Polymer stretch flow melt plasticizing system based on PLC control

Abstract

This invention discloses a PLC-controlled polymer stretching flow melting and plasticizing system in the field of polymer processing automation control equipment technology. The system includes: a setpoint input module, a processing equipment module, a PLC controller, and a control module. The control module includes a mounting cover for housing a second detector of the information acquisition module, a detection component housed within the mounting cover, and a drive component for moving the second detector. The PLC controller controls the drive component to move the second detector to contact the melt when the detection component detects that the ultrasonic velocity and attenuation coefficient in the melt reach a threshold. The system also includes an alarm module and a display module. This invention receives process parameters input from the setpoint input module and real-time data collected by the information acquisition module through the PLC controller, and uses a melting and plasticizing control model to calculate and generate corresponding optimized control parameters to adjust the processing equipment module, thereby achieving automated control of the melting and plasticizing process.

Description

Technical Field

[0001] This invention relates to the field of automated control equipment for polymer processing, and more specifically to a polymer stretching flow melting plasticizing system based on PLC control. Background Technology

[0002] In polymer extrusion processing, melt plasticization is one of the most critical steps. Traditional plasticizing systems mainly rely on shear flow to achieve polymer melting and mixing, but shear flow has drawbacks such as high energy consumption and a tendency to lead to polymer degradation. In recent years, stretching flow has been proven to be more effective in promoting polymer melting and mixing, with lower energy consumption. However, the temperature control of existing plasticizing systems is mostly based on overall control, which cannot achieve independent and precise temperature control of different functional areas, and the degree of automation is low. Furthermore, when detecting process parameters online, such as using an infrared online viscometer to obtain melt viscosity, existing systems generally lack a real-time detection mechanism for the melt filling state, which is a significant challenge in polymer extrusion processing. During operation, especially during equipment cold starts, raw material switching, material interruption recovery, or refeeding after cleaning, the extruder end and melt flow channel may be in a state of no melt filling or partial filling. If the infrared online viscometer is turned on too early under the above-mentioned unsteady conditions, it will be unable to obtain accurate viscosity data when there is no melt filling or the melt does not completely cover the optical probe. The signal fed back to the control system will have serious deviations. In addition, the infrared online viscometer is directly exposed to high temperature air without melt protection, and is very easy to be damaged by dry burning, local overheating, or mechanical impact from unmelted solid particles, resulting in equipment losses of tens of thousands of yuan or even more. Summary of the Invention

[0003] The purpose of this invention is to provide a polymer stretching flow melting plasticizing system based on PLC control, which solves the problems of existing plasticizing systems where temperature control is mostly based on overall control, and the inability to achieve independent and precise temperature control of different functional areas and the use of infrared online viscometers.

[0004] This invention achieves the above objective through the following technical solution: a PLC-controlled polymer stretching flow melting plasticizing system, comprising: The processing equipment module includes an extruder, a heating and cooling unit, a melt pump, and a feeding motor. The heating and cooling unit is respectively located in the feeding zone, compression zone, metering zone, and each reaction injection zone of the extruder. The setpoint input module is used to input the process parameters of the processing equipment module; The information acquisition module is used to collect melt temperature, melt pressure at the melt pump inlet and in the extruder screw area, melt viscosity, feeding speed of the feed motor, extruder screw shaft torque, and extruder screw drive motor speed; The PLC controller receives process parameters from the setpoint input module and real-time data from the information acquisition module, imports them into a pre-built melt plasticizing control model, calculates and generates corresponding optimized control parameters, and adjusts the processing equipment module accordingly. The control module includes a mounting cover for housing the second detector of the information acquisition module, a detection component inside the mounting cover, and a drive component for driving the second detector to move. The PLC controller is used to control the drive component to drive the second detector to move and contact the melt when the detection component detects that the sound velocity and attenuation coefficient of the ultrasonic wave in the melt reach a threshold, so as to detect its viscosity in real time. The alarm module is used to issue an alarm message when the parameters collected by the information acquisition module exceed a preset value; The display module is used to display the operating status and alarm information of the processing equipment module.

[0005] Preferably, the PLC controller is used to adjust the speed difference between the extruder screw drive motor and the melt pump in real time based on the melt viscosity obtained by the second detector.

[0006] Preferably, the PLC controller uses the melt pressure, melt temperature, feeding speed, extruder screw shaft torque, and extruder screw drive motor speed collected by the information acquisition module to build a verification model to calculate the predicted value. If the difference between the predicted value and the melt viscosity value collected by the information acquisition module is less than the threshold, the collected melt viscosity value is qualified; otherwise, it is unqualified.

[0007] Preferably, the mounting cover is provided with a partition, which is used to divide the inner cavity of the mounting cover into a first cavity and a second cavity that are separated from each other. The second detector is disposed in the second cavity, and the detection component is disposed in the first cavity.

[0008] Preferably, the drive assembly includes a mounting bracket for connecting to the second detector and a drive member for moving the mounting bracket, and a second baffle for housing the second detector is hinged in the second cavity.

[0009] Preferably, the mounting bracket is provided with a limiting member to limit the second cavity when the second baffle is rotated to open it.

[0010] Preferably, the detection assembly includes a receiving groove on the side wall of the partition, a first baffle slidably disposed in the receiving groove, a movable member disposed on the first baffle, an elastic member for supporting the first baffle, and a first detector slidably disposed in the first cavity and supported by the first baffle. The movable member is used to drive the first baffle to move when the melt flows, so that the support on the first detector disappears and it moves down to contact the melt, so as to detect that the sound velocity and attenuation coefficient of the ultrasonic wave in the melt reach a threshold.

[0011] Preferably, a bracket is slidably provided in the first cavity, and a flexible connector is provided between the bracket and the mounting frame. When the mounting frame drives the second detector to move outward of the second cavity, it pulls the flexible connector so that the bracket carries the first detector back into the first cavity.

[0012] Preferably, the second cavity is provided with a slot, and a movable push rod extending into the storage slot is slidably provided in the slot. The movable push rod is used to push the first baffle to move outward of the storage slot when the second baffle rotates to open the second cavity.

[0013] Preferably, a limiting block and an electromagnet for attracting the limiting block are slidably provided in the receiving groove. The electromagnet is de-energized when the second detector is driven to move outward of the second cavity, so that the limiting block moves down to restrict the first baffle.

[0014] The beneficial effects of this invention are as follows: 1. The PLC controller receives process parameters input from the setpoint input module and real-time data collected from the information acquisition module, and uses the melt plasticizing control model to calculate and generate corresponding optimized control parameters to adjust the processing equipment module. This achieves automated control of the melt plasticizing process, replacing traditional manual experience-based adjustments. It effectively overcomes the impact of material batch differences and environmental fluctuations on production, ensuring high consistency of the melt plasticizing process and stability of product quality. 2. The heating and cooling units are independently controlled by the PLC controller, which enables precise temperature adjustment of the feeding zone, compression zone, metering zone and each reaction injection zone, meeting the different temperature requirements of different functional zones. Furthermore, by adjusting the speed difference between the screw and the melt pump in the return channel, controllable stretching flow is induced in specific screw element areas, which significantly enhances the melting and plasticizing effect and reduces energy consumption. 3. The PLC controller is used to control the drive component to move the second detector to contact the melt when the detection component detects that the melt has completely melted and is flowing, so as to detect its viscosity. Only when the melt fully meets the detection conditions will the PLC controller control the drive component to drive the second detector to extend into the flow channel to contact the melt, which effectively prevents sensor damage caused by dry burning or mechanical impact, extends the service life of the equipment, and reduces maintenance costs. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the polymer stretching flow melting plasticizing system based on PLC control according to the present invention; Figure 2 This is a schematic diagram of the control module structure of the present invention; Figure 3 This is a schematic cross-sectional view of the mounting cover structure of the present invention; Figure 4For the present invention Figure 3 Enlarged schematic diagram of the structure at point A in the middle; Figure 5 For the present invention Figure 3 Enlarged schematic diagram of the structure at point B.

[0016] In the diagram: 1. Mounting base; 2. Mounting cover; 3. Moving part; 4. First baffle; 5. First detector; 6. Bracket; 7. Flexible connector; 8. Mounting frame; 9. Second detector; 10. Second baffle; 11. Limiting part; 12. Partition; 13. Storage slot; 14. Moving push rod; 15. Slot; 16. Limiting block; 17. Electromagnet; 18. Moving slide; 19. Protrusion; 20. Support block; 21. Moving block. Detailed Implementation

[0017] The present application will now be described in further detail with reference to the accompanying drawings. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0018] Example 1

[0019] Please see Figure 1 , Figure 2 and Figure 3 A polymer stretching flow melting plasticizing system based on PLC control includes: a setpoint input module, a processing equipment module, an information acquisition module, a PLC controller, a control module, an alarm module, and a display module; The setpoint input module is a human-machine interface used by staff to input process parameters of the processing equipment module (such as set temperature of each zone, screw speed, melt pump speed, etc.) and formula. The processing equipment module includes an extruder, a heating and cooling unit, a melt pump, and a feed motor. The screw assembly is installed inside the extruder barrel, and the screw is equipped with stretching flow induction elements (such as wedge grooves or convergent-divergent channels). Heating and cooling units are installed in sections around the barrel, corresponding to the feeding zone, compression zone, metering zone, and each reaction injection zone. Each zone has independent heating elements and cooling channels. The feeder is connected to the barrel, and the feed motor drives the feeder to deliver the polymer raw material into the barrel feed inlet. The inlet of the reflux channel is connected to the melt conveying section of the barrel (near the end of the metering zone), and the outlet of the reflux channel is connected back to the beginning of the melt section (near the front end of the compression zone). A melt pump is installed in series on the reflux channel for active control of the reflux flow rate. The extruder screw is driven by a drive motor, and the speed of the drive motor is controlled by a PLC controller. The information acquisition module includes a pressure detection unit (pressure sensor, installed at the melt pump inlet, outlet, and key locations in the barrel), a temperature detection unit (temperature sensor, installed on the walls of each functional area of ​​the barrel), a torque detection unit (torque sensor, installed on the screw drive shaft or coupling), and a viscosity detection unit (infrared online viscometer, installed at the end of the extruder); used to collect melt temperature, melt pressure at the melt pump inlet and in the extruder screw area, melt viscosity, feed rate of the feed motor, extruder screw shaft torque, and speed of the extruder screw drive motor; The PLC controller includes a temperature control module, a speed control module, a pressure control module, and a data analysis module. It receives process parameters input from the setpoint input module and real-time data collected by the information acquisition module. It imports the real-time data into the melt plasticizing control model, which calculates and generates corresponding optimized control parameters. The optimized control parameters include: the target temperature of each heating and cooling unit, the target feeding speed of the feeding motor, the target speed of the main screw, the target speed of the melt pump in the reflux channel, and the target speed difference between the main screw and the melt pump in the reflux channel. It should be noted that the specific optimized control parameters are generated using the melt plasticizing control model by reading the initial process parameters from the setpoint input module, and the target temperature T for each functional zone. set,i Target value of feeding speed F set Target speed N of the main screw set Target speed P of melt pump in reflux channel set Target speed difference ΔN set Real-time data is read from the information acquisition module, showing the actual temperature (T) of each functional area. act Actual pressure P at the melt pump inlet ract Actual pressure P in the screw region s,act Actual melt viscosity V act Actual feeding speed F act Actual screw torque T oract Actual main screw speed N act Actual melt pump speed P act Align the initial process parameters with the real-time data according to the timestamp to form the input feature vector X=[T set,i F set N set P set ΔN set T act,i P ract P s,act V act F act T oract N act P act ]; Calculate the deviation characteristics: temperature deviation eT,i=Tset,i -T act,i Feeding speed deviation eF=F set -F acte Speed ​​deviation eN=N set -N acte Speed ​​difference deviation eΔN=ΔN set -(N act -P act The deviation characteristics, along with real-time viscosity and torque values, are used as key dynamic variables for model input. The constructed feature vector and deviation characteristics are imported into a pre-trained melt plasticizing control model. Based on the difference between the current process parameters and the real-time state, combined with the formulation type and melt quality objectives (such as minimizing viscosity fluctuations and torque stability), the optimized control parameter vector Y=[T] is calculated and generated through a built-in nonlinear mapping relationship or multivariate predictive control algorithm. opt,i F opt N opt P opt ΔN opt The optimized parameter Y is converted into a control signal and output to the heating and cooling unit, the feeding motor, the main screw drive motor, and the melt pump motor in the reflux channel, respectively, to achieve closed-loop dynamic adjustment of each device. The control module includes a mounting cover 2, inside which is placed a second detector 9, which is an infrared online viscometer. The inner cavity of the mounting cover 2 is equipped with a detection component and a drive component. The drive component is used to drive the second detector 9 to move, so that the second detector 9 can enter and exit the mounting cover 2. The PLC controller is used to control the drive component to drive the second detector 9 to move and contact the melt and turn it on when the detection component detects that the melt has melted to a threshold (i.e., completely melted) and is flowing, so as to detect its viscosity in real time. The alarm module is used to issue an alarm when the parameters collected by the information acquisition module exceed the preset value (exceeding the safe range); The display module is used to display the operating status and alarm information of the processing equipment module.

[0020] In this embodiment, as a further optimization, please refer to... Figure 1 During the melting and plasticizing process, the PLC controller receives the real-time melt viscosity feedback from the second detector 9 and continuously imports the viscosity data into the melting and plasticizing control model. It calculates and adjusts the speed difference between the main screw speed and the melt pump speed in the return channel, generating controllable stretching flow in the stretching flow induction element area to enhance the melting and plasticizing effect and maintain stable melt quality.

[0021] In this embodiment, as a further optimization, please refer to... Figure 1The PLC controller uses the melt pressure, melt temperature, feeding speed, extruder screw shaft torque, and extruder screw drive motor speed collected by the information acquisition module to build a verification model to calculate the predicted value. If the difference between the predicted value and the melt viscosity value collected by the information acquisition module is less than the threshold, the collected melt viscosity value is qualified; otherwise, it is unqualified.

[0022] It should be noted that the calculation method for the difference between the predicted and measured values ​​is as follows: The infrared viscometer data, temperature, pressure, torque, rotational speed, and feeding speed are aligned to a uniform timestamp, such as a sampling point every 0.5 seconds, and obvious noise is removed; a temperature-pressure correction model (η) is established. cal1 =η0×exp×(R / Ea×(1 / T-1 / T0)+β×(P-P0)), where Ea is the activation energy, β is the pressure coefficient, η0 can be pre-calibrated through offline experiments, T0 is the standard temperature, P0 is the atmospheric pressure), torque-speed model (η cal2 =k×N Tor Tor = k × η × N, where Tor is torque, η is viscosity, and N is rotational speed; pressure difference-flow model (ΔP = η × (C1N)). p -C2Q), by using the measured ΔP and known pump characteristics, η can be calculated inversely. cal3 The weighted sum of the calculated values ​​is used to calculate the fusion value η. fusion =0.3×η cal1 +0.4×η cal2 +0.3×η cal3 Calculate the measured value (η) IR The relative deviation between the fusion value and the fusion value is δ=∣η IR -η fusion ∣ / η fusion .

[0023] Example 2

[0024] As a further optimization of Example 1, please refer to Figure 2 and Figure 3 The inner cavity of the mounting cover 2 is provided with a partition 12, which is used to divide the inner cavity of the mounting cover 2 into a first cavity and a second cavity that are separated from each other. The second detector 9 is located in the second cavity, and the detection component is located in the first cavity, so that the second detector 9 and the detection component are separated.

[0025] It should be noted that the bottom of the mounting cover 2 is provided with a mounting base 1, which is fixed to the outside of the end of the extruder by bolts, and the mounting cover 2 faces upward.

[0026] In this embodiment, as a further optimization, please refer to... Figure 3The drive assembly includes a drive element (such as an electric telescopic rod) and a mounting bracket 8 on the moving end of the drive element. The mounting bracket 8 is connected to the second detector 9. A second baffle 10 is hinged to the inner wall of the second cavity via a torsion spring shaft. The second baffle 10 is located below the second detector 9 and is used to house the second detector 9 in the second cavity. The drive element drives the mounting bracket 8 to move downward, causing the second detector 9 to push the second baffle 10 downward to rotate, thereby opening the second cavity and extending the probe of the second detector 9 to the outside of the second cavity to contact the melt.

[0027] It should be noted that after the product processing is completed, the driving component drives the mounting bracket 8 and the second detector 9 to move upward and reset, retracting them into the interior of the second cavity and shutting down the second detector 9.

[0028] In this embodiment, as a further optimization, please refer to... Figure 3 The mounting frame 8 is provided with a limiting member 11 on its side wall. When the mounting frame 8 moves downward and the second detector 9 pushes the second baffle 10 to rotate downward, the limiting member 11 moves downward with the mounting frame 8 and contacts the second baffle 10, limiting the rotation of the second baffle 10 so that it does not continuously contact the second detector 9.

[0029] In this embodiment, as a further optimization, please refer to... Figure 3 The detection component includes a receiving groove 13 formed on the side wall of the partition 12, located inside the first cavity. A first baffle 4 is slidably disposed in the inner cavity of the receiving groove 13. The first baffle 4 is horizontally positioned, and a movable part 3 (made of high-temperature resistant metal) is provided on the bottom wall of the first baffle 4. An elastic element (such as a spring) is provided between the receiving groove 13 and the first baffle 4. A first detector 5 is slidably disposed in the inner cavity of the first cavity. The first detector 5 is capable of moving up and down and is located above the first baffle 4, supported by the first baffle 4. The movable part 3 is located in the flow channel of the melt conveying section or the melt pump outlet. In the process, when the melt begins to flow, the moving part 3 is pushed to move so that the first baffle 4 moves into the interior of the receiving tank 13, causing the support on the first detector 5 to disappear. Under the action of gravity, the first detector 5 moves down to contact the melt, so as to detect whether the sound velocity and attenuation coefficient of the ultrasonic wave in the melt reach the threshold (i.e., to detect whether the melt is completely melted). The first detector 5 refers to the ultrasonic sensor (the buffer rod of the sensor is in contact with the melt). It judges the melting state by monitoring the sound velocity and attenuation coefficient of the ultrasonic wave in the material. When the polymer is completely melted, its physical state changes abruptly, the sound velocity will change significantly and tend to stabilize.

[0030] It should be noted that you should refer to [link / reference]. Figure 5The inner wall of the first cavity is provided with a movable groove 18, and the side wall of the first detector 5 is provided with a movable block 21. The movable block 21 is slidably disposed in the inner cavity of the movable groove 18. The bottom of the inner cavity of the movable groove 18 is provided with a support block 20 (rubber material), which has a certain elasticity. When the first detector 5 moves down, the movable block 21 contacts the support block 20, reducing the impact force of the first detector 5 falling. In addition, the inner wall of the movable groove 18 is provided with a protrusion 19, which is located in the middle part of the movable groove 18. When the movable block 21 moves down, it will pass through the protrusion 19. The protrusion 19 is used to slow down the downward movement of the movable block 21, reducing the impact force generated by the falling of the first detector 5.

[0031] In this embodiment, as a further optimization, please refer to... Figure 3 A bracket 6 is slidably provided in the inner cavity of the first cavity. The bracket 6 can move up and down and is located below the first detector 5. A flexible connector 7 (such as a rope, but not limited to a rope) is provided on the top wall of the bracket 6. An opening is provided on the side wall of the partition 12. The end of the flexible connector 7 away from the bracket 6 passes through the opening and is connected to the mounting frame 8. When the mounting frame 8 drives the second detector 9 to move outward of the second cavity, it pulls the flexible connector 7 so that the bracket 6 carries the first detector 5 back into the first cavity. This allows the first detector 5 to retract into the interior of the first cavity after completing the detection (i.e., when the second detector 9 begins to move downward), ensuring that the first detector 5 does not come into long-term contact with the melt, protecting the first detector 5 and extending its service life.

[0032] In this embodiment, as a further optimization, please refer to... Figure 3 and Figure 4 A slot 15 is provided on the inner wall of the second cavity, and a movable push rod 14 is slidably provided in the inner cavity of the slot 15. The movable push rod 14 is located below the second baffle 10, and the end of the movable push rod 14 extends into the inner cavity of the storage groove 13. When the second detector 9 is driven to move down and pushes the second baffle 10 to rotate and open the second cavity, the second baffle 10 pushes the movable push rod 14 to move into the inside of the storage groove 13, so that the movable push rod 14 squeezes the first baffle 4 and pushes the first baffle 4 to the outside of the storage groove 13, so that the first baffle 4 is reset and the first detector 5 is supported again.

[0033] In this embodiment, as a further optimization, please refer to... Figure 3 and Figure 4The storage slot 13 has an installation slot at the top of its inner cavity. A limiting block 16 is slidably installed in the inner cavity of the installation slot. An electromagnet 17 is installed in the inner cavity of the installation slot. The electromagnet 17 is located above the limiting block 16 and is used to attract the limiting block 16 (the limiting block 16 is made of a metal material that can be magnetically attracted, such as iron). When the first detector 5 detects that the melt has completely melted, and the PLC controller controls the drive to move the mounting bracket 8 and the second detector 9 downward, the PLC controller controls the electromagnet 17 to be de-energized, so that the magnetic attraction force on the limiting block 16 disappears. After the first baffle 4 is pushed to the left side of the limiting block 16 by the moving push rod 14, the limiting block 16 moves down to the right side of the first baffle 4, preventing the first baffle 4 from entering the storage slot 13. This ensures that after the second detector 9 retracts into the second cavity (at this time, the second detector 9 has completed its detection task and the product processing is completed), the first baffle 4 will not move into the storage slot 13.

[0034] It should be noted that during the period from when the second detector 9 is working until the next processing cycle of the equipment, the electromagnet 17 is in a de-energized state.

[0035] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A polymer stretch flow melt plasticizing system based on PLC control, characterized by, The application relates to a molten plasticization control system, comprising: a processing equipment module, including an extruder, a heating and cooling unit, a melt pump, a feeding motor, wherein the heating and cooling unit is respectively arranged at a feeding area, a compression area, a metering area and each reaction injection area of the extruder; a set value input module for inputting process parameters of the processing equipment module; an information acquisition module for acquiring melt temperature, melt pressure at a melt pump inlet and an extruder screw area, melt viscosity, a feeding speed of the feeding motor, an extruder screw shaft torque and a rotating speed of an extruder screw driving motor; a PLC controller for receiving process parameters input by the set value input module and real-time data acquired by the information acquisition module, introducing the parameters into a pre-constructed melt plasticization control model, calculating corresponding optimized control parameters and adjusting the processing equipment module; a regulation and control module, including a mounting cover (2) for accommodating a second detector (9) of the information acquisition module, a detection assembly arranged in the mounting cover (2) and a driving assembly for driving the second detector (9) to move, wherein the PLC controller is used for controlling the driving assembly to drive the second detector (9) to contact the melt to detect the viscosity of the melt in real time when the detection assembly detects that the sound speed and the attenuation coefficient of ultrasonic waves in the melt reach a threshold value; an alarm module for sending alarm information when parameters acquired by the information acquisition module are greater than preset values; a display module for displaying the running state of the processing equipment module and alarm information.

2. The polymer stretch flow melt plasticizing system based on PLC control according to claim 1, characterized in that, The PLC controller is used for adjusting the rotating speed difference between the extruder screw driving motor and the melt pump in real time according to the melt viscosity acquired by the second detector (9).

3. The polymer stretch flow melt plasticizing system based on PLC control according to claim 2, characterized in that, The PLC controller constructs a verification model by using melt pressure, melt temperature, a feeding speed, an extruder screw shaft torque and the rotating speed of the extruder screw driving motor acquired by the information acquisition module to calculate a predicted value, and if the difference between the predicted value and the melt viscosity value acquired by the information acquisition module is less than a threshold value, the acquired melt viscosity value is qualified, otherwise, the acquired melt viscosity value is unqualified.

4. The polymer stretch flow melt plasticizing system based on PLC control according to claim 1, characterized in that, A partition plate (12) is arranged in the mounting cover (2), the partition plate (12) is used for dividing an inner cavity of the mounting cover (2) into a first cavity and a second cavity which are separated from each other, the second detector (9) is arranged in the second cavity, and the detection assembly is arranged in the first cavity.

5. The polymer stretch flow melt plasticizing system based on PLC control according to claim 4, characterized in that, The driving assembly includes a mounting frame (8) connected with the second detector (9) and a driving piece for driving the mounting frame (8) to move, and the second cavity is hinged with a second baffle (10) for accommodating the second detector (9) in the second cavity.

6. The polymer stretch flow melt plasticizing system based on PLC control according to claim 5, characterized in that, A limiting piece (11) is arranged on the mounting frame (8) to limit the second baffle (10) when the second baffle (10) is rotated to open the second cavity.

7. The polymer stretch flow melt plasticizing system based on PLC control according to claim 5, characterized in that, The detection assembly comprises a receiving groove (13) arranged on the side wall of the partition plate (12), a first baffle (4) slidingly arranged in the receiving groove (13), a moving piece (3) arranged on the first baffle (4), an elastic piece for supporting the first baffle (4), a first detector (5) slidingly arranged in the first cavity and supported by the first baffle (4), the moving piece (3) is used for driving the first baffle (4) to move when the melt flows, so that the first detector (5) is no longer supported and moves downward to contact the melt, so as to detect that the sound speed and the attenuation coefficient of the ultrasonic wave in the melt reach the threshold value.

8. The polymer stretch flow melt plasticizing system based on PLC control according to claim 7, characterized in that, A bracket (6) is slidingly arranged in the first cavity, a flexible connecting piece (7) is arranged between the bracket (6) and a mounting frame (8), and the mounting frame (8) drives the second detector (9) to move outward of the second cavity, pulls the flexible connecting piece (7), so that the bracket (6) returns to the first cavity with the first detector (5).

9. The polymer stretch flow melt plasticizing system based on PLC control according to claim 8, characterized in that, A slot (15) is arranged in the second cavity, a moving push rod (14) extending into the receiving groove (13) is slidingly arranged in the slot (15), and the moving push rod (14) is used for pushing the first baffle (4) to move outward of the receiving groove (13) when the second baffle (10) is rotated to open the second cavity.

10. The polymer stretch flow melt plasticizing system based on PLC control according to claim 8, characterized in that, A limiting block (16) and an electromagnet (17) for adsorbing the limiting block (16) are slidingly arranged in the receiving groove (13), and the electromagnet (17) is used for being powered off when the second detector (9) is driven to move outward of the second cavity, so that the limiting block (16) moves downward to limit the first baffle (4).

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