JP3069226B2 - Method and apparatus for continuous immersion treatment of metal strip - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuously immersing a metal strip in a treatment liquid to perform a surface treatment, for example, a continuous immersion method such as pickling, washing, chemical conversion and plating of a steel strip. It relates to a device suitable for use in this method.

[0002]

2. Description of the Related Art This type of immersion treatment is represented by pickling of steel strip. In this pickling, for example, a steel strip is passed in a catenary shape in a pickling tank filled with hydrochloric acid, and is continuously pickled. (Steel Handbook III (1))
The Japan Iron and Steel Association, p. 518). In this process,
The acid solution touching the steel strip surface is entrained along with the steel strip, and when the reaction between the scale on the steel strip surface and the acid progresses to some extent, the acid decomposes due to the reaction, and the acid near the steel strip surface The acid concentration becomes low and a low concentration boundary layer is formed, so that the pickling efficiency is reduced.

[0003] In order to promote the pickling by destroying the low-concentration boundary layer with a jet, for example, Japanese Patent Publication No. 50-37613
No. 55-11749, JP-A-62-133089, 62-222089
And JP-A-63-270486, which are effective in shortening the pickling time.

[0004]

However, all of these methods require a large circulating system for feeding and spraying the acid solution and a strip holding structure, require a large installation space, and handle the acid solution. There is a disadvantage in that the total cost increases because of the rapid consumption. Therefore, an object of the present invention is to provide a method for more effectively destroying the low-concentration boundary layer at low cost.

[0005]

For example, in continuous pickling, attention is paid to the fact that the running speed of the strip is high and therefore the flow velocity of the accompanying acid solution is considerably high, and this entraining flow is caused to collide with an appropriate obstacle. As a result, they found that the low-concentration boundary layer could be destroyed, and reached the present invention.

That is, the present invention provides a metal strip,
When the metal strip is continuously passed through the processing bath filled with the processing solution and immersed in the processing solution, and subjected to surface treatment on the metal strip, the metal strip entering side near the front and back surfaces of the metal strip passing under tension A pair of upper and lower weirs whose edges are formed by a curved surface having an arcuate cross section are arranged, and the entrainment flow of the processing liquid generated along the metal strip in the sheet passing direction is intercepted by the weir and formed between the weirs. And a method of continuously immersing the metal strip in the direction in which the metal strip passes through the metal strip, and further injecting the processing liquid toward the metal strip on the exit side of the weir. A method for continuously immersing a metal strip.

Further, the apparatus used in the present invention is a processing tank for charging a processing liquid for immersing a metal strip, and at least one of the processing tanks which sandwiches a passage of the metal strip in the processing tank from the front and back sides of the metal strip. A pair of weirs are provided in the treatment tank, and the weirs form a bottom surface of a prismatic body having a width over the entire width of the metal strip, and form a side edge on the metal strip entry side with a curved surface having an arc-shaped cross section. A continuous immersion treatment device for a metal strip, characterized in that the flow path between the weirs is formed into an inclined surface that converges on the passageway in the direction of the metal strip passing through the plate, A device for continuous immersion of a metal strip, which is provided with a nozzle for the treatment liquid which is directed towards the through-passage, is advantageously suitable.

FIG. 1 shows an apparatus used when the method of the present invention is applied to pickling. In the drawing, reference numeral 1 denotes a steel strip which passes under tension. A pair of weirs 3 and 4 sandwiching the steel strip 1 from the front and back sides thereof are spaced apart in a plane perpendicular to the passage 2 of the steel strip 1. Place two pairs.

The weirs 3 and 4 have the bottom surface (which is the upper surface in the weir 4 but will be generally referred to as the bottom surface) of a prismatic body having a width covering the entire width of the steel strip 1, and the side edge on the entry side has an arc-shaped cross section. In addition to being formed with a curved surface, the steel strip 1 is formed so as to have a gradient that changes with a curvature so that the flow path between the weirs 3 and 4 converges on the passing plate path 2 toward the passing direction of the steel strip 1.

Here, the radii of curvature R ₁ and R ₂ shown in FIG.
If the value is too small, the flow of liquid into the weir is reduced, and the strip holding force due to the liquid pressure is reduced, so that there is a high possibility that scratches are generated on the steel strip surface. On the other hand, if it is too large, the effect of blocking the trailing flow of the steel strip by the weir decreases. Thus R ₁ is 20~100m
m, R ₂ is not less than 500 mm, strip passing speed, the thickness of the steel strip, in accordance with the specific gravity, it is preferred to select a combination of at optimal radii of curvature.

The R ₁ and R ₂ do not need to be the same in the upper and lower weirs. Conversely, in the case of steel having a large specific gravity, for example, the lower R ₁ and R ₂ are increased, and It is preferable to increase the holding force (lifting force). Conversely, in the case of a light strip, it is susceptible to the liquid flow, and it is preferable to increase R ₁ and R ₂ of the upper weir in order to prevent floating. There is also. By disposing the weirs 3 and 4 close to the front and back surfaces of the steel strip 1, that is, by narrowing the distance between the weirs 3 and 4, the entrainment flow of the acid solution 5 generated along the steel strip and in the passing direction of the steel strip is reduced. Cut off.

The shape of the bottom surface of the weir is not limited to the example shown in FIG. 1, but may be a type in which a flat inclined surface shown in FIG. 2 is given to the bottom surface. it is particularly important that a curved surface of the arc-shaped cross section of radius of curvature R ₁ described above. Further, as shown in FIG. 3, a nozzle 6 for ejecting the acid solution 5 is provided on the outlet side of the weirs 3 and 4, and the acid solution in this area is stirred, so that the pickling efficiency can be further improved.

[0013]

Next, the operation of the weirs provided above and below the steel strip passage will be described in detail with reference to FIG. When the steel strip 1 is continuously passed through the acid solution 5 at a particularly high speed, the acid solution 5 entrains the steel strip 1 and the entrainment flow 7 of the acid solution 5 is generated in the passing direction of the steel strip 1. The trailing flow 7 forms the low concentration boundary layer as described above, and the pickling efficiency in this layer is extremely low. The trailing flow 7 travels together with the steel strip 1, but is cut off by the weirs 3 and 4 in the installation area of the weirs 3 and 4, and the thickness of the trailing flow 7 between the weirs 3 and 4 is extremely reduced.

Further, the trailing flow 7 that has passed between the weirs 3 and 4 flows into the exit side of the weirs 3 and 4, and induces a turbulent flow area 8 therein.
Since the surrounding steady-state acid solution is mixed into the low-concentration entrained flow 7 by the turbulent flow zone 8, a decrease in the concentration of the entrained flow 7 is eliminated, and the pickling efficiency can be improved. Here, FIG.
As shown in the figure, the smaller the gap between the weirs 3 and 4, the more the pickling efficiency can be improved, and it is preferable to appropriately select and set it in relation to the thickness of the steel strip and the like.
It is good to use the range as usual. Also, as shown in FIGS. 1 and 2, the flow of the acid solution between the weirs 3 and 4 is defined as a focused flow by giving the flow path between the weirs 3 and 4 an inclination to converge on the passageway 2. Since the steel strip can be passed through the center of the weirs 3 and 4 by the trapped flow phenomenon, the gap between the weirs can be narrowed.

On the other hand, when a plurality of weirs are installed, it is desirable that the spacing be 1-2 m in a practical processing line. If it is less than 1 m, the above-mentioned turbulent flow area is insufficiently generated, and the boundary layer enters the weir while the boundary layer is not developed, so that the processing efficiency is reduced. Also, if it exceeds 2 m, the thickness of the low concentration layer becomes too thick.

Further, as shown in FIG. 3, by installing the nozzle 6 on the exit side of the weir to generate the jet flow of the acid solution, it is possible to further increase the pickling efficiency. That is, since the jet flow from the nozzle 6 directed to the outlet side of the weir reaches the turbulent flow area 8 shown in FIG. 5, the state of this turbulent flow area can be further strengthened, and the recovery of the concentration is promoted. is there. In other words, the efficiency of the jet used is relatively small and a large improvement in efficiency can be obtained. Therefore, the amount of the jet used is much smaller than that of the jet using no weir. Here, it is preferable that the jetting speed of the acid solution from the nozzle 6 be 5 m / s or more.

[0017]

EXAMPLE The apparatus according to the present invention was applied to the pickling equipment shown in FIG. That is, the steel strip 1 is first introduced into the pickling tank 10 via the tension leveler 9, and is pickled while passing through the tank. In a 20m long pickling tank 10,
The above-mentioned weirs 3 and 4 of FIG. 1 are installed at an interval of 1 to 1.5 m.
(9 pairs in the illustrated example), and the gap between the weirs 3 and 4 is
Was adjusted to 5 to 10 mm by an adjusting cylinder 11 attached to the above.

In passing the steel strip of hot rolled high-temperature rolled material of ultra-low carbon steel through the above pickling equipment and pickling in a 5% hydrochloric acid bath, the number of weir equipment was changed. The respective pickling rates were examined. For comparison, the pickling rate when the same pickling was performed in the same pickling facility without a weir was also examined, and the pickling rate according to the present invention when the pickling rate of this comparative example was set to 1 FIG. 7 shows the results of the index evaluation of the speed. From the figure, it can be seen that the pickling speed is greatly improved by installing the weir.

In order to perform highly efficient pickling, it is necessary to adjust the distance between the steel strip and the weir to about 5 to 10 mm. It is necessary to adjust the weir gap.

In addition, weirs are 7 m / year in our experiments.
Since it is worn by about m, it is necessary to correct it. Therefore, it is desirable to increase the weir gap when passing materials other than the scale-removable material and a defective shape portion. Particularly in a steel sheet manufacturing plant, as shown in FIG. 6, it is desirable to use together with a tension leveler. However, in the pickling according to the present invention, there is no need to perform catenary control, so that the capacity of the bridle on the exit side of the tension leveler can be reduced. Similarly, the bridle capacity on the exit side of the pickling tank can be made very small.
FIGS. 8A and 8B are examples of equipment for introducing a steel strip through a different route from the above-described example.

In the present apparatus, the destruction of the boundary layer is enhanced as the sheet passing through the apparatus is reached. In other words, even if the immersion time is shortened, the destruction effect of the boundary layer makes up for this,
It can be used over a wide speed range.

[0022]

According to the present invention, the entrainment flow of the metal strip passing through the processing solution, that is, the low-concentration boundary layer can be destroyed by low-cost and simple means. Efficient surface treatment can be realized by keeping the liquid concentration within a predetermined range.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a weir according to the present invention.

FIG. 2 is a schematic diagram showing a weir according to the present invention.

FIG. 3 is a schematic diagram showing a weir according to the present invention.

FIG. 4 is a schematic diagram showing a state of a trailing flow.

FIG. 5 is a graph showing the relationship between the weir gap and the pickling speed.

FIG. 6 is a schematic diagram showing a pickling facility.

FIG. 7 is a graph showing the pickling rate improvement rate.

FIG. 8 (a) is a schematic diagram showing another pickling facility according to the present invention. (B) is a schematic diagram showing another pickling facility according to the present invention.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI C25D 7/06 C25D 7/06 L (72) Inventor Shichio Suganuma 1-chome Mizushima Kawasaki-dori, Kurashiki City, Okayama Prefecture Inside the Mizushima Works, Kawasaki Steel Corp. No. 6-22 Mitsubishi Heavy Industries, Ltd. Hiroshima Research Laboratory (72) Inventor Naoyuki Nagai 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries, Ltd. Hiroshima Research Laboratory (56) References JP-A-3-267388 ( JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C23C 22/73 C23G 3/02

Claims (4)

(57) [Claims] The method according to claim 1 the metal strip, the treatment liquid was dipped using a continuous flow plate and processing liquid in a processing tank filled with, when subjected to a surface treatment to the metal strip, the front and back surfaces of the metal strip passing the plate under tension Nearby, metal
The side edge of the strip entry side was formed with a curved surface with a circular cross section,
Arrange a pair of upper and lower weirs together with the metal strip.
When the entrained flow of the processing liquid generated in the
In both cases, the flow path of the processing liquid formed between the weirs is
A method for continuously immersing a metal strip, wherein the metal strip is converged in a direction along which the trip passes . 2. The method according to claim 1, further comprising spraying a processing liquid toward the metal strip on the exit side of the weir. 3. A processing tank into which a processing liquid for immersing a metal strip is charged, and at least one processing tank which sandwiches a passage of the metal strip in the processing tank from the front and back sides of the metal strip.
The pair of weirs, Ri Na provided in the processing bath, weir is a metal string
The bottom surface of the prism having a width that covers the entire width of the
Form the side edge on the metal strip entry side with a curved surface with a circular cross section
At the same time, weir phase moves in the direction of the metal strip passing
A continuous immersion treatment apparatus for a metal strip, characterized in that the flow passages between them are inclined surfaces that converge on a passageway . 4. The continuous immersion treatment method for a metal strip according to claim 3, further comprising a nozzle for injecting the treatment liquid, which is directed to the passage on the exit side of the weir.