JPS63130714A - Annealing method for iron core - Google Patents

Abstract

PURPOSE:To uniformly heat the whole iron core and to prevent the development of deteriorated iron core by piling many pieces of steel sheets for ion core of small capacity motor in an induction heating apparatus, laying blocks for compensating heat-treatment, made of magnetic substance at both ends and setting frequency of the induction current to the specific range at the time of annealing by induction heat. CONSTITUTION:Many pieces of punching-worked annular iron core sheets 4a are piled in the cylindrical induction heating apparatus 3 burying oil 2 for induction heating into the side wall and at upper and lower sides thereof, the blocks 5, 5 for compensating heat-treatment, made of magnetic substance, such as ferrite series stainless steel, etc., are laid. Under this condition, DC current having 300-500Hz number of frequency is applied to the coil 2 for induction heating and the iron core 2 is heated to about 800 deg.C by the induction current, to anneal. The whole steel sheets for iron core is uniformly heated and also the iron core without any deterioration of insulating film caused by over-heating and iron-loss characteristic caused by low temp. is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an iron core annealing method for annealing a laminated iron core using an induction heating device.

(Prior art) Iron cores for small electric motors are generally manufactured by stacking a large number of punched steel plates, but it is known that the magnetic properties of the core deteriorate due to residual stress generated during the punching process. As a countermeasure to this problem, annealing of the iron core is performed.

Conventionally, the method of annealing has been to heat the iron core by adding heat generated by electrical resistance, gas, or combustion to the iron core by conduction or radiation. However, this method has the drawback of poor heating efficiency and increased equipment size. For this reason, in recent years, methods of heating the iron core by induction heating have been considered in order to improve the heating efficiency, and for example, there is a method as shown in JP-A-58-104125. In this method, a laminated iron core is housed inside an induction heating device equipped with an induction coil, and the iron core is heated by induction heating in this state. In this case, the frequency of the induced current during induction heating is 1°4 [KHz] to 1.8 [KHz]. In this case, the heating temperature of the iron core is set at T2O ['C] as the minimum temperature in order to remove the residual stress during punching, and on the other hand, the maximum temperature is set in consideration of the heat resistance of the interlayer insulation coating applied to the iron core feed. The temperature is usually 800[℃], maximum 850[℃]
Therefore, the heating temperature of the iron core is
Generally, a range of 750 ['C] to 11100 ['C] is considered to be good.

Incidentally, as one method of annealing an iron core using an induction heating device, a method disclosed in Japanese Patent Application No. 60-251656 has already been filed. This method employs a so-called batch production method for annealing iron cores in small lots.As shown in FIG. The induction heating device 3 is constructed by embedding the core 4 in a laminated state and a heat treatment compensation block 5 at the top of the laminated core 4.
．． 5 is arranged and stored, and induction heating is performed in this state. In this method, the present inventor applied induction heating to the laminated iron core 4 by applying a frequency of 1000 [Hzl, and heated it to 800 ['C] in about 10 minutes.
An experiment was conducted in which the material was heated to . At this time, as shown in FIG. 2, for each core plate 4a in the central part A in the height direction of the laminated core 4 and the part B near the heat treatment compensation block 5 at the end of the laminated core 4, the outer peripheral part a, the slot bottom part When the temperatures of the portion C and the inner peripheral portion C were measured using thermocouples, the results shown in Table 1 below were obtained.

As can be understood from Table 1, the temperature difference at the central portion A in the height direction of the laminated core 4 is 10 ['C], while the temperature difference at the portion B near the heat treatment compensation block 5 is 55°C. It is as large as [℃].

Therefore, in this case, considering that in the laminated core 4, the magnetic flux flow is likely to be disturbed especially in the vicinity of the heat treatment compensation block 5, the frequency of the induced current is 1000 [H4F or higher].
In the case of 2, there is a possibility that the temperature difference in 1 may exceed 50 [°C], so the minimum heating temperature is 750 [°C].
In the following cases, recovery of iron loss becomes insufficient, and on the other hand, when the maximum temperature significantly exceeds 800 [° C.], there is a drawback that there is a possibility that the interlayer insulation coating may deteriorate.

(Problems to be Solved by the Invention) In a device in which induction heating is performed with heat treatment compensation blocks 5 arranged at both ends of a laminated iron core 4 in a double series, the frequency of the induced current is 1000 [ H,
In the second case, the temperature difference in the radial direction of the laminated core 4 is large, especially in the vicinity of the heat treatment compensation block 5.
There was a risk that defective products would occur.

The present invention has been made in view of the two circumstances, and therefore, its purpose is to provide an iron core annealing method that can heat the entire iron core at a more uniform temperature and eliminate the occurrence of defective products.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides, when annealing a laminated core using an induction heating device, a heat treatment compensation block made of a magnetic material is provided at both ends of the core in the induction heating device. This method is characterized in that the induction heating is performed by setting the frequency of the induced current in the range of 300 Hz to 500 Hz.

(Function) Generally, when heating the iron core with an induction heating device, in order to uniformly heat the entire iron core, it is possible to slow down the temperature increase rate during induction heating, but the heating time becomes longer and the heating efficiency is poor. . By the way, in such induction heating, it is known that the current penetration degree δ with respect to the frequency f of the induced current is expressed by the following equation.

δ=5030 ψ (μ・f) However, ψ: Specific resistance of the heated object [00m] μ: Relative magnetic permeability of the heated object f: Frequency [Hz] As can be understood from this equation, the frequency f is small. As the frequency f decreases, the current penetration degree δ increases. Therefore, if the heating time is the same, there is a tendency for the iron core, which is the object to be heated, to be heated more uniformly as the frequency f decreases.

The present inventor focused on this point, and by setting the frequency of the induced current during induction heating in the range of 300 [Hzl to 500 [Hzl], the iron core can be heated without reducing the heating efficiency. Allows for more even heating.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 1 to 3. However, in FIGS. 1 and 2, the configuration is the same as the conventional one, so 3 is an induction heating device. It is constructed by burying it. Reference numeral 4 denotes a laminated core formed by laminating a large number of annular core plates 4a formed by punching steel plates.

A heat treatment compensation block 5 is made of a magnetic material having substantially the same magnetic properties as the iron core 4, such as a ferritic stainless steel material. In this case, the heating furnace 1 in the induction heating device 3 is set so that its outer diameter is 320 mm, its inner diameter is 280 mm, and its internal effective height is slightly larger than 800 mm. , and the laminated iron core 4 is
Its outer diameter is 190 [mm] and the stacking height is 400 mm.
Furthermore, the heat treatment compensation block 5 has the same outer diameter as the laminated core 4 and a height of 200 [mm].
mn+].

Now, in order to anneal the laminated core 4, first heat treatment compensation blocks 5, 5 are placed on the laminated core 4 and both end portions of the laminated core 4 in the heating furnace 1 of the induction heating device 3. Store it in the arranged state. Then, in this state, the induction heating device 3 is operated to inductively heat the laminated iron core 4, in this case, the frequency of the induced current is 500 [Hz], and the laminated iron core 4 is heated to 800 BiC in about 10 minutes. Heat. At this time, as in the conventional case, for each core plate 4a of the central part A in the height direction of the laminated core 4 and the part B near the heat treatment compensation block 5 at the end of the laminated core 4, the outer peripheral part a and the slot bottom part are all The temperatures of the inner circumferential portion C were measured using a thermal lightning pair, and the results shown in Table 2 below were obtained.

The temperature difference at the central portion A in the height direction and the temperature difference at the portion B near the heat treatment compensation block 5 are both 50 ['C
] We were able to obtain good results within .

In addition, in the same manner as described above, the heating furnace l in the induction heating device 3 has an outer diameter of 280 [mm] and an inner diameter of 1.
55 [mm], and the internal effective height dimension is set to 300 [mm], and the outer diameter of the laminated core 4 is set to 1.
25[m+nl, and the stacking height dimension is set to be 100[mn+:l, and further, the heat treatment compensation block 5 is set so that its height dimension is 100[+nm]. Then, a laminated iron core 4 is placed in the heating furnace 1 of the induction heating device 3.
The laminated core 4 is housed with heat treatment compensation blocks 5゜5 arranged at both end portions, and the laminated core 4 is heated by induction at a frequency of 309 [Hz] of the induced current. The iron core 4 was heated to 800['C] for about 12 minutes. At this time as well, when the temperature of each part of the laminated core 4 was measured using a thermal lightning pair, the results shown in Table 3 below were obtained.

= 9- Table 3 Temperature measurement results ('C') In this case, as understood from this Table 3, the temperature difference at the center part A in the height direction of the laminated core 4 and the temperature at the part B near the heat treatment compensation block 5 Good results were obtained in which the difference was within 50['C] in both cases.

Based on these results, a characteristic diagram of the relationship between the frequency f and the temperature difference Δt in the laminated core 4 is shown in FIG. In this case, the characteristic line C corresponds to the central portion A in the height direction of the laminated core 4.
Also, the characteristic line shows a characteristic line of a portion B near the heat treatment compensation block 5 at the end portion of the laminated core 4.

Incidentally, the broken line indicates a guideline for the allowable range of the temperature difference Δt.

As can be understood from Fig. 3, for the characteristic line C, the frequency f is 300 [Hz], 500 [Hz], 10
00[Hz], the temperature difference Δt is 50['C]
], and the variation in temperature difference Δt for each frequency f is small. On the other hand, regarding the characteristic line, when the frequency f is 1000 [Hz1 or more, the temperature difference Δt is 50 [Hz] or more.
'C] and as the frequency decreases, the temperature difference Δt
is on the decline. Therefore, using this characteristic line as a reference, as the frequency f becomes smaller, the temperature difference Δ
Although t is small, if it is less than 300 [Hz], it is expected that the temperature increase rate will be slow and the heating efficiency will be poor. On the other hand, if the temperature difference Δt is within 50 [℃],
The first limit of the frequency f is within the permissible range up to about 800 Hz, but considering temperature variations due to setting conditions, etc., it is considered desirable to have a frequency up to 500 Hz:l. Therefore, based on these results, in order to uniformly heat the laminated iron core 4 without reducing the heating efficiency, it is considered that the frequency f of the induced current during induction heating is preferably in the range of 300 [Hz] to 500 [Hz].

As described above, according to this embodiment, the induction heating is performed with the heat treatment compensation blocks 5 disposed at both ends of the laminated iron core 4, and the induction heating is performed by changing the frequency of the induced current to 300 [Hzl. By setting the heating frequency within the range of 50.0 [Hz], the laminated core 4 can be heated more uniformly without reducing the heating efficiency, and the generation of defective products can be eliminated.

[Effects of the Invention] As is clear from the above description, the present invention provides heat treatment compensation made of magnetic material at both ends of the core in the induction heating device when sintering and tying the laminated iron core using an induction heating device. In the method in which induction heating is performed with the blocks placed, heating efficiency is improved by setting the frequency of the induced current in the range of 300 [Hzl to 500 [Hzl]. This has the excellent effect of being able to heat the entire core more uniformly without lowering the temperature, thereby eliminating the occurrence of defective products.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal sectional view of the entire structure according to the present invention and the conventional method;
The figure is a plan view of the core plate, and FIG. 3 is a characteristic diagram of the relationship between frequency and temperature difference in the laminated core. In the drawings, 2 is an induction coil, 3 is an induction heating device, 4 is a laminated core, and 5 is a heat treatment compensation block. Agent Patent Attorney Noriyuki Chika Yudo Hiroshi Mitsumata Figure 1 Figure 2

Claims (1)

[Claims] 1. When annealing a laminated iron core using an induction heating device, in a method in which induction heating is performed with heat treatment compensation blocks made of magnetic material arranged at both ends of the core in the induction heating device, A method for annealing an iron core, characterized in that heating is performed by setting the frequency of an induced current in the range of 300 [Hz] to 500 [Hz].