JPH0320487A - Surface treatment of long-size material - Google Patents

Abstract

PURPOSE:To effectively carry out descaling treatment by allowing a steel strip to travel at high speed while pressing a pickling solution into a pickling tank confined in space at the time of passing a steel strip through a pickling solution and exerting descaling. CONSTITUTION:A pickling solution, such as aqueous solution of HCl, is pressed via press-in nozzles 8a, 8b into a pickling tank 2 confined in space, and a steel strip 1 after annealing is allowed to travel at high speed in a state where fluid pressure is formed in the whole region of the pickling tank 2, by which oxide scales on the steel-strip surface are dissolved by means of the pickling solution and removed. Plural staggeredly arranged skids 10 are provided in the pickling tank 2 and also discharge holes 9 for the pickling solution are provided in the bottom of the pickling tank 2, by which the pickling solution is formed into the state of turbulent flow in the tank 2 without forming voids free from the pickling solution in the pickling tank 2. Since, consequently, the steel-strip 1 surface is free from the associated flow of the pickling solution and a fresh pickling solution is always supplied, descaling reaction is accelerated and the descaling treatment for the steel strip can be effectively performed by a small device and with small amounts of pickling solution.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for surface treatment of long materials. For example, when a steel plate is descaled by pickling, it is possible to efficiently perform descaling. The Naoki invention, which relates to an improved method for obtaining a surface treatment, can be widely used as a surface treatment method for various long materials that can be treated while continuously running. The following is a representative example of a case in which a steel strip is descaled by continuous pickling treatment.

[Prior art] In continuous production of W4 strips, descaling by pickling is carried out in the final process to remove and clean the surface scale generated during hot rolling, rolling process, strain relief annealing process, etc. Processing is performed. The currently widely used method for this descaling treatment is to use heated hydrochloric acid (approximately 85 to 95°C) with a concentration of about 15 to 20% as the pickling solution. ■The dipping method in which the copper strip is continuously run while immersed in multiple pickling tanks charged with heated hydrochloric acid (SHAL with shallow pickling tanks)
(The LOW method is also included in this method) and (2) a spray method in which heated hydrochloric acid is injected onto both surfaces of the running #f, but among these methods, the former dipping method is currently the mainstream.

FIG. 2 is a conceptual diagram illustrating this dipping method, in which pickling 4i2a, 2b, . . . 2y, 2
z are arranged in series, the pickling liquid is supplied from the pickling liquid supply bomb 3 to the pickling phase 2Z on the most downstream side, and the pickling liquid overflowing from the pickling tank 2Z passes through the intermediate tank 4. The feed pump 5 sends it to the pickling 41 2 y on the upstream side,
In the same way, the pickling liquid is sequentially sent to the upstream pickling tank, and then
It is discharged from the pickling 49 2 a on the most upstream side. Then, the steel strip 1 is pickled by the guide roll 6 41 2 a ,
2 b . . . 2 y , 2 z are immersed in this order, and during this time oxides on the surface of the copper strip are removed with hot hydrochloric acid. The steel f1 that has exited the pickling tank 2z on the most downstream side has the pickling liquid removed by a rinsing device (not shown), then is dried and wound up.

[Problem to be solved by the invention] However, the dipping method as illustrated is not necessarily satisfactory in terms of descaling speed, and in order to achieve sufficient descaling, it is necessary to reduce the running speed of the copper strip or to reduce the running speed of the copper strip. Alternatively, the number of pickling tanks must be increased or the length of each pickling tank must be increased, resulting in problems such as decreased productivity or lengthened pickling equipment. Therefore, as a means to avoid these problems and increase the descaling rate, there are two methods: 1) Preheating the steel strip before pickling, 2) Applying mechanical descaler treatment, tensioning, skin bath treatment, etc. to the steel strip. A method has been implemented in which cracks are created in the scale to facilitate subsequent descaling. However, these methods require special equipment for preheating the copper strip or for preliminary treatment to promote descaling (descaler τ treatment, etc.), which not only increases equipment costs but also complicates process control. .

Therefore, as a method for improving the dipping method, a turbulence pickling method, which will be described later, was developed, but even this method has not been able to achieve the expected effect of improving cleaning power.

The present invention was made in view of these circumstances, and its purpose is to provide a method that can efficiently descale with simple equipment and processes, and to provide a method that can be used not only for descaling but also for other purposes. The purpose is to provide a method that can be applied to various surface treatments.

[Means for Solving the Problems] The structure of the surface treatment method according to the present invention that can solve the above problems involves introducing a treatment liquid under pressure into a narrow space and applying liquid pressure throughout the narrow space. The gist of this method is to run a long material at high speed within the narrow space while controlling the processing liquid to be discharged from any part of the system in the formed state.

[Function] In view of the problems of the prior art as described above, the present inventors conducted various studies in an attempt to clarify the reason why the descaling efficiency by the dipping method is not as high as expected. As a result, it was confirmed that the pickling effect (i.e. descaling effect) significantly differs depending on the running condition of the steel strip in the pickling tank and the flow condition of the pickling solution. That is, FIG. 3 is a schematic diagram showing the flow situation of the steel strip 1 and the pickling liquid L in one pickling tank 2 when the conventional dipping method is adopted. It is assumed that the pickling process is carried out while traveling at high speed in the pickling liquid L in the direction of the white arrow.

Now, when the steel strip 1 runs through the pickling solution L at high speed, the viscous pickling solution L in the open pickling cage 2 forms an accompanying flow as the steel strip 1 runs. , flows along the running direction of the steel strip 1. As a result, the pickling liquid L exhibits a fluid state close to laminar flow.

The pickling liquid L flowing close to the steel strip 1 undergoes a descaling reaction (F6203''6}ICI=2FeC13
” 3}+20 or FeO + 2HCl4 Fe
C12 + }1,0), or even after losing the cleaning activity, it continues to flow near the steel strip 1, and the fresh (with no cleaning activity) existing at a position away from wI%F1 It is thought that this prevents the cleaning liquid (which was carried by the descaling process) from flowing into the vicinity of the steel strip 1, and the descaling effect gradually decreases. In addition, this difficulty in moving fresh cleaning liquid to the vicinity of steel strip 1 also impedes heat transfer when trying to increase cleaning power by heating the surface of steel strip 1 with heated cleaning fluid. As a result, the cleaning efficiency further decreases.

On the other hand, in the turbulence pickling method, the pickling tank 2 is configured to be shallow as shown schematically in FIG. In this case, the pickling liquid L forms an accompanying flow similar to that explained in Fig. 3, but because the accompanying flow is disturbed by the upper M7, the pickling liquid L is more diffused than in the example of Fig. 2. The pickling effect is slightly enhanced. That is, in the wooden example, the pickling tank 2 is configured to be shallow, and the upper M7 is the steel strip 1.
The upper M7 is stationary compared to the steel strip 1 which is not far away from the steel strip 1 and is traveling at high speed. Therefore, the accompanying flow near the upper M7 is slower than the accompanying flow near the steel strip 1 due to the wall resistance of the upper M7, and this is thought to cause the accompanying flow to be disturbed and produce a somewhat turbulent flow. .

However, even with this turbulence method, the cleaning effect that was initially expected was not obtained, and the following facts were confirmed as the cause. That is, in this method, since the steel strip 1 is run at high speed through a relatively narrow pickling tank 2, the pickling liquid L is pushed in the running direction of the steel strip 1 by the accompanying flow, and for example, as shown in FIG. A void S is formed on the upstream side in the running direction of the steel strip 1 at 2. Since the liquid surface of the pickling liquid L facing this empty surface S is not subjected to wall resistance of the upper M7, the accompanying flow of the pickling liquid L in this part is not disturbed much, and this part is in a quasi-laminar flow state. As a result, the diffusion of the pickling liquid L becomes insufficient, and the third
It was thought that the cleaning effect would not improve for the same reason as explained in the figure.

Therefore, the present inventors believe that if the above-mentioned empty MS seen in the turbulence method is prevented from occurring, the pickling liquid L will be sufficiently diffused throughout the longitudinal direction of the pickling 4!2, and the pickling effect will be enhanced. As a result of further research with confidence, we came up with the configuration of the present invention.

That is, in the present invention, as mentioned above, the narrow space (i.e. pickling tank)
By introducing the pickling liquid under pressure into the pickling tank and creating liquid pressure in the entire area inside the pickling tank, a gap S as shown in FIG. 5 is created.
This creates a turbulent flow state by applying wall resistance to the accompanying flow of the pickling solution throughout the length of the pickling tank. As a result, the pickling liquid L is sufficiently diffused throughout the length of the pickling tank, and heat transfer is also carried out efficiently, so that the pickling efficiency is greatly increased.

FIGS. 1(A) to (C) are schematic explanatory diagrams illustrating the pickling device used in the present invention, FIG. 1(A) is a longitudinal sectional view, and FIG. 1(B) is a diagram with upper M7 removed. FIG. 1(C) is a plan view corresponding to the longitudinal cross-section taken along the line c-c of FIG. 1(A).
This device is manufactured as a long device, for example, about 3 to 8 m. In the figure, 1 is the steel strip, 2 is the pickling tank, 7 is the upper lid, 8a
, 8b is a slit nozzle for press-fitting pickling liquid L, 9 is a drain port,
10 shows skits arranged in a staggered manner.

When performing pickling using this device, be sure to use a narrow pickling area! Pickling liquid L from slit nozzles 8a, 8b6x in M2
By introducing pressure into the pickling tank 2 and creating liquid pressure in the entire area of the pickling tank 2, the steel strip 1 is prevented from being formed in the pickling tank 2 as shown in FIG. Drive at high speed. In this case, the pickling liquid L forms an accompanying flow in the running direction of the steel strip 1, but the pickling tank 2 is constructed narrowly and the wall surface is located close to the running position of the steel strip 1. The flow rate of the accompanying flow on the wall side is suppressed due to resistance, and the pickling liquid L becomes turbulent for the same reason as explained in FIG. 4 above. As a result, the pickling liquid L in the vicinity of 1l:1 of the steel is always replaced with fresh one, and the above-mentioned descaling reaction by pickling proceeds efficiently. Moreover, in the present invention, the pickling liquid L
Since liquid pressure is applied to the entire area inside the pickling tank 2 by introducing pressure, the gap S as explained in FIG. This condition allows pickling to proceed efficiently over the entire length. In the illustrated example, the pickling liquid L is supplied through slit nozzles 8a. Although we have shown an example of press-fitting from 8b, the press-fitting position is of course not limited to this example, and it is also possible to press-fit from the upper M7 or an appropriate position on the bottom. Any pressure means may be used as long as it does not create a gap. In addition, the pickling liquid L is discharged from drain ports 9 provided at appropriate positions on the bottom and side walls at any time to maintain the pickling power of the pickling liquid L at a high level. It is also effective to attach a baffle plate to the upper lid 7 to the extent that the flow of the pickling liquid L is not obstructed to promote turbulent flow of the pickling liquid. The liquid pressure generated in the pickling solution in the pickling tank varies depending on the running speed of the copper strip, so by introducing the pickling solution with enough pressure to overcome this pressure, the above-mentioned pressure can be created in the pickling tank. The formation of voids S can be prevented.

The devices shown in FIGS. 1(A) to (C) are merely examples of preferred devices used in the present invention, and are not intended to limit the present invention. Pickling so that the liquid pressure of the pickling liquid acts on the entire area inside the narrow pickling tank?
The specific configuration of the device can be arbitrarily changed as long as it allows the steel strip 1 to travel at high speed while introducing 1 t L under pressure.

[Example] Next, the following experiment was conducted to confirm the effects of the present invention.

That is, pickling 4 as shown in FIGS. 1(A) to (C)! (width:
300mm. Gap between copper band running position and bottom surface of top cover: 1
50a+m) was used to descale a steel strip of width 200mm x thickness 2mm (material for CAL material double continuous annealing), and the hydrochloric acid concentration at that time. The descaling effect when changing the pickling time, temperature, etc. was compared with the descaling effect when a conventional dipping method was adopted.

First, in FIGS. 6(A) to 6(D), the pickling temperature is set at 85°C, and the elongation rate applied to the copper strip by a tension leveler to promote descaling is 0%, 1%. 3%. The figure shows the relationship between the pickling time, hydrochloric acid concentration, and the time required for descaling (the time until the black scale on the surface of &iA-IIF can no longer be observed with the naked eye) when the acid pickling time was changed to 5%.

As is clear from FIGS. 6(A) to (D), when the method of the present invention is compared with the conventional dipping method, the method of the present invention shows an excellent descaling effect especially in the region of low hydrochloric acid concentration. It can be seen that a sufficient descaling effect can be obtained even when the hydrochloric acid concentration is considerably lowered. Next, FIG. 7 (A>.(B)) is based on the above method,
1 is a graph showing the effect of changing the elongation rate given to a steel strip before pickling by a tension leveler in order to promote descaling, comparing the method of the present invention and the conventional dipping method.

As is clear from this graph, in the method of the present invention [Figure 7 (A)], the time required for descaling hardly changes even when the elongation rate is changed (in contrast, in the conventional dipping method [Figure 7 In the case of Figure (B)], the time required for descaling varies considerably depending on the elongation rate, and this tendency becomes more noticeable when the hydrochloric acid concentration is lowered.In other words, from these results, it is clear that the present invention was adopted. If so, preparations for promoting descaling can be made.
It can be seen that an excellent descaling effect can be obtained even when the treatment (treatment for cracking the scale film) is omitted.

In Figure 8, the hydrochloric acid concentration is 3.0%, the temperature is 85°C, the elongation rate applied by the tension leveler is 5%, the gap in the pickling tank is 60 mm, and the flow rate of hydrochloric acid in the tank is 1.
Same as the above method except that it was set to 0m/sec,
This figure shows the results of investigating the relationship between pickling time and descaling rate for cases where the steel strip was preheated (85° C.) and cases where the steel strip was not preheated.

As is clear from this figure, even when the method of the present invention is adopted, the descaling rate is slightly higher due to preheating when the pickling time is short (i.e., in the initial stage of descaling), but At the end of the pickling time (the second half of descaling), there is no difference in the descaling rate between the presence and absence of preheating. That is, from this figure, it can be confirmed that according to the present invention, a sufficient descaling effect can be obtained without preheating the copper strip as long as the usual pickling time is used.

Next, in Figure 9, the following conditions are set: the hydrochloric acid concentration is 3.0%, the temperature is 85°C, the elongation rate by the tension leveler is 3%, and the steel strip is not preheated. When the inside of the washing tank is filled with water (method of the present invention) and when a void S is formed on the upstream side of the acid tank as shown in Fig. 5 (comparative example)
This figure shows the results of investigating the relationship between pickling time and descaling rate.

As is clear from this figure, the descaling effect changes significantly depending on whether or not voids S are created in the pickling tank. The descaling effect was quite low under these conditions (comparative example), whereas the descaling effect was very good when the liquid pressure in the pickling tank was increased to prevent the formation of voids S (the present invention). I can see that it is something.

[Effects of the Invention] The present invention is constructed as described above, and the pickling liquid is introduced under pressure into a narrow pickling tank, and the copper strip is run at high speed under conditions such that there are no voids in the tank. By carrying out pickling, descaling can be carried out extremely efficiently. Moreover, if this method is adopted, preliminary treatment to promote descaling (stretching with a tension leveler, descaling treatment, etc.)
Not only does this eliminate the need for preheating the steel strip,
Furthermore, the acid concentration for pickling can be lowered, simplifying the process and reducing acid consumption. Further, as explained above, the present invention disturbs the accompanying flow of the cleaning liquid that occurs in the cleaning tank to create a turbulent flow state, and improves the diffusion of the cleaning liquid in the tank, thereby achieving the above-mentioned effects. As can be easily understood from these effects, the present invention is not limited to the descaling treatment of copper strips as shown in the figure, but also includes surface treatments such as degreasing and alkali treatment of various long metal materials. It can also be widely applied to various surface treatments such as plastic materials.

[Brief explanation of drawings]

Figures 1 (^) to (C) illustrate the pickling apparatus used in the present invention, with Figure 1 (A) being a schematic vertical cross-sectional view and Figure 1 (B) showing the pickling device with the top lid open. Schematic plan view shown in Figure 1 (C)
is a view corresponding to a longitudinal cross-section taken along the line CC in FIG. 1(A). Figure 2 is a conceptual diagram showing the conventional dipping type pickling method, Figure 3 is an explanatory diagram showing the pickling situation when the dipping type pickling method is adopted, and Figure 4.5 is a turbulence type pickling method. Explanatory diagrams showing the situation, Figures 6 (A) to (D) are graphs showing a comparison of the relationship between hydrochloric acid concentration and pickling time when the method of the present invention and the dipping method are adopted, and Figure 7 (A), (B
) is a graph showing the relationship between the elongation rate and pickling time when the method of the present invention and the dipping method are adopted, FIG. 8 is a graph showing the relationship between the presence or absence of preheating before pickling and the descaling rate, and FIG. 9 is a graph showing the influence of the presence or absence of voids S in the pickling slag on the descaling rate. 1... Steel strip 2... Pickling tank 7... Upper ii
8a, 8b...Slit nozzle 9...
・Drain port IO...Skit L...Pickling liquid No. 6 Akane (A) Figure 6 (B)

Claims (1)

[Claims] (1) A processing liquid is introduced under pressure into a narrow space, and the processing liquid is controlled to be discharged from any part to the outside of the system with a liquid pressure formed throughout the narrow space. A method for surface treatment of a long material, characterized by running the long material at high speed inside the material.