DK2689873T3

DK2689873T3 - Process for preparing a powder of a metal alloy

Info

Publication number: DK2689873T3
Application number: DK13170994.1T
Authority: DK
Inventors: Karl Rimmer
Original assignee: Karl Rimmer
Priority date: 2012-07-25
Filing date: 2013-06-07
Publication date: 2018-11-26
Also published as: HRP20181769T1; EP2689873B1; ES2693553T3; EP2689873A1; TR201815838T4; LT2689873T; AT13319U1; SI2689873T1

Description

FIELD OF THE INVENTION

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, wherein the method comprises the following steps: - melting and alloying the first metal with the at least one further 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 occurs during sputtering and solidification in a water-cooled spray tower.

DESCRIPTION OF THE PRIOR ART

In order to apply a coat of paint to surfaces, especially metal surfaces, a primer is usually used. This means that the layer of paint is not applied directly to the surface, but first the primer is applied to the surface and then the layer of paint is applied to the primer.

On the one hand, this enables better adhesion of the paint, as the primer can be designed in such a way that, on the one hand, it adheres particularly well to the surface and, on the other hand, it ensures optimum adhesion to the paint. This means that the primer acts as a bonding layer or adhesion promoter between the surface and the paint.

On the other hand, in the case of metal surfaces, the primer can also provide additional protection against corrosion, for example in body panels, household appliances or in shipbuilding. EP 2016138 BI discloses in this respect a corrosion protection primer which contains alloyed metallic pigments, e.g. alloyed zinc-magnesium or alloyed zinc-aluminum-magnesium pigments, optionally mixed with zinc pigments, in an organic matrix, e.g. a paint or an adhesive. When such pigments are used which are not in inorganic mineral or ionar form, a reaction takes place in corrosive attacks in which the pigment metals are rearranged and, associated therewith, a corrosion-protective passive layer is formed on the metal surface to be protected. US 2004/045404 Al relates to a method for producing a zinc or zinc alloy powder for use in a battery. Sputtering of the melt occurs by means of a primary gas and a secondary gas, wherein the powder produced has coarse grains on the one hand and fine grains on the other. JPH 10280012 A relates to a metal powder as a coating pigment for rust protection applications and its manufacture. A spray process is disclosed for production. In this case, the melt is poured from a furnace via a hole in the bottom of the furnace, which can be closed with a plug, and sputtered by means of gas from a nozzle arranged laterally under the hole.

OBJECT OF THE INVENTION

It is the object of the present invention to provide a method for the production of such corrosion protection 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 a size distribution which is as defined as possible. The pigments produced in this way are intended to provide improved corrosion resistance and improved weldability.

OUTLINE 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 .

By generating droplets, a defined size distribution of the droplets or subsequently the powder grains can be achieved in particular. This ensures a defined size distribution of the pigments in the corrosion protection primer, which in turn has a positive effect on the course of a reaction that takes place in the event of corrosive attacks and in which the pigment metals are rearranged and, as a result, a corrosion-protective passive layer is formed on the metal surface to be protected.

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

Therefore, in a method for producing a powder of a metal alloy from a first metal and at least one other 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: - sputtering 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, wherein the second gas flow is less than the first gas flow and wherein both the primary gas and the secondary gas are preheated to 370°C to 430°C.

The metal droplets can be produced particularly easily and efficiently - and thus cost-effectively - by gasifying or sputtering in such a way that the material flow follows gravity, i.e. with a directional component pointing vertically from top to bottom. The greater the proportion of the material flow in this direction (vertically from top to bottom), the more efficient the production of metal droplets will be. For this reason, it is intended that the material flow should follow the force of gravity in a preferred embodiment of the method according to the invention.

In order to guarantee a melt temperature favorable for sputtering, a heated (atomization) crucible or heated tundish is used, at the lower end of which a nozzle system for sputtering as well as supply lines for the primary and secondary gas are provided. Here 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 into a heated tundish immediately before sputtering or continuously fed to a heated tundish via a pre-melt alloying furnace by means of a pump and/or gutter system, wherein the tundish has a nozzle system and supply lines for the primary gas and the secondary gas at a lower end.

In order to promote solidification of the metal droplets into powder grains, it is provided that the material flow during sputtering and solidification takes place in a water-cooled spray tower. A temperature in the range from 340°C to 700°C, preferably from 570°C to 630°C, more preferably of 600°C, has proven to be favorable for sputtering the melt. In further preferred embodiments, the temperature of the melt can lie in a range from 370°C to 670°C, preferably from 400°C to 640°C, especially preferably from 430°C to 610°C, especially from 460°C to 580°C, particularly from 490°C to 550°C. For this reason, it is provided that in a preferred embodiment of the method according to the invention 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 when both the primary gas and the secondary gas have a temperature in the range 0°C to 450°C, preferably 370°C to 430°C, more preferably 400°C. This prevents too rapid solidification, wherein the temperatures of the primary gas and the secondary gas can also be different. The primary gas and secondary gas can be heated by supplying the gases to the heated tundish or its nozzle system, i.e. by heat contact with the heated tundish or its nozzle system. Different gas temperatures can result accordingly from different flow velocities of the gases and/or different gas flows due to the different duration of the heat contact. It is therefore provided that both the primary gas and the secondary gas are preheated to between 370°C and 430°C. A further possibility to influence the sputtering process is the choice of the gas flows of the primary gas and the secondary gas. For example, the shape of the droplets and thus of the grains of the powder can be adjusted by varying the strength of the gas flows in particular. The primary gas may have a high (first) gas flow as the guide gas, the secondary gas may be intended for the actual sputtering process and may have a lower (second) gas flow than the primary gas. Accordingly, it is provided that the second gas flow will be lower than the first gas flow.

Particularly good results are achieved when the first gas flow is in the range from 300 kg/h to 900 kg/h, preferably 650 kg/h to 750 kg/h, particularly preferably 700 kg/h, and the second gas flow is in the range from 50 kg/h to 150 kg/h, preferably 70 kg/h to 120 kg/h, particularly preferably 90 kg/h. In other preferred embodiments, the first gas flow may be in a 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, especially preferably from 420 kg/h to 780 kg/h, especially from 450 kg/h to 750 kg/h, particularly from 480 kg/h to 720 kg/h. Furthermore, in other preferred embodiments, the second gas flow may be in a range from 80 kg/h to 120 kg/h, preferably from 90 kg/h to 110 kg/h. Accordingly, in a preferred embodiment of the method according to the invention, it is provided 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.

In principle, possible oxidation - especially on the surface - of alloying elements of the melt during sputtering (or atomization or gasification) must be taken into account. In most cases such oxidation is not desired, which is why it is provided in a preferred embodiment of the method according to the invention that as primary gas and/or as secondary gas an inert gas, preferably comprising N2 and/or Ar and/or He, is used in order to prevent oxidation. However, if oxidation is not important, air can of course also be used.

As already stated, a defined size distribution of the pigments in the corrosion protection primer is decisive for an optimal course of the protection reaction in the event of corrosive attacks. In order to better define or limit the size distribution of the powder grains, a further method step is provided to subdivide the powder grains into coarse material and fine material. The coarse material is then recycled by being returned to the melt. Powder grains of the coarse material have diameters of at least 100 pm, preferably at least 1000 pm. A classifier, preferably a screening machine, especially an ultrasonic screening machine, is used for the subdivision. Accordingly, it is provided in a preferred embodiment of the method according to the invention that the powder is separated into coarse material and fine material by means of a classifier, preferably by means of an ultrasonic screening machine, in order to remove coarse material with a grain diameter of at least 1000 pm, wherein the coarse material is returned to the melt.

As an alternative or in addition to screening, the powder can be (further) subdivided into fine and coarse material by means of a cyclone, wherein the fine material has a grain diameter of less than 1000 pm, preferably less than 100 pm. Therefore, a preferred embodiment of the method according to the invention is to separate the powder into fine and coarse material by means of a cyclone, with all grains of the fine material having diameters of less than 1000 gm. A particularly defined or sharp size distribution of the powder grains can thus be achieved. Accordingly, it is provided in a preferred embodiment of the method according to the invention that 90% of the grains of the fine material have diameters between 10 gm and 1000 gm, preferably between 15 gm and 20 gm, and that 50% of the grains of the fine material have diameters between 3 gm and 800 gm, preferably between 8 gm and 12 gm.

As already mentioned, the powder grains can have different shapes. In addition to the spherical shape, the powder grains can also be needle-shaped, i.e. have an elongated shape along an axis. Finally, an uneven shape is also possible, i.e. the powder grains can also be spattered. The dominant shape can be set by selecting the process parameters, such as gas flows. Accordingly, it is provided in a preferred embodiment of the method in accordance with the invention that the shape of the powder grains should be predominantly spherical, needle-like or spattered. It should also be noted that the term "grain diameter" or "diameter" in the case of non-spherical grain shapes (e.g. needle-shaped or spattered) refers to the diameter of an imaginary sphere enclosing the respective powder grain. This means that the "diameter" in such a case means the largest extension of a grain in one direction.

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

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

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now explained in more detail by reference to an exemplary embodiment. The drawings are exemplary and are intended to illustrate the idea of invention, but shall in no way restrict it or even reflect it conclusively, wherein :

Fig. 1 shows an overall flow diagram of a method in accordance with the invention;

Fig. 2 shows a measured size distribution of a powder which has been produced by a method in accordance with the invention .

DETAILED DSCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the overall flow diagram of a method according to the invention as shown in Fig. 1, Zn 18 is molten as the first step in a furnace 17 and then Mg 19a and/or Al 19b are added as at least one further metal in a melt 20. The product purity of the Zn 18 used is typically at least 99.995 wt.-%, while that of the Mg 19a or Al 19b used is typically at least 99.8 wt.-%.

The melt 20, which usually has a temperature in a range from 340°C to 700°C, typically a temperature of 600°C, is supplied by means of a pump (not shown) to a preheated atomizing crucible or tundish 2, which is tightly closed to the melt by means of a plug rod (not shown) on its bottom side 22. The plug rod is only pulled out when the melt 20 in the preheated tundish 2 has reached a certain liquid level, e.g. 30 cm.

By means of a heated nozzle system 3, which is also arranged on the bottom side 22 of the heated tundish 2, the melt 20 emerging from the tundish 2 due to gravity is now atomized or sputtered to metal droplets (not shown), i.e. droplets of melt 20. The atomization or sputtering also has a directional component that points from top to bottom according to gravity, which results in a particularly efficient generation of metal droplets.

During atomization or sputtering, preheated primary gas 6 is fed to nozzle system 3 via a supply line 4 and preheated secondary gas 7 is fed to nozzle system 3 via a supply line 5. Primary gas 6 or secondary gas 7 is heated to a temperature in the range from 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 lies in different gas flows. A first gas flow of primary gas 6 is 300 kg/h to 900 kg/h, preferably 700 kg/h; a second gas flow of secondary gas 7 is 50 kg/h to 150 kg/h, preferably 90 kg/h.

To avoid oxidation, especially on the surface of the alloying metals, inert gases, preferably N2 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 and thus form grains of a metal alloy powder 21. To promote solidification, a material flow 1, which takes place during sputtering and solidification and has a directional component perpendicularly from top to bottom, i.e. it follows gravity, passes through a cooled spray tower 8. Cooling the spray tower 8 is carried out using water, which is why the spray tower 8 has a double jacket 9 and a water connection 10 for water cooling.

At the lower end 16 of the spray tower 8, the solidified powder 21 emerges. In order to achieve the particularly well-defined size distribution of the grains of powder 21, the powder 21 is first divided into fine and coarse material by means of a cyclone 11, wherein the coarse material has a grain diameter of at least 1000 pm. The coarse material is discharged via a material discharge 12 of cyclone 11 and returned to 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 for sputtering can escape via a gas outlet 14. The powder 21 with a precisely defined or narrow size distribution of the powder grains is discharged as a finished product via a filter dust discharge 15 of the filter unit 13.

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, resulting in the histogram shown. 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 drawn as a solid line, wherein the values for the cumulative frequency in % can be read on the left y-axis. A diameter smaller than or equal to 5.54 pm is shown 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 numerals 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 8 Spray tower 9 Double jacket for water cooling 10 Water connection 11 Cyclone 12 Material discharge 13 Filter system 14 Gas outlet 15 Filter dust discharge 16 Lower end of spray tower 17 Melting furnace 18 Zn 19a Mg 19b Al 20 Melt 21 Powder 22 Bottom side of heated tundish D Grain diameter q3 Absolute frequency Q3 Cumulative frequency

Claims

A method of preparing a powder of a metal alloy from a first metal (18) and at least one additional metal (19a, 19b) for use as pigments of a corrosion protection primer for metals, comprising the steps of: - melting and alloying the first metal (18) having at least one additional metal (19a, 19b), the temperature of the melt (20) being 340 ° C to 700 ° C, preferably 600 ° C; - wherein the melt (20) cools during atomization and solidifies into a powder (21), wherein a material stream (1) occurs during atomization and solidification and wherein the material stream (1) proceeds during atomization and solidification in a water-cooled spray tower (8), characterized by the process comprises the following steps: - atomizing the melt (20) by means of a primary gas (6) with a primary gas stream and a secondary gas (7) with a second gas stream, wherein the second gas stream is smaller than the first gas stream and wherein both the primary gas (6) and the secondary gas (7) are preheated to 370 ° C to 430 ° C.

Method according to claim 1, characterized in that the material flow (1) follows the force of gravity.

Process according to one of claims 1 to 2, characterized in that the melt (20) is introduced immediately before atomization in a heated funnel (2) or is continuously supplied via a pre-melting alloy furnace by means of a pump and / or rinsing system for a heated funnel ( 2) wherein the distributor trough comprises a nozzle system (3) and supply lines (4, 5) to 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 takes place by supplying the gases to the heated funnel ( 2) or to its nozzle system, namely by thermal contact with the heated hopper (2) or its nozzle system.

Method according to one of claims 1 to 3, characterized in that the first gas flow is 300 kg / hour to 900 kg / hour, preferably 700 kg / hour, and the second gas flow is 50 kg / hour to 150 kg / hour, preferably 90 kg / hour.

Process according to one of claims 1 to 4, characterized in that an inert gas, preferably comprising N 2 and / or Ar and / or He, is used as the primary gas (6) and / or as the secondary gas (7) to prevent oxidation.

Method according to one of claims 1 to 5, characterized in that the powder (21) is divided by means of a classifier, preferably by means of an ultrasonic sieving machine, into coarse-grained material and fine material (12) for removing coarse-grained material having a grain size of at least 1000 µm, where the coarse-grained material is returned to the melt (20).

Process according to one of claims 1 to 6, characterized in that the powder (21) is divided by means of a cyclone (11) for fine material (12) and coarse-grained material, wherein all grains of the fine material (12) have diameters of less than 1000 µm, and 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.

Method according to one of claims 1 to 7, characterized in that the shape of the powder grains is predominantly spherical, needle-shaped or splash-shaped.

Process according to one of claims 1 to 8, characterized in that the first metal (18) is Zn and the at least one additional metal (19a, 19b) is Mg (19a) and / or Al (19b).

Process according to one of claims 1 to 9, characterized in that the melt (20) has a Zn content of 50 wt% to 99.9 wt% and a Mg content of 0.1 wt% to 50 wt% and / or an Al content of 0.1% to 50% by weight, and any inevitable impurities, especially Fe and / or Pb and / or Cd.