JPH0577752B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a pickling treatment method for long metal materials. This invention relates to an improved method that can be carried out. The present invention can be widely used as a pickling treatment method for various long metal materials that can be treated while continuously running, but in the following explanation, a steel strip is pickled continuously. A typical example of descaling will be explained below.

[Prior art] In the continuous production of steel strips, pickling is used in the final process to remove and clean surface scales generated during hot rolling, cold rolling, strain relief annealing, etc. The descaling process is performed by The currently widely used method for this descaling treatment is to use heated hydrochloric acid (approximately 85 to 95 degrees Celsius) with a concentration of about 15 to 20% as the pickling solution. , a dipping method in which the steel strip is continuously run while immersed in multiple pickling tanks charged with heated hydrochloric acid (the pickling tanks are made shallower).
There are two methods: the SHALOW method (also included in the Koko method) and the spray method, in which heated hydrochloric acid is injected onto both sides of the running steel strip, but the former immersion method is currently the mainstream.

FIG. 2 is a conceptual diagram illustrating this immersion method.
Along the running direction of the steel strip 1, pickling tanks 2a, 2b,...
...2y, 2z are arranged in series, the pickling liquid is supplied from the pickling liquid supply pump 3 to the pickling tank 2z on the most downstream side, and the pickling liquid overflowing from the pickling tank 2z is transferred to the intermediate tank 4. After that, the pickling liquid is sent to the pickling tank 2y on the upstream side by the feed pump 5, and in the same way, the pickling liquid is sequentially sent to the pickling tanks on the upstream side, and then from the pickling tank 2a on the most upstream side. It is discharged. Then, the steel strip 1 is moved by guide rolls 6 into pickling tanks 2a, 2b...2y,
During the dipping run in the order of 2z, oxides on the surface of the steel strip are removed with hot hydrochloric acid. The steel strip 1 that has exited the pickling tank 2z on the most downstream side has the pickling liquid removed by a rinsing device (not shown), and is then dried and wound up.

[Problems 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 steel strip or to reduce the running speed of the steel 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 is a method of preheating the steel strip before pickling.
Alternatively, a method has been implemented in which the steel strip is subjected to mechanical descaler treatment, tensioning, skin pass treatment, etc. to generate cracks in the scale, thereby facilitating subsequent descaling. However, these methods require special equipment for preheating the steel strip or for preliminary treatment to promote descaling (descaler 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 improve the turbulence pickling treatment method and to obtain even better pickling efficiency with simple equipment and official standards. It is intended to provide a method.

[Means for Solving the Problems] The structure of the pickling treatment method according to the present invention that can solve the above problems is that in the method of pickling a long metal material by the turbulence method, an acid is placed in the pickling tank. By introducing the washing liquid under pressure and applying liquid pressure to the entire area in the pickling tank, the pickling liquid is released from any part of the system to the outside of the system while creating a turbulent flow state in the entire pickling liquid. The gist of this method is to run a long metal material at high speed in the pickling tank while controlling the pickling tank.

[Operation] 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 (that is, the descaling effect) significantly differs depending on the flow state of the pickling solution when the steel strip is running in the pickling tank. 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 steel strip 1 runs at high speed in pickling liquid L,
The viscous pickling liquid L in the open pickling tank 2
forms an accompanying flow as the steel strip 1 runs, and 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 is
Descaling reaction (Fe ₂ O ₃ +6HCl→2FeCl ₃ +3H ₂ O
or FeO + 2HCl → FeCl ₂ + H ₂ O), the cleaning activity decreases, or even after losing the cleaning activity, it continues to flow near the steel strip 1, and the fresh (cleaning It is thought that this prevents the active cleaning liquid from flowing into the vicinity of the steel strip 1, and that the descaling effect gradually decreases. Also, the fact that it becomes difficult for fresh cleaning liquid to migrate to the vicinity of steel strip 1 means that
Heat transfer when attempting to increase the cleaning power by heating the surface of the steel strip 1 with the heated cleaning liquid is also inhibited, and the cleaning efficiency further decreases.

On the other hand, in the Turbulance pickling method, for example, as schematically shown in FIG. In this case, the pickling liquid L forms an accompanying flow similar to that explained in FIG. 3, but since the accompanying flow is disturbed by the upper lid 7, the pickling liquid L becomes easier to diffuse, and the pickling effect is slightly enhanced.

That is, in this example, the pickling tank 2 is configured to be shallow, the top cover 7 is not far away from the steel strip 1, and the top cover 7 is stationary with respect to the steel strip 1 running at high speed. Therefore, it is thought that the accompanying flow near the upper cover 7 is slower than the accompanying flow near the steel strip 1 due to the wall resistance of the upper cover 7, which disturbs the accompanying flow and produces a somewhat turbulent flow. .

However, even with this turbulence method, the cleaning effect as initially expected could not be obtained, and the following fact was 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. An empty space S is formed on the upstream side of the washing tank 2 in the running direction of the steel strip 1. Since the liquid surface of the pickling liquid L facing this air S is not subjected to wall resistance of the upper lid 7, the accompanying flow of the pickling liquid L in this part is not disturbed much, and this part becomes a quasi-laminar flow state. As a result, the diffusion of the pickling liquid L became insufficient, and it was thought that the cleaning effect would not be improved for the same reason as explained in FIG. 3.

Therefore, in the present invention, by preventing the above-mentioned void S seen in the turbulence method from forming, the pickling liquid L can be sufficiently diffused throughout the lengthwise direction of the pickling tank 2.
As a result of further research with the belief that the pickling effect can be enhanced, we arrived at the structure of the present invention.

That is, in the present invention, as described above, the pickling liquid is introduced under pressure into the pickling tank using the turbulence method, and by creating liquid pressure throughout the entire area in the pickling tank, the process shown in FIG. A turbulent flow state is created by preventing the formation of such voids, and by applying wall surface resistance to the accompanying flow of the pickling solution throughout the lengthwise direction of the pickling tank. As a result, the pickling liquid L is sufficiently diffused throughout the longitudinal direction of the pickling tank, and heat transfer also proceeds efficiently, so that the pickling efficiency is greatly increased.

1A to 1C are schematic explanatory diagrams illustrating the pickling apparatus used in the present invention, and FIG. 1A is a longitudinal sectional view;
Fig. 1B is a plan view with the top cover 7 removed, and Fig. 1C is a longitudinal cross-sectional view taken along line C-C in Fig. 1A. It is produced as a thing. In the figure, 1 is a steel strip, 2 is a pickling tank,
7 is an upper lid, 8a and 8b are slit nozzles for press-fitting the pickling liquid L, 9 is a drain port, and 10 is a slit arranged in a staggered manner.

When performing pickling using this equipment,
By introducing the pickling liquid L into the pickling tank 2 under pressure from the slit nozzles 8a and 8b and creating liquid pressure in the entire area of the pickling tank 2, the process described in FIG. To run a steel strip 1 at high speed while preventing the formation of such a void S. Then, the pickling liquid L forms an accompanying flow in the running direction of the steel strip 1, but the pickling tank 2
has a narrow structure and the wall surface is located close to the running position of the steel strip 1, so the accompanying flow on the wall side is resisted and the flow velocity is suppressed, similar to what was explained in Fig. 4 above. For this reason, the pickling liquid L is in a turbulent state.

As a result, the pickling liquid L near the steel strip 1 is always replaced with fresh one, and the above-mentioned descaling reaction by pickling proceeds efficiently. Moreover, in the present invention, liquid pressure is applied to the entire area inside the pickling tank 2 by pressurized introduction of the pickling liquid L, so that a void S as explained in FIG. 5 above may be formed in the pickling tank 2. Without,
A turbulent flow condition is given to the entire area inside the pickling tank 2, and it becomes possible to proceed with pickling efficiently over the entire length. In the illustrated example, the pickling liquid L is transferred to the pickling tank 2.
Although an example is shown in which press fitting is performed from the slit nozzles 8a and 8b provided at the front and rear ends of Any press-fitting means may be used as long as it does not create a void by applying hydraulic pressure to the entire area of the pickling tank 2.

In addition, the pickling liquid L is kept at a high level by draining the pickling liquid L from drain ports 9 provided at appropriate locations on the bottom and side walls. 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 liquid in the pickling tank varies depending on the running speed of the steel strip, so by introducing the pickling liquid with enough pressure to overcome this pressure, the above-mentioned effect can be achieved in the pickling tank. It is possible to prevent the formation of such empty spaces.

The apparatus shown in FIGS. 1A to 1C is merely an example of a preferable apparatus used in the present invention, and is not intended to limit the present invention. While introducing the pickling liquid L under pressure so that the liquid pressure of the pickling liquid acts on the entire area in the tank, the steel strip 1 is
The specific configuration of the device can be arbitrarily changed as long as it can run at high speed.

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

That is, a pickling tank (width:
300mm, gap between the steel strip running position and the bottom surface of the top cover:
150mm) to descale a steel strip (CAL material: material for continuous annealing) with a width of 200mm and a thickness of 2mm, and the descaling effect when changing the hydrochloric acid concentration, pickling time, temperature, etc. was compared with the descaling effect when using the conventional descaling method.

First, in Figures 6A to 6D, the pickling temperature is set at 85℃, and the elongation rate applied to the steel strip by a tension leveler to promote descaling is 0%, 1%, and 3.
% and 5%, the relationship between the pickling time, hydrochloric acid concentration, and the time required for descaling (time until black scale on the surface of the steel strip can no longer be observed with the naked eye) is shown.

As is clear from FIGS. 6A to 6D, 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, and the method of the present invention can significantly reduce the concentration of hydrochloric acid. It can be seen that a sufficient descaling effect can be enjoyed even when the temperature is lowered.

Next, Figures 7A and 7B show the effect of changing the elongation rate given to the steel strip before pickling by a tension leveler to promote descaling, in accordance with the above method.
1 is a graph showing a comparison between the method of the present invention and a conventional dipping method.

As is clear from this graph, the descaling time required for the method of the present invention [Fig. 7A] remains almost the same even when the elongation rate is changed, whereas the time required for descaling with the conventional descaling method [Fig. 7B] ], 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. That is, from these results, it can be seen that by employing the present invention, an excellent descaling effect can be enjoyed even if the preliminary treatment for promoting descaling (treatment for creating cracks in the scale film) is omitted.

Figure 8 shows the hydrochloric acid concentration at 3.0%, the temperature at 85℃, and the elongation rate applied by the tension leveler at 5.
%, the gap in the pickling tank was set to 60 mm, and the flow rate of hydrochloric acid in the tank was set to 1.0 m/sec, but the method was the same as described above, and the steel strip was preheated (85℃) and without preheating. This figure shows the results of investigating the relationship between pickling time and descaling rate for the following cases.

As is clear from this figure, even when 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 the descaling rate is slightly higher due to preheating. At the end of the washing 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 steel strip as long as a normal pickling time is used.

Next, in Figure 9, the hydrochloric acid concentration is 3.0%, the temperature is 85℃,
Figure 5 shows the case where the elongation rate by the tension leveler is set to 3%, the steel strip is not preheated, and the inside of the pickling tank is filled with water by adjusting the introduction pressure of hydrochloric acid (method of the present invention). This figure shows the results of investigating the relationship between the pickling time and the descaling rate in the case (comparative example) in which an empty space S is formed on the upstream side of the acid tank as shown in FIG.

As is clear from this figure, the descaling effect changes significantly depending on whether or not air is created in the pickling tank. The descaling effect is quite low under conditions where the pickling tank can be formed (comparative example), whereas the descaling effect is quite low when the liquid pressure in the pickling tank is increased to prevent the formation of empty water (the present invention). It turns out that it is very good.

[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 using the turbulence method, and the steel strip is processed under conditions such that no empty space is formed in the tank. By running at high speed and performing pickling, descaling can be accomplished extremely efficiently. Moreover, if this method is adopted, not only does pretreatment to promote descaling (stretching using a tension leveler, descaling treatment, etc.) become unnecessary, but preheating of the steel strip becomes unnecessary, and furthermore, it becomes unnecessary to preheat the steel strip. The acid concentration can also be lowered, simplifying the process and reducing the amount of acid consumed.

Further, as explained above, the present invention disturbs the accompanying flow of the cleaning liquid generated in the cleaning layer to create a turbulent flow state, and improves the diffusion of the cleaning liquid in the tank, thereby achieving the above-mentioned effects. This method can be used extremely effectively as a pickling treatment method for various long metal materials.

[Brief explanation of the drawing]

1A to 1C illustrate a turbulence type pickling apparatus used in the present invention, in which FIG. 1A is a schematic vertical sectional view, FIG. 1B is a schematic plan view with the top lid open, FIG. 1C is a view corresponding to the longitudinal section taken along the line CC in FIG. 1A. 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 Figures 4 and 5 are turbulence type pickling. Explanatory diagrams showing the situation, Figures 6A to 6D are graphs comparing the relationship between hydrochloric acid concentration and pickling time when the method of the present invention and the date piing method are adopted, and Figures 7A and B are graphs showing the relationship between the method of the present invention and the pickling time. A graph showing the relationship between the elongation rate and pickling time when the dipping method is adopted, Figure 8 is a graph showing the relationship between the presence or absence of preheating before pickling and the descaling rate, and Figure 9 is a graph showing the relationship between the descaling rate and the presence or absence of preheating before pickling. It is a graph showing the influence of the presence or absence of empty S on the descaling rate. 1...Steel strip, 2...Pickling tank, 7...Top lid, 8
a, 8b...Slit nozzle, 9...Drain port, 1
0...Skitt, L...Pickling liquid.

Claims (1)

[Claims] 1 In a method of pickling long metal materials by the turbulence method, a pickling solution is introduced under pressure into a pickling tank, and the entire pickling solution is A long metal material characterized in that the long metal material is made to run at high speed in the pickling tank while controlling the pickling liquid to be discharged from an arbitrary part to the outside of the system while forming a turbulent flow state. Pickling treatment method for materials.