EP2689873B1 - Method for producing a powder of a metal alloy - Google Patents

Description

FIELD OF THE INVENTION

• Schmelzen und Legieren des ersten Metalls mit dem mindestens einen weiteren Metall, wobei die Temperatur der Schmelze 340°C bis 700°C, vorzugsweise 600°C beträgt;
• wobei die Schmelze während des Zerstäubens abkühlt und zu einem Pulver erstarrt, wobei ein Materialfluss während des Zerstäubens und Erstarrens erfolgt und wobei der Materialfluss während des Zerstäubens und Erstarrens in einem wassergekühlten Sprühturm verläuft.

The present invention relates to a method for producing a powder of a metal alloy from a first metal and at least one further metal for use as pigments of a corrosion protection primer for metals, the method comprising the following steps:

• Melting and alloying the first metal with the at least one other metal, wherein the temperature of the melt is 340 ° C to 700 ° C, preferably 600 ° C;
• wherein the melt cools during sputtering and solidifies to a powder, wherein a material flow occurs during sputtering and solidification, and wherein the material flow during sputtering and solidification in a water-cooled spray tower passes.

STATE OF THE ART

In order to apply a color layer to surfaces, in particular to metal surfaces, a primer, also called a primer, is usually used. That The color layer is not applied directly to the surface, but it is first the primer applied to the surface and then the ink layer on the primer.

This allows for a better adhesion of the color, since the primer can be designed so that it adheres on the one hand on the surface particularly well and on the other hand ensures optimum connection to the color. That is, the primer acts as Bonding layer or bonding agent between the surface and the color.
On the other hand, in the case of metal surfaces, the primer can also provide protection against corrosion, for example for body panels, household appliances or shipbuilding. From the EP 2016138 B1 For this purpose, a corrosion protection primer is known which in an organic matrix, such as a paint or an adhesive, alloyed metallic pigments, for example alloyed zinc-magnesium or alloyed zinc-aluminum-magnesium pigments, optionally mixed with zinc pigments contains. When using such pigments, which are not in inorganic mineral or ionic form, a reaction takes place in corrosive attacks, in which a rearrangement of the pigment metals and concomitantly the formation of a corrosion-protective passive layer on the metal surface to be protected takes place.

The US 2004/045404 A1 relates to a process for producing a powder of zinc or a zinc alloy for use in a battery. There is a sputtering of the melt by means of a primary gas and a secondary gas, the powder produced on the one hand coarse and on the other hand has fine grains.

JPH 10280012 A relates to a metal powder as a coating pigment for antirust applications and its preparation. For the preparation, a spray method is disclosed. In this case, the melt is poured from a furnace via a hole located at the bottom of the furnace, which can be closed with a plug, and atomized by means of gas from a nozzle arranged laterally below the hole.

OBJECT OF THE INVENTION

The object of the present invention is to provide a process for producing such corrosion-protective pigments or a powder for use as pigments of a corrosion-protection primer. In particular, the Grains of the powder - and thus the pigments - have the largest possible size distribution. The pigments thus produced should allow improved corrosion resistance and improved weldability.

PRESENTATION OF THE INVENTION

According to the invention, pigments of a corrosion protection primer can be produced particularly efficiently by producing droplets of a molten metal alloy. The droplets are cooled and solidified to form a powder. The grains of the powder can be used as pigments of a corrosion protection primer.

In particular, a defined size distribution of the droplets or, as a consequence, of the powder grains can be achieved by the generation of droplets. Thus, a defined size distribution of the pigments in the anticorrosive primer is ensured, which in turn has a positive effect on the course of a reaction that takes place in corrosive attacks and in which a rearrangement of the pigment metals and, consequently, the formation of a corrosion-protective passive layer on the metal surface to be protected ,

The defined size distribution of the droplets can be achieved by gasifying the metal alloy melt using a primary gas and a secondary gas.

• Zerstäuben der Schmelze und Formgebung der Pulverkörner mittels eines Primärgases, welches einen ersten Gasfluss aufweist, und eines Sekundärgases, welches einen zweiten Gasfluss aufweist, wobei der zweite Gasfluss geringer als der erste Gasfluss ist und wobei sowohl das Primärgas als auch das Sekundärgas auf 370°C bis 430°C vorgewärmt sind.

Therefore, in a method for producing a powder of a metal alloy from a first metal and at least one further metal for use as pigments of a corrosion protection primer for metals, it is provided according to the invention that the method comprises the following step:

• Atomizing the melt and shaping the powder grains by means of a primary gas having a first gas flow and a secondary gas having a second gas flow, the second gas flow being less than the first gas flow and wherein both the primary gas and the secondary gas are at 370 ° C preheated to 430 ° C.

The metal droplets can be produced particularly simply and efficiently - and thus cost-effectively - by the gasification or atomization being carried out in such a way that the material flow follows the force of gravity, that is to say with a directional component which points vertically from top to bottom. The larger this directional component (perpendicular from top to bottom) of the material flow fails, the more efficient the metal droplet production. Therefore, it is at a preferred Embodiment of the method according to the invention provided that the material flow of gravity follows.

In order to guarantee a favorable for the atomizing temperature of the melt, a heated (atomizing) crucible or heated tundish is used, at its lower end a nozzle system for atomizing and supply lines for the primary gas and the secondary gas are provided. In this case, the nozzle system is preferably also heated. Accordingly, it is provided in a preferred embodiment of the method according to the invention that the melt is introduced immediately before sputtering in a heated tundish or continuously fed via a Vorschmelzlegierungsofen means of a pump and / or gutter system a heated tundish, the tundish at a lower end a nozzle system and supply lines for the primary gas and the secondary gas has.

In order to promote solidification of the metal droplets into grains of the powder, it is provided that the flow of material during atomization and solidification in a water-cooled spray tower runs.

As favorable for atomizing the melt, a temperature in a range of 340 ° C to 700 ° C, preferably from 570 ° C to 630 ° C, more preferably of 600 ° C has been found. In further preferred embodiments, the temperature of the melt may range from 370 ° C to 670 ° C, preferably from 400 ° C to 640 ° C, more preferably from 430 ° C to 610 ° C, especially from 460 ° C to 580 ° C, especially from 490 ° C to 550 ° C, lie. It is therefore provided in a preferred embodiment of the method according to the invention that the temperature of the melt is 340 ° C to 700 ° C, preferably 600 ° C.

In addition to the temperature of the melt, the temperatures of the primary gas and the secondary gas play an important role for the defined atomization. Best results can be achieved if both the primary gas and the secondary gas have a temperature in a range of 0 ° C to 450 ° C, preferably from 370 ° C to 430 ° C, more preferably from 400 ° C. As a result, too rapid solidification is prevented, wherein the temperatures of the primary gas and the secondary gas may also be different. The heating of the primary gas and the secondary gases can be effected by the supply of gases to the heated tundish or to its nozzle system, i. by thermal contact with the heated tundish or its nozzle system. Different gas temperatures can result in accordance with different flow velocities of the gases or different gas flows due to the different duration of thermal contact. Therefore, it is envisaged that both the primary gas and the secondary gas are preheated to 370 ° C to 430 ° C.

Another way to influence the sputtering process, is the choice of the gas flows of the primary gas and the secondary gas. In particular, by different strong gas flows, for example, the shape of the droplets and thus the grains of the powder can be adjusted. The primary gas may have a high (first) gas flow as a guide gas, the secondary gas may be intended for the actual sputtering process and a
have lower (second) gas flow compared to the primary gas. Accordingly, it is provided that the second gas flow is less than the first gas flow.

Particularly good results are achieved when the first gas flow in a range of 300 kg / h to 900 kg / h, preferably from 650 kg / h to 750 kg / h, more preferably at 700 kg / h and the second gas flow in one Range from 50 kg / h to 150 kg / h, preferably from 70 kg / h to 120 kg / h, more preferably at 90 kg / h. In further preferred embodiments, the first gas flow may range from 330 kg / h to 870 kg / h, preferably from 360 kg / h to 840 kg / h, preferably from 390 kg / h to 810 kg / h, more preferably from 420 kg / h to 780 kg / h, in particular from 450 kg / h to 750 kg / h, especially from 480 kg / h to 720 kg / h. Moreover, in other preferred embodiments, the second gas flow may range from 80 kg / h to 120 kg / h, preferably from 90 kg / h to 110 kg / h. Accordingly, it is provided in a preferred embodiment of the method according to the invention that the first gas flow is 300 kg / h to 900 kg / h, preferably 700 kg / h and the second gas flow 50 kg / h to 150 kg / h, preferably 90 kg / h H.

In principle, during atomization (or atomization or gasification) a possible oxidation - especially on the surface - of alloying elements of the melt must be taken into account. Most such oxidation is not desirable, which is why it is provided in a preferred embodiment of the method according to the invention that as the primary gas and / or secondary gas, an inert gas, preferably comprising N ₂ and / or Ar and / or He, is used for oxidation prevention. However, if oxidation is not important, it is of course also possible to use with air.

As already stated, a defined size distribution of the pigments in the anticorrosive primer is crucial for an optimal sequence of the protective reaction taking place during corrosive attacks. In order to define or limit the size distribution of the powder grains even better, therefore, a further process step for subdividing the powder grains into coarse material and fine material is provided. The coarse material is then recycled by re-feeding it to the melt. Powder grains of the coarse material have a diameter of at least 100 μm, preferably of at least 1000 μm. For the subdivision, a classifying device, preferably a screening machine, particularly preferably an ultrasonic screening machine, is used. Accordingly, it is provided in a preferred embodiment of the method according to the invention that the powder is separated by means of a classifier, preferably by means of an ultrasonic sieve in coarse and fine material to remove coarse material with a grain diameter of at least 1000 pm, the coarse material again Melt is supplied.

As an alternative or in addition to screening, a (further) subdivision of the powder into fine material and coarse material can take place by means of a cyclone, wherein the fine material has a particle diameter of less than 1000 μm, preferably less than 100 μm. Therefore, it is provided in a preferred embodiment of the method according to the invention that the powder is separated by means of a cyclone in fines and coarse material, wherein all grains of the fines have a diameter of less than 1000 pm.

It is thus possible to achieve a particularly defined or sharp size distribution of the powder grains. Accordingly, it is provided in a preferred embodiment of the method according to the invention that 90% of the grains of the fine material diameter between 10 pm and 1000 pm, preferably between 15 pm and 20 pm and that 50% of the grains of the fine material have diameters between 3 pm and 800 pm, preferably between 8 pm and 12 pm.

As already mentioned, the powder grains may have different shapes. In addition to the spherical shape, the powder grains may also be needle-shaped, ie have an elongated shape along an axis. Finally, a non-uniform shape is possible, i. The powder grains can also be spotty. The dominant shape can be adjusted by choosing the process parameters, such as the gas flows. Accordingly, it is provided in a preferred embodiment of the method according to the invention, that the shape of the powder grains is mostly spherical, needle-shaped or spratzig. It should also be noted that in the case of non-spherical grain shapes (e.g., acicular or sparse), the term "grain diameter" or "diameter" refers to the diameter of an imaginary sphere enclosing each powder grain. That the "diameter" in such a case denotes the largest extent of a grain in one direction.

The choice of alloy composition is decisive for the corrosion protection effect. The best results are achieved with a Zn-Mg, Zn-Al or Zn-Mg-Al alloy. Accordingly, in a preferred embodiment of the method according to the invention, it is provided that the first metal is Zn and the at least one further metal is Mg and / or Al.

The composition ideally moves in the range from 50% by weight to 99.9% by weight, preferably from 97% by weight to 98% by weight, preferably from 60% by weight to 89.9% by weight. -%, more preferably from 70 wt .-% to 79.9 wt .-% Zn content and from 0.1 wt .-% to 50 wt .-%, preferably 1.9 wt .-% to 2.2 Wt .-%, preferably from 10.1 wt .-% to 40 wt .-%, more preferably from 20.1 wt .-% to 30 wt .-% Mg content and / or Al content. In addition, the alloy may have unavoidable impurities with other metals, especially Fe and / or Pb and / or Cd. In the case of a Zn-Mg alloy, traces of Al may also occur as an impurity. Total impurities account for less than 1% by weight, preferably less than 0.1% by weight, more preferably less than 0.05% by weight. Accordingly, it is provided in a preferred embodiment of the method according to the invention that the melt has a Zn content of 50 wt .-% to 99.9 wt .-% and an Mg content of 0.1 wt .-% to 50 wt. -% and / or an Al content of 0.1 wt.% To 50 wt .-% and optionally unavoidable impurities, in particular Fe and / or Pb and / or Cd.

BRIEF DESCRIPTION OF THE FIGURES

The invention will now be explained in more detail with reference to an embodiment. The drawings are exemplary and are intended to illustrate the inventive idea, but in no way restrict it or even reproduce it.

Fig. 1

ein Gesamtfließschema eines erfindungsgemäßen Verfahrens

Fig. 2

eine gemessene Größenverteilung eines Pulvers, welches mittels eines erfindungsgemäßen Verfahrens hergestellt worden ist

Showing:

Fig. 1

a total flow diagram of a method according to the invention

Fig. 2

a measured size distribution of a powder which has been produced by means of a method according to the invention

WAYS FOR CARRYING OUT THE INVENTION

According to the in Fig. 1 shown overall flow diagram of a method according to the invention is initially in a Melting furnace 17 Zn 18 melted and then alloyed Mg 19a and / or Al 19b as at least one other metal in a melt 20. The product purity of the Zn 18 used is typically at least 99.995% by weight, and those of the Mg 19a or Al 19b used are typically at least 99.8% by weight.

The melt 20, which typically has a temperature in a range of 340 ° C to 700 ° C, typically a temperature of 600 ° C, is fed by means of a pump (not shown) to a preheated atomizer 2 via a stopper rod (not shown) is sealed at its bottom side 22 for the melt. Only when the melt 20 in the preheated Tundish 2 has reached a certain liquid level, for example 30 cm, the stopper rod is pulled out.

By means of a heated nozzle system 3, which is also located on the bottom side 22 of the heated tundish 2, the melt 20 emerging from the tundish 2 by gravity will now become metal droplets (not shown), i. Droplets of the melt 20, atomized or atomized. The atomization also has a directional proportion, which points in accordance with gravity from top to bottom, which causes a particularly efficient production of the metal droplets.

During atomization or preheating primary gas 6 is supplied by means of a feed line 4 and preheated secondary gas 7 by means of a supply line 5 to the nozzle system 3. The primary gas 6 or the secondary gas 7 is heated to a temperature in a range of 0 ° C to 450 ° C, typically to a temperature of 400 ° C, wherein the temperatures of the primary gas 6 and the secondary gas 7 may differ from each other.

The main difference between the primary gas 6 and the secondary gas 7 is in different gas flows. One first gas flow of the primary gas 6 is 300 kg / h to 900 kg / h, preferably 700 kg / h; a second gas flow of the secondary gas 7 is 50 kg / h to 150 kg / h, preferably 90 kg / h.

In order to avoid oxidation, in particular on the surface of the alloying metals, inert gases, preferably N ₂ and / or Ar and / or He, are used for both the primary gas 6 and the secondary gas 7.

During sputtering, the metal droplets of the melt 20 solidify to form grains of a metal alloy powder 21. To promote solidification, there is a flow of material 1 that occurs during sputtering and solidification and has a directionality perpendicular from top to bottom, i. Following gravity is, by a cooled spray tower 8. The cooling of the spray tower 8 by means of water, which is why the spray tower 8 has a double jacket 9 and a water connection 10 for the water cooling.

At the lower end 16 of the spray tower 8, the solidified powder 21 exits. In order to achieve the particularly well-defined size distribution of the grains of the powder 21, the powder 21 is first divided by means of a cyclone 11 into fines and coarse material, wherein the coarse material has a grain diameter of at least 1000 pm. The coarse material is discharged via a material discharge 12 of the cyclone 11 and fed back to the melt 20 (not shown).

The fine material is finally fed to a filter system 13, from which the primary gas 6 and secondary gas 7 used in the atomization can escape via a gas outlet 14. About a Filterstaubaustrag 15 of the filter unit 13, the powder 21 is discharged with a well-defined or narrow size distribution of the powder grains as a finished product.

Fig. 2 shows the result of a grain size measurement of a powder 21 of a Zn-Mg alloy. On the x-axis the grain diameter D is plotted on a logarithmic scale in pm, on the right y-axis the absolute frequency q3 of the grains detected in a diameter interval or a diameter class in arbitrary units, thus the histogram shown results. It covers in Fig. 2 the x-axis covers a range from 0.04 pm to 500 pm, which is divided into 100 classes.

In addition, a curve for the cumulative frequency Q3 in% is plotted as a solid line, with the values for the cumulative frequency in% on the left y axis. In this case, a diameter of less than or equal to 5.54 pm is reported for 10% of all detected grains. The diameter of 50% of all grains is less than or equal to 10.43 pm; the diameter of 90% of all grains is less than or equal to 15,74 pm.

LIST OF REFERENCE NUMBERS

1

material flow

2

Heated tundish

3

nozzle system

4

Supply line for primary gas

5

Supply line for secondary gas

6

primary gas

7

secondary gas

8th

spray tower

9

Double jacket for water cooling

10

mains water supply

11

cyclone

12

material discharge

13

filter system

14

gas outlet

15

Filter dust discharge

16

Lower end of the spray tower

17

furnace

18

Zn

19a

mg

19b

al

20

melt

21

powder

22

Bottom side of the heated tundish

D

Grain diameter

q3

absolute frequency

Q3

cumulative frequency

Claims (10)

1. A method of producing a powder of a metal alloy from a first metal (18) and at least one further metal (19a, 19b) for use as pigments of a corrosion protection primer for metals, wherein the method comprises the steps of:

   - melting and alloying the first metal (18) with the at least one further metal (19a, 19b), wherein the temperature of the melt (20) is 340°C to 700°C, preferably 600°C;

   - wherein the melt (20) cools during sputtering and solidifies to a powder (21), wherein a material flow (1) occurs during sputtering and solidification and wherein the material flow (1) extends during sputtering and solidification in a water-cooled spray tower (8), characterized in that the method comprises the following step:

   - sputtering the melt (20) by means of a primary gas (6) having a first gas flow and a secondary gas (7) having a second gas flow, wherein the second gas flow is less than the first gas flow and wherein both the primary gas (6) and the secondary gas (7) are preheated to 370°C to 430°C.
2. Method according to claim 1, characterized in that the material flow (1) follows the force of gravity.
3. Method according to one of claims 1 to 2, characterized in that the melt (20) is introduced immediately before sputtering into a heated tundish (2) or is fed continuously via a pre-melt alloying furnace by means of a pump and/or gutter system to a heated tundish (2), wherein the tundish comprises a nozzle system (3) and supply lines (4, 5) for the primary gas (6) and the secondary gas (7) at a lower end, so that the heating of the primary gas and the secondary gas occurs by supplying the gases to the heated tundish (2) or to its nozzle system, namely by thermal contact with the heated tundish (2) or its nozzle system.
4. Method according to one of the claims 1 to 3, characterized in that the first gas flow is 300 kg/h to 900 kg/h, preferably 700 kg/h, and the second gas flow is 50 kg/h to 150 kg/h, preferably 90 kg/h.
5. Method according to one of the claims 1 to 4, characterized in that an inert gas, preferably comprising N₂ and/or Ar and/or He, is used as the primary gas (6) and/or as the secondary gas (7) to prevent oxidation.
6. Method according to one of the claims 1 to 5, characterized in that the powder (21) is separated by means of a classifier, preferably by means of an ultrasonic screening machine, into coarse material and fine material (12) in order to remove coarse material having a grain diameter of at least 1000 µm, wherein the coarse material is fed back to the melt (20).
7. Method according to one of the claims 1 to 6, characterized in that the powder (21) is separated by means of a cyclone (11) into fine material (12) and coarse material, wherein all grains of the fine material (12) have diameters of less than 1000 µm, and wherein preferably 90% of the grains of the fine material (12) have diameters between 10 µm and 1000 µm, and preferably 50% of the grains of the fine material (12) have diameters between 3 µm and 800 µm.
8. Method according to one of the claims 1 to 7, characterized in that the shape of the powder grains is predominantly spherical, needle-shaped or spattered.
9. Method according to one of the claims 1 to 8, characterized in that the first metal (18) is Zn and the at least one further metal (19a, 19b) is Mg (19a) and/or Al (19b).
10. Method according to one of the claims 1 to 9, characterized in that the melt (20) has a Zn content of 50 wt.-% to 99.9 wt.-% and an Mg content of 0.1 wt.-% to 50 wt.-% and/or an Al content of 0.1 wt.% to 50 wt.-%, and optionally unavoidable impurities, in particular Fe and/or Pb and/or Cd.

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