JP3114572B2 - Method for controlling alloying of galvannealed steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling alloying of a galvannealed steel sheet, and more particularly to a method for controlling alloying in which proper alloying is uniformly performed on the entire surface of the sheet.

[0002]

2. Description of the Related Art As a method for controlling the alloying of a galvannealed steel sheet of this type, there is a technique disclosed in Japanese Patent Application Laid-Open Nos. 1-177351 and 2-200762.

[0003] In the technique disclosed in Japanese Patent Application Laid-Open No. 1-177351, a high-frequency induction heating furnace is used for alloying heating in the alloying treatment of a galvanized steel sheet, and the degree of alloying of the plated layer after the alloying treatment is determined. The on-line alloying meter is used to measure continuously, the deviation between the measured value and the reference value set in the calculator is determined, and the power supplied to the induction heating furnace is controlled according to the deviation.

[0004] The technique described in Japanese Patent Application Laid-Open No. 2-200762 is based on a technique of detecting the width of a steel plate in a heating furnace (alloying furnace) in which a plurality of cup burners are arranged in the width direction, and according to the width of the steel plate. In addition to shutting off the fuel of the burners arranged outside the width of the plate, the supply of combustion air is reduced and a very small flow is allowed to flow.

[0005]

In the manufacturing process of an alloyed hot-dip galvanized steel sheet, the steel sheet rises from a hot-dip galvanizing bath, and reaches a top roll through processes such as gas wiping, alloying treatment, heat retention, and cooling. Because the distance to is long, the steel sheet warps. Therefore, even if the method disclosed in Japanese Patent Application Laid-Open No. 1-177351 is implemented, there is a problem that unevenness in the amount of adhesion occurs due to warpage of the steel sheet.

The method described in JP-A-2-200762 cannot solve the problem that the amount of adhesion in the width direction becomes uneven due to the warpage of the steel sheet.

The present invention has been made to solve the above problems, and provides an alloying control method capable of performing a uniform alloying process even if a galvanized steel sheet warps in the width direction. The purpose is to:

[0008]

According to the present invention, when a hot-dip galvanized steel sheet of which the adhesion amount is adjusted is heated and alloyed, a heating means divided into n blocks in the width direction of the steel sheet is provided. In accordance with the amount of warpage in the width direction of the hot-dip galvanized steel sheet detected by a warpage amount measurement sensor provided on the upper part of the gas wiping nozzle, the output control of the heating means is performed for each block, front and back, and the alloy. This is a method for controlling alloying of a galvannealed steel sheet.

The heating means divided into n blocks is feed-forward controlled in accordance with the amount of warpage measured by the warpage amount measuring sensor. Therefore, even if the hot-dip galvanized steel sheet is warped, it is alloyed in the width direction. The degree is kept uniform.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

FIG. 1 is a schematic view showing a manufacturing process of an alloyed hot-dip galvanized steel sheet embodying the present invention, and FIG. 2 is a cross-sectional view of the heating furnace shown in FIG.

In FIGS. 1 and 2, reference numeral 5 denotes a heating furnace provided with six blocks 5a to 5f corresponding to the sheet width direction on the surface of the steel sheet and six blocks 5g to 5l corresponding to the sheet width direction on the back surface of the steel sheet. The region is divided, one or more cup burners are provided in each block, and a flow control valve is provided for each block, and the block is connected to a fuel supply pipe.

The flow control valves 6a to 6f and 6 for each block
g to 61 are connected to the control device 7 so that the combustion of the cup burners in each block can be controlled.

On the other hand, a warp measuring sensor 9 is provided above the gas wiping nozzle 4 so that measured values obtained from the warp measuring sensor 9 are continuously input to the controller 7.

Further, the controller 7 is supplied with alloying degree data, adhesion amount data and other data as data necessary for the alloying treatment of the galvanized steel sheet.

In the above manufacturing process, the plate size is 0.6 × 1
A 219 mm heat-treated steel sheet 1 is introduced into a molten zinc bath 2 via a snout 10 and plated. After the steel sheet 1 is turned over by the sink roll 3 in the molten zinc bath 2, the target coating amount (one-sided zinc coating amount 60 g) is
/ M ² ) and alloyed in the heating furnace 5. After that, heat retention by the heat retention device 12 and the cooling device 13,
After being cooled, it is pulled out horizontally via the top roll 14. Here, the warpage measurement sensor 9 installed above the gas-pink nozzle 4 continuously measures the amount of warpage in the width direction of the steel plate 1 whose passing amount has been adjusted and has passed through the gas-white pink nozzle 4, and the measured value is obtained. Is input to the control device 7. Table 1 shows the results. In Table 1, a positive warpage amount indicates that the steel sheet is closer to the measurement side, and a negative warpage amount indicates that the steel sheet is closer to the measurement side. . That is, the fact that the warpage amount is 2 mm in the block 5a (front side), which is one end surface of the steel plate, and the warpage amount is -2 mm in the corresponding back surface block 5g, indicates that the steel plate is shifted to the front side by 2 mm.

[0017]

[Table 1]

The control device 7 controls the input and output of
According to the measured value of the amount of warpage in the width direction, each block in the heating furnace 5
The combustion area divided into locks 5a to 5l is galvanized.
The flow rate of fuel gas required for alloying
The control valves 6a to 6l are adjusted as shown in Table 1 and supplied.
You. In other words, G / G₀With 1 or less
To reduce the fuel flow rate below the reference flow rate and
G / G on the side₀Set the fuel flow rate to 1 or more and use the fuel flow rate as the reference flow rate.
More. How much G / G for the amount of warpage ₀To be
For this, a relational expression is determined by experiment and set. Combination
Hot-dip galvanized steel sheet 1 is alloyed online
Is continuously measured by a densitometer 11 etc.
G, which is input to the₀Used for setting
It is. Reference flow rate G₀Indicates the degree of alloying by the controller 7.
The values are set separately for the front and back sides so as to be the target values. 8
a and 8b control the total fuel flow rate of each of the front and back surfaces
It is a fuel flow valve.

FIG. 3 is a diagram showing the amount of warpage in the width direction of a galvanized steel sheet. The amount of warpage is warped to the front side from the center to both ends in the width direction of the steel sheet 1.

When the steel sheet 1 having the above-mentioned amount of warpage and having an adjusted adhesion amount is alloyed in the heating furnace 5, the present invention blocks the flow rate of the fuel gas corresponding to the amount of warpage in the width direction of the steel sheet 1. The steel sheets 1 were supplied after being adjusted by the respective control valves 6a to 6l and burned in the combustion regions of the blocks 5a to 5l to perform the alloying treatment by heating the steel sheet 1.

FIG. 4 shows the degree of alloying (%) in the width direction on the front side of the steel sheet, and FIG. 5 shows the degree of alloying (%) in the width direction on the back side of the steel sheet 1 corresponding to FIG. It is. FIG.
In FIG. 5, an example of the present invention is indicated by a solid line, and a conventional control method based on the flow rate of fuel gas is indicated by a dotted line as a comparative example.

As is clear from FIGS. 4 and 5, in the present invention, both sides of the steel sheet obtained a uniform degree of alloying in the width direction of the sheet (± 0.5%), whereas the comparative example did not. The distribution of alloying degree in the width direction of both the front and back of the steel sheet varies in proportion to the amount of warpage (± 2%).

In the above embodiment, the gas heating method is used for the heating furnace. However, the amount of warpage is corrected by the gas heating method capable of controlling the combustion for each block, and the induction heating furnace or the like having excellent responsiveness is used.
A combination heating furnace that performs a certain degree of alloying treatment can also be used.

[0024]

As described above, according to the present invention, even if there is an amount of warpage of the steel sheet which is difficult to avoid, a uniform alloying treatment can be performed in the width direction of the steel sheet, so that the powdering resistance can be improved. It is possible to produce excellent galvannealed steel sheets.

[Brief description of the drawings]

FIG. 1 is a schematic view of a manufacturing process of an alloyed hot-dip galvanized steel sheet for performing a method of the present invention.

FIG. 2 is a cross-sectional view of the heating furnace shown in FIG.

FIG. 3 is a diagram showing a warp amount in a width direction of a hot-dip galvanized steel sheet according to the present invention.

FIG. 4 shows the degree of alloying (%) in the width direction on the front side of the steel sheet of the present invention.
FIG.

FIG. 5 is a view showing the degree of alloying (%) in the width direction on the back side of the steel plate 3 corresponding to FIG. 4;

[Explanation of symbols]

 Reference Signs List 1 steel sheet (galvanized steel sheet) 2 molten zinc bath 3 sink roll 4 gas wiping nozzle 5 heating furnace 5a to 5l block (in heating furnace) 6 control valves 6a to 6l 7 control devices 8a, 8b fuel flow valve 9 measurement of warpage amount Sensor 10 Snout 11 Online alloying meter 12 Heat retention device 13 Cooling device 14 Top roll

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-200760 (JP, A) JP-A-8-239745 (JP, A) JP-A-56-143265 (JP, U) (58) Field (Int. Cl. ⁷ , DB name) C23C 2/00-2/40

Claims (1)

(57) [Claims] 1. A heating means which is divided into n blocks in the width direction of a steel sheet and is provided at a top of a gas wiping nozzle in heating and alloying a hot-dip galvanized steel sheet having an adjusted adhesion amount. An alloying control method for an alloyed hot-dip galvanized steel sheet, comprising controlling the output of the heating means for each block and for each of the front and back sides according to the amount of warpage in the width direction of the hot-dip galvanized steel sheet detected by the amount measurement sensor. .