Common defects in the production process of pickled plates include iron oxide scale indentation, oxygen spots (surface landscape painting), waist fold (horizontal fold print), scratches, yellow spots, under-pickling, over-pickling, etc.

(Note: Defects are linked to the requirements of standards or protocols. Defects are called defects if they do not meet the requirements. Here, for the convenience of expression, defects are used to replace a certain type of morphology.)

1. Iron oxide scale indentation
Iron oxide scale indentation is a surface defect formed during hot rolling. After pickling, it is often pressed in the form of black dots or long strips, with a rough surface, generally with a hand feel, and appears sporadically or densely.
The causes of iron oxide scale are related to many factors, mainly the following aspects: heating in the heating furnace, descaling process, rolling process, roller material, and state, roller state, and rolling plan, etc.
Control measures: Optimize the heating process, increase the number of descaling passes, and regularly check and maintain the roller and roller, so that the rolling line remains in good condition.

2. Oxygen spots (surface landscape painting defects)
Oxygen spot defects refer to the dot-shaped, line-shaped or pit-shaped morphology left after the iron oxide scale on the surface of the hot-rolled coil is washed off. Visually, it appears as irregular color difference spots. Because the shape is similar to a landscape painting, it is also called a landscape painting defect. Visually, it looks like a dark pattern with ups and downs in the shape of a mountain peak, which is distributed as a whole or partially on the surface of the strip. It is essentially an iron oxide scale spot, which is a layer of things floating on the surface. It has no feel and may be darker or lighter in color. The dark part is relatively rough, and it has a certain impact on the appearance after electrophoresis, but it does not affect the performance.
Cause of oxygen spot (landscape painting defect): The defect is essential that the iron oxide scale on the surface of the hot-rolled strip has not been completely removed, and it is pressed into the matrix after subsequent rolling and stands out after pickling.
Control measures for oxygen spots: reduce the steel-out temperature of the heating furnace, increase the number of rough rolling descaling passes, and optimize the finishing rolling cooling water process.

3. Waist fold
Waist fold is a transverse wrinkle, bend, or rheological zone perpendicular to the rolling direction. It can be identified with the naked eye when unwinding, and it can be felt by hand if it is serious.
Causes of waist fold: Low-carbon aluminum-killed steel has an inherent yield platform. When the steel coil is unwinding, the yield deformation effect occurs under the action of bending stress, which makes the originally uniform bending become uneven bending, thus forming a waist fold morphology.

4. Yellow spots
Yellow spots appear on the part of the whole surface of the strip, which cannot be covered after oiling, affecting the appearance of product quality.
Causes of yellow spots: The surface activity of the strip just out of the pickling tank is high, the rinsing water fails to play the role of normal rinsing of the strip, and the surface of the strip is oxidized and yellowed; the spray beam and nozzle of the rinsing tank are blocked, and the angles are not equal.
Control measures for yellow spots include: regularly checking the status of the spray beam and nozzle, and cleaning the nozzle regularly; ensuring the pressure of the rinsing water, etc.

5. Scratches
The surface has a certain depth of scratches and irregular shapes, which affects the surface quality of the product.
Causes of scratches: improper loop tension; nylon lining wear; poor incoming material shape; hot coil inner ring loose coil, etc.
Control measures for scratches: 1) Appropriately increase the tension of the loop; 2) Regularly check the surface condition of the lining, and replace the lining with abnormal surface condition in time 3) Repair the steel coil with poor incoming material shape and loose inner ring.

6. Under-pickling
The so-called under-pickling means that the local iron oxide scale on the surface of the strip is not cleanly and fully removed, the plate surface is gray-black, and there are fish scales or horizontal water ripples.
Causes of under-pickling: This is related to the process of the acid solution and the surface condition of the steel plate. The main production process factors include insufficient acid concentration, low temperature, too fast strip running speed, and the strip cannot be immersed in the acid solution. The thickness of the hot coil iron oxide scale is uneven, and the steel coil has a wave shape. Under-pickling is often easy to occur at the head, tail, and edge of the strip.
Control measures for under-pickling: adjust the pickling process, optimize the hot rolling process, control the strip shape, and establish a reasonable process system.

7. Over-pickling
Over-pickling means over-pickling. The surface of the strip is often dark black or brown-black, with blocky or flaky black or yellow spots, and the surface is generally rough.
Causes of over-pickling: Contrary to under-pickling, over-pickling is easy to occur if the acid concentration is high, the temperature is high, and the strip speed is slow. Over-pickling should be more likely to appear in the middle and width of the strip.
Control measures for over-pickling: adjust and optimize the pickling process, establish a suitable process system, and carry out quality training to improve the quality management level.

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