A hydrogen-free continuous annealing process for low-grade silicon steel

Abstract

The present application belongs to the technical field of continuous annealing process, and provides a low-grade silicon steel hydrogen-free continuous annealing process, which comprises the following steps: S1, performing air tightness detection on an annealing furnace, introducing high-pressure nitrogen into the furnace, and controlling the oxygen content in the furnace to meet the requirements; S2, closing the air supply of the burners in the NOF non-oxidizing furnace that do not participate in combustion, adjusting the air-fuel ratio of the main burners, so that the NOF furnace is in an oxygen-deficient combustion state, and cleaning the strip steel before entering the annealing furnace. A furnace pressure setting value sequence that increases from front to rear along the running direction of the strip steel is adopted, and an online self-optimizing algorithm is used to optimize the pressure increase gradient in real time, so as to form a directional flow furnace atmosphere field, effectively prevent external air from being sucked into the furnace, cooperate with online oxygen content monitoring and automatic correction, and ensure that the oxygen content in the whole length range of the annealing furnace is always lower than 4 million per cent, thereby providing reliable non-oxidizing atmosphere protection for high-temperature section annealing.

Description

Technical Field

[0001] This invention belongs to the field of continuous annealing process technology, specifically a hydrogen-free continuous annealing process for low-grade silicon steel. Background Technology

[0002] Silicon steel is an indispensable soft magnetic material in the fields of power, electronics, and military industries. It is widely used in the manufacture of cores for transformers, motors, and generators. The continuous annealing process is a key step in the production of silicon steel. Its role is to eliminate work hardening after cold rolling, recrystallize grain growth, and form a favorable texture, thereby obtaining excellent electromagnetic properties. On the continuous annealing production line, the strip steel passes through the cleaning section, the non-oxidizing furnace (NOF), the radiant tube furnace (RTF), the soaking furnace (SF), and the cooling section in sequence to achieve the control of the crystal structure and surface quality of the strip steel. At present, continuous annealing units for silicon steel generally use hydrogen as a protective atmosphere. The high reducing power of hydrogen is used to reduce the surface of the strip steel to prevent oxidation of the strip steel in the high-temperature section, ensuring that the surface quality and magnetic properties of the product meet the standards.

[0003] However, the large-scale use of hydrogen has led to high production costs. Taking a silicon steel annealing unit No. 3 as an example, the design process requires a continuous hydrogen supply of 70 m³ / h to maintain the reducing atmosphere inside the furnace. As a high-value industrial gas, hydrogen requires high costs in its preparation, storage, transportation, and use. Secondly, hydrogen is flammable and explosive with a wide explosion limit range, posing serious safety hazards in high-temperature annealing furnaces. This places extremely stringent requirements on the equipment's sealing, nitrogen purging system, and safety interlock devices. Hydrogen leakage can easily lead to major safety accidents. More importantly, the existing process has formed a path dependence on hydrogen. Once the hydrogen supply is interrupted or cannot be introduced, the furnace will lose its reducing atmosphere, and the strip steel will oxidize rapidly in the high-temperature section, generating oxides such as FeO and Fe2O3 on the surface, causing the product surface to turn blue or gray, and the magnetic properties to deteriorate sharply. The unit will be forced to shut down. This rigid constraint of shutting down without hydrogen severely restricts the production line's flexibility and risk resistance, and also hinders the achievement of energy conservation and consumption reduction goals.

[0004] Therefore, the present invention provides a hydrogen-free continuous annealing process for low-grade silicon steel. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, at least one technical problem raised in the background art is solved.

[0006] The technical solution adopted by this invention to solve its technical problem is: a hydrogen-free continuous annealing process for low-grade silicon steel, comprising the following steps:

[0007] Step S1: Perform an airtightness test on the annealing furnace, introduce high-pressure nitrogen into the furnace, and control the oxygen content in the furnace to meet the requirements;

[0008] Step S2: Turn off the air supply to the burners that do not participate in combustion in the NOF non-oxidizing furnace, and adjust the air-fuel ratio of the main burner to make the NOF furnace in a state of oxygen-deficient combustion. Clean the strip steel before it enters the annealing furnace, and control the amount of residual oil and residual iron on the surface of the strip steel to remove oil stains, iron powder and water stains.

[0009] Step S3: Determine the target production speed of the current grade of silicon steel based on the heating capacity of the annealing furnace;

[0010] Step S4: Determine the reference pressure level of the entire furnace based on the current production speed, determine the optimal pressure increment gradient between each section through an online self-optimization algorithm, and generate a sequence of furnace pressure setpoints for each section that increase sequentially from front to back along the strip running direction based on the reference pressure level and the optimal pressure increment gradient.

[0011] Step S4: Based on the furnace pressure setpoint sequence for each segment, the furnace pressure setpoint and the target production speed are linked and sent to the annealing furnace actuator to enable synchronous execution of furnace pressure control and speed control. During the operation of the annealing furnace, the differential pressure at the furnace opening and the oxygen content in the furnace atmosphere are monitored in real time and used as feedback signals to correct the furnace pressure setpoint sequence online until continuous annealing is completed.

[0012] The beneficial effects of this invention are as follows:

[0013] This invention completely replaces hydrogen as the protective atmosphere for the annealing furnace with nitrogen, eliminating the investment in hydrogen preparation, storage, transportation and use, which significantly reduces the unit production cost of continuous annealing of low-grade silicon steel, eliminates the risk of explosion caused by hydrogen leakage in the annealing furnace, reduces the stringent requirements for equipment sealing level and safety interlock devices, and fundamentally improves the safety conditions of unit operation.

[0014] This invention combines nitrogen protection and oxygen-deficient combustion processes to enable the annealing furnace to continue operating normally when the hydrogen supply is interrupted or cannot be introduced, eliminating the passive situation of a complete production line shutdown due to hydrogen supply interruption, and improving the production line's risk resistance and the flexibility of production planning.

[0015] This invention employs a furnace pressure setpoint sequence that increases sequentially from front to back along the strip running direction. Combined with an online self-optimization algorithm, the pressure increase gradient is optimized in real time to form a directional flow furnace atmosphere field. This effectively prevents external air from being drawn back into the furnace. With online monitoring and automatic correction of oxygen content, the oxygen content is ensured to remain below four parts per million throughout the entire length of the annealing furnace, providing a reliable non-oxidizing atmosphere for high-temperature annealing.

[0016] This invention treats the three heating sections as independent constraint sections, calculates the maximum allowable speed of each section based on the current available heating power, and takes the minimum value as the speed limit. Under the premise of ensuring sufficient recrystallization of the strip steel, the production capacity is released to the maximum extent. At the same time, through the mechanism of speed and furnace pressure linkage and synchronous adjustment, the smooth transition of process conditions during the switching of operating conditions is ensured. Attached Figure Description

[0017] The invention will now be further described with reference to the accompanying drawings.

[0018] Figure 1 This is a flowchart of the steps in an embodiment of the present invention;

[0019] Figure 2 This is a step logic judgment diagram of an embodiment of the present invention. Detailed Implementation

[0020] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0021] Example

[0022] Please see Figures 1-2 As shown in the embodiment of the present invention, a hydrogen-free continuous annealing process for low-grade silicon steel includes the following steps:

[0023] Step S1: Perform an airtightness test on the annealing furnace, introduce high-pressure nitrogen into the furnace, and control the oxygen content in the furnace to meet the requirements;

[0024] Step S1 involves using the unit's maintenance window to stop the annealing furnace and cool it to room temperature, venting the residual gas inside the furnace, cleaning the inside of the furnace to remove accumulated dust, oxide debris, and impurities, ensuring the cleanliness of the furnace wall and the surface of the furnace rollers, and providing a clean environment for airtightness testing and nitrogen replacement.

[0025] With the annealing furnace in a sealed state, high-pressure nitrogen is introduced into the furnace to raise the pressure inside the furnace to the preset detection pressure value. All nitrogen inlet valves are then closed to keep the furnace body in a sealed and pressure-maintaining state, and the pressure decay inside the furnace is continuously monitored.

[0026] The preset detection pressure is preferably 150 Pa;

[0027] Using a portable leak detector, the following key potential leak points of the annealing furnace were checked one by one;

[0028] Specifically, key potential leak points include, but are not limited to:

[0029] Furnace shell welds and steel plate splices;

[0030] The bearing seal between the furnace roller and the furnace shell;

[0031] Sealing strips and flange mating surfaces of each section of furnace door (inlet sealing door, outlet sealing door, maintenance door);

[0032] Flange connections for various measuring holes, observation holes, and spare interfaces opened on the furnace top and bottom;

[0033] Wall penetration joints and valve packing points for various media pipelines (nitrogen pipes, gas pipes, cooling water pipes);

[0034] If a leak is detected, the leak point is rectified, then flushed and filled with high-pressure nitrogen for retesting until the leakage at all detection points meets the sealing qualification standard.

[0035] Leakage prevention measures include, but are not limited to: repair welding, replacing sealing strips, or tightening flange bolts after depressurization;

[0036] After the airtightness test is passed, continue to introduce high-pressure nitrogen into the furnace to gradually replace and remove the residual air in the furnace, so that the oxygen concentration in the furnace atmosphere continues to decrease.

[0037] During the replacement process, oxygen concentration values ​​of each section are read and recorded in real time by oxygen content analyzers installed in each section of the annealing furnace (including NOF section, RTF section, SF section and cooling section);

[0038] When the oxygen content in each section of the annealing furnace drops below the preset qualified threshold, the furnace atmosphere replacement is deemed qualified. The large flow rate of nitrogen replacement is stopped, and the small flow rate of nitrogen is switched to maintain the positive pressure state in the furnace. This prevents external air from being drawn back into the furnace through the gaps in the furnace door or the interface, ensuring that the oxygen content in the furnace remains below the qualified threshold during the subsequent heating and strip steel feeding process, thus providing an oxidation-free furnace atmosphere environment for hydrogen-free annealing.

[0039] The flow rate for high-flow nitrogen replacement is 500 to 1000 standard cubic meters per hour, and the flow rate for low-flow nitrogen replenishment is 50 to 100 standard cubic meters per hour.

[0040] The preset acceptable threshold is preferably 400 ppm. When the oxygen content in a certain section rises above 400 ppm, an alarm is automatically triggered and the flow rate of supplemental nitrogen is increased until the oxygen content falls back to the acceptable range.

[0041] By completely replacing hydrogen with nitrogen as the protective atmosphere in the annealing furnace, the unit production cost of continuous annealing of low-grade silicon steel has been significantly reduced. The elimination of hydrogen, which has flammable and explosive properties, has eliminated the risk of explosions caused by hydrogen leaks in the annealing furnace. This has also reduced the stringent requirements for equipment sealing levels and safety interlock devices, fundamentally improving the safety conditions of the unit's operation.

[0042] Step S2: Turn off the air supply to the burners that do not participate in combustion in the NOF non-oxidizing furnace, and adjust the air-fuel ratio of the main burner to make the NOF furnace in a state of oxygen-deficient combustion. Clean the strip steel before it enters the annealing furnace, and control the amount of residual oil and residual iron on the surface of the strip steel to remove oil stains, iron powder and water stains.

[0043] Step S2 is as follows: After completing the airtightness test and nitrogen replacement of the annealing furnace, the burners in the NOF non-oxidizing furnace are classified and identified to distinguish between the main burners that participate in the heating of the strip steel and the auxiliary burners / cooling burners that do not participate in combustion.

[0044] Close all combustion air manual valves of burners that are not involved in combustion, cut off the air supply channel, and lock the closed manual valves with lead seals or latches to prevent accidental opening of the manual valves due to vibration or misoperation during subsequent production, thereby preventing uncontrolled air from entering the furnace.

[0045] Based on the currently produced low-grade silicon steel varieties (including SG50W1300 and SG50W800) and strip steel specifications, the furnace atmosphere required for the NOF furnace is determined to be a target oxygen-deficient atmosphere.

[0046] Based on the target oxygen-deficient atmosphere, and combined with the theoretical air-fuel ratio of the gas used in the main burner (preferably natural gas or mixed coal gas), the actual air-fuel ratio of the main burner is set to a value lower than the theoretical air-fuel ratio, even if the supply of combustion air is less than the theoretical requirement.

[0047] Preferably, by adjusting the excess air coefficient of the main burner, the excess air coefficient is controlled within the range of 0.95-0.98, so that the oxygen concentration in the radiant tube and furnace space inside the NOF furnace is controlled below 100ppm, ensuring that the strip steel does not undergo surface oxidation due to the presence of free oxygen in the high-temperature heating section of the NOF furnace.

[0048] During the air-fuel ratio adjustment process, the oxygen and carbon monoxide content in the flue gas is monitored in real time by an exhaust gas analyzer installed on the NOF furnace outlet flue. The exhaust gas analyzer reading is used as a feedback signal to fine-tune the air-fuel ratio.

[0049] When the O2 content in the flue gas is higher than 1.0%, it indicates that the excess air coefficient is too high and the oxygen deficiency is insufficient. Gradually close the combustion air regulating valve to reduce the excess air coefficient towards 0.95.

[0050] When the CO content in the flue gas is higher than 500 ppm, it indicates that the excess air coefficient is too small, the oxygen deficiency is too deep, the combustion is serious, and the risk of carbon black formation is increased. Gradually open the combustion air regulating valve to bring the excess air coefficient back to 0.98.

[0051] The process is continuously fine-tuned until the O2 content in the flue gas stabilizes at 0.5%-1.0% and the CO content is ≤500ppm. At this point, the oxygen-deficient combustion state adjustment is deemed qualified, and the optimal excess air coefficient value under the current operating conditions is recorded.

[0052] After completing the classification and identification of NOF furnace burners, the cut-off of air supply and the adjustment of air-fuel ratio under-oxygen conditions, a comprehensive inspection of the equipment status of each process tank in the cleaning section is carried out to ensure that the cleaning system is ready for operation.

[0053] The cleaning section process tanks along the running direction of the strip steel include, but are not limited to: alkaline washing tank, brushing tank, electrolytic cleaning tank, hot water rinsing tank and hot air drying section;

[0054] Specifically, the equipment status confirmation and process parameter settings are as follows:

[0055] Alkali washing tank: Check whether the alkali solution level in the tank is within the normal range, confirm that the alkali solution circulation pump, heater and spray pipeline are working properly, set the alkali washing temperature to 70-85℃, and ensure that the rolling oil on the strip surface is fully saponified and emulsified at this temperature; test the alkali solution concentration to ensure that it is within the concentration range required by the process specification, and add fresh alkali solution if the concentration is insufficient.

[0056] Brushing tank: Inspect the condition of the brush roller surface to ensure that the bristles are not severely worn, deformed, or detached, and that the brush roller bearings rotate freely. Set the brush roller speed so that the speed ratio between the brush roller and the strip is initially controlled within the range of 1.2:1-1.5:1 to ensure that the bristles apply sufficient mechanical scrubbing force to the strip surface to remove residual iron powder and stubborn dirt. Check the working pressure of the brush roller clamping cylinder or hydraulic cylinder to ensure that the contact pressure between the brush roller and the strip surface is uniform and adjustable.

[0057] Electrolytic cleaning tank: Check the condition of the electrode plates to confirm that there is no severe corrosion or short circuit, and that the rectifier power supply output is normal. Set the electrolytic cleaning current density to 5-15A / dm². Utilize the mechanical peeling action of hydrogen bubbles and oxygen bubbles generated by electrolysis to peel off the tiny iron powder particles and residual oil film adhering to the strip surface from the strip surface.

[0058] Hot water rinsing tank: Check the condition of the spray pipes and nozzles to ensure there is no blockage and the spray is uniform. Set the hot water rinsing temperature to ≥80℃ and use high-temperature hot water to thoroughly wash away the residual alkali and stripped dirt on the surface of the strip steel after alkaline washing and electrolytic cleaning.

[0059] Hot air drying section: Check the working status of the hot air blower, electric heater or heat exchanger, and confirm that the hot air volume, air temperature and air speed meet the drying requirements. Set the hot air drying temperature to 100-120℃ to ensure that the surface of the strip steel is completely dry before entering the annealing furnace after leaving the cleaning section, with no residual water or liquid droplets, and to prevent moisture from being carried into the annealing furnace with the strip steel.

[0060] In this step, the rotation speed of each rotating device in the cleaning section (including brush roller, squeeze roller, tension roller and looper drive roller) is initially set according to the reference speed range of continuous annealing of low grade silicon steel. The reference speed range is 100-130m / min, which covers the expected speed range of low grade silicon steel SG50W1300 and SG50W800 under hydrogen-free process conditions.

[0061] It should be noted that after the target production speed is determined in the subsequent step S3, the rotational speed of each rotating device in the cleaning section is adjusted synchronously according to the ratio of the target speed to the current reference speed:

[0062] If the target production speed is higher than the current benchmark speed, the speed of the brush roller, the speed of the squeeze roller, and the speed of each tension roller will be increased linearly and proportionally according to the speed change rate, so that the ratio of the linear speed of each rotating roller to the strip speed remains constant. At the same time, according to the speed increase, the flow rate of alkaline spray and hot water rinsing will be increased appropriately according to the square root relationship, but the increase in spray flow rate shall not exceed 10% (when the speed increase is ≤20%) or shall not be lower than the safety lower limit corresponding to the minimum atomization pressure.

[0063] If the target production speed is lower than the current benchmark speed, the brush roller speed and the speed of each section of the roller are reduced linearly and proportionally according to the rate of change of speed. At the same time, the alkaline spray flow rate and the hot water rinsing flow rate are appropriately reduced according to the square root relationship to save energy. However, the spray flow rate reduction shall not exceed 15% and shall not be lower than the safety lower limit corresponding to the minimum atomization pressure (preferably not lower than 85% of the original flow rate). When the speed reduction exceeds 30%, the spray flow rate shall be maintained at 85% of the original flow rate and shall not be reduced further.

[0064] During the speed adjustment process, the speed ratio between the brush roller and the strip steel is always maintained within the range of 1.2:1-1.5:1 to ensure the consistency of mechanical scrubbing force under different speed conditions;

[0065] An online strip surface cleanliness detection device is installed at the outlet of the cleaning section and before the strip enters the annealing furnace to continuously detect the upper and lower surfaces of the strip that is about to enter the furnace.

[0066] Preferably, the online detection device includes a surface residual oil meter and a surface residual iron meter, used to detect the amount of residual oil and residual iron on the surface of the strip steel, respectively; the detection control objective is:

[0067] Residual oil content on strip surface ≤5mg / m² (single side);

[0068] Residual iron content on the strip surface ≤3mg / m² (single side);

[0069] Simultaneously, a manual visual inspection station is set up at the outlet of the cleaning section, where operators conduct auxiliary visual inspections of the strip surface to confirm that there are no visible water stains, oil spots, rust spots, or obvious scratches on the strip surface.

[0070] If online testing data or visual inspection reveals that the surface cleanliness of the strip steel is unqualified, the cleaning effect is deemed unsatisfactory, and a cleaning effect correction procedure is immediately initiated. The correction procedure includes, but is not limited to, one or more of the following measures:

[0071] Increase the concentration of alkali solution in the alkali washing tank and add fresh alkali solution to the upper limit required by the process specifications;

[0072] Increase the contact pressure of the brush roller on the strip surface to improve the mechanical scrubbing intensity;

[0073] Reduce the running speed of the strip in the cleaning section and extend the residence time of the strip in each cleaning tank to enhance the cleaning effect;

[0074] Replace part or all of the contaminated cleaning solution in the cleaning tank to restore the chemical activity and cleaning ability of the cleaning solution;

[0075] Inspect and replace severely worn brush rollers or squeeze rollers to restore the equipment's mechanical cleaning capability;

[0076] After the corrective measures are implemented, the surface of the strip steel shall be re-inspected until the residual oil and residual iron content both fall back to the qualified range before the strip steel can continue to be put into the furnace.

[0077] After the cleaning section exit and the hot air drying section, the dryness of the strip surface is confirmed to ensure that the moisture carried on the surface of the strip has been completely removed when it leaves the cleaning section.

[0078] Preferably, an online dew point meter or infrared moisture detector is installed at the outlet of the cleaning section to continuously detect the residual moisture on the upper and lower surfaces of the strip steel, and control the residual water content on the strip steel surface to be lower than the instrument detection limit, that is, the strip steel surface is completely dry.

[0079] If residual water or excessive moisture content is detected on the strip surface, the following dryness correction procedure shall be performed:

[0080] Check the condition of the squeeze roller surface to confirm that there is no wear, hardening, scratches, or foreign objects embedded on the surface of the squeeze roller, and that the roller surface has good elasticity.

[0081] Check and adjust the clamping force of the squeeze rollers to ensure that the squeeze rollers apply sufficient squeezing pressure to the strip to remove the water film carried on the surface of the strip.

[0082] Check the hot air temperature in the hot air drying section. If it is below 100℃, increase the hot air temperature to the range required by the process.

[0083] Check the air volume and air speed of the hot air drying section. If the air volume is insufficient, clean the air duct filter or adjust the fan speed to ensure that the hot air has sufficient blowing force on the surface of the strip steel.

[0084] Check whether cold air is entering the strip steel running channel in the drying section, and adjust the inlet and outlet sealing devices of the drying section if necessary;

[0085] After the corrective measures are implemented, the surface dryness of the strip steel is re-tested until it is confirmed to be completely dry before the strip steel can be allowed to enter the furnace.

[0086] After the surface cleanliness (residual oil ≤ 5 mg / m², residual iron ≤ 3 mg / m²) and dryness (completely dry, no residual water) of the strip steel are confirmed to be qualified, the qualified strip steel is sent from the cleaning section to the annealing furnace through the inlet looper.

[0087] During continuous production, the surface of the strip steel at the exit of the cleaning section is regularly sampled and tested. Ideally, this should be done at least twice per shift to continuously monitor the stability of the cleanliness index. When the test data shows a deteriorating trend, process intervention and parameter adjustment are carried out in advance to avoid large-scale oxidation of strip steel in the furnace or nodule formation on the furnace rolls due to poor cleaning, thus ensuring the long-term stable operation of the annealing furnace.

[0088] Step S3: Determine the target production speed of the current grade of silicon steel based on the heating capacity of the annealing furnace;

[0089] Step S3 is as follows: Confirm that the annealing furnace has completed the heating and is in the pre-production heat preservation state. The judgment criteria are: the measured temperature of all thermocouples in the three sections of the non-oxidizing heating section, the radiant tube heating section and the soaking section has reached its respective set temperature, and the deviation has been stable within ±5 degrees Celsius in the past 30 minutes. At the same time, the furnace pressure in each section is stable in the slightly positive pressure range of 20 Pa to 50 Pa. After both conditions are met, proceed to the subsequent speed determination operation.

[0090] The process control system reads the real-time operating data of the three sections mentioned above. Each section needs to read four parameters: the total number of burners currently in operation (only the main burners involved in heating are counted in the non-oxidizing heating section); the current output power percentage of each operating burner; the real-time temperature readings of all thermocouples arranged along the length of the furnace in the section (usually no less than six temperature measuring points); and the current furnace pressure value of the section.

[0091] Temperature deviation diagnosis is performed on each section. If the measured temperature of any thermocouple in any section deviates from the set temperature by more than ±10 degrees Celsius, the heating power of the section is determined to be abnormal, and an alarm is issued. The operator must check the working status of the burner, the gas pressure or the air supply. After the problem is resolved and the temperature deviation of all thermocouples in the section returns to within ±10 degrees Celsius and remains stable for five minutes, subsequent operations can continue.

[0092] Once the temperature deviation of all sections is within the acceptable range, the maximum allowable throughput speed is calculated separately for the non-oxidizing heating section, the radiant tube heating section, and the soaking section.

[0093] The logic behind the calculation is as follows: during the process of the strip steel absorbing heat and raising its temperature, the faster the strip steel runs, the more cold material enters the furnace per unit time, and the greater the heat that needs to be supplied. Since the heating power of each section is fixed, the maximum strip steel speed that the section can support must be calculated by taking the total heating power that is currently available as the upper limit.

[0094] For the non-oxidizing heating section, count all the main burners that are turned on, multiply the rated maximum power of each burner by the current output percentage, and sum them up to get the current total heating power. Calculate the mass of the strip per meter based on the strip width and thickness, and then multiply it by the required temperature rise and specific heat capacity of the section to get the heat required per meter of strip. Multiply the total heating power by the heat transfer efficiency correction coefficient, divide by the heat required per meter of strip, and then convert it to length per minute to get the maximum allowable passing speed.

[0095] The calculation process for the heat transfer efficiency correction coefficient is as follows: The temperature deviation is obtained by subtracting the current average furnace temperature from the design reference temperature. If the temperature deviation is positive, the temperature correction coefficient is 1; if it is negative, the ratio of the absolute value of the temperature deviation to the design reference temperature is subtracted from 1. Simultaneously, the pressure deviation is obtained by subtracting the current furnace pressure from the design reference pressure. If the pressure deviation is positive, the pressure correction coefficient is 1; if it is negative, the ratio of the absolute value of the pressure deviation to the design reference pressure is subtracted from 1. Finally, the temperature correction coefficient and the pressure correction coefficient are multiplied together to obtain the final heat transfer efficiency correction coefficient.

[0096] For the radiant tube heating section, count all activated radiant tube burners, multiply the rated maximum power of each burner by the current output percentage, and sum them to obtain the current total heating power; calculate the mass of strip per meter based on the strip width and thickness, then multiply by the required total temperature rise (i.e., the target temperature at the inlet of the soaking zone minus the measured temperature at the outlet of the non-oxidizing heating zone) and the specific heat capacity of the strip to obtain the heat absorption required per meter of strip; read the measured temperatures of all thermocouples arranged along the length of the furnace, and compare each thermocouple temperature with the reference temperature required by the process at that location; sum the results... The number of thermocouples whose measured temperature is lower than the reference temperature is counted. The sum of the temperature deviations below the reference temperature is divided by the sum of the reference temperatures of all thermocouples to obtain the temperature deficit ratio. The temperature deficit ratio is subtracted from one to obtain the length direction temperature distribution correction coefficient. If the measured temperature of all thermocouples is not lower than the reference temperature, the length direction temperature distribution correction coefficient is taken as one. The total heating power is multiplied by the length direction temperature distribution correction coefficient to obtain the effective heating power. This is divided by the heat absorbed per meter of strip steel and then converted to length per minute to obtain the maximum allowable passing speed.

[0097] For the soaking section, all activated heating elements are counted, and the rated power of each element is multiplied by the current output percentage, and the sum is obtained to get the current total heating power. The minimum holding time required for recrystallization of the current grade of silicon steel at the target annealing temperature is retrieved from the process database. The physical length is divided by the minimum holding time, and then converted to length per minute to obtain the upper limit of the speed that meets the recrystallization requirements. The current average furnace temperature is read and compared with the target annealing temperature required by the process. If the average temperature is lower than the target temperature, the difference is divided by the target temperature to obtain the temperature deficit ratio, and the temperature maintenance coefficient is obtained by subtracting the deficit ratio from one. If the average temperature is not lower than the target temperature, the temperature maintenance coefficient is set to 1. The total heating power is divided by the standard power required to maintain the target temperature to obtain the power margin coefficient. The maximum allowable speed of the soaking section is obtained by multiplying the upper limit of the speed by the temperature maintenance coefficient and then by the power margin coefficient.

[0098] Wherein, the power margin coefficient is taken as 1 when it is greater than 1;

[0099] The minimum maximum permissible speed among the three sections—non-oxidizing heating section, radiant tube heating section, and soaking section—is taken as the initial target speed limit, and the corresponding section is marked as the speed constraint bottleneck section under the current operating condition.

[0100] Step S4: Determine the reference pressure level of the entire furnace based on the current production speed, determine the optimal pressure increment gradient between each section through an online self-optimization algorithm, and generate a sequence of furnace pressure setpoints for each section that increase sequentially from front to back along the strip running direction based on the reference pressure level and the optimal pressure increment gradient.

[0101] Step S4 is as follows: Based on the specific value of the current target production speed, retrieve the corresponding reference furnace pressure value of the inlet sealing chamber from the process specification database;

[0102] The reference furnace pressure value is determined using a segmented correspondence rule:

[0103] When the current target production speed is in the range of 100 meters per minute to 110 meters per minute, the reference furnace pressure value of the inlet sealing chamber is 30 Pa.

[0104] When the current target production speed is in the range of 110 meters per minute to 120 meters per minute, the reference furnace pressure value of the inlet sealing chamber is 35 Pa.

[0105] When the current target production speed is in the range of 120 to 130 meters per minute, the reference furnace pressure value of the inlet sealing chamber is 40 Pa.

[0106] When the current target production speed is in the range of 130 meters per minute to 140 meters per minute, the reference furnace pressure value of the inlet sealing chamber is 45 Pa.

[0107] If the current target production speed is at the midpoint between any two speed ranges mentioned above, the corresponding reference furnace pressure value for the inlet sealing chamber is calculated using linear interpolation. If the current target production speed exceeds 140 meters per minute, extrapolation is performed based on the slope of adjacent intervals. If the current target production speed is less than 100 meters per minute, 30 Pa is directly taken as the reference furnace pressure value for the inlet sealing chamber.

[0108] Based on the current target production speed, retrieve the pressure increment gradient benchmark value corresponding to the target production speed from the process specification database. The unit of the pressure increment gradient benchmark value is Pascal per meter, which represents the value that the furnace pressure should increase per meter length along the strip running direction in the annealing furnace.

[0109] The baseline value for the pressure increment gradient is set as follows: when the current target production speed is higher than 120 meters per minute, it is 1.5 Pa per meter; when the current target production speed is lower than 100 meters per minute, it is 0.5 Pa per meter; when the current target production speed is between 100 meters per minute and 120 meters per minute, the corresponding intermediate value is calculated according to a linear ratio.

[0110] Using the reference furnace pressure value of the inlet sealing chamber as the starting value of the entire sequence, along the strip running direction, the initial furnace pressure setting value of each section is calculated sequentially according to the physical distance between the center points of each section of the annealing furnace;

[0111] The specific calculation method is as follows: multiply the target value of the pressure increment gradient by the physical distance between the center point of the current section and the inlet sealing chamber along the running direction of the strip to obtain the pressure increment value relative to the inlet sealing chamber. Then add the reference furnace pressure value of the inlet sealing chamber to the pressure increment value to obtain the initial furnace pressure setting value of the section.

[0112] Following the above method, the initial furnace pressure setting values ​​for the following sections are calculated sequentially: inlet sealing chamber, non-oxidizing heating section, radiant tube heating section, soaking section, and outlet sealing chamber. After the above calculations are completed, a sequence of initial furnace pressure setting values ​​with values ​​increasing sequentially from small to large along the strip running direction is obtained.

[0113] The initial furnace pressure setting value of each section is compared with the pre-stored upper and lower safe furnace pressure values ​​of the corresponding section.

[0114] The upper limit of furnace pressure safety is determined by the strength of the furnace shell structure and the back pressure capacity of the flue gas system, and is uniformly taken as 150 Pa for all sections; the lower limit of furnace pressure safety is the minimum micro-positive pressure required to prevent the intake of external air, and is uniformly taken as 10 Pa for all sections.

[0115] If the initial furnace pressure setting value of all sections is within the range of 10 Pa to 150 Pa, then the current sequence is directly used as the initial furnace pressure setting value sequence.

[0116] If the initial furnace pressure setting value of any segment is higher than the safe upper limit of the furnace pressure of the corresponding segment by 150 Pa, then the furnace pressure setting value of all segments in the entire sequence will be reduced by the same compression ratio, so that the setting value of the segment exceeding the limit is reduced to 150 Pa. The setting value of the remaining segments will be reduced synchronously by the same ratio, and the compressed sequence will be used as the initial furnace pressure setting value sequence. At the same time, a prompt message will be issued that the current target production speed is too high and the furnace pressure demand is close to the equipment limit.

[0117] If the initial furnace pressure setting value of any segment is lower than the corresponding segment's safe lower limit of 10 Pa, then the furnace pressure setting value of all segments in the entire sequence will be increased proportionally so that the segments below the lower limit reach 10 Pa, and the increased sequence will be used as the initial furnace pressure setting value sequence.

[0118] The initial furnace pressure setpoint sequence is sent to the corresponding furnace pressure actuators in each section of the annealing furnace.

[0119] The furnace pressure actuator includes exhaust gas regulating valves and nitrogen replenishment regulating valves installed in each section. By adjusting the opening of the exhaust gas regulating valves and the nitrogen replenishment regulating valves, the actual furnace pressure in each section reaches the corresponding initial furnace pressure setting value.

[0120] Once the actual furnace pressure in each section stabilizes within ±3 Pa of its initial furnace pressure setting for two minutes, the online self-optimization algorithm is activated.

[0121] Specifically, the online self-optimization algorithm is executed round by round in the following manner:

[0122] Based on the target value of the pressure increment gradient, the pressure increment gradient value is increased by 5%; the furnace pressure set value of each section is recalculated based on the increased gradient value; and the new furnace pressure set value is sent to the furnace pressure actuator and operated stably for five minutes.

[0123] During the five-minute stable operation, the actual differential pressure value at the furnace inlet, measured by the differential pressure sensor installed at the sealing chamber of the annealing furnace inlet, and the oxygen content value of the furnace atmosphere in each section, measured by the oxygen content analyzer installed in the non-oxidizing heating section, the radiant tube heating section, and the soaking section, are continuously read. After this round of reading is completed, the pressure increment gradient value is reduced by a margin of -5%, and the furnace pressure setpoint for each section is recalculated and issued for execution. The system is run stably for five minutes, during which the same feedback data is recorded.

[0124] The actual differential pressure value at the furnace mouth and the oxygen content value of the furnace atmosphere in each section will be recorded when the gradient cycle is increased and decreased.

[0125] Each value is compared with the corresponding baseline value recorded under the current gradient value;

[0126] If the actual differential pressure at the furnace mouth increases and the oxygen content in each section decreases after increasing the gradient, then the direction of increase is determined to be effective, and the adjustment will continue in the direction of increase in the next round.

[0127] If the actual differential pressure value at the furnace mouth can still be maintained at no less than 8 Pa after reducing the gradient, and the oxygen content in each section is lower than the qualified threshold of 4 parts per million, and the furnace pressure fluctuation amplitude is reduced compared with the current gradient, then the direction of reduction is determined to be an effective direction, and the next round of adjustment will be made in the direction of reduction.

[0128] If neither increasing nor decreasing the gradient can simultaneously satisfy the two conditions of no decrease in furnace mouth differential pressure and no increase in oxygen content, then the current gradient value is determined to be the optimal value, and the self-optimization process is terminated.

[0129] The online self-optimization algorithm terminates when any of the following conditions are met:

[0130] Condition 1 is: In three consecutive iterations, neither increasing nor decreasing the gradient direction can further increase the actual differential pressure value at the furnace mouth nor further decrease the oxygen content in each section, while the current oxygen content in each section is below the qualified threshold of four parts per million.

[0131] Condition 2 is: in three consecutive iterations, the fluctuation range of the actual furnace pressure in each section is within ±3 Pa, and the actual differential pressure value at the furnace mouth is not less than 10 Pa.

[0132] Condition 3 is: the total running time of the self-optimization algorithm reaches thirty minutes;

[0133] When any one of the above three conditions is met first, the self-optimization algorithm is terminated, and the pressure increment gradient value used in the current round is taken as the optimal pressure increment gradient.

[0134] Save the optimal pressure increment gradient to the process control database. Based on the optimal pressure increment gradient value, recalculate the furnace pressure setpoints for each section along the strip running direction from front to back (the calculation method is the same as the process of calculating the initial furnace pressure setpoints mentioned above), and obtain the optimal furnace pressure setpoint sequence for each section.

[0135] The purpose of step S4 is to establish and optimize the gradient furnace pressure distribution along the strip running direction from the inlet to the outlet of the annealing furnace. When hydrogen is replaced by a hydrogen-free nitrogen atmosphere as the protective atmosphere, the directional guidance effect of the pressure gradient ensures that the atmosphere in the furnace always flows unidirectionally from the inlet side to the outlet side, fundamentally preventing external air from being drawn back into the furnace through the furnace opening and furnace door gaps. Combined with oxygen content monitoring in each section, it ensures that the oxygen content is always below four parts per million along the entire length of the annealing furnace, thereby providing an oxidation-free furnace environment for high-temperature annealing under hydrogen-free conditions.

[0136] Step S5: Based on the furnace pressure setpoint sequence of each segment, the furnace pressure setpoint and the target production speed are linked and sent to the annealing furnace actuator to enable the furnace pressure control and speed control to be executed synchronously. During the operation of the annealing furnace, the furnace mouth differential pressure and the oxygen content of the furnace atmosphere are monitored in real time and used as feedback signals to correct the furnace pressure setpoint sequence online until continuous annealing is completed.

[0137] Step S5 is as follows: The current target production speed is linked and bound with the optimal furnace pressure setpoint sequence for each segment. The current target production speed and the optimal furnace pressure setpoint sequence for each segment are retrieved simultaneously from the process control database and set as synchronous distribution objects in the control logic to ensure that speed changes and furnace pressure changes correspond and respond simultaneously during subsequent execution.

[0138] The speed value and furnace pressure setting value of each section are sent to the annealing furnace actuator, and the current target production speed value is sent to the annealing furnace main drive control system. The main drive control system adjusts the speed of each section tension roller and looper drive roller so that the strip steel runs at the current target production speed.

[0139] Each segment setting value in the optimal furnace pressure setting value sequence is sent to the corresponding furnace pressure actuator.

[0140] The furnace pressure actuators for the non-oxidizing heating section include: a flue gas regulating valve and a nitrogen replenishment regulating valve installed in this section; the furnace pressure actuators for the radiant tube heating section include: a flue gas regulating valve and a nitrogen replenishment regulating valve installed in this section; the furnace pressure actuators for the soaking heat section include: a flue gas regulating valve and a nitrogen replenishment regulating valve installed in this section; and the furnace pressure actuators for the inlet sealing chamber and the outlet sealing chamber each include a nitrogen replenishment regulating valve installed in their respective sections.

[0141] Each actuator automatically adjusts the valve opening based on the received set value, so that the actual furnace pressure in each section approaches the set value;

[0142] During the operation of the annealing furnace, key feedback parameters are continuously monitored. After the strip is fed into the furnace and continuous annealing begins, real-time data is continuously read through the following detection devices:

[0143] A differential pressure sensor installed at the inlet sealing chamber is used to measure the actual differential pressure value at the furnace mouth;

[0144] Oxygen content analyzers installed in the non-oxidizing heating section, the radiant tube heating section, and the soaking section are used to measure the actual oxygen content of the furnace atmosphere in each section.

[0145] And furnace pressure transmitters installed in each section to measure the actual furnace pressure value of each section;

[0146] The readings from all the above-mentioned detection devices are continuously entered into the process control database at a sampling frequency of once per second;

[0147] The actual furnace pressure value of each section is compared with the corresponding furnace pressure setting value one by one, and the furnace pressure deviation value of each section is calculated. The deviation value is the actual furnace pressure minus the set furnace pressure.

[0148] If the furnace pressure deviation in a certain section exceeds the allowable range of ±3 Pa, an adjustment command is sent to the furnace pressure actuator of that section. By adjusting the opening of the flue gas regulating valve or the nitrogen injection regulating valve, the actual furnace pressure is brought back to within ±3 Pa of the set value.

[0149] The actual differential pressure value at the furnace mouth is compared with the preset safe lower limit value for differential pressure at the furnace mouth, which is set to eight Pa.

[0150] If the actual differential pressure at the furnace mouth is lower than eight Pa, it indicates that there is a risk of external air backflow at the inlet sealing chamber. Immediately perform the following linkage operation: gradually increase the opening of the nitrogen supply regulating valve of the inlet sealing chamber in increments of five percent, and at the same time, increase the nitrogen supply in each subsequent section in the same proportion to raise the overall pressure level of the furnace until the actual differential pressure at the furnace mouth recovers to above eight Pa.

[0151] If the actual differential pressure at the furnace mouth is higher than 15 Pa, it indicates that the high furnace pressure may cause excessive nitrogen leakage at the furnace shell seal. Gradually close the nitrogen supply regulating valve of the inlet sealing chamber in increments of 5% to reduce the differential pressure at the furnace mouth to the preferred operating range of 8 Pa to 15 Pa.

[0152] The actual oxygen content of the furnace atmosphere in each section is compared with the qualified oxygen content threshold of four parts per million.

[0153] If the actual oxygen content in all sections is below four parts per million, the furnace pressure setpoint remains unchanged, and normal operation is maintained.

[0154] If the actual oxygen content in a certain section rises above four parts per million, an oxygen content exceeding the limit alarm will be triggered immediately, and the following two corrective actions will be performed simultaneously:

[0155] The first measure is to increase the opening of the nitrogen supply regulating valve in this section by 10 percent, and at the same time increase the opening of the nitrogen supply regulating valve in all upstream sections of this section by the same amount of time, so as to increase the furnace pressure in this section and upstream area and enhance the driving effect of directional airflow on oxygen.

[0156] The second step is to check whether the furnace pressure setting value of the downstream adjacent section is higher than that of this section. If the pressure gradient is abnormal (i.e., the furnace pressure of the downstream section is lower than or equal to that of this section), the setting value between this section and the downstream section will be automatically corrected according to the target value of the pressure gradient to ensure that the furnace pressure of the downstream section is always higher than that of this section.

[0157] After the above two corrective operations are performed, the oxygen content in this section is continuously monitored. If the oxygen content still cannot drop below four parts per million within three minutes, an equipment abnormality warning will be issued, prompting the operator to check the furnace shell sealing, furnace door sealing strip status, and whether the flue gas system is blocked in this section.

[0158] During the continuous operation of the annealing furnace, if the operator or upstream process requests a change in the current target production speed, the following linkage correction is performed: When the speed needs to be increased, firstly, according to the calculation logic of step S3, the maximum allowable speed of each of the three heating sections is recalculated with the new speed value. After confirming that the new speed value does not exceed the initial target speed limit allowed by the current heating capacity, the corresponding optimal furnace pressure setting value sequence for each section is regenerated based on the new speed value according to the determination method of step S4. The new speed value and the new furnace pressure setting value sequence are simultaneously sent to each actuator. During the speed increase, the furnace pressure of each section is gradually adjusted to the new setting value in a step unit of 10 meters per minute to ensure that the speed and furnace pressure change synchronously rather than sequentially. When the speed needs to be decreased, the corresponding optimal furnace pressure setting value sequence for each section is also regenerated based on the new speed value and sent synchronously. However, the step unit for speed decrease is widened to 20 meters per minute to avoid furnace pressure response speed lagging behind speed change and causing furnace pressure fluctuation.

[0159] Online correction is performed cyclically throughout the continuous annealing process until the annealing of all strip steel is completed. During the entire period when the strip steel continuously passes through the annealing furnace, the control cycle is continuously repeated every ten seconds, including deviation correction between the actual furnace pressure and the set value in each section, maintenance and adjustment of the furnace mouth differential pressure, monitoring and handling of oxygen content exceeding the standard in each section, and linkage and synchronous correction when the speed changes.

[0160] Once the continuous annealing of this batch of low-grade silicon steel is completed and the tail of the strip leaves the outlet sealing chamber, the control system stops the above-mentioned cyclic correction operation and stores all feedback data, correction records and alarm logs from the entire production process into the process control database, which is archived as a complete process history of this production.

[0161] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A low grade silicon steel hydrogen-free continuous annealing process characterized by: Includes the following steps: Step S1: Perform an airtightness test on the annealing furnace, introduce high-pressure nitrogen into the furnace, and control the oxygen content in the furnace to meet the requirements; Step S2: Turn off the air supply to the burners that do not participate in combustion in the NOF non-oxidizing furnace, and adjust the air-fuel ratio of the main burner to make the NOF furnace in a state of oxygen-deficient combustion. Clean the strip steel before it enters the annealing furnace, and control the amount of residual oil and residual iron on the surface of the strip steel to remove oil stains, iron powder and water stains. Step S3: Determine the target production speed of the current grade of silicon steel based on the heating capacity of the annealing furnace; Step S4: Determine the reference pressure level of the entire furnace based on the current production speed, determine the optimal pressure increment gradient between each section through an online self-optimization algorithm, and generate a sequence of furnace pressure setpoints for each section that increase sequentially from front to back along the strip running direction based on the reference pressure level and the optimal pressure increment gradient. Step S4: Based on the furnace pressure setpoint sequence for each segment, the furnace pressure setpoint and the target production speed are linked and sent to the annealing furnace actuator to enable synchronous execution of furnace pressure control and speed control. During the operation of the annealing furnace, the differential pressure at the furnace opening and the oxygen content in the furnace atmosphere are monitored in real time and used as feedback signals to correct the furnace pressure setpoint sequence online until continuous annealing is completed.

2. The hydrogen-free continuous annealing process for low-grade silicon steel according to claim 1, characterized in that: In step S1, after stopping the annealing furnace and cooling it to room temperature, high-pressure nitrogen is introduced into the furnace to raise the pressure inside the furnace to 150 Pa. All nitrogen inlet valves are closed to maintain a sealed and pressure-maintaining state and the pressure decay is monitored. Key potential leak points of the annealing furnace are checked one by one. After the leak points are detected, leak elimination treatment is performed and the leaks are retested until the leakage of all detection points meets the sealing qualification standard. After the airtightness test is passed, high-pressure nitrogen is continuously introduced for replacement, and the oxygen concentration value is read in real time. When the oxygen content in each section drops below four parts per million, the flow rate of nitrogen is switched to maintain the positive pressure state in the furnace.

3. The hydrogen-free continuous annealing process for low-grade silicon steel according to claim 1, characterized in that: In step two, the control method for the oxygen-deficient combustion state is as follows: the combustion air supply channel of the burners that do not participate in combustion in the non-oxidizing heating section is closed and locked; the excess air coefficient of the main burner is controlled within a range lower than the value corresponding to the theoretical air-fuel ratio, so that the oxygen concentration in the non-oxidizing heating section is controlled below the level at which free oxygen does not cause oxidation of the strip surface; during the air-fuel ratio adjustment process, the oxygen content and carbon monoxide content in the flue gas are monitored in real time as feedback signals for adjustment until the oxygen content and carbon monoxide content in the flue gas are both stable within the qualified range.

4. The hydrogen-free continuous annealing process for low-grade silicon steel according to claim 1, characterized in that: In step two, the strip steel is sequentially subjected to alkaline washing, brushing, electrolytic cleaning, hot water rinsing, and hot air drying. The temperature and current density of each process tank are set according to the process specifications. An online detection device is installed at the outlet of the cleaning section to continuously detect the surface cleanliness of the strip steel. The residual oil and residual iron on the surface of the strip steel are controlled to be lower than the qualified values ​​required by the process specifications. The strip steel can be allowed to enter the annealing furnace after the surface of the strip steel is completely dry.

5. The hydrogen-free continuous annealing process for low-grade silicon steel according to claim 1, characterized in that: The target production speed is determined as follows: After confirming that the annealing furnace has completed heating and that the deviations between the measured temperatures of all thermocouples in the non-oxidizing heating section, the radiant tube heating section and the soaking section and the set temperatures are stable within the allowable range, the real-time operating data of the three sections are read. When the temperature deviations of each section are within the allowable range, the maximum allowable speed of each section under the current heating power is calculated. The minimum value among the maximum allowable speeds calculated for the three sections is taken as the initial target speed limit, and the section corresponding to the minimum value is marked as the speed constraint bottleneck section.

6. The hydrogen-free continuous annealing process for low-grade silicon steel according to claim 5, characterized in that: The maximum permissible speed for each segment is calculated as follows: The current total heating power is obtained by summing the actual output power of all currently activated main burners. The heat absorption required per meter of strip is calculated based on the strip specifications. The total heating power is then corrected based on the current furnace temperature and pressure, divided by the heat absorption required per meter of strip, and converted into a length per minute. This gives the maximum allowable speed through the non-oxidizing heating section. The current total heating power is obtained by summing the actual output power of all currently activated radiant tube burners. The heat absorption required per meter of strip is calculated based on the strip specifications and the total temperature rise required for this section. The total heating power is corrected based on the temperature distribution along the length of the furnace and then divided by the heat absorption required per meter of strip and converted to length per minute, thus obtaining the maximum allowable speed through the radiant tube heating section. The current total heating power is obtained by summing the actual output power of all currently activated heating elements. The minimum holding time required for recrystallization of the current grade of silicon steel is retrieved from the process database. The upper limit of speed is calculated based on the physical length of the soaking section and the minimum holding time. The upper limit of speed is corrected based on the deviation between the current furnace temperature and the target annealing temperature, as well as the comparison between the current heating power and the power required to maintain the target temperature. Thus, the maximum allowable speed through the soaking section is obtained.

7. The hydrogen-free continuous annealing process for low-grade silicon steel according to claim 4, characterized in that: In step two, when the online detection data finds that the surface cleanliness of the strip steel is unqualified, the cleaning effect correction program is started. The correction program includes one or more of the following: increasing the alkali concentration, increasing the brush roller contact pressure, reducing the running speed of the cleaning section, changing the cleaning fluid, or replacing the worn roller system. After correction, the cleanliness index is re-detected until it is qualified.

8. The hydrogen-free continuous annealing process for low-grade silicon steel according to claim 1, characterized in that: In step four, the generation method of the furnace pressure setpoint sequence for each segment is as follows: taking the reference furnace pressure value of the inlet sealing chamber as the starting value, multiplying the pressure increment gradient reference value by the physical distance between each segment and the inlet sealing chamber as the pressure increment of each segment, and calculating the initial furnace pressure setpoint for each segment in sequence to form an initial furnace pressure setpoint sequence that increases sequentially along the strip running direction; comparing the setpoint of each segment in the sequence with the upper and lower limits of the furnace pressure safety, and if there are segments that exceed the limits, adjusting the entire sequence in the same proportion.

9. The hydrogen-free continuous annealing process for low-grade silicon steel according to claim 1, characterized in that: In step four, the initial furnace pressure setpoint sequence is sent to the furnace pressure actuators of each section. After the actual furnace pressure of each section stabilizes, self-optimization is initiated. Based on the pressure increment gradient benchmark value, the gradient value is adjusted round by round in both the positive and negative directions. The furnace pressure setpoint values ​​of each section are recalculated and sent back. After each round of stable operation, the actual differential pressure value at the furnace mouth and the oxygen content value in the furnace atmosphere are read as feedback. The effective adjustment direction is determined based on the feedback results. When multiple consecutive iterations fail to improve the situation, or the furnace pressure fluctuation amplitude and furnace mouth differential pressure of each section meet the stability conditions, or the running time reaches the preset upper limit, self-optimization is terminated, and the current gradient value is taken as the optimal pressure increment gradient.

10. The hydrogen-free continuous annealing process for low-grade silicon steel according to claim 1, characterized in that: In step five, the specific process of linkage issuance and online correction is as follows: the current target production speed is linked and bound with the optimal furnace pressure setpoint sequence for each section, and then synchronously issued to the annealing furnace actuator to make the strip running speed and furnace pressure of each section be adjusted synchronously. During operation, the differential pressure value at the furnace mouth, the actual furnace pressure value in each section, and the oxygen content value in each section are continuously read as feedback signals. Adjustments are made when the actual furnace pressure in each section deviates from the set value beyond the allowable range. When the differential pressure at the furnace inlet is lower than the lower safety limit, increase the amount of nitrogen supplied to the inlet sealing chamber; when it is higher than the upper safety limit, decrease the amount of nitrogen supplied to the inlet sealing chamber. An alarm is triggered when the oxygen content in each section rises above the qualified threshold. The nitrogen supply to that section and the upstream section is increased, and the pressure gradient with the downstream section is corrected. If the oxygen content cannot fall back within the specified time, an equipment abnormality warning is issued. When the speed changes, it is gradually adjusted according to the preset step unit, and online correction is performed cyclically in the preset cycle until the strip annealing is completed.

Images