I. Zinc slag
【Definition and Characteristics】
Have you seen those small particles or irregular lumps like grains of rice? That is the so-called “zinc dross”. This zinc dross can be divided into three cases:
① Coarse dross particles are those embedded in the metal coating, the size of about 0.5 mm to 2.0 mm between the dross particles;
② Fine dross particles are those that are striped or aggregated in the plating layer, with a diameter of less than 0.5 millimeters of small dross particles;
③ dross spots are those embedded in the metal plating layer, the size of about 2.0 millimeters to 10 millimeters between the dross particles.
These zinc drosses are formed as a result of the accumulation of bottom dross, suspended dross, and floating surface dross on the steel strip. Other causes include fluctuations in liquid zinc temperature, poor slag removal, prolonged use of sinker rolls, and excessive aluminum content.
In order to reduce the production of zinc dross, we can do the following:
① Control the temperature of zinc liquid in the range of 460 degrees Celsius plus or minus 5 degrees Celsius, to improve the stability of the temperature of the zinc liquid;
② When we find that there are more defects of zinc dross, we have to increase the frequency of dross fishing, timely clean up the floating dross in the zinc pot, and at the same time reduce the height of the scraper appropriately (adjusted according to the specifications of the steel strip in the range of 50 mm to 450 mm). Adjustment). If we want to produce galvanized sheet with high surface requirements, we also need to use nitrogen tube for slag blowing treatment;
③ Before installing the immersed rollers, we need to make sure the repair quality of the immersed rollers, especially the grooves, surface roughness and smoothness of the immersed rollers should meet the process requirements, and replace the immersed rollers in a timely manner in accordance with the stipulated cycle;
④ We need to control the aluminum content in the zinc solution, stabilizing it at between 0.18% and 0.22%.
【Identification and judgment】
We can use the naked eye to check. If the dross particles are larger or the dross spots are more obvious, you will feel them in your hand, and they will protrude into dots, blocks or strips on the surface of the galvanized sheet. For galvanized sheets with high surface requirements, dross defects are not allowed.
2.Zinc gray
【Definition and Characteristics】
Zinc gray is those white dots, pinpoint size or slender comet flakes (like dragging a tail) defects.
Causes] The zinc dust is caused by the accumulation of zinc dust inside the furnace nose, which falls to the surface of the steel strip due to vibration during the operation of the strip.
【Prevention and Correction】
In order to prevent the generation of zinc dust, we can take the following measures:
① Regularly replace the zinc nose and zinc pump;
② Increase the humidification device of the furnace nose and remove the zinc dust device;
③ Improve the stability of the submerged rollers to reduce the fluctuation of the liquid level.
【Identification and judgment】
We can check it with naked eyes. Compared with other zinc slag, the degree of zinc ash is lighter; and it is not obvious to the touch. Judgment is made according to the standard.
3.Cloudy plating
【Definition and Characteristics】
The thickness of the plating layer shows a water wave-like change is called “plating cloud”. Plating cloudiness can be divided into the following three cases:
① parking plating cloudiness refers to the corrugated fluctuation is larger, showing the sea waves, defects distribution is not regular, feel very serious, and there will be local iron defects;
② deceleration plating cloudiness refers to the corrugated fluctuation is larger, showing a watery pattern, there is a certain degree of regularity, the feel is also more serious;
③ zinc flow trace plating cloudiness refers to the fluctuation of corrugated smaller, showing a fish scale shape, regular, but no feel. Showing a fish scale-like, regular, but no feel.
Parking coating cloud: The temperature and speed of the steel strip entering the zinc pot cannot meet the process requirements due to the stopping of the unit. Deceleration plating cloud: the running speed of the steel strip is too low, the zinc liquid on the steel strip flows downward due to gravity, resulting in deceleration plating cloud; Zinc flow ripples plating cloud: the production speed of the unit is low, the thickness of the plating layer is large, the temperature of the steel strip entering the zinc pot and the temperature of the zinc liquid is low, and the roughness of the surface of the steel strip is low, and other reasons.
【Prevention and Correction】
In order to prevent cloudy plating, we can take the following measures: ①Control the temperature of the steel strip entering the zinc pot and the temperature of the zinc liquid to ensure that the process requirements are met. When restarting after stopping for a period of time, try to use the fast warming method and reduce the output of the spray cooling section of the annealing furnace; ② For different specifications of steel strip, avoid reducing the speed to the minimum operating speed of the corresponding specifications. In the case of the need to reduce the speed of the sudden situation, the use of a number of small-amplitude speed reduction, to avoid a one-time speed reduction of more than 20 m / min; ③ in the production of thick material thick coating galvanized sheet, try to maximize the production speed of production, and at the same time reduce the air knife knife lip distance, reduce the height of the air knife and so on.
【Identification and judgment】
We can check with the naked eye. Galvanized cloudiness is not easily confused with other defects, and usually appears when stopping, starting after stopping, or dropping speed sharply. Judgment is made according to the standard, and plating clouds are not allowed on galvanized sheets.
4.Submerged roll mark
【Definition and characteristics】
The shape of the grooves of the sunken rolls will be printed on the surface of the steel strip, forming longitudinal (or diagonal) stripes along the direction of rolling, known as the “sunken roll mark”. Sunken roll marks are usually the same as the shape of the grooves of the sunken rolls.
【Causes】
The surface of the immersed roller scratches, pits or grooves of the grinding quality does not meet the requirements; immersed roller head and sleeve clearance is too large, resulting in the immersed roller in the operation of the vibration of the larger; zinc pot tension is not properly adjusted; zinc pot in the aluminum content is low, the free slag is more, adhering to the grooves of the immersed rollers. Sinking roll marks are caused by streak-like deposits on the sinking roll in the zinc pot scratching the surface of the cold rolled steel strip, and sometimes related to the interruption of the growth of the alloy layer.
【Prevention and correction】
In order to prevent the generation of sunken roll marks, we can take the following measures: ① The surface and grooves of the sunken rolls are not allowed to have obvious scratches, and all protective measures should be taken to avoid damage to the surface of the rolls during assembly; ② During the assembly of the sunken rolls, make sure that the accuracy of the installation; ③ When the defect of sunken roll marks occurs, each time, adjust the tension of the zinc pot within the range of 10%, and observe the extent of the defect and adjust it again and again; Do not use it for producing thick material in the initial stage just after replacing the immersed roller; ④ When immersed roller marks occur and the aluminum content in the zinc pot is found to be low, add high aluminum ingots to the four corners of the zinc pot to appropriately increase the aluminum content.
【Identification and Judgment】
We can check it with naked eyes. Sunken roller marks are not easily confused with other defects, and according to the standard judgment, sunken roller marks are not allowed to exist.
5.zinc flower uneven
【Definition and Characteristics】
The zinc flower on the surface of the steel plate in the local area of the size is too large or too small, does not meet the normal requirements, is called “zinc flower uneven”. Zinc flower uneven block or strip distribution, in the steel strip surface localized or the whole coil.
【Causes]
Zinc flower formation rate is not consistent.
【Prevention and correction】
In order to prevent uneven zinc flower, we can take the following measures: ① in the discovery of uneven zinc flower or zinc flower small defects, reduce the production speed to ensure that the heating and cooling of the steel strip is uniform; ② increase the concentration of lye, increase the insertion of brush rollers, increase the amount of emissions and frequency, improve the cleaning effect. Appropriately increase the temperature of the annealing furnace to enhance the cleaning capacity of the annealing furnace; ③ control the content of antimony in the zinc pot to meet the process requirements, add zinc ingots to take a small amount of the principle of multiple times.
【Identification and judgment】
We can use the naked eye to check. Usually, some of the zinc flowers are small or basically can not see the obvious zinc flowers, and the surrounding zinc flowers are normal. There may be more zinc flowers at the head and tail of the belt. Not easily confused with other defects. Determined according to the standard, small amounts are allowed at the head and tail of the strip.
6.Side twill
【Definition and Characteristics】
During the cooling process of a steel strip, a feathery, diagonal stripe is formed on the edge, which is known as the “edge diagonal stripe”.
The cooling of the zinc layer at the edge is insufficient. The zinc layer on the surface may be cooled, but the internal zinc liquid is not sufficiently cooled, and the un-cooled portion of the zinc liquid will have a tendency to flow, resulting in the formation of diagonal stripes.
【Prevention and Correction】
In order to prevent the generation of slanting pattern at the edge, we can take the following measures: ① Increase the height between the air knife and the zinc liquid surface, stretch the distance between the air knife and the steel strip, and increase the pressure of the air knife; ② Decrease the temperature of the zinc liquid, and reduce the production speed of the unit.
【Identification and judgment】
We can use the naked eye to check. Side slash is not easily confused with other defects. Judge it according to the standard.
7.edge thickening
【Definition and characteristics】
The thickness of the metal coating on the edge of the steel strip increases locally, known as “edge thickening”.
【Causes】
The edge of the burrs lead to zinc in the air knife through the knife blocking knife lip; zinc liquid temperature is low; edge baffle clearance is too large, the air knife angle is not adjusted appropriately, resulting in turbulence phenomenon; steel belt in low-speed operation, due to the side of the heat loss is serious, resulting in an increase in the viscosity of the zinc liquid, the side of the zinc scraped less than the center.
In order to prevent the thickening of the edge, we can take the following measures: ① Strictly control the quality of the edge of the steel strip, and refuse to put on line the production of coils with burrs or broken edges; ② Strictly control the temperature of the zinc liquid; ③ Regularly check the gap of the edge baffle, and reasonably adjust the angle of the air knife; ④ When running at a low speed, increase the amount of blowing air, and appropriately lower the height of the air knife, so as to blow off the excess of zinc liquid, and make it detach before cooling. detach before cooling.
【Identification and Judgment】
We can judge by visual inspection. The more serious cases can be directly observed, and the more minor cases can be judged by hand touch. If the edge thickening is not obvious, you can use a micrometer to measure the thickness for comparison. Edge thickening is not allowed to exist.
8.Spotting
【Definition and Characteristics】
After galvanization, the surface of the steel strip appears as spots of local bumps or pits, known as “pitting”. Spots are usually point-like, irregularly distributed on the surface of the steel strip, and has a slight color change.
【Causes】
Insufficient post-cooling, resulting in scratches or pits at the top rollers, or uneven cooling; rust or incomplete removal of dirt from the substrate prior to galvanizing.
Prevention and correction] In order to prevent pitting, we can take the following measures: ① Control the output of the fan in the after-cooling section to ensure the temperature in front of the horizontal top stick and ensure the normal use of the horizontal top stick scraper; ② Increase the insertion amount of the brush stick appropriately to increase the hydrogen content in the annealing furnace when rusting of the raw material or dirt is found.
【Identification and judgment】
We can use the naked eye to check. Judgment according to the standard.