JPS5980733A - Sealing method of inner cover in finish annealing furnace for steel sheet coil - Google Patents

Abstract

PURPOSE:To prevent the deterioration of a steel sheet that may be resulted from the intrusion of air into an inner cover in a finish annealing furnace for a steel sheet coil by using spherical refractories having a small diameter for a sealant to be used in the rest part at the bottom end of the inner cover and providing a flange part at the bottom end of the inner cover. CONSTITUTION:Mullite spherical refractories 14 having <=1.2mm. grain size are used as a sealant to be packed in the rest part 1a at the bottom end of an inner cover 3 in a finish annealing furnace for a steel sheet coil C. A flange 3a is provided at the bottom end of the cover 3 or a seal protective plate 6 is provided on the sealant 14 in the outside position of the cover 3. Since the sealant 4 is spherical, the sealant can follow up easily the movement of the bottom end part of the cover 3 owing to the thermal expansion or shrinkage on cooling of said cover; at the same time, the flange 3a and the plate 6 prevent the intrusion of the air from the outside into the cover 3, thereby preventing the deterioration in the bending characteristic of the steel sheet coil by the effect of N2 in the air.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for sealing an inner cover in a finish annealing furnace for steel plate coils.

For example, in the production of grain-oriented electrical steel sheets, 0.
085% or less, silicon content of 4 or less, sulfur, aluminum, etc., 0607 elemental system to promote secondary recrystallization.
After annealing and cold rolling at least once, a hot-rolled steel sheet whose composition has been adjusted to contain the following: Wind it into a coil and perform final annealing.

This final annealing is performed for the purpose of secondary recrystallization of the steel sheet, formation of a surface film, and removal of impurities in the steel.
After heating (soaking at 1100C or more for 10 hours or more),
Cool to below 0C.

Finish annealing of a steel plate coil is carried out by placing the coil C to be annealed on a stand 2 on the coil holder on the hearth 1 in an annealing furnace, covering the coil C with an inner cover 3, and removing the inner The lower part of the cover 3 is inserted into the annular inner cover holder formed on the upper surface of the hearth 1 into the part 1a, and the inner cover holder is filled with a sealing material 4f such as sand into the part 1a.
Hydrogen is supplied into the inner cover 3 through an atmosphere gas supply pipe 5 provided to penetrate the coil receiver from the center of the hearth 1 to the center of the stand 2, and the inner cover 3 is heated from outside to perform annealing.

In this case, the atmospheric gas pressure inside the inner cover 3 is set to be slightly higher than the pressure outside the inner cover 3, and the air from outside the inner cover 3 is sealed by the sealing material 4 so that the air outside the inner cover 3 does not enter inside. Conventionally, since a long rectangular material such as sand is used as the sealing material, it has poor followability with respect to the movement of the inner cup (-3).

That is, the inner cover 3 is made of heat-resistant steel, and when heated to, for example, 1000 C, as shown in FIG.
The inner cover 3 expands by about 2 Or, in the radial direction.
When the seal depth on the inside of the lower part approaches Omm, and when cooling starts again, the inner cover 3 contracts in the radial direction as shown in Fig. 3, and the seal depth on the inside and outside of the lower part of the inner cover 3 both reaches Omrrt. A missing part of the seal occurs as the seal gets closer.

Therefore, air outside the inner cover 3 easily enters into the inner cover 3, and nitrogen enters into the gap of the coil C to be annealed, causing problems such as deterioration of the bending properties of the product.

The present invention has been made to solve the problems of the conventional inner cup (-) sealing means, and its gist is that the inner cover holder on the upper surface of the hearth has a part,
As a sealing material with the lower part of the inner cover, the particle size is 1m.
It is characterized by using a spherical refractory of x91 or less, and when the inner cover expands or contracts, the sealing material moves together with the inner cover, making it possible to maintain the seal of the inner cover completely.

Each embodiment of the present invention will be described below with reference to FIGS. 4, 5, and 6.

FIG. 4 shows a first embodiment group of the present invention, in which the annular inner cover holder on the upper surface of the hearth 1 is located at a portion 1a.
The lower part of the inner cover 3 is inserted into this inner cover receiver ila, and the inner cover receiver is made of mullite-based spherical refractories with a grain size of 1.2 mm in the inner cover receiver ila. When filled with the sealing material 14 (Example A A1), when filled with the spherical refractory sealing material 14 with a grain size of 1.0 (AA2), also with the spherical refractory with a grain size of 0.5zi and f2G This is the case when the sealing material 14 is filled (AA3).

Further, FIG. 5 shows a second embodiment group of the present invention, in which the inner cover receiver has a height of the portion 1a (seal height).
20 yrtttc, and this inner cover receiver has an inner cover 3 having a flange 3a whose lower end is bent outward at right angles for 20 degrees in part la, and the inner cover receiver has a mullite type material in part la. particle size 0.7mtn9
When filled with the spherical refractory sealing material 14 of No. 1 (Example A
BI), the inner cover receiver has a height of part 1a (seal height) of 50 mm, and this inner cover receiver has the same (This is the case where the spherical refractory sealing material 14 of 0.7+++i96 is filled (71LB2).

Further, Fig. 2g6 shows a third embodiment of the present invention, in which the inner cover receiver has a height of 50mm (seal height) in section 1a, and the inner cover receiver has the same height in section 1a. <20111+! The inner cover 3 having a flange 3a of In the conventional example shown in FIGS. 2 and 3, the height of the inner cover receiver 1a (seal height) is 150ii, and the sealing material 4 is sand. .

Therefore, each of the sealing means of the embodiments of the present invention and the conventional example has a plate thickness of 0.30+;+m- and a plate width of 1000a+.
i, using a grain-oriented electromagnetic steel coil to be finish annealed with an outer diameter of 1400 mu and an inner diameter of 500 u, using hydrogen (flow rate 2 ''/h) as the atmospheric gas in the inner cover,
The atmosphere outside the inner cover was air, and after heating for 70 hours and holding at 1200C as an annealing cycle,
Compare the changes in the inner cover internal pressure (relative pressure imHzO to the inner cover external pressure) during temperature rise and cooling when cooling over 70 hours, and the frequency at which product bending characteristics deteriorate due to intruding nitrogen. investigated.

The comparative survey results are shown in Table 1 below.

Table 1 As can be seen from Table 1 above, in the conventional sealing means, since angular sand is used as the sealing material as described above, the sealing material can easily follow the expansion and contraction of the inner cover. This results in poor sealing, which makes it difficult for air to enter the inner cover, and the bending characteristics of the product deteriorate by as much as 30% due to nitrogen.

In contrast, Example AA in the sealing means of the present invention
In I, the frequency of deterioration of the bending properties of fine products is 20, and in A2, it is 1.
0%, 5ch for A3, and 0% for B1-C.

Here, A1. The reason why the bending property deterioration frequency of the product in A2 is 20% and 10ch, respectively, is as follows.
Even if spherical refractories are used as sealing materials, their particle sizes are relatively large (fl, 2, p, t, o, 2), so there are many gaps between the sealing materials and the sealing performance is poor. This is not so good because the atmosphere outside the inner cover partially enters), and the particle size of the sealing material is set to 0.5 as shown in Aa. By setting @, g, it is possible to minimize the intrusion of the atmosphere outside the inner cover, and the frequency of deterioration of the bending characteristics of the product can be suppressed to 5%.

In addition, for B1 to C, the frequency of product bending property deterioration was 0%.
However, this means that the particle size of the sealing material is 0.7mx
This is because the length of the sealing portion, which has a small surface, is increased and the sealing effect is further improved by forming the flange at the lower end of the inner cover.

However, in this case, if the height of the soft seal is increased, the flange of the inner cover will rest on the sealing material,
The seal height should be 10 to 50 mm as the sealing effect will be smaller.
Dish level is most desirable.

In addition, the particle size of the sealing material must be 1 mtny5 or less in order to maintain a good internal pressure of the inner cover, but if the particles are too small, it will be difficult for water vapor generated by condensation inside the inner cover to escape. Therefore, it is desirable that Oelmm, l' or more is 0. Furthermore, in C, since a seal protection plate is placed on the top surface of the sealing material, it is possible to prevent scale from entering the sealing material, and therefore the sealing material is In other examples, the lifespan until it turns into a ball is 1 month, but it can be extended to 6 months.

Furthermore, in each embodiment of the present invention, as a sealing material,
Although mullite-based spherical refractories were used, alumina-based or silica-based spherical refractories may also be used.

As described above, according to the present invention, the seal between the inner cover holder on the upper surface of the hearth and the lower part of the inner cover can be
Since the inner cover can always be maintained in good condition even when it expands and contracts, it can greatly contribute to improving the quality of finished annealed product steel sheet coils.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a conventional example of sealing means for an inner cover in a finish annealing furnace for steel plate coils, FIG. 2 is an explanatory diagram showing the behavior of the sealing material when the inner cover expands in the conventional sealing means, and FIG. This figure is also an explanatory diagram showing the behavior of the sealing material when the inner cover is contracted, and FIGS. 4 to 6 are schematic diagrams of essential parts showing each embodiment of the sealing means of the present invention. Applicant Kawasaki Steel Corporation Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] A method for sealing an inner cover in a finishing annealing furnace for steel plate coils, characterized in that a spherical refractory with a grain size of 1 mm96 or less is used as a sealing material between the inner cover receiver on the upper surface of the hearth and the lower part of the inner cover.