JPS5855231B2 - Spray-pickling method for strips - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for uniformly pickling the upper and lower surfaces of a strip in spray pickling of a strip.

Figure 1 shows an example of strip spray pickling, in which the acid solution sprayed from the spray nozzle 1-1.1-2 onto the upper and lower surfaces of the strip S forms a thick layer on the upper surface of the strip (hereinafter simply referred to as the upper surface) It moves while being stirred and falls from both ends of the board.

Therefore, the pickling efficiency is high because a wide area of the upper surface is constantly washed away with new acid solution.

On the other hand, the acid solution sprayed onto the lower surface of the strip (hereinafter simply referred to as the lower surface) falls immediately after the collision.

For this reason, the acid solution does not spread over a wide area like the upper surface and is only pickled locally, resulting in poor pickling efficiency.

However, in the past, spray nozzles were installed equally on the top and bottom sides, making it impossible to pickle the top and bottom surfaces evenly.

For this reason, if an attempt was made to completely pickle the lower surface, the upper surface would be over-pickled, resulting in rough skin and metal loss, and this would lead to the problem of accelerated deterioration of the acid solution.

Incidentally, by tilting the spray nozzle on the lower surface side, it is possible to move the sprayed acid solution along the plate surface to some extent, but in this case, the pickling effect does not improve on the upper surface side columns.

It has also been confirmed that the pickling effect decreases as the inclination of the spray nozzle increases.

Based on this knowledge, the present invention aims to perform uniform pickling on the upper and lower surfaces, by making the nozzle installation interval in the strip length direction smaller on the lower surface than on the upper surface, and increasing the flow rate of acid solution supplied to the upper surface. The feature is that there is more space on the lower surface side than on the nozzle.

The present invention will be explained below with reference to embodiments shown in the drawings.

FIG. 2 shows a spray pickling device for explaining the present invention, where S is a strip, 2 is a nozzle header in which a predetermined number of spray nozzles are arranged in the strip width direction,
Four nozzle nozzles are installed on each of the upper and lower surfaces of the strip, and an acid liquid supply pipe 3 is connected to each nozzle header.

Reference numeral 4 indicates a pump for pumping the acid solution in the storage tank 5 to the header 2.

The strip S is continuously pickled by spraying an acid solution from the spray nozzle of the nozzle header 2 while being fed in the direction of the arrow at a constant speed.

Figure 3 shows the relationship between the nozzle interval and strip metal weight loss for each upper and lower surface of the strip by varying the nozzle interval in the longitudinal direction of the strip, that is, the interval t between the nozzle headers 2, during spray pickling using the apparatus shown in Figure 2. It is something.

As is clear from FIG. 3, as the nozzle spacing increases on both the upper and lower surfaces, the metal weight loss decreases, but the metal weight loss on the plate side side is particularly markedly reduced.

In order to make the metal weight loss the same on the upper and lower surfaces of the plate, for example, if the nozzle interval on the upper plate side is set to 225 mm, the interval on the plate side side is 150rnrIt.

The first feature of the present invention is that the nozzle spacing in the longitudinal direction of the strip is smaller on the bottom side of the strip than on the top side in order to equalize metal loss on the top and bottom surfaces of the strip.

FIG. 4 shows an example in which the nozzle spacing is 225 mm on the upper surface side of the strip and 150 mm on the lower surface side according to the above, and in the figure, the strip S is pickled while being fed at a constant speed in the direction of the arrow.

In this case, since the metal loss per unit length in spray zone L is the same between the top and bottom of the strip, the metal loss of the strip that has passed through the spray zone will be smaller by Ll-L2 on the lower side where the spray zone is shorter. .

In order to equalize the metal weight loss on the upper and lower surfaces, the length of the spray zone must be equal on the upper and lower surfaces.

In FIG. 4, two nozzle headers 2 may be additionally installed as indicated by dotted lines.

In this case, the flow rate of the acid liquid increases as the number of nozzle headers 2 increases.

In Figure 4, the flow rate on the bottom side is approximately V4 compared to the flow rate on the top side.
It will be doubled.

Therefore, the second feature of the present invention is that the amount of acid solution sprayed onto the strip is greater on the bottom surface of the plate than on the top surface.

Note that the nozzle header in the present invention may be of a type in which a plurality of nozzles are arranged in the longitudinal direction of the nozzle header, or a type in which slit nozzles are arranged in the longitudinal direction of the nozzle header.

Examples of the present invention will be shown below.

5US304 stainless steel hot rolled strip with HNO3 4
0 g/l, 1 HF! When spray pickling is performed using an acid solution heated to 45°C containing 1 kg/7" of acid, use four nozzles each on the top and bottom sides of the strip as shown in Figure 2. When the headers were installed at equal intervals, the weight loss of the strip metal was 16.5 g/m2/15 seconds on the top side and 15.5 g/m2/15 seconds on the bottom side.

In this case, when the desired pickling was carried out on the lower surface of the strip, the upper surface became 6% overpickled.

On the other hand, as shown in Figure 4, the spacing between the nozzle headers is 150 mm on the bottom side of the strip and 225 mm on the top side, and the number of nozzle headers installed is 7 mm on the bottom side of the strip.
When spray pickling is performed using the method of the present invention with 5 strips installed on the top side, the weight loss of the strip metal is 15g/m・1 on the top side.
5 seconds, lower surface 15g/m2, almost equivalent to 15 seconds.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a spray pickling method for strips, FIG. 2 is a schematic diagram showing a spray pickling device for explaining the method of the present invention, and FIG. 3 is a diagram showing nozzle spacing and strip metal in the device according to FIG. FIG. 4 is an explanatory diagram showing an example of a spray device for carrying out the method of the present invention. S... Strip, 2... Nozzle header 3... Supply pipe, 4... Pump,
5...Storage tank.

Claims (1)

[Claims] 1. In a method of spray pickling in which multiple spray nozzles are installed in the strip length direction to inject an acid solution toward the upper and lower surfaces of a strip running in a substantially horizontal direction, the spacing of the spray nozzles in the length direction of the strip is A spray pickling method for a strip, characterized in that the lower surface side is made smaller than the upper surface side, and the amount of acid solution sprayed onto the strip is larger on the lower surface side than on the upper surface side of the strip.