Control device and method for screw extruder

Abstract

The present invention discloses a control device and method for a screw extruder, and relates to the field of extruder control technology. The device includes a control mechanism controlling a weighing mechanism and a driving mechanism, the driving mechanism is connected to a transmission mechanism; the transmission mechanism includes a twin-screw and a single-screw, the twin-screw includes two first screws arranged parallel to each other, the two first screws rotate in opposite directions, and a gap is provided between the two first screws; the weighing mechanism includes at least one weight sensor, and the weight sensor is installed on the outer wall of the feeding mechanism; the method includes setting raw material ratio parameters; outputting monitored data to a PID controller through the weighing mechanism; comparing with the set parameters; outputting the raw materials to the transmission mechanism; and realizing the control process from feeding to discharging. The present invention uses a structure combining a counter-rotating twin-screw and a single-screw, and adopts two screws rotating in opposite directions to generate high shear force, better mixing and homogenizing the materials, thereby producing a more uniform product.

Description

Technical Field

[0001] The present invention relates to the technical field of extruder control, and in particular to a control device and method for a screw extruder. Background Art

[0002] As the world recognizes the impact of plastics on the environment, demand for sustainable solutions to reduce pollution is growing. Recycling waste plastics into raw materials to achieve a resource-cycle approach is one effective solution. However, whether recycled waste plastics can achieve the desired properties after processing has always been a key technical research topic in this field. The recycling process for waste plastics generally involves recovery, crushing, sorting, and reshaping. The extruder is a core component in the reshaping process. Based on the number of screws, it is broadly categorized as a single-screw extruder or a twin-screw extruder. Currently, single-screw extruders are predominant on the market, followed by twin-screw extruders, often designed for virgin materials. However, when using conventional extruders for regrind extrusion, the high level of impurities in regrind can easily lead to screw clogging over time. Compared to virgin materials, regrind causes significantly more wear on the screw, severely impacting the machine's lifespan. Furthermore, conventional screw extruders lack effective control over the amount of raw material added, leading to overfeeding and subsequent clogging, which can also affect the screw's lifespan.

[0003] The Chinese patent with announcement number CN212046106U discloses an extrusion device with twin-screw feeding and single-screw discharging, including a frame and a discharging device installed on the frame, a feed bin, a gear transmission box, and a drive device; wherein the discharging device includes a shell, a long screw, and a short screw; the shell includes a long screw cavity and a short screw cavity, the long screw cavity and the short screw cavity are arranged horizontally and parallel, and the long screw cavity and the short screw cavity are connected at the intersection to form a material outlet; a partition plate is respectively provided on the cavity opening on one side of the long screw cavity and the short screw cavity; a stripping mold is installed on the cavity opening on the other side of the long screw cavity, and a long screw positioning sleeve is provided at the inner center of the stripping mold; an elliptical pressure cover is installed on the cavity opening on the other side of the short screw cavity; a short screw positioning sleeve is provided on the inner side of the pressure cover. Although this patent sets a spacer between the two screws, which reduces the friction overheating between the screws to a certain extent, this patent cannot automatically control the weight and proportion of the added raw materials, and it is easy for excessive addition of raw materials to cause blockage, thereby affecting the service life of the extrusion device. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, the present invention provides a control device and method for a screw extruder.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A control device for a screw extruder comprises a driving mechanism, a weighing mechanism, a conveying mechanism, a feeding mechanism and a control mechanism, wherein the control mechanism controls the weighing mechanism and the driving mechanism by communication, and the driving mechanism is connected to the conveying mechanism;

[0007] The conveying mechanism includes a twin screw and a single screw. The twin screw includes two first screws arranged parallel to each other. The two first screws rotate in opposite directions and a gap is provided between the two first screws.

[0008] The weighing mechanism includes a weight sensor, which is installed on the outer wall of the feeding mechanism and is used to measure feeding data and transmit the measured feeding data to the control mechanism.

[0009] Based on the above technical solution, further, the control mechanism includes a PID controller, a PLC control module, a frequency converter and a solenoid valve module. The PLC control module is respectively connected to the frequency converter and the solenoid valve module. The frequency converter is connected to the driving mechanism. The driving mechanism is a first motor. The output shaft of the first motor is connected to the first transmission. The two output shafts of the first transmission are respectively connected to the two first screws.

[0010] Based on the above technical solution, further, a gear selection cylinder and a gear shift cylinder are installed on the first transmission, and the PLC control module supplies power to the gear selection cylinder and the gear shift cylinder respectively by controlling the solenoid valve module.

[0011] Based on the above technical solution, further, the driving mechanism also includes a second motor, the single screw and the two first screws are on the same horizontal line, and the single screw is connected to the second transmission through a connecting rod, and the second transmission is connected to the output shaft of the second motor.

[0012] Based on the above technical solution, further, the PLC control module includes a first PLC controller and a second PLC controller, and the first PLC controller controls the first transmission, and the second PLC controller controls the second transmission.

[0013] Based on the above technical solution, further, the control mechanism also includes a data display module and a data adjustment module, and the adjusted data is displayed by the data display module.

[0014] Based on the above technical solution, further, the conveying mechanism is also provided with a shell, a twin-screw and a single-screw are provided inside the shell, and a feed port is opened in the shell.

[0015] Based on the above technical solution, further, the control device also includes a fixed platform, the lower end of the feeding mechanism is provided with a support rod extending downward, the support rod is fixed on the fixed platform, and the discharge position of the feeding mechanism is provided with a control valve for controlling the discharge of raw materials, and the discharge position of the feeding mechanism is connected to the feed port of the shell.

[0016] Based on the above technical solution, further, a number of holding tanks are provided inside the feeding mechanism for holding different raw materials, and each holding tank is provided with a corresponding weighing sensor for weighing the weight of the raw materials in the corresponding holding tank, and the monitored weight data is transmitted to the total weighing mechanism through communication.

[0017] A method for controlling a screw extruder, characterized in that it comprises the following steps:

[0018] Step 1: Set the raw material ratio parameters;

[0019] Step 2: Place the raw materials into the feeding mechanism, and monitor the actual data of the raw material feeding in real time through the weighing mechanism, and output the monitored actual data to the PID controller;

[0020] Step 3: The PID controller compares the received data with the raw material ratio parameters. If the comparison result meets the set conditions, it proceeds to step 4, otherwise it returns to step 2;

[0021] Step 4: Output the raw materials to the conveying mechanism, and control the conveying mechanism through the driving mechanism until the material is discharged;

[0022] Step 5: Then realize the control process from feeding to discharging.

[0023] Based on the above technical solution, further, the raw material ratio parameters set in step 1 include the weight of the raw materials and the weight ratio of multiple groups of raw materials.

[0024] Based on the above technical solution, further, in step 2, the weight of the raw material placed in the feeding mechanism is sensed by a weight sensor, and the sensed data is transmitted to the PID controller. When the set conditions are met, the control valve is opened and the raw material enters the conveying mechanism; otherwise, the control valve is closed.

[0025] Based on the above technical solution, further, the setting condition met in step 3 is: the absolute value of the difference between the actual data of the raw material feeding and the set ratio parameter is within 1% of the raw material ratio parameter.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention improves the extruder and uses an extruder structure that combines a counter-rotating twin-screw and a single screw. The extruder uses two screws rotating in opposite directions to generate high shear force, allowing for better mixing and homogenization of materials, thereby producing a more uniform and consistent product. In addition, the high shear force generated by the extruder helps to remove impurities in recycled plastics. When the twin screws are transformed into a single screw from the middle, the pressure of the single screw is more stable compared to the twin screw, and it is more conducive to the molding of recycled products at the end. In addition, the spacing between the screws in the present invention is enlarged. Enlarging the spacing can effectively prevent local overheating, reduce screw friction loss, and increase equipment life. The twin screws rotating in two opposite directions can effectively increase the shear force of the recycled material to compensate for the impact of the enlarged screw spacing and maintain the required performance. At the same time, the present invention is improved based on the characteristics of recycled waste plastics. The improved extruder can effectively control the added weight of raw materials, has a higher degree of automation, and increases service life. It also has advantages such as increased output, reduced energy consumption, and enhanced various modification capabilities. These advantages make it an ideal solution for manufacturers who want to maintain the quality and efficiency of recycled materials while increasing the service life of equipment. In the future, it will be beneficial to manufacturers in the production process of recycled plastics and create favorable products that meet the needs of manufacturers and improve the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a side view of the control device of the present invention;

[0029] Figure numerals: 1. first motor; 2. weighing mechanism; 3. feeding mechanism; 4. control mechanism; 5. conveying mechanism; 6. fixed platform; 7. cavity. DETAILED DESCRIPTION

[0030] The present invention will be further described and illustrated below with reference to the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention may be combined accordingly, provided that there is no conflict between them.

[0031] In order to make the above-mentioned objects, features and advantages of the present invention more clearly understood, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. The technical features in the various embodiments of the present invention can be combined accordingly without conflicting with each other.

[0032] In the description of the present invention, it is important to understand that when an element is considered to be "connected" to another element, it can be directly connected to the other element or indirectly connected, i.e., with the presence of an intermediate element. In the description of the present invention, it is important to understand that the terms "first" and "second" are used solely for descriptive purposes and are not to be construed as indicating or implying relative importance or implicitly specifying the number of technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of such features.

[0033] Example 1

[0034] like Figure 1 Figure 2 shows a simplified schematic diagram of a screw extruder control device, comprising a drive mechanism, a weighing mechanism 2, a conveying mechanism 5, a feeding mechanism 3, and a control mechanism 4. The control mechanism 4 uses communication to control the weighing mechanism 3 and the drive mechanism, which is connected to the conveying mechanism 5. The conveying mechanism 5 includes a twin-screw and a single-screw extruder. The twin-screw extruder includes two parallel primary screws that rotate in opposite directions and are spaced apart. The single-screw extruder is located behind the twin-screw extruder. The weighing mechanism 2 includes a weight sensor mounted on the outer wall of the feeding mechanism 3, which measures feeding data and transmits the measured feeding data to the control mechanism 4.

[0035] The control mechanism 4 includes a PID controller, a PLC control module, a frequency converter, and a solenoid valve module. The PLC control module is connected to the frequency converter and the solenoid valve module, respectively. The frequency converter is connected to the drive mechanism, which comprises a first motor 1. The output shaft of the first motor 1 is connected to the first transmission, and the two output shafts of the first transmission are respectively connected to the two first screws. The first transmission is equipped with a shift cylinder and a gearshift cylinder. The PLC control module controls the solenoid valve module to supply power to the shift cylinder and the gearshift cylinder, respectively. Specifically, the solenoid valve module includes a shift valve and a gearshift valve, wherein the shift valve is connected to the shift cylinder, and the gearshift valve is connected to the gearshift cylinder. The PID controller is used to receive the weight of the added raw materials for automated monitoring. The control mechanism 4 may also be provided with control buttons and indicator lights. The control buttons are connected to the PLC control module, and multiple control buttons can be provided. The number of indicator lights can be set to correspond to the number of control buttons.

[0036] Furthermore, the drive mechanism includes a second motor. The single screw is co-horizontally aligned with the two first screws and connected to a second transmission via a connecting rod. The second transmission is connected to the output shaft of the second motor. The PLC control module includes a first PLC controller and a second PLC controller, with the first PLC controller controlling the first transmission and the second PLC controller controlling the second transmission. The control mechanism 4 also includes a data display module and a data conditioning module, with the conditioned data displayed by the data module.

[0037] Specifically, the conveying mechanism 5 further comprises a housing, within which are located a twin-screw and a single-screw extruder, and an inlet opening. The control device further comprises a fixed platform 6, the lower end of which is provided with a cavity 7, within which various connecting wires, etc., can be placed. A support rod extends downward from the lower end of the feeding mechanism 3, which is fixed to the fixed platform 6. A control valve is provided at the discharge point of the feeding mechanism 3 to control the discharge of the raw materials, and the discharge point of the feeding mechanism 3 is connected to the inlet opening of the housing. Furthermore, the feeding mechanism 3 is internally provided with several holding tanks for accommodating different raw materials. Each holding tank is provided with a corresponding load cell for weighing the raw materials in the corresponding holding tank and transmitting the monitored weight data via communication to the main weighing mechanism 2. By providing multiple holding tanks and corresponding load cells, different raw materials can be weighed separately and monitored in real time, increasing the diversity of the raw materials weighed and the accuracy of the weighing data. The weight sensor of the weighing mechanism measures the weight of all raw materials, while each load cell measures the weight of a single raw material in its corresponding holding tank. In order to ensure that the loading meets the required weight, each holding tank is also connected to a return device through a pipeline. The pipeline is equipped with a corresponding regulating control valve. When the loading amount increases, the raw materials in the holding tank can be output to the external return device through the regulating control valve, which not only saves labor, but also saves raw materials and reduces economic costs.

[0038] The working principle of this device is:

[0039] When the raw materials that meet the set ratio are added to the feeding mechanism 3, they enter the feeding port of the conveying mechanism 5 through the discharge end of the feeding mechanism 3. The speed of the transmission is controlled accordingly by controlling the speed of the driving mechanism, and then the speed of the twin-screw and single-screw is controlled. The raw materials are first processed by the reverse rotation of the twin-screw and then processed by the rotation of the single screw.

[0040] Among them, during the control process, the speed of the motor will be controlled to a certain extent according to actual needs. Specifically, the set PLC control module controls the drive of the first motor 1 by controlling the frequency converter and the solenoid valve module, that is, the PLC control module can control the speed of the first motor 1, and the first motor 1 drives to transmit power to the first transmission, and the PLC control module controls the shift cylinder and the shift cylinder on the first transmission through the shift valve and the shift valve. The shift cylinder and the shift cylinder can be connected to the air supply system through the air pipe assembly, and the transmission speed can be adjusted by the shift cylinder and the shift cylinder; the first transmission can transmit the speed information to the PLC control module, and the data of the PLC control module can be displayed on the data display module, and the drive motor speed can be controlled by controlling the control knob connected to the PLC control; at the same time, the PLC control module is also connected to the indicator light. During the shifting or shifting process, the PLC control module controls the corresponding gear indicator light to light up, so that the operator can know that the shifting or shifting has been successful. Likewise, the control process of the second PLC controller, the second motor, the second transmission and the single screw is the same as the control process of the first PLC controller, the first motor 1, the first transmission and the twin screw.

[0041] Example 2

[0042] A method for controlling a screw extruder, characterized in that it comprises the following steps:

[0043] Step 1: Set the raw material ratio parameters. In this step, the raw material ratio parameters set include the weight of the raw materials and the weight ratio of multiple groups of raw materials. The specific ratio is set according to actual needs.

[0044] Step 2: Place the raw materials into the feeding mechanism 3, and the weighing mechanism 2 monitors the actual feeding data of the raw materials in real time, and outputs the monitored actual data to the PID controller. The weight of the raw materials placed in the feeding mechanism 3 is sensed by a weight sensor, and the sensed data is transmitted to the PID controller. When the set conditions are met, the control valve is opened, and the raw materials enter the conveying mechanism 5; otherwise, the control valve is closed. Specifically, the weight of the raw materials in each holding tank is monitored by the corresponding weighing sensor, and the monitored data is transmitted to the weighing mechanism. The weighing mechanism can clearly know the specific weight of each raw material, and the weighing mechanism's weight sensor also measures the total weight of all raw materials. If the weight sensor data differs significantly from the total weight of the raw materials measured by each weighing sensor, the operator can receive a real-time alert and verify whether each raw material meets the corresponding ratio, avoiding unusable materials after discharge, which increases usage costs. The difference here can be determined based on the operator's experience or if it is within a certain range of actual needs.

[0045] Step 3: The PID controller compares the received data with the raw material ratio parameters. If the comparison result meets the set conditions, it proceeds to step 4, otherwise returns to step 2; among which, the set conditions that meet the conditions are: the absolute value of the difference between the actual data of the raw material feed and the set ratio parameters is within 1% of the raw material ratio parameters.

[0046] Step 4: Output the raw materials to the conveying mechanism 5, and control the conveying mechanism 5 to convey the raw materials through the driving mechanism until the raw materials are discharged;

[0047] Step 5: Then realize the control process from feeding to discharging.

[0048] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A method for controlling a screw extruder, characterized in that: A control device for a screw extruder is used, the control device comprising a driving mechanism, a weighing mechanism, a conveying mechanism, a feeding mechanism and a control mechanism, the control mechanism controlling the weighing mechanism and the driving mechanism by communication, and the driving mechanism being connected to the conveying mechanism; The conveying mechanism includes a twin screw and a single screw. The twin screw includes two first screws arranged parallel to each other. The two first screws rotate in opposite directions and a gap is provided between the two first screws. The weighing mechanism includes a weight sensor, which is installed on the outer wall of the feeding mechanism and is used to measure feeding data and transmit the measured feeding data to the control mechanism; The feeding mechanism is internally provided with a number of holding tanks for holding different raw materials, and each holding tank is provided with a corresponding weighing sensor for weighing the weight of the raw materials in the corresponding holding tank; the weighing sensor of the weighing mechanism measures the weight of all raw materials, while each weighing sensor measures the weight of a single raw material in the corresponding holding tank; each holding tank is also connected to a return device via a pipeline, and a corresponding regulating control valve is provided on the pipeline; the raw materials in the holding tank are output to the external return device through the regulating control valve; The control method includes the following steps: Step 1: Set the raw material ratio parameters; Step 2: Place the raw materials into the feeding mechanism, and monitor the actual data of the raw material feeding in real time through the weighing mechanism, and output the monitored actual data to the PID controller; The weight of the raw materials in each holding tank is monitored by the corresponding weighing sensor, and the monitored data is transmitted to the weighing mechanism. The weighing mechanism knows the specific weight of each raw material, and the weight sensor of the weighing mechanism also measures the total weight of all raw materials. When the data measured by the weight sensor differs from the total weight of the raw materials measured by each weighing sensor by more than a certain value, the operator receives a real-time alert; the certain value is determined according to actual needs. Step 3: The PID controller compares the received data with the raw material ratio parameters. If the comparison result meets the set conditions, it proceeds to step 4, otherwise it returns to step 2; Step 4: Output the raw materials to the conveying mechanism, and control the conveying mechanism through the driving mechanism until the material is discharged; Step 5: Then realize the control process from feeding to discharging.

2. The control method of a screw extruder according to claim 1, characterized in that: The control mechanism includes a PID controller, a PLC control module, a frequency converter and a solenoid valve module. The PLC control module is respectively connected to the frequency converter and the solenoid valve module. The frequency converter is connected to the driving mechanism. The driving mechanism is a first motor. The output shaft of the first motor is connected to the first transmission. The two output shafts of the first transmission are respectively connected to the two first screws.

3. The control method of a screw extruder according to claim 2, characterized in that: The first transmission is equipped with a gear selection cylinder and a gear shift cylinder, and the PLC control module supplies power to the gear selection cylinder and the gear shift cylinder respectively by controlling the solenoid valve module.

4. The control method of a screw extruder according to claim 2, characterized in that: The driving mechanism also includes a second motor. The single screw and the two first screws are on the same horizontal line, and the single screw is connected to the second transmission through a connecting rod. The second transmission is connected to the output shaft of the second motor.

5. A control device for a screw extruder according to claim 4, characterized in that: The PLC control module includes a first PLC controller and a second PLC controller, wherein the first PLC controller controls the first transmission and the second PLC controller controls the second transmission.

6. The control method of a screw extruder according to claim 4, characterized in that: The control mechanism further comprises a data display module and a data adjustment module, and the adjusted data is displayed by the data display module.

7. The control method of a screw extruder according to claim 1, characterized in that: The conveying mechanism is further provided with a shell, a double screw and a single screw are arranged inside the shell, and a feed port is provided in the shell.

8. The control method for a screw extruder according to claim 7, characterized in that: The control device also includes a fixed platform, a support rod extending downward from the lower end of the feeding mechanism, the support rod is fixed on the fixed platform, and a control valve for controlling the discharge of raw materials is provided at the discharge position of the feeding mechanism, and the discharge position of the feeding mechanism is connected to the feed port of the shell.

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