JPH03115585A - Formation of insulating film for grain oriented silicon steel sheet - Google Patents

Abstract

PURPOSE:To uniformly control the sliding characteristic of the surface of the grain oriented silicon steel sheet by decreasing the ratio of the coarse granular NgO in an annealing and separating agent essentially consisting of MgO to a specific ratio or below at the time of applying the annealing and separating agent on the surface of the silicon steel sheet. CONSTITUTION:The coarse grain components of the MgO in a slurry which do not pass a 200-mesh wire net or >=74mum grain size are regulated by weight to <=1.0% at the time of applying the slurry essentially consisting of the MgO as the annealing and separating agent on the surface of the steel sheet in order to form the insulating film of the grain oriented silicon steel sheet. The MgO in the annealing and separating agent reacts with the SiO2 on the steel sheet surface to form a forsterite film at the time of the finish annealing of the silicon steel sheet and the amt. of the coarse granular MgO to be formed in the forsterite insulating film is extremely little at this time and, therefore, the roughness of the silicon steel sheet surface is small and the grain oriented silicon steel having the forsterite insulating film which is uniform in the sliding characteristic is stably obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for producing a grain-oriented silicon steel sheet, and particularly to a method for forming a forsterite insulating film with uniform surface smoothness.

<Prior art> In connection with the formation of an insulating film on grain-oriented silicon steel sheets, gAst!, mainly containing MgO, is used. Many patents related to separating agents have been proposed, but all of them aim to improve magnetism, film uniformity, and adhesion, and none of them relate to slipperiness.

For example, in Japanese Patent Publication No. 52-31296, the particle size distribution of MgO is regulated, but the purpose of this is to obtain a uniform insulation coating and prevent the occurrence of uneven distortion in the steel plate, which is the aim of the present invention. They are different and do not overlap in particle size range.

By the way, it is often experienced that dimensional errors become large during processing of electromagnetic steel sheets, for example, when shearing them to a fixed length, or that the space factor decreases when stacked.

The inventor of the present invention found that the cause of this problem lies in the slipperiness of the coating surface.

<Problems to be Solved by the Invention> Therefore, the present invention aims to solve the problem of forming an insulation coating on a grain-oriented silicon steel sheet coated with MgO as a main component, which may lead to dimensional errors and a decrease in space factor during shearing at a fixed length. The purpose is to eliminate roughness.

<Means for Solving the Problems> The present invention provides a method for applying an annealing separator containing MgO as a main component to the surface of a grain-oriented silicon steel sheet in the form of a slurry for the purpose of forming an insulating film on the surface of the steel sheet. This is a method for forming an insulating film on a grain-oriented silicon steel sheet, characterized in that the unthreaded portion of the 200-mesh wire mesh or the coarse grain portion with a particle size of 74 pm or more is 1.0% or less by weight.

<Function> 1 of grain-oriented silicon steel sheets! ! Edge film formation is carried out with the following reaction.

510! +2 MgO→2 MgO・SIO.

sio is formed as an oxide layer on the surface of the steel sheet during decarburization annealing, and then reacts with hgO applied as an annealing separator during final annealing to form a forsterite film. Here, if coarse particles of MgO are included in this MgO, the coarse particles 11go will stick to the forsterite surface, increasing the roughness of the surface, and as a result, the frictional resistance of the surface will increase, making the electrical steel sheet The inventors of the present invention have found that problems such as large dimensional errors and a decrease in the space factor when stacked are caused during shearing to a fixed length in the processing stage.

Therefore, the inventor further precisely analyzed and investigated the deposits on the surface of the silicon steel plate, and found that the particle size was 880-150.
1I, the component of the deposit was MgO, and the deposit was found to be sintered on the forsterite film.

Incidentally, the annealing separator is applied in the form of a slurry and dried, but when we conducted an experiment to determine the relationship between the coarse particle ratio in the slurry immediately before application and the roughness of the surface after final annealing, we obtained the results shown in Figure 1. It became clear that as the ratio of coarse particles to dirt increased, the roughness also increased.

From these findings, the occurrence of surface roughness can be substantially tolerated by controlling the coarse particles of 74 μm or larger or those not passed through the 200-mesh wire mesh in the MgO slurry to a dry weight ratio of 1.0% or less. It was confirmed that the range could be reduced.

By the way, the average particle size of MgO for silicon is 1.0 to 1.5 μm.
Usually, only a small amount of coarse particles with a diameter of 80 μm or more is included, but the cause of the coarse particles is that particles poorly dispersed in water remain when MgO is made into a slurry. In other cases, solid matter deposited in the piping system that feeds the slurry to the coating device may fall off and become mixed in.

Therefore, as a means to reduce or remove these coarse particles, for the former cause, improve the stirring efficiency in the mixer. Regarding the latter, there are methods such as filtering with a sieve, but the present invention is not limited to these methods.
It is necessary to maintain the coarse particle content ratio in the O slurry within a specified range.

Naturally, 20 coarse particles ratio is originally preferably 0%, but 1.0
% is defined as an allowable upper limit for small roughness in industrial production.

Note that the roughness of 74 μm or more and the portion not passed through the 200-mesh wire mesh refer to substantially the same coarse particles.

<Example> A silicon steel plate containing 3.0% Si was decarburized and annealed in a wet hydrogen atmosphere, then coated with three types of MgO slurries shown in Table 1, wound into a coil shape, and made into a box shape. Finish annealing was performed in a furnace to form a forsterite film, and the roughness of the surface was evaluated.

The results are shown in Table 1.
For those with a large amount of unfiltered material, rough deposits were observed on the surface, and when the friction coefficient of the surface was investigated, a clear difference was observed.

<Effects of the Invention> According to the present invention, the smoothness of the silicon steel sheet surface becomes uniform,
It is now possible to prevent winding misalignment due to differences in slipperiness during the processing of silicon steel sheets and the expansion of dimensional errors during shearing to a fixed length. It was also possible to prevent deterioration of the space factor.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the coarse MgO ratio in the MgO slurry and the roughness occurrence rate.

Claims (1)

[Claims] When applying a slurry of an annealing separator mainly composed of MgO to the surface of a grain-oriented silicon steel sheet for the purpose of forming an insulating film, the annealing separator contains particles that do not pass through the 200-mesh wire mesh or particles with a particle size of 74 μm or more. The coarse particle content is 1.
A method for forming an insulating film on a grain-oriented silicon steel sheet, the method comprising: forming an insulating film on a grain-oriented silicon steel sheet.