EP0979317B1 - Process for application of an inorganic coating to an electrically conducting body - Google Patents

Abstract

PCT No. PCT/DE97/02661 Sec. 371 Date May 13, 1999 Sec. 102(e) Date May 13, 1999 PCT Filed Nov. 13, 1997 PCT Pub. No. WO98/21382 PCT Pub. Date May 22, 1998A process of applying an inorganic coating to an electrically conducting body, in particular a metallic workpiece, is characterized with respect to a precisely controllable temperature variation with short temperature changes in an economical and energy-saving operation in that the body first undergoes a preparation. Thereafter, if need be, the body is degreased and/or chemically pretreated and/or blasted. Subsequently, a coating medium is applied to at least the surface region of the body being coated. Then, at least the surface region of the body being coated is heated by induction to a reaction temperature before and/or while and/or after applying the coating medium. Finally, the coating medium is fully reacted to a coating, whereupon the body undergoes a cooling.

Description

The invention relates to a method for applying an inorganic Coating on an electrically conductive body, especially on a metallic one Workpiece.

The most varied of methods for applying a are from practice known inorganic coating on an electrically conductive body. The The coating is built up under the influence of temperature, whereby a reaction of the coating medium after its application to the body or the surface of the body is caused. The reaction leads to Establishment of an essentially inorganic network. Depending on the used Coating medium different reaction temperatures are required. Such reactions differ in terms of thermodynamics and Kinetics crucial for reactions with organic coating media. The The coating described often serves to protect the often metallic body against corrosion. The reaction described above usually takes place in a convection oven after applying the coating medium. The reaction temperature is depending on the coating medium between 180 ° C and 300 ° C. With these The coating medium reacts to temperatures for coating.

When using such convection ovens it is problematic that the heating process of the body to be coated is very sluggish, with a change of Temperature takes a lot of time. Because of the sluggish temperature runout in the reaction of the coating medium in the surface area of the Body mostly the whole body unnecessarily due to heat conduction mitaufgeheizt. By heating up the whole body this becomes a big one Amount of energy needed without contributing to the reaction process.

Furthermore, it is disadvantageous when using the known convection ovens that it it is necessary to design the convection ovens so voluminous that the one to be coated Body is completely absorbed in the oven. Hence, that requires Implementation of the known coating process in an uneconomical manner a lot of space.

The present invention is therefore based on the object of a method for Application of an inorganic coating on an electrically conductive body specify a precisely controllable temperature curve with short Temperature change processes with economical and energy-saving Operation is enabled.

The object presented above is by a method with the features of the claim 1 solved. After that is a method of applying an inorganic Coating on an electrically conductive body by the following Process steps marked:

First, the body is made available. Then the body optionally degreased and / or chemically pretreated and / or blasted, e.g. sandblasted. This allows the surface of the body if necessary be prepared for the coating. This is followed by the application of a Coating medium on at least the surface area to be coated of the body.

In the manner according to the invention, at least the one to be coated is now Surface area of the body before and / or during and / or after application of the coating medium is inductively heated to a reaction temperature. By means of this inductive heating according to the invention there is first a energetically very advantageous heating of the body realized, because only the surface area to be coated and not necessarily the entire area Body is heated. By directly coupling to the electrically conductive body generates cyclones in the body that are due to the electrical resistance of the body material to warm the body to lead. Energy losses due to heating a heating medium in the form of For example, circulating air and its inevitable heat radiation are excluded. The warming is consequently targeted in the body or in the body Surface area caused by a suitable control of the Induction device with it a precisely controllable temperature curve resulting short temperature change processes is enabled. By the inductive heating the body is heated from the inside, so to speak highly efficient heating of the coating medium is also effected.

The heating process according to the invention is summarized by means of an inductive one Heating in a simple manner via the energy supply to the associated Induction heating device adjustable, which then results from the direct inductive energy transfer principle in addition to a short heating phase extremely short reaction times to temperature control and changing processes result. Due to the direct heating of the surface area to be coated is an economical and energy-saving mode of operation without the requirement a spacious convection oven.

Depending on the requirements specified by the coating medium, the surface area of the body to be coated in a simple manner and / or during and / or after the application of the coating medium be heated to a reaction temperature. This is a high flexibility of the Procedure guaranteed.

After the coating medium has reacted to form the coating, as last step of the process of the invention is cooling the Body. The body can be exposed to room temperature, which ultimately results in an independent cooling of the body. The cooling can but also by an active process step using a cooling medium respectively.

Consequently, the method according to the invention is an application method specified an inorganic coating on an electrically conductive body, in which a precisely controllable temperature curve with short Temperature change processes with economical and energy-saving Operating mode is realized.

With regard to a particularly flexible process, which is individual Requirements at least due to the coating medium used could be sufficient the surface area of the body to be coated before Application of the coating medium heated inductively to a preheating temperature become. The preheating temperature could prevent premature Initiate the reaction of the coating medium below the reaction temperature lie.

If necessary, the coating medium could react to the coating with the participation of water. This would be a separate one Supply of the amount of water required for the reaction is conceivable. The water supply but could also be done in a simple manner by an independent withdrawal of water from the atmospheric humidity of the surrounding atmosphere.

To protect the body against corrosion, the coating medium and so that the coating preferably has pigments made of zinc and / or aluminum. This would be an active protection against corrosion by the coating medium realized.

Depending on the coating requirements, this could be the case Coating medium additives such as internal lubricants, viscosity regulators, Have leveling agents and / or anti-crater additives. An individual This means there are no limits to the design of the coating medium set.

In view of particularly favorable usage properties, this could Coating medium a binder from at least one organic and / or have inorganic metal compound. Here are titanium, zirconium, chrome, Metal compounds containing boron, aluminum, silicon, cobalt, nickel or magnesium very cheap. The aforementioned elements can in the metal compound available individually or in combination. Furthermore, as a binder for the Coating medium a high molecular aminically crosslinked epoxy / phenoxy binder advantageous.

With regard to a favorable course of the layer-forming crosslinking reaction could the binders in an optionally commercially available organic solvent and / or be dissolved in water. In case of preheating the body could be the preheating temperature between room temperature and the Boiling temperature of the solvent or water. This would be a controlled escape of the solvent or water from the build-up Layer guaranteed and thus an optimal compression of the layer reached. Such preheating could be done both before applying the coating medium as well as after application. In the latter The case would then be a gradual heating of the surface area to be coated of the body with the coating medium already applied.

Since the heating of the body to be coated and the application of the coating medium could take place in two different parts of the plant it in this case - when preheated before applying the coating medium Body - sufficient after applying the coating medium Time to allow the solvent or water to protect the surface below the boiling temperature during the transfer of the body into the heating area can escape. Once the solvent has escaped, the temperature can rise the surface to be coated to the necessary in just a few seconds Reaction temperature are brought to the optimal function and Achieve coating quality.

With regard to a particularly favorable energy balance, inductive heating could of the body only within partial areas. By such targeted heating of only the areas to be coated, it is possible to adjacent and / or non-electrically conductive substances or surface areas little or no warming up. A warming of these areas would be then only possible by heat conduction. The targeted introduction of heat also enables the coating of individual parts of an overall device and, on the other hand, complete complete devices. Doing so e.g. fully assembled bearings coated entirely or only at selected points become.

In a particularly energy-saving manner, the heating could be carried out in one Surface area with a depth of max. 0.5 mm. With accordingly Short-term warming would be conduction into the remaining areas to neglect the body to be coated.

To avoid heating or not to be coated temperature sensitive areas the body could partially or totally during and / or cooled after heating with a suitable cooling medium become. A gaseous or liquid cooling medium could be used as the cooling medium Form of, for example, air, water or oil can be used. This would be temperature sensitive Areas easily protected from the effects of temperature. Only by using induction heating is it possible to be temperature sensitive Places or areas of the body to be coated at the same time as the heating the surface areas to be coated with air or liquid Cool cooling media.

With such cooling it can be taken into account that the invention Induction heating processes shorten the response time with a significant increase in the crosslinking temperature to achieve a fully crosslinked Coating conditionally, which is only in their fully networked scope their favorable Features fully. Too high a temperature can, however Destruction of the network or the pigments and additives embedded in it to lead. As a result, cooling the body at the appropriate time may differ bring positive effects. The cooling could only be achieved after this the reaction temperature can be used.

With regard to a particularly high protective effect, the coating could be a have cathodic effect. Depending on the requirement, the coating could in addition or as an alternative to the cathodic effect, it is electrically and / or thermally conductive his. Almost metallic conductivity could be achieved.

With regard to the smallest possible change in the dimension of the body by applying the coating, the coating could have a layer thickness from about 2 to 30 microns. This might be the case extreme corrosion protection in the thinnest layers. In more advantageous The coating could also be weldable.

To avoid excessive environmental pollution, the coating could have no heavy metals and in particular free of chromium VI and cadmium his.

The control of the layer thickness could, on the one hand, be based on the viscosity of the Coating medium and on the other hand or additionally via a mechanical Deduction must be set. With a view to mechanical removal this can be done in a simple manner by skidding. All other known Paint application methods are also applicable.

If necessary, an additional organic top layer could be applied to the coating be upset. The composition of the top layer could be considered for the best possible adhesion to the composition of the coating be coordinated. The binder has a significant influence. in the In connection with the application of organic cover layers are high molecular weight aminically cross-linked epoxy / phenoxy binders of the top layer in particular Cheap.

The coating medium and / or the top layer is applied in in a particularly simple manner by spraying, in particular electrostatic Spraying, or a dipping process. The diving process in connection with Skidding is particularly used for bulk goods.

With regard to a particularly precisely controllable temperature curve could the heating and / or cooling or cooling take place under computer control. This would allow a fully automated process.

Controlling the coating parameters could be particularly simple Way through the AC voltage frequency of the inductor and / or the induction duration and / or the reaction temperature.

The method according to the invention can be used with all known technologies.

Applying an organic cover layer can reduce the coloring, insulation, setting a constant coefficient of friction and improving the Contact corrosion resistance serve.

In particular, transistorized converters are used as induction devices Application, as this particularly the execution of precise computer-controlled processes favor.

The inventive method for applying an inorganic coating has a high protective effect against the chemical and electrochemical Corrosion as well as contact corrosion of e.g. Steel versus aluminum Episode. Furthermore, a high resistance of the coating in salt spray, Condensation and Kestemichtest reached. A hydrogen embrittlement to the coated surfaces do not occur.

There are short cycle times of seconds while the process is being carried out possible. A decrease in component strength is due to the short The effect of temperature is far less critical than with conventional heating.

With the method according to the invention one is due to the low energy costs and disposal costs realized extremely environmentally friendly process, whereby the construction of a small and compact system is possible.

einzige Figur

im Rahmen eines Blockdiagramms schematisch den Ablauf eines Ausführungsbeispiels eines erfindungsgemäßen Verfahrens zum Aufbringen einer anorganischen Beschichtung auf einen elektrisch leitfähigen Körper.

There are now various possibilities for advantageously designing and developing the teaching of the present invention. For this purpose, reference is made to the subordinate claims, on the one hand, and to the following explanation of an exemplary embodiment of the method according to the invention with reference to the drawing. In conjunction with the explanation of the preferred exemplary embodiment of the method according to the invention with reference to the drawing, preferred configurations and developments of the teaching are also explained in general. In the drawing, the

only figure

in the context of a block diagram, the sequence of an exemplary embodiment of a method according to the invention for applying an inorganic coating to an electrically conductive body.

The single figure shows a schematic representation of the sequence of an example Method according to the invention for applying an inorganic coating on an electrically conductive body. The individual process steps distinguished by the reference numbers 1 to 6.

Reference number 1 denotes the first method step in which a Deploying the body is done. Method step 2 consists of a optional degreasing and / or chemical pretreatment and / or blasting of the Body, e.g. sandblasting. If the body provided in step 1 is none this step 2 can be omitted.

In the next process step marked with the reference number 3 applying a coating medium to at least the one to be coated Surface area of the body. The coating medium could also applied to surface areas of the body that are not to be coated be what a subsequent removal of the coating medium from the surface areas not to be coated.

The following inductive heating, identified by the reference number 4 at least the surface area of the body to be coated on a Reaction temperature could be before and / or during and / or after application of the coating medium. Depending on the requirement, there is preheating at least the surface area to be coated before the application of the Coating medium possible. This could be an escape from the Crosslinking reaction of the coating medium does not require solvents favor.

The coating usually has a high thermal resistance up to approx. 350 ° C. Too high a temperature can destroy the coating. One too high temperature, especially over a long period of time, is also for heat-sensitive areas of the body to be coated harmful, so that the short-term treatment by induction is particularly advantageous here comes. In any case, care must be taken that a maximum temperature is not exceeded.

Furthermore, it is only possible using inductive heating temperature-sensitive areas of the body to be coated at the same time heating of the coated areas with air or liquid media cool.

After inductive heating, reaction takes place in method step 5 of the coating medium for coating. Inductive heating enables with less effort compared to conventional air-conditioning technology rapid formation of a fully networked coating or protective layer. This rapid reaction thermodynamics and kinetics cause the shortening of the Response time to achieve a significant increase in the crosslinking temperature a fully networked layer that only fully exhibits the properties mentioned having. Because too high a temperature to destroy the network or can lead to pigments and additives embedded in them is temperature control advantageous.

In the last method step, designated by reference number 6, one Embodiment of the method according to the invention, the body is cooled. On the one hand, this can be done by passive cooling in, for example, ambient air or by means of active cooling using a special cooling medium like water or oil.

Inductive heating is ideal for the reaction of the coating media on partially coated, more or less large bodies, for Reaction of the entire coated body or also for coating Massengütem. The method described is advantageous in that There is no need for multiple coatings due to imperfections and contact points. The Spraying of preheated bulk goods while moving the bed is guaranteed when coating such bodies, a particularly uniform coating without missing parts.

When using a dipping process to apply the coating medium preheated bodies can also be immersed.

With regard to further advantageous embodiments of the invention Procedure is used to avoid repetition on the general part of the Description and reference to the accompanying claims.

Finally, it should be expressly noted that this was discussed above Embodiment of the method according to the invention only for discussion serves the teaching claimed, but not on the embodiment limits.

Claims (10)

1. Process for the application of an inorganic coating to an electrically conductive body, especially to a metal workpiece, having the following process steps:

   making the body ready;

   optional degreasing and/or chemical pretreatment and/or blasting of the body;

   application of a coating medium to at least that surface region of the body which is to be coated, the coating medium having a binder comprising at least one organic and/or inorganic metal compound and the binder being dissolved in an organic solvent and/or in water;

   inductive heating of at least that surface region of the body which is to be coated, after bringing the coating medium to a reaction temperature;

   fully reacting the coating medium for coating;

   cooling the body;

   characterised in that at least that surface region of the body which is to be coated is heated inductively, before the application of the coating medium, to a preheating temperature lying below the reaction temperature, and in that the preheating temperature lies between room temperature and the boiling temperature of the solvent or the water.
2. Process according to claim 1, characterised in that the full reaction of the coating medium for coating takes place with the participation of water, the water being drawn preferably from the moisture of the surrounding atmosphere.
3. Process according to claim 1 or 2, characterised in that the coating medium comprises pigments of preferably zinc and/or aluminium and/or additives, such as, for example, internal lubricants, viscosity-regulators, flow agents and/or anticrater additives and/or in that the metal compound comprises titanium, zirconium, chromium, boron, aluminium, silicon, cobalt, nickel or magnesium.
4. Process according to any one of claims 1 to 3, characterised in that the inductive heating of the body takes place only within partial regions and/or in that the heating takes place in a surface region with a depth of a maximum of 0.5 mm.
5. Process according to any one of claims 1 to 4, characterised in that the body is cooled partially or totally with a cooling medium during and/or after the heating operation, the cooling medium preferably being gaseous or liquid in the form of, for example, air, water or oil.
6. Process according to any one of claims 1 to 5, characterised in that the coating has a cathodic anticorrosive action and/or in that the coating is electrically conductive and/or heat-conductive and/or in that the coating has a layer thickness of approximately from 2 to 30 micrometres and/or in that the coating does not comprise heavy metals and is, in particular, free from chromium(VI) and cadmium.
7. Process according to any one of claims 1 to 6, characterised in that the layer thickness is adjusted by means of the viscosity of the coating medium and/or in that the layer thickness is adjusted by means of mechanical removal of material, the mechanical removal of material preferably being effected by centrifuging.
8. Process according to any one of claims 1 to 7, characterised in that an additional organic cover layer is applied to the coating, the composition of the cover layer preferably being tuned to the composition of the coating with a view to as good an adhesion as possible and the binder of the cover layer preferably being a high-molecular-weight epoxy/phenoxy binder crosslinked by means of amines.
9. Process according to any one of claims 1 to 8, characterised in that the application of the coating medium and/or of the cover layer is effected by spraying, especially electrostatic spraying, or by an immersion process.
10. Process according to any one of claims 1 to 9, characterised in that the heating and/or the passive or active cooling is effected under the control of a computer and/or in that the coating parameters are controlled by means of the alternating voltage frequency of the inductor and/or the induction period and/or the reaction temperature.

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