JP3227326B2 - Method for controlling alloying of galvannealed steel strip - 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 the alloying of a galvannealed steel strip.

[0002]

2. Description of the Related Art When alloying a galvanized steel strip which is fed with at least steel strip coils having different thicknesses connected to each other, the galvanized steel strip is rapidly alloyed by electric induction heating and gas heating in a heating zone. Heating temperature, and then
It is known to complete alloying in the preservation zone. Such alloying control enables rapid heating as described above, thereby improving productivity and improving quality.

[0003]

In the alloying control as described above, when heating a plated steel strip by electric induction heating, when the thickness of the plated steel strip becomes thin, the magnetic saturation phenomenon contributes to heat generation. The upper limit value of the power is reduced, and even if more power is supplied, the calorific value (heating capacity) does not increase, resulting in reactive power and power loss. Therefore, sufficient alloying cannot be performed, and so-called burning (insufficient alloying) occurs, resulting in a significant decrease in quality.
In order to avoid such difficulties, the iron content in the target plating layer is controlled by lowering the passing speed and increasing the residence time of the plated steel strip in the alloying furnace (heating zone). However, such alloying control has a problem that the productivity is naturally lowered. The method of the present invention has been made in order to advantageously solve such problems, when changing to a thin plate thickness of the plated steel strip,
Accurately grasp the upper limit value of the power input of the plated steel strip, stop the power input exceeding the upper limit value, avoid power loss, and compensate for the shortage of heating capacity by gas heating to make accurate alloy It is intended to control the conversion.

[0004]

SUMMARY OF THE INVENTION The present invention relates to a method for heating a hot-dip galvanized steel strip, which is fed by connecting steel strip coils having at least different plate thicknesses, to alloy the steel strip. When the thickness of the galvanized steel strip is changed to be thinner than the current material, the upper limit value of the power supply for electric induction heating of the next material is grasped in advance, and power within this upper limit value is supplied, and electric induction heating is performed. The present invention relates to a method for controlling alloying of a galvannealed steel strip, wherein the shortage is compensated by increasing the gas heating capacity.

[0005]

As described above, when the thickness of the hot-dip galvanized steel strip is reduced, the upper limit value of the power contributing to heat generation by the magnetic saturation phenomenon is reduced, and the input power exceeding this value becomes reactive power, resulting in power loss. Become. Therefore, as described above, during the alloying process of the current material, the power input upper limit value of the electric induction heating of the next material thickness is previously grasped by calculation based on, for example, the changed thickness, and the amount of power to be applied to the electric induction heating is determined by the above-described method. The alloying control is performed so that the amount of the electric heating is reduced within the upper limit value and the insufficient amount of the electric induction heating is increased by increasing the gas heating capacity so that the iron amount in the target plating layer becomes the target.

In order to grasp the upper limit value of power supply for electric induction heating, in addition to the calculation based on the change in thickness as described above, for example, the upper limit value of power supply for plate thickness and electric induction heating is set in a table. The reduced amount of power is compensated for by increasing the gas heating capacity to control the target amount of iron in the plating layer. When using such a setting table,
For example, it is preferable to determine the power supply upper limit value (maximum supplied power) by linearly interpolating between the plate thickness level and the power supply upper limit value. The relation between the electric energy and the heat capacity of the gas is as follows: electric induction heating capacity 5 kw = gas heating capacity (coke oven generated gas) 1 Nm ³ , but varies depending on the calorific value of the gas used.

As described above, in addition to the change to a thin plate, the induction heating is performed in consideration of, for example, a change in the width of the plate, a change in the speed of the plate passing, and a change in the amount of plating applied. By determining the power upper limit value, the power upper limit value can be grasped more precisely, the accuracy of alloying control can be improved, and power loss can be further reduced.

When the upper limit value of power supply for electric induction heating is increased due to the change of the sheet thickness to a thicker one, and there is a surplus in electric induction heating, alloying control is performed with the surplus, and the next material When the plate thickness is changed to a thin one, heating control can be performed by changing the power input amount, so that the change can be made quickly, which is preferable.

[0009]

Next, examples of the method of the present invention will be described. In FIG. 1, a steel strip 1 is introduced into a hot-dip galvanizing bath 2, subjected to galvanization, and adjusted to a predetermined adhesion amount.
Heating is rapidly performed to the alloying temperature in a heating zone 5 composed of a gas heating zone 4 (direct heat heating), and then iron is uniformly diffused into the plating layer in a preserving zone 6 (exhaust gas convection heating in the gas heating zone 4). After performing the heating alloying control to a predetermined content (7 to 13%), it is rapidly cooled in the steam cooling zone 7 and transported to the next step.

In controlling the alloying of the hot-dip galvanized steel strip, the temperature at which alloying of the galvannealed steel strip 1 is completed is measured by a sheet thermometer 8 and the temperature is led to a calculator 9. From 9, the heating zone 5 is instructed to the heating zone 5 and the preserving zone 6 so that the above-mentioned alloying completion temperature is reached. The calculator 9 stores a calculation formula of the upper limit value of the electric power of the electric induction heating zone 3 based on the thickness of the sheet, and when the thickness of the galvanized steel strip 1 as the next material is changed to a thin material, the current material is alloyed. During the process, the changed plate thickness is introduced into the calculator 9, the upper limit value of the electric power is calculated, and when the next material is passed through the electric induction heating zone 3, the lower limit of the upper limit value of the electric power is instructed, and at the same time, the gas heating is performed. It instructs the tropics 4 to increase the heating shortage due to the downward correction of the upper power limit value.

Next, an example of a calculation formula of the upper limit power value in the calculator 9 will be described.

P = A × [MF × HC / F (t, w)] + B A, B: correction coefficient

MF = t × w × v × 1000/60 × p 1000/60: unit correction coefficient

[Formula 3] HC = k × (Tq−Ti) k: constant

(Equation 4) In the above formula, P: required power MF: threading amount per unit time (kw / s) HC: heat capacity of steel strip (kw · s / kg) F (t, w): induction heating rate, t : Plate thickness (mm), w: Plate width (mm), v: Passing speed (m / min), p: Density (kg / mm ³ ), Tq: Outgoing plate temperature (° C) Ti: Inlet plate temperature ( ° C) αj: a constant depending on the plate thickness.

In addition to calculating the upper limit value of electric power for electric induction heating based on the thickness and the like as described above, a table of the thickness, width, passing speed and upper limit value of power is set as follows. The electric power upper limit value is corrected when changing the plate thickness or the like based on the above, and at the same time, control is performed manually or automatically so that the insufficient heating is increased by gas heating.

[Table 1]

[0013]

According to the present invention, when the thickness of the plated steel strip is changed to a thinner one, it is possible to surely prevent an electric loss due to an electric power input exceeding the upper limit electric power of the electric induction heating, thereby saving energy. . In addition, since the insufficient heating of the electric induction heating is compensated for by gas heating, excellent effects such as insufficient alloying (burning) of the plated steel strip and improvement in quality can be obtained.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an embodiment of the method of the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tetsuya Miyazaki 5-3 Tokai-cho, Tokai-shi, Aichi Nippon Steel Corporation Nagoya Works (56) References JP-A-6-336668 (JP, A) JP-A-4-235268 (JP, A) JP-A-3-199365 (JP, A) JP-A-2-153060 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 2 / 00-2/40

Claims (3)

(57) [Claims] When a galvanized steel strip after hot-dip galvanization, which is sent by connecting steel strip coils having at least different thicknesses, is heated and alloyed, the thickness of the galvanized steel strip as the next material is reduced. When changing to a thinner material than the current material, grasp the power supply upper limit value for electric induction heating of the next material in advance, supply power within this upper limit value, and increase the gas heating capacity to compensate for the shortage of electric induction heating. A method for controlling alloying of a galvannealed steel strip, comprising: 2. The method for controlling alloying of a galvannealed steel strip according to claim 1, wherein the upper limit value of power supply for electric induction heating is grasped by calculation. 3. The method according to claim 1, wherein the upper limit value of power supply for electric induction heating is grasped by setting a table showing a relation between the thickness of the hot-dip galvanized steel strip and the upper limit value of power supply. A method for controlling alloying of galvannealed steel strip.