Good surface condition and cleanliness of strip steel before hot galvanizing is the precondition to get good coating.No bright, cohesive and corrosion resistant coatings can be obtained on the surface of greasy strip steel.Therefore, before the steel belt enters the annealing furnace, it must go through the cleaning section, which mainly includes chemical alkaline cleaning, electrolytic alkaline cleaning and brushing.
(1) spray cleaning and circulating spray cleaning are mainly to complete the heating and rough cleaning of strip steel.It is carried out in the form of spray, and the thick rolling oil and iron powder of cold-rolled strip steel are removed by the chemical action of hot alkali liquid.These rolling oils are often contaminated with lubricants and hydraulic oils and must be chemically washed first and then removed by electrolysis.Oil and grease are divided into two categories: saponified oil and non-saponified oil.And is (RCOO)3C3H3, which can react with the alkali to form fertilizer, they can form emulsion under certain conditions, relying on the milk is to use the hot alkali liquid to remove saponified oil, using the emulsifier to spray cleaning section is important to control the concentration: the opposite side reduces the cleaning effect, but also can cause!The main components of alkylated oil are glycerol containing various high - grade fatty acids, its general form, and glycerol.Non-saponifiable oil refers to mineral oil, which cannot react with alkali. However, it can remove non-saponifiable oil from the surface of strip steel.Chemical alkali washing action, remaining non - royal oil.1 the temperature.The concentration is too high, today's t fat waste, and thick!The concentration is controlled at 2-3%, and the degreasing temperature is contradictory from the point of view of saving the source.The higher the temperature, the surface-adhesive grease and degreasing must be added to the degreasing agent in order to reduce the temperature.The solubility of E soap and the stability of emulsion decrease, too low, the cleaning will not be effective.In general lye, the degree should be as low as possible, but the faster the physical and chemical reaction speed is, the easier the removal of oil is.For the cleaning of the unit, to control the temperature at 6080 ℃,
(2) as there is a large amount of grease and iron powder attached to the surface of the rolled coil, only chemical alkaline cleaning effect is not very good, it must be treated together with chemical alkaline cleaning and brushing.Scrubbing can remove grease and dust mechanically to improve the cleaning effect.In addition to controlling the thickness, degree, temperature and injection pressure of the unit, the current of the brush roller must be controlled. The current of the brush roller reflects the compaction of the brush roller on the strip steel.During the washing process, the silver brush hand will also) when the brush hair is too short to timely change the roll
(3) the mechanism of electrolytic cleaning and electrolytic cleaning is that when the strip is used as a cathode or anode, the oil film attached to the strip surface will be damaged because the electrolytic water will precipitate hydrogen bubbles or oxygen on the surface of the strip correspondingly.The small bubble is separated from the strip steel attached by the oil droplet and stays on the surface of the oil droplet and stays on the interface between the oil droplet and the degreasing liquid. As the new bubble continues to precipitate out, the small bubble gradually becomes larger, so the oil droplet is separated from the strip steel surface under the action of gas berthing and is carried to the degreasing liquid by the bubbles.At the same time, the resulting stingy xunxun can bring out the surface oxidized skin and some dirt in the gap.
The methods commonly used for electrolytic degreasing include: intermediate conductor method and conductive silver method.This unit adopts intermediate conductor method.That is, the strip steel is not directly connected to the power supply. The power supply is connected to the electrode plate above and below the strip steel. When the upper plate is connected to the anode, the lower plate is connected to the cathode.Compared with the positive plate, the strip steel has a negative potential and a cathode. At this time, the reaction on the strip steel surface is :.Compared with cathode plate, the strip steel has positive potential and is anode. At this time, the strip steel's reaction is:
4H20 +4e = 2H2 +40H, that is, the recovered gas was precipitated on the strip steel.In this way, the water is decomposed by an electrochemical reaction, producing hydrogen and oxygen.In the electrolytic cleaning section, the concentration and temperature of the lye should be slightly increased to enhance the electrical conductivity.Due to the large amount of hydrogen and oxygen produced in the process of electrolysis, hydrogen is a inflammable and explosive gas. Therefore, there should be a suction device in the cleaning section of electrolysis to timely extract the gas generated.
.(4) the hot water scrubbing in the hot water scrubbing tank adopts mechanical method to remove the dust and dirt attached to the steel plate after electrolysis cleaning and further enhance the cleaning effect. The difference from the previous alkaline spraying operation is that the dark water is hot water, and the operation of the brush roller is similar.
(5) after the hot water rinsing strip steel is washed by hot water, it is dried by extrusion and rolling, but there is still some degreasing liquid on the surface. If it enters the annealing furnace directly, it is easy to form spots on the surface of the strip steel.Therefore, the strip surface must be rinsed with hot water.A three-stage overflow is used for hot water rinsing, in which the last section is used to replenish new water. The temperature, overflow flow and circulation should be controlled well during operation.
(6) strip steel shall be dried to remove moisture from the surface of strip steel. During operation, the circulating amount of hot air and the temperature of hot air shall be controlled, and the nozzle shall be inspected frequently to prevent cold plugging.
(7) the effect of post-cleaning inspection on cleaning can be observed with the naked eye when the hot air dry strip steel.If the surface of the board is black and there is black ash on the surface, it indicates that the cleaning is not good. The concentration, temperature and condition of the brush roller should be checked.If there is water mark on the plate surface, it indicates that the coking is not good, the hot air temperature should be adjusted and the nozzle condition should be checked.