A screw extruder temperature control system

Abstract

The application discloses a screw extruder temperature control system, which comprises a cylinder, a PLC control module, a temperature adjusting module and a temperature detecting module; the temperature adjusting module acts on the surface of the cylinder to form a temperature control layer on the surface of the cylinder, and the temperature control layer and the material in the cylinder are heat conduction objects; the temperature detecting module comprises a cylinder surface temperature detecting unit and a cylinder internal temperature detecting unit, and the cylinder surface temperature detecting unit and the cylinder internal temperature detecting unit are signal connected with the PLC control module to transmit temperature information to the PLC control module; the PLC control module controls the temperature adjusting module according to the obtained temperature information to keep the measurement value of the cylinder surface temperature detecting unit within a set threshold value. The application can improve the control precision of the temperature in the cylinder and reduce the fluctuation of the temperature in the cylinder.

Description

Technical Field

[0001] This invention relates to the field of screw extruder technology, and more particularly to a screw extruder temperature control system. Background Technology

[0002] During the operation of a screw extruder, it is necessary to control the temperature of the material inside the barrel to obtain a product of acceptable quality. Temperature regulation inside the barrel is generally achieved through heating and cooling mechanisms outside the barrel. However, there is a certain temperature difference between the surface temperature of the barrel and the temperature of the material inside. Traditional screw extruders typically only measure and control the temperature inside the barrel, neglecting to control the surface temperature.

[0003] During the heating process, the heating mechanism typically stops heating when the internal temperature of the barrel reaches the set value. However, at this point, the surface temperature of the barrel is still higher than the internal temperature. Therefore, even after heating stops, the internal temperature of the barrel will still rise to some extent due to heat conduction. Conversely, during the cooling process, the cooling mechanism stops cooling when the internal temperature of the barrel reaches the set value. At this point, the surface temperature of the barrel is lower than the internal temperature. Therefore, even after cooling stops, the internal temperature of the barrel will still decrease to some extent.

[0004] This results in the barrel's internal temperature not being maintained at the set value, but rather fluctuating around the set value, making the control of the barrel's internal temperature insufficient. Summary of the Invention

[0005] Purpose of the invention: In order to overcome the shortcomings of the existing technology, the present invention provides a temperature control system for screw extruders, which can improve the control accuracy of the temperature inside the barrel and reduce the fluctuation of the temperature inside the barrel.

[0006] Technical Solution: To achieve the above objectives, the present invention provides a temperature control system for a screw extruder, comprising a barrel, a PLC control module, a temperature adjustment module, and a temperature detection module. The temperature adjustment module acts on the surface of the barrel to form a temperature-controlled layer, which is a heat transfer object between the temperature-controlled layer and the material inside the barrel. The temperature detection module includes a barrel surface temperature measurement unit and a barrel interior temperature measurement unit, which are signal-connected to the PLC control module to transmit temperature information. The PLC control module controls the temperature adjustment module based on the acquired temperature information to maintain the measured value of the barrel surface temperature measurement unit within a set threshold.

[0007] Furthermore, the temperature measuring unit on the cylinder surface detects the temperature of the temperature control layer, and the temperature measuring unit inside the cylinder detects the temperature of the material inside the cylinder.

[0008] Furthermore, the temperature setting threshold of the temperature control layer includes an upper limit value for the cylinder surface temperature and a lower limit value for the cylinder surface temperature. The temperature control module controls the temperature of the cylinder by including a preheating stage and a fine-tuning stage. During the preheating stage, under the control of the PLC control module, the measured value of the cylinder surface temperature measuring unit does not exceed the upper limit value for the cylinder surface temperature. During the fine-tuning stage, under the control of the PLC control module, the measured value of the cylinder surface temperature measuring unit is maintained between the upper limit value for the cylinder surface temperature and the lower limit value for the cylinder surface temperature.

[0009] Furthermore, the inside of the barrel corresponds to a material temperature setpoint, and the temperature regulation module includes a cooling unit and a heating unit; when the measured value of the temperature measuring unit inside the barrel is less than the material temperature setpoint, and the measured value of the temperature measuring unit on the barrel surface is less than the upper limit of the barrel surface temperature, the heating unit is in the energized working state; when the measured value of the temperature measuring unit inside the barrel is greater than the material temperature setpoint, and the measured value of the temperature measuring unit on the barrel surface is greater than the lower limit of the barrel surface temperature, the cooling unit is in the energized working state.

[0010] Furthermore, the heating unit and the cooling unit are connected in parallel on the same temperature control circuit. The heating unit is connected in series with the upper limit detection switch of the external cylinder temperature to form a heating control circuit, and the cooling unit is connected in series with the lower limit detection switch of the external cylinder temperature to form a cooling control circuit. The power supply of the temperature control circuit controls the on / off state of the heating control circuit and the cooling control circuit through the double-throw switch for internal cylinder temperature detection. When the measured value of the internal cylinder temperature measuring unit is less than the material temperature set value, the double-throw switch for internal cylinder temperature detection is connected to the heating control circuit; when the measured value of the internal cylinder temperature measuring unit is greater than the material temperature set value, the double-throw switch for internal cylinder temperature detection is connected to the cooling control circuit; when the measured value of the cylinder surface temperature measuring unit is less than the upper limit value of the cylinder surface temperature, the upper limit detection switch of the external cylinder temperature is in the on state; when the measured value of the cylinder surface temperature measuring unit is greater than the lower limit value of the cylinder surface temperature, the lower limit detection switch of the external cylinder temperature is in the on state.

[0011] Furthermore, the cooling unit and the heating unit act uniformly on the temperature control layer on the surface of the barrel.

[0012] Furthermore, the heating unit includes heating elements uniformly disposed on the surface of the barrel.

[0013] Furthermore, after receiving the temperature information measured by the cylinder surface temperature measuring unit and the cylinder interior temperature measuring unit, the PLC control module controls the cylinder interior temperature detection double-throw switch, the cylinder exterior temperature upper limit detection switch, and the cylinder exterior temperature lower limit detection switch to turn on and off accordingly.

[0014] Furthermore, the temperature control circuit is also equipped with a main switch, which is in an open circuit state when the temperature regulation module stops running.

[0015] Furthermore, the barrel is divided into several heating sections along the material moving direction. Each heating section has an independent temperature control module and a temperature detection module, and each independently sets the upper limit value of the barrel surface temperature, the lower limit value of the barrel surface temperature, and the set value of the material temperature.

[0016] Beneficial effects: The temperature control system for a screw extruder of the present invention has the following beneficial effects:

[0017] 1) Simultaneously detect and control the temperature inside and on the surface of the barrel, so that the temperature on the surface of the barrel is also kept within the set threshold, thereby reducing the fluctuation range of the surface temperature of the barrel. Correspondingly, since heat conduction occurs between the inside and outside of the barrel, the temperature fluctuation inside the barrel will also be reduced.

[0018] 2) The temperature control circuit was redesigned and combined with the PLC control module. After considering the temperature values ​​measured inside and outside the barrel, the heating and cooling units can be controlled to ensure that the temperature value measured on the surface of the barrel is kept within the set threshold.

[0019] 3) The heating unit includes heating plates evenly arranged on the surface of the barrel, and the cooling unit is an air-cooled unit, including an external gas circulation pipeline and an internal gas circulation pipeline, so that the cooling unit and the heating unit can act evenly on the surface of the barrel, making the temperature of the barrel surface uniform. In this way, the barrel surface temperature value measured by the barrel surface temperature measuring unit is representative, and the barrel surface temperature can be better controlled to be maintained within the set threshold. Attached Figure Description

[0020] Appendix Figure 1 This is a schematic diagram of the circuit structure of the control system of the present invention;

[0021] Appendix Figure 2 This is a schematic diagram of the structure of an existing temperature control system;

[0022] Appendix Figure 3 This is a schematic diagram of the existing barrel heating and cooling units;

[0023] Appendix Figure 4 This is a schematic diagram of the cooling unit of the present invention. Detailed Implementation

[0024] The invention will now be further described with reference to the accompanying drawings.

[0025] As attached Figures 1 to 4 The aforementioned temperature control system for a screw extruder includes a PLC control module 5, a temperature regulation module, and a temperature detection module applied to the screw extruder.

[0026] An existing temperature control system is shown in the attached figure. Figure 2As shown, the S7-1200 PLC control module is the core of the entire control system. The heaters for the barrel and die are connected to the auxiliary contacts of an intermediate relay via contactors. The coil of the intermediate relay is connected to the output of the EM222 digital expansion module, indirectly controlling the heaters. Heater temperature detection is transmitted to the input of the EM231 analog input / output module via a K-type thermocouple temperature sensor. A complete temperature control loop is implemented through a PID control algorithm. The output of the EM232 extended analog output module is sent to the external analog signal receiver of the frequency converter. The frequency converter adjusts the motor speed, thereby controlling the speed of the extruder's main unit and the feeder. During operation, if the current measured value is lower than the set value, the PLC sends a signal to energize the heater; if the current temperature is higher than the set temperature, the PLC sends a signal to energize the fan. However, due to the difference between the surface temperature and the internal temperature of barrel 1, this operating mode causes significant fluctuations in the internal temperature of barrel 1.

[0027] In this invention, the screw extruder includes a barrel 1. A temperature control module acts on the surface of the barrel 1 to form a temperature control layer 2. The temperature control layer 2 and the material inside the barrel 1 are heat conduction objects. The temperature detection module includes a barrel surface temperature measuring unit 3 and a barrel interior temperature measuring unit 4. The barrel surface temperature measuring unit 3 detects the surface temperature of the barrel 1, and the barrel interior temperature measuring unit 4 detects the internal temperature of the barrel 1. The barrel surface temperature measuring unit 3 and the barrel interior temperature measuring unit 4 are connected to a PLC control module 5 to transmit temperature information. The PLC control module 5 controls the temperature control module based on the acquired temperature information to keep the measured value of the barrel surface temperature measuring unit 3 within a set threshold, reducing temperature fluctuations on the surface of the barrel 1. Since the temperature control layer 2 and the material inside the barrel 1 are heat conduction objects, the temperature fluctuations inside the barrel 1 are also reduced accordingly.

[0028] The cylinder surface temperature measuring unit 3 is used to detect the temperature of the temperature control layer 2, and the cylinder internal temperature measuring unit 4 is used to detect the temperature of the material inside the cylinder 1.

[0029] The temperature setting threshold of the temperature control layer 2 includes an upper limit value for the cylinder surface temperature and a lower limit value for the cylinder surface temperature. The temperature control module controls the temperature of the cylinder 1 through a preheating stage and a fine-tuning stage. During the preheating stage, the material inside the cylinder 1 is preheated. Under the control of the PLC control module 5, the measured value of the cylinder surface temperature measuring unit 3 does not exceed the upper limit value for the cylinder surface temperature. Once the measured value of the cylinder surface temperature measuring unit 3 first reaches the upper limit value, the preheating stage ends, and the fine-tuning stage begins. During the fine-tuning stage, under the control of the PLC control module 5, the measured value of the cylinder surface temperature measuring unit 3 remains between the upper limit value and the lower limit value for the cylinder surface temperature.

[0030] The barrel 1 has a corresponding material temperature setpoint inside. The temperature regulation module includes a cooling unit 6 and a heating unit 7. When the measured value of the temperature measuring unit 4 inside the barrel is less than the material temperature setpoint, and the measured value of the temperature measuring unit 3 on the barrel surface is less than the upper limit of the barrel surface temperature, the heating unit 7 is in a powered-on state; when the measured value of the temperature measuring unit 4 inside the barrel is greater than the material temperature setpoint, and the measured value of the temperature measuring unit 3 on the barrel surface is greater than the lower limit of the barrel surface temperature, the cooling unit 6 is in a powered-on state. Under other circumstances, both the cooling unit 6 and the heating unit 7 are in a powered-off state and do not heat or cool the barrel 1.

[0031] The heating unit 7 and cooling unit 6 are connected in parallel on the same temperature control circuit. The heating unit 7 and the cylinder external temperature upper limit detection switch 8 are connected in series to form a heating control circuit 21. The cooling unit 6 and the cylinder external temperature lower limit detection switch 9 are connected in series to form a cooling control circuit 10. The power supply 11 of the temperature control circuit controls the on / off state of the heating control circuit 21 and the cooling control circuit 10 through the cylinder internal temperature detection double-throw switch 12. When the measured value of the cylinder internal temperature measuring unit 4 is less than the material temperature set value, the cylinder internal temperature detection double-throw switch 12 is connected to the heating control circuit 21. When the measured value of the cylinder internal temperature measuring unit 4 is greater than the material temperature set value, the cylinder internal temperature detection double-throw switch 12 is connected to the cooling control circuit 10. When the measured value of the cylinder surface temperature measuring unit 3 is less than the cylinder surface temperature upper limit value, the cylinder external temperature upper limit detection switch 8 is in the closed state. When the measured value of the cylinder surface temperature measuring unit 3 is greater than the cylinder surface temperature lower limit value, the cylinder external temperature lower limit detection switch 9 is in the closed state.

[0032] The temperature control circuit is also equipped with a main switch 17 to control the start and stop of the entire temperature control circuit. When the temperature regulation module stops running, the main switch 17 is in the open circuit state.

[0033] In one embodiment of the present invention, the following settings are made: the material temperature setting is 150 degrees, the upper limit of the cylinder surface temperature is 155 degrees, and the lower limit of the cylinder surface temperature is 145 degrees. During the preheating stage, the main switch 17 is closed, the measured value of the cylinder internal temperature measuring unit 4 is less than the material temperature setting, so the cylinder internal temperature detection double-throw switch 12 is connected to the heating control circuit 21, and the measured value of the cylinder surface temperature measuring unit 3 is less than the upper limit of the cylinder surface temperature, so the cylinder external temperature upper limit detection switch 8 is in the open state. Therefore, the heating unit 7 is started to continuously heat the surface of the cylinder 1.

[0034] When the surface temperature of barrel 1 reaches 155 degrees, the preheating stage ends and the fine-tuning stage begins. Since the temperature control layer 2 conducts heat with the material inside barrel 1, the internal temperature of barrel 1 will be lower than 155 degrees, assuming it is 145 degrees. At this time, due to the presence of the upper limit detection switch 8 for the external temperature, the surface temperature of barrel 1 will be maintained within 155 degrees. However, the surface temperature of barrel 1 will still be higher than the internal temperature of barrel 1. Therefore, under the action of heat conduction, the internal temperature of barrel 1 will continue to rise until the internal temperature of barrel 1 reaches 150 degrees.

[0035] After the internal temperature of barrel 1 reaches 150 degrees Celsius, the internal temperature of barrel 1 will continue to rise due to the frictional heat generated by the screw and the material. Therefore, the double-throw switch 12 for detecting the internal temperature is switched to be connected to the cooling control circuit 10. Moreover, the measured value of the barrel surface temperature measuring unit 3 is greater than the lower limit of the barrel surface temperature, and the lower limit detection switch 9 for detecting the external temperature is in the open state. Therefore, the cooling unit 6 is activated to cool barrel 1. When the surface temperature of barrel 1 drops to 145 degrees Celsius, the lower limit detection switch 9 for detecting the external temperature is disconnected. Therefore, the surface temperature of barrel 1 will not be lower than 145 degrees Celsius. Due to heat conduction, the surface of barrel 1 will cool the inside of barrel 1, preventing the internal temperature of barrel 1 from continuing to rise due to the heat generated by the screw and the material. The lower limit of the barrel surface temperature needs to be low, otherwise the internal temperature of barrel 1 cannot be cooled. Thus, the internal temperature of barrel 1 is maintained at around 150 degrees Celsius. Compared with the traditional negative feedback temperature control circuit, the fluctuation range of the internal temperature of barrel 1 is lower, which is beneficial to the precise control of the internal temperature of barrel 1.

[0036] The cooling unit 6 and heating unit 7 act uniformly on the temperature control layer 2 on the surface of the barrel 1, ensuring a uniform surface temperature. Otherwise, the temperature value measured by the barrel surface temperature measuring unit 3 would not accurately represent the surface temperature of the barrel 1. A conventional cooling unit 6 is shown in the attached diagram. Figure 3 As shown, the blower only blows air from one side of the cylinder 1, resulting in a temperature difference between the two sides of the cylinder 1. This leads to uneven cooling of the cylinder 1, and the measured surface temperature value of the cylinder 1 is not representative, making it impossible to accurately maintain the surface temperature of the cylinder 1 within the set threshold. However, in this invention, as shown in the attached diagram... Figure 4 As shown, the heating unit 7 includes heating plates 13 uniformly arranged on the surface of the barrel 1, which can uniformly heat the surface of the barrel 1.

[0037] The barrel 1 is divided into several heating sections along the material moving direction. The temperature requirements of each heating section are different. Therefore, each heating section has an independent temperature control module and a temperature detection module, and each independently sets the upper limit value of the barrel surface temperature, the lower limit value of the barrel surface temperature, and the material temperature setting value. Correspondingly, each heating section has an independent cooling chamber 16, a heating unit 7, and a cooling unit 6, so as to independently control the temperature of each heating section.

[0038] After receiving the temperature information measured by the cylinder surface temperature measuring unit 3 and the cylinder interior temperature measuring unit 4, the PLC control module 5 controls the corresponding on / off states of the cylinder interior temperature detection double-throw switch 12, the cylinder exterior temperature upper limit detection switch 8, and the cylinder exterior temperature lower limit detection switch 9, thereby controlling whether the cooling unit 6 and the heating unit 7 operate. In actual operation, the PLC control module 5 uses the touch screen configuration screen to run animations to monitor the system's operation status in real time. On-site operators no longer need to directly touch the machinery, providing safety for workshop workers and maximizing worker efficiency. The touch screen uses simple button controls and is installed on a movable operating platform, allowing for centralized control management.

[0039] PLC control module 5 is an S7-1200 series PLC. The S7-1200 PLC is the core of the entire control system. In addition to controlling the temperature regulation module and temperature detection module, it can also control the feeding system, speed regulation system and vacuum exhaust system, which together constitute the overall control of the screw extruder.

[0040] The feeding system consists of a quantitative feeding system comprising a motor, a gearbox, a feeding screw, and a feeding hopper. The feeding screw features stepless speed regulation, with its speed determined by the screw rotation speed. The feeding rate increases with the increase of the twin-screw rotation speed.

[0041] The speed control system mainly consists of a frequency converter and a motor. When the speed control system receives the speed signal from the PLC control module 5, the feeder's frequency converter sets the corresponding speed and direction to make the motor run. Simultaneously, the frequency converter sends feedback signals back to the PLC control module 5 to monitor whether the armature temperature, speed, and torque exceed the set values. The extruder system's PLC process control controls the operation of the feeding, main unit, conveying, and cooling units 6 based on field signals, and provides corresponding operating status displays for operator monitoring.

[0042] The vacuum exhaust system is used to remove volatile gases from inside the extruder barrel 1. During the heating and extrusion process inside the extruder barrel 1 and die, the material often carries air, adsorbed moisture, and volatile gases generated at the high molding temperature. If these mixed gases are not promptly removed from the extruder, they will affect the quality and appearance of the plastic products, causing surface and internal defects such as pores, bubbles, and scars. The vacuum exhaust system uses a vacuum pump to draw these mixed gases out of the barrel's exhaust port and remove them from the extruder, thus ensuring product quality. The vacuum level inside the extruder can be adjusted via a stopcock valve, typically controlled below -0.075 MPa. The vacuum exhaust system also includes a solenoid valve on the vacuum pump's water inlet pipe. This valve opens only when the vacuum pump is operating and closes when the pump stops. The water inlet flow rate can be adjusted via the stopcock valve.

[0043] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A temperature control system for a screw extruder, characterized in that: The system includes a barrel (1), a PLC control module (5), a temperature regulation module, and a temperature detection module. The temperature regulation module acts on the surface of the barrel (1) to form a temperature control layer (2) on the surface of the barrel (1). The temperature control layer (2) and the material inside the barrel (1) are heat conduction objects. The temperature detection module includes a barrel surface temperature measurement unit (3) and a barrel interior temperature measurement unit (4). The barrel surface temperature measurement unit (3) and the barrel interior temperature measurement unit (4) are connected to the PLC control module (5) to transmit temperature information to the PLC control module (5). The PLC control module (5) controls the temperature regulation module according to the acquired temperature information to keep the measured value of the barrel surface temperature measurement unit (3) within the set threshold. The cylinder surface temperature measuring unit (3) is used to detect the temperature of the temperature control layer (2), and the cylinder inside temperature measuring unit (4) is used to detect the temperature of the material inside the cylinder (1); The temperature setting threshold of the temperature control layer (2) includes the upper limit of the cylinder surface temperature and the lower limit of the cylinder surface temperature. The temperature control module controls the temperature of the cylinder (1) in two stages: a preheating stage and a fine-tuning stage. In the preheating stage, under the control of the PLC control module (5), the measured value of the cylinder surface temperature measuring unit (3) does not exceed the upper limit of the cylinder surface temperature. In the fine-tuning stage, under the control of the PLC control module (5), the measured value of the cylinder surface temperature measuring unit (3) remains between the upper limit of the cylinder surface temperature and the lower limit of the cylinder surface temperature. The barrel (1) has a corresponding material temperature setting value inside. The temperature adjustment module includes a cooling unit (6) and a heating unit (7). When the measured value of the temperature measuring unit (4) inside the barrel is less than the material temperature setting value, and the measured value of the temperature measuring unit (3) on the barrel surface is less than the upper limit of the barrel surface temperature, the heating unit (7) is in the power-on working state. When the measured value of the temperature measuring unit (4) inside the barrel is greater than the material temperature setting value, and the measured value of the temperature measuring unit (3) on the barrel surface is greater than the lower limit of the barrel surface temperature, the cooling unit (6) is in the power-on working state. The cooling unit (6) and heating unit (7) act uniformly on the temperature control layer (2) on the surface of the barrel (1).

2. The temperature control system for a screw extruder according to claim 1, characterized in that: The heating unit (7) and cooling unit (6) are connected in parallel on the same temperature control circuit. The heating unit (7) is connected in series with the cylinder external temperature upper limit detection switch (8) to form a heating control circuit (21). The cooling unit (6) is connected in series with the cylinder external temperature lower limit detection switch (9) to form a cooling control circuit (10). The power supply (11) of the temperature control circuit controls the on / off state of the heating control circuit (21) and the cooling control circuit (10) through the cylinder internal temperature detection double-throw switch (12). When the measured value of the cylinder internal temperature measuring unit (4) is less than the material temperature, the heating unit (7) is connected in series with the cylinder external temperature upper limit detection switch (9) to form a cooling control circuit (10). Temperature setpoint, the cylinder temperature detection double-throw switch (12) is connected to the heating control circuit (21); when the measured value of the cylinder temperature measuring unit (4) is greater than the material temperature setpoint, the cylinder temperature detection double-throw switch (12) is connected to the cooling control circuit (10); when the measured value of the cylinder surface temperature measuring unit (3) is less than the upper limit of the cylinder surface temperature, the cylinder outer temperature upper limit detection switch (8) is in the open state; when the measured value of the cylinder surface temperature measuring unit (3) is greater than the lower limit of the cylinder surface temperature, the cylinder outer temperature lower limit detection switch (9) is in the open state.

3. The temperature control system for a screw extruder according to claim 2, characterized in that: The heating unit (7) includes heating plates (13) uniformly arranged on the surface of the barrel (1).

4. The temperature control system for a screw extruder according to claim 3, characterized in that: After receiving the temperature information measured by the cylinder surface temperature measuring unit (3) and the cylinder inside temperature measuring unit (4), the PLC control module (5) controls the cylinder inside temperature detection double-throw switch (12), the cylinder outside temperature upper limit detection switch (8) and the cylinder outside temperature lower limit detection switch (9) to switch on and off.

5. A temperature control system for a screw extruder according to claim 4, characterized in that: The temperature control circuit is also equipped with a main switch (17). When the temperature regulation module stops running, the main switch (17) is in an open circuit state.

6. The temperature control system for a screw extruder according to claim 5, characterized in that: The barrel (1) is divided into several heating sections along the material moving direction. Each heating section has an independent temperature adjustment module and a temperature detection module, and each independently sets the upper limit value of the barrel surface temperature, the lower limit value of the barrel surface temperature, and the material temperature setting value.

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