Injection molding process of foam plastics
DATE：2022/4/19 8:35:51 / READ： / SOURCE：This station
Injection molding process of foam plastics
We introduce the injection foaming molding process, which mainly includes two parts: the process and the main foaming process parameters. They are formulated according to the requirements for products, the properties of raw materials and the structure of forming equipment. When the raw materials and molding equipment are determined, the molding process conditions will become foaming as the main factor affecting the product quality and output. Therefore, when formulating process conditions, we must understand the impact of process conditions on product production.1、 Process casting film production line www.handern.com com
The process of injection foaming molding consists of raw material preparation, heating and plasticization, metering, mold closing, injection, foaming molding, cooling and setting, mold opening and pre production. The above processes are carried out on the injection molding device and mold locking device respectively, as shown in Figure 6-1. Some products need post-treatment.
1. Preparation of raw materials casting film production line www.handern.com com
For injection foaming with single screw injection molding machine, the components of raw materials shall be mixed and granulated according to the formula. Mixing is generally carried out in the kneader. Granulation can be carried out by mixing and pressing tablets in the open mill, injection, heating and plasticization, metering, injection, injection part, mold leading part, mold closing, foaming, cooling and setting, mold opening, product demoulding, mold closing and re granulation. Granulation can also be carried out directly by double screw or single screw extruder. Foaming agent is divided into chemical foaming agent and physical foaming agent. When using chemical foaming agent, the foaming agent and other components can be mixed and granulated together, or the chemical foaming agent can be made into a paste, which is then injected at the top of the screw through the metering device, mixed with the melt, and then injected for foaming. When using physical foaming agent, it is generally injected directly into the mixing chamber of man-machine barrel or nozzle through a special metering and conveying device (similar to extruder) to mix evenly with the melt, and then injected into the mold cavity through the nozzle for foaming. The injection of physical foaming agent must cooperate with the periodicity of screw plasticization. Instead of injecting people continuously like an extruder.
2. Plasticizing and metering casting film production line www.handern.com com
The granulated material of the plasticized barrel of the injection machine is pushed forward and plasticized gradually under the action of the rotation of the screw. The heat required for plasticization comes from the external heating device of the barrel and the shear heat of the screw on the material. One kind of plasticized plastic melt is gathered at the top of the screw, and the screw retreats under the push of the material pressure. When the accumulated material reaches the injection volume, the screw stops rotating, and the screw moves forward quickly during injection, The gathered plastic melt is injected into the mold cavity for foaming process. The injection plunger in the storage chamber moves backward under the pressure of the melt. When the plastic melt is stored for one injection, the screw stops and the injection plunger moves forward quickly to press the plastic melt into the shop. The chapter must maintain sufficient pressure. Therefore, when the screw or plunger retreats, it must be kept enough. In order to prevent the plastic melt containing foaming agent from being lifted in the material Jane for the process of ventilation. The degree of pressure should exceed the critical pressure at which bubbles appear in the melt. The soldering body is sprayed. In order to prevent the melt from casting and foaming under the action of back pressure, the hair for injection foaming must be of closed collar type and can be opened only when the plastic melt is injected. Casting film production line www.handern.com com
3. Mold closing
The mold locking device of the injection machine is provided with a fixed template and a moving template, and the moving, fixed or concave convex molds of the mold are fixed on the moving template and the fixed template respectively. Before injection, the moving template moves to the fixed template, and the mold closes to form a mold cavity. When the plastic melt is injected into the mold, due to the material pressure and the foaming expansion force of the melt, the closed mold must have sufficient locking force (i.e. mold locking pressure) to prevent the melt from flowing from the mold
Die expansion force. The overflow of the parting surface of the foam causes flash and affects the quality of the foam. Therefore, the clamping pressure must be greater than
4. Injection
When the plastic melt accumulated in the barrel or storage chamber reaches the one-time injection volume, the screw stops and moves forward quickly to quickly inject the plasticized melt into the mold cavity for foaming molding. The injection seat is moved forward to make the nozzle outlet close to the population of the main sprue of the mold. Then screw or column casting film production line www.handern.com com
5. Foaming molding and cooling shaping
Thermal plastic injection foaming molds are generally equipped with a cooling system. After the plastic melt enters the mold, on the one hand, the melt foams and expands due to the decrease of external pressure. On the other hand, the temperature and speed of cooling must adapt to the requirements of foaming and expansion. It directly affects the foaming, so the required cooling and shaping time is also relatively long. Quality and yield of type. Because the thermal conductivity of foam plastics is relatively low, the wall thickness of products is compared.
6. Mold opening and stripping products
After the foamed plastic products are cooled and shaped in the mold cavity, the mold can be opened and the products can be removed. Because the thermal conductivity of foam plastics is poor, the product cortex has been cooled and stereotyped, but the core part is still at a higher temperature. After demoulding, the heat of the core part of the product is transmitted, so that the cortical temperature rises and gradually loses strength and rigidity, which leads to the deformation of the products. It may also cause the core bubble at a higher temperature to continue to expand and crack the cortex. Therefore, there must be enough cooling and setting time for thick wall foam products. In order to improve productivity, when the skin of the product is cooled to withstand the expansion pressure of the foam core and the stripping jacking force, it can be demoulded, and then continue cooling outside the mold, so that the skin temperature of the product cannot rise back. The initial speed of ejection should not be too fast to prevent the cortex of vesicular breaker from being ejected. The opening and closing speed generally adopts the law of slow, fast and slow.
Author：admin