KR910009495B1 - Annealing of thermally ensulated core - Google Patents

Abstract

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Description

Annealing method of magnetic core

1 is a graph showing the time-temperature relationship of magnetic cores annealed according to a conventional annealing method.

2 is a graph showing the time-temperature relationship of the magnetic core annealed according to the annealing method of the present invention.

The present invention relates to an improved annealing method for an amorphous metal alloy core, and more particularly, to a rapid heat treatment and annealing method for an amorphous metal alloy core capable of appropriately changing magnetic properties according to a specific use. Amorphous metal alloys are known to have better magnetic properties than conventional crystalline alloys.

Such amorphous alloys can be wound to form a magnetic core close to a toroid, and thus are suitably used in magnetic device cores such as transformers, inductors and electrodeless fluorescent lamps.

Amorphous metal cores suitable for use in electrodeless fluorescent lamps are disclosed in US Pat. No. 4,227,120 (Luborsky).

Amorphous metal cores have been annealed to improve their magnetic properties. Typically, the annealing method includes heating and cooling the core to a temperature at which the crystallization does not start and the stress is sufficiently removed in the presence of a magnetic field. Annealing methods of this type are disclosed in US Pat. Nos. 4,116,728, 4,249,969, 4,262,233, and 4,298,409.

One of the major problems with conventional annealing methods is that a long time is required to perform the heating step effectively. This problem is particularly acute on larger cores. Rapid heating of the core to the annealing temperature creates a hot spot on the outside, thereby degrading the magnetic properties of the core so that the core cannot be used properly for this particular application. Therefore, in order to solve the above problem, the core must be heated to an annealing temperature by a complicated method including a plurality of graduated heating steps, which is time-consuming and uneconomical.

Accordingly, an object of the present invention is to provide an improved annealing method of a magnetic core that fundamentally reduces annealing time and significantly improves its magnetic properties.

In general, a magnetic core wound with an amorphous metal ribbon to form an outer surface, an inner surface, and upper and lower surfaces is heated, maintained at a first temperature for a predetermined time, and then cooled to a second temperature. Insulating the inner and outer surfaces of the core further comprises. By insulating the inner and outer surfaces of the core prior to the heating step, the core can be annealed with economy and reliability.

Heat is conducted rapidly along the metal passage through the upper and lower surfaces, while the thermal conductivity to the inner and outer surfaces of the core is greatly reduced. Since the heating step is the rate determining step, the total annealing time and production rate are minimized. In addition, since the conventional progressive heating step is omitted, the number of process steps is reduced, thereby increasing the reliability of the annealing method.

The core is heated very uniformly without fundamental temperature changes that form mechanical strain, thermal stress and hot spots.

The magnetic core produced according to the method of the present invention has an AC core loss of about 0.16-0.25 W / kg, an excitation power of about 0.25-0.45 VA / kg, and a magnetic flux density of 1.40 Tesla and a frequency of 60 Hz. It exhibits an improved magnetic property with a coercive force of 1.1-1.6 A / m. Therefore, the magnetic core annealed according to the present invention is particularly suitably used for inductors, transformers and electrodeless fluorescent lamps.

Amorphous metal alloys are prepared in the form of thin ribbons or wires having a glassy structure by rapidly quenching the molten metal at a rate of approximately 10 ⁶ ° C./sec. Typically, the ribbon thickness is approximately 20-30 μm and the ribbon width is approximately 25-100 mm. The magnetic core is an amorphous ribbon that is wound to form an outer surface, an inner surface, and upper and lower surfaces.

The outer surface and the inner surface are defined by a major surface, the upper and lower surfaces are defined by a minor surface, and the inner surface extends in essentially the same axis as the center of the core. Define the central opening. In addition, the upper and lower surfaces are located at surfaces essentially perpendicular to the rectangular surface formed by the inner and outer surfaces, respectively.

The present invention provides a method of annealing a magnetic core that fundamentally reduces the time required for annealing and significantly improves the magnetic properties of the core, thereby insulating the inner and outer surfaces of the core prior to the heating step of the annealing method. Includes adding.

The insulation step further includes the step of selecting a thermal insulator having a thermal conductivity of approximately 0.03-0.14 W / m ° C. and a bow rate of approximately 1-3% up to 500 ° C. If an insulator is selected, the insulator is applied to the inner and outer surfaces by one method selected from the group consisting of wrapping, painting, casting and dipping. The wrapping method of the insulator can be easily carried out at a low cost since using a conventional apparatus and method.

Thus, lapping is the preferred method for applying the insulator to the core. Typically, an insulator is used such that its thickness dimension extends radially outwards from the outer surface of the core and radially inwards from the inner surface and is approximately 25-75 mm.

By annealing according to the invention the magnetic properties of the core can be improved. The annealing method usually consists of rapidly heating the core and maintaining the core at a first temperature for a predetermined time.

The first temperature is a temperature at which all stresses are sufficiently removed but no crystallization occurs. The oven containing the core is preferably heated quickly to the peak temperature of the furnace 100-160 ° C. above the first temperature of the particular amorphous alloy selected. As the core approaches the annealing temperature, the furnace temperature is lowered to match the temperature of the core (see Figure 2).

According to this method, the time required for heat treatment of the core is essentially reduced. The core is cooled to a second temperature of approximately 200-25 ° C. at a cooling rate of approximately 0.1 ° C./minute-100° C./minute.

The first temperature is typically below the Curie temperature of the particular amorphous alloy selected as approximately 325 ° C.-400 ° C., while the second temperature is usually ambient temperatrue.

Preferably at least the heating step, most preferably the heating and cooling steps, are carried out in the presence of a magnetic field, and the magnetic field direction may be perpendicular or parallel to the longitudinal axis of the core, depending on the particular use of the core.

Some alloys of the composition consisting of members selected from the group consisting of Co ₆₆ Fe ₄ Ni ₁ B ₁₄ Si ₁₅ and Fe _76.95 Cr ₂ B _16.1 Su _4.8 C _0.25 can be annealed in the absence of a magnetic field to obtain a substantial improvement in magnetic properties. Magnetic cores are fabricated so that a percentage of their gross area is air, which is trapped between the guns of the spirally wound ribbon.

Moreover, as is already known, metals are good conductors but gaseous ones are bad conductors. The thermal conductivity values K for metal and air are 50.2Js ^-1 m ^-1 (C) ^-1 and 0.024Js ^-1 m ^-1 (C) ^-1, respectively.

Therefore, the air trapped in the ribbon layer yarn of the non-insulated core serves to block the heat flow (H) to the center along the ribbon thickness, the heat flow (H) can be expressed as follows.

K is the thermal conductivity of the material, A is the cleavage area of the material, T ₂ -T ₁ is the temperature difference between the two points, and d is the distance between the two points.

Because of such poor conductivity, the hot spots are formed on the outside of the core, so that the magnetic properties of the core deteriorate, and thus it cannot be appropriately used in transformers, induction cars, electrodeless fluorescent lamps, and the like. In addition, thermal conductivity tests (400 ° C.) performed on non-insulated specimens showed that the thermal conductivity through the ribbon width in the heating and cooling steps was more than 20 times greater than the thermal conductivity through the ribbon thickness.

While the inner and outer surfaces are thermally insulated prior to the heating step, it can be seen that by exposing the upper and lower surfaces, essentially large cores can be economically and reliably annealed, which allows the heat to pass through the upper and lower surfaces. This is because the conduction along the metal passage along the inside of the core is reduced while the rate of heat conduction to the inner and outer core surfaces is reduced. Since the heating step is a rate determining step, the total annealing time and production cost are minimal. Since the progressive heating step is typically omitted, the number of process steps is reduced and the reliability of the annealing method is increased.

The core is heated very uniformly without fundamental temperature changes that form mechanical strain, thermal stress, and hot spots.

The magnetic core produced according to the method of the present invention has an AC core loss of about 0.16-0.25 W / kg, an excitation power of about 0.25-0.45 VA / kg, and about 1.1-1.6 A at a magnetic flux density of 1.40 Tesla and a frequency of 60 Hz. It shows an improved magnetic property with a coercive force of / m. Thus, the magnetic core annealed according to the invention is particularly suitably used for inductors, transformers and electrodeless fluorescent lamps.

Hereinafter, the present invention will be described in detail through examples.

Example 1

Prepare a torodial test sample in which a 100 mm width alloy ribbon of Metglass 2605 S-2 with a nominal composition of Fe ₇₈ B ₁₃ Si ₉ is wound in a spiral manner.

The average internal and external diameters of the various test specimens were 172 mm and 377 mm, respectively, with an average weight of 55 kg. The high temperature magnetic wire is rotated six times in parallel to the longitudinal axis of the core to form an 800 A / m magnetic field for annealing. Some specimens are annealed in a conventional manner without insulation, and others are annealed by the method of the present invention in an insulated state. The specimens are heated to their respective annealing temperatures under an inert gas atmosphere and a magnetic field of 800 A / m applied to the heating and cooling steps. The specimens are cooled to 200 ° C. at an average rate of 1.5 ° C./min.

The time-temperature curves for the specimen annealed by the conventional annealing method and the specimen annealed by the method of the present invention are shown in FIGS. 1 and 2, respectively. Thermocouples are placed 0.5 mm from the center 2 of each core and the outer surface 1 of the core to check for temperature changes during the annealing process. As shown in FIG. 1, the temperature at the center 2 of each core annealed by the conventional method differs significantly from the temperature at its outer surface 1.

However, as shown in FIG. 2, when the core is annealed by the method of the present invention, the temperature difference between the center 2 and the outer surface 1 is minimal. Thus, the core with the time-temperature curve shown in FIG. 2 is annealed in a fundamentally reduced time and has significantly improved magnetic properties.

The magnetic properties of the specimens, namely coercive force (A / m), A-C core loss (W / kg), and excitation power (V-A / kg) were measured at a magnetic flux density of 1.40 Tesla and a frequency of 60 Hz.

The magnetic property values of the specimens by conventional annealing and the specimens annealed by the method of the present invention are shown in Table I and Table II, respectively.

TABLE I

TABLE II

Three or more specimen cores were quickly heat treated without insulation, and their magnetic properties were measured at a magnetic flux density of 1.40 Tesla and a frequency of 60 Hz.

The magnetic properties of the specimen cores quickly annealed without insulation are shown in Table III.

TABLE III

In contrast to the cores of Table II, the cores of Table III demonstrated high coercivity and high magnetic loss.

Claims (10)

An upper and lower surface composed of a plurality of amorphous metal ribbon layers and defined by outer and inner surfaces defined by the major surface of the amorphous metal ribbon and minor surfaces of the amorphous metal ribbon. A method of annealing a magnetic core, comprising: a) an insulating step of insulating the inner and outer surfaces of the magnetic core so that the upper and lower surfaces are non-insulated; b) a heating step of heating the magnetic core insulated in the insulating step to a first temperature within a first time; c) a holding step of maintaining the magnetic core heated to the first temperature in the heating step for a second time at the first temperature; And d) a cooling step of cooling the insulating core maintained at the first temperature to a second temperature. 2. The method of claim 1, wherein said first temperature and said first time are temperatures and times sufficient to achieve stress relief without initiating crystallization. The method of claim 1, wherein the cooling step is performed in the cooling rate range of 0.1-100 ℃ / min. The method of claim 1, wherein the heating and cooling steps are performed in the presence of a magnetic field applied in a direction parallel to the outer surface of the core. The method of claim 1, wherein the heating and cooling steps are performed in the presence of a magnetic field applied in a direction perpendicular to the outer surface of the core. The method of claim 1, wherein the first temperature is in the temperature range of 325-400 ° C and is less than or equal to the Curie temperature of the amorphous metal ribbon. The method of claim 1, wherein the second temperature has a temperature range of 25-200 ° C. The method of claim 1, wherein the core is heated in a furnace having a peak oven temperature 100-160 ° C. higher than the first temperature, wherein the core temperature approaches 15-45 ° C. near the first temperature. Annealing the magnetic core such that the peak temperature is lowered to the first temperature when in the range. The method of claim 1, wherein the insulating step of thermally insulating the inside and outside of the core comprises: a) forming a thermal insulator having a thermal conductivity of 0.03 to 0.14 W / m ° C and a bow shrinkage of 1-3% to 500 ° C; b) applying the thermal insulator to the inner and outer surfaces of the core; c) annealing of the magnetic core consisting of attaching the thermal insulator so that the thickness dimension of the thermal insulator extending radially outwardly from the outer surface of the core and radially inwardly from the inner surface of the core is 25-75 mm. Way. 10. The method of claim 9, wherein applying the thermal insulator is selected from the group consisting of painting, casting, dipping, and wrapping.

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