inner contour.

In a favorable embodiment, the converging nozzle section is insulated from the inside or consists overall of an insulating material, in particular ceramic.

In a favorable embodiment, the pressure vessel and / or the mixing chamber and / or the convergent section and / or the divergent section may consist in whole or in part of titanium or aluminum and their alloys.

By using titanium as a construction material, the spray gun can be made particularly easy, as well as by the use of aluminum. The latter is particularly cost-effective as a construction material for the cold gas spray gun.

In a favorable design, the distance between the particle feed in the mixing chamber and the nozzle throat 40 to 400 mm, preferably 100 to 250 mm.

Depending on the flow rate of the process gas, a sufficiently long residence time of the particles in the heated gas can be achieved by heating the particles.

Advantageously, the flow cross-section of the mixing chamber and / or the convergent section may be between 5 and 50 times the nozzle throat cross-sectional area, preferably between 8 and 30 times, more preferably between 10 and 25 times to at least 70% of the distance from the particle feed to the nozzle throat amount.

As a result, the flow velocity in the region between the particle feed and the nozzle throat is not too small, so that the two-phase flow of gas and particles is maintained. Particle agglomerations and deposits on walls, which can disturb the operation of the cold gas spray gun sensitive, such as in the case of a nozzle clogging, are prevented.

In a favorable embodiment, the nozzle throat has a diameter between 2 and 4 mm, the diverging portion has a length which corresponds to 30 to 90 times the diameter of the nozzle throat, and at the same time the area ratio of the cross section at the end of the diverging portion to that of the nozzle neck cross section 3 and 15 and the inner contour is conical, or convex or concave.

Advantageously, the gas is supplied under a pressure of 15 to 100 bar, preferably from 20 to 60 bar, more preferably from 25 to 45 bar and a flow rate of 30 and 600 m ³ / h.

This allows larger particles to be accelerated to the required speeds.

The particle feed can consist of a tube supplied sideways at any angle or of one or more bores at the end of the high-pressure gas heater or in the mixing chamber.

The heating power of the heating element related to the flow cross section in the nozzle throat is advantageously 1.5 to 7.5 kW / mm ² , preferably 2 to 4 kW / mm ² .

The power volume of the heating element may be from 10 to 40 MW / m ³ , preferably from 20 to 30 MW / m ³ .

This makes a compact design possible.

The spray gun, the gas via a plastic tube, in particular Teflon, which is connected to a second high-pressure gas heater, preheated to up to 230 ° C, or via a Heißgasmetallschlauch, preheated to up to 700 ° C, fed.
In a favorable embodiment, the total heat output of the high-pressure gas heater and the second high-pressure gas heater relating to the flow cross section in the nozzle throat is 4 to 16 kW / mm ² , preferably 5 to 9 kW / mm ² .
The gas can be supplied in a method according to the invention after the high-pressure gas heater in the mixing chamber with temperatures greater than 600 ° C, preferably greater than 800 ° C, more preferably greater than 1000 ° C.
Advantageously, more than 80 percent by weight of the particles fed into the mixing chamber in the nozzle throat reach 70% of the gas temperature in the nozzle throat, measured in Kelvin.
This ensures a sufficient quality of the forming coating, since a sufficient proportion of the particles has the energy required for the formation of the layer upon impact.
Advantageously, a mixture of particles may be used whose mass is at least 80% of particles of grain size between 5 and 150 microns, preferably between 10 and 75 microns and more preferably between 15 and 50 microns.

With the cold gas spray gun according to the invention, the impact temperature of coarser particles (from 15 μm) can be significantly increased by efficient preheating of the particles in the hot process gas stream. Such coarser particles lose in the expanding gas jet of the nozzle not so quickly back to temperature and the use of high quality and precisely specified powder of particles in coarser fractions (-38 + 11 microns, -45 + 15 microns, -75 + 25 microns; 105 + 45 microns) unproblematic and cheaper. Also, the handling and promotion of spraying is much easier than with conventional powder fractions with -22 microns and - 25 + 5 microns.

Fig. 1

schematisch ein Ausführungsbeispiel einer erfindungsgemäßen Kaltgasspritzpistole im Längsschnitt,

Fig. 2

schematisch eine weiteres Ausführungsbeispiel einer erfindungsgemäßen Kaltgasspritzpistole im Längsschnitt und

Fig. 3

schematisch eine weiteres Ausführungsbeispiel einer erfindungsgemäßen Kaltgasspritzpistole im Längsschnitt und

An advantageous embodiment of the device according to the invention for high-pressure gas heating is explained in more detail with reference to the accompanying drawings. Show

Fig. 1

schematically an embodiment of a cold gas spray gun according to the invention in longitudinal section,

Fig. 2

schematically another embodiment of a cold gas spray gun according to the invention in longitudinal section and

Fig. 3

schematically another embodiment of a cold gas spray gun according to the invention in longitudinal section and

Fig. 1 schematically shows an advantageous embodiment of the cold gas spray gun according to the invention in longitudinal section. A pressure vessel 1 has on its inside an insulation 2. Inside the pressure vessel 1, a heating element 3 is arranged, here in the form of a filament heater, which consists of a plurality of electrical heating wires. The gas to be heated is supplied to the pressure vessel 1 via a gas supply line 4. In the present example, the pressure vessel 1 is a rotationally symmetrical body. A gas outlet 5 directs the heated or further heated gas in a mixing chamber 6, to which the converging portion 7 of a Laval nozzle 8 connects. The Laval nozzle 8 further consists of a nozzle throat 9 and a diverging section 10. A particle tube 11 can supply particles to the mixing chamber 3. In this case, the mouth of the particle tube 11 is aligned with the forming gas stream.

The gas flows through the pressure vessel 1 and with this linearly aligned mixing chamber 6 and Laval nozzle 9 as indicated by the arrows, wherein it is distributed uniformly over the cross section of the heating element 3. Due to the internal insulation 2 is achieved that only a few heat energy reaches the wall of the pressure vessel 1 and the mixing chamber 6. Since the pressure vessel 1 and the mixing chamber 6 at the same time give off heat to the environment, the pressure vessel 1 and the mixing chamber 6 is a considerably lower temperature than the heated gas has. The pressure vessel 1 and the mixing chamber 6 can therefore be relatively thin-walled and lightweight. In the mixing chamber 3, the heated gas via the particle tube 11, the particles to be sprayed admixed. This is done by the particles are transported through the particle tube via a carrier gas stream. On the route between particle injection and the narrowest cross-section of the Laval nozzle 9, the nozzle throat 10, the particles are heated, wherein more than 80 percent by weight of the particles in the nozzle throat reach 0.7 times the temperature of the gas jet in Kelvin at this location. This distance has in the present embodiment, a length between 40 and 400 mm, preferably between 100 and 250 mm, depending on the particles and gases used. Early particle injection, together with the use of larger particles and higher gas temperatures, has a major impact on the quality and efficiency of the coating. Because a very significant increase in the impact temperature of the particles is achieved.

In the diverging section 11 of the Laval nozzle 4, the expanding gas is accelerated to speeds above the speed of sound. The particles are strongly accelerated in this supersonic flow and reach speeds between 200 and 1500 m / s. An extension of the diverging nozzle section 11 has a particularly strong effect together with an inventively possible temperature and pressure increase of the gas. The effective use of elongate diverging nozzle sections 11 requires a high enthalpy of the gas. Advantageous lengths of the diverging nozzle section 11 are 100 mm and more, preferably 100 to 300 mm, particularly preferably 150 to 250 mm.

A uniform flow through the heating element is ensured by the cross-sectional area of the heating cartridge is not greater than 1500 times, preferably not more than 1000 times the area of the flow cross-section in the nozzle throat 9. Such a cold gas spray gun is characterized by a compact design and high power density. The length to diameter ratio is between 3 and 6. The power density of the cold gas spray gun, the quotient of heating power to total mass is between 1 and 8 kW / kg, with a well-realizable range between 2 and 4 kW / kg. The heating element 3 used has a power volume of 10 to 40 MW / m ³ . This allows temperatures of the gas at the gas supply from 400 ° C to 700 ° C. This temperature can be achieved by a second stationary preheater, which is connected to the cold gas spray gun via a hose. If a metal hot gas hose is used, 700 ° C is possible.

Fig. 2 schematically shows a further embodiment of a cold gas spray gun according to the invention in longitudinal section. Identical components are provided with the same reference numerals. The pressure vessel 1 and the mixing chamber 6 have on their inside an insulation 2. Inside the pressure vessel 1, the heating element 3 is arranged. Adjoining the mixing chamber 6 is a converging section 12 of the Laval nozzle 8, which further comprises the nozzle throat 9 and the diverging section 10. The particle tube 11 can supply the mixing chamber 3 particles. The converging section 12 also has an insulation 13.
As a result, thermal stress on the nozzle and thermal losses are avoided.
Fig. 3 schematically shows a third embodiment of a cold gas spray gun according to the invention in longitudinal section. Identical components are again provided with the same reference numerals. The pressure vessel 1 has on its inside an insulation 2 and in its interior, the heating element 3 is arranged. A mixing chamber 14 is at the same time a converging section 15 of the Laval nozzle 8, which further comprises the nozzle throat 9 and the diverging section 10. The particle tube 11 can supply 3 particles in the mixing chamber. The converging section 15 or the mixing chamber 14 also has an insulation and has a length of between 50 to 250 mm. This results in a simpler construction of the cold gas spray gun.

LIST OF REFERENCE NUMBERS

1

pressure vessel

2

insulation

3

heating element

4

gas supply

5

gas outlet

6

mixing chamber

7

converging section

8th

Laval

9

nozzle throat

10

diverging section

11

particle pipe

12

converging section

13

insulation

14

mixing chamber

15

converging section

Claims (14)

1. A cold gas spray gun with a high-pressure gas heater having a pressure vessel (1) through which a gas flows and a heating element (3) arranged in the pressure vessel (1) and with a mixing chamber (6, 14) in which particles can be supplied to the gas by a particle feed (11) and with a Laval nozzle (8) consisting of a converging portion (7, 12, 15), a nozzle throat (9) and a diverging portion (10), characterized in that the high-pressure gas heater is arranged at the mixing chamber (6, 14) and the mixing chamber (6, 14) is arranged at the Laval nozzle (9) in succession in the flow direction of the gas, and wherein the high-pressure gas heater and the mixing chamber (6, 14) are at least partially internally insulated at the contact surfaces contacting the gas and that the pressure vessel of the high-pressure gas heater and / or the mixing chamber are insulated by a gas gap between an inner shell enclosing the gas and an outer shell.
2. A cold gas spray gun according to claim 1, characterized in that the pressure vessel of the high-pressure gas heater and / or the mixing chamber (6, 14) are lined with an insulation consisting of solid or flexible ceramic insulation material.
3. A cold gas spray gun according to anyone of the preceding claims, characterized in that the high-pressure gas heater, the mixing chamber (6, 14) and the Laval nozzle (8) are aligned linearly and concentrically to each other.
4. A cold gas spray gun according to anyone of the claims 1 to 3, characterized in that the flow direction of the gas between the high-pressure gas heater and the mixing chamber is deflected by an angle of up to 60° to each other.
5. A cold gas spray gun according to anyone of the preceding claims, characterized in that the mixing chamber simultaneously is the converging portion (15) of the Laval nozzle (8).
6. A cold gas spray gun according to anyone of the preceding claims, characterized in that the converging portion (15) of the Laval nozzle (8) has a length between 50 and 250 mm and has a conical or concave or convex internal contour.
7. A cold gas spray gun according to anyone of the preceding claims, characterized in that the converging nozzle portion (12, 15) is internally insulated or consists overall of an insulating material, in particular ceramic.
8. A cold gas spray gun according to anyone of the preceding claims, characterized in that the pressure vessel and / or the mixing chamber and / or the converging portion and / or the diverging portion consist overall or partially of titanium or aluminum and the alloys thereof.
9. A cold gas spray gun according to anyone of the preceding claims, characterized in that the distance between the particle feed (11) in the mixing chamber (6, 12, 15) and the nozzle throat (9) is 40 to 400 mm, preferably 100 to 250 mm.
10. A cold gas spray gun according to anyone of the preceding claims, characterized in that the flow cross-section of the mixing chamber and / or of the converging portion on at least 70% of the distance from the particle feed to the nozzle throat is between 5 times and 50 times the nozzle throat cross-sectional surface, preferably between 8 times and 30 times, particularly preferred between 10 times and 25 times.
11. A cold gas spray gun according to anyone of the preceding claims, characterized in that the nozzle throat has a diameter between 2 and 4 mm, the diverging portion has a length corresponding to 30 to 90 times the diameter of the nozzle throat, and at the same time, the surface ratio of the cross-section at the end of the diverging portion to that of the nozzle throat cross-section is between 3 and 15, and the internal contour is conical or convex or concave.
12. A cold gas spray gun according to anyone of the preceding claims, characterized in that the particle feed consists of a pipe (11), which is laterally fed at any desired angle, or of one or more bores at the end of the high-pressure gas heater or in the mixing chamber.
13. A cold gas spray gun according to anyone of the preceding claims, characterized in that the heat output of the heating element (3) based on the flow cross-section in the nozzle throat is 1,5 to 7,5 kW/mm², preferably 2 to 4 kW/mm².
14. A cold gas spray gun according to anyone of the preceding claims, characterized in that the output volume of the heating element (3) is 10 to 40 MW/m³, preferably 20 to 30 MW/m³.

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