JP6024922B2 - Coil cooling method after finish annealing - Google Patents

Description

  The present invention relates to a method for cooling a coil after finish annealing, and specifically relates to a cooling method after finish annealing a grain-oriented electrical steel sheet in a batch-type annealing furnace.

  The grain-oriented electrical steel sheet is a soft magnetic material having excellent magnetic properties, which is composed of crystal grains containing Si at 7 mass% or less and having a crystal orientation highly accumulated in the {110} <001> orientation. Control of the crystal orientation in such a grain-oriented electrical steel sheet is generally performed by utilizing a high-temperature grain growth phenomenon called secondary recrystallization. Since this secondary recrystallization requires heat treatment for a long time at a high temperature, it is currently manifested in finish annealing using a batch annealing furnace (box annealing furnace).

Finish annealing using the batch-type annealing furnace is performed by placing a steel sheet (steel strip) wound in a coil shape on a hearth (base) so that the axis of the coil is in the vertical direction (up-end), A container called an inner cover is placed thereon, the atmosphere inside is controlled by N ₂ gas, H ₂ gas, etc., and a furnace body is placed on the inner cover, and heated from the outside of the inner cover. It is done by doing.

  In order to develop secondary recrystallization by the above finish annealing, it is necessary to heat and hold at a temperature of 800 ° C. or higher. In addition, in order to improve the magnetic characteristics, after the secondary recrystallization is caused, the mixture is further heated to a temperature of about 1100 to 1200 ° C. and maintained for several hours to remove the inhibitor component and the like. . In order to send the coil after the finish annealing to the next step, it is necessary to cool to a temperature of about 100 to 200 ° C. However, the time required for the cooling is the longest of the finish annealing times, and is one of the factors that hinder productivity.

  Therefore, in order to shorten the cooling time, a method for forcibly cooling the coil after the finish annealing has been proposed. For example, in Patent Document 1, when winding a steel sheet in a coil shape, a corrugated insertion plate is provided between the steel sheet layers to provide a space, and the atmosphere gas during annealing or air during cooling (cooling medium) is passed. The technology for shortening the annealing time for heating and cooling is disclosed in Patent Document 2, in which the coil after the finish annealing is cooled with a winding machine having a diameter smaller than the inner diameter of the coil, creating a space between the coil layers. The technique of cooling by blowing a cooling medium from the coil side surface to the space is disclosed in Patent Document 3 in the cooling zone of a batch type annealing furnace having a heating zone and a cooling zone, and having a water supply / drainage means, and on the coil side surface. A heat treatment furnace provided with a cooling facility composed of a water-cooled box capable of contact and separation is disclosed in Patent Document 4, in which a thin plate is placed on a coil support base installed in a gas flow path formed in the furnace. Wound roughly with a gap Yl placed towards the axis in the vertical direction, the coil heat treatment furnace or to cool or heat the coil by the atmosphere gas ejected from the plurality of gas injection nozzles formed in the coil supporting stand is disclosed.

JP 57-116731 A JP 2003-328038 A Japanese Examined Patent Publication No. 62-056211 Japanese Patent Publication No. 07-000814

  However, the technique disclosed in Patent Document 1 has a problem that it is difficult to wind a coil-shaped insertion plate between coil layers and wind it around the coil, and the insert causes wrinkles on the steel plate. In addition, the technique disclosed in Patent Document 2 requires a coil to be rewinded after annealing in order to create a space between the layers of the coil and to spray a cooling medium from the side of the coil into the space. There is a problem of causing poor shape and appearance. In addition, the techniques disclosed in Patent Documents 3 and 4 require equipment for increasing the efficiency of cooling in the annealing furnace, increasing equipment costs and maintenance costs, and are problematic in terms of manufacturing costs.

  The present invention has been made in view of the above-described problems of the prior art, and the purpose thereof is to provide a space between the layers of the coil, and does not require special processing such as rewinding the coil, and Another object of the present invention is to propose a method for cooling a coil after finish annealing that can efficiently cool the coil without making a large capital investment.

  Inventors repeated earnest examination in order to solve the said subject. As a result, the grain-oriented electrical steel sheet after finish annealing has a glassy film made of forsterite formed on the steel sheet surface, so the inner cover is removed at a temperature of about 500 to 600 ° C., which is higher than that of a general cold-rolled steel sheet. Since it is taken out from the finish annealing furnace, it has been conceived that if the chimney effect due to the residual heat is utilized, the coil can be efficiently cooled while being placed on the up end, and the present invention has been developed.

That is, the present invention is a material steel sheet coil for grain-oriented electrical steel sheets in which a forsterite film is formed on the steel sheet surface after finishing the inner annealing in a batch-type annealing furnace, removing the inner cover, and taking it out of the furnace. The coil of 300 ° C. or higher taken out of the furnace is placed on the up end on a spacer having an opening in the center and spaced apart from the floor, and is cooled. It is the cooling method of the coil after finish annealing characterized by this.

  The coil cooling method after finish annealing according to the present invention is characterized in that the distance between the spacer and the floor surface is 50 mm or more.

  Further, the spacer used in the method for cooling a coil after finish annealing according to the present invention is characterized in that a gap is provided in a contact portion with the coil.

  Further, the spacer used in the method for cooling a coil after finish annealing according to the present invention is characterized in that the void ratio of the void portion provided in the contact portion with the coil is 10% or more.

  Moreover, the said coil in the cooling method of the coil after finish annealing of this invention is a raw material steel plate for grain-oriented electrical steel sheets, It is characterized by the above-mentioned.

  According to the present invention, the coil after finish annealing can be efficiently cooled without any special treatment or capital investment, which contributes to improvement of productivity and reduction of manufacturing cost. Furthermore, according to the cooling method of the present invention, the compressive stress in the inner diameter portion of the coil during cooling is relaxed, and the temperature distribution in the coil is homogenized, thereby reducing the shape defect after finish annealing. As a result, it can contribute to yield improvement and product quality improvement.

It is a figure which illustrates typically the cooling method of the coil of this invention. It is the graph which showed the effect which the separation distance of a spacer and a floor surface has on cooling. It is a figure which illustrates the spacer used for this invention typically. It is a figure which illustrates typically the example of another spacer used for this invention.

  As described above, in finish annealing of grain-oriented electrical steel sheets using a batch annealing furnace, the coil core is placed on the hearth (base) so that it is in the vertical direction (up-end), and on that An inner cover is put on, and a furnace body is put on the inner cover and heated. Further, at the time of cooling, the furnace body is removed, and after cooling to a predetermined temperature while covering the inner cover, the inner cover is removed, taken out of the furnace, placed on the coil yard or the like as an up-end, and 100 It is cooled to a temperature of about ~ 200 ° C.

  In the case of a grain-oriented electrical steel sheet, the inner cover is removed at a temperature of 500 to 600 ° C. higher than that of a general cold-rolled steel sheet because a forsterite film is formed on the surface of the steel sheet. However, it takes a long time of 20 to 50 hours to place the coil after finish annealing on a coil yard or the like and cool it to a temperature of about 100 to 200 ° C., which is a factor that hinders productivity. It has become one.

  Therefore, as shown in FIG. 1, the present invention provides a coil mounting table with a gap between the floor surface and a coil after finishing annealing on the coil mounting table. The high-temperature residual heat of the coil causes an air flow (upward airflow) in the inner diameter portion of the coil and promotes cooling of the coil by a so-called “chimney effect (draft force)”.

  Therefore, in order to utilize the above-described chimney effect, it is desirable that the temperature of the coil taken out from the annealing furnace is high. In the present invention, the coil temperature (the temperature of the coil side surface in contact with the base of the annealing furnace) is 300 ° C. or higher. And Preferably it is 350 degreeC or more. However, the cooling promotion effect by the chimney effect can be obtained even at 300 ° C. or lower. The upper limit of the coil temperature is not particularly limited, but is preferably 650 ° C. or lower so as not to adversely affect the magnetic properties and quality when exposed to the atmosphere.

  Here, in the coil mount shown in FIG. 1, the H-shaped steel 3 is radially arranged on the floor surface 2 with the flange portion being vertical, and the coil 1 which is made up-end is placed thereon. For this purpose, a disc-like spacer 4 having an opening 5 at the center is laid, and the above-described ascending airflow flows through the opening 5. Note that the coil mount of FIG. 1 is one example, and any other coil mount can be used as long as a gap through which air flows can be provided between the coil mounted on the up-end and the floor surface. It's okay.

Here, the separation distance between the spacer of the coil mount and the floor surface, that is, the gap through which air flows is preferably 50 mm or more. FIG. 2 shows the effect of the size of the gap on the heat transfer coefficient ratio as a reference (1.00) when there is no gap. Here, the heat transfer coefficient is measured by measuring the temperature change when the coil is cooled from 400 ° C. to 150 ° C. when the separation distance between the spacer of the coil mount and the floor surface is changed from 0 mm to 300 mm. And the result of the following formula:
T (t) = T _a + (T ₀ + T (t)) exp (−αAt / C _p M)
Here, T _a : Air temperature (K)
T ₀ : Initial coil temperature (K)
T (t): Coil temperature (K)
A, A ': Coil surface area
α: Heat transfer coefficient (W / m ² · K)
C _p : Specific heat (J / kg · K)
M: Mass (kg)
The value of α when expressed as A in the above formula is the coil surface area (the sum of the area of the coil upper surface and the area of the outer peripheral surface) when the separation distance is 0 mm, and when the separation distance exceeds 0 mm, An area A ′ obtained by adding the area of the inner peripheral surface to the surface area A is used.
From FIG. 2, it can be seen that the cooling capacity can be increased to 1.3 times or more by providing a gap of 50 mm or more between the spacer of the coil mount and the floor surface. However, even if the height exceeds 200 mm, the above effect is saturated, so 200 mm or more is sufficient.

  Further, the spacer laid on the coil mounting base preferably has a size and strength capable of mounting a coil of up to about 30 tons and is excellent in thermal conductivity. Or it is preferable that it is a thing made from cast iron. For example, any spacer using a thick steel plate defined in JIS G3101 “Rolled steel for general structure” can be preferably used.

  Further, as shown in FIG. 3, the spacer 4 of the present invention needs to have an opening 5 through which a rising air current flowing through the inner diameter of the coil passes. The shape and size of the opening are not particularly limited as long as the cooling medium air can flow smoothly and uniformly, but the shape is circular for ease of manufacture and subsequent maintenance. The thickness (inner diameter) is preferably 80% or more of the inner diameter of the coil and not more than the inner diameter of the coil. If it is less than 80%, the air flow becomes insufficient. On the other hand, if it is larger than the inner diameter of the coil, the inner diameter of the coil may hang down into the opening due to contraction during cooling.

  Further, in order to enhance the heat dissipation from the coil to the atmosphere, the spacer is preferably provided with a gap in the portion that contacts the side surface of the coil. For example, as shown in FIG. It may be formed radially or may be formed by dispersing circular gaps 7 as shown in FIG. 4B, and the shape and distribution of the gaps are not particularly limited. However, in order to express the effect of increasing the heat dissipation, the area ratio (void ratio) of the gap is preferably 10% or more. The upper limit is not particularly limited as long as the strength of the spacer can be secured.

  In addition, when the coil after finish annealing is cooled using the above coil stand, in addition to the improvement effect of the cooling efficiency that significantly shortens the cooling time, the shape of the steel plate after finish annealing is further improved, The effect of reducing the defect rate to about 1/3 or less is obtained. The mechanism that can achieve such an effect has not yet been fully clarified. However, when cooling with a coil mount, cooling from the inner circumference side of the coil is promoted, so the residual stress in the inner diameter part of the coil is reduced. It is thought that this is because the temperature distribution in the coil during cooling is made uniform or it is made uniform.

A raw steel plate for a grain-oriented electrical steel sheet is wound around a coil having an inner diameter of 508 mm, subjected to secondary recrystallization annealing using a batch-type annealing furnace, and further purified and annealed at a temperature of 1200 ° C. or 1150 ° C., and then cooled. Finish annealing was performed. The secondary recrystallization annealing and the purification annealing of the finish annealing were performed by placing the coil on the up end on the base of the annealing furnace, covering the inner cover, and further covering the furnace body and heating it. On the other hand, cooling was performed by removing the furnace body and allowing to cool, and cooling until the coil side surface temperature in contact with the base of the annealing furnace reached a temperature of 550 ° C. or 580 ° C., and then removing the inner cover and taking it out of the furnace. The atmosphere in the inner cover was N ₂ gas during heating and cooling, and H ₂ gas atmosphere during secondary recrystallization annealing and purification annealing.

The coil taken out of the furnace was cooled under the following four conditions A to D, and the cooling time until the coil temperature decreased to 200 ° C. or lower was measured for each coil by 10 coils. The coil temperature was measured at the center of the winding thickness on the upper side surface of the coil placed at the up end as shown in FIG.
Condition A: H-shaped steel with a flange height of 200 mm is arranged radially with the flange portion being vertical, and an opening with a diameter of 450 mmφ is formed on the center as shown in FIG. As shown in FIG. 1, the above-described coil of 550 ° C., which is provided with a coil mounting base provided with a disk-shaped steel spacer (material: SS400, thickness: 25 mm) and taken out of the furnace, is made of the above steel. Place on the up end on the spacer to cool.
Condition B: H-shaped steel with a flange height of 250 mm is arranged radially with the flange portion being vertical, and an opening of 430 mmφ is formed on the center as shown in FIG. And a coil pedestal provided with a disk-shaped steel spacer (material: SS400, thickness: 20 mm) in which a large number of slits are formed radially (15% porosity), and is taken out of the furnace described above As shown in FIG. 1, the 580 ° C. coil was placed on the steel spacer on the up end and cooled.
Condition C: After cooling to 550 ° C., the coil taken out of the furnace was placed on the floor of a coil yard where a thick steel plate (thickness: 20 mm) was laid and cooled.
Condition D: After cooling to 580 ° C. as described above, the coil taken out of the furnace was placed on the floor of a coil yard where a thick steel plate (thickness: 20 mm) was laid and cooled.

  The coil cooled to 200 ° C. or less as described above was then subjected to flattening annealing, and the length of the defective shape portion generated in the coil was measured at that time to determine the occurrence rate of the defective shape.

  The results of the above measurements are shown in Table 1 together with the cooling conditions, the coil temperature after cooling for 10 hours, and the cooling time to 200 ° C. or lower. From Table 1, it can be seen that the cooling time for the coil cooled on the coil mount is significantly shortened compared to the case without the coil mount, and the rate of occurrence of coil shape defects is reduced to about 1/3 or less. Recognize. In particular, the above effect is significant when a spacer having a slit is used.

  The technology of the present invention is not limited to the method of cooling a coil after finish annealing of grain-oriented electrical steel sheets, but can be applied to cooling of coils after annealing of other steel sheets and metal plates such as general cold-rolled steel sheets. it can.

1: Coil 2: Floor surface 3: H-shaped steel 4: Spacer 5: Opening 6: Slit-shaped gap 7: Circular gap

Claims (5)

This is a method of cooling a steel plate coil for grain-oriented electrical steel sheets with a forsterite film formed on the steel sheet surface after finishing the inner annealing in a batch-type annealing furnace and then removing the inner cover and taking it out of the furnace. ,
Finish annealing, characterized in that a coil of 300 ° C. or more taken out of the furnace is cooled by being placed on the up end on a spacer that has an opening in the center and is spaced apart from the floor surface. Cooling method for the rear coil. The method for cooling a coil after finish annealing according to claim 1, wherein the distance between the spacer and the floor surface is 50 mm or more. The method for cooling a coil after finish annealing according to claim 1 or 2, wherein the spacer is provided with a gap in a contact portion with the coil. The method for cooling a coil after finish annealing according to claim 1, wherein the spacer has a void ratio of 10% or more in a gap provided in a contact portion with the coil. The method for cooling a coil after finish annealing according to any one of claims 1 to 4 , wherein the finish annealing is annealing that causes secondary recrystallization in the grain-oriented electrical steel sheet.

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