Design of electrical control system for Paraffin forming machine
Although the waste film recycling paraffin forming machines used in the BOPP production line are different, the production process is roughly the same. The general production process of waste film recycling and molding can be roughly divided into the following four parts: the conveying and feeding process of crushed waste film, the re-cutting and extrusion process of the material compactor, the extrusion molding process of the extruder, and the molding process. Machine forming recycling process, specific process.
1、Conveying and feeding process
The waste transfer is one step in the work of the paraffin forming machine. The purpose is to transport the small film pieces produced by the large film crusher to the feeding bin through the conveyor belt. The film waste is driven forward by a three-phase motor on the conveyor belt. A metal detector is installed on the conveyor belt to detect possible metal debris. If metal debris appears, an alarm will be issued, and then the operator will press a button to make the conveyor belt retreat. After the metal debris is detected, the operation continues to send the waste material into the feeding bin. In the feeding bin, the movement of the feeding motor is adjusted by the frequency converter to control the flow of the waste material to the material compactor system below. The conveyor belt can work in two modes: automatic and manual. The manual mode is only used when starting the conveyor belt and closing the conveyor belt. It works normally in the automatic mode. We can pre-set the conveyor speed based on the output of the material compactor. When the scrap detects the presence of metal and is transported to a stop near the metal detector, we can automatically set the stop running time of the conveyor belt and select the feeding speed and automatic/manual working mode through the touch screen.
2 、Material compaction process
Material compaction is an important process in the work of the paraffin molding machine. The main purpose is to complete the re-cutting of the waste material and mix the heating, extrusion and pre-drying processes. The material compaction process is controlled by a motor. During the material compaction process, the heat generated by friction melts the waste. After the waste materials are transported to the material compactor by the conveyor belt, the waste materials can be mixed, heated and pre-dried in the material compactor. The temperature adjustment of the material compactor can be carried out through the filling rate of the material compactor. A high filling rate indicates a high temperature, and a low filling rate indicates a low temperature. The temperature of the material compactor is also related to the output of the paraffin molding machine. As the output decreases, the temperature decreases. If the temperature of the material compactor is too high, it can be adjusted by starting the cooling water valve. The start of the material compaction motor is controlled by a start gate, which can realize the start and emergency stop of the material compaction motor through the control circuit.
3、 Extrusion plasticizing process
Extrusion plasticization is an important part of the work of the paraffin molding machine. The main purpose is to complete the extrusion molding of the molten material. The film head extrudes the molten material into strips, and then it is cooled by the cooling system and enters the molding machine for cutting and granulation. After entering the extruder, it is bitten by the screw thread of the extruder. As the screw rotates, it is forced by the thread toward the machine head, forming a mechanical conveying process. When running from the feeding port to the machine head, due to the gradual reduction of the thread of the screw and the existence of resistance such as the filter screen, splitter plate and machine head, a high pressure is formed during the plasticizing process, and the waste is pressed very densely. , changing its thermal conductivity, helping to melt quickly, while gradually increasing the pressure to allow the gas originally existing between the film scraps to be discharged from the vents. When the pressure rises, it is heated by the outside. On the other hand, it also generates a large amount of heat due to internal friction during the movement of compression, shearing, and stirring. Under the combined action of external and internal forces, the temperature gradually increases. As the height increases, its physical state also undergoes changes from glassy state to highly elastic state to viscous flow state. At the same time, it gradually melts to achieve plasticization. Finally, the plasticized plastic is extruded from the machine head at a constant pressure and quantitatively by the screw thrust. . In the paraffin molding machine control system, we have an adjustable sliding door that can control the flow of waste materials through the material compactor. When the screw motor of the paraffin molding machine is overloaded, the position of the sliding door can be adjusted on the touch screen To achieve the reduction of waste materials. The door also has two automatic control functions: the function of automatically cleaning the screw blade of the paraffin molding machine and the function of automatic shifting according to the amount of waste. If the sliding door is in the closed position and the molten solid turns into pellets, in this case the scrap discharge stops and the sliding door reverses. The system can realize its function by controlling the sliding door motor load. This control function can be achieved by adjusting the time of screw rotation direction.
4 、Molding recycling process
Molding recovery is the last step in the entire paraffin molding machine work. The molten material that continuously flows out from the paraffin molding machine passes through an annular nozzle and becomes strips. The molding unit has a rotary cutter to cut these strips. The cut small particles enter the molding chamber for cooling and molding, and then are dried. After the machine is air-dried, the pellets will be transported by the discharge device to a storage tank and then bagged. The size of the pelletizing chamber is sufficient to allow the pelletizing knife to freely rotate across the die surface without restricting the water flow. After the molten polymer is extruded from the die head of the extruder into filaments, the material is cut by a rotary cutter and turned into spherical particles with a diameter of 4-5mm, and then cooled under water and entered into a centrifugal dryer. In the dryer, the water is discharged to the return storage tank, cooled and recycled; the pellets pass through the centrifugal dryer to remove moisture, and then the finished product is bagged.
