JPH0621331B2 - Bottom dross winding method and device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for suppressing bottom dross winding in hot dip galvanizing, especially hot dip galvanizing.

(Prior Art) As is well known, in North America and Canada, road salt is sprayed to prevent roads from freezing in order to prevent a car slip accident in winter.

However, due to the rock salt spraying, the car body is exposed to a severe corrosive environment from the viewpoint of corrosion, and a surface-treated steel sheet having high corrosion resistance is being used in terms of material. Therefore, an alloyed steel sheet, which has the same weldability and workability as that of a cold-rolled steel sheet and has excellent corrosion resistance, has attracted attention as a steel sheet for exteriors. In addition, materials with increasingly stringent specifications are being demanded, such as the need for sharpness for exterior applications.

By the way, in a hot-dip galvanizing line, for example, a hot-dip galvanizing line, a normal hot-dip galvanized steel sheet in the as-plated state and an alloyed steel sheet (galvanneale steel sheet) that undergoes an alloying treatment after plating are manufactured. This 2
Steel sheets of various types are continuously manufactured by appropriately switching in the same line.

However, in the hot dip galvanizing tank that manufactures galvannealed steel sheets, the Al in the tank is kept low, so
Fe is eluted to form dross containing FeZn ₇ as a main component, and the dross is deposited on the bottom of the plating tank.

FIG. 3 is an explanatory view of how bottom dross is generated and wound during such hot dip galvanizing, and the strip 14 sent to the plating tank 12 via the snout 10 is shown.
Is plated while circulating around the sink roll 16, and after the plating is completed, it is taken out from the plating tank via the guide roll 18.
The dross floating in the plating bath gradually accumulates at the bottom of the plating tank to form a bottom dross 20. Part of the floating dross combines with Al in the bath and floats as top dross 22 on the bath top.

The bottom dross thus deposited is wound up in the bath by the accompanying flow of the strip near the bottom of the sink roll and adheres to the upper surface of the strip.

As mentioned above, when the specifications for plated steel sheets have become stricter, when such bottom dross adheres to the strip, not only surface unevenness called press butts occurs at the time of pressing, but not only the sharpness is impaired. As a result of the formation of a non-uniform portion called a dross spot, a local defect is formed and a surface defect that causes deterioration of corrosion resistance occurs,
This causes quality defects in the plated steel sheet.

Conventionally, in order to prevent the dross from adhering to the strip, a general method of suppressing the formation of bottom dross is to enrich the Al content in the plating bath and float and recover Fe ₂ Al ₅ as top dross by the following reaction. is there.

2FeZn ₇ ＋5 Al → Fe ₂ Al ₅ ＋ 14Zn (Problem to be solved by the invention) However, since Al has an action of suppressing alloying of the plating film, it is possible when the object of production is an alloyed steel sheet. Since the amount is limited to the smallest possible amount, when Al is added to promote floating of the top dross, a part of the Al remains in the plating bath, causing poor alloying and causing a problem of quality deterioration.

In particular, as already mentioned, from the current situation that the surface properties such as excellent image clarity are required even in the alloyed steel sheet, there is a strong demand for a means capable of preventing dross adhesion by means not involving addition of Al. There is. Furthermore, if there is no method for discharging bottom dross out of the system, bottom dross may gradually accumulate and eventually come into contact with the plated steel sheet and adhere to the surface thereof, which may also cause quality defects on the surface of the plated steel sheet. is there.

Thus, the object of the present invention is to solve the above problems in producing an alloyed steel sheet, and finally to produce a steel sheet having excellent plating appearance and corrosion resistance, and a method and apparatus for suppressing winding of bottom dross. The purpose is to provide.

Further, a more specific object of the present invention is to produce an alloyed steel sheet under conditions of low Al concentration in the plating bath, particularly an alloyed steel sheet having excellent image clarity, in order to produce an Al in the plating bath during treatment. An object of the present invention is to provide a method and an apparatus for suppressing the bottom dross from winding on a plated steel sheet without significantly increasing the concentration.

(Means for Solving the Problems) The inventors of the present invention suppress the winding of bottom dross based on the results of hydrodynamic studies to achieve the above-mentioned object, and reduce the adhesion of dross to the strip. Therefore, various investigations were repeated and the following findings were obtained.

It is difficult to control the occurrence of bottom dross itself.

Bottom dross adherence is based on the generation of wake associated with the running of the strip in the plating bath.

By providing a shielding plate between the sink roll and the bottom of the plating bath, such a flow of the plating bath is effectively suppressed.

The bottom dross is generated near the snout part, and even if such a shielding plate is provided under the sink roll, bottom dross does not accumulate on it, and the flow under the sink roll is fast and does not accumulate on the shielding plate. .

The inventors of the present invention have made extensive studies based on the findings shown below and completed the present invention.

Here, the gist of the present invention is, when performing the molten metal plating, between the sink roll and the molten metal plating tank bottom portion immersed in the plating bath in the molten metal plating tank,
A method for suppressing bottom dross winding in a molten metal plating tank, which is characterized in that a shield plate that suppresses the flow of a plating bath from below the sink roll is mainly arranged to suppress an increase in bottom dross accumulated at the bottom of the plating tank.

According to a preferred aspect of the present invention, a space in which bottom dross can be deposited is left below the shielding plate, and the bottom dross generated in the plating tank is accumulated around the shielding plate around the shielding plate. .

Further, in the above-described present invention and the preferred embodiment of the present invention, it is effective to add Al to the bath at the time of stoppage and at the same time blow N ₂ to float the bottom dross and discharge it from the bath. That is, by injecting a Zn ingot containing Al into a low Al bath in which bottom dross has accumulated and blowing N ₂ at the same time, the reaction of 2FeZn ₇ + 5Al → Fe ₂ Al ₅ + 14Zn proceeds promptly and the bottom dross rises. To take advantage of that.

From another aspect, the present invention provides a flow of the plating bath mainly from below the sink roll, which is disposed between the sink roll immersed in the plating bath in the molten metal plating bath and the bottom of the molten metal plating bath. A bottom dross roll-up suppressing device for a molten metal plating tank, comprising a shielding plate for suppressing the rise of bottom dross accumulated at the bottom of the plating tank.

The shape of the shielding plate may be a curved surface that is convex downward in the lower position of the sink roll, or a substantially horizontal plane, and the shielding plate may be a metal plate to be plated on a plating tank. The entrance side azimuth and / or the exit side azimuth may be configured to have inclined surfaces each having an inclination in the same direction.

Further, the bottom dross winding suppressing apparatus according to the present invention described above, it is effective to install a N ₂ inlet tube for blowing N ₂ into the plating bath which is Al enriched during stop machine.
By installing the N ₂ blowing tube in this way, the Al concentration in the bath can be increased by, for example, introducing a Zn ingot containing Al at the time of stop, as described above. 2FeZn ₇ + 5Al → Fe ₂ Al ₅ Using the reaction of + 14Zn, the bottom dross (FaZn ₇ ) is converted to Fe ₂ Al ₅ and floats on the surface of the bath, and if it is discharged to the outside of the system by a normal method, the bottom dross accumulated at the bottom of the main pot is discharged to the outside of the system. it can. At this time, N ₂ which is an inert gas is added to accelerate the reaction.
If it is blown at the same time as the Zn ingot is charged, it can be discharged in a short time. Further, the influence of the product can be avoided if the amount of Al to be added is such that the reaction is completed.

Examples of the above-mentioned hot metal plating include hot-dip zinc plating, hot-dip aluminum plating, lead plating, and lead-tin alloy plating, but are not limited to particular ones.

(Operation) Next, the present invention will be described in more detail with reference to the accompanying drawings.

2 (a), 2 (b), 2 (c), and 2 (d)
FIG. 4 is a schematic explanatory view of a bottom dross roll-up suppressing device equipped with a shielding plate according to the present invention.Each shielding plate is considered to be U-shaped, Z-shaped, inverted Z-shaped, or flat plate-shaped as shown in the drawings, Various other modifications are conceivable, but it is understood that all of them are within the scope of the present invention as long as they do not violate the above-mentioned spirit.

In each drawing, the strip 14 entering the plating bath goes around the sink roll 16 and is pulled up again, but the shielding plate 30 is installed below the sink roll 16. That is, when there is no shielding plate, the bottom dross 20 accumulated on the bottom of the bot by the strip adjoint flow is wound up as shown in FIG. 3, and is narrowed by the sink roll 16 and the strip 14 at the broken line portion A, and the strip plating layer is formed. Although it is pushed into the inside and becomes a dross defect, in the present invention, the influence of the accompanying flow due to the traveling of the strip 14 is shielded by the shielding plate 30 and is greatly reduced, and the bottom dross (Fig. Since it does not affect (not shown), the winding of the bottom dross is greatly reduced, and the occurrence of dross defects is suppressed.

As described above, it is effective that Al is added to the bath and N ₂ is blown at the same time as the bottom dross is floated and discharged from the bath when stopped.

Thus, according to the present invention, by installing various shielding plates,
The amount of bottom loss can be reduced by 50-80%,
At the time of stoppage, it is possible to constantly suppress dross defects by alternately repeating the work of enriching Al and discharging bottom dross itself out of the system.

(Example) Here, a preliminary experiment example and an example of the present invention will be described.

Preliminary Experiment Example Using the device schematically shown in Fig. 1, the effect of suppressing the winding of various shield plates was investigated by a 1/3 water model experiment in which the hydrodynamic similarity condition with the actual plating tank was taken into consideration.

This experiment using the water model was performed as follows.

As shown in Fig. 1, a container 32 corresponding to a plating tank is filled with water, and acrylic powder (specific gravity 1.2, average diameter 250 μ) is attached to the bottom.
m) 80 kg / 1.4 m ³ was raised, the strip 34 was loaded from the snout portion 33 provided on the upper part of the bath, the sink roll 35 was orbited, and then it was pulled out of the bath through the guide rolls 36, 36. A suction sampling tube 37 is arranged above the area where the strip 34 contacts the sink roll 35, the bath is sucked from the surroundings, and the filtration installation 40 is provided with the amount of acrylic powder wound up due to the accompanying flow generated as the strip runs 40. It was detected by measuring the concentration of the filtration treatment.

FIG. 1 shows an example in which a U-shaped shield plate is installed. An experiment was conducted by replacing the Z-shaped, inverted Z-shaped, and flat plate-shaped shield plates shown in the figure with the U-shaped shield plate. For comparison, the winding amount was evaluated when the snout length was a normal length and when it was extended.

That is, about 500 cc was sampled from a portion immediately above the strip 34 immediately before the sink roll 35, and after the filtration treatment, the weight was measured to evaluate the winding amount.

As a comparison standard for the shielding plate at this time, one with a normal snout length The one with the snout extended to the upper tangent of the sink roll A rectangular plate folded into a Z shape (the lower tangent and edge of the sink roll are Contact) A structure in which a rectangular plate is folded in an inverted Z shape (the reverse structure) A rectangular plate is folded in a U shape and has a structure in which the center and the edge of the sink roll are in contact with each other. Was placed at the same position as the center of the Z-shape, and a combination with a shield was used.

The results of some of the tests are summarized graphically in FIG.

The winding amount changes with time as shown in Fig. 4 by way of example.
The data after 40 minutes was adopted as the comparison data, because it becomes almost constant in minutes.

As a comparison standard, the effect of each shielding plate was compared in relative value, with the winding amount at the snout normal length (without shielding plate) being 100%.

Table 1 shows a summary of these results. As is clear from Table 1, the Z-type shielding plate exhibited a remarkable effect of suppressing winding.

The accumulation of bottom dross when using the Z-shaped shield was changed from the hollow shape shown in FIG. 3 to a flat shape as shown in FIG.

In this way, by installing various shielding plates directly under the sink roll by the water model considering the hydrodynamic similarity condition, the winding amount can be suppressed by 50 to 90%.

Example 1 In this example, the actual hot-dip galvanizing bath shown in FIG. 5 was used, and the Z-shaped shield plate 30 was placed at the dimensional position shown in FIG.

The other shields were also placed as in the case of the water model and data was collected.

The operation mode was limited to GA operation where the Al concentration of the plating bath was 0.10% and the actual value was 0.09 to 0.11%. After the plating was completed, the number of dross adhered on the surface was examined by setting the sampling area to the plate width x 500 mm. . In this case, the front side means the pushing side of the sink roll.

The number of N was 50, and the data was compared by simple average.

The test results are summarized in Table 2.

Furthermore, by using the Z-type shielding plate that has obtained the best results in the water model in the actual machine, the amount of dross adhered is the dross steel plate on the steel plate, and the number of press pits generated is the number of double-sided press pits when performing 100 ton press. Measured and investigated. Test method No. 5
The results are shown in Tables 3 and 4. It can be seen that the effect is reduced to 1/3 in both cases compared to the case without the Z-type shield.

Example 2 In a production line in which bottom dross is likely to be deposited, in which the manufacturing ratio of galvannealed steel sheets (GA steel sheets) is about 60%
At the time of stoppage, the operation of enriching Al and blowing N ₂ and discharging bottom dross was performed, and the results shown in FIG. 6 and Table 5 were obtained.

Test conditions: Concentration in Al bath before test: 0.10% Zn pot capacity: 160 tons Input Zn amount: 2 tons (containing 10% Al) The present invention enabled steady suppression of dross defects. 87% of the sedimented bottom dross was removed at about 1.5 hr.

(Effects of the Invention) According to the present invention, reduction of dross adhesion, which has been the greatest quality problem of hot-dip galvanized alloy-treated steel sheet for exterior, is achieved by hydrodynamic means without changing Al concentration or significantly increasing it. It turns out that the effect of being able to achieve is achieved.

Especially, the Z-type shield plate can reduce the bottom loss adhesion by 80 to 90%. In addition, the dross can be floated and discharged by blowing N ₂ when the engine is stopped, resulting in long-term operation, which is extremely beneficial to the industry.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of a test procedure of a water model of the method of the present invention; FIGS. 2 (a), (b), (c) and (d) are schematic diagrams of a bottom dross winding suppression device according to the present invention, respectively. Explanatory diagram; FIG. 3 is a schematic explanatory diagram of various dross generation situations; FIG. 4 is a graph collectively showing the results of the examples of the present invention; and FIG. 5 is a shielding plate in the examples of the present invention. FIG. 6 and FIG. 6 are illustrations of the relationship between the change in Al concentration in the bath and the reaction time.

Claims (7)

[Claims] 1. When performing the molten metal plating, a flow of the plating bath mainly from below the sink roll is provided between the sink roll immersed in the plating bath in the molten metal plating bath and the bottom of the molten metal plating bath. Place a shielding plate to suppress,
A method for suppressing rolling up of bottom dross in a molten metal plating tank, characterized by suppressing an increase in bottom dross accumulated at the bottom of the plating tank. 2. The method for suppressing winding of bottom dross according to claim 1, wherein a space where bottom dross can be accumulated is left below the shielding plate. 3. At the time of stoppage, Al is added to the bath and at the same time N ₂ is blown up to float the bottom dross and discharge it from the bath. Suppression of bottom dross winding in the molten metal plating tank according to claim 1 or 2. Method. 4. A shield plate arranged between a sink roll immersed in a plating bath in a molten metal plating bath and the bottom of the molten metal plating bath, which mainly suppresses the flow of the plating bath from below the sink roll. A bottom dross roll-up suppressing device for a molten metal plating bath, comprising: 5. The bottom dross roll-up suppressing device according to claim 4, wherein the shape of the shielding plate is a curved surface that is convex downward or a substantially horizontal plane below the sink roll. 6. The shielding plate further comprises inclined surfaces each having an inclination in the same direction in the entrance direction and / or the exit direction of the metal plate to be plated into the plating tank. 5. The device for suppressing bottom dross winding according to item 5. 7. The bottom dross roll-up suppressing device according to claim 4, wherein a N ₂ blowing pipe for blowing N ₂ into the Al-enriched plating tank at the time of stoppage is installed.