WO2019076602A1

WO2019076602A1 - Passive electrical component having an insulating layer produced in situ during casting

Info

Publication number: WO2019076602A1
Application number: PCT/EP2018/076247
Authority: WO
Inventors: Ralph Wilken; Franz-Josef Wöstmann
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung eingetragener Verein
Priority date: 2017-10-17
Filing date: 2018-09-27
Publication date: 2019-04-25
Also published as: DE102018101186A1; DE102018101186B4

Abstract

The invention relates to a method for producing a passive electrical component by casting, having an insulating layer produced in situ, to a passive electrical component produced or producible by said method, and to a mold for producing a passive electrical component, which component has an insulating layer on the surface thereof.

Description

Passive electrical component with in-situ generated insulating layer

The present invention relates to a method for producing a passive electrical component by casting with an insulating layer produced in situ during casting, a passive electrical component manufactured or producible by this method, and a molding tool for producing a passive electrical component which is on its surface having an insulating layer.

In the course of the introduction and spread of electromobility, the lightweight construction of electric motors is gaining in importance. For this purpose, it is necessary to form passive components such as coils, helices, rectangular conductors and round conductors made of aluminum or an aluminum alloy or an alloy containing aluminum. The shaping of such aluminum components is advantageously carried out by a casting process in which a melt of aluminum or an aluminum alloy or an alloy containing aluminum is poured into a cavity of a mold and allowed to solidify there, wherein the shape of the cavity determines the shape of the component to be produced.

Casting produced coils are known for example from DE 10 2010 020 897 A1 and EP 2 688 183 A2. DE 10 2015 1 13 858 A1 discloses a coil produced by casting. It is also proposed to apply an electrical insulation to the coil when it is in the extended state. The individual turns of the coil are thereby electrically isolated from each other. For example, the insulation may be applied to the extended coil by a dipping or spraying process.

DE 30 36 436 A1 discloses a process for the production of metallic injection moldings with an undercut region, wherein a molten metal is injected into an injection mold whose casting surface has at least one lost sand core which forms an undercut region on the injection molding, wherein at least a sand core comprising from about 0.25 to 5% by weight (based on the molding sand) of a binder, which is substantially an acid-curable resin, about 20 to 70 wt.% (Based on the resin) of an oxidizing agent and the rest consists of molding sand, and the injected metal can be solidified, demolded the formed Spritzgießling and freed from the sand core. Sand and an acid-hardening resin are mixed to make the lost cores. Optionally, a silane is added. Finally, the addition of the oxidizing agent takes place. The entire mixture can then be blown into a core box with air or introduced by hand. To harden the resin, sulfur dioxide is passed through the core box. The function of the oxidizing agent is to react with gaseous sulfur dioxide to form sulfur trioxide or sulfuric acid, which in turn hardens the resin. The core is then removed as a solid mass from the core box and used in injection molding.

DE 10 2007 020 586 A1 discloses a size for coating casting molds, wherein the size comprises a carrier liquid, a pulverulent refractory material and a reducing agent. DE 15 46 196 B discloses a method for producing aluminum electrodes for electrolytic capacitors, in which the surface of the electrode body is first roughened by chemical means and then coated after cleaning with an acting as a dielectric oxide layer, the electrode body after roughening, but before the coating with the oxide layer for cleaning be treated without current with dilute, aqueous phosphoric acid solution.

DE 29 09 107 A1 discloses a method for the production of bodies of granular and / or fibrous material with sodium silicate or potassium silicate as a binder, wherein a surface-active substance is added when the material is mixed. DE 37 28 993 A1 discloses a method for protecting aluminum and aluminum alloys by means of a protective coating comprising contacting the cleaned aluminum with a basic aqueous solution containing an alkali metal permanganate and a compound selected from alkali metal chlorides, alkali metal tetraborates, alkali metal metaborates, alkali metal carbonates, benzoic acid, alkali metal benzoates and mixtures of alkali metal meta- and tetraborates, said solution having a pH in the range of from 7 to 12.5, wherein a conversion coating is formed on the aluminum, and then wherein excess coating solution is removed from the aluminum.

Passive electrical components for use in electric motors usually have to be provided with an insulating layer that satisfies both high electrical (high dielectric strength) and high mechanical requirements (low abrasion, strong adhesion to the body of the component). According to the state of the art, suitable for this purpose are insulating wet paints, insulating powder paints, anodizing films and plasma polymer coatings or combinations thereof, which in each case after the molding of the component by casting in one or more downstream, time-consuming and costly steps (optionally with - And post-treatments such as curing in the case of paints) must be applied.

The object of the present invention is therefore to provide a method for producing a passive electrical component having an insulating layer on its surface, wherein the formation of the insulating layer takes place in-situ during the casting process, so that the cost of downstream processing steps is significantly reduced ,

This object is achieved by a method for producing a passive electrical component having an insulating layer on its surface. The method according to the invention comprises the steps

Providing a mold having a cavity which comprises a shaping chamber which corresponds to the shape of the component to be produced,

Coating the wall surface of the forming chamber with an oxidizing agent so that a layer containing the oxidizing agent is formed,

Pouring a melt of aluminum or an aluminum alloy or an aluminum-containing alloy into the cavity, Oxidizing the aluminum at the interface between the melt and the oxidant-containing layer and solidifying the melt in the cavity so as to form a blank comprising the passive electrical component,

Removing the formed blank from the mold,

- Working out of the passive electrical component from the blank.

In the method according to the invention is advantageously on the surface of the resulting by solidification of a melt of aluminum or an aluminum alloy or an aluminum-containing alloy in the cavity blank in situ an alumina-containing insulating layer formed by oxidation of aluminum at the interface between the solidifying melt and the the oxidant-containing layer on the wall surface of the forming chamber of the cavity. In this case, aluminum is oxidized by the oxidizing agent at the interface between the solidifying melt and the layer containing the oxidizing agent. Thus, the casting process according to the invention is referred to as "reactive casting." The process according to the invention thus makes it possible to integrate the formation of the insulating layer into the molding by molding, so that subsequent steps for forming the insulating layer are not required According to the invention, an aluminum alloy is understood to mean an alloy whose main constituent is aluminum, ie the aluminum content is at least 50%, based on the total mass of the alloy Alloy containing aluminum is understood according to the invention an alloy with a lower aluminum content.

The casting process takes place, for example, in die-casting, low-pressure casting or precision casting, the corresponding technologies are known in the art.

For the inventive method, a mold is used with a cavity which determines the shape of the blank formed from the solidified melt. Typically, such a cavity comprises one or more sprue channels for filling the melt, one or more overflow channels, and a shaping chamber, which corresponds to the shape of the component to be produced. The shaping chamber of the Forming tool has, for example, the shape of a coil, a helix, a rectangular conductor or a circular conductor. Particularly preferably, the forming chamber of the mold on the shape of a coil.

Such molds and processes for their preparation are known in the art. The molding tool is selected from the group consisting of one-piece molding tools and multi-part molding tools.

The blank removed from the molding tool after casting has a shape which has material projecting beyond the shape of the desired passive electrical component, which material is formed in particular in the region of the sprue channels and the overflow channels of the cavity. The working out of the passive electrical component from the blank involves removal of this material (with respect to the desired shape of the component), e.g. the knocking off of overhanging sprues.

In order to form an insulating layer on the surface of the passive electrical component to be produced, at least the entire wall surface of the shaping chamber cavity of the mold must be covered with a layer containing the oxidizing agent. However, it is not excluded that the layer containing the oxidant extends to further areas of the wall surface of the cavity of the mold, e.g. the wall surfaces of one or more overflow channels. Preferably, the oxidant-containing layer does not extend to the wall surfaces of the runner channels to prevent contamination of the molten metal by oxides formed.

In a preferred embodiment of the method according to the invention molds are used, the cavity has a chamber in which one or more cores are inserted, so that a forming chamber is formed, the wall surface of the wall surface of the chamber of the cavity of the mold and the surface of the in this chamber consists of inserted core or cores inserted in that chamber. That is, the shape of the cavity defined by the wall surface of the chamber of the mold and the surfaces of the core inserted into the chamber or the cores inserted into the chamber, to be filled by the melt corresponds to the shape of the component to be produced. The shaping chamber is formed in this preferred embodiment by inserting one or more cores in a designated chamber which is part of the cavity of the mold, while before inserting the core or this chamber does not yet correspond to the shape of the component to be produced So there is no shaping chamber yet. In this preferred embodiment of the method according to the invention, the provision of the molding tool comprises the following steps:

Providing a mold with a cavity having a chamber for receiving one or more cores and coating the wall surface of said chamber with an oxidizing agent so as to form on the wall surface of the chamber an oxidant-containing layer,

Providing a core or cores and coating the surface of the core or cores with an oxidizing agent such that an oxidant-containing layer is formed on the surface of the core or cores,

Inserting the coated core or coated cores into the chamber of the cavity of the molding tool so as to form a molding chamber whose wall surface is made up of the wall surface of the chamber of the mold cavity and the surface of the core inserted in said chamber or inserted therein Cores exists and having an oxidant-containing layer.

The mold provided in this way has a shaping chamber whose wall surface consists of the wall surface of the chamber of the cavity of the mold and the surface of the core inserted into this chamber or of the cores inserted in this chamber and has a layer containing the oxidizing agent.

Such cores, e.g. in the form of cores, cores or cores, as well as their preparation and use are known in the art. In a preferred embodiment of the method according to the invention, the cores are salt cores. For example, a two-part, i. consisting of two surrounding the cavity shells existing mold with an inserted into the forming chamber of the cavity core (core as depositors).

In the method according to the invention, a melt of aluminum or an aluminum alloy or an alloy containing aluminum is poured into the cavity of a mold, wherein the wall surface of the molding chamber of the cavity of the mold has a layer containing an oxidizing agent which is capable during the Solidifying the melt at the interface between the solidifying melt and the oxidant-containing layer of aluminum to alumina to oxidize, so that the surface of the blank formed from the solidified melt Having an at least 1 μιη thick aluminum oxide-containing insulating layer. This insulating layer is formed by oxidizing the oxidizing agent to alumina at the interface between the solidifying melt and the oxidant-containing layer of aluminum. Preferably, the oxidizing agent has a standard potential higher than 1V, preferably 1.2V or higher, more preferably 1.5V or higher. The oxidizing agent is preferably selected from the group consisting of permanganates, perborates, peroxycarboxylic acids, percarbonates, peroxides and salts of halo-oxygen acids.

Coating with the oxidizing agent is preferably carried out by contacting the wall surface of the chamber to be coated with the cavity of the mold and, if cores are required to form the shaping chamber, contacting the surface of the cores with a solution of the oxidizing agent in a solvent and then the solvent is removed by drying so that a layer containing the oxidizing agent is formed on the wall surface of the chamber of the cavity of the mold and optionally on the surface of the cores.

Preferred solvents for the oxidizing agent are water, molten salts and solutions of crown ethers in organic solvents such as alcohols and aromatics, e.g. Toluene. The concentration of the oxidizing agent in the solution is preferably from 1% to 40% of its saturation concentration at the use temperature of the solution, more preferably from 5% to 30% of its saturation concentration, more preferably from 7.5% to 20% of its saturation concentration, most preferably 10% % of its saturation concentration, in each case at the operating temperature of the solution.

When using salt cores, the skilled person must take care that the cores are not dissolved or dissolved by the solvent when the surface of the cores is brought into contact with the solution of the oxidizing agent. For this purpose, a solvent is selected either for the solution of the oxidizing agent, in which the salts from which the salt core is formed, are only slightly soluble (such as the above-mentioned solutions of crown ethers in toluene), and / or the process parameters are designed so that when contacted with the solution of the oxidizing agent less material is removed from the salt core is applied as an oxidizing agent. This can be achieved by a low temperature of the solution, a short contact time between salt core and solution and rapid drying of the salt cores coated with the solution. One or more further constituents selected from the group consisting of surfactants, mold release agents, electrically non-conductive particles, pigments and metal salts may be added to the solution of the oxidizing agent.

Surfactants serve to support the wetting of the wall surface of the cavity or the surface of the cores. Suitable surfactants are known to the person skilled in the art. Mold release agents facilitate demolding, ie. the removal of the formed blank from the mold. Suitable mold release agents, e.g. Silicone oils and silicone elastomers are known to those skilled in the art.

If one or more further constituents selected from the group consisting of surfactants, mold release agents, electrically non-conductive particles, pigments and metal salts are added to the solution of the oxidizing agent, a layer is produced after drying which selects a mixture of the oxidizing agent and these further constituents from the group consisting of surfactants, mold release agents, particles, pigments and metal salts. If one or more constituents selected from the group consisting of electrically nonconductive particles, pigments and metal salts are added to the solution of the oxidizing agent, an insulating layer is formed in the process according to the invention on the surface of the main body, which contains these other constituents in addition to aluminum oxide. Thus, in addition to the dielectric properties of the insulating layer, the method according to the invention can advantageously also provide further properties, e.g. the color of the insulating layer to be influenced.

Preferred electrically non-conductive particles are i.a. PTFE particles, mica and benetonites. Preferred pigments are inorganic color pigments, among others. Iron oxide, zirconium silicate, bismuth, chromate pigments and manganese dioxide. Corresponding pigments are known to the person skilled in the art. Preferred metal salts are coloring metal salts. Corresponding metal salts, e.g. Cr (II) salts, bismuth vanadate, ZrSiO 4, Cd salts and Mn salts are known to the person skilled in the art.

By incorporated in the insulating layer coloring metal salts or pigments, the insulating layer is given a coloring or shading. This can be used to characterize the layer thickness of the insulating layer, as a quality assurance measure or as component marking (eg as an indication that an insulating layer is present or for allocation to a particular batch or to a specific type of component or to a particular customer).

If a release agent-containing solution of the oxidizing agent is used, it makes sense to also contact the wall surfaces of the overflow passages of the mold with this solution to facilitate demolding. The wall surfaces of the runners of the mold are preferably not brought into contact with the solution of the oxidizing agent in order to prevent contamination of the molten metal by oxides formed. To facilitate demoulding, the wall surfaces of the sprues of the mold are preferably coated with a mold release agent.

For the coating of the wall surface of the chamber of the cavity of the mold and - if needed to form the forming chamber cores - the surface of the cores with the oxidizing agent, various techniques known in the art are available, for example

the mold is or the cores are immersed in a solution of the oxidizing agent,

the cavity of the mold is or the cores are flooded or rinsed with a solution of the oxidizing agent,

the wall surface of the cavity of the mold or the surface of the cores is impregnated with a solution of the oxidizing agent,

the wall surface of the cavity of the mold or the surface of the cores is brought into contact with an aerosol of a solution of the oxidizing agent.

For coating the wall surface of the chamber of the cavity of the mold and the surface of the associated cores with the oxidizing agent, the same or different techniques may be used. Preferably, the cores are coated with the oxidizing agent prior to insertion into the chamber of the cavity of the mold, because after inserting the cores into the chamber of the cavity of the mold, the surface of the cores is often difficult to access. However, it is not excluded according to the invention that the cores are first inserted into the chamber of the cavity of the mold, and then the surface of the cores is coated together with the wall surface of the chamber of the cavity of the mold with the oxidizing agent. The expert will choose the appropriate procedure depending on the design of the mold and the cores.

Advantageously, the mold, when brought into contact with the solution of the oxidizing agent, has a residual heat from the previous casting cycle, which is sufficient for drying, i. can be used to evaporate or evaporate the solvent. Preferably, the mold has a temperature in the range of 120 ° C to 200 ° C when brought into contact with the solution of the oxidizing agent. Higher temperatures are often unsuitable as they can cause premature decomposition of the oxidizing agent. In the case of aqueous solutions of the oxidizing agent, dehydration is achieved by the drying as well as the high temperatures during the casting process, so that the formation of boehmite (aluminum oxide hydroxide) is limited to aluminum oxide. The formation of alumina is preferred over boehmite because alumina has better insulating properties. After drying, the wall surface of the forming chamber, i. the wall surface of the chamber of the cavity of the mold and the surface of the cores (if the mold comprises cores) a closed layer containing the oxidizing agent. The layer containing the oxidizing agent on the wall surface of the forming chamber of the cavity of the molding tool has a thickness of 1 μιη or more after drying, preferably in the range of 2 μιη to 50 μιη, particularly preferably in the range of 5 μιη to 20 μιη. The thickness of the layer containing the oxidizing agent is determined nondestructively by means of the eddy current method according to DIN EN ISO 2360, for example by means of a leptoscope from Karl Deutsch Prüf- und Messgerätebau GmbH + Co. KG, Wuppertal (Germany). The thickness of the layer containing the oxidizing agent is set by the person skilled in the art about the concentration of the oxidizing agent in the solution used for coating and / or the application amount of the solution during coating.

When immersed in a solution of the oxidizing agent, the application rate of the solution of the oxidizing agent depends on the rate at which the mold or cores are removed from the solution and the temperature and viscosity of the solution. When coating with an aerosol of a solution of the oxidizing agent, the applied amount of aerosol (duration of spraying) and the concentration of the solution determine the thickness of the layer containing the oxidizing agent. Methods and tools (atomizers) for the production of an aerosol are known in the art. Preferably, the droplets of the aerosol have droplet diameters in the range of 0.1 μm and 1 mm, preferably in the range from 1 μm to 300 μm, particularly preferably in the range from 5 μm to 50 μm.

The thickness of the oxidant-containing layer on the wall surface of the forming chamber (ie, on the wall surface of the cavity of the mold and on the surfaces of the inserted cores when the mold comprises cores) determines the thickness of the insulating layer on the surface of the mold chamber blank. The thicker the oxidant-containing layer, the thicker the insulating layer formed on the surface of the blank formed in the forming chamber. The thickness of the oxidant-containing layer may vary across the wall surface of the forming chamber (ie, over the wall surface of the chamber of the cavity of the mold and the surfaces of the cores inserted therein when the mold comprises cores) by the thickness of the formed insulating layer to vary over the component surface.

In a preferred variant of the method according to the invention, the thickness of the layer containing the oxidizing agent varies over the wall surface of the forming chamber so that regions of different thickness of the layer containing the oxidizing agent are formed, e.g. in one or more areas of the wall surface of the forming chamber, the oxidant-containing layer is thicker than in one or more other areas of the wall surface of the forming chamber. In this way, an insulating layer can be formed whose thickness varies across the device surface, so that regions with different thicknesses of insulating layer are formed, e.g. in one or more regions of the component surface, the insulating layer is thicker than in one or more other regions of the component surface.

To facilitate demoulding, ie removal of the formed component from the mold, it is preferable to coat the wall surface of the cavity of the mold (including the sprue and overflow channels) and optionally the surfaces of the cores with a mold release agent before the wall surface the forming chamber is coated with the oxidizing agent. Suitable mold release agents are known to the person skilled in the art. If necessary, the inventive method comprises, after removing the formed blank from the mold and working out of the passive electrical component from the blank one or more further steps selected from the group consisting of

- Applying an insulating wet paint, an insulating powder coating and / or a potting compound on the insulating layer

Wrapping in insulating paper, in insulating foil and / or in a shrink tube

Depositing a plasma polymer layer on the insulating layer

Annealing of the component at a temperature in the range of> 50 ° C to 250 ° C, preferably from 100 ° C to 200 ° C, more preferably 130 ° C to 160 ° C.

By the first three steps, a further insulating layer is produced on the insulating layer produced by the method according to the invention, so that the dielectric strength of the component is further increased. By annealing the component, boehmite present in the insulating layer produced by the method according to the invention is converted into aluminum oxide, so that the proportion of aluminum oxide in the insulating layer is further increased and the proportion of boehmite is reduced even further.

The subject matter of the present invention is also a passive electrical component produced and / or producible by the method according to the invention described above.

An inventively produced or producible passive electrical component comprises

a basic body made of aluminum or an aluminum alloy or an aluminum-containing alloy

an insulating layer on the surface of the base body,

wherein in this insulating layer the mass ratio of alumina to boehmite is greater than 5,

wherein this insulating layer has a thickness of 1 μιη or more.

A passive electrical component according to the invention comprises a base body made of aluminum or of an aluminum alloy or of an aluminum-containing alloy and an insulating layer on the surface of the base body. This means that the component has a basic body made of aluminum or an aluminum alloy or of having an aluminum-containing alloy and an insulating layer on the surface of the base body. This insulating layer contains alumina and optionally one or more components from the group consisting of boehmite and other aluminum compounds. In the said insulating layer, the mass ratio of aluminum oxide to boehmite is greater than 5. The condition defined here with regard to the mass ratio of aluminum oxide to boehmite is according to the invention in a region extending from the component surface to the interior of the component of at least 1 μm thickness (measured perpendicularly) to the component surface). Preferably, the mass ratio of the proportions of aluminum oxide and boehmite in the insulating layer is greater than 6, more preferably greater than 7, particularly preferably> 10.

According to the invention, it is not excluded that aluminum oxide is also present in a region further away from the component surface (that is to say below the insulating layer defined above).

At least 90% of the surface of the passive electrical component according to the invention are covered by the above-defined insulating layer, preferably at least 95% of the surface of the passive electrical component according to the invention, more preferably at least 99% of the surface of the passive electrical component according to the invention.

If, when the passive electrical component is removed from the blank, excess material (typically in the area of the gate and the overflow) is removed, surface areas are thereby exposed on the component which do not have an insulating layer (as defined above). By contact with atmospheric oxygen, an aluminum oxide layer can spontaneously form on the exposed aluminum surface, but this layer is substantially thinner than the insulating layer produced according to the invention.

Preferably, in the mold, the sprue and overflow channels are positioned so that the surfaces of the passive electrical component exposed upon removal of the supernatant from the sprue and overflow channels from the blank correspond to surface areas where an insulating layer is not desired, such as e.g. at the intended for electrical contacting of the component bodies.

The mass ratio of the proportions of aluminum oxide and boehmite in the insulating layer is determined by means of X-ray diffraction (XRD) with an incident angle of 70 ° relative to the surface normal. The diffraction pattern obtained is determined by the diffraction pattern of adapted to various modifications of the aluminum oxide, of boehmite and aluminum, optionally further crystal modifications of non-aluminum oxides (eg, manganese dioxide) by a best-fit routine and determines the mass ratio of alumina to boehmite.

In addition to aluminum oxide and possibly boehmite, and other aluminum compounds, the insulating layer may contain reaction products formed by reduction of the oxidizing agent, e.g. in the case of potassium permanganate as reducing agent, compounds of manganese (in a lower oxidation state than in potassium permanganate) and compounds of potassium. In addition, the insulating layer may contain compounds contained in the release agent, e.g. Compounds of carbon. In the case of using salt cores, the insulating layer may also contain compounds of elements of the salts of the salt core, e.g. Compounds of sodium, potassium, magnesium and chlorine in the case of salt cores from mixtures of sodium, potassium and magnesium chlorides.

In addition to aluminum oxide (and optionally boehmite, further aluminum compounds and reaction products formed by reduction of the oxidizing agent), the insulating layer may contain one or more of the following constituents:

pigments

metal salts

electrically non-conductive particles.

If present, said components are incorporated in the alumina insulating layer. Preferred electrically non-conductive particles are i.a. PTFE particles, mica and bentonite. Preferred pigments are inorganic color pigments, i.a. Iron oxide, zirconium silicate, bismuth, chromate pigments and manganese dioxide. Corresponding pigments are known to the person skilled in the art. Preferred metal salts are coloring metal salts. Corresponding metal salts, e.g. Cr (III) salts, bismuth vanadate, ZrSiO 4, Cd salts and Mn salts are known to those skilled in the art.

By incorporated in the insulating layer coloring metal salts or pigments, the insulating layer is given a coloring or shading. This can be used to characterize the layer thickness of the insulating layer, as a quality assurance measure or for component identification (eg as an indication that an insulating layer is present, or for assignment to a particular batch or type of components or to a specific customer). In the insulating layer embedded electrically non-conductive particles enhance the insulating effect.

The elemental composition of the insulating layer, and thus the content of aluminum and oxygen, can be determined by means of energy-dispersive X-ray spectroscopy EDX, wherein the expert selects the acceleration voltage so that the information depth is as large as the minimum thickness (1 μιη) of the insulating layer.

Optionally, X-ray photoelectron spectroscopy can also be used. In order to be able to record the element composition in lower layers (> 10 nm), the skilled person uses depth profiling (sputtering). When determining the elemental composition, the person skilled in the art will take into account any preferential sputtering which may occur.

If different elemental compositions are determined by different methods, the value determined by EDX is decisive.

The thickness of the insulating layer is determined non-destructively by means of the eddy current method according to DIN EN ISO 2360, for example by means of a leptoscope from Karl Deutsch Prüf- und Messgerätebau GmbH + Co. KG, Wuppertal (Germany).

Alternatively, the thickness of the insulating layer formed on the surface of the component at a cryogenic fracture surface can be determined by scanning electron microscopy.

The passive electrical component according to the invention is for example selected from the group consisting of coils, helices, rectangular conductors and round conductors. A passive electrical component according to the invention may have one or more form elements from the group consisting of undercuts, bores and channels. Particularly preferably, the passive electrical component according to the invention is a coil.

Preferably, the insulating layer has a thickness in the range of 10 μιη to 100 μιη. Within this thickness, the mass ratio of aluminum oxide to boehmite is greater than 5, preferably greater than 6, more preferably greater than 7, particularly preferably> 10.

Preferably, the insulating layer has a dielectric strength of 40 V / μιη or more, measured according to DIN EN 60243-1 and DIN EN 60243-2 for a current of up to 3 mA maximum. More preferably, the insulating layer has a thickness of 10 [in or more, and is resistant to breakdown of a voltage of 400 V or more, more preferably 2500 V or more.

The insulating layer also improves the corrosion resistance and aging resistance of the passive electrical component.

Preference is given to passive electrical components according to the invention, in which the dielectric strength of the insulating layer drops by less than 20% after 1000 hours at a temperature in the range from -80.degree. C. to 300.degree.

In certain embodiments, a passive electrical component according to the invention comprises a further layer arranged on the surface of the insulating layer containing one or more materials selected from the group consisting of insulating lacquer layers, plasma polymers, insulating papers, insulating films, heat-shrinkable tubing and casting compounds. Materials and methods for making such layers are known to those skilled in the art. Another object of the present invention is a mold for producing a passive electrical component by casting a melt of aluminum or an aluminum alloy or an aluminum-containing alloy, wherein the mold has a cavity comprising a forming chamber, which corresponds to the shape of the component to be produced and the wall surface of the forming chamber comprises a layer containing an oxidizing agent or consisting of an oxidizing agent.

The molding tool according to the invention has a cavity which is filled with a melt of aluminum or an alloy in the casting process and which determines the shape of the blank formed from the solidified melt. The blank formed in the molding tool comprises the passive electrical component to be produced. Typically, the cavity of the mold according to the invention comprises one or more sprue channels for filling the melt, one or more overflow channels, and a shaping chamber, which corresponds to the shape of the component to be produced. The shaping chamber of the molding tool has, for example, the shape of a coil, a helix, a rectangular conductor or a circular conductor. Such molds and processes for their preparation are known in the art. The molding tool is selected from the group consisting of one-piece molding tools and multi-part molding tools.

Preferably, in the mold, the sprue and overflow channels are positioned so that the surfaces of the passive electrical component that are exposed from the runner and overflow channels when separating the supernatant material correspond to surface areas where an insulating layer is not desired, such as eg at the intended for electrical contacting of the component bodies.

At least the entire wall surface of the forming chamber cavity of the mold is covered with a layer containing the oxidizing agent. However, it is not excluded that the layer containing the oxidant extends to further areas of the wall surface of the cavity of the mold, e.g. on the wall surfaces of one or more overflow channels. Preferably, the oxidant-containing layer does not extend to the wall surfaces of the runner channels to prevent contamination of the molten metal by oxides formed.

The oxidant-containing layer may contain further constituents selected from the group consisting of surfactants, mold release agents, electrically non-conductive particles, pigments and metal salts.

In a preferred embodiment of the mold according to the invention, the cavity has a chamber in which one or more cores are inserted, so that a shaping chamber is formed whose wall surface from the wall surface of the chamber of the cavity of the mold and the surface of the inserted into this chamber Kerns or inserted into this chamber cores consists. That is, the shape of the cavity defined by the wall surface of the chamber of the mold and the surface of the core inserted into the chamber or the cores inserted into the chamber, to be filled by the melt corresponds to the shape of the component to be produced. The forming chamber is formed in this preferred embodiment by inserting one or more cores in a dedicated chamber which is part of the cavity of the mold, while before inserting the core or this chamber does not yet correspond to the shape of the component to be produced, ie is not yet a shaping chamber. This preferred mold according to the invention has a shaping chamber whose wall surface consists of the wall surface of the chamber of the cavity of the mold and the surface of the core inserted into this chamber or the cores inserted in this chamber and has a layer containing the oxidizing agent. Preferably, the oxidizing agent has a standard potential higher than 1 V, preferably 1.2 V or higher, more preferably 1.5 V or higher. The oxidizing agent is preferably selected from the group consisting of permanganates, perborates, peroxycarboxylic acids, percarbonates, peroxides and salts of halo-oxygen acids.

The wall surface of the forming chamber of the mold (i.e., the wall surface of the chamber of the cavity of the mold and the surfaces of the cores if the mold comprises cores) has a closed layer on which the oxidizing agent is contained. The layer containing the oxidizing agent on the wall surface of the shaping chamber of the cavity of the molding tool has a thickness of 1 μm or more, preferably in the range of 2 μm to 50 μm, particularly preferably in the range of 5 μm to 20 μm. The thickness of the layer containing the oxidizing agent is determined nondestructively by means of the eddy current method according to DIN EN ISO 2360, for example by means of a leptoscope from Karl Deutsch Prüf- und Messgerätebau GmbH + Co. KG, Wuppertal (Germany).

The thicker the layer containing the oxidizing agent, the thicker the insulating layer produced on the surface of the component formed in the shaping chamber. The thickness of the oxidant-containing layer may vary over the wall surface of the forming chamber (ie, over the wall surface of the chamber of the cavity of the mold and the surfaces of the cores inserted therein when the mold includes cores) over the thickness of the formed insulating layer to vary the component surface.

In a preferred variant of the mold according to the invention, the thickness of the oxidant-containing layer varies over the wall surface of the forming chamber, so that regions of different thickness of the oxidant-containing layer are formed, wherein, for example, in one or more areas of the wall surface of the forming chamber Oxidant-containing layer is thicker than in one or more other areas of the wall surface of the forming chamber. In this way, an insulating layer can be produced, the thickness of which varies over the surface of the component, so that regions with different thicknesses of insulating layer are formed, wherein, for example, in one or more areas of the component surface, the insulating layer is thicker than in one or more other areas of the component surface.

In order to avoid demolding, i. For example, in order to facilitate removal of the formed blank from the mold, it is preferred that a mold release agent-containing layer is disposed between the wall surface of the cavity of the mold and the coating containing an oxidizing agent. Suitable mold release agents are known to the person skilled in the art.

The invention will be explained in more detail by way of examples. Example 1 :

A die-casting tool made of tool steel 1.2343, which is characterized by high heat resistance and thermal shock resistance, is provided. The mold has a cavity with a sprue, an overflow and a cuboid forming chamber. The shaping chamber corresponds to the negative of the component to be cast in the form of a cuboid rectangular conductor with the dimensions 10 mm x 1 mm x 200 mm. The mold is in two parts, i. It consists of two halves surrounding the cavity.

A 0.1 molar solution of the oxidizing agent KMnO4 in water is prepared. This solution is mixed with a commercially available release agent in the ratio 60: 1.

In this embodiment, the method for producing a blank comprises the following steps:

a) opening the mold and removing the blank produced in the previous casting cycle

b) cleaning the cavity of the mold with compressed air

c) spraying the solution described above containing KMnO 4 as oxidizing agent and a release agent in the cavity of the mold by means of a spray gun (analogous to the typical procedure when applying a release agent) and drying, with a 30 μιη to 50 μιη thick layer of a mixture of KMn04 and Release agent is created

d) closing the mold e) casting in die-cast with subsequent solidification of the melt in the cavity and oxidation of the aluminum on the wall surface of the cavity by the oxidizing agent,

f) opening the mold and removing the blank produced

For die casting, a Frech plant with 250 t clamping force was used. The melt in the antechamber is heated to 760 ° C and consists of rotor aluminum (Al content 99.7%).

The casting process e) is divided into 3 phases:

1. Slow movement of the piston to fill the filling chamber to the sprue

2. Inject the melt at a piston speed of 5 m / s until the cavity is filled

3. Press for 4 seconds at 180 MPa (1800 bar)

After opening the tool, the blank has an average temperature of 450 ° C. The mold temperature is maintained at 150 ° C by tempering by means of a heating-cooling device. After removal from the tool, the blank is dipped in deionized water to remove impurities in the form of potassium salts.

The blank has a closed insulating layer whose thickness varies depending on the thickness of the layer produced in step c) from a mixture of KMnÖ4 and release agent. The insulating layer contains alumina and oxides of manganese. Minimal layer thicknesses of the insulating layer of 2 μm were found in the area of the gate, maximum layer thicknesses of the insulating layer of 50 μm in areas located 200 mm from the gate. The thickness of the insulating layer was determined by means of a Leptoscope 2050 with a straight microprobe for NFe substrates (non-ferrous metal substrates).

The elemental composition of the insulating layer in the region of a thickness of 1 μm determined by means of EDX is as follows: Al (25 at%), O (53 at%), Mn (12 at%), C (9 at%) and traces of K ( from the used as oxidizing agent KMnÖ4). The mass ratio of alumina to boehmite was determined by X-ray diffraction (XRD) using an angle of incidence of 70 ° with respect to the surface normal to 15 ± 3. The breakdown measured according to DIN EN 60243-1 and DIN EN 60243-2 at a maximum current flow of 3 mA occurred in the region of the gate at a voltage of 92 V ± 9 V, in areas which are 200 mm from the gate, at a voltage of 1600 V ± 150 V.

Example 2:

The production of a passive electrical component according to the invention was carried out essentially analogously to Example 1, apart from the following differences:

The cavity of the mold has a shaping chamber with the dimensions 20 mm x 160 mm x 50 mm.

In the chamber of the cavity, a cuboid salt core is inserted whose outer dimensions correspond to the dimensions of the cavity. In the wall surfaces (except the base and top surface) of the parallelepipedic salt core, a spiral-shaped (5 mm) depth and 1 mm wide indentation is incorporated, which is rounded at its bottom (radius 0.3 mm). The salt core consists of a mixture of 65% by weight of Na ₂ C0 ₃ and 35% by weight of KCl.

The salt core is immersed in a 0.1 mol / l solution of KMnC in water (temperature 15 ° C.) and dried immediately. The salt core is rotated evenly along the main axis (160 mm) until the surface is dry. The salt core is dried for one hour at 100 ° C in a drying oven.

The cavity is cleaned analogously to Example 1 and sprayed with the solution described in Example 1 containing KMnO 4 as the oxidizing agent and a release agent, after drying a 30 μιη to 50 μιη thick layer of a mixture of KMn04 and release agent is formed.

The salt core is inserted into the cavity and the die casting process is carried out analogously to Example 1.

After removal from the mold, the salt core is removed by dissolving in water, so that a blank comprising a component in the form of a coil with an insulating layer remains on the surface. This was rinsed with deionized water. The layer thickness of the insulating layer in the coil interior was at least 4 μιη. The thickness of the insulating layer was determined by means of a Leptoscope 2050 with a straight microprobe for NFe substrates (non-ferrous metal substrates). The elemental composition of the insulating layer in the region of a thickness of 1 μm determined by means of EDX is as follows: Al (31 at%), O (53 at%), Mn (12 at%), C (2 at%) and traces of K, Na and Cl. The mass ratio of alumina to boehmite was determined by X-ray diffraction (XRD) using an incidence angle of 70 ° with respect to the surface normal to 10 ± 2. The breakdown measured in accordance with DIN EN 60243-1 and DIN EN 60243-2 with a maximum current flow of 3 mA was in the region of the coil interior at a voltage of 170V ± 12V.

Claims

claims

A method of making a passive electrical component, comprising the steps

Coating the wall surface of the forming chamber with an oxidizing agent to form a layer containing the oxidizing agent,

Pouring a melt of aluminum or an aluminum alloy or an aluminum-containing alloy into the cavity,

Oxidizing the aluminum at the interface between the melt and the oxidant-containing layer and solidifying the melt in the cavity to form a blank comprising the passive electrical component,

Removing the formed blank from the mold, working out of the passive electrical component from the blank.

2. The method of claim 1, wherein providing the mold comprises the steps of:

Providing one or more cores and coating the surface of the cores or cores with an oxidizing agent such that an oxidant-containing layer is formed on the surface of the cores,

Inserting the coated core (s) into the cavity cavity of the mold so as to form a shaping chamber having a wall surface made up of the wall surface of the cavity cavity of the mold and the surface of the cores inserted into said cavity and having a layer containing the oxidizing agent , The method of claim 1 or 2, wherein the forming chamber of the mold has the form of a coil, a helix, a rectangular conductor or a circular conductor.

Method according to one of the preceding claims, wherein the oxidizing agent is selected from the group consisting of permanganates, perborates, peroxycarboxylic acids, percarbonates, peroxides and salts of halo-oxygen acids.

Method according to one of the preceding claims, wherein for coating with the oxidizing agent, the wall surface of the chamber of the cavity of the mold to be coated and optionally the surface of the cores is brought into contact with a solution of the oxidizing agent in a solvent, and then the solvent is removed by drying in that a layer containing the oxidizing agent is formed on the wall surface of the chamber of the cavity of the molding tool and optionally on the surface of the cores.

The method of claim 5, wherein the mold has a temperature in the range of 120 ° C to 200 ° C when brought into contact with the solution of the oxidizing agent.

Method according to one of claims 5 and 6, wherein the solution of the oxidizing agent, one or more further ingredients selected from the group consisting of surfactants and mold release agents are added.

Method according to one of the preceding claims, wherein after drying, the layer containing the oxidizing agent on the wall surface of the forming chamber has a thickness of 1 μιη or more, preferably in the range of 2 μιη to 50 μιη.

A method according to any one of the preceding claims, wherein the thickness of the layer containing the oxidizer varies across the wall surface of the forming chamber.

Method according to one of the preceding claims, wherein the wall surface of the chamber of the cavity of the mold and optionally the surface of the Cores are coated with a mold release agent before coating with the oxidizing agent.

1 1. Passive electrical component

full

an insulating layer on the surface of the base body,

wherein said insulating layer has a thickness of 1 μιη or more and / or

preparable by a method according to one of claims 1 to 10.

12. Passive electrical component according to claim 1 1, wherein the passive electrical component is selected from the group consisting of coils, helices, rectangular conductors and round conductors.

13. Passive electrical component according to claim 1 1 or 12, wherein the passive electrical component comprises one or more mold elements from the group consisting of undercuts, bores and channels.

14. Passive electrical component according to one of claims 1 1 to 13, wherein the insulating layer has a dielectric strength of 40 V / μιη or more, measured according to DIN EN 60243-1 and DIN EN 60243-2 up to a maximum current flow of 3 mA