EP1482072B1 - Metallic object provided with electrically insulating coating as well as process for making electrically insulating coating - Google Patents

Description

Metallic article with electrically insulating coating and method for producing an electrically insulating coating

The invention relates to a metallic object, in particular a magnetic semi-finished product, which is provided with an electrically insulating coating. Furthermore, the invention relates to a method for producing an electrically insulating coating.

Magnesium oxide coatings have been known for a long time, and were first used in the US 2,796,364 described. There, organometallic magnesium compounds are prepared, which are dissolved in solvents, in particular in organic solvents, and applied to a metallic surface. This coating is then annealed on the metallic surface so that the solvent components disappear and a thin magnesium oxide coating remains on the metallic surface. This magnesium oxide coating is formed by the calcination associated with annealing.

A magnetic semi-finished product with an electrically insulating coating is for example from EP 0 597 284 B1 known. There, inter alia, a coating is described which consists of magnesium oxide.

A major disadvantage of these known from the prior art magnesium oxide coatings is that they have an annealing resistance of only a maximum of 1000 ° C.

In the methods known from the prior art, a thin layer of a solution of magnesium methylate in methanol is first applied to the metallic surface. Typically, the applied thicknesses are in the wavelength range of visible light, so that the applied layers are iridescent in interference colors. As a result of the extremely low layer thicknesses, there are generally no problems in the conventional shaping methods, e.g. when punching, to be processed magnetic semi-finished product due to abrasion or an abrasion-related tool impairment. In the magnetic final annealing which takes place after shaping, the conversion of the layer of hydrated magnesium hydroxide adhering to the semifinished product after drying to a thin adherent magnesium oxide coating then takes place.

A major disadvantage of this procedure is that this layer has a low temperature resistance. When annealing under an atmosphere of pure hydrogen with a sufficiently low dew point, the attainment of the boiling point of magnesium leads to a pronounced layer degradation of the insulation by reduction of the magnesium oxide and subsequent vaporization of the magnesium metal formed.

Dew point is understood here and below to mean the temperature at which the gaseous water vapor content of the annealing atmosphere condenses.

Thus, in the prior art annealing under a dry hydrogen atmosphere with a dew point below -30 ° C only below 1000 ° C feasible.

However, there are many alloys or metals that require a much higher annealing temperature. In particular, there is a need to provide soft magnetic nickel-iron alloys with an electrical insulation layer that easily withstands annealing above 1000 ° C.

If the final magnetic anneals are carried out in hydrogen atmospheres with a poorer dew point, i. H. a dew point of more than -30 ° C, by, of course, annealing temperatures above 1000 ° C can be achieved. However, these anneals under these poor annealing atmosphere conditions are not suitable for setting optimum magnetic properties in the soft magnetic alloys. In particular, optimal permeabilities and suitably low coercive forces can not be set.

The AP 0 348 288 A and DE 199 43 789 A1 and the JP 63 310 969 A each disclose a method of coating a substrate with zirconia.

The object of the present invention is therefore to provide a novel high-temperature-resistant electrically insulating coating, in particular to provide a magnetic semi-finished product with an electrically insulating, high-temperature-resistant coating. Furthermore, it is the object of the present invention to provide a novel method by which metallic objects, in particular magnetic semi-finished products, can be provided with a high-temperature-resistant, electrically insulating coating.

According to the invention, this object is achieved by a metallic object with an electrically insulating, high temperature resistant Zirconia coating dissolved. As a metallic object, a magnetic semi-finished product is provided, which has the form of bands or sheets or strips or the shape of a laminated core. The magnetic semi-finished product consists of a soft magnetic alloy. The soft magnetic alloy is magnetically final annealed at a temperature above 1000 ° C. Zirconium oxide (ZrO ₂ ) is thermodynamically much more resistant than magnesium oxide (MgO), which can be seen in " J. Barin et al., Thermochemical Properties of Inorganic Substances, Springer-Verlag, Berlin 1977 "is described.

This coating is used for magnetic semi-finished products. The magnetic semi-finished product has the form of bands, sheets or strips and is typically assembled into laminated cores. The coating of zirconium oxide is particularly suitable for nickel-iron alloys, which consist essentially of between 36.0 and 82.0 weight percent nickel, balance iron.

These nickel-iron alloys usually require a magnetic annealing at temperatures above 1000 ° C.

The coating densities of metallic zirconia p vary between 0.2 ≦ ρ ≦ 1.2 grams per m ² metal surface.
Typically, coatings are provided at a coverage of 0.4 ≤ ρ ≤ 0.6 gram per m ² metal surface. The covering densities p are an indirect and manageable measure of the coating thickness d. Since there is no suitable measuring method for the coating thicknesses, one typically follows the way of quantifying the content of metallic zirconium on the treated surface.

• Bereitstellen einer in einem Lösungsmittel gelösten organischen Zirkonverbindung (Lösung);
• Aufbringen der Lösung auf die Oberfläche; und
• Glühen des metallischen Gegenstandes, wobei die weichmagnetische Legierung bei einer Temperatur oberhalb 1000°C magnetisch schlussgeglüht ist.

The inventive method for producing such electrically insulating coatings of zirconium oxide on a surface of a metallic article, wherein as a metallic object, a magnetic semi-finished product is provided which has the form of bands or sheets or strips or the shape of a laminated core, wherein the magnetic semifinished product of a soft magnetic alloy. The method comprises the following steps:

• Providing an organic zirconium compound (solution) dissolved in a solvent;
• Applying the solution to the surface; and
• Annealing of the metallic article, wherein the soft magnetic alloy is magnetically final annealed at a temperature above 1000 ° C.

Typically, a zirconium alkylate is provided which is dissolved in an organic solvent. The zirconium alkylate is preferably zirconium butoxide or zirconium propylate which is dissolved in an organic solvent which is as water-free as possible.

Suitable organic solvents are alcohols or mixtures of alcohols. Particularly suitable are the corresponding alcohols or mixtures of alcohols corresponding to the alkylates. That is, a propanol or a butanol is particularly suitable for the solution of zirconium propylate or zirconium butoxide.

However, other solvents can be used, such. As aliphatic solvents or ether alcohols or aliphatic ether alcohols or mixtures thereof. Furthermore, so-called low-boiling-point petrol comes into consideration.

By low-boiling point petrol is meant a besitimmte gasoline fraction with a defined Siedebreich.

Typically, a solution having a concentration between 0.2 and 10 percent by weight of zirconium is then prepared from the abovementioned solvents or solvent mixtures and the organometallic zirconium compound.

In a preferred embodiment care is taken in the preparation of the solution and also in its subsequent processing that no contamination takes place with water.

All contemplated organometallic zirconium compounds are decomposed on contamination with water via hydrolysis over several intermediates in water-insoluble hydroxides. When these water-insoluble zirconium hydroxides are formed, they are precipitated and processing is very difficult.

In particular, when using aliphatic ether alcohols as solvents processing of coating solutions is possible with which very thick and abrasion-resistant zirconia coatings are possible.

For the application of the electrically insulating coating solution to the semi-finished parts to be coated both a simple dipping process (vacuum impregnation) and various continuous processes are considered.

To achieve very thin layers can be worked in particular with a simple flow method. The use of other application methods, eg. B. a rotary screen printing or spraying, is basically possible. A pretreatment of the semi-finished or metal parts to be coated is usually not required.

In a first embodiment, the object to be coated is drawn in a suitable (closed) system through a dilute solution and then dried by means of hot air. In this process variant, the coating thickness of the concentration of the solution used, the viscosity and the flow rate of the semifinished product to be coated depends. Typically, coating solutions less than 1 weight percent are used Containing zirconium, typically solutions containing 0.3% by weight zirconium propylate in n-propanol.

In a second embodiment, especially when using more highly concentrated coating solutions, i. H. Thus, coating solutions containing more than 1 percent by weight zirconium in the coating solution, the coating solution is applied to the semifinished product via a capillary-saturated distributor felt or, after the free passage of the semifinished product through the solution between two suitable squeezing rollers. As a result, the entrained amount of solution is limited to the desired level. In this case, the layer thickness is determined by the concentration of the solution, by the type of distributor felt used and by the profile of the squeezing rollers used.

In a third embodiment, the semifinished products to be coated are likewise provided with a more highly concentrated coating solution. Subsequently, to set a defined layer thickness, the applied solution is blown off with an inert gas. In this case, solutions can be processed which contain about 2 percent by weight or more zirconium. Typically, solutions containing aliphatic ether alcohols as solvents are processed. The advantage of this variant is the relatively high throughput speed. A large-scale rational procedure is thereby made possible.

In the latter two embodiments, the solvent consumption can be significantly reduced and thus the coating can be carried out very efficiently.

In the subsequent drying of the solvent in all embodiments, there is usually a reaction of the organometallic zirconium compound with the residual air moisture contained in the dry air. This chemical reaction leads via various intermediates of partially hydrolyzed zirconium alcoholates to hydrated zirconium hydroxides. Alcohol is split off. Partly zirconium oxide is formed with elimination of water.

The thus coated semi-finished products can be stored without major problems. Under normal conditions, there is no corrosion of the semifinished product through the coating. There are also no other types of reactions of the coating in the context of conventional processing. The coating does not react chemically with the punching or lubricating oils generally used in further processing.

In the final (magnetic) final annealing, the coatings are completely converted to zirconia. This transformation corresponds to a calcination.

• Figur 1 zeigt die Ergebnisse von Verlustmessungen an verschiedenen losen Stanzringstapeln nach der vorliegenden Erfindung im Vergleich zum Stand der Technik.
• Figur 2 zeigt die Ergebnisse der Verlustmessungen an verschiedenen druckbeaufschlagten Stanzringstapeln nach der vorliegenden Erfindung im Vergleich zum Stand der Technik.

The invention will be explained in detail below with reference to embodiments and comparative examples and the figures. Showing:

• FIG. 1 Figure 2 shows the results of loss measurements on various loose punching ring stacks according to the present invention compared to the prior art.
• FIG. 2 Figure 4 shows the results of loss measurements on various pressurized punch ring stacks of the present invention as compared to the prior art.

1. A) Es wurde ein Band der Dicke 0,20 mm mit einer Magnesiummethylat-Lösung versehen. Die dabei erzielte Magnesiumkonzentration lag bei 0,3 g/qm. Daraus wurden Stanzringe gefertigt, die in einem Haubenofen bei einer Glühdauer von fünf Stunden bei einer Temperatur von 1030°C unter Wasserstoff-Atmosphäre mit einem Taupunkt von -20°C magnetisch schlussgeglüht wurden.
2. B) Es wurde ein Band der Dicke 0,20 mm mit einer Magnesiummethylat-Lösung versehen. Die Magnesiummethylat-Beschichtung wies eine Konzentration von 0,3 g/qm an Magnesium auf. Es wurden Stanzringe hergestellt. Diese Stanzringe wurden in einem Haubenofen bei einer Temperatur von 1150°C bei einer Glühdauer von fünf Stunden unter Wasserstoff-Atmosphäre mit einem Taupunkt < -30°C magnetisch schlussgeglüht. Die erzählten Stanzringe wiesen danach keine Magnesiumoxid-Beschichtung auf. Die Stanzringe waren metallisch blank.
3. C) Es wurde ein Band der Dicke 0,20 mm mit einer Magnesiummethylatlösung beschichtet. Die dabei verwendete Konzentration wies 0,3 g/qm an Magnesium auf. Daraus wurden wiederum Stanzringe gefertigt. Diese Stanzringe wurden in einem Durchlaufofen bei einer Temperatur von 1020°C schlussgeglüht. Die magnetische Schlussglühung fand unter einer Wasserstoff-Atmosphäre mit einem Taupunkt von -28°C und einer Durchlaufzeit von 0,75 Stunden statt.
4. D) Es wurde ein Band der Dicke 0,20 mm mit Zirkoniumpropylat-Lösung beschichtet. Die dabei erzielte Konzentration wies 0,5 g/qm an Zirkon auf. Daraus wurden wiederum Stanzringe gefertigt. Die Stanzringe wurden in einem Haubenofen für eine Glühdauer von fünf Stunden bei einer Temperatur von 1150°C unter einer Wasserstoff-Atmosphäre mit einem Taupunkt < -30°C magnetisch schlussgeglüht.
5. E) Es wurde ein Band der Dicke 0,20 mm mit Zirkonpropylat beschichtet. Die dabei verwendete Konzentration wies 0,5 g/qm an Zirkon auf. Daraus wurden wiederum Stanzringe gefertigt, die in einem Durchlaufofen bei einer Glühtemperatur von 1140°C unter einer Wasserstoff-Atmosphäre mit einem Taupunkt von < -30°C und einer Durchlaufzeit von 0,75 Stunden schlussgeglüht.

Electrical insulation coatings on soft magnetic semifinished product made of a nickel-iron alloy with the composition of 47.5 weight percent nickel 0.5 weight percent manganese, 0.2 weight percent silicon and the remainder iron and melting and / or accidental impurities from the prior art such compared according to the present invention. The following test series are carried out:

1. A) A band of thickness 0.20 mm was provided with a magnesium methylate solution. The magnesium concentration achieved was 0.3 g / m². From this punch rings were produced, which were magnetically final annealed in a hood furnace at a temperature of 1030 ° C under a hydrogen atmosphere with a dew point of -20 ° C at an annealing time of five hours.
2. B) A band of thickness 0.20 mm was provided with a magnesium methylate solution. The magnesium-methylate coating had a concentration of 0.3 g / m 2 of magnesium. Punch rings were made. These punch rings were magnetically final annealed in a bell-type furnace at a temperature of 1150 ° C. with an annealing time of five hours under a hydrogen atmosphere with a dew point <-30 ° C. The narrated punch rings had no magnesium oxide coating afterwards. The punch rings were metallic bright.
3. C) A band of thickness 0.20 mm was coated with a magnesium methylate solution. The concentration used was 0.3 g / m 2 of magnesium. This in turn punched rings were made. These punch rings were in one Continuous furnace finally annealed at a temperature of 1020 ° C. Magnetic final annealing took place under a hydrogen atmosphere with a dew point of -28 ° C and a flow time of 0.75 hours.
4. D) A band of thickness 0.20 mm was coated with zirconium propoxide solution. The concentration achieved was 0.5 g / m² zirconium. This in turn punched rings were made. The punch rings were magnetically final annealed in a hood furnace for a period of five hours at a temperature of 1150 ° C under a hydrogen atmosphere with a dew point <-30 ° C.
5. E) A tape of thickness 0.20 mm was coated with zirconium propoxide. The concentration used was 0.5 g / m 2 zircon. This in turn punched rings were manufactured, which finally annealed in a continuous furnace at an annealing temperature of 1140 ° C under a hydrogen atmosphere with a dew point of <-30 ° C and a flow time of 0.75 hours.

The punch rings had an outside diameter of 14.8 mm, an inside diameter of 10.5 mm and a thickness of 0.20 mm.

wobei A und B Fitparameter sind.For physical and magnetic characterization, several punch rings were then stacked to form a punching ring package from all tests A) to E). The re-magnetization losses were determined for an amplitude of B = 1.0 T as a function of the frequency f. It was a "sinusoidal induction" taken as a measurement condition. The total losses P _Fe are the hysteresis losses P _h and the eddy current losses P _WS together. In the first approximation, the following relationship applies: $${\mathrm{P}}_{\mathrm{Fe}}={\mathrm{P}}_{\mathrm{H}}+{\mathrm{P}}_{\mathrm{WS}}=\mathrm{A}\cdot \mathrm{f}+\mathrm{B}\cdot {\mathrm{f}}^{\mathrm{2}}$$

where A and B are fit parameters.

In a plot of the losses per cycle, ie a representation of the losses P _Fe per cycle as a function of the frequency f, the intercept corresponds to the hysteresis losses per cycle. The slope B determines the eddy current losses in the case of classic eddy current losses. A more or less perfect insulation of the punch rings leads to individual contacts between the punch rings, which ultimately manifests itself in increased eddy current losses, since the effective punch ring thickness increases.

In the case of poor insulation, therefore, the slope B increases in such a plot. The hysteresis losses P _h are generally smaller, the higher the annealing temperature and annealing time of the magnetic annealing and the better the dew point of the hydrogen atmosphere.

The punched rings were either stacked loosely (p = 0) or pressurized in a measuring device. The measurement under pressure was used to determine the insulation quality. Due to the magnetostriction of the investigated nickel-iron alloys, which is approximately λ _S = 25 ppm, however, this led to an increase in the hysteresis losses during the measurement

The measurement simulates the later use of stator laminations in motors. There punch rings are stacked to form a punching ring package. To ensure a sufficient filling factor they are pressurized. The punching ring package is then infiltrated with a low-viscosity adhesive. In this type of die ring package production, sufficient isolation of the individual stator punch rings is essential to keep the eddy current losses in the stator as low as possible.

From the FIGS. 1 and 2 It can be seen that the zirconium oxide coatings according to the invention lead to the lower hysteresis losses compared to the magnesium oxide coatings of the prior art. Using the method according to the invention, hysteresis losses of less than 5.0 mJ / kg, in particular less than 4.5 mJ / kg and less than 4.0 mJ / kg, can be achieved on nickel-iron alloys.

In case B), such a value has not been realized despite annealing at 1150 ° C. This can be explained by the fact that previously an annealing was performed as in A). As a result of the poor dew point, damage has occurred to the alloy surfaces which have caused a limitation of grain growth due to the formation of oxides on the grain boundaries. These damages can not be compensated by a second annealing. The oxides can be largely reduced by an increased annealing temperature and an improved dew point. The driving force for grain growth, however, is only small, which leads to a significantly increased coercive force. Of course, this significantly increased coercive field strength is noticeable in the increased hysteresis losses. The influence of the reduction of the insulation layer in example B) is from the FIG. 2 clearly visible. The slope and the associated eddy current losses increase significantly.

In the attached Table 1, all values for the hysteresis losses, the total losses and the fit parameters A and B are given from the equation [1].

Claims (12)

1. Metallic object with an electrically insulating, high temperature resistant coating of zirconium oxide, wherein a magnetic semi-finished product in the form of bands, sheets or strips or in the form of a laminated core is provided as a metallic object,
   characterised in that
   the magnetic semi-finished product consists of a soft-magnetic alloy and is magnetically final-annealed at a temperature above 1000°C.
2. Metallic object according to claim 1, wherein the coating has coverage thicknesses p of metallic zirconium between 0.2 ≤ ρ ≤ 1.2 grams per m² metal surface.
3. Metallic object according to claim 2, wherein the coating has coverage thicknesses p of metallic zirconium between 0.4 ≤ ρ ≤ 0.6 grams per m² metal surface.
4. Metallic object according to any of claims 1 to 3, wherein a nickel-iron alloy consisting substantially of nickel with a content between 36.0 and 82.0 percent by weight, rest iron, is provided as a soft-magnetic alloy.
5. Metallic object according to claim 4, wherein an alloy of 47.5 percent by weight nickel, 0.5 percent by weight manganese, 0.2 percent by weight silicon, rest iron and melt-related and/or accidental impurities, is provided as a magnetic alloy.
6. Method for producing an electrically insulating coating of zirconium oxide on a surface of a metallic object, wherein a magnetic semi-finished product in the form of bands, sheets or strips or in the form of a laminated core is provided as a metallic object, wherein the magnetic semi-finished product consists of a soft-magnetic alloy, the method comprising the following steps:

   - providing an organic zirconium compound (solution) dissolved in a solvent;

   - applying the solution to the surface;

   - annealing the metallic object

   - characterised in that the soft-magnetic alloy is magnetically final-annealed at a temperature above 1000°C.
7. Method according to claim 6, wherein a zirconium alkylate dissolved in an organic solvent is provided.
8. Method according to claim 7, wherein a zirconium alkylate from the group of zirconium butylate and zirconium propylate, which is dissolved in an anhydrous organic solvent, is provided.
9. Method according to claim 8, wherein an alcohol or a mixture of alcohols is provided as an organic solvent.
10. Method according to claim 9, wherein an aliphatic solvent is provided as an organic solvent.
11. Method according to any of claims 6 to 10, wherein a solution containing between 0.2 and 10 percent by weight of zirconium is produced.
12. Method according to any of claims 6 to 11, wherein a forming operation of the metallic object is carried out between the application of the solution on the surface of and the annealing of the metallic object.

Images