JPH05247619A - Vertical type galvannealing furnace for manufacturing galvannealed steel sheet - Google Patents

Abstract

PURPOSE:To stably manufacture a thick galvannealed steel sheet having excellent powdering resistance and flaking resistance, in a vertical galvannealing furnace for manufacturing the galvannealed steel sheet by pulling up the steel sheet after dipping into a hot-dipping galvanizing bath, gas-wiping, quickly heating, holding to execute galvannealing reaction and cooling. CONSTITUTION:In this galvannealing furnace, a temp. adjusting zone 12 for adjusting temp. of a holding zone 7 to the suitable temp. range for developing the galvannealing reaction by mixing cold blast with exhaust gas in a heating zone 5 is arranged in between the heating zone 5 for quickly heating the steel sheet 1 after gas-wiping by a directly firing type heating means 6 and the holding zone 7 for developing the galvannealing reaction by holding the steel sheet in a prescribed temp. range after quickly heating. Further, a pressure resistant body 13 freely adjusting the pressure loss resistance to a gas flow is arranged in the lifting gas flow passage from the temp. adjusting zone 12 to the holding zone 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vertical alloying furnace for producing an alloyed zinc-plated steel sheet by immersing the steel sheet in a hot dip galvanizing bath and pulling it up, heating it by gas wiping, and cooling it by holding cooling. is there.

[0002]

2. Description of the Related Art In recent years, the demand for alloyed galvanized steel sheets as materials for automobiles has been increasing, and the demand for strengthening rust prevention has been increasing. Along with this, the amount of plating adhesion 40
The technology for producing alloyed galvanized steel sheets having excellent workability such as powder ring resistance and flaking resistance along with the thickening of 70 g / m ² has been developed.

As an alloying furnace for producing this alloyed galvanized steel sheet, for example, a vertical type furnace as shown in FIG. 7 is known. In this vertical alloying furnace, the steel sheet 1 after the pickling treatment is dipped in a hot dip galvanizing bath 2 to plate the hot-dip galvanized zinc on the steel sheet 1, and a gas wiping treatment by a wiping nozzle 4 is performed while pulling up through a sink roll 3. Then, it is sent to the heating zone 5 while adjusting the coating weight, and heated there by induction heating or direct-heating type heating means 6 and retained in the retention zone 7 to generate an alloying reaction. It adapted to discharge out of the furnace by the cooling after the transport roller 9 a plated steel sheet 1 ₀ in the refrigerator 8. The rear end of Hojotai 7 flue 10 is provided which can air volume adjustment, between the Mataho Condition 7 cooling device 8, inhibit the draft furnace atmosphere gases with the unloading of the galvannealed steel sheet 1 ₀ Gas seal part 1
1 is provided.

[0004]

The heat cycle in this conventional alloying furnace is as shown in FIG.
In order to suppress the ζ phase generation at low temperature steel plate temperature below 0 ° C, A
The steel sheet temperature of 470 ° C. or higher and rapidly heated into the l concentration and determined from the temperature time, and 520 ° C. or less for Γ phase suppression, and alloying treatment at a proper temperature of four hundred seventy to five hundred and twenty ° C., [delta] ₁
It is supposed to promote the formation of phases.

Conventionally, the heat treatment cycle has an upper limit temperature of 560 ° C.
The alloying treatment may be performed below, but in order to satisfy the above conditions, rapid heating must be possible and the heat treatment temperature cycle must be within a narrow upper and lower limit range.
In other words, the major issues in terms of equipment technology to take appropriate measures based on the difference in heat cycle are as follows.

Suppressing the furnace lengthening due to low temperature and long time and satisfying the two-phase reaction suitability, that is, satisfying the temperature permissible width for each basis weight rate, and the optimum combination of alloying temperature and time and alloy It is necessary to determine the total length of conversion.

It is necessary to develop a rapid heating direct-burning burner by determining the rapid heating capacity and the allowable equipment length for each basis weight, plate thickness, and speed from the life of the Al concentrated layer.

Under a huge direct heating capacity, a model was constructed to simulate heat balance and furnace pressure balance so as to satisfy the restraint zone overshoot prevention and heat cycle for each processing condition of unit weight and plate thickness speed Technical methods need to be evaluated.

It is necessary to be able to determine optimum equipment specifications for a realistic individual equipment system.

[0010] with the above is a way to ensure Atsumekki good processability quality, stable quality be applied in place of the prior art to the subject other than the Ki thick Tsu of 40 g / m ² or less or 70 g / m ² greater Enables production.

On the other hand, in terms of investment efficiency, it is desirable that the equipment capacity scale be improved to an appropriate level, but in the prior art, the line for exclusive use of alloyed steel sheets was kept below 30,000 tons per month. The cause is due to the plating apparatus that controls the amount of Zn adhered by gas wiping or the like.

It is more difficult to control the adhesion amount as the adhesion amount decreases. In addition, including securing the appearance quality, at present, the upper limit of the processable speed is 130 to 150 MPM when the adhesion amount is 45 g / m ² for automobiles and the like, and 15 when it is equivalent to 60 g / m ^2.
0 to 180 MPM. On the other hand, in the alloying process, the thicker the plating, the longer the processing time because of the diffusion from the base metal to the plating surface layer, which is a huge equipment capacity. The following needs to be suppressed. Therefore, there is a need for equipment for thick plating, which has a greater facility capacity than ever, meets the above requirements, and is capable of obtaining an alloyed galvanized steel sheet of optimum quality with high productivity. As a result of investigating the heat / gas behavior in the furnace from the principle of the two-phase reaction behavior of the δ ₁ phase and the Γ phase, the conventional technology has many defects and requires a new equipment configuration.

The present invention makes it possible to stably produce alloyed steel sheets having a conventional adhesion amount including powder-plated alloyed steel sheets and having excellent powder ring resistance and flaking properties, and significantly improve the facility capacity. An alloying furnace having high thermal efficiency performance is provided.

In particular, it is important to secure a rapid heating capacity, prevent overshooting of the retaining band, controllability of alloying temperature, heat balance, furnace pressure balance, etc., and in the past, in view of these points, it is particularly structurally sufficient. It is hard to say that the plating thickness is 40 g / m ² or less per side, and the plating processing speed is 1
At 0 to 120 m / min, this is expressed as a processing capacity of 6
Since it is 0 t / Hr or less, the above-mentioned required level cannot be stably met.

[0015]

According to the present invention, a steel sheet is dipped in a hot dip galvanizing bath, pulled up, gas wiped, rapidly heated and held to cause an alloying reaction, and then cooled to produce an alloyed galvanized steel sheet. In the vertical alloying furnace, between the heating zone for rapidly heating the steel sheet after gas wiping by the direct heating type heating means, and the retaining zone for retaining the alloy in the predetermined temperature region after the rapid heating to generate the alloying reaction, A temperature adjusting zone for adjusting the temperature of the retaining zone to an appropriate temperature region for alloying reaction generation by mixing cold air with the exhaust gas of the heating zone is provided, and the rising gas flow passage from the temperature adjusting zone to the retaining zone is provided with the temperature adjusting zone. A vertical alloying furnace for producing an alloyed galvanized steel sheet, characterized in that a pressure loss resistor whose pressure loss resistance to a gas flow is adjustable is arranged. If necessary, a seal gas jet nozzle is installed on the steel plate inlet side upstream of the heating zone to prevent air from entering the furnace, and the exhaust gas in the furnace is passed through the seal gas jet nozzle in the plate passing direction. And a vibration suppressing structure of a steel plate for ejecting exhaust gas in the furnace to the steel plate through the gas injection nozzle.

[0016]

In the present invention, the direct heating type heating means is used for rapid heating to suppress the residue of the ζ phase which hinders the formation of a good alloyed layer. Further, a temperature adjusting zone is provided between the heating zone and the retaining zone to adjust the temperature of the retaining zone to a temperature range suitable for alloying reaction and quality stabilization. Furthermore, a pressure loss resistor is provided in the ascending gas flow passage from the adjustment zone to the retention zone to adjust the pressure loss to the gas flow, improve the retention of the combustion gas especially in the heating zone, and prevent gas from the retention zone. By suppressing the draft, the steel sheet can be rapidly heated, and the retaining efficiency in the retaining band is improved.

Further, a gas seal structure using exhaust gas of the heating zone is provided on the steel plate entrance side of the heating zone to suppress atmospheric intrusion into the furnace, thereby preventing heat loss in the heating zone and the retaining zone. Stable control accuracy is ensured. Further, a gas ejection nozzle is provided in the pressure loss resistor to eject the exhaust gas from the heating zone onto the steel sheet, thereby suppressing vibration (fluttering) of the steel sheet, smoothing the passage of the steel sheet, and preventing damage to the plating film.

The present inventor found out the conditions under which the two-phase reaction is effectively generated in the average heat treatment temperature and time region,
We have developed an alloying furnace that is highly suitable for securing these temperature conditions efficiently and stably.

That is, in order to appropriately generate the δ ₁ phase and effectively suppress the generation of the Γ phase, as shown in FIG. 3, first, as shown in FIG. It is necessary to rapidly raise the temperature from a low temperature range of 470 ° C. or lower at which the ζ phase is generated to a preferable δ ₁ phase formation promoting temperature range of 470 ° C. or higher within the reaction incubation period of the Al concentrated layer (aluminum barrier layer) to be generated. This requires a very high heat transfer coefficient within a very short heating distance. This is a condition necessary for suppressing the ζ phase that inhibits the formation of a good alloyed layer, and in order to satisfy the equivalent average temperature and the time required for the completion of alloying, after heating to a temperature higher than 470 ° C. It is advantageous to do Therefore, in the present invention, the heating zone is provided with a direct-fired heating means such as a direct-fire radiant burner that enables rapid heating.

Next, since the Γ phase is excessively generated at 520 ° C. or higher, it is necessary to suppress the excessive generation of the Γ phase. For this purpose, a large amount of exhaust gas is retained in the retention zone at a high temperature from the heating zone. It is necessary to control the inflow. Also, if the exhaust gas draft amount fluctuates greatly, the pressure in the lower part of the alloying furnace, which is a negative pressure with respect to the normal atmosphere, also decreases, and the amount of air entering from the opening in the lower part also increases, resulting in a decrease in thermal efficiency and rapid heating zone. As a result, the stable alloying reaction will not be generated.

Therefore, in the present invention, cold air is sucked between the heating zone and the retaining zone, and the temperature of the gas introduced from the heating zone to the retaining zone is lowered to control the temperature of the retaining zone to 520 ° C. or lower.
Prevents overproduction of the Γ phase. Further, in order to suppress the invasion of air from the lower part of the furnace, a pressure loss resistor capable of causing a pressure loss comparable to a draft with respect to the rising gas flow is provided in the rising gas flow passage from the adjustment zone to the retention zone.

In this case, the smaller the gap between the pressure loss resistor and the steel sheet, the greater the pressure loss effect on the rising gas flow. Therefore, when the pressure loss resistor is brought close to the steel sheet, the steel sheet vibrates and becomes a pressure loss resistor. Since there is a risk of contact, damage, and deterioration of quality, a gas injection nozzle is provided in the pressure loss resistor as a measure to prevent this, and gas is injected from this nozzle to the steel plate to suppress flapping and to function as a pressure loss resistor. It is better to prevent contact with the steel plate. As the gas used in this case, a gas in a retention zone whose temperature is adjusted is highly suitable for reducing the temperature effect on the steel sheet.

Further, after the completion of the Waipink, in the zone of a length of only a little less than 2 m to the direct heating type heating means, the temperature of the steel sheet drops due to contact with the atmosphere, and this temperature drop is disadvantageous to the rapid heating. In the present invention, although the pressure loss resistor is used to suppress the invasion of air into the furnace, it cannot be said that the air intrusion from the heating zone entrance side opening is completely prevented. This air entry not only lowers the temperature of the steel sheet but also lowers the thermal efficiency in the furnace, so it is desirable to prevent air entry on the steel sheet entry side as much as possible.

Therefore, it is advisable to provide a seal gas ejection nozzle on the inlet side of the heating zone and inject air from this nozzle to reduce the invading air. As this jet gas,
A heating gas is preferable in the sense that the temperature of the steel sheet is raised and the heating efficiency of the heating zone is improved. For example, it is effective to adjust the temperature of the exhaust gas in the heating zone before use. Exhaust gas in the temperature adjustment zone or the retention zone may be used. This seal gas ejection nozzle is an important alloying furnace constituent element for improving the thermal efficiency, but it is not an essential element in the production of alloyed steel sheet and can be omitted.

[0025]

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

In this embodiment, similarly to the conventional example shown in FIG. 7, a pickled steel plate 1 is immersed in a hot dip galvanizing bath 2, the steel plate 1 is plated with hot dip zinc, and pulled up through a sink roll 3. After the gas wiping with the wiping nozzle 4, it is introduced into an alloying furnace and rapidly heated, retained and cooled to produce an alloyed galvanized steel sheet.

[0027] In the present invention, the heating zone 5 is formed by a first heating zone second heating zone 5 _0, the direct heat as the two heating zones are shown in FIG. 4 respectively burner 6 _0, 6 ₁ The steel plates 1 are arranged so as to be close to and face each other with the steel plate 1 interposed therebetween, and the steel plates 1 can be directly heated from both sides thereof by a burner flame for rapid heating. The burner 6 _0,
Structure of 6 ₁ flame outlet 6 ₂ has become a slit-shaped, flame diffusion path 6 ₃ to increase the area relative to the outer from the air outlet 6 _second end is formed. The diffusion path 6 ₃ parallel to the conveying direction parallel to surface 6 ₄ of the steel plate 1 at the end is formed, it flows in laminar flame from the burner 6 ₀ along the surface of the steel sheet 1, so that it can sufficiently heat the steel plate 1 It has become.

[0028] Between the second heating zone 5 ₀ and Hojotai 7, providing a temperature adjusting zone 12 for the steel plate 1 from the second heating zone 5 ₀ a mixture of cold air can be inhibited from excessive Atsushi Nobori .. In this temperature adjustment zone 12, a plurality of cold air blowing ports are arranged at intervals so that the cold air is sufficiently mixed.

A pressure loss resistor 13 is provided between the temperature adjusting zone 12 and the retaining zone 7 to provide pressure loss resistance to the gas flow from the temperature adjusting element 12. As a result, the steel plate 1 enters the retaining band 7 after the temperature of the gas is sufficiently adjusted by blowing cold air. Further, the gas temperature to the restraining zone 7 is stably maintained at an appropriate temperature, and the draft from the restraining zone 7 is suppressed, as shown in FIG.
As shown in (3), the gas can be sufficiently retained in the retention zone 7 to increase the utilization factor and reduce heat loss.

This pressure loss resistor 13 is shown in FIG.
As shown in (b), it is made up of resistors 13 ₁ and 13 ₂ that are opposed to each other with the steel plate 1 sandwiched therebetween, and the installation interval l is adjustable. The resistors 13 ₁ and 13 ₂ have a structure shown in FIG.
As shown in (b), a plurality of slit-shaped gas ejection nozzles 14, 14 ₁ , 14 ₂ for injecting gas onto the surface of the steel plate 1
The exhaust gas sucked from the retaining band 7 by the blower 15 is injected from the nozzles 14, 14 ₁ and 14 ₂ to both sides of the steel plate 1 to suppress flapping and to suppress the pressure loss resistor 13 and the steel plate. Prevent contact with 1. The gas injected here is combustion temperature gas from the temperature-controlled retention zone 7, and has no adverse effect on the steel plate quality.

Further, a seal gas jet nozzle 16 is arranged on the steel plate entrance side of the heating zone 5 for introducing the steel sheet 1 after gas wiping. From this jet nozzle 16, suction is made by the blower 17 from the adjusting zone 12 Inject the exhaust gas obtained by
Air intrusion from the steel plate entrance side of the heating zone 5 is suppressed.

The main specifications and set values in this embodiment are shown in Table 1, and the heat cycle in this embodiment is shown in FIG. 2 together with the conventional heat cycle.

[0033]

[Table 1]

In this embodiment, the sealing gas having a temperature of 500 ° C. is injected into the seal portion to start heating the steel sheet 1, the steel sheet 1 is rapidly heated to 470 ° C. in the first heating zone, and the second heating zone is heated. After being suppressed and heated to 504 ° C., the temperature adjustment zone 12 and the pressure loss resistor 13 act to enter 470 to 520 ° C., which is an appropriate temperature region where the δ ₁ phase and the Γ phase are effectively generated in the retention zone 7 504
After being held at ℃, it was cooled to produce an alloyed steel sheet.

As a result, in a hot-dip galvanized steel sheet having a coating thickness of 60 g / m ² , Γ ≦ 0.8 μ and ζ phase zero can be achieved, and the surface characteristics and alloying formation are good, and the alloying is excellent in workability. The galvanized steel sheet could be manufactured with a target processing capacity of 94 t / Hr. Also, the thermal efficiency could be improved by about 25%.

[0036]

According to the present invention, the steel sheet after gas wiping is rapidly heated in the heating zone, and the flow rate of introduced gas to the retaining zone and the temperature for producing good alloying are set to Γ.
Phase, δ ₁ phase can be efficiently adjusted to an appropriate temperature range, and heat loss can be reduced by suppressing air intrusion, and alloying plating thickness is 30 g / m
It is possible to stably manufacture an alloyed galvanized steel sheet having excellent workability of ² or more with high productivity and low cost.

[Brief description of drawings]

FIG. 1 is a vertical plane explanatory view showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an example of a heat pattern in one example of the present invention and a conventional example.

FIG. 3 is an explanatory diagram showing a relationship between a heating rate in alloying zinc plating and an Al barrier that affects an alloying reaction.

FIG. 4 is a diagram showing an example of a direct-fired burner used in the present invention, FIG. 4 (a) is a sectional explanatory view, and FIG. 4 (b) is a front explanatory diagram.

5A and 5B are views showing an arrangement example of pressure drop resistors according to the present invention, FIG. 5A is a partial vertical cross-sectional explanatory view, and FIG. 5B is a view taken along the line AA 'in FIG. 5A. It is a section explanatory view.

FIG. 6 (a) is a front explanatory view of the pressure loss resistor of the present invention as seen from the steel plate side, and FIG. 6 (b) is a B- of FIG. 6 (a).
FIG. 9B is a cross-sectional view taken along the arrow B ′.

FIG. 7 is a vertical plane explanatory view showing an example of a conventional alloying furnace.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Steel plate 1 ₀ Alloyed galvanized steel plate 2 Hot dip galvanizing bath 3 Sink roll 4 Wiping nozzle 5 Heating zone 5 ₀ Second heating zone 6 Heating means 6 ₀ Direct flame burner 6 ₁ Direct flame burner 6 ₂ Flame outlet 6 ₃ Flame diffusion path 6 ₄ Parallel surface 7 Holding band 8 Cooling device 9 Conveying roller 10 Flue 11 Gas seal part 12 Temperature adjustment band 13 Pressure loss resistor 13 ₁ Resistor 13 ₂ Resistor 14 Gas ejection nozzle 14 ₁ Gas ejection nozzle 14 ₂ Gas ejection nozzle 15 Blower 16 Seal gas ejection nozzle 17 Blower

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshihiro Okochi 5-3 Tokai-cho, Tokai-shi, Aichi Nippon Steel Stock Company Nagoya Works

Claims (3)

[Claims] 1. A vertical alloying furnace for producing an alloyed zinc-plated steel sheet by immersing the steel sheet in a hot dip galvanizing bath, pulling it up, gas wiping, rapidly heating and retaining it to cause an alloying reaction, and cooling it to produce a galvannealed steel sheet. Cold air is mixed with the exhaust gas in the heating zone between the heating zone where the steel sheet after wiping is rapidly heated by the direct heating type heating means and the retaining zone where the alloying reaction is generated by holding the steel sheet in this temperature range after the rapid heating. A temperature adjustment zone for adjusting the temperature of the retention zone to an appropriate temperature range for alloying reaction generation is provided, and the pressure loss resistance to the gas flow can be adjusted in the rising gas flow passage from the temperature adjustment zone to the retention zone. Vertical alloying furnace for the production of galvannealed steel sheets, which is characterized by arranging various pressure loss resistors. 2. A seal gas injection nozzle for preventing air from entering the furnace is provided on the steel plate entrance side upstream of the heating zone,
2. A vertical alloying furnace for producing an alloyed galvanized steel sheet according to claim 1, further comprising a gas seal structure for ejecting exhaust gas in the furnace through the seal gas jet nozzle in a direction intersecting with a passage direction. .. 3. A vibration suppressing structure for a steel plate, wherein the pressure drop resistor is provided with a gas ejection nozzle, and exhaust gas in the furnace is ejected to the steel plate through the gas ejection nozzle.
Alternatively, the vertical alloying furnace for producing the alloyed galvanized steel sheet according to 2.