JPH07102355A - Alloying method for galvanized steel sheet and device therefor - Google Patents

Abstract

PURPOSE:To avoid the formation of a device into a huge one by increasing the heating efficiency and to prevent the dispersion of the quality by making the responsibility of the regulation of the heating quality into good one, at the time of continuously applying galvanizing to a steel sheet and thereafter executing alloying treatment. CONSTITUTION:The passage of a steel sheet l after a hot-dip zinc bath 2 and before a cooling device 5 is annularly surrounded by an annular transformer 4, and the hot-dip zinc bath 2 and a top roll 6 after the cooling device 5 are connected by a conductive member 8. This steel sheet 1 is immersed in the hot-dip zinc bath 2 and is galvanized, and an AC current is flown through the annular transformer 4 from the external power source, by which, via the hot-dip zinc bath 2 and the top roll 6, the steel sheet 1 is energized with an induced current and is heated electrically, and the alloying reaction between iron and zinc is produced. After that, the steel sheet 1 is cooled by the cooling device 5, and the hot-dip plating layer is solidified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for continuously hot-dip galvanizing a steel sheet and then alloying it.

[0002]

2. Description of the Related Art Conventionally, a gas-fired heating furnace has been generally used for alloying treatment after continuously galvanizing a steel sheet. That is, after dipping a steel sheet in a hot dip zinc bath and hot dip galvanizing, the basis weight is adjusted by gas wiping, and then the steel is passed through a gas-fired heating furnace to heat the alloying reaction of iron and zinc. Let it be done. After the alloying reaction, the cooling device cools the plating layer to a temperature at which it does not adhere to the roll or the like.

[0003]

However, the gas-fired heating furnace is based on the principle of heating the steel sheet by heat transfer from the gas, and the furnace is a vertical furnace and the air intruding from the lower part of the furnace rises in the furnace together with the steel sheet. In some cases, the thermal efficiency is extremely low at 30% or less. Further, this heating furnace is provided after the gas wiping for adjusting the basis weight, but since the gas wiping blows the gas onto the steel sheet at a speed close to the sonic velocity, the steel sheet temperature is lowered by 40 to 50 ° C. For this reason, it is necessary to reheat after cooling once, so that an effective reaction time cannot be secured, and in addition to the above-mentioned poor heating efficiency, it is inevitable that the heating furnace becomes large. Furthermore, the responsiveness when adjusting the heating amount is extremely poor, and therefore, in the case of changing conditions such as changing the coating weight of the plating or the dimensions of the steel sheet, it is not possible to quickly respond by adjusting the heating amount. However, this may cause variations in quality.

The present invention provides a method and an apparatus for alloying a hot-dip galvanized steel sheet, which has a high heating efficiency and can avoid the lengthening of the apparatus, and also has a good responsiveness in adjusting the heating amount and can prevent quality variations. provide.

[0005]

The summary of the present invention is as follows.

A method for alloying a galvanized steel sheet, which comprises immersing the steel sheet in a hot dip galvanized bath for hot dip galvanizing, and heating the galvanized steel to cause an alloying reaction between iron and zinc.

A steel sheet is immersed in a hot dip zinc bath for hot dip galvanizing, and an electric current is applied to the steel sheet through a hot dip zinc bath and a roll after a cooling device to electrically heat the steel sheet to cause an alloying reaction between iron and zinc. A method for alloying a hot-dip galvanized steel sheet, which comprises:

The method for alloying a galvanized steel sheet, wherein the roll after the cooling device is a top roll.

[0009] Fusion comprising a hot dip zinc bath for hot dip galvanizing a steel plate, a heating device for heating the steel plate to cause an alloying reaction of iron and zinc, and a cooling device for cooling the steel plate to solidify the hot dip coating layer. An apparatus for alloying a galvanized steel sheet, wherein the heating device is an electric heating device.

[0010] Fusion comprising a hot dip zinc bath for hot dip galvanizing a steel sheet, a heating device for heating the steel sheet to cause an alloying reaction of iron and zinc, and a cooling device for cooling the steel sheet to solidify the hot dip coating layer. In the galvanized steel sheet alloying apparatus, the heating apparatus is an electric heating apparatus that heats the steel sheet by passing an electric current through the steel sheet through a molten zinc bath and a roll after the cooling apparatus. Equipment for alloying plated steel sheets.

The alloying treatment apparatus for a hot-dip galvanized steel sheet, wherein a passage of the steel sheet after the hot-dip galvanizing bath and before the cooling device is annularly surrounded by an annular transformer, and the hot-dip zinc bath and the roll after the cooling device are connected by a conductive member.

The apparatus for alloying a hot-dip galvanized steel sheet, wherein the roll after the cooling device is a top roll.

[0013]

In the present invention, electric heating is adopted for heating for the alloying reaction. The energization heating is a method in which an electric current is passed through the steel sheet and the Joule heat of the steel sheet itself is used for heating. high. Further, since the steel sheet can be heated from the place where it exits the molten zinc bath, cooling of the steel sheet due to gas wiping can also be prevented, and an effective reaction time can be ensured, thus preventing the apparatus from becoming large. Furthermore, the heating amount can be easily adjusted by the current value, and since there is no thermal inertia, the responsiveness is extremely good, and since the heating amount can be quickly adjusted in response to various condition changes, variations in quality can also be prevented. . Further, it is easy to obtain an extremely large heating capacity by increasing the current value.

For the electric heating, as described in Japanese Patent Publication No. 60-26818, a metal strip is directly energized from an external power source through an electric roll, and Japanese Patent Application Laid-Open No. 1-14.
As described in JP-A-2032 and JP-A-1-187789, an energizing roll is provided before and after a metal band passage penetrating an annular transformer, and both energizing rolls are connected by a conductive member to energize the metal band and energize. There is one in which a closed circuit is constituted by a roll and a conductive member, and an induction current is generated by using the closed circuit as a secondary coil by supplying an alternating current to an annular transformer from an external power source. Can be adopted.

By the way, the heating described in each of the above-mentioned publications is conducted through the energizing rolls on the inlet side and the outlet side, but in the present invention, the plating layer must be heated while being melted, and as it is. It cannot be energized by contact with the energizing roll. Therefore, it was decided to energize using a molten zinc bath instead of the energizing roll on the entry side, but this is because it is possible to ensure sufficient contact with the steel plate because of the liquid, and from the viewpoint of energization, it is rather superior to the roll. It can be said that there is. In addition, as the delivery-side energizing roll, a roll arranged after the cooling device, for example, a top roll is used. Since the steel sheet is cooled to about 350 ° C. by the cooling device, there is no problem of adhesion of the plating layer to the roll after the cooling device. Then, when directly energizing from an external power source, the external power source may be directly connected between the molten zinc bath and the roll after the cooling device, and when an annular transformer is used, the steel plate before the cooling device after the molten zinc bath is used. The passage may be surrounded by an annular transformer in an annular shape, and the molten zinc bath and the roll after the cooling device may be connected by a conductive member.

As described above, when the steel sheet is energized between the molten zinc bath and the roll after the cooling device, the steel sheet is heated by Joule heat in the section where the current flows. That is, since the steel sheet is heated immediately after leaving the molten zinc bath,
As mentioned above, heating can be continued during gas wiping and the problem of steel plate temperature drop can be solved, but at the same time, Joule heat will continue to be emitted even while passing through the cooling device. Therefore, as the cooling device, for example, a cooling device using a mist having a cooling capacity exceeding Joule heat is adopted.

[0017]

EXAMPLE FIG. 1 shows an example of the alloying treatment apparatus of the present invention.

This is an example in which the top roll 6 is used as an energizing roll. The molten zinc bath 2, the gas wiping 3, the annular transformer 4, the cooling device 5, the top roll 6 and the pressing member are arranged in the traveling direction along the passage of the steel plate 1. It is arranged with roll 7. The molten zinc bath 2 and the top roll 6 are connected by a conductive member 8, and the molten zinc bath 2, the steel plate 1, the top roll 6, and the conductive member 8 form a closed circuit. Therefore, when an alternating current is supplied from the external power source to the annular transformer 4, an induced current flows in the closed circuit, and the steel sheet 1 itself is heated by Joule heat.
Can be heated to cause an alloying reaction of iron and zinc. In addition to using the top roll 6 as an energizing roll as in this example, a mode in which an exit-side energizing roll is separately provided before or after the top roll 6 can also be adopted.

FIG. 2 shows a temperature change of the steel sheet when the steel sheet is hot dip galvanized by the alloying apparatus and alloyed, and a conventional case using a gas fired heating furnace is shown as a comparative example. It is shown by a broken line. In the embodiment, the temperature of the steel sheet does not decrease due to the gas wiping, and the alloying reaction time can be secured, so that the processing time as a whole and hence the length of the apparatus can be shortened. For example, 0.8mm thickness x 1200mm
The effective heating length: cooling length can be increased from 450 ° C to 500 ° C in 20 seconds by passing a current with a line current density of 5 A / mm through the width steel plate, and there is no loss of heat energy in the heating itself. = 3: 1, the heating efficiency is about 65%.

[0020]

EFFECTS OF THE INVENTION According to the present invention, it becomes possible to efficiently heat a steel sheet after hot dip galvanizing to cause an alloying reaction, and to make the alloying apparatus compact. In addition, since it is possible to quickly respond to changes in conditions such as the coating weight and the dimensions of the steel sheet by adjusting the current value, it is possible to prevent quality variations. Further, since the temperature distribution in the width direction of the steel plate is uniform, the quality in the width direction of the steel plate can be homogenized.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of an alloying treatment apparatus of the present invention.

FIG. 2 is a diagram showing a temperature change of a steel sheet in an alloying process.

[Explanation of symbols] 1 steel plate 2 molten zinc bath 3 gas wiping 4 annular transformer 5 cooling device 6 top roll 7 pressing roll 8 conductive member

Claims (7)

[Claims] 1. A method for alloying a hot-dip galvanized steel sheet, which comprises immersing the hot-dip galvanized steel sheet in a hot-dip galvanized bath for hot dip galvanizing, and heating the galvanized steel to cause an alloying reaction between iron and zinc. 2. An alloying reaction between iron and zinc by immersing a steel sheet in a hot dip zinc bath for hot dip galvanizing, and applying electric current to the steel sheet by passing an electric current through the hot dip zinc bath and a roll after a cooling device to heat the steel. A method of alloying a hot-dip galvanized steel sheet, which comprises: 3. The method for alloying a galvanized steel sheet according to claim 2, wherein the roll after the cooling device is a top roll. 4. A molten zinc bath for hot dip galvanizing a steel sheet, a heating device for heating the steel sheet to cause an alloying reaction of iron and zinc, and a cooling device for cooling the steel sheet to solidify the hot dip layer. An apparatus for alloying a galvanized steel sheet, wherein the heating device is an electric heating device. 5. A molten zinc bath for hot dip galvanizing a steel sheet, a heating device for heating the steel sheet to cause an alloying reaction of iron and zinc, and a cooling device for cooling the steel sheet to solidify the hot dip coating layer. In the apparatus for alloying a galvanized steel sheet, the heating apparatus is an electric heating apparatus for heating the steel sheet by passing an electric current through the galvanized bath and a roll after the cooling apparatus to the steel sheet. Equipment for alloying galvanized steel sheets. 6. The hot dip galvanized steel sheet according to claim 5, wherein the passage of the steel sheet after the hot dip galvanizing bath and before the cooling device is surrounded in an annular shape by an annular transformer, and the hot dip galvanizing bath and the roll after the cooling device are connected by a conductive member. Alloy processing equipment. 7. The apparatus for alloying a galvanized steel sheet according to claim 5, wherein the roll after the cooling device is a top roll.