Compared with hot-rolled silicon steel sheets, an obvious feature of cold-rolled silicon steel sheets is that they are coated with a layer of coating on the surface during the production process. This coating not only has higher insulation properties, but also has corrosion resistance and processing properties. , good heat resistance, the surface coating of oriented steel has the effect of improving magnetism, and the interlayer insulation of the finished hot-rolled silicon steel sheet is mainly completed by dipping in varnish and drying after pickling. Let me give you the coating process of silicon steel:
The role of magnesium oxide coating
After decarburization (or no decarburization or nitriding) and annealing of oriented steel (including high magnetic induction oriented steel) cold rolled to the finished thickness, a 2FeO·SiO2 oxide film is formed on the surface of the strip, and a magnesium silicate bottom layer is finally formed after high temperature annealing. , and to prevent the steel strips from bonding to each other during high-temperature annealing, it is also necessary to apply MgO isolation coating on the surface of the steel strips.
Main equipment for magnesium oxide coating
Equipment composition: This system is located in the pit on the transmission side of the coating machine. It is used to prepare coating liquid and supply the coating machine with a certain temperature and concentration of circulating coating liquid. It consists of various tanks, pumps, and chillers. , piping, corresponding detection instruments and control systems and platforms.
The main technical parameters
-2 coating liquid preparation tanks (3m3, with mixer and serpentine cooling pipe);
-2 coating liquid circulation tanks (2m3, with mixer and serpentine cooling pipe);
- 1 cold water circulation tank (2m3);
-2 sets of chillers (1 for use and 1 for standby, cooling capacity ~100kw);
- 2 sets of coating liquid supply pumps (1 for use and 1 for backup, Q=6m3/h, H=25m);
- 2 sets of coating liquid circulation pumps (1 for use and 1 for backup, Q=15m3/h, H=20m);
- 2 sets of cold water circulation pumps (1 for use and 1 for backup, Q=15m3/h, H=25m);
- 2 sets of waste liquid transfer pumps (1 for use and 1 for backup, Q=15m3/h, H=30m);
- 1 set of pure water production device (the water production capacity of the pure water production device is to be determined, 5Kw, with 8m3 storage tank);
-1 pure water storage tank (10m3);
-2 sets of pure water delivery pumps (1 for use and 1 for backup, Q=5m3/h, H=10m);
- 1 set of sewage pump (Q=10m3/h, H=10m).
-1 set of mud pump.
Main processes:
The tap water is sent to the pure water preparation device. After primary filtration by the sand filter, removal of organic matter by activated carbon, and further removal of impurities by the fine filter, it enters the cation and anion exchange columns to initially remove the anions and cations in the water, and then enters the mixed ion exchange column. Further remove the anions and cations in the water, turn the water into pure water, and send it to the pure water storage tank for storage.
Send the raw materials and pure water into the coating liquid preparation tank, stir evenly and then flow into the coating liquid circulation tank. During normal operation, the coating liquid circulation pump supplies recycled coating liquid to the coating machine.
In order to ensure the quality of the coating liquid, a chiller is installed in the system, and the temperature of the coating liquid is controlled below a certain temperature through the serpentine cooling pipes installed in each tank. The waste coating liquid is discharged into the waste liquid pit. After settling in the pit, the supernatant liquid is sent to the water treatment station with a pump; the precipitated mud is sent to the slag yard or water treatment station with a mud pump.
Operating mode, control and interlocking requirements:
① Pressure sensors 38.42/PRT01-01 and 02 are used to detect the squeezing force 2F between the upper and lower coating rollers, and their setting value range is F (the F value is set on site);
② Lifting gear motors 38.42/M0301-01 and 02 are used to control the lifting and lowering of the lower coating roller. Lifting gear motors 38.42/M0301-01 and 02 operate synchronously in the forward direction (the lower coating roller rises), stop, and synchronously operate in the reverse direction ( Lower coating roller descends). 38.42/M0301-01 forward jog (the operating side of the lower coating roller rises), reverse jog (the operating side of the lower coating roller drops), 38.42/M0301-02 forward jog (the transmission side of the lower coating roller rises) ), reverse inching (the transmission side of the lower coating roller drops);
--When the gear motors 38.42/M0301-01 and 02 for lifting are operated in the forward direction simultaneously and any one of the pressure sensors 38.42/PRT01-01 and 02 is ON (reaches F, the same below), 38.42/PRT01-01 and 02 OFF at the same time.
--When 38.42/M0301-01 and 02 perform forward jog operation separately, when 38.42/PRT01 is ON, 38.42/M0301 is OFF, when 38.42/PRT02 is ON, 38.42/M0302 is OFF; when 38.42/M0301-01 and 02 are synchronously reversed To operate in the running direction, when the lower limit position detection switch 38.42/LTS01 is ON, 38.42/M0301-01 and 02 are OFF at the same time; 38.42/M0301 and 02 should all adopt over-current protection control;
③ The traveling gear motor 38.42/M0101 is used to control the traveling of the coating machine.
Main components and requirements of magnesium oxide coating liquid
⑴Main ingredients
① MgO: An alkaline oxide with a high melting point, divided into light and heavy. According to the requirements of the oriented silicon steel sheet production process, a specially manufactured special magnesium oxide between light and heavy is used.
② TiO2: a white chemical raw material, divided into rutile type and rutile type. Because rutile type converts into rutile type at high temperature and releases atomic oxygen, and has good dispersion performance in water, our factory uses rutile type. Minerals are used in magnesium oxide barrier coatings.
③ Other additives.
⑵ Requirements for coating fluid
① When the water temperature is lower than 5℃, add MgO half an hour before use;
② During the preparation, storage and use of magnesium oxide slurry, it must be continuously stirred to ensure good suspension;
③ Control the slurry viscosity at 10.5 to 11 seconds. If it is too thin, it will affect the coating amount. If it is too thick, streaks will easily appear;
④ Magnesium oxide is stored for a long time. When preparing slurry for coating, it is easy to produce painted faces or stripes. In order to improve the uniformity of the coating, a nylon thread can be pulled on the coating roller;
⑤ In order to lower the usage temperature of the coating liquid, two coating liquid circulation tanks can be connected in series to fully cool the coating liquid, lower the liquid temperature, reduce hydration, and meet the process requirements of moisture content;
⑥ When the moisture content exceeds 4% or the liquid temperature exceeds 12°C, the slurry should be scrapped in principle. Generally, the storage time of the slurry should not exceed 8 hours in summer and 12 hours in winter.
Main reasons affecting the quality of magnesium oxide coating fluid
① Effect of temperature
Generally it should be controlled below 5℃.
Due to the influence of temperature on the coating liquid, the coating system has a separate refrigeration system, using water as the medium. A circulation pump is used to pass cold water into various cooling points (including circulation tanks and storage tanks). There are serpentine tubes distributed in the tank. , cold water is continuously circulated in the tube to keep the temperature of the coating liquid at <20°C, thereby ensuring the freshness of the coating liquid.
② The influence of time
When the moisture content exceeds 4% or the liquid temperature exceeds 12°C, the slurry should be scrapped in principle. Generally, the storage time of the slurry should not exceed 8 hours in summer.
It should not exceed 12 hours in winter. If the liquid preparation time is too early or the slurry is stored for too long due to unit failure, the moisture content of the coating liquid will increase, resulting in painted faces or streaks on the coating. It may also extend the heat preservation time of high-temperature annealing. Influence the formation of magnesium silicate bottom layer.
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 replenished to prevent the coating liquid from deteriorating and causing poor coating.
When the unit encounters a failure or the coating system needs to be stopped for a long time for maintenance, the coating fluid in the circulation tank and storage tank should be drained in time and flushed with water to prevent the coating fluid from clumping and blocking the pump and pipes after deterioration.
Operation of magnesium oxide coating systems
⑴ Preparation before magnesium oxide coating
① Confirm that the sewage system of the MgO waste coating pit is normal and put it into operation;
② Confirm that the 1# and 2# MgO circulation tanks have been cleaned and circulated clean water, and confirm that the coating system return pipe and its piping are smooth and not blocked;
③ Confirm that the pressure of 1# and 2# MgO circulating pumps is normal;
④ Install and clean the coating roller, and pull up the fishing line;
⑤ Confirm that the coating machine moves forward and backward normally, and the coating roller opens and closes normally;
⑥ After confirming that the coating group has started the freezer and the MgO coating liquid has been prepared for production use, put the prepared MgO coating liquid into the 1# and 2# circulation tanks, and start the agitator for use.
⑵ Magnesium oxide coating
① Confirm that the finished steel coil has started running on the entry side of the operation line;
② Jog the 1# or 2# coating machine to enter the online state;
③ Operate the coating roller lifting motor to make the coating roller closed, and shake up the MgO coating pan;
④ Start the 1# or 2# coating circulation pump;
⑤ Visually observe the coating amount of the coating roller and the pressure gauge of the coating machine, and adjust the reduction amount of WS and DS to make the coating amount meet the requirements of the process.
⑶ Control of coating amount
Coating amount: The weight of the coating per unit area of the steel strip, in g/m2.
