JPH06151153A - Calcinated powder for manganese-zinc ferrite and manufacture thereof - Google Patents

Abstract

PURPOSE:To suppress cracks during baking of a manganese-zinc ferrite core. CONSTITUTION:A calcinating temperature pattern during the manufacture of calcinated powder for manganese-zinc ferrite is permitted to be suitable and suitable oxidation state for the calcinated powder is provided. Expansion and contraction due to excessive oxidation and reduction during the core baking is suppressed by permitting the oxidation state of the calcinated powder to be suitable and cracks are suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a calcined powder which is a raw material for producing a manganese-zinc ferrite core and has a low rate of crack generation during firing of the core, and a method for producing the same.

[0002]

2. Description of the Related Art When manufacturing a manganese-zinc ferrite core, cracks often occur on the surface of the core during firing of the core. There are various forms of cracks that occur in the core, but this not only causes defects in appearance, but also causes problems such as deterioration of the mechanical strength of the core body and, in extreme cases, deterioration of the magnetic properties of the core. . Regarding the cracking during firing, the main cause has been the uneven density generated inside the green core during core molding. To suppress the occurrence of cracks,
Up to now, the focus has been mainly on the particle size distribution of powder and optimization of molding conditions from the viewpoint of powder moldability, but these are intended to eliminate density unevenness inside the core after molding. It was something that was done.

The molding conditions of the core are often restricted by the capacity of equipment such as a press and lack in flexibility, so that it is extremely difficult to optimize the change of the manufacturing conditions due to the increase of the production amount. Also, when the atmosphere in the firing furnace changes,
It is difficult to deal with problems such as the increased incidence of cracks. That is, it is difficult to sufficiently suppress the occurrence of cracks during core firing only by the particle size distribution of the calcined powder and the molding conditions of the core,
The demand for a calcined powder that is less susceptible to fluctuations in manufacturing conditions cannot be fully met.

On the other hand, it has been clarified that shrinkage and expansion due to reduction and reoxidation of the core during firing is also one of the causes of cracking. According to this, the occurrence of cracks during firing of the core is considered to be due to the synergistic effect of the uneven density in the core during molding and the excessive reduction and oxidation of the core during firing. By suppressing reduction and reoxidation during firing, it is possible to effectively suppress the occurrence of cracks during firing of the core.

Reduction and reoxidation during firing occur when the amount of oxygen required for burning the binder contained in the molded body is not supplied. It is thought that the generation of cracks can be suppressed by blowing sufficient oxygen into the firing furnace during binder combustion, but this method may disturb the temperature distribution inside the firing furnace when the thermal capacity of the firing furnace is not sufficient. However, there is a possibility of adverse effects. Therefore, there is a demand for a means capable of supplying sufficient oxygen for binder combustion without blowing oxygen into the firing furnace.

[0006]

SUMMARY OF THE INVENTION The present invention relates to manganese-
The purpose of the present invention is to obtain a calcined powder that is not easily affected by fluctuations in manufacturing conditions while significantly reducing the rate of core cracking during firing of a zinc ferrite core.

[0007]

According to the present invention, by positively increasing the amount of oxygen in the calcined powder, binder combustion is achieved even when manufacturing conditions (such as changing the core shape) are changed. It is possible to prevent excessive reduction and reoxidation at the time of firing the core due to the lack of the oxygen content of the above, and to prevent the occurrence of cracks at the time of firing the core.

More specifically, the ratio between the amount of hematite and the amount of spinel contained in the calcined powder is optimized, and the difference in the amounts of oxygen contained in one molecule is utilized to make the calcined powder for binder combustion. It retains oxygen and supplies the oxygen released when hematite becomes spinel to the combustion of the binder to make up for the shortage of oxygen in the atmosphere in the firing furnace. Here, the ratio between the amount of hematite and the amount of spinel is
The spinelization rate of the calcined powder is determined from the intensity of each main peak of the powder X-ray diffraction, and is defined as follows.

Spinelization rate (%) = Im / (Im + Ih) Here, Im is the strength at which the d value of spinel is 2.53, and Ih is the strength at which the d value of hematite is 2.69.

The reason why the spinelization rate of the calcined powder is limited to 55 to 75% is that when the spinelization rate exceeds 75%, the amount of oxygen released from hematite is not sufficient for binder combustion and cracks occur. Cannot be effectively suppressed. On the other hand, if it is less than 55%, it becomes difficult to appropriately maintain the shrinkage ratio during firing, and the effect of performing calcination becomes insufficient. Preferably, the spinelization rate is 6
Even better results are obtained if it is 0 to 70%. The calcined powder having a spinelization rate in this range can be obtained by optimizing the oxygen concentration in the atmosphere during calcining and the firing temperature pattern.

From the viewpoint of the calcination temperature, the optimization of the particle size distribution of the calcination powder and the optimization of the spinelization rate are contradictory, and in the conventional method in which the treated powder is rapidly cooled when leaving the calcination furnace, If the spinelization rate of the fired powder is 55 to 75%, the effect of the calcination is not sufficient, so that there is a problem that the molding pressure becomes high during core molding. However, by optimizing the maximum temperature of calcination to promote sintering and grain growth of the raw powder and adjusting the oxidation degree of the treated powder when cooling the treated powder, the particle size distribution and spinelization rate of the calcined powder can be improved. Optimization can be achieved at the same time. That is, by taking an appropriate temperature pattern during calcination, it is possible to obtain a calcined powder having target powder characteristics. The maximum temperature of calcination is set to 900 to 1100 ° C., because if the temperature is higher than this, it becomes difficult for sintering to proceed during the main firing, and if the temperature is lower than this, the effect of calcination is not sufficient. .

Further, the cooling rate of 50 ° C./min or less is maintained at a temperature of 700 ° C. to 1000 ° C. for at least 100 ° C., and the spinelization rate is controlled only by operating the temperature pattern outside the temperature range. Difficult to do,
If the cooling rate is higher than this, the spinelization rate cannot be 75% or less. The calcined powder according to the present invention can be used as a raw material for a manganese-zinc ferrite core obtained through a normal forming and firing manufacturing process.

[0013]

EXAMPLES The present invention will be further described below based on examples. Raw material powders having the following compositions were prepared, which were calcined in the atmosphere at different calcination temperatures, and then pulverized to obtain calcined powders having different spinelization rates.

Composition: Fe ₂ O ₃ 52.9, MnO 3
6.7, ZnO 10.4 mol% FE30B (JIS-C with a density of 3.0 g / cm ³
FIG. 1 shows the occurrence rate of cracks in the core after the molded product of No. 2514) was fired at 1300 ° C. for 4 hours. As is clear from FIG. 1, the calcination powder having a spinelization rate of 75% or less has an improved crack generation rate, and particularly the spinelization rate is 70%.
In the region of less than or equal to%, the crack occurrence rate is remarkably improved and the occurrence rate is almost zero.

Further, as shown in Table 1, in order to set the spinelization rate of the calcined powder to 55 to 75%, the cooling rate is set to 50.
It will be understood that the temperature may be set to not more than ° C / minute.

Table 1 Relationship between cooling rate and spinelization rate Cooling rate (° C./min) Spinelization rate (%) 4.1 58 10 63 12.1 63 63 17 63 20 20 65 27 27 67 34 67 67 42 70 50 75 75 54 78 (Calcination temperature 1070 ° C)

[0017]

EFFECTS OF THE INVENTION By setting the spinelization rate of the calcined powder to 55 to 75%, it is possible to prevent excessive reductive oxidation during core firing, and to significantly reduce the core crack generation rate.
It is possible to obtain a calcined powder that is less susceptible to changes in manufacturing conditions such as changes in molding conditions or the atmosphere in the firing furnace.
Further, the oxygen concentration of the atmosphere during calcination is set to 10 to 30%,
The maximum temperature is 900 ° C to 1100 ° C, the high temperature treatment including this maximum temperature is the first half, and the latter half of the calcination is 1100 to 70 ° C.
50 ° C / up to 0 ° C over at least 100 ° C
When processed at a cooling rate of less than 5 minutes, the spinelization rate is 55 to 7
It is possible to obtain 5% of calcined powder.

[Brief description of drawings]

FIG. 1 is a diagram showing a crack generation rate depending on a spinelization rate.

[Procedure amendment]

[Submission date] December 14, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction content]

Spinelization rate (%) = Im / (Im + Ih) Here, Im is the intensity of spinel dvalue of 2.53 angstrom, and Ih is the hematite dval.
The ue has an intensity of 2.69 angstrom.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

[0017]

EFFECTS OF THE INVENTION By setting the spinelization rate of the calcined powder to 55 to 75%, it is possible to prevent excessive reductive oxidation during core firing, and to significantly reduce the core crack generation rate.
It is possible to obtain a calcined powder that is less susceptible to changes in manufacturing conditions such as changes in molding conditions or the atmosphere in the firing furnace.
In addition, the maximum temperature during calcination is set to 900 ° C to 1100 ° C,
When the treated powder is cooled from this maximum temperature, 1100 ° C to 70
50 ° C for at least 100 ° C up to 0 ° C
If processed at a cooling rate of less than 1 minute, the spinelization rate is 55 to 7
It is possible to obtain 5% of calcined powder.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuo Kusakabe 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Shin-Nippon Steel Corporation Advanced Technology Research Laboratories

Claims (2)

[Claims] 1. A calcined powder for manganese-zinc ferrite, which has a spinelization rate of 55 to 75%. 2. The maximum temperature during calcination is 900 ° C. to 1100 ° C.
In cooling the treated powder from this maximum temperature, 11
A method for producing a calcined powder for manganese-zinc ferrite, which comprises treating at a temperature of at least 100 ° C between 0 and 700 ° C at a cooling rate of 50 ° C / min or less.