JPS5835590B2 - Finishing method and apparatus for hot-plating ferrous base metal strip with hot-melt coating metal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a finishing method and a finishing apparatus for a conventional continuous hot-dip coating process of a ferrous base metal strip with a molten coated metal, and more particularly to a finishing method and a finishing apparatus for a coated ferrous base metal strip. The present invention relates to a method and apparatus in which the strip, upon exiting the coating bath, is maintained in an essentially oxygen-free atmosphere until it is subjected to jet finishing with a non-oxidizing or inert gas.

The method and apparatus of the present invention are suitable for forming oxides on zinc, zinc alloys, aluminum, aluminum alloys, turn metal, lead, and other materials which cannot be produced to a satisfactory finish by conventional jet or conventional exit roll processes. It is applied to the hot-dip coating of ferrous base metal strips with coating metals or alloys.

Although not limited thereto, as an example of the method of the present invention, a case where it is applied to galvanizing will be described.

This method can be implemented in various types of galvanizing lines.

For example, the method of the invention requires a pretreatment to remove oxides from the strip surface and to heat the strip to a temperature close to that of the zinc or zinc alloy molten coating bath preferably through which the strip is immersed. Applied to fluxless hot-dip coating of plain metal strips.

One of the major types of in-line annealing fluxless pretreatment is U.S. Pat.
This is the so-called Sendzimir method or the oxidation/reduction method described in No. 622.

Another commonly used in-line annealing fluxless pretreatment method is U.S. Pat.
This is the so-called Ceras method or the high-density direct firing furnace method described in No.

In the Sendzimir process, a ferrous blank metal strip is heated in an oxidation furnace (which can be a direct firing furnace) to a temperature of about 370°C to about 485°C without atmosphere control, and then drawn out into air to brighten it. forming a controlled surface oxide layer with an appearance ranging from yellow to purple or blue; introduced into a reduction furnace containing an atmosphere consisting of hydrogen and nitrogen;
The material is heated therein from about 735°C to about 925°C to completely reduce the controlled oxide layer.

The material is then passed through a cooling section containing a protective reducing atmosphere, such as a hydrogen/nitrogen mixture, to bring it to about the temperature of the molten coating metal bath, and then the bath surface remains surrounded by the protective atmosphere. lead down.

In the Ceras process, a ferrous blank metal strip is passed through a direct firing preheating furnace section.

- Heating by direct combustion of a fuel/air mixture producing a combustion product gas containing at least about three combustibles in the form of carbon oxides and hydrogen.

The strip reaches temperatures of about 35°C to about 760°C while retaining a completely oxide-free bright surface.

This strip is then transferred to the reducing section.

The reduction section is in sealed relation to the preheating section and contains a hydrogen/nitrogen atmosphere.

Therein, the strip is further heated by a radiant tube to about 50 DEG C. to about 925 DEG C. and then cooled to about the molten coating metal bath temperature.

The strip is then guided below the surface of the bath while being surrounded by an insulating atmosphere.

Related pretreatment techniques other than those mentioned above are disclosed in U.S. Patent Re-Patent No. 2972.
No. 6, No. 3837790, No. 4123291, No. 4123292 and No. 4140
It is described in No. 552.

These related patents are but not limited to a few examples of fluxless continuous galvanizing methods to which the method of the present invention can be applied.

When using the strip preparation methods described in these prior art techniques, the green metal strip must be kept under a protective atmosphere until it is subsurface of the bath of molten zinc or zinc alloy.

Such a protective atmosphere is not necessary when using flux-type or chemical-type strip manufacturing processes of the type described in US Pat. Nos. 2,824,020 and 2,824,021.

Briefly, when using this type of chemical type strip manufacturing technique, a ferrous base metal strip is passed through a flux bath and means for ensuring the proper thickness of the Franks coating on the strip.

The strip is then introduced into a heating chamber in which the strip is heated to evaporate the moisture and produce a flux solution.

The strip is then further heated to a temperature close to the maximum stable temperature of the Franks coating on the strip.

The strip is then passed beneath the surface of a molten zinc bath or a hot lead alloy bath.

The method of the invention is also applicable to galvanizing lines using such flux-type or chemical-type pretreatment systems.

As is clear from the foregoing, the method of the present invention is not limited to the use of any particular pretreatment method for ferrous metal strips in a galvanizing line (hereinafter referred to as ferrous metal strips). The term ``pretreatment'' or ``pretreated'' (as used in connection with bare metal strip) should be broadly construed to include any conventional pretreatment system exemplified by the aforementioned prior patents. .

Generally speaking, during the actual coating step in which the strip is passed through a molten bath of zinc or zinc alloy, any suitable preparatory steps are taken to ensure that the strip has reached a suitable coating temperature and that no oxides are present on its surface. Refers to processing technology.

During conventional continuous hot dip galvanizing, the strip coated on both sides is typically exposed to the outside air from the hot dip coating metal bath.

The most widely used finishing/coating weight control technique involves passing the coated strip through the middle of multiple jet knives or jet nozzles that impinge jets of air or water vapor against both sides of the strip. Allow any excess coating metal to return to the bath.

However, this finishing technique has a number of critical drawbacks.

One drawback is the formation of floating scum on the surface of the bath.

The formation of such floating scum is accompanied by a large loss of zinc, and some of this scum is often carried along with the strip through the jet stream, leaving an obvious floating scum mass on the coated strip. resulting in surface defects.

Another common coating defect or non-uniformity associated with traditional jet finishing processes is often referred to as "coating ripple" or "ocean waves."

Coating ripple can be described as a wavy non-uniformity in the coating thickness in the machine direction (rolling direction) of the coated strip.

Coating ripple ranges from virtually zero to non-focal ripple, often referred to as "coating sag."

It is extremely difficult to completely remove coating ripples using normal jet finishing methods, and every minute
It is almost impossible to eliminate ripple at speeds below 5.5 m.

High speed coating methods, proximity of the jet nozzle to the strip, high aluminum content in the zinc bath, and minimal coating weight are methods that reduce the occurrence of coating ripple in conventional methods;
Even if coating ripples do form, they are smoother and less pronounced.

Another type of non-uniformity associated with hot dip galvanizing is what is commonly referred to as "flowering".

This flower pattern protrusion has two characteristics.

One aspect is the variation of the surface profile (zinc thickness) across the zinc crystal from one boundary to the other.

Another aspect is the recessed border surrounding each floral pattern or zinc crystal.

Both of these aspects are related to the dendritic solidification properties of the zinc coating.

- These flower patterns can be produced by intentionally alloying part of the zinc coating with the ferrous base metal, or by reducing the lead content of the zinc bath, or by adding antimony to the zinc bath. It can be reduced.

However, none of these methods is completely satisfactory.

As a result, many methods have been developed to inhibit the formation of floral patterns.

That is, in order to reduce the final flower pattern size to the extent that the flower pattern is almost invisible to the naked eye, for example, US Pat. No. 3,379,557
No. 3,756,844 describes a flower pattern reduction method.

Many methods include spraying water or an aqueous solution onto the coating to quench the molten coating and create multiple nucleation sites.

Although flower pattern reduction methods are effective in reducing flower pattern protrusions, this method has operational and maintenance drawbacks in its implementation, and the results obtained by these methods are not always consistent. Not yet.

Also, this flower pattern reduction method does not help at all to resolve ripple and floating scum defects caused by jet finishing.

Hot-dip coating non-uniformities such as those described above that exist in conventional jet finished zinc coatings can be masked, but not eliminated, by skin pass rolling.

Temper rolling causes non-uniformities to be etched into the base metal strip beneath the coating.

As a result of such non-uniform cold working of the base metal, these defects can reappear when precision surface items such as automobile body parts are stamped or formed.

Another important problem with traditional jet finishing methods is that
It is a matter of coating control at the edges of the strip.

One problem is that of the zinc coating thickness, which is a narrow band adjacent the edge of each coated strip.

This coating thickness is greater than the thickness of other parts of the strip width.

If this difference in coating thickness is large enough, an edge build-up or spooling phenomenon will appear when the continuous strip is wound under tension.

Yet another troublesome problem is that of edge grains (small balls of oxide) that stick to the edges of the strip and are pulled by the jet stream.

Additionally, there are edge defects commonly known as "wing oxides" in slow jet finishes.

This winged oxide consists of unevenly spaced patchwork-like pieces of a voluminous coated metal oxide pulled together by a jet stream.

These discrete patches are in the form of vanes extending inwardly from the edges of the strip with their tips directed toward the center of the strip.

Many methods have been used by many researchers in the past to alleviate build-up problems and oxide control problems at the strip edges.

Generally, a tapered jet nozzle slot opening is used, the slot opening having a width that increases continuously from the center of the jet nozzle to the ends.

A jet finishing nozzle with this shape is disclosed in U.S. Patent No. 413.
It is described in No. 7347.

Other methods of controlling edge coating include curving the nozzle so that it is closer to the strip at the strip edge than at the strip center.

Also, vanes or nozzle extensions were used at the strip edges to place the nozzles closer to the strip edges than to the center of the strip.

It further includes the use of shutters and auxiliary jets inside and outside the main jet nozzle to vary the wiping force at the edges of the strip relative to the jet wiping force at the center of the strip.

All conventional methods fail to provide optimal edge control with minimal operator attention, maximum savings in coating metal, sufficient edge control at low speed operations, and a wide range of Proper edge control in strip width cannot be achieved.

Still other problems with conventional jet finishing are coating weight and line speed issues.

The viscous interaction between the coating metal and the strip is proportional to the strip speed.

In the prior art, problems with ripple formation occurred at low speed operations.

As a solution, it was discovered that reducing the finishing jet flow rate would break up the oxide and distribute it more evenly.

However, the low finishing jet pressure and close placement of the jet nozzle to the strip create edge build-up problems.

Therefore, traditional researchers had to adjust parameters to control edge buildup and ripple, which required higher line speeds.

- As an example, practical class coating weight (ASTM
A325, G-90) It has been customary to use conventional jet finishing methods at strip speeds of just over 30 meters per minute.

G-90 coating (coating weight 275g/m
) edge build-up problem is typically 45.57 times per minute.
Occurs at strip speeds below 7L.

The minimum operating speeds for heavier coatings such as 5649/d (0185) are more severe and the edge-to-edge coating uniformity deteriorates as the coating weight increases.

Another practice in many prior jet finishing operations has been to place the jet nozzles in virtually directly opposite positions so that the jet streams directly interact beyond the edges of the strip.

As a result of such mutual interference of jet flows, the nozzle level became extremely high, which caused a problem.

If the jet nozzles are operated offset relative to each other, a wrap-around effect is created such that the last jet to act on the strip forms a bead of copious coating metal along the opposite edge of the strip. .

In addition to the nozzle problems and the need for the operator to accurately adjust the nozzles when operating jet nozzles located in opposite positions on both sides of the strip, one nozzle removes the coated metal from the edge of the strip. This creates the problem of droplets being blown off and entering the opening of the opposite nozzle.

Prior art has proposed jet finishing a strip with nitrogen that is hot dipped on both sides with zinc and aluminum.

However, such jet finishing methods are performed in air.

This jet finishing requires less nitrogen than air.

However, the results obtained with such finishing are closer to those of jet finishing methods carried out in atmospheric air than those obtained with the present invention.

US Pat. Nos. 4,107,357 and 4,114,563 and German Patent No. 2,656,524 illustrate methods for coating only one side of a ferrous blank metal strip.

In carrying out these methods, the coated strip in contact with the coating bath is maintained in a protective, non-oxidizing atmosphere and jet finished with nitrogen or a non-oxidizing gas.

However, the purpose of these steps is to prevent oxidation of the uncoated side of the strip, or, if the uncoated side is provided with an oxide film, to prevent adhesion of the coating metal to this oxide film. To prevent this.

If, in a conventional continuous hot-dip galvanizing process, the coated metal is surrounded by an enclosure as it exits the coating bath, and a substantially oxygen-free atmosphere is maintained within this enclosure; The present invention is based on the discovery that if the coated strip is jet finished with a non-oxidizing or inert gas, the problems found in conventional finishing methods are significantly reduced or eliminated. .

The finishing method of the present invention produces a very flat flower pattern, and the border protrusions of this flower pattern are so small that there is actually no need to use flower pattern reduction techniques to obtain excellent surface quality.

In addition, the amount of floating debris is greatly reduced, eliminating various problems associated with floating debris, and even during low-speed operation, the problem of ripples on jet finishing is eliminated.

Along with the significant reduction in floating scum formation, the loss of zinc associated with skimming the coating bath surface is also greatly reduced.

One of the most important aspects of the present invention is the discovery that by excluding oxygen from the finishing process, all coating control problems at the strip edges are completely eliminated.

In this case, the minimum operating speed is no longer limited by edge build-up problems, but only by the ratio of the desired coating weight to the coating metal weight pulled up by the strip to the finishing jet nozzle.

For example, it has been discovered that high quality coatings of 2r51/m can be readily produced at speeds as low as 9.1 m/min.

There are also no edge wrap problems, so the jet nozzle can be offset in line, eliminating the need for precise nozzle placement, greatly reducing noise, and eliminating the risk of zinc splash.

Simplify the jet nozzle design to ensure uniformity along the entire length.
Nozzles with wide slot-like nozzle openings can be used, eliminating the need for a variety of specialized jet nozzle structures, methods, and accessories that have been used for edge build-up control.

Also, because it is no longer necessary to provide a thicker coating in the center of the strip to compensate for large edges, a very uniform coating from edge to edge is obtained for the total coating weight.

Heretofore, neither the mechanism of ripple formation nor the mechanism leading to edge build-up problems when performing two-sided jet finishing was fully understood.

In traditional jet finishing methods, the air wall effect (pn
A eumatic wall effect) is created and the desired amount of coating metal is metered through the jet stream to form the finished coating.

At this metering point, excess coating metal lifted by the strip in excess of the required amount of finish coating is returned to the coating bath.

This process is described in detail in US Pat. No. 4,078,103.

Although the inventors do not wish to be bound by theory,
As a result of the present invention, it is assumed that coating ripple and heavy edge coating in conventional jet finishing are all caused by coating metal oxides.

No. 4,078,103 at a point in the jet interference zone, perhaps just above the zero surface velocity point.
As described in that patent, the unoxidized coating metal is exposed and forms a very thin oxide film upon exposure.

This continuous flow or distribution of a very thin oxide film over the finished coating is what determines the occurrence of coating ripple.

In conventional methods, the jet periodically limits the formation of the oxide film, but when the film has formed to such an extent that the jet can no longer limit the formation of the film, relatively large oxide fragments are removed. It breaks and this fragment goes with the finishing coat.

This fragment then entrains a larger amount of coating underneath than would be metered out when the oxide film was limited.

This process is repeated many times each time a ripple is formed.

A similar mechanism is believed to operate when large coatings are formed along the strip edges.

However, at the strip edge, there is no wiping force acting on the edge surface, so at the edge the geometry is
constitutes an important factor.

Relatively large oxides are passed through the jet interaction zone, more or less continuously entraining the large coating underneath.

Such an oxide envelope surrounding the surface of each strip edge forms an outer "container" that allows the molten zinc to wrap around the edge of the strip when the jet nozzle is vertically offset. container)
” work as.

Such coating non-uniformity is caused by oxides in the molten coating metal, and in the present invention, this non-uniformity is eliminated by preventing oxidation.

The galvanized products produced by the method of the present invention, after temper rolling, exhibit the highest quality suitable for use in exposed body panels of automobiles, equipment application parts and the like.

The method of the present invention is compatible with short-dip, shallow coating pots using partially immersed pot rolls.

According to the invention, a ferrous green metal strip is introduced into a molten coating metal bath contained in a coating pot, said strip being previously heated to a temperature sufficiently high and excessive to prevent casting of the coating metal on said strip. prevents alloying between coating metal and base metal,
a ferrous substrate coated on both sides as the strip exits said bath, subjected to a heat treatment to heat the strip to a coating temperature low enough to render its surface clean and free of oxides as it exits said bath; an enclosure for metal strip disposed in sealing relationship with said bath, an outlet for said coated strip in said enclosure, and a jet finishing nozzle for each side of said coated strip within said enclosure; In a finishing method of a coating process in which both sides of a ferrous base metal strip are continuously hot-dip plated with a molten coating metal, the coating process is of a type in which the coated strip is jet-finished with a non-oxidizing gas. maintaining a non-oxidizing atmosphere therein; and maintaining the jet finishing gas and the atmosphere within the enclosure at an oxygen level of less than about 200 Jm, thereby:
A finishing method is provided that prevents coating non-uniformity due to oxides in said strip coated on both sides.

A finishing apparatus according to the present invention for carrying out the method includes means for retaining a non-oxidizing gas within the enclosure at an oxygen level of about 200 pIIm or less and jet finishing the non-oxidizing gas at an oxygen level of about 200 pIIm or less. and means for supplying the nozzle.

Although the method of the present invention is not limited thereto, for purposes of illustration it will be described as applied to a Ceras type galvanizing line.

Referring to FIG. 1, the coating line is indicated generally at 1.

The strike IJ tube preparation furnace of this coating line includes a direct firing furnace 2, a controlled atmosphere heating furnace 3, a first cooling section 4, a second cooling section 5, and a snout 6.

The snout 6 has a shape that extends below the surface of a bath 7 of molten coating zinc or zinc alloy contained in a coating pot 8 .

The ferrous base metal strip 9 to be prepared is rolled into a roll 10
and 11, and enters the direct firing furnace 2 through the middle of the seal rolls 12 and 13.

These seal rolls are arranged to minimize the escape of combustion products from the inlet 14 of the preheating direct firing furnace 2.

The direct firing furnace 2 operates at a temperature on the order of 1260°C.

The function of the direct firing furnace is to rapidly burn off oil and the like from the surface of the ferrous metal strip and at the same time to carry out partial heating for strip annealing.

The furnace operating at said temperature heats the strip to a temperature in the range of about 535°C to about 760°C while the strip passes from the furnace to the controlled atmosphere furnace 3. would be sufficient.

The ferrous base metal strip 9 travels along the outer periphery of the winding rolls 15 and 16 and begins to travel upward within the controlled atmosphere heating roll 3.

Thereafter, the strip passes downward through the outer periphery of the winding roll 17 and passes through the furnace 3 again.

The controlled atmosphere furnace 3 can be of the radiant tube type and, depending on the nature of the IJ tube and its desired final properties, the temperature of this strip 9 can be kept at about 65°C.
The temperature is increased from 0°C to about 925°C.

The strip preparation furnace of coating line 1 can have one or more cooling chambers.

For purposes of illustration, the strip preparation furnace is shown as having two cooling chambers 4 and 5.

The strip 9 enters the cooling chamber 4 from the controlled atmosphere furnace 3 through the circumference of the winding rolls 18 and 19.

The cooling chamber 4 can be of a known tube cooling type.

In the illustrated embodiment, the ferrous strip 9 is connected to the cooling chamber 4.
It travels along the outer periphery of the winding rolls 20 and 21 within the interior of the shaft, making three vertical strokes.

The metal strip 9 then runs along the outer periphery of the winding rolls 22 and 23 and enters the second cooling chamber 5.

This cooling chamber can also be of the known jet cooling type.

The target temperature for cooling the iron strip 9 will depend on many factors.

Since the molten coating metal bath 7 in the coating pot 8 is zinc or a zinc alloy, the metal strip will preferably be cooled to about 450°C.

However, in some cases the strip itself can be used as an additional means for introducing heat into the molten coating metal bath 7.

In such a case, the metal strip 9 may be placed in this bath 7 at a temperature slightly higher than the melting point of the zinc or zinc alloy in the metal bath 7.
can be introduced.

If the strip 9 is not used as one heat source for the bath 7, the strip can be introduced into the bath at a temperature slightly below the bath temperature.

In any case, the temperature of the strip must be high enough to prevent casting of the molten coating metal thereon.

Similarly, the strip temperature should not be so high as to cause excessive alloying between the coating metal/base metal.

The ferrous base metal strip 9 advances from the cooling chamber 5 along the outer periphery of the winding roll 24 and enters the snout 6.

Note that the free end of the snout 6 is below the surface of the zinc or zinc alloy bath T.

The metal strip then runs downwards along the roll 25,
Enter the bath 7 below.

The strip exits the bath along a generally vertical track.
It is guided inside the bath by one or more coating pot rolls.

In the illustrated embodiment, a single coating pot roll 26 is shown.

The strip 9a coated on both sides leaves the molten coating metal bath 7 and enters the enclosure 2T.

The lower end of this enclosure enters the bath 7 and forms a seal with the metal bath.

The metal strip 9a coated on both sides is advanced between a pair of jet finishing nozzles 28 and 29.

As is clear from FIG. 1, the upper end of the furnace 2 is connected by a conduit 30 to an exhaust fan 31.

The outlet 32 of the exhaust fan 31 is directly connected to a chimney or waste gas heat recovery means (not shown).

By controlling the discharge rate of the combustion products leaving the direct firing furnace 2, the strip preparation furnace with the coating line can be operated at pressures above atmospheric pressure (in order to prevent the introduction of oxygen into its interior from the outside air). ).

For this purpose, a damper 33 can be placed in the conduit 30.

The parameters for operating the strip preparation furnace of coating line 1 do not constitute a limitation to the invention.

Now, referring to Figure 2, this figure shows the snout 6, coating pot 8, and enclosure 27 of Figure 1.
is shown enlarged.

Identical parts are designated by the same numbers.

In the embodiment of FIGS. 1 and 2, the snout 6 and enclosure 27 are shown as being completely separate structures.

However, it will be understood by those skilled in the art that enclosure 27 can form a component of snout 6.

Snout 6 if chemical/flux pretreatment is used
You can also remove it.

According to the method of the present invention, approximately 200 p.
A non-oxidizing atmosphere is maintained having an oxygen content of less than pffi, preferably less than about iooppm.

Any suitable non-oxidizing or active atmosphere can be used.

A nitrogen atmosphere is preferred because it is the most economical.

Jet nozzles 28, 29 can be used as the source of atmosphere inside the enclosure 27, although other atmosphere inlets such as the inlet 34 can be provided if desired.

A portion of the nitrogen atmosphere within enclosure 27 may be extracted and circulated through jet finishing nozzles 28 and 29.

This scheme is schematically illustrated in FIG.

The enclosure 27 includes an exhaust port 35 . This vent is preferably a hot back house 3 for collecting zinc oxide particles.
5a.

The atmosphere extracted from enclosure 27 is this back house 37
a to the heat exchanger 36.

This heat exchanger 36 is connected to the inlet 38 of the blower 39.
Connected at 7.

The purpose of this heat exchanger is to cool the nitrogen coming from enclosure 27 before blower 39 to prevent heating of the bearings and seals in the blower.

The back house 35a can be placed between the heat exchanger 36 and the blower 39, but in order to prevent the fins of the heat exchanger from being blocked by zinc dust,
It is preferable to place it in front of the heat exchanger.

Outlet 40 of blower 39 is connected to jet finishing nozzles 28 and 29 by conduits 41 and 42.

Conduits or lines 41 and 42 are provided with valves 43 and 44, respectively, to adjust the plenum pressure of jet finishing nozzles 28 and 29.

By using such a backhouse/heat exchanger/blower/sealed conduit system, 50% of the required amount of high-purity nitrogen can be reduced.
It has been discovered that more than φ can be circulated from enclosure 27 through jet finishing nozzles 28, 29 and in this way reduce nitrogen consumption.

Makeup nitrogen is introduced into the system through a conduit 45 connected to line 37 between heat exchanger 36 and intake 38 of blower 39 .

The atmosphere circulation rate is adjusted such that the coated strip 9a prevents the ingress of air through the slot 46 exiting the enclosure 27.

Jet nozzles 28 and 29 are arranged opposite each other on each side of the blank metal strip 9a, which is coated on both sides, as shown in FIG.

However, since the aforementioned edge problems, including the envelopment problem, have been solved by the method of the present invention, these jet nozzles 28 and 29 can be vertically offset relative to each other as shown in FIG. is preferred.

This can prevent nozzle clogging due to zinc splashing and blowing from one nozzle to the other, as described above.

Either jet knife can be placed above the other jet knife.

The higher of these two jet nozzles (in this case nozzle 28) may be located about 0.6 m or more above the bath.

Nozzles 28 and 29 can be vertically offset relative to each other by any desired amount.

Generally these jets are offset by 5 to 15.25 cIIL.

Typically these nozzles are within about 3.8 cm of the strip.

When the jet finishing nozzles are offset relative to each other, the noise level of the finishing steps produced by these nozzles is greatly reduced.

Jet nozzles 28 and 29 may be of simple construction with simply rectangular jet openings and no curved lips, shutters, vanes or other devices.

Excellent results were obtained using a jet finishing nozzle with a simple rectangular opening having a uniform width of 1.25-2.05 Ilit along its length.

The enclosure 27 is provided with an outlet opening or slot 46 in a ferrous blank metal strip 9a coated on both sides.

Care must be taken to ensure that outside air is not drawn through the slot 46 by the turbulent action of the high velocity gas acting near the slot 46 inside the enclosure 27.

If outside air is sucked through this slot 46, the enclosure 27
There will be excess oxygen inside.

Providing a baffle or separate nitrogen purge flow around the strip outlet 46 may help prevent such air aspiration.

However, excellent results have been obtained by simply providing a short chimney 47 with an outlet slot 46 at the top of the chimney.

The encapsulated finishing method of the present invention allows for short-dip, shallow coating pot coatings using partially immersed coating pot rolls.

This is because the method of the invention minimizes oxide formation on the surface of the bath and on partially immersed pot rolls.

Such a method has many advantages.

First of all, small coating baths can be used.

Furthermore, by greatly reducing the immersion depth and immersion time of the ferrous base metal strip, the amount of iron leached from the ferrous base metal strip into the coating metal is reduced.

FIG. 3 shows the implementation of such a short-dip, shallow coating pot.

In FIG. 3, the coating pot is illustrated at 48.

This coating pot is the same shape as pot 8 of FIG. 2 except that it is shallower.

Coating pot 48 contains a bath of molten coating metal 49, which is much smaller than bath 7 of FIG.

Snout 50 is similar to snout 6 of FIG. 2, and its lower end is located below the surface of bath 49 and is sealed by this bath.

The snout 50 accommodates a roll 51 in the downward direction which is equivalent to the roll 25 in the downward direction in FIG.

The pot roll is indicated at 52.

The difference between pot roll 52 and pot roll 26 of FIG. 2 is that it is only partially immersed in molten metal bath 49.

The apparatus of FIG. 3 includes an enclosure 53 whose trailing edge 53a is bent slightly downwardly to form a seal with the molten coating bath 49 while downwardly facing the roll 5.
It is identical in all respects to enclosure 27 of FIG. 2, except for providing clearance for the run of uncoated metal strip 54 between 1 and pot roll 52.

In this FIG. 3, coated metal strip 54a
passes between a pair of jet finishing nozzles 55 and 56,
Proceeding upwardly, it passes through chimney 57 and outlet slot 58, which correspond to chimney 47 and outlet slot 46 in FIG.

The operation of the coating/finishing apparatus illustrated in FIG. 3 is substantially identical to that described with respect to FIG.

In this case as well, jet finishing nozzles 55 and 56 can be connected to a circulation system (not shown) of the type shown in FIG.

The main difference between the operation illustrated in FIG. 3 and the operation illustrated in FIG. 2 is that the pot roll 52 is only partially immersed, which provides the advantages described above.

The amount by which pot roll 52 is immersed in bath 49 can be varied.

In FIG. 3, more than half of the pot roll 52 is immersed.

Appropriate shape of snout 50 and rear lower end 53a of enclosure 53
Therefore, the degree of immersion of the pot roll 52 can be less than half, especially if it is desired to keep the roll bearing (not shown) above the surface of the bath.

A pool of molten metal 59 between the pot roll 52 and the metal strip 54 that engages the pot roll is
It must be large enough to ensure sufficient coating of the rear side of the metal strip or the side of the roll.

It will be appreciated that as the amount of immersion of pot roll 52 is reduced, the size of this pool 59 is reduced.

Within the scope of the invention, the grooved pot roll 5
2 or by providing a means for pumping additional amounts of coating metal into pool 59 (described below). FIG. Other constructions are shown to completely cover the back side or roll side of the roll.

In FIG. 4, the enclosure is indicated at 60, and this enclosure is
It has the same shape as the enclosure 27 shown, and includes a pair of jet finishing nozzles 61 and 62, an outlet chimney 63, and an inert non-oxidizing atmosphere inlet 64.

The enclosure 60 may be equipped with an atmosphere circulation system as described with respect to FIG.

The lower end of enclosure 60 is immersed in a molten coating metal bath 65 contained in a shallow pot 66.

Further, FIG. 4 shows a normal type snout 67 having the same shape as the snout 6 of FIG. 2.

Note that the lower end of this snout 67 again extends below the surface of the bath 65.

The ferrous bare metal strip to be coated is shown at 68.

This strip is attached to the roll 6 in the downward direction inside the snout 67.
9, the hook is rotated, and then the hook is rotated around the outer periphery of the first pot roll 70 and enters the plating bath.

Strip from pot roll 70 to second pot roll 7
1 and this second pot roll coated strip 68a is passed upwardly through the enclosure 60.

The amount that pot rolls 70 and 11 are immersed in molten coating bath 65 can be varied.

In the illustrated embodiment, these pot rolls 70 and 71
are immersed in the bath 65 in an amount equal to or less than 1/2 of their respective diameters.

The presence of a dipped strip section 68b intermediate the pot roll TO and 71 ensures sufficient coating of the rear or roll side of this strip.

The shallow pot embodiment described with respect to FIGS. 3 and 4 does not significantly affect the enclosed nitrogen finishing method and its advantages described with respect to FIGS. 1 and 2.

As previously disclosed, the apparatus of the present invention can utilize a variety of pot roll configurations.

In another embodiment shown in FIG. 5, a conventional coating pot 72 contains a bath 73 of molten coating metal.

The lower end of the snout 74, which has the same shape as the snout 6 in Figure 2, is melted 7.
3, and is provided with a roll 75 on the downward side, which is equivalent to the roll 25 on the downward side in FIG.

The lower end of enclosure 76 is immersed inside bath 73.

The enclosure 76 has the same shape as the enclosure 27 of FIG. 2 and is provided with a chimney 77 for drawing out the strip and, if necessary, an atmosphere introduction lower 8.

Enclosure 76 houses a pair of jet finishing nozzles 79.80 similar to jet finishing nozzles 28.29 of FIG.

Again, the enclosure 76 may be equipped with the atmosphere circulation system (not shown) of FIG.

In this embodiment, a ferrous substrate metal strip 81 to be coated enters a molten coating metal bath 73 and a series of three pot rolls 82, 83, 84
The hook is passed around.

Rolls 83 and 84 are stabilizer rolls that control the shape of the strip and stabilize the coated strip.
This is to ensure the flatness of the IJ knob 81a when it passes between the nozzles 79 and 80.

In all of the embodiments described above, the enclosure and snout were illustrated as separate structures.

However, within the scope of the invention it is also possible to
It is also possible to have a snout and an enclosure that form a piece structure.

This is illustrated in FIG. In FIG. 6, a conventional coating pot 85 is replaced by a bath 86 of molten coating metal.
It accommodates.

The snout enclosure structure is illustrated generally at 87 and includes a snout portion 87a and an enclosure portion 87b.

The snout portion 87a has the same shape as the snout 6 shown in FIG. 2, and a roll 88 is disposed downwardly inside the snout portion 87a.

The downward direction of the roll 88 is equivalent to the downward direction of the roll 25 in FIG.

The enclosure portion 87b is of the same shape as the enclosure 27 and is provided with a strip drawer chimney 89.

The enclosing portion 87b also includes an atmosphere inlet 90 similar to the inlet 34 in FIG.

Jet knives 91 and 92 are arranged in the enclosed portion 87b and are equivalent in all respects to the jet knives 28, 29 of FIG.

It will be appreciated that the enclosure portion 87b may be equipped with an atmosphere circulation system (not shown) similar to that described with respect to FIG.

In the embodiment of FIG. 6, the soaked pot roll is
Indicated by 3.

Under normal operating conditions, the snout section 87a and the enclosure section 87b contain different atmospheres, so some type of sealing means must be provided between these sections.

This sealing means can take any suitable shape.

In the illustrated embodiment, this sealing means consists of two pairs of sealing rolls 94-95 and 96-97.

Within the scope of the present invention, seal roll 94-9
5 and the seal rolls 96-97, an appropriate non-oxidizing gas inlet 98 is provided.

The non-oxidizing atmosphere between the seal rolls 94-95 and the seal rolls 96-97 is provided at the snout portion 87a, respectively.
It is preferable that the pressure is slightly higher than the gas pressure in the surrounding portion 87b.

In this way, the enclosure portion 87b and the strip preparation furnace connected to the snout 87a are closed off without mutual contamination.

This also prevents contamination of the atmosphere inside the enclosed portion 87b from an atmosphere source at the inlet end of a conventional strike IJ tube preparation device.

The strip 99 to be coated is placed downwardly on the roll 8
8 is rotated, and seal roll pairs 94-95 and 96-
It passes between 97 and 97.

This strip 99 then enters a plating bath and is passed around a pot roll 93.

The coated strip 99a then passes upwardly between jet finishing nozzles 91 and 92 and exits the strip drawer chimney 89.

In this manner, the operation of the device of this embodiment, as well as its advantages, is essentially the same as that described with respect to FIGS. 1 and 2.

The integrated snout/enclose structure shown in Figure 6 can also be applied to shallow pot structures.

This is illustrated in FIG.

In FIG. 1, the snout/enclosure structure is identical to that in FIG. 6, with like parts designated by like numbers.

In the embodiment of FIG. 1, the shallow pot is designated 100.

This pot contains a shallow bath 102 of molten coating metal.

In this case, pot roll 103 is partially immersed in bath 102.

In the illustrated embodiment, pot roll 103 is immersed to less than half its diameter.

Of course, this pot roll 103 could be immersed in an amount equal to or more than half its diameter, as described for the pot roll 52 in FIG.

It would also be possible to provide the apparatus of FIG. 7 with a pair of pot rolls of the type described in connection with FIG.

However, the apparatus illustrated in FIG. 7 is equipped with a pump to transport the molten coating metal into the plating bath 102.

The outlet of this pump is indicated at 104. Pump outlet 104 creates a pool 105 of molten coated metal between strip 99 and pot roll 103;
ensures sufficient coating of the rear or roll side of the strip.

The embodiment of FIG. 3 could also be provided with such a coated metal pump if the pool 59 of FIG. 3 was insufficient.

In all embodiments of the invention where the pot roll is only partially immersed, grooved pot rolls could be used within the spirit of the invention, these grooves allowing the molten coated metal to flow through the strip. Convey to the side of the roll.

Because the method of the invention solves the oxide problem associated with the strip and its edges, relatively heavy coatings can be applied at relatively low line speeds, and the coatings have excellent surface properties. It's been found.

For example, experimentally, coating weights up to about 543 g/m (about 1.78 ounces/square foot) have been achieved at line speeds of 12 rrL/min with minimal controlled wiping with a jet finishing nozzle.

An experimental galvanizing line using 10.16 m strips was equipped with an enclosure having the same shape as enclosure 27 in FIG.

The chimney 47 has a height of 15.25 crIL and a width of 31.7
It was equipped with a strip drawer slot 46 of 5 mm and length 12.7 CIrL.

This enclosure was equipped with a pair of finishing nozzles (equivalent to nozzles 28 and 29 in FIG. 2).

Each nozzle had a 1.27 mm wide slot opening along its entire length.

Insert the lower nozzle of the two jet finishing nozzles from the bath surface.
held at a distance of inches.

The other jet nozzle was offset vertically upward by L2.7 mm.

The nozzles were also held at a distance of approximately 6.35 mm from the strip.

The enclosure was equipped with a circulation system of the type shown in FIG.

Make-up nitrogen was added at a rate of 85-per-hour, and the nitrogen atmosphere inside the enclosure was maintained at a pressure of 12.7 mm of water.

The ferrous base metal strip was 0.381 mm cold rolled steel with a relatively smooth surface of 1.27 μm and 3.546 K/m.

During this run, 1s3. ! A line speed of 21.4 m/min was used while the ir/- coating was applied.

The effect of oxygen contamination inside the enclosure containing high purity nitrogen was determined by incrementally metering compressed air into the circulation system until defects were observed in the molten coating.

At less than 50 pp1 oxygen, the fused coating was shiny, smooth, free of visible oxides, and had no signs of edge problems.

The hardened coating exhibited a perfectly flat flower pattern without border protrusions.

When intentionally increasing the amount of oxygen, no ripples appeared even at the oxygen level of 1140 m.

At an oxygen level of about 200 pIll inside the enclosure, for the first time a deleterious finishing effect of oxide grains, ripples, ridges and a kind of flower pattern was observed on the edges.

This condition became certainly more pronounced when the oxygen level was increased to 6001)Ill.

A surface oxide band appeared when the oxygen level reached about 700 pya.

These oxide bands extend inward from the edge of the strip and have an oxygen level of 850p11m? When this point was reached, it increased to a coarse oxide feather pattern.

This run shows that the enclosed nitrogen finish method of the present invention results in a smooth, uniform hot-dip coating without the edge ripples, loose scum, oxide aten and edge build-up defects commonly associated with conventional finishing methods. It was shown that a finished zinc coating could be produced.

A completely flat flower pattern suitable for temper rolling for extremely smoothness is created, eliminating the need for a step to reduce the flower pattern.

Simple jet finishing nozzles with uniform slotted openings can be used and these nozzles can be offset vertically to eliminate zinc spray and to eliminate heavy edge coating or coating wrap-around effects. can.

The noise level during the finishing stage was significantly reduced by offsetting the nozzles with respect to each other.

The correlation between the oxygen contamination of the finishing gas and the quality of the coating surface was clearly demonstrated.

The oxygen level within the enclosure must be maintained below about 200 ppI11, preferably below about 100 ppI111.

In another similar run, a flow rate of 85 m3 per hour of nitrogen was circulated through the jet finishing nozzle, while at the same time about 4 m3 per hour.
Using make-up nitrogen of 2.5771" or less, the ability to recirculate more than 50% of the required amount of high-purity finishing gas was confirmed in this manner.

Although in all the embodiments illustrated in the accompanying figures the enclosure is shown schematically, the enclosure may be provided with suitable support means or the like.

Furthermore, the enclosure may be fully or partially removable for its maintenance or if periodic air conditioning is to be carried out.

The present invention is not limited to the above description, and can be modified or implemented as desired within the scope of the spirit thereof.

The embodiments of the present invention are as follows.

1. A method according to claim 1, characterized in that the hot-dip coating metal is selected from the class consisting of zinc, zinc alloys, aluminum, aluminum alloys, turn metal and lead.

2. A method according to claim 1, wherein the non-oxidizing jet finishing gas and the atmosphere within the enclosure include an inert gas.

3. A method according to claim 1, comprising the step of vertically offsetting the jet finishing nozzles with respect to each other.

4. Each of the jet finishing nozzles mentioned above has a uniform finish along its entire length.
2. A method according to claim 1, characterized in that it comprises a rectangular nozzle opening equidistant from the coated strip along its entire length.

5. A method according to claim 3, comprising the step of recycling at least 5o% of said nitrogen from said enclosure through said jet finishing nozzle.

6. The method according to claim 2, comprising the step of circulating at least 501% of the inert gas from the enclosure through the jet finishing nozzle.

7. The method according to claim 5, comprising the step of vertically offsetting the jet finishing nozzles with respect to each other.

8. Each of the jet finishing nozzles mentioned above has a uniform width along its entire length.
8. A method according to claim 7, characterized in that it has a rectangular nozzle opening equidistant from the coated strip along its entire length.

9. The method of claim 8, comprising the step of maintaining the nitrogen at an oxygen level below about 11001)I1.

10. The molten coating metal is zinc, zinc alloy,
Finishing device according to claim 4, characterized in that it is selected from the class consisting of aluminum, aluminum alloys, turn metal and lead.

11. At least 5 of the non-oxidizing gas inside the enclosure
5. A finishing apparatus according to claim 4, further comprising means 35 to 42 for circulating zero air from said enclosure through said jet finishing nozzle.

12. The strip preparation means comprises a snout 87a extending into the molten coating metal bath and means 38 disposed within the snout for guiding the ferrous green metal strip from the preparation means to the bath. said enclosure 87.87b being an integral part of said snout and disposed within said snout for separating non-oxidizing gases within said enclosure from said strip preparation means. Finishing device according to claim 4, characterized in that it comprises sealing means (94,97).

13. At least one pot roll 26,52°71
．． 82 to 84.93.103, and the above-mentioned sl-IJ
The finishing device according to claim 4 or claim 12, characterized in that the whelk is passed around the pot roll and passed through the bath, upwardly exiting the bath and entering the enclosure. .

14. Short chimney above the enclosure 47, 57, 63°77.
89, the lower end of the chimney communicates with the inside of the enclosure,
Also, its upper end is provided with the slot 46.58 for pulling out the strip.
A finishing device according to claim 4 or claim 12, characterized in that it comprises:

15. The circulation means includes an exhaust port 35 for non-oxidizing gas inside the enclosure and a bag house 35 connected to the exhaust port.
a, a heat exchange detector 36 connected to the bag house, a blower 39 connected to the heat exchanger and having an outlet 40 connected to the jet finishing nozzle, and supplying non-oxidizing gas for replenishment. 12. A structure according to claim 11, characterized in that it comprises means 45 provided in said circulation system for the purpose.

16. The finishing apparatus according to claim 13, wherein said at least one pot roll 93 is completely immersed within said molten coating metal bath.

17. The finishing device according to claim 13, characterized in that said at least one pot roll 52 is immersed within said bath to a depth greater than 1/2 of its diameter.

18. Said at least one pot roll 71°103
14. The finishing device according to item 13, wherein the finishing device is immersed in the bath to a depth of 1/2 or less of its diameter.

19. To ensure the flatness of the strip as it passes through the jet finishing nozzle, the strip is curved after it has been passed around the at least one pot roll 82 and before exiting the bath. 17. Finishing apparatus according to claim 16, characterized in that it includes a pair of stabilizer rolls 83, 84 arranged in said bath so as to pass therethrough.

20. Said at least one pot roll 71°103
Finishing device according to paragraph 18, characterized in that it comprises a grooved pot roll.

21. A pump is provided for transferring molten metal from the bath, the outlet 104 of the pump supplying the molten metal sufficiently to the pot roll side of the marking strip so that the strip first contacts the pot roll. 19. A finishing device according to claim 18, characterized in that it is arranged to form a pool 105 of molten metal on the pot roll side intermediate the strip and the pot roll.

[Brief explanation of the drawing]

Fig. 1 is a schematic partial cross-sectional view of a continuous hot-dip galvanizing line that carries out the method of the present invention; Fig. 2 is a partial enlarged cross-sectional schematic view of the coating end of the galvanizing line shown in Fig. 1; 4 and 5 are views similar to FIG. 2 showing various pot roll structures, and FIGS. 6 and 7 are views similar to FIG. 2 showing the integral structure of the snout enclosure. 27, 53, 60, 76, 87... Enclosure, 28°29.55, 56, 61.62, 79, 80
゜91.92...Jet finishing nozzle, 34,
64°78.90...Non-oxidizing gas holding means,
39-45... Non-oxidizing gas supply means, 46,
58...Slot for strip drawer.

Claims (1)

[Scope of Claims] 1. A ferrous base metal strip is introduced into a molten coating metal bath contained in a coating pot, and the ferrous base metal strip is previously prevented from casting of the coating metal on the strip. high enough to
Also, a pre-treatment to prevent excessive alloying reactions between the coating metal/base metal and to heat the strip to a low enough coating temperature to leave the surface clean and oxide-free as it passes through the bath. an enclosure in sealing relationship with the bath for the ferrous bare metal strip coated on both sides exiting the bath; an outlet for the coated strip within the enclosure; Both sides of the ferrous base metal strip are coated with molten coating metal of the type that jet finishing nozzles are disposed internally on each side of the coated strip and jet finishing the coated strip with a non-oxidizing gas. A method for finishing a continuous hot-dip coating process includes the steps of maintaining a non-oxidizing atmosphere within an enclosure, and maintaining a jet finishing gas within the enclosure and the atmosphere at an oxygen level of about 200% or less. A finishing method for a coating process, characterized in that it prevents coating non-uniformity due to oxides in said strip coated on both sides. 2. A method according to claim 1, including the step of maintaining the jet finishing gas and the atmosphere within the enclosure at an oxygen level of about 100 pI11 or less. 3 Coating pot 8, 48, 66, 72
. 85.100 and the molten coating metal bath 7,49,65,73°86.102 inside the coating pot.
and means 25.26, 51.52 for guiding said ferrous blank metal strip through said molten coating metal bath;
69 to 71, 75° 82 to 84, 88, 93 to 9
7.103 and sufficiently high to prevent casting of the coating metal on the strip and prevent excessive alloying reactions between the coating metal/base metal and the surface of the strip passing inside the bath. Strip preparation 1 to 6 for heating said strip to a sufficiently low coating temperature to achieve a clean, oxide-free state and an enclosure 27, 53, 60 for said strip exiting said bath. γ6,8
T, the enclosure having an open bottom projecting into said bath, said enclosure having an enclosure formed therein with outlets 46, 58 for said strip withdrawal, and said enclosure having an opening above said bath inside said enclosure. a pair of jet finishing nozzles 28, 29° 55, 56, located on each side of said strip;
61.62,79,80,91. In finishing equipment used with a conventional coating line for hot-dip coating both sides of ferrous base metal strips 9, 54, 68° 81.99 with hot-dip coating metal of the type having 92.
means 34.64,78,90 for retaining a non-oxidizing gas within said enclosure having an oxygen level of less than 200 pm;
and means 39 to 40 for supplying a non-oxidizing gas with an oxygen level of pI 11 or less to the jet finishing nozzle. 4 Said jet finishing nozzle 28, 29, 55°56.
Finishing device according to claim 3, characterized in that 61, 62, 79, 80, 91, 92 are offset perpendicularly to each other. 5. A finishing apparatus according to claim 3, wherein each said jet finishing nozzle has a rectangular nozzle opening of uniform width along its entire length and equidistant from said coated strip along its entire length.