How Does Plastic Pelletizer Work?

2022-10-31
Article Paragraph
Ⅰ Introduction of plastic granulator
Ⅱ The working principle of plastic granulator
Ⅲ Composition of plastic granulator
Introduction of plastic granulator

According to different raw material properties and customer needs, a variety of different shapes and sizes of particles can be produced. With the increase in the market demand for granulators, traditional manual granulation has been unable to meet the market demand. Therefore, the plastic granulator came into being. Plastic granulator is a commonly used plastic processing equipment, which can make plastic sheets or powdered plastics into small balls or granules suitable for molding. Its working principle is: first put plastic sheets or powdered plastics into the machine, and then mix them through the propeller. Some additives are added during the mixing process to make the plastic sheet or powder easier to shape. Next, the mixed plastic material is divided by the rolling knife and discharged from the discharge port.

plastic granulators
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The working principle of plastic granulator
The plastic granulator uses the physical and chemical properties of plastic materials to make granules of a certain size and shape by cooling water or wind under appropriate temperature, pressure and rotation speed. The working principle of the plastic granulator is as follows: first, the plastic material is crushed or mixed, and then it is input into the plastic granulator for processing. During the processing, particles of a certain size and shape will be formed.
Plastic granulator is now suitable for various plastic processing occasions, and it is suitable for many types of plastics, such as PP, PE, PS, ABS, PA, PVC, PC, POM, EVA, LCP, PET, PMMA, etc. Reproduction, processing and granulation of various plastics. So, what is the working principle of the plastic granulator? as follows:
1. First put the plastic raw material into the feeding port of the plastic granulator, and send it into the main body by the feeding wheel.
2. Inside the main body, the plastic raw material will be melted by high temperature, and a uniform melt will be formed while the screw is stirring and rotating.
3. When the melt reaches a certain fluidity, it will flow out from the outlet of the main body.
4. Then, the melt will be cooled by cooling water, and a solid substance will be formed in the cooling water, which will be pelletized, dehydrated by vibration, and transported to the silo.
Plastic granulator composition
The main engine of the plastic granulator is the extruder system, which consists of an extrusion system, a transmission system, a heating and cooling system and a control system.
1. Extrusion system: The extrusion system includes a screw, a barrel, a hopper, a head, and a mold. The plastic is plasticized into a uniform melt through the extrusion system, and under the pressure established in this process, the screw is continuously extruder head.
(1) Screw: It is the most important part of the extruder, which is directly related to the application range and production efficiency of the extruder. It is made of high-strength and corrosion-resistant alloy steel.
(2) Barrel: It is a metal seamless tube, generally made of alloy steel with high heat resistance, high compressive strength, strong wear resistance and corrosion resistance or composite steel pipe lined with alloy steel. The barrel cooperates with the screw to realize the pulverization, softening, melting, plasticizing, exhausting and compacting of the plastic, and continuously and uniformly convey the rubber material to the molding system. Generally, the length of the barrel is 16:1 of its diameter, so that the plastic can be fully heated and fully plasticized.
(3) Hopper: The bottom of the hopper is equipped with a cutting device to adjust and cut off the material flow, and the side of the hopper is equipped with a sight hole and a calibration metering device.
(4) Machine head and mold: The machine head is composed of an alloy steel inner sleeve and a carbon steel outer sleeve, and a forming mold is installed in the machine head. The function of the machine head is to convert the rotating plastic melt into parallel linear motion, evenly and smoothly introduce it into the mold sleeve, and give the plastic the necessary molding pressure. The plastic is plasticized and compacted in the barrel, and the porous filter plate flows into the molding die of the die through the neck of the die along a certain flow channel. A continuous and dense tubular cladding layer is formed around the core wire. In order to ensure that the plastic flow channel in the machine head is reasonable and eliminate the dead corners of the accumulated plastic, a shunt plate (sleeve) is often installed. In order to eliminate the pressure fluctuation during plastic extrusion, a pressure equalizing ring is also installed. The machine head is also equipped with a mold correction and adjustment device, which is convenient for adjusting and correcting the concentricity of the mold core and the mold sleeve. According to the angle between the material flow direction of the head and the center line of the screw, the extruder divides the head into an oblique head (120 degrees) and a right angle (90 degrees) head. The shell of the machine head is fixed on the fuselage with bolts. The mold in the machine head has a core seat and is fixed to the wire inlet port of the machine head with a nut. The front of the mold core seat is equipped with a mold core, a mold core and a mold core seat. There is a hole in the center for passing the core wire; a pressure equalizing ring is installed in the front of the machine head to equalize the pressure; the extrusion molding part is composed of a die sleeve seat and a die sleeve, and the position of the die sleeve can be adjusted by bolts through the support , in order to adjust the relative position of the die sleeve to the die core, so as to adjust the uniformity of the thickness of the extruded cladding layer. The outside of the machine head is equipped with a heating device and a temperature measuring device.
2. Transmission system: The function of the transmission system is to drive the screw and supply the torque and speed required by the screw in the extrusion process, and it is usually composed of a motor, a reducer and a bearing.
3. Heating and cooling device: Heating and cooling are necessary conditions for the plastic extrusion process to be carried out.
(1) At present, the extruder usually uses electric heating, which is divided into resistance heating and induction heating. The heating device heats the plastic in the cylinder externally to heat it up to the temperature required for the process operation.
(2) The cooling device is set up to ensure that the plastic is in the temperature range required by the process. Specifically, it is to remove the excess heat generated by the shear friction of the screw rotation, so as to avoid the plastic decomposition, scorch or difficulty in shaping due to excessive temperature. Barrel cooling is divided into water cooling and air cooling. Generally, air cooling is more suitable for small and medium-sized extruders, and water cooling or a combination of the two forms is used for large extruders. The screw cooling mainly adopts central water cooling, in order to increase the solid conveying rate of the material. , to stabilize the glue output and improve the product quality at the same time; but the cooling at the hopper is to strengthen the conveying effect of the solid material, prevent the plastic pellets from sticking and block the material port due to the temperature rise, and the second is to ensure the normal operation of the transmission part.
4. Control system: The control system of the plastic granulator includes a heating system, a cooling system and a process parameter measurement system, which is mainly composed of electrical appliances, instruments and actuators (ie, control panel and console). Its main functions are: control and adjust the driving motor of the main and auxiliary machines, output the speed and power that meets the process requirements, and enable the main and auxiliary machines to work in harmony; detect and adjust the temperature, pressure, and flow of the plastic in the extruder; Control or automatic control of the entire unit. The electrical control of the extrusion unit is roughly divided into two parts: transmission control and temperature control, which realizes the control of the extrusion process including temperature, pressure, screw rotation, screw cooling, barrel cooling, product cooling and outer diameter, as well as traction speed. , neatly arrange the wire and ensure the constant tension control of the take-up reel from the empty reel to the full reel.
(1) Temperature control of the extruder host: The plastic extrusion of wire and cable insulation and sheath is carried out in a viscous flow state according to the deformation characteristics of thermoplastics. In addition to requiring external heating of the screw and barrel, which is transmitted to the plastic to melt and extrude, the heat generated by the screw itself when extruding the plastic is also required. Therefore, the temperature of the host should be considered as a whole, including the opening and closing of the heater. It is necessary to consider the factor of the extrusion heat overflow of the screw to cool it, and there must be effective cooling facilities. And it is required to correctly and reasonably determine the position and installation method of the thermocouple of the measuring element, so that the actual temperature of each section of the host can be accurately reflected from the reading of the temperature control instrument. And the accuracy of the temperature control instrument is required to be well coordinated with the system, so that the fluctuation stability of the entire host temperature control system can meet the requirements of the extrusion temperature of various plastics.
(2) Pressure control of the extruder: In order to reflect the extrusion situation of the die, it is necessary to detect the pressure of the die during extrusion. Since the domestic extruder does not have a die pressure sensor, it is generally the measurement of the thrust after the screw is extruded. Instead of measuring the head pressure, the screw load meter (ammeter or voltmeter) can correctly reflect the extrusion pressure. The fluctuation of extrusion pressure is also one of the important factors that cause unstable extrusion quality. The fluctuation of extrusion pressure is closely related to factors such as extrusion temperature, the use of cooling device, and the length of continuous operation time. When abnormal phenomena occur, those that can be eliminated can be eliminated quickly, and those that must be reorganized should be stopped decisively, which can not only avoid the increase of waste products, but also prevent the occurrence of accidents. Through the detected pressure gauge reading, you can know the pressure state of the plastic when it is extruded. Generally, the limit value of the rear thrust is used for alarm control.
(3) Control of screw speed: The adjustment and stability of screw speed is one of the important technological requirements of the main engine drive. The screw speed directly determines the amount of glue and the extrusion speed. In normal production, it is always desirable to achieve the highest speed and high output as much as possible. When the screw speed of the extruder is required to be from the start to the required working speed, the available speed regulation range should be large. . Moreover, the stability of the rotational speed is required to be high, because the fluctuation of the rotational speed will lead to the fluctuation of the extrusion amount and affect the extrusion quality. Therefore, when the speed of the pulling line does not change, the outer diameter of the cable will change. In the same way, if the line speed of the traction device fluctuates greatly, the outer diameter of the cable will also change. The speed of the screw and the traction line can be reflected by the corresponding instrument on the operating table. It should be closely observed during extrusion to ensure high quality and high yield.
(4) Control of outer diameter: As mentioned above, in order to ensure the outer diameter of the product cable, in addition to the requirement to control the dimensional tolerance of the wire core (cable core), the extrusion temperature, screw speed, and linear speed of the traction device should be controlled. There is a control guarantee, and the measurement control of the outer diameter comprehensively reflects the accuracy and level of the above-mentioned control. In the extrusion unit equipment, especially the high-speed extrusion production line, an online outer diameter detector should be equipped to detect the outer diameter of the cable at any time, and feedback the out-of-tolerance signal to adjust the speed of the traction or screw and correct the outer diameter. Very bad.
(5) Electrical automation control of the whole machine: This is the process control requirement for realizing high-speed extrusion production line, mainly: start-up temperature interlock; working pressure protection and interlock; extrusion and traction proportional synchronization of the two components control; synchronous control of take-up and traction; online detection and feedback control of outer diameter; single-machine and complete-machine tracking control of components according to various needs.
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