Annealing furnace electric heating control method and control system thereof
By employing a real-time data acquisition and graded protection-based electric heating control method, the problems of belt breakage, tensionless short circuits, and overheating in the annealing furnace were solved, thereby ensuring equipment safety and production stability, extending equipment lifespan, and reducing maintenance costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHANXI TAIGANG STAINLESS STEEL CO LTD
- Filing Date
- 2026-04-15
- Publication Date
- 2026-06-23
AI Technical Summary
The existing annealing furnace control methods fail to effectively prevent belt breakage/tensionless short circuits, heater overheating, and temperature rise shocks in the low-temperature section, leading to equipment damage and production instability.
By collecting real-time data on the electric heater body temperature, strip tension, and strip breakage signal, combined with PLC logic judgment and graded protection, the system can achieve automatic shutdown in case of strip breakage, power limit for heater over-temperature, and gradual temperature rise in the low-temperature section. A temperature rate control model is established, PID output is limited, and a bypass mode is configured to handle maintenance or temperature rise when there is no strip.
It achieves safe and reliable electric heating control, prevents equipment burn-out, extends the life of heaters and refractory materials, reduces downtime due to malfunctions, improves production stability and equipment utilization, and reduces maintenance costs.
Smart Images
Figure CN122256648A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of automated control technology for metallurgical heat treatment equipment, specifically a method for electric heating safety protection and intelligent temperature control of annealing furnaces in silicon steel production lines, applicable to electric heating systems for strip steel heat treatment such as continuous annealing furnaces and vertical annealing furnaces. Background Technology
[0002] The annealing furnace is a key heat treatment equipment in the production of cold-rolled silicon steel and non-oriented silicon steel. The electric heating system consists of a thermocouple temperature measurement module, a PLC control module, a power adjustment unit, and an electric heater (resistance strip / radiant tube). Traditional control methods use the furnace top thermocouple as the sole temperature measurement point, and the PLC only adjusts the power based on the deviation between the set temperature and the measured temperature using PID control. This fails to incorporate key parameters such as the strip's operating status and the heater's body temperature, resulting in the following technical defects in actual production: 1. Risk of strip breakage / short circuit without tension: When the strip breaks suddenly or is threaded in a jogging manner, the strip sags and comes into contact with the electric heater. Because the strip is conductive, a short circuit to ground is formed, which directly burns the heater, terminal block and furnace lining, causing unplanned shutdown. 2. No overheat protection for heater: Only the furnace temperature is monitored, not the heater body temperature. The heater is prone to overheating, red-hot deformation, and a significantly shortened service life. 3. Large temperature rise shock at low temperatures: The set value and the measured value at low temperatures deviate greatly, the PID output is instantly maxed out, the heater runs at full power for a long time, and the current exceeds the limit and is easily damaged; at the same time, the heating rate is too fast, the refractory material in the furnace is severely damaged by thermal shock, and the service life is reduced. 4. Simple control logic: There is no safety bypass mechanism, and the maintenance heating scenario cannot be flexibly switched, which affects production organization.
[0003] Existing publicly available technologies mostly focus on furnace temperature PID optimization, power distribution, and communication modification. They do not link tension signals, belt break signals, heater body temperature with electric heating start / stop and power output control, nor do they design a rate model for gradual temperature rise in the low-temperature section. Therefore, they cannot fundamentally solve the three major problems of short circuit, over-temperature, and thermal shock. Summary of the Invention
[0004] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art and provide a safe, reliable, precise, and low-cost electric heating control method for annealing furnaces, which realizes automatic shutdown due to strip breakage / tension loss, graded protection for heater over-temperature, gradual heating rate in the low-temperature section, extends the life of heaters and refractory materials, reduces downtime and scrap losses due to malfunctions, and improves the continuous operation capability of the unit.
[0005] The technical solution adopted in this invention is: an electric heating control method for an annealing furnace, comprising the following steps: Step 1: Real-time acquisition of the temperature of the electric heater body of the annealing furnace, strip tension signal, and strip breakage signal; Step 2: The PLC makes logical judgments based on the collected signals: when a strip breakage signal is detected, or the actual tension value of the strip is less than the tension alarm value, the electric heater is automatically turned off; when the temperature of the electric heater body is higher than the first alarm threshold, the electric heating power output is limited; when the temperature of the electric heater body is higher than the second alarm threshold, heating is stopped. Step 3: Establish a temperature rate control model and adjust the PID setpoint according to the furnace temperature in segments: when the furnace temperature is lower than the real-time temperature setpoint (i.e., low temperature), the PID setpoint gradually increases according to the set heating rate; when the furnace temperature is higher than the real-time temperature setpoint (i.e., high temperature segment), the PID setpoint directly adopts the operator input value.
[0006] The first alarm threshold is the furnace temperature measurement value plus 30°C, and the second alarm threshold is the furnace temperature measurement value plus 60°C.
[0007] The strip tension signal and strip breakage signal are obtained by communication between the annealing furnace PLC and the main line primary PLC.
[0008] The PLC operation screen has a bypass mode button: during maintenance / when there is no strip for heating, the bypass can be manually engaged, the interlock can be disengaged, and the electric heater can be automatically shut down / preheating can be performed according to the set preheating temperature; after the tension is restored after the strip is threaded, the program automatically restores the interlock to prevent long-term misuse of the bypass.
[0009] In the temperature rate control model, the slope K = T / 3600, and the real-time temperature setpoint T V =K×t+T0; where T is the set heating rate in °C / h, t is time in seconds, and T0 is the initial temperature setpoint.
[0010] The maximum output value of the PID is limited to 80% of the theoretical maximum output value of the PID, to avoid long-term high-power operation of the electric heater.
[0011] An electric heating control system for an annealing furnace, comprising: The temperature acquisition module is used to acquire the temperature of the electric heater body and the temperature inside the furnace; The signal acquisition module is used to acquire strip tension signals and strip breakage signals; The PLC control module is connected to the temperature acquisition module and the signal acquisition module, and is used to execute the control method described in any one of claims 1-6; The execution module is used to perform power limiting, heating stop, and bypass interlock operations according to PLC instructions.
[0012] The beneficial effects of this invention are: comprehensive safety protection: triple protection against belt breakage, tension loss, and overheating, eliminating short circuit burnout and overheating failures; extended equipment life: low-temperature gradual temperature rise reduces thermal shock, increasing the lifespan of heaters and refractory materials by more than 30%; stable and efficient operation: reduces abnormal downtime by 48 hours per year, increases production by 604 tons, and reduces equipment maintenance costs by 80,000 yuan; low investment cost: based on existing PLCs, instruments, and communication upgrades, no new large hardware is required; flexible operation: bypass mode balances safety and production, and automatic reactivation avoids human error. Attached Figure Description
[0013] Figure 1 Overall logic control diagram of this invention; Figure 2 Electric heating protection flowchart; Figure 3 Temperature-rate model control flowchart; Figure 4 Comparison curve of temperature setpoints before and after improvement. Detailed Implementation
[0014] An electric heating control method for an annealing furnace is implemented through four parts: signal acquisition, logic judgment, graded protection, and segmented temperature control. Heater body temperature acquisition and graded protection.
[0015] A 500mm long armored thermocouple is installed on the side wall of the annealing furnace at the location corresponding to the electric heater to collect the heater radiation temperature Td (temperature of the electric heater body of the annealing furnace) in real time; the PLC is set with two levels of protection thresholds: Level 1 alarm T1 = furnace temperature measurement value + 30℃: When T2≥Td>T1, the electric heating output power is limited to no more than 50% of the rated electric heating power; in one embodiment, the electric heating output power P = 50%*P0(T2-Td) / (T2-T1), where P0 is the electric heating output power.
[0016] Level 2 alarm T2 = furnace temperature measurement value + 60℃: When Td > T2, heating should be stopped immediately and the output should be locked.
[0017] Belt breakage and tension safety interlock The annealing furnace PLC establishes TCP / IP communication with the main line's primary PLC to acquire strip breakage and strip tension signals in real time. If a break in the belt is detected during operation, the electric heating will be stopped immediately. If the actual tension is less than the set tension alarm value (no tension state), immediately stop electric heating; The operation screen has a bypass mode button: when performing maintenance or heating without strip steel, the bypass can be manually engaged and the interlock released; after the tension is restored after the strip is threaded, the program will automatically restore the interlock to prevent long-term misuse of the bypass.
[0018] Segmented temperature rate control model Dual-mode control is implemented with the furnace temperature Ts (empirical setpoint) as the dividing point: High temperature range (Td > Ts): Operator setpoints (experienced setpoints) are directly used as PID setpoints (target temperature values) to meet the requirements of rapid heating and stable control of the process; Low temperature range (Td≤Ts): Trigger rate model, the set value increases gradually at a preset rate, calculation formula: Slope K: K=T / 3600, where T is the set heating rate in °C / h and K is in °C / s.
[0019] Real-time setting value (preset rate): TV = K × t + T0, where t is the running time and T0 is the initial setting value.
[0020] At the same time, the upper limit of the PID (temperature rate control model) output is limited to 80% of the theoretical maximum output value of the PID. That is, the upper limit of the PID output value of this invention is 80% of the upper limit of the original PID output value (which is 80% of the theoretical maximum output value), so as to avoid long-term full-power operation.
[0021] This invention improves upon existing methods. Existing PID control models, similar to those used throughout the high-temperature section of this invention, directly employ operator-setpoints (empirical setpoints) as PID setpoints (target temperature values). This invention improves upon this by using the furnace temperature Ts (empirical setpoint) as the dividing point to implement dual-mode control.
[0022] The invention will now be described in detail below, taking into account on-site implementation examples of the DCL and FCL units of the Taiyuan Iron & Steel Silicon Steel Division.
[0023] System Configuration Unit type: Silicon steel continuous annealing furnace (electrically heated radiant tube type) PLC system: Siemens S7–400 / S7–1500 Communication method: TCP / IP communication with the main PLC. Temperature measuring instruments: Standard thermocouple on furnace top + 500mm armored thermocouple on side wall Actuators: power regulator, electric heater assembly Implementation date: May 2023 Scope of application: Annealing furnaces for DCL and FCL units Step 1: Hardware Installation and Signal Connection On both sides of the annealing furnace, a 500mm armored thermocouple is installed on each heating zone corresponding to the heater, fixed at the radiation center of the heater, and the wire is connected to the PLC analog module to collect the heater body temperature Td. The annealing furnace PLC establishes data interaction with the main line's first-level PLC and reads: Disconnect signal (DI switch quantity) Actual tension value of strip steel (AI simulation) Add the following to the HMI operation screen: Tension alarm value setting window Heating rate setting window (°C / h) Bypass mode selection button (with permission lock) Real-time heater temperature display and fault alarm pop-up window Step 2: PLC logic program writing and debugging Heater body temperature protection logic Real-time calculation: T1 = furnace temperature (measured furnace temperature) + 30℃, T2 = furnace temperature (measured furnace temperature) + 60℃; T2≥Td>T1: Output limit flag, PID output upper limit is forced to 50%, electric heating output power P=50%*P0(T2-Td) / (T2-T1), P0 is electric heating output power.
[0024] Td > T2: Trigger emergency stop logic, set electric heating output to 0, and maintain this until manual reset.
[0025] Disconnection / Tension Interlocking Logic Belt break signal = 1 (belt break): Heating stops immediately, audible and visual alarm sounds; If the measured tension value is less than the set alarm value, it is determined that there is no tension, and heating is stopped. Bypass mode = 1: Shielded band breakage, tension interlock (segmented temperature rate control model not used) Heating), allows preheating without strip steel, and can be selected to preheat to a certain temperature or stop heating (no preheating) according to the settings. Bypass mode = 0 and tension returns to normal: automatic interlocking.
[0026] Temperature rate model logic Set the boundary temperature Ts = 500℃ (can be modified according to the process); Ts > 500℃: Directly use the operator setting value as the PID setting value; Ts≤500℃: Enable rate model and set heating rate T=120℃ / h; The slope is calculated as K = 120 / 3600 ≈ 0.0333℃ / s; Real-time setpoint T V The value of TV increases gradually as TV = 0.0333 × t + T0. The upper limit of the PID (temperature-rate control model) output is limited to 80% of the theoretical maximum output value of the PID throughout the entire process. That is, the upper limit of the PID output value of this invention is 80% of the upper limit of the original PID output value (which is 80% of the theoretical maximum output value), thus avoiding long-term full-power operation.
[0027] Step 3: Parameter Tuning and On-site Debugging The tension alarm value is set to ≥5kN according to the unit specifications; if it is below 5kN, it is determined that there is no tension. In the high-temperature range (Ts > 500℃), the operator setting is 100–150℃ / h to avoid excessively rapid heating. Perform single-point testing on each heating zone: Simulated circuit break: Electric heating stops immediately, response time <200ms; Simulated low tension: Electric heating stops immediately, with reliable interlocking; Simulated heater overheating: Level 1 power limit, Level 2 heating shutdown; Low temperature rise: The set value changes smoothly and gradually, without any abrupt changes.
[0028] Key Parameter Table of Implementation Examples
[0029] Step 4: Verify the running effect Safety protection: No accidents such as belt breakage / tensionless short circuit or heater burnout have occurred since implementation; Temperature control performance: Stable temperature rise in the low-temperature range, with no peeling or cracking of the refractory material; Figure 4 As shown, in the original temperature control process, the temperature setpoint instantly increases to the given value after the operator inputs it on the screen. In the case of low temperatures inside the furnace, this sudden increase in the temperature setpoint causes the electric heater to continuously output full power. The operating current remaining at the upper limit for an extended period can easily lead to overcurrent damage to the equipment. Furthermore, excessively rapid temperature rise causes significant damage to the refractory material, affecting the annealing furnace's lifespan. In contrast, the rate model setpoint gradually increases with the set rate, achieving gradual adjustment. Figure 4 For example: the horizontal axis represents time, and the vertical axis represents the temperature PID setpoint. The conventional setpoint changing from 100 to 600 is an instantaneous change, while the rate model setpoint increases according to the slope K when the temperature is below 500 (T2), and is an instantaneous change when the temperature is above 500 (T2).
[0030] Equipment lifespan: The heater replacement cycle has been extended from 6 months to more than 9 months; Production targets: Reduce downtime by 48 hours per year, increase silicon steel production by 604 tons, save 80,000 yuan in equipment maintenance costs, and achieve a total annual benefit of 1.08 million yuan.
Claims
1. A method for controlling the electric heating of an annealing furnace, characterized in that, Includes the following steps: Step 1: Real-time acquisition of the temperature of the electric heater body of the annealing furnace, strip tension signal, and strip breakage signal; Step 2: The PLC makes logical judgments based on the collected signals: when a strip breakage signal is detected, or the actual tension value of the strip is less than the tension alarm value, the electric heater is automatically turned off; when the temperature of the electric heater body is higher than the first alarm threshold, the electric heating power output is limited; when the temperature of the electric heater body is higher than the second alarm threshold, heating is stopped. Step 3: Establish a temperature rate control model and adjust the PID setpoint according to the furnace temperature in segments: when the furnace temperature is lower than the real-time temperature setpoint (i.e., low temperature), the PID setpoint gradually increases according to the set heating rate; when the furnace temperature is higher than the real-time temperature setpoint (i.e., high temperature segment), the PID setpoint directly adopts the operator input value.
2. The electric heating control method for an annealing furnace according to claim 1, characterized in that: The first alarm threshold is the furnace temperature measurement value plus 30°C, and the second alarm threshold is the furnace temperature measurement value plus 60°C.
3. The electric heating control method for an annealing furnace according to claim 1, characterized in that: The strip tension signal and strip breakage signal are obtained by communication between the annealing furnace PLC and the main line primary PLC.
4. The electric heating control method for an annealing furnace according to claim 1, characterized in that: The PLC operation screen has a bypass mode button: during maintenance / when there is no strip for heating, the bypass can be manually engaged, the interlock can be disengaged, and the electric heater can be automatically shut down / preheating can be performed according to the set preheating temperature; after the tension is restored after the strip is threaded, the program automatically restores the interlock to prevent long-term misuse of the bypass.
5. The electric heating control method for an annealing furnace according to claim 1, characterized in that: In the temperature rate control model, the slope K = T / 3600, and the real-time temperature setpoint T V =K×t+T0; where T is the set heating rate in °C / h, t is time in seconds, and T0 is the initial temperature setpoint.
6. The electric heating control method for an annealing furnace according to claim 1, characterized in that: The maximum output value of the PID is limited to 80% of the theoretical maximum output value of the PID, to avoid long-term high-power operation of the electric heater.
7. An annealing furnace electric heating control system according to any one of claims 1-6, characterized in that, include: The temperature acquisition module is used to acquire the temperature of the electric heater body and the temperature inside the furnace; The signal acquisition module is used to acquire strip tension signals and strip breakage signals; The PLC control module is connected to the temperature acquisition module and the signal acquisition module, and is used to execute the control method described in any one of claims 1-6; The execution module is used to perform power limiting, heating stop, and bypass interlock operations according to PLC instructions.