Annealing furnace temperature control from the conventional instrument type to the programmable controller type The emergence of programmable controllers, led to a comprehensive reform of the hard-wired relay control system. With the extension of programmable controller technology to the field of process control (on the basis of its original logical operations and sequential control functions, and the enhancement and addition of many functions according to the specific requirements of process control), it began in the mid-1980s. In the field of process control. The emergence of this situation has led to a shift in the temperature control of the annealing furnace from traditional conventional instruments to new electronic control technologies such as programmable controller thyristors and frequency converters. Figure 7 is a schematic diagram of the principle of a programmable controller temperature control system used by Bowman an electric heating annealing furnace. The annealing furnace has a total of nine control sections (which constitute the same as the previously described Bowman conventional instrument controlled annealing furnace). Figure 7 (For the article space problem. The specific chart can be accessed on the home page of Xuzhou Hongyuan Glass Bottle Manufacturing Co., Ltd.) Only control circuits for one heating section (first section) and one cooling section (section six) are drawn. The system of FIG. 7 has the same function as the system of FIG. 2 , however, both work based on completely different principles. Figure 7 Boeman programmable controller annealing furnace temperature control system principle wiring diagram Figure 8 is the annealing furnace programmable controller system composition. Host is the United States AB (ALLEN-BRADLEY) PLC-5 series programmable controller products. It uses a single processor to perform all logic, sequence control, and process control. The CPU processor module is a single-slot structure. When the basic system is configured, only the CPU module is inserted in the leftmost slot of the 1771 Universal I/O rack, and the I/O modules are inserted into the remaining slots in sequence. As shown in Figure 8, the 1785-L20 B processor, the 1771-IXE/B thermocouple input card (2), and the 1771-IFE analog input card (1) are installed from left to right within the 1771-A3B12 slot rack. Block), 1771-OFE2 analog output card (3 blocks), 1771-IAD/C digital input card (2 blocks), 1771-OAD/B digital output card (1 block), and 1771-OW16/B relay output card (1 Piece). Since the 1771-A3B rack contains no power, it is also equipped with a 1771-P7 power supply (120/220VA C, 16A) on the left side. The power supply and CPU are connected using the 1771-CP2 cable. The I/O module communicates with the processor through the backplane of the I/O rack. Used together with the PCC-5 programmable controller host is a highly functional industrial site-hardened CRT-2711-KC type 1 Panelview 1200 operator interface. Bowman used Panelview software to develop software for the temperature control of the annealing furnace. Its unique and unique features are: various start/stop operations, temperature settings, PID parameter changes, and alarm operations for the annealing furnace temperature control system. , press the relevant function key on the "corresponding operator window" (display screen). Figure 8 Poehman Electric Annealing Furnace Programmable Controller System Figure 7 shows the connection diagram of the I/O module and related external components of PLC-5 with one heating section and one cooling section controlled in Figure 7 to illustrate how the system is Temperature control work: thermoelectric (1TC1.1) and 6th cooling section thermocouples connected to the #17, #18 and #5 and #6 terminals of the 1771-IXE/B thermocouple input card respectively. The annealing furnace temperature was measured evenly (6TC1.6). Temperature setpoints and PID parameters are set on the operator interface display. The PLC-5 processor reads and writes data to the operator interface through the I-O chain. The PID control algorithm is implemented in the ladder programming language by calling the PID function block in the PLC-5 instruction set. PID calculation result, output the 4-20mA signal to the thyristor 1SCR1.1 trigger signal terminal via the 1771-OFE2 analog output card (RACKO GROUP 3)'s #A, #O terminals, to adjust the thyristor main circuit electric heating element current, After outputting 4~20mA signal from #A and #O of another 1771-OFE2 analog output card (RACKO GROUP 4) to M72 84A Model 1004 "90-control motor" (6CM1.1) to adjust the cooling section blower damper Opening degree. The necessary interlocking signals for switching on the electric heating element are all connected to the I/O module in the form of digital (switching) signals, including: the output of the temperature overload relay 1HLC1.1 (if the temperature does not exceed the alarm value, Open contacts are closed. Connect to the #00 end of the 1771-IAD/C (RACKO GROUP 6) digital input card. The auxiliary normally open contact of the AC contactor 1MP1.1 that starts the 1st heating section blower is connected to the same digital input card. On the #02 side, the 1SS1.1 speed relay contact is connected to the #03 end of the same input card, and the auxiliary contact 1B1.1 of the #1 heating element power switch is connected to the #01 end of the same digital input card. The "AND" logic functions implemented by ladder logic for these interlock signals input to PLC-5 are the same as those performed by the relay contacts in series in the circuit of FIG. In addition, the AC contactors 1MP1.1 and 6MP1.5 for starting two blowers are excited by the voltage signals output from #00 and #12 of the 1771-OAD/B digital output card (RACK 1 GROUP 0). 3 Electronic Control Improvement of Annealing Furnace Energy Saving Technology Glass bottle annealing generally requires additional heating of the heat bottle fed into the annealing furnace, which consumes a certain amount of energy. In addition, the motor driving the annealing furnace mesh belt also needs a certain amount of electric energy. Therefore, successfully eliminating heat stress and reducing energy consumption are two major technical indicators of the annealing furnace. In order to save energy, annealing furnace manufacturers have taken many measures in the mechanical construction, such as the use of high-insulation ceramic fiber insulation materials and monolithic metal structures to reduce heat loss, using lightweight annealing furnace mesh belt and low-friction sports. Components to reduce the power loss of the annealing furnace drive. However, the considerable amount of heat taken by the thermos when moving from the hot side to the cold side of the annealing furnace is not prevented by mechanical construction measures. In response to this situation, the German PENNEKAMP programmable controller electric heating annealing furnace programmed a unique "heat recovery" program (ladder logic) to control the air flow inside the annealing furnace - to establish a reverse glass transfer inside the annealing furnace The direction of the airflow, to prevent the loss of this part of the heat, opened up a new way for the annealing furnace energy-saving technology. Figure 9 shows the layout of a German PENNEKAMP annealing furnace using this heat recovery technology. The annealing furnace has 8 control sections. The first 4 sections are heating sections, the 5th section is the transition section (neutral section), and the last 3 sections are cooling sections (each section is 2250mm long, and the annealing furnace has a total length of 29.8m. The widest section is 6235mm, mesh width 5250mm). It is equipped with the same basic components as the aforementioned Pohmann electric annealing furnace - electric heating element, blower, exhaust fan above the sixth paragraph used for "heat recovery" and suction above paragraphs 7 and 8. Air throttle. Relying on the blasting effect of the circulating fan above the annealing furnace, the suction damper sucks cold air from the external space into the furnace and establishes a positive pressure for blowing the airflow to the hot end (in order to ensure the establishment of positive pressure, the cold end outlet door of the annealing furnace must be Close as much as possible, higher than the product 5 ~ 10mm, while the hot end entrance door opened larger, higher than the product 50 ~ 70m m). By adjusting the damper opening of the exhaust fan, the air flow (reverse air flow) to the hot end is adjusted (Fig. 10). Figure 9 PENNEKAMP Electric Heating Annealing Furnace (Control Section) Equipment Layout The adjustment of the intake and exhaust damper opening is performed by the output signal of the programmable controller output connected to the forward and reverse loop of the electric actuator ( This circuit is omitted. The programmable controller system components of the annealing furnace include: PLC-5/11 programmable controller, Panelvi ew1200 operator interface, 32-bit digital input card (2 blocks), 32-bit digital output card (4 blocks) and analog input Card (1). The basic structure is the same as that of the previously described Bowman system (Fig. 8). However, due to the difference of the I/O modules used, the thermocouple millivolt signal needs to be converted by a dedicated device before it is connected to the analog input card. The control signal to the thyristor is from Digital output card "switch" signal, not continuous signal. Fig. 10 Principle diagram of hot air circulation technology of PENNEKAMP annealing furnace The basic point of the “heat recovery†ladder logic inside the programmable controller is to determine the exhaust flap and suction according to the temperatures of #1, #5 and #8 segments. The throttle opening controls the reverse flow. For example, when the temperature in segment #1 is lower than the lower limit, the reverse flow volume should be increased (close the exhaust throttle) so that the heat in #3, #4, and #5 segments is returned to the hot end. When the temperature of segment #1 rises above the lower limit, and if the temperature of segments #3, #4 and #5 is still higher than the upper limit, a large reverse flow should be maintained to return excess heat ( Reduce the amount of heat drawn from the electric heating element in section #1). When the temperature in segment #5 is lower than the lower limit, the reverse flow is reduced (opening the exhaust throttle) to allow the temperature in #5 to rise. Since the temperature of the #8 section needs to be kept at a certain value due to the temperature of the cold-side spraying, the suction throttle should be turned on or off with the temperature of the #8 section. The change of the intake damper opening will affect the reverse flow, so the opening of the exhaust damper should be changed along with the opening of the intake damper, so as to maintain the temperature according to # 1 and # 5 sections. The reverse air flow determined is unchanged.
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