JPS5810984B2 - Hot dip metal plating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing roll coating of single-sided or double-sided hot-dip galvanized steel sheets.

Furthermore, as will be clear from the detailed description, metals with relatively low melting points, such as aluminum, lead, tin, or alloy plating thereof, can also be employed as the molten metal of the present invention.

Further, zinc-iron alloy plating is also possible by optimizing the temperature range of the copper strip to be coated or the temperature range of the copper strip after being coated, and therefore all of these are included within the scope of the present invention.

There are many methods for producing hot-dip galvanized steel sheets, but all methods for continuous hot-dip galvanizing copper strips, which are mass-production equipment, involve immersing a cleaned steel strip in a hot-dip zinc bath and raising it in a row to remove the molten metal that adheres to the surface of the steel sheet. This method involves squeezing the zinc layer to a predetermined thickness.

Apply molten zinc that has adhered to the copper strip to an arbitrary thickness (zinc adhesion amount)
Methods to control this are to use rolls to squeeze the molten zinc adhering to the steel strip rising from the molten zinc bath, or to direct superheated steam or gas onto the steel strip from a slit-shaped nozzle. The method of spraying and squeezing is widely used.

The disadvantages of the conventional galvanizing method are as follows: 1. The hot-dip zinc bath requires a large amount of zinc, for example around 100 yuan, so the bath becomes extremely large, requiring a large amount of space and an extremely strong foundation.

Further, heating and temperature control of molten zinc requires a large amount of cost.

2. Since the amount of molten zinc is large, it is difficult to change the soluble components such as aluminum in the bath, and it takes a long time.

3 The line speed that can be plated is usually 12
The maximum speed is about 0 m/min, and about 160 m/min for the gas wiping method, and if the speed is higher than that, the molten zinc will scatter violently.

4. When manufacturing a so-called single-sided galvanized steel sheet in which only one side is galvanized and the other side is the iron side, it is necessary to physically shield only one side corresponding to the iron side from molten zinc. Special ingenuity and equipment are required.

The present invention provides a method for overcoming the disadvantages of the conventional method, the characteristics of which are to allow a moving copper strip to uniformly deposit a predetermined amount of molten zinc on the surface of a coating roll;
The present invention then relates to a method of bringing the coating roll into contact with a steel strip to be plated to obtain a uniformly plated steel sheet on one or both sides having a predetermined amount of zinc coating.

That is, in the first aspect of the present invention, coating rolls are provided horizontally on both sides or one side of a copper strip that moves diagonally upwardly and/or diagonally downwardly, and each coating roll is provided so that the steel strip to be plated is disposed around the coating roll. This is a method of plating both sides or one side of a steel strip by supplying molten metal to the coating roll, which is placed in contact with the steel strip in an arc shape or dot shape.

The equipment and location (position) to which the present invention is applied are hot-dip galvanizing equipment using an in-line annealing method, which is generally referred to as an oxidation furnace type or non-oxidation furnace type, or a dry type out-of-line annealing method, which is referred to as a wheeling type. It is most reasonable to apply it to the pass line of the steel strip in or near the molten zinc bath of Franks type hot dip galvanizing equipment.

Furthermore, the present invention has the advantage that its component equipment is extremely simple and space-saving compared to conventional methods, and generally CAL
It is also possible to obtain the effects of the present invention by installing it in the middle of a continuous annealing line for cold-rolled steel sheets or original sheets for electroplating.

The molten metal applied to the present invention is inevitably limited by the molten metal resistance of the coating roll, that is, corrosion resistance, the maintenance of dimensional accuracy of the coating roll at high temperatures, and the prevention of excessive molten metal adhering to the coating roll. It is something you receive.

Therefore, it is in a molten state at 900°C or lower and has a viscosity in the range of 10 to 1 centipoise, more preferably 2 to 5 centipoise.
Molten metals in the centipoise range are preferred.

Therefore, the main targets are zinc, aluminum, lead, tin, or alloys containing these as main ingredients with various additive elements.

The amount of molten metal lifted by the rotating roll can be approximated by the following equation, if the scattering of molten metal due to the centrifugal force of the roll is ignored.

However, k: constant μ: Viscosity (CP) (kg/m-5ec:) μ.

: Roll circumferential speed (m/sec) σ : Surface tension [
15eC2] ρ: Density (kg/m'') 9: Acceleration of gravity.

Therefore, the amount of molten metal lifted by the roll increases as the viscosity increases and as the roll rotation speed increases.

On the other hand, as the surface tension and density increase, the lifting amount decreases.

In the roll coating method of the copper strip according to the present invention, the moving speed of the copper strip is up to 500 m/min, usually 30-250 m.
/min, and therefore the maximum circumferential speed of the coating roll is also approximately the same.

For this reason, the weight of the molten metal lifted by the surface of the rotating roll increases rapidly as the peripheral speed of the roll increases7, causing various problems.

As an example of molten metal, the case of zinc will be explained with reference to FIG.

In Figure 1, the roll diameter is 310% and the roll body length is 4o.

The lower part of the 5 US 270-roll was immersed in a molten zinc bath with a bath temperature of 460 °C (immersion depth 50 mm).While maintaining the entire system in an atmosphere of 99% nitrogen gas and 1% hydrogen gas, the peripheral speed of the roll and the lift of the zinc were measured. This study investigated the relationship with quantity.

The amount of zinc lifted on the rotating roll surface is approximately 800g/m2
Until then, the zinc adhesion on the roll surface can be considered uniform.

This was determined from the appearance of the rotating roll and the sharpness of the pattern outline under a spotlight.

To uniformly deposit zinc on the roll surface, the roll comes into contact with the moving copper strip and transfers some of the zinc to the copper strip, creating a hot-dip galvanized steel sheet with a uniform zinc coating amount and coating appearance. It is indispensable for profit.

The amount of zinc lifted on the roll surface is 800g/m2 to 1600
Between g/m2, the molten zinc adhering to the roll surface gathers and forms dense parts and discrete parts.

When the zinc lifting amount exceeds about 16009/m, molten zinc begins to scatter from the rotating roll surface.

If one tries to pump up molten zinc with one roll, it is difficult to control the amount of zinc lifted by the roll into the above-mentioned tub at high speeds.

However, if a doctor roll or a doctor blade is combined with the roll that lifts molten zinc to reduce the amount of zinc deposited immediately after lifting, the amount of zinc deposited on the roll can be controlled as shown in Figure 17, and the amount of zinc deposited on the roll surface can be reduced. It was found that the amount of zinc deposited could be made uniform.

It is important that the doctor roll and doctor blade do not come into contact with or be immersed in the molten surface of the molten zinc.If they do, the squeezing action of the molten zinc will be severe
<Decreased, which is preferable.

When a doctor roll is attached to a roll that lifts molten zinc, the effect of the doctor roll is obvious up to a roll peripheral speed of tsom/min, but the effect tends to decrease when the roll peripheral speed exceeds 150 m/min.

In this case, if a doctor blade is attached to the doctor roll and the amount of zinc adhering to the doctor roll is reduced by the doctor blade, the effect will continue even if the roll circumferential speed exceeds 150 m/min.

If a doctor blade is attached to the roll that lifts molten zinc, the effect will be maintained up to the high speed range, or the cutting edge of the doctor blade will wear out, so it is more reasonable to combine the doctor roll with the doctor blade as an auxiliary means in the high speed range. It is true.

As mentioned above, the roll that lifts molten zinc also serves as a coating roll, and the basic usage of doctor rolls and doctor blades has been explained in detail, but the following combinations have been found to be useful as application forms: did.

The desired effect can be achieved by separating the rolls that lift the molten zinc from the coating hanger, and moving the molten zinc previously lifted by the rolls to the coating roll and bringing it into contact with the moving copper strip.

If the amount of zinc deposited on the surface of the coating roll becomes excessive,
Although the disadvantageous phenomenon described in Fig. 1 occurs, excessive zinc on the coating roll can be prevented by changing the roll diameter ratio of the molten zinc lifting roll and the coating roll, or by changing the contact pressure between these rolls. Adhesion can be suppressed.

In this case, in order to completely suppress excessive zinc adhesion to the coating roll up to the high copper strip speed range, one or more metaling rolls should be installed between the zinc lifting roll and the coating roll to prevent zinc movement. It is also effective to use an intermediate medium, to press a doctor roll to the coating roll, and to install a doctor blade on this doctor roll.This effect enables high-speed rotation of the coating roll, and also reduces the amount of trace amounts of zinc. Completely prevents scattering and further prevents scattering zinc from re-adhering to the roll.
It can prevent adhesion to moving steel strips, mechanical equipment, housings, etc.

All of the detailed explanations described above involve lifting molten zinc from a molten zinc bath using a roll and depositing the zinc uniformly on a moving copper strip to a predetermined plating thickness.

Therefore, the amount of molten zinc lifted by the rolls is determined by the dimensions of the equipment, the roll material, the immersion depth of the molten zinc lifting rolls in the molten zinc bath, and the roll rotation speed.

A simple method for maintaining a constant lifting amount of molten zinc is to supply a specified amount of molten zinc between a coating roll and a metering roll in contact with the coating roll.

By doing so, the supply of molten zinc can be carried out at any prescribed supply rate, regardless of the moving speed of the steel strip, the rotational speed of the rolls, etc., so that the variable factor 1) can be reduced, which is extremely convenient.

To supply molten zinc between the coating roll and the metering roll, there are two methods: pumping molten zinc with a zinc pump, etc.
Alternatively, molten zinc may be supplied from a molten zinc bath placed on the upper surface of the roll through a passage such as piping using gravity.

In this way, the roll coating method of the present invention has made it possible to rationally perform hot-dip galvanizing up to high speeds, but in principle the rotational direction of the coating roll is the same as the downward movement of the copper strip, which is the so-called natural coating method. It is.

It is important that a specified amount of molten zinc spreads uniformly over the surface of the moving copper strip, and for this purpose, it is necessary to ensure the wettability of the surface of the steel strip to the molten zinc.

In order to ensure this wettability, it is necessary to bring the moving copper strip into surface contact to increase the contact time between the surface of the steel strip and the molten zinc, or to bring the coating roll into contact with the moving copper strip with a slight slippage. It turned out that this can be overcome by

Therefore, it is desirable to arrange presser rolls and deflector rolls as necessary for this purpose.

A reverse coating method in which the direction of rotation of the coating roll is different from the direction of movement of the copper strip is also included within the scope of the present invention.

In this case, the effects of the doctor roll and doctor blade are the same as in the case of the natural coating method.

According to the inventor's experimental results, when a doctor roll or a doctor blade is not used and the roll circumferential speed ratio (roll circumferential speed/steel strip moving speed) is 0.5, the amount of molten zinc that adheres to the copper strip increases as the copper strip moves. 400g/m2 at a speed of 80m/min, same <40
In the case of m/min, it is 110 g/m2, and when the roll circumferential speed ratio is 1, it is about 800 g/m2 at a copper strip moving speed of 80 m/min, and 230 g/m2 at the same <40 m/min.

The amount of zinc deposited on the copper strip expected in the present invention is usually 10~
200g/m2, rarely 200-650g/r
In some cases, a zinc coating amount of ri' is required.

Since the reverse coating method has a higher rate of zinc transfer to the moving copper strip than the natural coating method, it is necessary to increase the burden on the doctor roll and doctor knife in order to keep the amount of zinc adhesion low, which is not efficient.

Therefore, the reverse coating method is an effective method when aiming for a thick coating, and the natural coating method is usually preferred.

By adopting the roll coating method according to the present invention, both single-sided plating and double-sided plating can be manufactured rationally and with compact equipment.

Further, using the same equipment, it is extremely easy to change from double-sided plating to single-sided plating, or from single-sided plating to double-sided plating, and can be changed in a short time.

If necessary, it is of course possible to use equipment exclusively for single-sided plating.

Next, the moving direction of the steel strip and the positional relationship of the coating roll will be described.

This point is particularly important when constructing a plating process using a roll coating method that can perform both single-sided plating and double-sided plating and can be quickly switched.

The moving direction of the copper strip in contact with the coating roll is related to the rotating direction of the coating roll, the installation position of the doctor roll or doctor blade, the roll coating mechanism such as the method of supplying molten metal, the method of supporting the plated copper strip, and the plating properties. do.

If the direction of movement of the steel strip is horizontal, there is no problem with the roll coating mechanism or the plating properties, but if the copper strip is moved horizontally on both sides for plating, there is a disadvantage that the plated copper strip cannot be supported. There is.

For example, in the case of zinc plating, if forced air cooling is performed from the plating temperature of 460°C to the solidification temperature of zinc of 420°C, the plate thickness is 1.
．． At a line speed of 200 m/mm and a line speed of 200 m/mm, a distance of about 15 m to the support roll is required after plating, which is unfavorable for operation because the copper strip is warped.

If the direction of movement of the copper strip is vertical, it is advantageous in terms of supporting the copper strip after double-sided plating.
Since the copper strip is suspended for more than 100 m, the vibration causes the copper strip to dance, which causes non-plating due to contact failure, especially in the subsequent roll coating, and causes defects in uneven plating thickness called chatter marks.

Furthermore, if the viscosity of the molten metal is low, a dripping pattern will occur, which is not preferable.

Due to the roll coating mechanism, the molten metal cannot be supplied to the coating roll at the bottom surface of the coating roll.
Requires special feeding method.

It has been found that in order to solve this disadvantage, the direction of movement of the copper strip can be made diagonally upward or diagonally downward.

In other words, if the direction of movement of the copper strip is set diagonally upward or diagonally downward, and the subsequent coating roll is installed on the surface on which the plated copper strip bends and rides, the unplated and coated thickness caused by the flapping of the steel strip due to the vibration mentioned above can be reduced. Uneven patterns can be prevented and sagging patterns can also be reduced.

Furthermore, when considering an entire continuous hot-dip plating line or when adding a roll coating mechanism to an existing line, it is often preferable to install the coating roll at a position where the copper strip is passed diagonally upward or downward. .

By making the direction of the steel strip move diagonally upward or downward, molten metal can be supplied to the coating roll by the simplest and most reliable method of immersing the lower surface of the roll in a bath.

Next, embodiments of the present invention will be described in detail.

FIG. 2 shows an example of an application of the present invention.

The steel strip 26 unwound from the payoff reel 21 passes through a non-oxidation furnace 22 and a reduction furnace 23 to have its surface cleaned and annealed, and then passes through an adjustment cooling zone 24 where the temperature is adjusted to the optimum temperature for the roll coating method. be done.

The shaded area 25 in the figure shows the location where the present invention is applied, and it may be applied at any location.

By optimally setting the ambient temperature in 25 and the steel strip temperature in 25, an alloying reaction between zinc and the copper strip can be carried out after galvanizing, and an alloyed galvanized steel sheet can be obtained.

FIG. 3 shows an example in which the present invention is applied to the lower part of the snout in FIG. 2, and for the sake of simplicity, shows an example of a single-sided roll coating method.

In the case of double-sided plating, points 5, 6, 7, 8, and 9 in FIG. 3 may be installed on the opposite side of the steel strip.

The steel strip 1 passes through the snout 14, the sealing roll 18, the bellows 2 and enters the housing 15, ie the roll coating system of the invention.

The traveling direction of the steel strip is adjusted obliquely by deflector rolls 3 and 4, and a predetermined amount of zinc coating is uniformly applied to one side of the copper strip by a coating roll 5, and the copper strip exits from the outlet opening 16 of the housing 15.

The lower part of the molten zinc lifting roll (pickup roll) 6 is immersed in the molten zinc surface of the molten zinc bath 7, and as the roll rotates, it lifts the molten zinc and uniformly applies a predetermined amount of molten zinc to the coating roll 5 on the roll surface. supply to.

The pickup roll 6 is driven by a motor, and furthermore, the pressure contact force with the coating roll 5 can be arbitrarily adjusted, and the roll position is variable so that it can be separated from the coating roll when unnecessary.

The metering roll 9 is equipment used when the above-mentioned zinc pumping and supplying method is not used. Molten zinc is supplied to the molten zinc stock container 8 by a zinc pump or the like, and the molten zinc is supplied from the 8 to the contact area between the metaling roll 9 and the coating roll 5. Coating roll 5 and metering roll 9 supplying
are each driven independently, and the amount of molten zinc that moves uniformly onto the surface of the coating roll depends on the contact pressure and circumferential speed ratio between the coating roll 5 and the metaling roll 9, and the container 8.
It can be adjusted by the amount of molten zinc supplied from.

Note that the container 8 is not indispensable, and is unnecessary if the amount of molten zinc supplied by a zinc pump or the like is always constant and the flow rate can be controlled arbitrarily.

In this case, the molten Zn bath 7 may be emptied and the pickup 6 may be brought into contact with the coating roll 5 to be used as a doctor roll.

The deflation cooler roll 4 and the restraining roll 10 are movable back and forth.

This is because if the shape of the copper strip to be coated is poor, it is necessary to shorten the arc length of contact with the coating roll.

Furthermore, if the surface cleanliness of the copper strip to be roll coated is rather poor, molten zinc may not be completely coated on the steel strip.

In this case, increasing the contact arc length is extremely effective, and the ratio of the peripheral speed of the coating roll to the moving speed of the copper strip becomes better as it deviates from 1.0.

However, care should be taken that if this speed ratio differs by a wide margin from 1.0, slip flaws will occur in the copper strip, which will have an adverse effect on the life of the coating roll.

The heating element 11 is a device for maintaining the temperature inside the housing at a specified temperature.

For example, in the case of hot-dip galvanizing, the temperature of the steel strip entering the housing is usually 400°C to 550°C, and the temperature inside the housing is also maintained at 450°C to 550°C.

Generally, this temperature is any temperature below 900° C. depending on the purpose of production.

The demand air inside the housing must be a non-oxidizing atmosphere.

For this purpose, for example, in Fig. 3, a mixed gas of 97 to 99% nitrogen and 1 to 3% hydrogen, preheated to 300 to 600°C, is supplied into the housing system from the gas injection hole 12. .

In addition, room temperature nitrogen gas is injected into the vicinity of the outlet opening 16 of the steel strip to cool the copper strip after plating and to prevent air from entering from outside.

The composition of the gas atmosphere within the housing and the gas supply system can be changed as desired depending on the purpose.

An example of application of the present invention will be shown with respect to A to H in FIG.

For simplicity, only the roll coating part according to the present invention is shown and the others are omitted.

In the figure, 5 is a coating roll 9, a metering roll 19, a doctor roll 1T is a doctor blade (doctor knife), 20 is a plate for the amount of surplus zinc, 8 is a container for the amount of zinc, 6 is a molten zinc lifting roll (pickup roll),
7 is a molten zinc bath, 3 is a deflector roll, 1 is a moving steel strip, a doctor blade (not shown), and 17 may be replaced by a slit-shaped nozzle for injecting gas.

The arrow indicates the direction of progress of the steel strip.

All figures show the case of double-sided plating, but when switching to single-sided plating, the Z
All you have to do is stop the supply of n.

In addition to the combinations shown in this figure, the effects of the invention can be obtained by using any combination of the coating units on one side of the copper strip (I to E) depending on the equipment, working conditions, etc.

FIGS. 5A to 5E show application examples of the present invention other than those described in detail so far.

For simplicity, the molten zinc supply section is omitted and only the coating roll is shown.

As shown in FIGS. 3 and 4, the method for supplying molten zinc that best matches the copper strip passage form and purpose of use may be adopted.

In FIG. 5, 10 represents a deflector roll, and 1 represents a coating roll.

By applying plating using a coating roll while moving the steel strip to be plated diagonally upward or downward,
Compared to vertical or horizontal movement, it reliably prevents poor contact between the steel strip and coating roll due to vibration of the copper strip, prevents quality deterioration due to poor contact, and supplies plated metal to the coating roll, for example, on the bottom surface of the roll. The simplest and most reliable method of immersing the plated metal in water can be adopted, making it easy to supply plated metal.

Furthermore, the amount of plating deposited can be accurately controlled, line speed can be improved, and productivity can be greatly increased.

Furthermore, it is possible to easily switch between double-sided plating and single-sided plating, and there is no need for a large-capacity plating bath, so the line space can be reduced.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the amount of zinc lifted onto the roll surface when the roll is partially immersed in a molten zinc bath and rotated. FIG. 2 is an example of a part for implementing the present invention, and shows the optimum location for implementing the present invention using in-line annealing continuous hot-dip galvanizing equipment. FIG. 3 is an explanatory diagram of an apparatus for carrying out the method of the present invention. Figure 4 I20, C, 2, Ho, Figure 5 I20, C. 2 and E are explanatory diagrams of other apparatuses for carrying out the method of the present invention. 1... Steel strip, 2... Bellows, 3... Deflector roll, 4... Stomach/deflector roll, 5... Coating roll, 6... Pick-up roll, 7... Molten Zn
Bath, 8... Zn stock container, 9... Metering roll, 10... Errosis suppressor roll, 11... Heating body, 12... Gas injection hole, 13... Nearby portion, 14... Snout, 15...
Housing, 16... Exit side opening part, 17... Doctor blade, 18... Sealing roll, 19... Doctor roll, 20... Surplus zinc receiver, 21... Payoff reel, 22... Non-oxidizing furnace, 23 ... Reduction furnace, 24 ... Adjustment cooling zone, 25 ... Place where the present invention is applied.

Claims (1)

[Claims] 1. Coating rolls are provided horizontally on both sides or one side of a copper strip that moves diagonally upward and/or diagonally downward, and each coating roll is arranged so that the steel strip to be plated contacts the circumference of the coating roll in an arc shape or a dot shape, A molten metal plating method comprising plating both or one side of a copper strip by supplying molten metal to the coating roll.