Silicon steel coating process introduction(1)

24 Nov 2023
Reading Volume :
GNEE Steel Silicon Steel Coil
Compared with hot-rolled silicon steel sheets, cold-rolled silicon steel sheets have an obvious feature that a layer of coating is coated on the surface during the production process. This layer of coating not only has high insulation performance, but also has corrosion resistance and processing performance. , Good heat resistance, the surface coating of oriented steel can improve the magnetic properties, and the interlayer insulation of the finished hot-rolled silicon steel sheet is mainly completed by soaking in varnish and drying after pickling. Let me give you a look at the coating process of silicon steel:
The insulating coating currently used for non-oriented silicon steel is an inorganic-organic hybrid insulating coating, referred to as a semi-organic coating (T4 chromate-organic resin): T0: water, boric acid (H3BO3), chromic anhydride (CrO3), additives, etc. ;T0 specific gravity (1.1611.175g/cm3, 25℃)
Grain oriented silicon steel
oriented silicon steel

Main reasons affecting the quality of coating liquid
1) Influence of temperature
As the temperature rises, the effective storage time of T4 coating solution is shorter, that is, 10°C-5 days, 20°C-3 days, 30°C-2 days.
2Influence of time
At the same temperature, as time goes on, the color of the coating liquid becomes darker and darker, and finally deteriorates and is scrapped. Due to the influence of temperature on the coating liquid, the coating system has a separate refrigeration system, using water as the medium, and a circulating pump Pass cold water into each cooling point (including circulation tank and storage tank), there are serpentine pipes distributed in the tank, and the cold water circulates continuously in the pipes to keep the temperature of the coating solution at <20°C. Thereby to ensure the freshness of the coating liquid.
Due to the influence of time on the coating liquid, the coating liquid should be used up as soon as possible during production, and then fresh coating liquid should be added to prevent the coating liquid from deteriorating and causing poor coating; when the unit encounters failure and maintenance, the coating should be stopped for a long time The system should empty the coating liquid in the circulation tank and storage tank in time and flush it with water to prevent the coating liquid from agglomerating and blocking the pump and pipeline after deterioration.
3Coating amount control
Coating amount: the weight of the coating on the steel strip per unit area, in g/m2. In order to ensure the comprehensive performance of the coating, all kinds of coatings must be tested in advance to determine the target value and control range of the optimal coating amount.
Grain non oriented silicon steel
non oriented silicon steel
 Factors affecting the amount of coating
1 The specific gravity of the coating solution: the higher the specific gravity, the higher the coating amount;
2) Unit speed: Since the coating roller is a follower roller, the coating amount is proportional to the unit speed, the higher the speed, the thicker the coating amount;
3The reduction of the coating roller: the coating amount is inversely proportional to the reduction of the coating roller, the greater the reduction, the thinner the coating;
4Roller shape of the coating roller: The coating roller is made of acid-resistant rubber. The roller shape factors include the hardness, diameter, angle, depth, and number of teeth of the rubber roller, etc. Larger, deeper grooves, and more teeth, the thicker the amount of coating.
Principles of Equipping Coating Rollers
(1) Try to choose the same type of coating roller for the roller type factor;
(2) Due to gravity, the amount of coating on the lower surface is relatively thin, so the coating roller with high hardness, small diameter and deep groove should be used as the lower roller;
(3) The coating rollers must be replaced in pairs.

Adjustment of spray angle and spray volume of coating liquid
Non oriented silicon steel
Cold rolled Silicon Steel
Among them, the injection directions of c and e are correct, and the other directions will cause coating defects.
The principle of adjusting the spray angle and spray volume of the coating liquid should ensure that the coating liquid is sprayed onto the coating roller smoothly and evenly without interruption, and it is necessary to prevent the spraying pressure of the coating liquid from being too high or the spraying direction of the coating liquid header from being sprayed incorrectly. Bubbles are generated, and it is also necessary to prevent the spraying pressure of the coating liquid from being too low or the spraying direction of the coating liquid header is not correct, resulting in no coating liquid spraying or spraying on the coating roller, resulting in coating defects such as missing coatings and spots.
Causes and Countermeasures of Main Defects of Coatings
(1) Leak coating:
Cause: It is caused by the blockage of nozzles, headers, circulation pumps and other equipment, incorrect spray angle pressure of coating liquid or lack of coating liquid.
Countermeasures: Check frequently during operation, dredge and clean the header in time to adjust the injection pressure and angle of the header.
(2) Double lines:
Causes: The specific gravity of the coating liquid is too high; the viscosity of the coating liquid is high; the hardness of the coating roller is high; the reduction of the coating roller is small.
Countermeasures: Strictly standardize the liquid preparation operation, control the proportion of the coating liquid within the target range according to the process; reasonably control the temperature of the coating liquid, the high temperature coating liquid is easy to age, but the temperature is too low, the viscosity of the coating liquid is high, and the diffusion is slow during coating, resulting in Double lines (best at 10-20°C); the hardness of the coating roller is high, and the coating is easy to produce double lines, so the coating roller with lower hardness should be selected according to the speed of the unit, and the coating roller should be adjusted reasonably according to the actual coating situation The amount of depression.
(3) Uneven color tone:
Causes: poor alkali cleaning, oil stains on the steel plate; uneven coating; aging of coating rollers; improper control of drying and firing temperatures, etc.
Countermeasures: improve the quality of alkali cleaning; strictly control the amount of coating according to the coating standard, and adjust the reduction of the coating roller in time to ensure that the coating amount of the entire steel plate surface is controlled within the target range and the deviation is as small as possible, so as to ensure the coating. Uniformity; if the aging phenomenon of the coating roller is found, the coating roller should be replaced in time, and the temperature of the drying and sintering furnace can be controlled in a timely and reasonable manner according to the change of the speed of the unit.

 
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