JPH1161368A - Hot rolled steel sheet hot dip coating equipment - Google Patents

Abstract

(57) [Summary] [Problem] A problem that a descaling process of a hot-rolled steel sheet is incorporated in a continuous hot-dip galvanizing line to reduce production costs and that the pickling apparatus becomes long due to a slow pickling speed. And the problem that plating defects occur due to residual smut after pickling. SOLUTION: A continuous hot-dip plating facility having an annealing furnace, a heating section provided with a gas jet type preheater using combustion exhaust gas of the annealing furnace on an entrance side thereof, and a heating section provided between the heating section and the continuous hot-dip plating facility A pickling tank section in which a steel plate is immersed is provided. When the steel sheet is heated to a predetermined temperature higher than the acid solution in the heating section and the steel sheet is immersed in the pickling tank, a thermal shock occurs due to a temperature difference between the steel sheet and the acid solution, and the scale falls off the interface with the steel sheet, Or cracks occur inside the scale,
The pickling speed is improved, and smut residue is reduced. Since the steel sheet is heated using the gas jet preheater, the heating section can be made compact, and the heat possessed by the combustion exhaust gas can be efficiently recovered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-dip plating apparatus for hot-dip galvanizing a zinc-based metal on a hot-rolled steel sheet.

[0002]

2. Description of the Related Art Generally, a hot-rolled hot-dip galvanized steel sheet is formed by winding a hot-rolled steel sheet rolled in a hot rolling line into a coil, cooling it to room temperature, and then pickling it at about 80 to 90 ° C. in a pickling line. By pickling at the temperature of
The scale formed on the surface of the steel sheet during hot rolling is removed, and in a continuous hot-dip plating line, the steel sheet is subjected to reduction annealing at a temperature of about 700 to 800 ° C. in an annealing furnace maintaining a predetermined reducing atmosphere, and the atmosphere is maintained. It is manufactured by subjecting a zinc-based metal to hot dip plating continuously.

That is, as shown in FIG. 5, a conventional continuous hot-dip line has a hot-dip plating apparatus 3 having an annealing furnace 4 and a hot-dip plating tank 5, and a hot-rolled steel sheet 2 fed from a coiler 1. However, first, reduction annealing is performed in the annealing furnace 4, and thereafter, hot-dip plating is continuously performed in the hot-dip plating tank 5.

[0004] Traveling through the pickling line leads to an increase in transportation costs and operating costs. Therefore, it has been proposed that the pickling process and the plating process are continuously performed on the same line.

For example, Japanese Patent Publication No. 51-40018 discloses a technique in which a hot-rolled steel sheet is passed through a pickling treatment solution comprising a mixed acid of sulfuric acid and hydrochloric acid to remove scale, and then is subjected to a continuous plating step to perform galvanizing. (Hereinafter referred to as prior art 1). Also, JP-A-4-30435
Japanese Patent Application Laid-Open No. 7-81748 describes a technique of performing hot-dip plating after buffing with baffle after pickling (hereinafter referred to as “prior art 2”). Then, a technique of hot-dip galvanizing (hereinafter referred to as prior art 3) is described.

In addition, regarding high-speed pickling treatment of a hot-rolled steel sheet,
Japanese Unexamined Patent Publication No. 7-197282 (hereinafter referred to as prior art 4) discloses that a nucleate boiling state can be obtained with a pickling apparatus including a steel sheet heating section for heating a steel sheet and a pickling tank section in which the steel sheet is immersed. A high-speed pickling apparatus for a thin steel sheet capable of increasing the pickling speed by immersing a steel sheet heated to a temperature range in an acid solution and promoting the destruction of scale by thermal shock and the flow of the acid solution by boiling is described. .

[0007]

When the pickling process and the plating process are continuously performed on the same line, it is desirable that the pickling tank be made compact and the cost of the pickling process be reduced as much as possible. It is also necessary that the surface properties after the pickling treatment are good and that a plated steel sheet of good quality after plating is obtained.

In the prior art 1, however, smut mainly composed of cementite remains on the surface of a hot-rolled steel sheet descaled by pickling, and plating repelling (so-called non-plating) caused by smut which is not decomposed and removed during reduction annealing. ) Occurs.

In the prior art 2, the smut generated at the time of pickling is removed to some extent by grinding with a buff roll. However, if the steel sheet is curved or micro unevenness is present on the surface of the steel sheet, the brush must be uniform. , The smut tends to remain locally. In addition, hair loss of the brush roll may cause defects, uneven cleaning of the brush roll, uneven chatter marks, etc.
There are also problems such as impairing the appearance of the steel sheet after plating.

In the prior art 3, the prior art 1,
Although the problems such as 2 are solved, an electrolytic facility is required, which causes an increase in operating costs.

Further, the prior arts 1 to 3 each include:
No consideration is given to making the pickling section compact.

According to the prior art 4, since the pickling speed can be increased, the pickling tank can be made compact. However, it is not considered that the pickling process and the plating process are economically performed in a line with a restriction that the pickling process and the plating process are continuously performed on the same line, and that the surface properties after the pickling process are improved. There is no mention of obtaining a steel plate of good plating quality.

The present invention has been made in view of such circumstances, and incorporates a usual descaling process of a hot-rolled steel sheet into a continuous hot-dip galvanizing line to reduce production costs and reduce the pickling speed. Reduced operating costs and equipment costs with a compact pickling system capable of high-speed pickling, by improving the problem of long pickling equipment and the problem of plating defects caused by remaining smut after pickling. It is another object of the present invention to provide a hot-rolled steel sheet hot-dip steel plate equipment capable of producing a hot-dip coated steel sheet having excellent plating quality.

[0014]

Means for Solving the Problems The present inventor has made the prior art 4
Focusing on the fact that the pickling apparatus described in (1) has a high pickling speed and can make the pickling apparatus compact, this pickling apparatus is installed on the entrance side of the continuous hot-dip plating equipment to further reduce operating costs. In addition to examining the quality, the descaling state after the pickling treatment and the plating quality were also investigated.

As a result, when pickling is performed using the pickling apparatus described in the prior art 4, not only the pickling speed is high, but also
It was found that the remaining smut after descaling was reduced and the quality after plating was excellent.

Usually, in an annealing furnace, a steel sheet is heated by a high-temperature combustion gas obtained by burning a fuel gas such as a coke oven gas, a natural gas, and an LPG gas. The high-temperature combustion gas after heating the steel sheet is discharged into the atmosphere. On the other hand, conventional technology 4
In the pickling apparatus described in (1), a heating section for heating the steel sheet is required before the pickling tank section. If the heat possessed by the combustion exhaust gas discharged into the atmosphere can be efficiently used as a heat source of the heating section in front of the pickling tank section, the operating cost can be reduced. Therefore, a study was made on a device that efficiently uses the retained heat of the combustion exhaust gas for the heating unit.

The present invention has been obtained from such findings and studies. The characteristic features of the present invention are that a continuous hot-dip galvanizing equipment having an annealing furnace and a combustion furnace of the annealing furnace arranged on the inlet side thereof. A heating unit provided with a gas jet type preheater utilizing exhaust gas, and a hot-rolled steel plate characterized by comprising a pickling tank unit in which a steel plate is immersed, provided between the heating unit and the plating equipment. It is a hot-dip plating facility.

When the steel sheet is heated to a predetermined temperature higher than the acid solution in the heating section and the steel sheet is immersed in the pickling tank, a thermal shock occurs due to a temperature difference between the steel sheet and the acid solution, and the thermal expansion of the scale and the steel sheet occurs. Due to the difference in the coefficient, the scale falls off the interface with the steel sheet,
Alternatively, cracks are generated inside the scale without dropping, and the pickling speed is improved, so that the pickling tank can be made compact. In addition, since less smut remains, the occurrence of surface defects such as non-plating and poor plating adhesion after plating can be reduced.

In particular, when the heating temperature of the steel sheet is in a temperature range in which a nucleate boiling state is obtained when the steel sheet is immersed in the acid solution, bubbles are generated on the surface of the steel sheet by the immersion in the acid solution, and the scale is broken. In addition, since the flow of the acid solution is promoted and a decrease in the dissolution rate of the scale is prevented, the above-mentioned effects are more excellent. The temperature of the steel sheet in such a state is 100 to 300 ° C. in the case of pickling with hydrochloric acid, and more preferably 150 to 300 ° C.
A temperature range of -200 <0> C is preferred.

Further, when the operating speed fluctuates, for example, in the case of a change in the dimensions of the steel sheet, the time of immersion in the pickling tank fluctuates and the descaling state fluctuates, so it is desirable to be able to adjust the pickling speed. By adjusting the heating temperature of the steel sheet in the heating unit, the pickling rate can be adjusted to obtain an optimal descaling state, so that a steel sheet with better plating quality can be obtained.

Since the heating of the steel plate in the heating section is performed by heat transfer by a gas jet impinging jet using a gas jet type preheater utilizing the combustion exhaust gas of the annealing furnace, the heating section can be made compact and the combustion exhaust gas is retained. Since heat can be efficiently recovered and no extra heating source such as the use of steam is required, the heating cost can be reduced.

In the present invention, the use of the flue gas includes not only the case where the flue gas is directly used for heating the steel sheet but also the case where another gas heated by exchanging heat with the flue gas is used. I have.

[0023]

Embodiments of the present invention will be described below. FIG. 1 is a schematic configuration diagram showing a hot-dip plating facility for describing an embodiment of the present invention.

In FIG. 1, reference numeral 30 denotes a heating device having a gas jet type preheater, 32 denotes an pickling tank, and 34 denotes a continuous hot-dip plating apparatus. The continuous hot-dip plating apparatus 34 includes an annealing furnace 35 and a hot-dip plating bath 39, and the annealing furnace 35 includes a non-oxidizing furnace 36, a radiation tube heating furnace 37, and a cooling furnace 38.
The heating device 30 is provided in a space below the structure of the pickling tank 32.

Reference numeral 40 denotes an exhaust pipe for the combustion exhaust gas of the non-oxidizing furnace 36, 41 denotes an exhaust blower, 42 denotes a pressure gauge for measuring the internal pressure of the non-oxidizing furnace 36, 43 denotes a control valve for controlling the internal pressure of the non-oxidizing furnace, 44 is a supply pipe for sending the combustion exhaust gas from the exhaust pipe 40 to the heating device 30, A is a branch point between the two, 45 is a return pipe returning the combustion exhaust gas from the heating device 30 to the exhaust pipe 40, B is a confluence point between the two, 46 is A circulation blower for circulating the combustion exhaust gas between the exhaust pipe 40 and the heating device 30, a control valve 47 for controlling the circulation amount, and a thermometer 48 for measuring the temperature of the steel sheet after the heating by the heating device 30.

The high-temperature flue gas discharged from the non-oxidizing furnace 36 passes through the exhaust pipe 40 as described below.
After being circulated and used to heat the steel sheet by the heating device 30, the steel sheet is discharged outside using the exhaust blower 41.

That is, the combustion exhaust gas is sent to the heating device 30 through the supply pipe 44 by using the circulation blower 46 at the branch point A of the exhaust pipe 40, and the heating apparatus 30 heats the steel sheet.
The flue gas whose temperature has decreased due to the heating of the steel sheet is returned to the return pipe 4.
5, the exhaust pipe 40 at the junction B upstream of the branch point A.
Return to The reduced temperature of the flue gas returned from the return pipe 45 merges with the high-temperature flue gas discharged from the non-oxidizing furnace 36 at the junction B, and the temperature of the lowered flue gas rises. The combustion exhaust gas whose temperature has risen is sent to the heating device 30 via the supply pipe 44 at the branch point A of the exhaust pipe 40. The combustion exhaust gas is circulated and used between the exhaust pipe (between the junction B and the branch A) and the heating device 30.

The temperature of the steel sheet after being heated by the heating device 30 is measured by a thermometer 48, and the temperature of the steel sheet is set to a predetermined temperature.
The control valve 47 controls the amount of circulation of the combustion exhaust gas.

Further, a part of the combustion exhaust gas is discharged outside through the branch point A by using the exhaust blower 41. At this time, the pressure in the furnace of the non-oxidizing furnace 36 is measured by the pressure gauge 42, and the flow rate of the combustion exhaust gas discharged to the outside is controlled using the control valve 43 so that the pressure becomes a predetermined pressure.

FIGS. 2A and 2B show a main part of a heating device 30 provided with the gas jet type preheater of FIG. 1, wherein FIG. 2A is a sectional view of the heating device, and FIG. FIG.

The heating device 30 is surrounded by a member 64 except for the inlet portion 62 and the outlet portion 69 of the steel sheet S and has a substantially hermetic structure. A heat insulating material 65 is attached to the inner and outer surfaces of the member 64. . 66 is a gas header, 67 is a gas jet nozzle, and a large number are provided above and below the steel sheet in the running direction of the steel sheet. The gas jet nozzle 67 is, as shown in FIG. 3, a circular nozzle having a number of small holes 62 on the side facing the steel plate.

The combustion exhaust gas supplied through the supply pipe 44 passes through a gas header 66 and passes through a gas jet nozzle 67.
The steel sheet is further injected into the steel sheet and heats the steel sheet by heat transfer by the impinging jet. The combustion exhaust gas whose temperature has decreased after heating the steel sheet is discharged from gas outlets (not shown) provided on the upper and lower surfaces of the member 64 facing the steel sheet S, and returns to the exhaust pipe 40 via the return pipe 45.

A pair of seal rolls 60 and 71 are arranged near the inlet 62 and the outlet 69 of the heating device 30, respectively, between the inlet 62 and the seal roll 60 and between the outlet 69 and the seal roll 71. In addition, seal members 61 and 70 for preventing the combustion exhaust gas from flowing out of the heating device 30 are provided. In the vicinity of the sealing members 61 and 70 and the sealing rolls 60 and 71, a sealing device 63,
72 are provided.

Since the heating device 30 is configured as described above, the outflow of the combustion exhaust gas to the outside of the heating device can be minimized, and the combustion exhaust gas can be circulated and used. Can be used efficiently.

In this apparatus, a zinc-based metal or alloy is hot-dip plated as follows. That is, as described above, the hot-rolled steel sheet S fed from a coiler (not shown) is circulated through the combustion exhaust gas, and
Then, the steel sheet S is immersed in the acid solution stored in the pickling tank 32 immediately after the heating to descaling. Next, the descaled steel sheet S is heated in a non-oxidizing furnace 36 using a high-temperature combustion gas obtained by burning a fuel gas such as a coke oven gas, and then heated to a predetermined annealing temperature in a radiation tube heating furnace 37. Then, it is cooled in a cooling furnace 38, and is subjected to predetermined hot-dip plating in a plating tank 39.

If necessary, when the steel sheet is immersed in the acid solution, the steel sheet is heated to a temperature range in which the acid solution becomes a nucleate boiling state or a film boiling state, or the dimensions of the steel sheet to be charged,
The heating temperature of the steel sheet can be controlled according to the steel sheet speed.

In particular, when the heating temperature of the steel sheet is in a temperature range in which a nucleate boiling state can be obtained when the steel sheet is immersed in the acid solution, bubbles are generated on the surface of the steel sheet by the immersion in the acid solution, and scale destruction is promoted. In addition, since the flow of the acid solution is promoted and a decrease in the dissolution rate of the scale is prevented, the above-mentioned effects are more excellent. The temperature of the steel sheet in such a state is 100 to 300 ° C. in the case of pickling with hydrochloric acid, and more preferably 150 to 300 ° C.
To 200 ° C., and the temperature of the acid solution is 80 to 90 ° C.
C is preferred.

When a steel sheet heated to a temperature higher than the acid solution is immersed in the acid solution, a thermal shock is generated due to a temperature difference between the steel sheet and the acid solution. Even if it does not fall off from the interface with the surface, cracks will be generated inside the scale and it can damage the scale from the initial stage of immersion,
The descaling speed increases, and the pickling tank can be made compact. Further, since the heating device provided in the horizontal path is installed in the space below the structure of the pickling tank, there is no increase in the line length due to the provision of the heating device.

As a high-temperature combustion exhaust gas from a heating furnace, which has not been effectively used in the past, is used as a heat source for heating the steel sheet to a temperature higher than the acid solution, the heating cost can be reduced.

Conventionally, since the temperature of the combustion exhaust gas discharged outside exceeds the allowable temperature limit of the exhaust blower 41, the dilution air is supplied from the dilution air supply pipe 49 to the exhaust pipe 40 using a blower (not shown). After being supplied and the temperature of the combustion exhaust gas was lowered to the heat-resistant temperature of the exhaust blower 41 or lower, the exhaust gas was discharged outside. In the apparatus of FIG. 1, the temperature of the flue gas is reduced by circulating the flue gas and heating the steel plate in the middle of the exhaust pipe 40, so that the dilution air is not supplied to the exhaust pipe 40, or Only by supplying a small amount of dilution air, the temperature of the combustion exhaust gas can be made lower than the heat resistant temperature of the exhaust blower 41. That is, since the increase in the exhaust capacity of the exhaust blower 41 can be suppressed to a minimum, there is an effect that the load on the exhaust blower 41 can be reduced.

In the apparatus shown in FIG. 1, an induction heating device 31 may be provided between the heating device 30 and the pickling tank 32. In the present invention, the induction heating device 31 is not essential, but if strict control of the temperature of the steel sheet immersed in the pickling tank 32 is required or if the annealing furnace has a low combustion load, the combustion exhaust gas temperature is low. In a case where the heating device cannot heat the steel plate to a predetermined temperature, the induction heating device 31 may be provided as necessary, and the steel plate may be heated together with the heating device 30.

In the apparatus shown in FIG. 1, the flue gas of the furnaceless oxidation furnace was directly circulated, but the gas to be circulated was not only the flue gas of the furnaceless oxidation furnace, but also the flue gas of the radiant tube heating furnace. The flue gas of the annealing furnace can be used. In addition to directly circulating the combustion exhaust gas, another gas heated by heat exchange with the combustion exhaust gas may be circulated.

Further, a recuperator for preheating combustion air of fuel gas used in a non-oxidizing furnace, a radiation tube type heating furnace, or the like can be provided in the middle of the exhaust pipe 40.

In the apparatus shown in FIG. 1, it is desirable to install a water washing tank and a neutralization tank as a post-treatment for pickling in the pickling tank 32. Further, an alkali degreasing tank may be provided as a post-treatment of the pickling tank 32.

Next, another embodiment of the present invention will be described. FIG. 4 is a schematic configuration diagram showing a hot-dip plating facility for explaining another embodiment of the present invention. The apparatus in FIG. 4 has the same configuration as the apparatus in FIG. 1 except that the pickling tank 32 in FIG.

The acid solution spraying device 33 can spray the acid solution onto at least one surface of the steel plate immersed in the pickling tank 32, and can adjust the flow rate of the acid solution to be sprayed. Has become.

By providing the acid solution injection device 33,
Further, the following operation and effect can be obtained. By injecting an acid solution from the acid solution spraying device 33 to the steel plate immersed in the pickling tank 32, a boiling film or bubbles generated in a nucleate boiling state or a film boiling state can be discharged out of the system. Even when the heating temperature does not reach boiling, the scale in which cracks have occurred due to thermal shock can be quickly removed, so that the dissolution of the scale can be promoted and the remaining smut after pickling can be further reduced.

When the operating speed fluctuates, for example, in the case of a change in the size of a steel sheet, the time of immersion in the pickling tank fluctuates and the descaling state fluctuates. By adjusting the pickling rate, an optimal descaling state can be obtained, and a steel sheet having better plating quality can be obtained.

[0049]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus shown in FIG.
3 mm x width of 1250 mm, line speed: 46 mpm (efficiency of 62 t / h), and the temperature on the inlet side of the heating device 30 (T
5) After heating the hot-rolled steel sheet at 30 ° C. so that the outlet temperature (T6) of the heating device 30 becomes 170 ° C., pickling is performed.
Next, the energy reduction effect of the present invention when hot-dip plating is performed after predetermined annealing in a non-oxidizing furnace or a radiation tube heating furnace will be described. Gas temperature T in the following description
1 to T6 and gas flow rates Q1 to Q4 correspond to the reference numerals shown in FIG.

The temperature (T1) of the combustion exhaust gas discharged from the non-oxidizing furnace to the exhaust pipe 40 is 700 ° C., and the gas flow rate (Q
1) is 10300 Nm ³ / h.

The steel plate is heated from 30 ° C. to 170 ° C.
Circulating gas flow rate (Q3) required for heating to 3750 is 3750
Was 0 nm ³ / h, in this case, combustion exhaust gas temperature of the heating apparatus the secondary side (return pipe 45) (T4) is 350 ° C., flue gas temperature after merging at the merging point B, ie, the heating device primary (supply The flue gas temperature (T3) of the pipe 44) is 420 ° C.
Became. The gas temperature (T2) discharged outdoors is lower than the gas temperature (T3) 420 ° C. on the take-out pipe 45 side, so that the supply of dilution air is not required. In this case, the required power of the exhaust blower 41 is about 42 kW.

On the other hand, in the case of the conventional method in which the combustion exhaust gas is directly discharged to the outside without being used for heating the steel sheet, the flow rate (Q4) is reduced to about 8100 Nm ³ /
h of normal temperature dilution air is supplied from the dilution air supply pipe 49 into the exhaust pipe 40, and the total flow rate (Q2) is 18400N.
The exhaust gas of m ³ / h is discharged outside using the blower 41. In this case, the required power of the exhaust blower 41 is about 75 k
W.

In the method of the present invention, 102.3 × 10 4 kc
Since the energy of al / h can be recovered and the supply of the dilution air is not required, the required power of the exhaust blower 41 can be reduced by about 40%.

[0054]

According to the present invention, the descaling process of a hot-rolled steel sheet, which is usually performed, is incorporated into a continuous hot-dip galvanizing line to reduce the production cost and to reduce the pickling speed. To solve the problems of the conventional technology, that is, the problem that the part becomes long and that plating defects occur due to the remaining smut after pickling, enabling high-speed pickling with compact equipment, reducing operating and equipment costs. It is possible to manufacture a hot-dip coated steel sheet that is less expensive and has excellent plating quality.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a hot-dip plating facility according to an embodiment of the present invention.

FIG. 2 is a diagram showing a main part of a heating unit of the hot-dip plating equipment shown in FIG.

FIG. 3 is a view showing a gas jet nozzle of a heating unit of the hot-dip plating equipment shown in FIG.

FIG. 4 is a schematic configuration diagram showing a hot-dip plating facility according to another embodiment of the present invention.

FIG. 5 is a schematic configuration diagram showing a conventional hot-dip plating facility.

[Explanation of symbols]

 Reference Signs List 30 heating unit (heating device) 31 induction heating device 32 pickling tank unit (pickling tank) 33 acid solution injection device 34 continuous hot-dip plating device 35 annealing furnace 36 non-oxidizing furnace 37 radiation tube soaking furnace 39 hot-dip plating bath 40 Exhaust pipe 41 Exhaust blower 46 Circulating blower 48 Thermometer 67 Gas jet nozzle S Hot rolled steel plate

Claims (1)

[Claims] 1. A continuous hot-dip plating facility having an annealing furnace;
A heating unit provided with a gas jet preheater disposed on the inlet side thereof and utilizing combustion exhaust gas of an annealing furnace, and a pickling bath provided between the heating unit and the continuous hot-dip plating equipment, in which a steel sheet is immersed. A hot-dip steel sheet hot-dip plating facility comprising a tank section.