To ensure optimal pickling effect, the following parameters are extremely important.
A free metal surface, that is, a good crack from the surface of iron oxide to the metal matrix;- rapid establishment of potential;High kinetic energy of acid at a metal phase boundary;
The temperature of an acid solution and the rapid heating of strip steel;
The ratio of acid concentration to metal concentration ensures the optimal pickling time and the most economical amount of acid needed.
The turbulence pickling process in our factory provides the optimal solution for the above parameters.
A granite sliding table is arranged above and below each acid groove with an interval of 2 meters. The middle cover connected with the upper cover is designed with multiple baffles, each baffle 2 meters long. Each groove is divided into many different compartments by a special design of the lower part of the acid tank and the middle cover connected with the upper cover.
When the strip is running at a certain speed, the small chamber can cause the acid liquid on the upper and lower surfaces of the strip to produce stagnation pressure, thus producing high turbulence area. In this way, the strip can be heated and diffused faster, thus greatly shortening the pickling time. When the strip speed increases, the turbulent effect increases synchronously.
At the same time, the technology of setting a small chamber in the acid tank makes part of the stagnant acid liquid recycle and eliminates the surge of acid liquid rushing to the outlet of the acid tank due to high speed, thus reducing the acid liquid taken out due to the movement of the strip steel. At the same time squeeze dry rod seal can be greatly simplified.
A. Pickling section process
The pickling part includes 3 acid tanks, each section is about 34m in length between rollers, the maximum pickling speed is 306 m/min, and the minimum pickling time is 20 seconds. When pickling of coiling temperature is 650 ℃ steel coil, pickling time must be the shortest to 23 seconds, so must slow down pickling.Each groove is provided with a nozzle collector at the inlet and outlet of the strip, which is used to separate the pickling part from the roller and charge the acid into the groove.
Place two more acid points on each side of the first chamber below the production line. One or more spillages, and the sluice flows the acid into the corresponding circulating tank.
When the strip stops running, the delivery pump will be disconnected and the acid will flow freely into the circulation tank.The acid discharge and filling time is about 2-3 minutes. The strip disengages from the acid solution for about 2 minutes.3 pickling tanks are equipped with 3 recycling tanks to ensure the optimal acid concentration gradient required by the pickling process.The circulating tanks are interconnected via cascades. Regenerated acid is added to the third cycle tank. The waste acid is discharged from the first cycle tank.Each of the three tanks has a capacity of 45m2 and the acid cycle is conducted with the respective acid tank. It works with 50% of its volume of acid for pump use.
When the production line stops, the acid liquid in the acid tank flows into the circulation tank. With built-in heat exchanger pump circuit will acid circulation, about 25 times and acid heated to a temperature of 75-90 ℃.
A reverse loop is provided for heating and maintaining the temperature of the circulating tank when the production line is stopped.There is a Fe concentration measuring device in tank 1, which is connected to the acid automatic processing system. When the Fe content reaches 125g /1 to 130g/1, the acid in tank 1 is pumped into the collecting tank, and the new acid of the same volume is pumped into tank 3 from the regenerated acid tank..Two separate nozzles (one upper, one lower) are installed between the nozzle manifold of the third pickling tank outlet and the roller.
This header is sprayed with 25001/h regenerated acid to reduce the FeCl2 entering the rinsing tank and to prevent the rust from forming when the strip speed is too low.A set of undriven roller is installed in the discharge chamber before the first pickling tank, which forms an alternate rinsing device with the rear roller and nozzle manifold. When the strip runs backward from the pickling part, a set of nozzle collector is used to spray condensation water to the strip surface. The consumption water is collected into the discharge chamber and sent to the washing tower.
Two pairs of roller are installed at the outlet of the third pickling tank. There is a pre-rinse unit between the two squeegee rollers, which is equipped with two jet sets (one top, one bottom) to spray water from the first rinse section.
This water is provided for the following purposes: to ensure that the residual acid does not dry when the strip passes at low speed. It compensates the partial evaporation loss of pickling and reduces the amount of acid when the strip enters the liquorous region, and at the same time reduces the angular phase of ferric acid and acid complex by the liquorous method in the latter 5 segments.