Plasticizing and injection device
DATE：2022/4/18 8:35:27 / READ： / SOURCE：This station
Plasticizing and injection device
There are many structural types of plasticizing injection device of injection foaming molding machine, but they have something in common with screw. Different types of foam injection molding machines have different functions and structures of the cuttlebone. Some screws only have the function of plasticization, and their operation can be continuous. It can also be intermittent; Some screws have the dual functions of plasticization and pressure injection, and the screw operation can only be intermittent; Physical foaming agent and chemical foaming agent have different requirements for screw structure. Generally, chemical foaming is used to mix the chemical foaming agent with other raw material components before adding it into the plasticizing barrel for plasticization, while physical foaming is often used to inject the foaming agent directly into the plastic melt from the front end of the barrel. Therefore, the screw should not only have a special structure in the injection section, but also be equipped with mixing elements to fully mix the foaming agent with the plastic melt. Several plasticizing injection devices are introduced below. Honeycomb panel production line www.handern.com comFor the plasticizing injection device, the screw operates continuously. Only the plasticizing function and the plasticized plastic melt containing foaming agent are sent to the pressure injection Jane 2 first. When it is full, it passes through valves 4 and 5 Press the stored materials in the injection mold 2 and the plastic melt continuously sent out by the screw into the injection mold 3. When the amount of material in the injection mold 3 reaches an injection volume, switch the valve 45 to the injection mold 3 channel, connect the channel between the injection mold 2 and the injection mold 2, and make the plasticized plastic melt enter the injection mold 2 again. During injection, connect the plastic melt under the pressure cylinder 3 and inject it into the mold cavity for injection foaming molding. Then repeat the above process. With this kind of structure, an injection cylinder 2 must be equipped, which is used for short-term storage in the middle, so the volume and transmission thrust can be reduced, and the plasticizing screw works continuously. Its structural parameters can be selected according to the screw parameters for extruding foamed plastics. For the plasticizing screw with physical foaming agent, the head of the screw is equipped with a mixing element to fully mix the foaming agent with the plastic melt and extrude foaming at a lower temperature. The specific form is pin type. Barrier type, split ring type, local reverse thread reflux area and other screw head structures dominated by mixing. Honeycomb production line com
Another kind of plasticization and injection foaming adopts the same screw structure, as shown in figure 6-45. Because the screw needs to retreat in the plasticization process, the relative position between the screw and the barrel needs to be changed. Therefore, the scheme of injecting foaming agent through the barrel wall should not be adopted, otherwise the content distribution of foaming agent in the melt will be uneven. Fig. 6-45 shows that the foaming agent is injected into the melted plastic through the central pipe of the screw. The physical foaming agent is pumped from the central pipe at the tail end of the screw to the end of the melting zone of the screw, and then to the surface of the screw through the radial thin pipe and check valve. The gas from the blowing agent source is pumped into the central pipe of the screw by pump 3. The air pump can be variable pump or constant pump, and a check valve is set between the air source and the pump. The pumping pressure is 10.5 ~ 42MPa, and the inner diameter of the screw is provided with a check valve socket 5 towards the outlet of the thin pipe. Its structure is shown in figure 6-45 (2), which is connected with the screw with threads. When the air pump 3 works, the gas with certain pressure enters the melt through the central pipe of the screw and the check valve at the outlet of the radial thin pipe. The check valve 7 with spring is mainly used to prevent the gas from entering the melt when the air pump stops working. The check valve 6 mainly prevents the melt from entering the internal pipeline of the screw, and the outlet position of the pipeline shall be set in the decompression area of the screw. Since the screw operates intermittently, the input of foaming agent must also be intermittent. The transmission system of pump and screw must be coupled to inject foaming agent timely, accurately and quantitatively. The biggest advantage of this method is that the gas outlet is arranged on the screw, which eliminates the non-uniformity of gas content distribution in the melt caused by the movement of the screw. One rod can continuously provide plastic melt with and without foaming agent. Its structural principle is shown in figure 6-46. The screw is long. A radial pipe 3 is opened on the wall of the machine shell in the rear section of the screw melting zone and connected with a control valve 4. The plasticized plastic melt without foaming agent is sent to the pressure injection shell 5 through the pipe for storage. The feeding speed can be controlled by the valve. After storing enough injection volume, the valve is closed. An air inlet pipe 6 is arranged behind the pipe 3. The gas from the air source 7 passes through the check valve 8 and the pump 9 passes the gas through the pipe 6 into the plastic melt. The plastic melt containing foaming agent is pressed by the screw into the injection cylinder 10 for storage. When the injection volume reaches one time, the screw stops running and the air pump stops working. When the hydraulic cylinders 11 and 12 work, the plastic melt in the injection cylinder can be injected in one component or two-component injection structure foaming products, However, the pipeline needs to be properly modified and strictly controlled for synchronous or sequential injection foaming molding
Generally, the screw length for injection foaming molding is about 18D, the metering section accounts for 20%, and the compression ratio is 2 ~ 3. For plastics with good air permeability, such as PP, the screw should be longer, which can generally be greater than 20d. There is a check valve at the head of the screw, and a locking nozzle is used to maintain a certain pressure in the injection cylinder. Honeycomb panel production line www.handern.com com
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