JPH0323609B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous annealing furnace for producing electrical steel sheets, which is equipped with a hearth roll type and floating type combination furnace support means, and its purpose is to prevent the occurrence of indentations in steel sheets. It is an object of the present invention to provide an annealing furnace which prevents the above problems, allows easy sheet threading, and is economical.

Generally, in continuous annealing furnaces in which decarburization, magnetism, and strain relief annealing are performed on electrical steel sheets, either singly or in combination, a hearth roll method is adopted as a method for supporting the continuous steel strip in the furnace. Conventionally used hearth rolls include: (1) Metal rolls made of heat-resistant alloys (Ni-Cr alloy, etc.) that are water-cooled or non-water-cooled and used for conveyance.

(2) A carbon roll used for conveying graphite or graphite fibers in the form of a sleeve.

(3) Ceramic rolls that are used for transportation either by themselves or by spraying ceramic onto the surface of a heat-resistant alloy.

etc. have been devised and used.

However, not all furnace rolls satisfy all desired characteristics. In other words, with water-cooled metal rolls, the roll surface temperature can be kept low, so even in areas where the heat treatment conditions are not different at high temperatures, the roll pick-up phenomenon (scale, etc. on the surface of the continuous steel strip adheres to the surface of the continuous steel strip, However, since it is water-cooled, the heat loss is extremely large.

In addition, in a certain low temperature range for non-water cooled rolls, carbon rolls, and ceramic rolls, the furnace atmosphere gas is either a reducing atmosphere (H ₂ −N ₂ atmosphere) or a weakly oxidizing atmosphere (H ₂ −N ₂ −H ₂ O atmosphere), but the heat treatment conditions can change significantly, such as at high temperatures and by switching the furnace atmosphere between a reducing atmosphere and a weakly oxidizing atmosphere. However, it is extremely difficult to suppress the roll pickup phenomenon.

For example, as a decarburization annealing method for electrical steel sheets,
Generally, it is known that the annealing temperature is 750 to 850°C in a weakly oxidizing atmosphere. (See Figure 3 for an example).Also, as seen in Japanese Patent Publication No. 54-24686 ``Method for manufacturing unidirectional silicon steel sheets (strips) with excellent magnetic properties,'' the first half of the annealing furnace is One manufacturing method involves decarburizing in a reducing atmosphere, followed by magnetic annealing in a reducing atmosphere at 890-1050°C. (See Figure 4 for an example.) When these two annealing methods with different conditions are performed in different continuous annealing furnaces, each uses a dedicated hearth roll, so the roll pick-up phenomenon is relatively minor and does not become a problem. Although this is unlikely to happen, the number of furnaces will increase due to the creation of dedicated furnaces. Therefore, the latter half of the reannealing furnace in which this process is carried out in one continuous annealing furnace serves as both a weakly oxidizing atmosphere and a reducing atmosphere. Let us consider a case where, for example, a carbon roll is used when a hearth roll system is used as a means for supporting a continuous steel strip in an annealing furnace having different temperatures and heat treatment conditions.

A carbon sleeve impregnated with chromium oxide as shown in Special Publication No. 47-13165 "Roll for Heat Treatment Furnace" is suitable for use in areas with relatively low temperatures such as 900℃ or less in a weakly oxidizing atmosphere, i.e., as mentioned above. In the first half when two types of annealing methods are performed in one continuous annealing furnace, the roll pickup phenomenon can be suppressed because both are in a weakly oxidizing atmosphere. However, since the latter part is a part that serves both a weakly oxidizing atmosphere and a high-temperature reducing atmosphere, such carbon rolls suffer from excessive oxidative wear and tear.
It is difficult to use it for a long time.

The present invention provides a means for supporting a continuous steel strip in a continuous annealing furnace for producing electrical steel sheets. The conventional hearth roll method is used for the parts where the heat treatment conditions are, for example, a weakly oxidizing and reducing atmosphere, and where the furnace temperature is relatively high, a floating method is used. By adopting this method, we have discovered that electrical steel sheets can be manufactured without any defects on the product and under stable threading conditions.

The advantages of having such a combination support means of floating type and hearth roll type are as follows.

First, if the whole is made into a floating type continuous annealing furnace, for example, if the total length is 100
In the case of a model furnace with a length of ~200 m, from an economic point of view, there are huge equipment costs and running costs such as blower power costs. In addition, the stable threadability of the steel strip during conveyance through the furnace becomes very poor, and therefore the furnace width must be made very wide.

On the other hand, for example, when the first half of a continuous annealing furnace is used as a hearth roll method in a weakly oxidizing atmosphere, and the second half is used as a floating method for both weakly oxidizing and reducing purposes, the first half , it can withstand the hearth rolls that have been used conventionally, and only the second half uses a floating method, so overall equipment costs and running costs can be reduced. Furthermore, since the first half is of the hearth roll type, more stable sheet threading performance can be obtained than that of the floating type, and the furnace width can be made smaller than if the whole was of the floating type.

Note that if the temperature of the part where the floating method is adopted is a high temperature of, for example, 900° C. or higher, it is preferable to use a material that can withstand high temperatures, such as ceramic, as the material of the blower that circulates the floating atmospheric gas.

Embodiments of the present invention will be specifically described below with reference to the drawings.

Figure 1 shows the furnace configuration and equipment of a continuous annealing furnace that employs a combination support system of a hearth roll system and a floating system. According to this,
The continuous steel strip 1 enters the hearth roll type heating zone 2 from the left in the figure and is heated. Next, it is soaked in a hearth roll soaking zone 3. After that, there is a floating heating zone 4, where the sheet is further heated depending on the type of steel being passed. Then, it is heated in a floating soaking zone 5 and enters a floating jet cooling zone 6. When the temperature of the continuous steel strip falls below a certain temperature in the cooling zone, it passes through the cooling zone 7 of the hearth roll method,
Annealing is completed. 8 is a hearth roll being transported in the furnace, 9 is a wind box for flotation in the furnace, 10 is a radiant tube for heating, and 11 is an electric heater for soaking. In addition, the sectional view of the floating heating zone is shown in the second figure.
Shown in the figure. 12 is a floating blower,
13 is a blower motor.

Next, a specific example of operation will be explained below.

As the steel type through which the plate was passed, Si: 3.12%, Mn: 0.09
%, C: 0.04%, P: 0.01%, S: 0.007%, Al:
A grain-oriented electrical steel sheet with a composition of 0.22% Fe and the balance was used. The sheet threading conditions were a sheet width of 1005 mm, a sheet thickness of 0.50 mm, and a line speed of 60 m/min. The hearth roll material for the support device of the first half hearth roll method was a heat-resistant steel shaft fitted with a Cambon sleeve impregnated with chromium oxide. SiC ceramic was used as the blower blade material for the latter half floating type support device. The processing conditions are
Two types were used, as shown in FIG. 3 (cycle 1) and FIG. 4 (cycle 2). In the case of conventional electrical steel sheets manufactured by continuous annealing under these conditions, all of which were made using the hearth roll method, the roll pick-up phenomenon occurred frequently during the heat cycle shown in Figure 4 (cycle 2). According to the present invention, it was possible to obtain an electrical steel sheet with an extremely flat surface without any roll pickup phenomenon occurring.

As described above, according to the present invention, by using a combination support system of a hearth roll system and a floating system in a continuous annealing furnace for manufacturing electrical steel sheets, one It has become possible to perform multiple types of heat treatment in an annealing furnace, making it possible to economically manufacture electrical steel sheets.

[Brief explanation of drawings]

1 and 2 show embodiments of the present invention;
The figure is an overall view, and FIG. 2 is a sectional view taken along the line AA in FIG. 1. FIGS. 3 and 4 show examples of two different processing conditions. 1... Continuous steel strip, 2... Hearth roll type heating zone, 3... Hearth roll type soaking zone, 4... Floating type heating zone, 5... Floating type soaking zone, 6... Floating type cooling zone Band, 7... Hearth roll type cooling zone, 8... Hearth roll, 9...
Floating wind box, 10...Radiant tube for heating, 11...Electric heater for soaking, 12
...Floating blower, 13...Floating motor.

Claims (1)

[Claims] 1 Heat treatment of electrical steel sheet in a slightly oxidizing atmosphere,
In a continuous annealing furnace for electrical steel sheets, in which two types of heat treatment, the first half using a weak oxidizing atmosphere and the second half using a reducing atmosphere, are performed in the same furnace, a furnace that has a common weak oxidizing atmosphere between the above two types of heat treatment. The first half of the furnace is equipped with a steel plate support system using hearth rolls, and the second half of the furnace, which switches between a weakly oxidizing atmosphere and a reducing atmosphere, is equipped with a floating steel plate support system. Continuous annealing furnace for steel plates.