JPH0456781A - Separating agent for annealing for grain-oriented silicon steel sheet - Google Patents

Abstract

PURPOSE:To enhance the performance of a grain-oriented silicon steel sheet by using a separating agent based on magnesia obtd. by burning a mixture of magnesium hydroxide with a specified wt.% of Cu basing on the amt. of MgO after burning. CONSTITUTION:A magnesia-based separating agent for annealing is used to form a forsterite coating film on a grain-oriented silicon steel sheet during final annealing at a high temp. At this time, the magnesia is obtd. by adding Cu or a Cu compd. to magnesium hydroxide by 0.1-10 wt.% (expressed in terms of Cu) basing on the amt. of MgO after burning, mixing them and burning the mixture. The properties of the forsterite coating film can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an annealing separator for grain-oriented silicon steel sheets containing magnesium oxide as a main component.

<Prior art> As a method of forming a forsterite insulating film on a grain-oriented silicon steel sheet, a silicon steel strip cold-rolled to a desired final thickness is continuously annealed for several minutes at a temperature of 700 to 900°C in wet hydrogen. After decarburizing the carbon in the steel plate and oxidizing the silicon at the same time to form an oxide film containing SiO□ on the surface of the steel plate,
Apply an annealing separator mainly composed of MgO on the W4 board,
In a series of steps of winding into a coil and subjecting it to high-temperature annealing, MgO-3iO
A method of forming a □ system, that is, a forsterite film, has been adopted.

Various improvements have been made to the annealing separator used in the above process, since its physical properties greatly affect the properties of the insulating coating formed thereon, and ultimately the performance of the grain-oriented silicon steel sheet.

Generally, HGO is used as the main ingredient as an annealing separator, but the addition of many elements and compounds has been proposed to further improve the uniformity, adhesion, and magnetic properties of the forsterite film. There is.

For example, in Japanese Patent Publication No. 54-14567, in order to improve the magnetic properties of grain-oriented silicon steel sheets using AIN, in the process of applying an annealing separator, Cu and Sn are added to the annealing separator.
, Ni, Co or one or two of these compounds
It has been disclosed that the magnetic properties can be improved by applying a separating agent to which more than one species is added.

By the way, at the time of applying the annealing separator to a silicon steel sheet, the powders of these disclosed elements or compounds are mixed with MgO powder, which is the main component thereof, and water is added and stirred, followed by application as a water slurry.

However, according to the above-disclosed method, the forsterite coating obtained by adding these additives to MgO powder has local spot defects where there is no coating, and the formation of spot deposits due to agglomerated particles of the additive. The appearance of the film, such as the presence of
There was still room for further improvement in terms of uniformity, space factor, etc. In addition, it is not always easy to consistently obtain a certain effect regarding magnetic properties, and the difficulty lies in the fact that there are many factors that are controlled by the powder properties of the additives used and the conditions for adjusting the mixed slurry with MgO. there were.

On the other hand, when these additives are added to water-soluble substances such as sulfates and nitrates, the oxidation effect of the decomposed gas of these additives during the high-temperature annealing process results in a scalloped film or a film with poor density unevenness. , and the amount added was often naturally limited.

<Problems to be Solved by the Invention> The present invention relates to an annealing separator mainly composed of MgO to which Cu or its compound is added for the purpose of improving magnetic properties, and the present invention relates to an annealing separator mainly composed of MgO to which Cu or its compound is added for the purpose of improving magnetic properties. The object of the present invention is to provide an annealing separator that makes it possible to form a sound insulating film in which no rough dots are observed, that is, a film with excellent film appearance, uniformity, and space factor.

The present inventors aimed to prevent undesirable film defects in the conventional technology of adding various elements and compounds to MgO, and decided to change the timing of addition to -MgO manufacturing process. Thinking back in time, various fine powders were added to magnesium hydroxide (Mg (Oll) t ), which is an intermediate product during MgO production, and this mixture was calcined to form magnesia powder into a silicon steel sheet using a conventional method. When we tried a method in which magnesia containing Cu or Cu compounds was coated on a surface and subjected to high-temperature annealing, we found that the above-mentioned difficulties were significantly improved with magnesia containing Cu or Cu compounds, and it greatly contributed to improving the uniformity and adhesion of the coating. This led to this invention.

That is, the present invention is a magnesia-based annealing separator used for forming a forsterite film in the final high-temperature annealing process of a grain-oriented silicon steel sheet, in which a C11 or Cu compound is added to magnesium hydroxide, and a metal is added to MgO after firing. This annealing separator for grain-oriented silicon steel sheets is characterized in that it is mainly composed of magnesia, which is blended in a range of 0.1 to 10% by weight in terms of element and is obtained by firing this mixture.

<For production> First, the present invention will be explained in detail based on experimental results.

To Mg(OH)t obtained by the bittern method, an industrial chemical of CuO powder with a passing rate of 98% or more through a 325 mesh sieve was added to the MgO after calcination in an amount of 3% by weight in terms of metal elements.
The mixture was added to a concentration of 10% by weight, wet-mixed, dehydrated, and baked in air at 980'C for 3 hours.
M'gO containing u compound was prepared.

On the other hand, according to the conventional method, Mg (OIIL was also 980
Separating agents in which 3% by weight and 10% by weight of the above CuO powder were added to MgO obtained by firing at °C for 3 hours, and a separating agent without additives were prepared as comparative separating agents.

Cut plates of oriented silicon copper plates (0.30 mm thick x 1000 mm wide x 0.30 mm thick x 1000 mm wide x
The coil was applied to a length of 300 mm), inserted into the inside of an actual coil, and annealed at high temperature to obtain the results shown in Table 1.

It can be seen that when CuO powder is added in the Mg (011) z stage according to the present invention, it is superior to the conventional method in terms of uniformity of coating appearance, adhesion, and space factor.

Although it is difficult to make a clear conclusion about the mechanism by which the selection of the timing of adding and blending additives works effectively, it is possible to infer the following facts.

MgO undergoes considerable sintering and grain growth in the process of firing the raw material Mg(Off)i, and the particles tend to aggregate significantly, so even if powder is added at this stage, it will not be possible to mix uniformly. However, in this invention, extremely fine Mg (OH) particles and additives are brought into contact at the raw material stage, so the degree of microscopic mixing of MgO and these additives after firing is extremely high. It can be assumed that it will be excellent.

The magnesia containing the Cu compound according to this invention can be used as it is, or it can be used as a main component to improve coating properties.
Various additives that have been known to improve magnetic properties, such as Ti, Mn oxides, Ca,
It goes without saying that Sr sulfate, 115B(h) and its salts can be effectively incorporated.

By the way, the raw material MP, 0 for this separating agent is usually obtained by adding milk of lime (Ca (Off) 2 ) directly to seawater, or by adding milk of lime to the bittern left over from the salt production in the salt industry. , magnesium ion (Mg”) in seawater
) is precipitated in the form of magnesium hydroxide (Mg (Off) 2 ), and if necessary, the crystals are aged, then filtered and washed with a filter press to form a cake, which is then made into pellets of appropriate size. It is often produced through an industrial manufacturing process in which it is shaped and charged into a rotary kiln or batch furnace, fired at a temperature of around 1000°C, and then crushed and classified.

In order to form a high-quality forsterite film, many improvements have been made to the MgO production method, and in particular, many proposals have been made regarding appropriate conditions regarding purity, particle size, etc.

The separating agent of this invention can be obtained by adding Cu or its compound at the Mg (OH) Z stage, mixing well, and then firing. It is most rational and industrially easy to blend these additives in the reaction tank or aging tank in which the precipitation occurs.

If the additive is a simple substance, oxide, or water-soluble additive that is insoluble in water, first disperse it well with water in a separate container, mix it into the Mg (Off) z tank, and slowly mix the entire liquid. It is sufficient to proceed to the next filtration step while stirring, and there is no need to make any special changes to the conditions of the MgO production process itself.

On the other hand, water-soluble additives can also be achieved according to Dogu's method. As the additive, Cu sulfates, nitrates, and acetates are preferable. These compounds decompose in a relatively low pr temperature range below the firing temperature of MgO, and exist in the form of Cu oxides after firing, so that film defects caused by decomposed gases seen in the prior art can be avoided.

However, the free acids of these sulfates and nitrates are Mg (01
1) Combines with 2, depending on the amount added, Mg (Off)
The addition of an insoluble fine powder, which preferably does not affect the production conditions of MgO, as it may affect the crystal growth of MgO, is advantageous since improved methods for the production of annealing separators described above can be utilized. be.

The amount of Cu or its compound added to Mg(Oll)z is limited to a total amount of 0.1 to 10% by weight in terms of metal elements based on MgO after firing. If the amount is less than 0.1% by weight, there will be little effect of addition, whereas if it exceeds 10% by weight, the properties of the forsterite coating will be adversely affected.

It is preferable that the additive agent be in a fine powder form. However, in this invention, in particular, Mg (OH) Defects are effectively avoided. Therefore, there is no major problem even with particles having a normal particle size distribution that are generally commercially available as industrial chemicals.

The present invention will be explained below based on Examples.

<Example> Example I C: 0.030% by weight (hereinafter simply expressed as %), S
i: 2.97%, Mn: 0.070%, Se
A silicon steel strip with a bond thickness of 0.30 and a width of 1020 mm containing Sb: 0.019% and Sb: 0.020% was heated at a dew point of 66°C in an atmosphere consisting of 111□55% and the remainder N2.
Decarburization annealing was performed at 20°C for 14 minutes. A test material with a length of 300n+m was cut from this steel strip, and each annealing separator shown in Table 2 was coated with 12g of In (per). After holding for recrystallization, high-temperature annealing at 1180° C. for 5 hours and cooling in a furnace.Table 2 shows the appearance and adhesion of the obtained coating.
Indicates the occupancy rate.

As is clear from the examples in Table 2, when the annealing separator of the present invention is used, a smooth coating with excellent appearance and adhesion can be obtained more easily than when using the conventional method, and the magnetic It can be seen that the characteristics are also advantageous.

<Effects of the Invention> As described above, the present invention can advantageously improve the performance of grain-oriented silicon steel sheets by improving the properties of the forsterite coating.

Claims (1)

[Claims] A magnesia-based annealing separator used for forming a forsterite film in the final high-temperature annealing process of grain-oriented silicon steel sheets, in which Cu or Cu compound is added to magnesium hydroxide in an amount of 0.1 in terms of metal element relative to MgO after firing. ~10% by weight
1. An annealing separator for grain-oriented silicon steel sheet, characterized in that the annealing separator for grain-oriented silicon steel sheets is mainly composed of magnesia obtained by blending within the following range and firing this mixture.