JP2006257486A - Method for annealing grain oriented electrical steel sheet, and inner cover for batch annealing of grain oriented electrical steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nethod for annealing a grain oriented electrical steel sheet by which the "ribbing" of a steel sheet caused during the finish annealing can be suppressed than heretofore, and to provide an inner cover for batch annealing of the grain oriented electrical steel sheet. <P>SOLUTION: In the grain oriented electrical steel sheet annealing method, the grain oriented electrical steel sheet wound in a coil is charged and placed in a batch-annealing furnace with the axis of the coil being in a vertical direction, and covered by an inner cover and heated. Radiation heat-transfer from a side wall of the inner cover toward an outer circumferential surface side of the coil is suppressed as much as possible by lining a heat insulating sheet on an inner wall surface of the inner cover so that the temperature distribution of the heated coil is uniform. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method of annealing a grain-oriented electrical steel sheet and an inner cover for batch annealing of grain-oriented electrical steel sheets. In particular, during final finish annealing of a grain-oriented electrical steel sheet, “longitudinal wrinkles” are generated in the steel sheet. It is a technology that suppresses and improves product yield.

  Generally, a grain-oriented electrical steel sheet is manufactured as follows. First, molten steel whose components are adjusted for the grain-oriented electrical steel sheet in the steelmaking process is melted. And this molten steel is cast with a continuous casting machine etc., and a steel slab is manufactured. The obtained steel slab is transferred to a rolling process, and once hot-rolled, the steel slab is subjected to one or two or more cold rolling sandwiching intermediate annealing and rolled to the final thickness. Next, the grain-oriented electrical steel sheet having the final plate thickness is decarburized and annealed, and further coated with an annealing separator on the surface, and then wound into a coil shape. The coil is continuously loaded and placed in a furnace 1 called a “batch annealing furnace” (also referred to as a box annealing furnace) as shown in FIG. A so-called “finish annealing” is performed by making the gas atmosphere and heating to a high temperature (for example, 900 to 1200 ° C.) to obtain a final product.

  In addition, as shown in FIG. 4, the batch annealing furnace 1 has a structure in which a gas burner 2 or an electric heat source is arranged on the upper portion and the coil 3 is heated by radiant heat transfer from above. It is called a cover (also referred to as an inner case) 4 and is covered with a cover composed of a side wall portion and a ceiling portion.

  By the way, the finish annealing using the batch annealing furnace 1 is heated by the radiant heat from the inner cover, so that the amount of heat input varies depending on the position of the coil 3 when the temperature is raised, and the temperature distribution (particularly in the height direction) is increased. There is a problem that it is not uniform. That is, the portion close to the inner cover is overheated, and defects such as “ear distortion (ear extension)”, “belly extension”, and “vertical wrinkle” occur in the product, thereby reducing the product yield. Here, “ear distortion” is the shape defect that can be formed at the lower edge of the coil during batch annealing, and “ear extension” is the shape defect that can be formed at the upper part of the coil during batch annealing. The shape defect in which the central portion in the width direction extends, “vertical wrinkle” refers to a shape defect that occurs on the coil outer winding side.

  Further, if the temperature distribution is slowly raised, the temperature difference can be reduced to some extent. However, recently, due to the necessity of increasing the production amount, there is a tendency to operate with a short heating time.

  Therefore, as a countermeasure, a technique of sticking a heat insulating material to a portion corresponding to the four corners of the annealing furnace in the outer peripheral surface of the inner cover is disclosed (see Patent Document 1). An annealing technique is also disclosed in which a rotary hearth type continuous annealing furnace is used instead of a box annealing furnace, and the inner cover is further covered with a heat insulating material cover (see Patent Document 2).

However, in the technique described in Patent Document 1, “ear extension” and “belly extension” are certainly suppressed, and in the technique described in Patent Document 2, “ear distortion (ear extension)” is suppressed. There was no mention and it was not actually a countermeasure.
Japanese Utility Model Publication No. 61-043260 JP 05-271790 A

  In view of such circumstances, an object of the present invention is to provide a method for annealing a grain-oriented electrical steel sheet that can suppress “longitudinal wrinkles” of a steel sheet that occurs during finish annealing, and an inner cover for batch annealing of a grain-oriented electrical steel sheet. It is said.

  The inventor has intensively studied to achieve the above object, and the results have been embodied in the present invention.

  That is, the present invention relates to a method for annealing a grain-oriented electrical steel sheet in which an electromagnetic steel strip wound in a coil shape is inserted and placed in a batch annealing furnace with the axis of the coil vertical, covered with an inner cover, and heated. The method of annealing a grain-oriented electrical steel sheet according to claim 1, wherein the inner cover has a side wall portion and a ceiling portion, and is annealed using an inner cover in contact with the inner wall side of the side wall portion and provided with a heat insulating material. It is.

  Further, the present invention is an inner cover that covers a coil of a directional electromagnetic steel strip placed in a batch annealing furnace with its axis vertical, wherein the inner cover has a side wall portion and a ceiling portion. An inner cover for a batch annealing furnace for grain-oriented electrical steel sheets, wherein a heat insulating material is installed in contact with the inner wall side of the side wall portion.

  According to the present invention, overheating on the coil end face side can be suppressed, and the temperature distribution in the coil can be reduced. As a result, shape defects near the outermost winding of the coil are suppressed.

  Hereinafter, the best embodiment of the present invention will be described based on the background of the invention.

First, the inventor examined the mechanism of occurrence of “longitudinal wrinkles” frequently occurring in the steel strip layer near the outermost winding of the coil. The mechanism was considered to be based on the fact that the following phenomena occur sequentially.
(1) Heat is input mainly from the outer peripheral surface of the coil. (2) The outermost wound steel sheet layer is overheated by heating from the side wall direction of the inner cover. (3) The outermost wound steel sheet layer expands. (4) The steel sheet layer near the outermost winding creeps due to its own weight and temperature difference, and so-called “vertical wrinkles” are generated that extend in the horizontal direction. In other words, in a conventional batch annealing furnace, An inner cover 4 is placed on the coil 3 and is annealed. Heating is performed by combustion in the gas burner 2 provided above the inner cover 4, and the coil 3 is heated by the radiant heat. When the heat insulating material 5 is wound around the outer peripheral surface of the inner cover 4, heat input to the coil 3 from the outside of the inner cover 4 can be suppressed to some extent. However, the radiant heat from above heats the upper part of the inner cover 4, and the heat is transferred to the side wall surface by heat conduction. As a result, heat is mainly input from the outer peripheral surface of the coil 3, the outermost winding is overheated, and the degree of reducing the temperature distribution in the radial direction in the coil 3 is not as great as expected (of the coil 3). The difference between the hot point and the cold point was Max: 550 ° C.).

  If “longitudinal wrinkles” are generated by such a mechanism, heating from the side wall direction of the inner cover 4, that is, radiant heat transfer, is possible in order to prevent overheating of the coil outer peripheral surface and reduce the temperature distribution in the coil 3. It is considered necessary to suppress this. That is, when the heat insulating material 5 is lined on the inner wall surface of the inner cover 4 (the inner wall side of the side wall portion), the heat input to the coil 3 is the same as (1) above, but the temperature of the side wall surface of the inner cover 4 is heat conduction. Even if it rises, there is no release of radiant heat, so overheating of the outer peripheral surface of the coil is suppressed.

  Therefore, as shown in FIG. 1, the inventor lining a ceramic fiber having a thickness of 25 mm as the heat insulating material 5 on the inner wall surface of the inner cover 4 to suppress radiant heat transfer from the side wall direction of the inner cover 4. Overheating of the outer peripheral surface was prevented, and the temperature distribution of the coil 3 was made uniform. As a result, the temperature distribution is such that the difference between the hot point and the cold point can be reduced to Max: 350 ° C. and the occurrence of “vertical wrinkles” can be suppressed. The invention was completed.

  In the present invention, the type and thickness of the heat insulating material 5 lining the inner wall surface of the inner cover 4 are not particularly limited. This is because any type and thickness of the heat insulating material 5 may have a heat insulating effect. However, since it is desirable that the heat insulation effect is larger, it is recommended to use a heat insulating material that can withstand an annealing temperature range such as ceramic fiber and a thickness of 15 to 40 mm. The reason why the thickness is 15 to 40 mm is that if the thickness is less than 15 mm, the heat insulating effect is too low, and if it exceeds 40 mm, the heat insulating effect is saturated and is economically meaningless.

  A large number of coils made of grain-oriented electrical steel sheets containing 3% by mass of Si, having a thickness of 0.3 mm, a width of 1160 mm, and a length of about 3000 m are sequentially formed using a batch annealing furnace 1 as shown in FIG. Finish annealed. At that time, an annealing method (invention example) according to the present invention in which the inner cover 4 has a thickness of 25 mm and a material: ceramic fiber heat insulating material 5 is lined over the entire inner wall surface, and an annealing method in which no heat insulating material is lined (comparative example, Two types (see FIG. 4) were implemented. In addition, the heating rate of the coil was also different in two levels. The result of annealing was evaluated by the length of “vertical wrinkles” generated in the electrical steel sheet, and the “longitudinal wrinkles” were measured by visually determining the presence or absence thereof. The annealing temperature is 1200 ° C., the atmosphere is hydrogen gas, and the annealing time is 10 hours.

  2 and 3, the coil annealing rate is (a) a temperature range of 500 ° C. to 1000 ° C. is 20 to 30 ° C./hr (referred to as a rapid heating pattern), and (b) a temperature range of 500 ° C. to 1000 ° C. is 10 to 10. The lengths of “longitudinal wrinkles” generated in the electrical steel sheet when the temperature is less than 20 ° C./hr (referred to as a slow heating pattern) are shown.

  From these figures, in the comparative example, the “length of vertical wrinkles” is an average value in the case of the rapid heating pattern: 126.7 m, in the case of the slow heating pattern: 78.7 m, It is clear that it is reduced to 56.3 m and 0 m.

It is a cross-sectional view explaining the annealing method of the grain-oriented electrical steel sheet which concerns on this invention. It is the figure which compared the length of the "longitudinal wrinkles" which arose in the magnetic steel sheet of this invention method and comparative method which implemented the temperature range of 500-1000 degreeC with the temperature increase rate of 20-30 degreeC / hr. It is the figure which compared the length of the "longitudinal wrinkles" which arose in the electrical steel sheet of this invention method and comparative method which implemented the temperature range of 500-1000 degreeC with the temperature increase rate of 10-20 degrees C / hr. It is. It is a cross-sectional view explaining the method of annealing the electromagnetic steel plate coil in the conventional batch annealing furnace. It is a cross-sectional view explaining the method to anneal the magnetic steel sheet coil in the conventional batch annealing furnace which stuck the heat insulating material to the outer peripheral surface of the inner cover.

Explanation of symbols

1 Batch annealing furnace 2 Gas burner 3 Magnetic steel sheet coil 4 Inner cover 5 Thermal insulation

Claims (2)

In the annealing method of the directional electrical steel sheet, in which the electrical steel sheet wound in a coil shape is placed and placed in a batch annealing furnace with the coil axis vertical, covered with an inner cover and heated,
An annealing method for grain-oriented electrical steel sheets, characterized in that annealing is performed using an inner cover having a side wall portion and a ceiling portion as the inner cover and having a heat insulating material in contact with the inner wall side of the side wall portion. In the batch annealing furnace, an inner cover that covers the coil of the directional electromagnetic steel strip placed with its axis vertical,
An inner cover for a batch annealing furnace for grain-oriented electrical steel sheets, wherein the inner cover has a side wall portion and a ceiling portion, and is provided with a heat insulating material in contact with the inner wall side of the side wall portion.

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