System and method suitable for bell-type furnace heat preservation stage furnace fan motor frequency control

Abstract

The invention belongs to the technical field of heat treatment process control, and provides a frequency control system and method suitable for a furnace fan motor in the heat preservation stage of a bell-type furnace, the system comprises a temperature sensor, a frequency converter and a programmable controller, and the programmable controller is connected with the temperature sensor and the frequency converter. The temperature sensor is arranged in the load space to measure the temperature of the load space; the frequency converter is connected with the furnace fan motor to control the operation frequency of the furnace fan motor; according to the frequency control method, logic is formulated through temperature conditions to control the frequency of the furnace fan motor. According to the method, uniform conduction of the load space temperature in the heat preservation stage and stable approaching of the temperature of the core and the edge of the annealing material are facilitated; and finally, the difference between the temperature of the core part and the temperature of the edge part of the annealed steel coil stably reaches the deviation range required by the process, so that the recrystallization annealing quality is ensured, and meanwhile, a very good energy-saving effect is achieved after the method is used.

Description

Technical Field

[0001] The invention belongs to the technical field of heat treatment process control, and relates to the heating and insulation process control of a full hydrogen bell-type furnace, and specifically is a furnace table fan motor frequency control system and method suitable for the bell-type furnace insulation stage. Background Art

[0002] A bell-type furnace is an annealing furnace. In the normal production annealing process, pure hydrogen is used in the load space (the area where the annealing material is located), which is also called a full hydrogen bell-type furnace. In the metallurgical industry, it is mostly used for recrystallization annealing to restore and improve the internal crystal structure of the annealing material. Heating and insulation are two main process steps in an annealing process. That is, heat is continuously supplied according to the preset slope to make the load space reach the preset temperature (heating stage), and then the load space is kept at this temperature for a specified time (insulation stage), so that the core and edge temperatures of the annealing material are finally consistent (that is, within the specified deviation range). Among them, insulation is the most important, and it is also the most critical stage in the entire annealing cycle, which is directly related to the annealing quality. To maintain the temperature of the load space, a method of intermittent heating with a constant heating amount is used according to the deviation between its temperature and the specified value. That is, when the temperature of the load space reaches the set value, the fire is turned off, that is, no more heat is supplied. When the temperature of the load space is lower than the set value by a certain amount, the ignition is turned on to resume heating. This is repeated, so it is also called switch control. When the switch is controlled, the heat supply per unit time is constant each time the ignition is turned on, and is significantly smaller than the heating stage, that is, "constant heat supply". Of course, the calorific value of the fuel is also stable.

[0003] In bell-type furnace production, the heat source of the load space is the combustion of the heating hood burner. The burner generally adopts pulse type, that is, there are only two states of open and closed, and generally all burners act synchronously. So when the burner is turned on, the amount of heat supplied per unit time is determined by the opening of the regulating valve on the fuel main pipe in front of the burner. "Switch control" means that the opening of the regulating valve is fixed at a moderate position and remains unchanged, and only the burner is opened and closed. The burner is arranged in the middle and lower part of the hood. So how can the upper furnace charge get heat or how to ensure the uniformity of the temperature in the load space? It depends on an important equipment: the furnace fan.

[0004] The furnace table fan is the main component of the bell-type furnace table and is installed at the bottom of the furnace table. During production, its operation makes the gas in the load space move and is the starting point of strong convection. For the annealing material in the load space, it can also be regarded as the power source of heat transfer.

[0005] The furnace fan motor adopts variable frequency motor. From the control perspective, the frequency converter of the variable frequency motor is controlled by PLC and is divided into low speed and high speed. In actual production, under normal working conditions and normal process periods, the furnace fan motor generally runs at high speed.

[0006] The furnace fan plays a decisive role in the temperature conduction of the load space, especially the temperature uniformity. Especially in the insulation stage, when the temperature of the load space reaches the set value, the heating has stopped. What should we do if the temperature of the load space continues to exceed the set value? From common sense, if the surface temperature is too high and the convection is too strong, it is not conducive to the heat conduction from the edge of the annealing material to the core, affecting the uniform and stable increase of the temperature of the core of the annealing material. At this time, the only thing that can be adjusted and must be adjusted is the frequency of the furnace fan motor. Summary of the invention

[0007] The purpose of the present invention is to provide a frequency control system and method for a furnace table fan motor during the insulation stage of a bell-type furnace. In the production process of a full-hydrogen bell-type furnace, when the load space temperature during the insulation stage continues to be higher than the set value to a corresponding degree and continues for a corresponding time, the frequency of the furnace table fan motor is controlled accordingly to facilitate heat conduction and facilitate the core temperature of the annealing material to be uniformly and stably close to the set value.

[0008] The technical solution adopted by the present invention to achieve the above-mentioned purpose is: A furnace table fan motor frequency control system suitable for the heat preservation stage of a hood-type furnace comprises a temperature sensor, a frequency converter and a programmable controller. The programmable controller is connected to the temperature sensor and the frequency converter respectively. The temperature sensor is arranged in a load space to measure the load space temperature. The frequency converter is connected to the furnace table fan motor to control the operating frequency of the furnace table fan motor.

[0009] Furthermore, the frequency converter, as a substation of the programmable controller CPU, communicates with the programmable controller CPU through a bus, receives operation instructions from the programmable controller CPU and feeds back the motor operation frequency; the temperature sensor is connected to the programmable controller analog input module, and the programmable controller CPU receives the temperature sensor signal in real time.

[0010] Furthermore, the programmable controller is Siemens S7-300, the CPU of the programmable controller is 315-2DP, the analog input module model for receiving the temperature sensor signal is 6ES7331-7KF02-0AB0 or ​​6ES7331-7SF00-0AB0; the frequency converter adopts Siemens MICROMASTER430 or its upgraded model, and the frequency converter and the programmable controller are connected by a cable; the temperature sensor adopts a K-type thermocouple.

[0011] The method for controlling the frequency of the fan motor of the bell-type furnace during the insulation stage includes: S1. When the annealing process is in the insulation stage and the heating is under stable switch control, the normal frequency of the furnace fan motor is high speed; S2. When the annealing process is in the insulation stage, the heating mode is switch control, and the load space temperature is continuously stable within the required temperature difference for the set time, under this premise, if the load space temperature continuously exceeds the insulation temperature setting value, and the temperature difference reaches the corresponding set degree and is maintained for the corresponding set time, the furnace table fan motor is reduced to low speed; S3. After the furnace fan motor enters low speed, as long as the load space temperature is continuously stable within the required temperature difference, the furnace fan motor maintains low speed; S4. When the load space temperature is lower than the insulation temperature setting value and exceeds the corresponding setting level, there is no delay and the furnace fan motor returns to high speed;

[0012] Furthermore, the high-speed frequency of the furnace table fan motor is 65Hz, and the low-speed frequency is 25Hz.

[0013] Furthermore, during the change of the frequency of the furnace table fan motor, the heating mode remains unchanged.

[0014] The beneficial effects of the present invention are: The method of the present invention is used to control the frequency of the fan motor in the insulation stage of the full hydrogen bell-type furnace annealing process, which is beneficial to meet and ensure uniform temperature conduction, and finally the difference between the core temperature and the edge temperature of the annealed steel coil is stably within the deviation range required by the process, thereby ensuring the quality of recrystallization annealing. At the same time, the method has a good energy-saving effect. DETAILED DESCRIPTION

[0015] The present invention will be further described below in conjunction with embodiments: A furnace table fan motor frequency control system suitable for a hood-type furnace insulation stage, comprising a temperature sensor, a frequency converter and a programmable controller, the programmable controller is connected to the temperature sensor and the frequency converter respectively, the temperature sensor is arranged in a load space to measure the load space temperature, and the frequency converter is connected to the furnace table fan motor to control the furnace table fan motor operating frequency; As a substation of the CPU of the programmable controller, the frequency converter communicates with the CPU of the programmable controller through the bus, receives the CPU operation instructions of the programmable controller and feeds back the motor operation frequency; the temperature sensor is connected to the analog input module of the programmable controller, and the CPU of the programmable controller receives the temperature sensor signal in real time; The programmable controller is Siemens S7-300, the CPU of the programmable controller is 315-2DP, the analog input module model for receiving the temperature sensor signal is 6ES7331-7KF02-0AB0 or ​​6ES7331-7SF00-0AB0; the frequency converter is Siemens MICROMASTER430 or its upgraded model, the frequency converter and the programmable controller are connected by Profible cable; the temperature sensor is K-type thermocouple;

[0016] A method for controlling the frequency of a fan motor of a bell-type furnace during the heat preservation stage, comprising the following contents: First, make sure that the annealing process is in the insulation stage and in the stable switch control heating. At this time, the frequency of the furnace fan motor is normally high, and the high-speed frequency is set to 65Hz; When the annealing process is in the insulation stage, the heating mode is switch control, and the load space temperature is continuously stable within the required temperature difference for a set time, such as the load space temperature is required to be not less than 6°C below the set value, that is, the load space temperature is ≥ the set value -6°C, for 1 hour and 30 minutes; under the above premise, if the load space temperature exceeds the set value continuously, and the temperature difference reaches the setting, and is maintained for the set time, such as the load space temperature is greater than or equal to the set value by 5°C, that is, the load space temperature is ≥ the set value + 5°C, for 5 minutes, then the frequency of the furnace table fan motor is reduced to low speed, and the low speed frequency is 25Hz; After the furnace fan motor frequency enters low speed, as long as the load space temperature is continuously stable within the required temperature difference, such as the load temperature is not less than 6°C below the set value, that is, the load space temperature is ≥ the set value -6°C, the furnace fan motor maintains low speed; When the load space temperature breaks the above premise, that is, the load space temperature is lower than the set value and exceeds the set level, such as the load space temperature is not greater than 8°C below the set value, that is, the load space temperature ≤ the set value -8°C, there is no delay, and the furnace fan motor frequency returns to the high-speed frequency of 65Hz.

[0017] During the above process of changing the frequency of the furnace fan motor, the heating mode of the bell-type furnace remains unchanged.

[0018] The method of the present invention formulates logic to control the frequency of the furnace table fan motor through temperature conditions, so as to achieve uniform temperature conduction in the load space during the heat preservation stage in the furnace and stable temperature approximation between the core and edge of the annealing material.

Claims

1. A frequency control system for a fan motor of a bell-type furnace in the heat preservation stage, characterized in that: It includes a temperature sensor, a frequency converter and a programmable controller. The programmable controller is connected to the temperature sensor and the frequency converter respectively. The temperature sensor is arranged in the load space to measure the load space temperature. The frequency converter is connected to the furnace fan motor to control the operating frequency of the furnace fan motor.

2. The frequency control system for the fan motor of a bell-type furnace in the heat preservation stage according to claim 1 is characterized in that: The frequency converter communicates with the CPU of the programmable controller through the bus, receives the CPU operation instruction of the programmable controller and feeds back the operation frequency of the furnace table fan motor; the temperature sensor is connected to the analog input module of the programmable controller.

3. The frequency control system for the fan motor of a bell-type furnace in the heat preservation stage according to claim 1 is characterized in that: The programmable controller is Siemens S7-300, the CPU of the programmable controller is 315-2DP, the frequency converter is Siemens MICROMASTER430, the frequency converter and the programmable controller are connected by a cable; the temperature sensor is a K-type thermocouple.

4. A method for controlling the frequency of a fan motor of a bell-type furnace during the heat preservation stage, characterized in that: include: S1. When the annealing process is in the insulation stage and the heating is under stable switch control, the normal frequency of the furnace fan motor is high speed frequency; S2. When the annealing process is in the insulation stage, the heating mode is switch control, and the load space temperature is continuously stable within the required temperature difference for the set time, under this premise, if the load space temperature continuously exceeds the insulation temperature setting value, and the temperature difference reaches the corresponding set degree and is maintained for the corresponding set time, the furnace table fan motor is reduced to a low speed frequency; S3. After the furnace fan motor enters low speed, as long as the load space temperature is continuously stable within the required temperature difference, the furnace fan motor maintains low speed frequency; S4. When the load space temperature is lower than the insulation temperature setting value and exceeds the corresponding setting level, there is no delay and the furnace fan motor resumes high-speed frequency.

5. A method for controlling the frequency of a fan motor of a bell-type furnace in the heat preservation stage according to claim 4, characterized in that: The high-speed frequency of the furnace table fan motor is 65Hz, and the low-speed frequency is 25Hz.

6. The method for controlling the frequency of a fan motor of a bell-type furnace in the heat preservation stage according to claim 4 is characterized in that: During the change of the furnace table fan motor frequency, the heating mode remains unchanged.