JPS58120730A - Continuous annealing furnace for electric steel sheet - Google Patents

Abstract

PURPOSE:To enable a heat treatment of plural kinds, by applying a steel sheet supporting system using a hearth roll to the part in which the heat treatment conditions of annealing furnace are not different and applying the steel sheet supporting system using floating to the part in which such condition are different. CONSTITUTION:For instance, a grain-oriented electric continuous band steel 1 is charged to a heating zone 2 of hearth roll type for heating and soaked at a soaking zone 3 of hearth roll type. the steel strip is then heated at a heating zone 4 of floating type, soaked at a soaking zone 5 of floating type and entered to a jet type cooling zone 6 of floating type in which the temp. becomes below the predetermined temp., passed through a cooling zone 7 of hearth roll type and the annealing is finished. Thereby unlike the usual case of hearth roll type alone, the roll pick up phenomena at the heat cycles don't occur completely.

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 combination furnace support means of hearth roll type and floating type, and its purpose is to prevent the occurrence of indentations in steel sheets. At the same time, it is an object of the present invention to provide an annealing furnace that is easy to pass through 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. As this no-throttle roll, the one conventionally used is (IJ heat-resistant alloy (Ni-C
Metal rolls made of (alloy, etc.) used for water-cooled or non-water-cooled conveyance.

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

(3) Ceramic rolls used for conveyance, either singly or by spraying ceramic on 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 pink-up phenomenon (scale, etc. on the continuous steel strip surface adheres to the roll surface, and the continuous steel strip surface 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 surrounding gas in the furnace is either a reducing atmosphere (Hz - N2 atmosphere) or a weakly oxidizing atmosphere (Hz -N2 atmosphere).
-NZ -H20 atmosphere), but the heat treatment conditions must be changed so that the temperature is high and the furnace atmosphere is switched between a reducing atmosphere and a weakly oxidizing atmosphere. It is very difficult to suppress the roll pickup phenomenon.

For example, as a decarburization annealing method for electrical steel sheets, a method is generally known in which the annealing temperature is set at 750 to 850° C. in a slightly oxidizing atmosphere. (See Figure 3 for an example.) Also, as seen in Japanese Patent Publication No. 54-24686 ``Method for manufacturing unidirectional silicon steel plate (strip) with excellent magnetic properties'', the first half of the annealing furnace is 750 to 870' Decarburize in a slightly oxidizing atmosphere,
There is a manufacturing method in which the latter half is magnetically annealed in a reducing atmosphere at 890 to 1050°C.

(See Figure 4 for an example.) When these two annealing methods with different conditions are performed in different continuous annealing furnaces, the roll pick-up phenomenon is relatively slight because a dedicated (7) hearth roll method is used for each. 5Although it is unlikely to be a problem, the number of furnaces will increase because a dedicated furnace will be created. Therefore, when attempting to perform this in one continuous annealing furnace, the latter half of the annealing furnace becomes a portion that serves both as 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 Japanese Patent Publication No. 47-13165 "Roll for Heat Treatment Furnace"
In the part where the temperature is relatively low, such as 900'C or less in a weak oxidizing atmosphere, that is, in the first half when the above-mentioned 2s type annealing method is carried out in one continuous annealing furnace, the weak acid Because of the chemical atmosphere, the roll pickup phenomenon can be suppressed. However, since the latter part serves both as a weakly oxidizing atmosphere and a high-temperature reducing atmosphere, such a carbon roll suffers too much oxidative wear and tear, making it difficult to use it for a long period of 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 this part, and the heat treatment conditions are, for example, 70 - By adopting the scratching method, the product will not be damaged at all (,
Furthermore, it has been discovered that electrical steel sheets can be manufactured 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 entire annealing furnace is a floating type continuous annealing furnace, the total length is 10, for example, for electromagnetic steel sheets.

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 copper strip during conveyance through the furnace is also very poor (
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 is It can withstand the conventional hearth rolls, and only the second half is a floating system, so overall equipment costs and running costs are low.Also, since the first half is a hearth roll system, , more stable sheet threading performance than the floating method can be obtained, and the width of the furnace can be made smaller than when the entire structure is a floating method.

Note that when 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 hearth roll system and floating system. According to this, the continuous steel strip 1 enters the slow step type heating zone 2 from the left in the figure (71) and is heated.

Next, it is soaked in a hearth roll soaking zone 3. After that, there is a floating type 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. The plate temperature of continuous steel strip is
When the temperature in the cooling zone reaches a certain level or lower, it passes through the hearth roll type cooling zone 7 and the annealing is completed. 8 is a no-throttle roll for transportation in the furnace, 9 is a wind box for floating in the furnace,
10 is a radiant tube for heating, and 11 is an electric heater for uniform heating.

Further, a cross-sectional view of the floating heating zone is shown in FIG. 12 is a floating blower, and 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, Si23.12%, Mn:
0.09chi, C2 0.04%, P
: 0.01%, S: 0.00
7%.

A grain-oriented electrical steel sheet with the following composition: An: 0.22%, Fe: balance. The sheet threading conditions are sheet width 110051Il.
1, the plate thickness was 0.50 m, the fin speed was 60 m/-, and the material for the first half of the first half of the no-throttle type support device was a heat-resistant steel shaft fitted with a campon sleeve impregnated with chromium oxide. SiC ceramic was used as the blower blade material of the latter half floating type support device. Two types of processing conditions were used, as shown in FIG. 3 (cycle 1) and FIG. 4 (cycle 2). For electrical steel sheets manufactured by continuous annealing under these conditions, the roll pickup phenomenon occurred frequently in the heat cycle shown in Figure 4 (cycle 2) in the conventional case where all hearth rolls were used. According to the invention, the roll pickup phenomenon did not occur at all, and an electrical steel sheet with a very flat surface could be obtained.

As described above, according to the present invention, in a continuous annealing furnace for producing electrical steel sheets, by using a combination support system of hearth roll system and floating system,
It has become possible to economically produce electrical steel sheets without any Roll Big Amplification phenomenon (multiple types of heat treatment can be performed in one annealing furnace).

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 and FIG. 2 show an embodiment of the present invention, where FIG. 1 is an overall view and FIG. 2 is a sectional view taken along line AA in FIG. 1. FIGS. 3 and 4 show examples of two different processing conditions. 1. Continuous steel strip, 2..〕--roll type heating zone, 3-
・Hearth roll type soaking zone, 4Φ-floating type heating zone, 5...Floating type soaking zone, 6...Floating type cooling zone, 7-・No1-roll type cooling zone, 8@・
Hearth roll, 9m8 float box, 10...
Radiant tube for heating, 11... Electric heater for soaking, 12... Blower for floating 113... Motor for floating. Patent applicant Representative patent attorney Tomoyuki Yabuki (and 1 other person)

Claims (1)

[Claims] In a continuous annealing furnace that performs multiple types of heat treatment on electrical steel sheets,
A continuous annealing furnace for electrical steel sheets, characterized in that a steel plate support system using hearth rolls is used for parts of the annealing furnace where heat treatment conditions do not differ, and a steel plate support system using floating is used for parts that have different heat treatment conditions.