JPS6237364A - Method and apparatus for alloyed galvanized steel sheet - Google Patents

Abstract

PURPOSE:To produce an alloyed galvanized steel strip having excellent paintability and beautiful appearance by passing the steel strip emerged from a plating bath through an alloying treatment furnace consisting of a hood for wiping under a specific pressure as well as a heating zone and holding zone. CONSTITUTION:The steel strip 2 is passed through the inside of a Zn hot dipping bath 4 and is pulled up. The plated strip is subjected to gas wiping in the hood 8 which is provided to the upper part of the plating bath and in which the atmosphere of <=5% O2 concn. is maintained to adjust the coating weight of the plating. The strip is then passed through the alloying treatment furnace 12 consisting of the heating zone 14 and the holding zone 16, by which the strip is heated and the plating Zn and the Fe of the steel strip are diffused to each other and are alloyed. The internal pressures of the atmospheric gases in the hood 8, the heating zone 14 and the holding zone 16 are respectively set as A, B, C and the O2 in the atmosphere in the holding zone is maintained at <=5% and when the air-fuel ratio of a direct firing type burner of the heating zone is >=1, the pressures are maintained under C<=B and 0<=A-B<=5mm water column, by which the surface of the galvanized steel strip subjected to the alloying treatment is roughened and beautiful alloyed galvanized steel strip having excellent paintability is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method and apparatus for producing alloyed galvanized plating @temporary.

More specifically, the present invention eliminates mutual influence by adjusting the atmosphere of each treatment area when performing alloying treatment of heating and holding, following atmosphere-adjusted plating in which the atmosphere of the area around the gas wiping nozzle is adjusted. The present invention relates to a method and apparatus for manufacturing an alloyed galvanized steel sheet that enables high-speed 1111 sheet production by reducing the amount of carbon dioxide as much as possible, and increasing the furnace temperature by reducing the oxygen content and preventing surface oxidation.

(Prior art) Conventionally, after hot-dip galvanizing, heating is performed to transfer F'! from the steel base to the plating layer. 3. In the so-called initial manufacturing process of alloyed steel sheets,
It is known that the heating atmosphere affects the surface condition. For example, in JP-A No. 60-7797, a post-heating step is provided after the alloying treatment, and the oxygen concentration in the heating atmosphere at that time is set to 5000 pp11 or less, and the treatment time and surface temperature are specified in a certain relationship. It has been proposed to create fine irregularities only on the surface layer. Furthermore, it has been proposed to use a non-oxidizing gas as a wiping gas to control the amount of plating deposited, and to surround the plating with a hood and perform atmospheric plating (Japanese Patent Publication No. 57-53429).

(Problems to be Solved by the Invention) These conventional methods aim to improve corrosion resistance after coating, and also aim to enable high-speed sheet threading to increase productivity. However, it was still not completely satisfactory, and problems were observed in terms of ease of operation, compactness of the device, etc.

Accordingly, an object of the present invention is to provide a method for producing an alloyed galvanized steel sheet that is easy to operate and can be made compact as a whole, and an apparatus for carrying out the method.

Furthermore, the object of the present invention is atmospheric plating,
An object of the present invention is to provide a method and apparatus for producing extremely beautiful alloyed steel sheets by performing an atmosphere heating alloying treatment, which is easy to operate, and has a compact apparatus as a whole.

(Means for solving the problem) By the way, factors that affect the corrosion resistance of alloyed steel sheets (hereinafter simply referred to as "GA material") after painting include zinc phosphate treatment properties, surface roughness, etc. .

Zinc phosphate treatment is the surface formed during the alloying process A7!
Pb contained in the oxide and the plating layer is involved.

It is said that the smaller the A 1 /Zn ratio, the better the zinc phosphate treatment properties. Regarding surface roughness, Rmax tends to increase as the alloying temperature decreases. In order to improve the zinc phosphate treatment properties and post-painting corrosion resistance, it is thought that alloying treatment at low temperatures is preferable. It is in operation.

However, according to the findings of the present inventors, by suppressing the oxygen concentration in the retaining zone atmosphere, it is possible to reduce surface oxidation and increase the roughness Rma even if the GA furnace has a high attitude. This means that the GA furnace temperature can be made sufficiently high, and furthermore, this makes it possible to perform high-temperature rapid heating and improve productivity.

Thus, the gist of the present invention is to provide a hot-dip galvanized steel sheet continuously drawn from a hot-dip galvanizing bath.
Alloyed zinc plating consists of adjusting the basis weight by gas wiping and then performing alloying treatment in a continuous vertical alloying furnace equipped with a heating zone and a holding zone. 4. An alloy with excellent paintability, characterized in that a non-oxidizing gas with an oxygen concentration of 5% or less is used for the gas wiping, and the atmosphere of the retaining band is made to have an oxygen concentration of 5% or less. This is a method for producing galvanized steel sheets.

According to one example B, the area where the gas wiping is being performed is surrounded by a hood, and the internal pressure is adjusted to AmmAq.
When the internal pressure of the heating zone is set to a positive pressure of Bmw+Aq, the influence of the mutual zones may be reduced as much as possible by setting 0≦A−B≦5 mmAq.

Further, when the heating zone is a direct burner type with an air-fuel ratio of 1 or more, and the internal pressure of the holding zone is a positive pressure of CmmAq, B
≦C, so that the influence of mutual bands may be further reduced. Alternatively, if the heating zone is a direct burner type with an air-fuel ratio of less than 1 and 0.9 or more, and the internal pressure of the holding zone is a positive pressure of CIIIAq, C
By setting <B, the influence of mutual bands may be further reduced.

According to still another feature, the present invention includes a hot-dip galvanizing bath, a hood provided above the hot-dip galvanizing bath so as to surround a gas wiping nozzle provided above the hot-dip galvanizing bath, and An apparatus for manufacturing an alloyed galvanized steel sheet comprising a continuous vertical alloying furnace provided above the hood and equipped with a heating zone and a holding zone, the apparatus comprising: a first internal pressure measuring device of the hood; a first internal pressure measuring device of the hood; a second internal pressure measuring device of the holding band, and a third internal pressure measuring device of the holding band, and a first
1 pipe, a second pipe for discharging IJP gas from the heating zone.
An alloy characterized in that a damper mechanism interlocked with the first, second, and third internal pressure measuring devices is provided in each of a conduit path and a third conduit path through which (J\ gas is discharged from the holding band). The present invention is a galvanized steel plate manufacturing apparatus.The first conduit may be connected to the holding band to guide exhaust gas from the hood to the holding band.

(effect) The invention will now be described in further detail in connection with the accompanying drawings.

FIG. 1 is a schematic explanatory diagram of an apparatus for manufacturing an alloyed galvanized steel sheet according to the present invention.

The steel plate 2, which has been appropriately pretreated, is continuously supplied to a hot-dip galvanizing bath 4 in which the PB concentration is adjusted to, for example, 0.04% or less. The fil plate 2 pulled out from the plating bath via the snap roll 6 is surrounded by a hood 8 and has its basis weight adjusted by a gas wiping nozzle 10, and is then transferred to an alloying processing apparatus, which is a continuous vertical furnace, i.e., GA.
It is sent to the furnace 12.

The GA furnace consists of a heating zone 14 and a holding zone 16. In the heating zone, it is heated to a predetermined temperature, for example, by direct burner fire or high-frequency induction heating.

Here, according to the present invention, the hood 8 is equipped with a first internal pressure measuring device 20, and the heating device is equipped with a second internal pressure measuring device 22.
However, a third internal pressure measuring device 24 is provided on the retaining band.

The hood 8 is provided with a first conduit 26 for exhaust gas discharge, which may be continuous with the retaining band. The amount of exhaust gas, that is, the internal pressure can be adjusted by the damper 28. Similarly, the second conduit 30 and the third conduit 30 are connected to the heating zone and the holding zone, respectively.
A conduit 32 is provided and each damper 34, 36 is provided.

As already mentioned, according to the present invention, since the oxygen concentration in the holding zone is limited to 5% or less, high temperature and rapid heating is possible, and the length of the heating zone can be shortened.

However, when the heating method is a direct burner type, if the internal pressure of the heating zone ≧ the internal pressure of the retaining zone, the heating zone 14
This may make it difficult to control the oxygen concentration in the retention zone, but in such cases, in order to keep the oxygen concentration in the retention zone low at 4 degrees Celsius, the heating zone burner air-fuel ratio should be set to less than 1.0. It is preferable to set a to 0°9 or more.

The most effective way to reduce the oxygen concentration in the retention zone is to prevent the combustion exhaust gas from the heating zone from being introduced into the retention zone at all by making the internal pressure of the retention zone at least not lower than that of the heating zone. However, in terms of thermal balance, the holding zone furnace temperature needs to be raised by the heating zone exhaust gas.
Preferably, the heating zone internal pressure is adjusted to be slightly higher than the retaining zone internal pressure. All of these internal pressures are preferably adjusted to be higher than atmospheric pressure so as to reduce external influences.

On the other hand, by employing atmospheric plating, dross generated on the bath surface is reduced and surface oxidation is suppressed, but it is preferable that the internal pressure of the hood is also a positive pressure.

From experience in actual operation lines, it is desirable that the internal pressure of the atmospheric hood be 211IIIAq to 10 nvAq higher than the atmospheric pressure; within this range, the atmospheric components within the hood are stable, and this is necessary to prevent the intrusion of surrounding air. However, when the internal pressure of the atmosphere hood is set to positive pressure, there is a risk that the atmosphere gas will be blown from the upper opening and the atmosphere gas will be blown into the G^furnace heating zone located directly above, preventing the furnace temperature from rising.

Therefore, according to one aspect of the invention, G^ reactor power I
It is necessary to measure the tropical internal pressure and balance it with the atmospheric hood internal pressure to minimize the amount of air blowing into the heating zone from the opening.

In addition, in FIG. 1, since the steel plate 2 leaving the plating bath passes through each of these zones at high speed, mutual interference between the atmospheres cannot be avoided. Furthermore, for example, in a continuous vertical furnace, the distance between the upper end of the hood and the heating zone is about 300 to 500 mm, so that the flow of exhaust gas from the heating zone into the hood cannot be avoided.

From the above, the appropriate internal pressure of the G^furnace heating zone and holding zone is determined based on the atmospheric hood internal pressure.

By considering these points, the alloyed galvanized steel sheet manufacturing apparatus according to the present invention has the following features:
In addition to providing internal pressure measuring devices for each zone, each zone is adjusted as follows.

Hood internal pressure≧Heating zone internal pressure>Atmospheric pressureHeating zone internal pressure≧Retaining zone internal pressure or heating zone internal pressure <Retaining zone internal pressure It is sufficient that the pressure difference between these zones is 5IIIIIIAq or less.

For example, according to one aspect of the present invention, each internal pressure measuring device 20
．． 22. By 24, raise the atmosphere hood to 6 +
By introducing a furnace pressure control system by setting the GA furnace heating zone and holding zone to 6 mnAq and 3 mmAq, respectively, there is almost no intrusion of surrounding air into the G^ furnace, and the air-fuel ratio of the heating zone is kept at 1. By suppressing the oxygen concentration to less than .0 and introducing the gas inside the atmosphere hood into the holding zone, it is possible to make the atmospheric gas inside the holding zone almost as low as the oxygen concentration inside the atmosphere hood.

Next, the present invention will be further explained in connection with examples.

Example 1 Zinc alloy hot-dip plating was carried out at a sheet passing speed of 100 m7 using the apparatus shown in the first jump.

At this time, the internal pressures of the hood, heating zone, and holding zone and the atmospheric gas composition were adjusted as shown in Table 1. In either case, by introducing the gas in the atmosphere hood into the holding zone, the oxygen concentration in the Ga furnace holding zone could be suppressed to 5% or less.

Example 2 The gas composition and heating furnace temperature were changed for the case of ml with an air-fuel ratio of 0.95 in Example 1, and the secondary adhesion and chemical conversion coating after painting were determined for each alloyed plated steel sheet obtained in that case. Adhesion was evaluated.

The results are summarized in Table 2.

Table 1 Table 2 (m ``Secondary adhesion after painting... salt tape peeler width'' (b)

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram of an apparatus for manufacturing an alloyed galvanized steel sheet according to the present invention. 2: Steel plate 4: Hot-dip galvanizing bath 6: Snut roll 8: Hood 10: Gas wiping nozzle 12: Alloying treatment furnace 14: Heating zone 16: Holding zone 20.22.24: First, second, third internal pressure measurement device 26
．． 30.32: First, second, third conduit line 28.34.3
6: Damper

Claims (6)

[Claims] (1) Hot-dip galvanized steel sheets are continuously pulled out of the hot-dip galvanizing bath, and after adjusting the basis weight by gas wiping, they are alloyed in a continuous vertical alloying furnace equipped with a heating zone and a holding zone. The method for producing an alloyed galvanized steel sheet comprises using a non-oxidizing gas with an oxygen concentration of 5% or less for the gas wiping, and setting the atmosphere of the retaining zone to an oxygen concentration of 5% or less. A method for manufacturing an alloyed galvanized steel sheet with excellent paintability. (2) If the area where the gas wiping is being performed is surrounded by a hood, the internal pressure of which is a positive pressure of AmmAq, and the internal pressure of the heating zone is a positive pressure of BmmAq, 0≦A.
The method according to claim 1, wherein -B≦5 mmAq. (3) When the heating zone is a direct burner type with an air-fuel ratio of 1 or more, and the internal pressure of the holding zone is a positive pressure of CmmAq, B
3. The method according to claim 2, wherein ≦C. (4) When the heating zone is a direct burner type with an air-fuel ratio of less than 1 and 0.9 or more, and the internal pressure of the holding zone is a positive pressure of CmmAq, C<B. The method described in section. (5) A hot-dip galvanizing bath, a hood provided above the hot-dip galvanizing bath so as to surround a gas wiping nozzle provided above the hot-dip galvanizing bath, and a heating zone provided above the hood. An apparatus for manufacturing an alloyed galvanized steel sheet comprising a continuous vertical alloying processing furnace equipped with a first internal pressure measuring device of the hood, a second internal pressure measuring device of the heating zone, and the retaining zone. the third
Each of a first conduit line for discharging exhaust gas from the hood, a second conduit line for discharging exhaust gas from the heating zone, and a third conduit line for discharging exhaust gas from the holding zone, each including an internal pressure measuring device. An apparatus for manufacturing an alloyed galvanized steel sheet, characterized in that a damper mechanism is provided in conjunction with the first, second, and third internal pressure measuring devices. (6) The apparatus according to claim 5, wherein exhaust gas from the hood is guided to the holding band by connecting the first conduit to the holding band.