JPH07122097B2 - Partial adiabatic annealing method for amorphous alloys - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a method for annealing an annular magnetic core made of an amorphous alloy (hereinafter referred to as an iron core).

[Prior Art] An amorphous alloy is produced by quenching a molten metal at about 10 ⁶ ° C / sec, and its shape is a thickness of 20 to 30 µmm and a width of 25 to 10 µm.
It is a foil of about 0 mm.

Since amorphous alloys have much less excitation loss than ordinary magnetic materials with a crystalline structure, it has been proposed to use them in distribution transformers and the like.

The iron core is manufactured by winding an amorphous alloy, and its cross section is usually quadrangular (rectangular or square), and its surface has four faces.

That is, the surface of the central opening coaxial with the core axis (hereinafter referred to as the inner peripheral surface), the outer peripheral surface of the core coaxial with the core axis (hereinafter referred to as the outer peripheral surface), and the inner peripheral surface at right angles to the core axis. It is composed of two surfaces surrounded by the outer peripheral surface (hereinafter referred to as an upper surface and a lower surface).

The iron core is annealed after forming to recover the deterioration of the magnetic properties due to processing strain.

Generally, a method called magnetic field annealing, in which an exciting coil is wound around an iron core and is annealed while being excited, is used.

In order to prevent oxidation of the iron core, annealing is performed in an inert gas atmosphere, and an iron core annealing temperature of around 350 ° C is adopted.

The heat conduction in the radial direction (stacking direction) of the iron core is much worse than that in the iron core axial direction, so the inner and outer peripheral surfaces of the iron core closely follow the ambient temperature in the furnace, but the center of the iron core in the radial direction The temperature of the parts follows very slowly.

When a temperature difference occurs in the iron core, thermal stress increases, which adversely affects the magnetic properties.

For this reason, it is necessary to avoid increasing the temperature difference in the iron core, and it is necessary to prevent the atmosphere temperature in the furnace from rising rapidly.

Fig. 3 shows an example of time characteristics of the furnace atmosphere temperature and the iron core temperature in the conventional method. According to this, the maximum holding temperature of the furnace atmosphere is around 400 ° C, but it reaches 300
An intermediate holding temperature time zone around ℃ is provided.

By providing such an intermediate holding temperature time zone, the annealing time becomes longer.

After the intermediate holding time around 300 ° C, the temperature of the furnace atmosphere is raised again, and when it reaches the maximum holding temperature of the furnace atmosphere (around 400 ° C), the temperature is kept constant for a predetermined time and then the iron core Lower the annealing temperature to slightly higher than 360 ℃,
Keep constant at this temperature.

The iron core annealing temperature becomes slightly higher than 360 ° C, and the iron core temperature becomes uniform while the atmosphere in the furnace is maintained.
After reaching 360 ° C and maintaining this state for a while, cooling begins.

Although the iron core temperature finally falls to room temperature, the annealing time is defined as the period from the start of annealing to the cooling of the iron core temperature to 200 ° C through the above-mentioned process. The annealing time in Fig. 3 is about
It takes 10 hours.

Looking at the iron core temperature in FIG. 3, despite the fact that the temperature of the atmosphere inside the furnace is adjusted as described above, a considerable temperature difference occurs between the center of the iron core and the inner and outer peripheral surfaces. I know that

Since the temperature difference between the center of the core and the inner and outer peripheral surfaces that occurs during the annealing process increases as the thickness of the amorphous alloy stack increases, the larger the core, the greater the risk of deterioration of magnetic properties due to thermal stress. Will increase.

[Problems to be Solved by the Invention] Since the response difference between the central portion of the iron core and the inner and outer peripheral surface portions is large (the central portion is slow and the inner and outer peripheral surface portions are fast),
Thermal stress easily occurs due to the temperature difference in the core during annealing.

In order to suppress this thermal stress, it is necessary to adjust the temperature rising rate during the temperature rising process of the furnace atmosphere, which makes the control of the furnace atmosphere temperature complicated and requires a long time for annealing. It was

Further, even if the temperature rising rate is adjusted as described above, there is a problem that the effect of improving the magnetic characteristics of the annealing is hindered by the thermal stress generated by the temperature difference in the iron core during the annealing process.

[Means for Solving Problems] In the present invention, heat-resistant heat insulating materials are attached to the inner and outer peripheral surfaces of the iron core during annealing to reduce the temperature difference in the iron core when the ambient temperature changes.

Further, the temperature condition of the furnace atmosphere in the present invention is set to be larger than the conventional furnace atmosphere temperature and its rising speed.

As a result, the iron core annealing time is made shorter than before, and the risk that the effect of improving the magnetic properties by annealing is obstructed by thermal stress is eliminated.

[Operation] The thermal conductivity of the object in which the metal plates are laminated is much smaller in the direction perpendicular to the laminating surface (laminating direction) than in the direction parallel to the laminating surface. This is because heat conduction in the direction parallel to the stacking plane is carried out along with the metal plate, whereas heat conduction in the stacking direction goes through the space between the stacks or through the contact parts of the stacks. However, since the space is filled with air or nitrogen at the time of annealing, the thermal conductivity of these gases is much smaller than that of metal, and there is contact resistance at the contact part. is there.

According to the results of measuring the thermal conductivity of the iron core at 400 ° C. in the axial direction of the iron core and the radial direction of the iron core, the thermal conductivity in the axial direction was 20 times that in the radial direction.

From this, if the inner and outer peripheral surfaces of the iron core are heat-insulated and annealed, the temperature in the radial direction becomes almost uniform and a temperature difference occurs in the axial direction. It is much smaller than the temperature difference, and the thermal stress generated in the iron core is also small.

Even if the inner and outer peripheral surfaces of the iron core are not insulated, the heat flow in the radial direction is extremely small compared to the heat flow in the axial direction, so even if the heat insulation is performed, the thermal response of the core center (this part is the slowest) The delay is very small.

By the above-mentioned heat insulation treatment, the temperature difference in the iron core during annealing becomes extremely small, so that the rate of rise of the atmosphere temperature in the furnace can be increased.

Further, since the response to the atmospheric temperature near the inner and outer peripheral surfaces of the iron core is delayed, the core can withstand a transient high temperature atmosphere, and the maximum holding temperature of the furnace atmosphere can be made higher than in the conventional case.

With the above, the annealing time can be shortened.

In order to perform the above heat insulation, a heat resistant heat insulating material (heat conductivity 0.03 to 0.14 W / m ° C,
Attach a shrinkage rate of 1 to 3% up to 500 ° C.

As these heat insulating materials, glass wool and other inorganic fiber materials are suitable.

As a method of attaching to the iron core, there are a method of winding a sheet-shaped heat insulating material, a method of filling the heat insulating material using a frame, and the like.

The method of wrapping the sheet-shaped heat insulating material is easy, and the wrapping thickness is 25 to 75 mm.

In this way, the exciting coil for magnetic field annealing is wound around the iron core having the heat insulating material attached to the inner peripheral surface and the outer peripheral surface.

Use an exciting coil that can withstand a temperature of 500 ° C or higher.

The iron core is placed in an atmosphere of an inert gas such as nitrogen gas and annealed under a predetermined temperature condition while applying direct current to the exciting coil.
Iron cores should normally be magnetically annealed, but some amorphous alloys such as (Co ₆₆ Fe ₄ Ni ₁ B ₁₄ Si ₁₅ ) and (Fe _76.85 Cr ₂ B
_16.1 Si _4.8 C _0.25 ) etc. may be annealed without applying a magnetic field.

FIG. 1 shows a schematic view of an iron core (state before winding an exciting coil for magnetic field annealing) in which heat insulating materials are attached to the inner peripheral surface and the outer peripheral surface in the present invention, and FIG. 2 shows a temperature during annealing according to the present invention. An example of time characteristics is shown.

Hereinafter, the present invention will be described in detail with reference to FIG. Ts is selected from the iron core annealing temperature, a temperature sufficient for removing work strain of an amorphous alloy, and lower than the crystallization temperature (325 ° C to 400 ° C).

The maximum holding temperature (Tmax) of the atmosphere in the furnace is 100 ℃ to 1 than Ts.
Set 60 ℃ higher.

After the start of annealing, the temperature of the atmosphere in the furnace was rapidly and uniformly increased to Tmax and kept at the temperature Tmax (maintained at a constant temperature).

When the iron core temperature approaches Ts, the furnace atmosphere temperature is lowered to Ts.

After the iron core temperature reaches Ts and a predetermined time has elapsed, the heat input to the annealing furnace is stopped and cooling is started.

The cooling rate of the iron core temperature is selected within the range of 0.1 to 100 ° C / min according to the shape of the iron core.

Energization for magnetic field annealing of the iron core is continued until the iron core temperature drops to about 200 ° C.

EXAMPLES consisting elemental composition (Fe ₇₈ B ₁₃ Si ₉₎ amorphous alloy Metglas
(Product name) 2605S-2 100mm width ribbon was wound to manufacture an annular core for a transformer.

The core dimensions and weight are shown in Tables 1 to 3.

The iron cores in Table 1 are according to the embodiments of the present invention, and glass wool is wound around the inner and outer peripheral surfaces of the iron core to perform heat insulation.

An exciting coil for magnetic field annealing is wound around an iron core around which a heat insulating material is wound using a high heat resistant electric wire.

The number of turns of the coil is 6 turns, and the magnetizing force when energized (DC) is 800 AT / m.

FIG. 2 is an example of temperature-time characteristics when the iron cores of Table 1 are annealed by the method of the present invention. The solid line shows the temperature of the atmosphere in the furnace, the one-dot chain line shows the temperature of the core center, and the broken line shows the center of the iron core. The temperature is measured with a thermocouple at the point where the point 5 mm inside the core from the inner peripheral surface and the point 5 mm inside the core from the outer peripheral surface.

The iron core annealing temperature is 360 ° C.

The iron core is magnetically annealed in a nitrogen gas atmosphere in an annealing furnace.

When the annealing is started, the exciting coil is energized to raise the temperature of the atmosphere in the furnace uniformly and rapidly, keeping the maximum holding temperature slightly lower than 500 ° C.

When the iron core temperature approaches the iron core annealing temperature of 360 ° C and is slightly lower than that, the furnace atmosphere temperature is lowered to 360 ° C and kept at this temperature. The temperature of the iron core also reaches 360 ° C while the atmospheric temperature in the furnace is kept at 360 ° C.

After holding the iron core temperature near 360 ° C for about 1 hour, stop the heat input to the annealing furnace and start cooling.

When the iron core temperature falls to around 200 ° C, the excitation coil is de-energized and the magnetic field annealing is completed.

The average cooling rate of the iron core down to 200 ° C is 1.5 ° C / min.

Table 1 shows the magnetic characteristic data of the iron cores annealed according to the present invention.

The iron cores in Tables 2 and 3 are not according to the present invention, and are manufactured to confirm the effects of the present invention.

Here, in order to compare the annealing method of the present invention with the conventional annealing method, the characteristics of the conventional annealing method were also measured.

Fig. 3 is an example of temperature-time characteristics when the iron cores in Table 2 are annealed by the conventional method. The solid line is the atmosphere temperature in the furnace, the one-dot chain line is the iron core center temperature, and the broken line is the iron core axial center part. It is the temperature of the inner peripheral part and the outer peripheral part of the iron core (measurement is by a thermocouple), and the magnetic properties are shown in Table 2.

Table 3 shows that the iron core during annealing is not attached with a heat insulating material as in the conventional case, and the temperature and time conditions for annealing are based on the atmosphere temperature conditions in the furnace shown in FIG. 2, but the temperature data for the iron core is not shown. .

Comparing the characteristics of the present invention shown in FIG. 2 with the conventional characteristics shown in FIG. 3, it can be seen that in the present invention, the temperature of the atmosphere inside the furnace is rapidly increased and the maximum holding temperature of the atmosphere inside the furnace itself is high. Compared with the conventional annealing method, the annealing time is shortened and the temperature difference in the iron core during annealing is smaller.

Further, according to the method of the present invention, the control of the atmospheric temperature in the furnace is easy.

Comparing Tables 1 and 2 clearly shows numerically the effect of shortening the annealing time and improving the magnetic properties (decreases with coercive force and excitation loss) according to the present invention.

The improvement of the magnetic characteristics according to the present invention is due to the attachment of the heat insulating material to the outer peripheral surface and the inner peripheral surface of the iron core,
Even if the annealing temperature time condition of the present invention as shown in FIG. 2 is applied in order to shorten the annealing time while simply maintaining the conventional appearance of the iron core (without attaching the heat insulating material), the magnetic properties Far from improving, it decreases.

This is theoretically estimated, but it is proved by comparing the data in Table 3 with those in Tables 1 and 2.

[Effects of the Invention] According to the present invention, it is possible to obtain an iron core having a short annealing time, easy control of the atmosphere temperature in the furnace, and excellent magnetic properties (small coercive force and excitation loss).

[Brief description of drawings]

FIG. 1 is a schematic view of attaching a heat insulating material to an iron core during annealing according to the present invention, FIG. 2 is a graph showing a temperature time example of annealing according to the present invention, and FIG. 3 is a temperature time example of annealing according to a conventional method. It is a graph shown. 1 ... Iron core, 2 ... Insulation material, a ... Curve showing the atmospheric temperature in the furnace, b ... Curve showing the temperature of the center of the iron core, c ... 5 mm from the inner peripheral surface of the iron core at the center of the iron core axial direction A curve showing the temperature of the part inside the core and the temperature of the part 5 mm inside the core from the outer peripheral surface of the core, c '... At the center of the core axial direction, the temperature of the inner peripheral surface of the core and the temperature of the outer peripheral surface of the core are shown. Curve

Claims (2)

[Claims] 1. When annealing a ring-shaped magnetic core wound with a foil-shaped amorphous alloy, the outer peripheral surface and the inner peripheral surface of the ring-shaped magnetic core are covered with a heat-resistant material to process the amorphous alloy. The iron core annealing temperature is set within a temperature range that is sufficient for removing strain and does not exceed the crystallization temperature, and the atmosphere temperature in the furnace is rapidly and uniformly increased during heating in the initial stage of annealing, and the temperature is higher than the iron core annealing temperature. Then, the temperature of the annular magnetic iron core is approached to the iron core annealing temperature, the furnace atmosphere temperature is lowered to the iron core annealing temperature, and the iron core is held at this temperature. Is maintained near the iron core annealing temperature for a predetermined time, and then the temperature of the atmosphere in the furnace is lowered to cool the annular magnetic core. 2. An annealing method in which an exciting coil is wound around an annular magnetic iron core to which a heat insulating material is attached, and the exciting coil is energized to perform annealing while generating a magnetic field in the annular magnetic iron core. The method for annealing a ring-shaped magnetic core according to the item.