EP2524973A1 - Arc spraying method for manufacturing a leak-proof coating - Google Patents

Abstract

The method involves applying electrical voltage to two electrically conductive spray wires (2) in a melting zone (7) so as to form an arc (6) between spray wires such that melt (8) is formed in melting zone. A fluid (4) is applied to melt. The oxidized particles (11) are sprayed for sealing the melt partly with oxidized particles. The melt containing oxidized particles is transported to a substrate (10) so as to form a dense layer (18) on substrate.

Description

The invention relates to an arc spraying method for producing a dense layer according to the preamble of the independent method claim. The invention further relates to a dense layer made according to such a method.

Coatings produced by thermal spraying are often exposed to corrosive stresses. For example, floor coatings on ships are very much exposed to the salt water-containing sea air and therefore particularly susceptible to corrosion damage. Although it is known to apply anti-corrosion coatings, for example in the form of special paints or coatings, but it is not uncommon for the effect referred to as undercutting that occurs under the coating on the substrate to corrosion. This corrosion can lead to the coating - for example the protective ink or the thermally sprayed protective layer - peeling off the substrate. Of course, the cause of this undercorrosion may be damage to the protective coating through which the corrosion causing material, e.g. Salt water, reaches the substrate and leads there to corrosion. However, it is also possible for the material causing the corrosion to penetrate the inherently intact protective layer via capillary effects or diffusion processes and thus reach the substrate. The protective layer is therefore virtually not dense enough. This effect is particularly favored even if the protective layer has a high roughness. However, high roughness of the protective layer is often desirable for safety reasons, for example on the bottom of ships to minimize the risk of slipping for the crew of the ship.

It is therefore an object of the invention to provide a low cost and simple method of forming a dense layer on a substrate to propose, which allows protection of the underlying substrate, in particular against corrosion. Furthermore, the invention provides a corresponding dense layer.

The objects of the invention which solve this object are characterized by the independent claim of the respective category.

According to the invention, therefore, an arc spraying method is proposed for producing a dense layer on a substrate, in which an electrical voltage is applied to two electrically conductive injection wires, with which an arc is ignited between the injection wires, wherein a melt is produced from the injection wires in a melting region, wherein the melt is subjected to a fluid which transports the melt to the substrate where the melt is deposited to form the layer. The melt is supplied with oxidizable particles which are deposited together with the melt on the substrate, and after the completion of spraying, the oxidizable particles are at least partially oxidized to seal the layer.

Arc spraying, which is often also referred to more precisely as arc wire spraying, is a thermal spraying method with which layers can be deposited on a substrate in a cost-effective and simple manner. The melt-supplied oxidizable particles are at least partially oxidized after the injection process. As a result of the oxidation, the particles increase their volume and thus seal the layer, or the layer is sealed. Hereby, the substrate located under the layer can be protected particularly efficiently, in particular against corrosion. Since the particles are distributed throughout the layer, not only is the surface of the layer sealed, but the entire layer is sealed inside.

In practice, it has proven to be particularly favorable when the oxidizable particles occupy a volume fraction of 3% to 20% of the volume of the layer.

According to a first preferred method, the oxidizable particles are added to the fluid before the fluid acts on the melt.

The particles then impinge on the melting region together with the fluid and transport the melt onto the substrate from there.

Another preferred methodology is to add the oxidizable particles of the melt between the melting region and the substrate. In this variant, the oxidizable particles are thus introduced downstream of the melting range in the "beam", which transports the melt to the substrate.

Furthermore, it is possible that the oxidizable particles are part of at least one spray wire. The spray wire is then designed, for example, as a hollow wire or as a so-called "cored wire", d. H. the oxidizable particles are integrated in the spray wire.

Another possible procedure is that a third spray wire is provided, which contains the oxidizable particles.

In a preferred embodiment, the oxidizable particles contain iron or zinc or aluminum or magnesium or alloys of these elements. These elements or their alloys are particularly easy to oxidize. With respect to iron, there are a variety of oxidizable iron compounds or iron base materials having an iron content of at least 50 weight percent, which are suitable for the inventive method, for example iron base material with chromium and / or aluminum. Also, elemental aluminum or magnesium or zinc are suitable because of their easy oxidation and the associated volume increase. For example, oxidized aluminum powder has about three times the volume of unoxidized aluminum powder. Furthermore, the alloy ZnAl 85/15 is suitable which contains 85% by weight of zinc and 15% by weight of Al. A criterion for the proper choice of the oxidizable particles is that they have no pronounced tendency to form alloys with the spray material. It is quite possible, although not necessary, for the oxidizable particles to be used in the process according to the invention melt or plasticized and then solidify again when they have been applied to the substrate along with the melt. In such cases, it is not desirable for the oxidizable particles to form alloys with the spray material and then optionally no longer or at least no longer easily oxidizable. An exception to this may be possible if the oxidizable particles with components of the spray material form easily oxidizable alloys or other compounds. Then, of course, it can be specifically used that the oxidizable particles are generated only during the injection process or that the oxidizable particles enter into compounds, which in turn represent oxidizable particles.

A particularly simple possibility is when the oxidizable particles are oxidized by means of water.

The inventive method is particularly suitable for those applications in which the substrate is made of steel, or has a surface made of steel. In particular, the undercutting of the steel under the layer can be at least efficiently inhibited or delayed, if not completely and permanently prevented, by the sealing of the layer or by the density of the layer.

The invention further proposes a dense layer, which is produced by a method according to the invention.

The dense layer preferably has residual compressive stresses. These residual compressive stresses in the layer can be selectively generated by the oxidation of the oxidizable particles, because the increase in volume associated with the oxidation leads to the formation of residual compressive stresses which can markedly improve the durability or the adhesion of the layer to the substrate.

Further advantageous measures and preferred embodiments of the invention will become apparent from the dependent claims.

Fig. 1

die wesentlichen Teile einer Lichtbogenspritzvorrichtung zum Durchführen eines ersten Ausführungsbeispiels des erfindungsgemässen Verfahrens,

Fig. 2

wie Fig. 1 jedoch für ein zweites Ausführungsbeispiel des erfindungsgemässen Verfahrens,

Fig. 3

einen Spritzdraht für ein weitere Ausführungsbeispiel des erfindungsgemässen Verfahrens, und

Fig. 4

eine schematische Darstellung zur Verdeutlichung eines weiteren Ausführungsbeispiels.

In the following the invention will be explained in more detail by means of embodiments and with reference to the drawing. In the schematic drawing show partly in section:

Fig. 1

the essential parts of an arc spray device for carrying out a first embodiment of the method according to the invention,

Fig. 2

as Fig. 1 however, for a second embodiment of the method according to the invention,

Fig. 3

a spray wire for a further embodiment of the inventive method, and

Fig. 4

a schematic representation to illustrate a further embodiment.

Fig. 1 shows a schematic representation of the essential parts of an arc spray device, which is suitable for carrying out a first embodiment of the inventive method, and with which a dense layer 18 on a substrate 10 can be produced.

The arc spray device comprises a spray gun 1, a first feeder 3, an oxidizable particle reservoir 12, which is usually in powder form in the reservoir 12, and a drive unit 14 for controlling the process. The spray gun 1 comprises in a conventional manner two electrically conductive spray wires 2, which are connected to the supply of electrical energy to a power source 16, so that ignited between the spray wires 2 in a melting region 7, an arc 6 and stably maintained for a predetermined period can be. The spray wires 2 are fed from a storage device, not shown, a wire guide 5. The wire guide 5 comprises a wire feed 13, which is suitable for feeding the spray wire 2 through a guide device 17 to the melting region 7. The Guide device 17 is preferably designed such that it is connectable to the energy source 16 as an electrically conductive device and is electrically conductively in contact with the spray wire 2, so that via the guide means 17 necessary for the generation of the arc 6 electrical energy supplied to the spray wire 2 can be. Since during the arc spraying in the melting region 7 material of the spray wire 2 is continuously transferred into a melt 8, the spray wire 2 must be continuously fed to maintain the arc 6 through the wire guide 5 in the melting region 7.

Arc spraying may or may not be performed under a controlled atmosphere. In this case, the method is performed in a process chamber 30, which in Fig. 1 is only indicated and whose atmosphere is adjustable or controllable in a conventional manner with pumps and gas supplies not shown.

The melt 8 formed from the material of the spray wire 2 in the arc 6 is acted upon by a fluid 4, which is supplied via the first feed device 3 from a gas reservoir 19. The fluid 4 transports the melt 8 onto a surface 9 of the substrate 10 to be coated, whereby the layer 18 is formed. By the fluid 4, which is preferably a gas, in particular oxygen, nitrogen, argon, helium, ambient air, a mixture of these or another gas, the melt 8 is acted upon by a predeterminable working pressure, whereby the melt 8 on the surface 9 of the substrate 10 is thrown. There, the melt condenses 8 in a solid state.

According to the invention, the melt 8 is supplied with the oxidisable particles 11 in such a way that the oxidizable particles 11 together with the melt 8 are deposited on the substrate 10. For this purpose, according to the first exemplary embodiment described here, the oxidizable particles 11 are added to the fluid 4 before the fluid 4 acts on the melt 8.

For this purpose, a connection 15 is provided, through which the oxidizable particles 11 can pass from the reservoir 12 into the feed device 3, where they are entrained by the fluid 4, so that the particles 11 act together with the fluid 4, the melt 8 in the melting region 7. Thus, the melt 8 are supplied by the fluid 4, the oxidizable particles 11, so that the particles 11 are mixed in the melting region 7 with the melt 8 and applied together with the melt 8 on the surface 9 of the body 10.

In this process, the oxidizable particles 11 can be melted or plasticized. In this case, the material for the particles 11 should preferably be so gewält that it does not come to a substantial alloy or compound formation between the particles 11 and the material of the spray wires 2. But it is also possible that the oxidizable particles 11 remain substantially solid and dimensionally stable during their transport in the melt 8. The particles 11, which are usually solid particles, are then not melted in the melt 8 itself, but retain their outer shape and remain substantially solid. Of course, it is possible that only a slight melting of the particles 11 on their surface occurs.

After completion of the thermal spraying process, the oxidizable particles 11 in the layer 18 are oxidized. This is done by exposure to an oxidizing agent. One possible oxidizing agent is water. This may for example be sprayed onto the layer 18 or the layer 18 or the substrate 10 with the layer 18 are brought into a dipping bath. Of course, other oxidizing agents than water can be used. Due to the oxidation, the volume of the oxidizable particles 11 compared to non-oxidized state, so the particles 11 "swell" so to speak, whereby pores, capillary channels or other openings or passages in the layer 18 are closed or filled. By this oxidation, the layer 18 is thus sealed. This sealing takes place not only on the surface of the layer 18, but also everywhere in the layer 18. This has the consequence that then practically no more liquids can penetrate the layer 18, so that the substrate 10 is very efficiently protected, especially against under corrosion. Since the seal or the seal takes place in the entire layer 18, it is possible without loss of quality to make the surface of the layer 18 rough. This is advantageous, for example, as slip protection when the layer 18 is a floor, eg a ship's floor, on which persons are walking.

A further advantageous measure, which can be realized by the increase in volume of the particles 11, is the generation of residual compressive stresses in the layer 18. By the swelling of the particles 11 during the oxidation, compressive stresses are generated in the layer 18, which have a positive effect on the durability or ., affect the adhesion of the layer 18.

If it is desired that the oxidizable particles 11 do not melt during the injection process, the dimensional stability of the particles 11 in the melt 8 can be ensured by a few parameters, of course by a suitable choice of material for the particles 11, on the other hand Size of the particles 11 or by the flow rate of the fluid 11. By the same parameters, of course, a melting of the particles 11 can be realized.

As oxidizable particles 11, which serve for the subsequent sealing of the layer 18, very many materials are suitable, in particular in the form of solid particles. Suitable examples are: zinc, aluminum, magnesium, iron, or alloys of these elements with each other or with other elements. In particular iron-base compounds with an iron content of more than 50% are suitable or also the alloy ZnAl 85/15 which contains 85% zinc and 15% iron.

For controlling or regulating the process, the arc spraying device has, for example, a freely programmable drive unit 14 with which, in particular, the following parameters can be regulated or set: the working pressure with which the fluid 4 acts on the melt 8, the quantity of particles 11 fed in, the wire feed 13, the injection wires 2 supplied electrical energy. For this purpose, the drive unit 14 is connected via signal lines 20 to the respective components of the device. Furthermore, the control unit 14 may comprise sensor lines 21, by means of which the control unit 14 can transmit various operating parameters, such as actual working pressure, gas pressure in the process chamber, ambient pressure, temperature, electrical operating parameters of the energy source or other parameters.

To produce the dense layer 18, the melt 8 generated in the melting region 7 is then first transported by the fluid flow laden with the particles 11 to the surface 9 of the substrate 10 by means of the arc spraying process, where the melt 8 is deposited in the form of splashes or droplets becomes. In the forming layer 18, the oxidizable particles 11, which are in the form of solid particles or in other or molten form, incorporated. Once the desired layer thickness has been reached, the thermal spraying process is ended. In one Further processing step, the oxidizable particles 11 are now oxidized in the solidified layer 18, whereby the layer 18 is sealed.

Fig. 2 shows the essential parts of an arc spray device for carrying out a second embodiment of the inventive method. In the following, only the differences from the first embodiment will be discussed. The preceding explanations with regard to the first exemplary embodiment also apply analogously to the second exemplary embodiment. The same reference numerals denote the same parts or functionally equivalent parts as in the first embodiment.

The essential difference from the first exemplary embodiment lies in the fact that, in the second exemplary embodiment, the oxidizable particles 11, viewed in the flow direction, are added only after the melting region 7.

For this purpose, a second feed device 31 is provided, through which the oxidizable particles 11 can be introduced from the reservoir 12 into the melt 8, wherein the entry of the particles 11 takes place here only between the melting region 7 and the substrate 10. For this purpose, the second feed 31 has an orifice 32 which, however, is arranged in the vicinity of the melting region 7 on the substrate side of the melting region 7, so that the particles 11 can be introduced from there into the coating jet formed by the melt 8 and the fluid 4. The particles 11 can also be transported in this embodiment by means of the fluid 4 through the second feeder 31. For this purpose, for example, the second feed 31 is connected to the gas reservoir 19 or a separate fluid reservoir (in Fig. 2 not shown).

In the Fig. 2 Of course, the apparatus shown also has an energy source 16, the representation of which has been omitted here for reasons of clarity.

The melt 8 formed from the material of the spray wire 2 in the electric arc 6 is applied to the surface 9 of the substrate 10 by the fluid 4 via the first supply device 3 from a gas reservoir 19 analogously to the previously described embodiment. The oxidizable particles 11 pass from the orifice 32 into the melt 8 and are then transported together with the latter to the substrate 10.

According to a further embodiment of the method according to the invention, the oxidizable particles can also be provided in one or both of the sprayed wires 2. The spray wire 2 is then configured as a cored wire, which in addition to the actual, for example, metallic coating material additionally contains the oxidizable particles 11. Fig. 3 shows such a spray wire 2 in cross section. In this embodiment, it is then no longer necessary to supply the oxidizable particles 11 in addition from a reservoir such as that in the Fig. 1 and 2 is shown. In this further embodiment, the oxidizable particles 11 are released during melting of the spray wire 2 in the melting region 7 and then get transported by the fluid 4 together with the melt 8 to the substrate 10. The achieved volume fraction of the particles 11 on the layer 18 can then be above the relative Set the proportion of particles 11 in the spray wire 2.

Another embodiment is shown schematically in FIG Fig. 4 clarified. In this embodiment, at least one third spray wire 22 is provided which contains the oxidizable particles 11. This third spray wire 22 is introduced into the melting region 7, where its tip is melted, whereby the oxidizable particles 11 are released, and then together with the melt 8 of the fluid 4th to be transported to the substrate 10. It is understood that a wire feed is also provided for the third spray wire 22. The third spray wire 22 can be supplied energized or de-energized. If the third spray wire 22 is energized, then it can be switched either as a cathode or as an anode. For example, at least one further arc is produced. However, it is also possible to conduct the third spray wire without current, so that it melts only by the heat of the melting range, which is generated by the arc between the two spray wires 2.

Claims (11)

Arc-spraying method for producing a dense layer on a substrate, in which an electrical voltage is applied to two electrically conductive spray wires (2), with which an arc (6) between the spray wires (2) is ignited, wherein from the spray wires (2) in a melt (8) is produced in a melting region (7), the melt (8) being supplied with a fluid (4) which transports the melt (8) to the substrate (10) where the melt (8) is produced the layer (18) is deposited, characterized in that the melt (8) oxidizable particles (11) are supplied, which are deposited together with the melt (8) on the substrate (10) and that after completion of the spraying, the oxidizable particles (11) are at least partially oxidized to seal the layer (8). Process according to Claim 1, in which the oxidisable particles (11) occupy a volume fraction of from 3% to 20% of the volume of the layer (18). Method according to one of the preceding claims, in which the oxidisable particles (11) are added to the fluid (4) before the fluid (4) acts on the melt (8). Method according to one of the preceding claims, wherein the oxidizable particles (11) of the melt (8) between the melting region (7) and the substrate (10) are added. Method according to one of the preceding claims, in which the oxidisable particles (11) are part of at least one spray wire (2). Method according to one of the preceding claims, wherein a third spray wire (22) is provided, which contains the oxidizable particles (11). Method according to one of the preceding claims, in which the oxidisable particles (11) contain iron or zinc or aluminum or magnesium or alloys of these elements. Method according to one of the preceding claims, in which the oxidisable particles (11) are oxidized by means of water. A method according to any one of the preceding claims, wherein the substrate (10) is made of steel or has a steel surface. Dense layer produced by a process according to one of the preceding claims. Dense layer according to claim 10, which has residual compressive stresses.

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