The good surface condition and cleanliness of strip steel before hot-dip galvanizing are prerequisites for obtaining a good coating. On the surface of the strip steel with oil stains, a bright, well bonded, and superior corrosion resistance coating cannot be obtained. Therefore, before the strip steel enters the annealing furnace, it must first go through the cleaning section of the brush washing unit, which mainly includes chemical alkali washing, electrolytic alkali washing, and brush roller cleaning.

(1) Spray cleaning and circulation

Spray cleaning mainly completes the heating and rough cleaning of the steel strip. It is carried out in the form of spraying, using the chemical action of hot alkaline solution to remove the thicker rolling oil and iron powder on the surface of cold-rolled strip steel. These rolling oils are often contaminated by lubricating oil and hydraulic oil, and must first be washed with chemical alkali before being removed by electrolytic alkali washing.

(2) Due to the large amount of oil and iron powder adhering to the surface of the hard rolled coil, the effect of chemical alkaline cleaning is not very good. Therefore, it is necessary to use both chemical alkaline cleaning and brush roller clening for treatment. Brush roller cleaning can mechanically remove oil and dust to improve cleaning efficiency. For the brushing of this unit, in addition to controlling its concentration, temperature, and spraying pressure, it is also necessary to control the brush roller current. The brush roller current reflects the degree of compression of the brush roller on the strip steel, and the amount of compression of the brush roller can be adjusted by the motor. During the brushing process, the bristles of the brush roller will also be constantly worn out. It is necessary to regularly check the length of the bristles on the brush roller. When the bristles are too short, the brush roller should be replaced in a timely manner.

(3) Electrolytic cleaning

The mechanism of electrolytic cleaning is that when the strip is used as the negative or positive end, hydrogen or oxygen bubbles are correspondingly precipitated by the electrolytic water on the surface of the strip, which will damage the oil film attached to the surface of the strip. Small bubbles detach from the steel strip attached to the oil droplets and remain on the surface of the oil droplets, staying at the interface between oil and degreasing solution. As new bubbles continue to precipitate, the small bubbles gradually become larger. Therefore, the oil droplets detach from the surface of the steel strip under the action of the bubbles and are carried into the degreasing solution by the bubbles. At the same time, the generated small bubbles can remove the oxide skin on the surface and some dirt in the gaps.

(4) The hot water brushing tank uses mechanical methods to remove the dust and dirt attached to the steel plate after electrolytic cleaning, further enhancing the cleaning effect. The difference from the previous alkaline spraying operation is that the spraying liquid is hot water, and the operation of the brush roller is similar.

(5) Hot water rinsing

After hot water brushing, the strip steel is squeezed dry by a drying roller, but there is still a certain amount of degreasing liquid remaining on the surface. If it directly enters the annealing furnace, it is easy to form spots on the surface of the strip steel. So it is necessary to rinse with hot water to clean the surface of the strip steel. Hot water rinsing adopts three end overflow, with one section replenished with fresh water. During operation, the temperature, overflow flow rate, and circulation rate should be well controlled.

(6) Drying of strip steel

Remove the moisture from the surface of the strip steel, control the circulation rate and temperature of the hot air during operation, and regularly inspect the nozzle to prevent blockage.

(7) Inspection after cleaning

For the cleaning effect, the strip steel that has just been dried by hot air can be observed with the naked eye. If the board surface turns black and there is black ash on the surface, it indicates poor cleaning. The concentration, temperature, and condition of the brush rollers in each slot should be checked; If there are spots on the surface of the board, it indicates that the rinsing is not sufficient, and the amount of supplementary water, circulating water, and overflow should be increased. If there are water stains on the board surface, it indicates poor drying. The hot air temperature should be adjusted and the condition of the nozzle should be checked.