In the injection molding of plastic parts, there are many factors that affect the quality of injection molding plastic parts, but after the plastic raw materials, injection molding machine and mold structure are determined, the selection and control of injection molding process conditions is to ensure the smooth progress of molding and the quality of plastic parts. One of the key factors, the most important process conditions for injection moulding process parameter are temperature, pressure and action time. Today, Green Vitality will show you how to choose the temperature parameters of the injection mold.
The temperatures that need to be controlled in injection molding are barrel temperature, nozzle temperature and injection mold temperature. The barrel temperature and nozzle temperature mainly affect the plasticization and fluidity of the plastic; while the injection mold temperature mainly affects the filling and cooling solidification process.
The temperature distribution of the entire injection mold barrel should maintain a certain gradient, which gradually increases from the end near the hopper to the nozzle. One end of the hopper is mainly for preheating the plastic: the first half of the compression section is slightly lower than the melting point of the plastic, and the temperature in the second half is higher than the melting point of the plastic: the temperature at the front end of the nozzle is the highest. Plastics with higher humidity can appropriately increase the temperature of the rear end of the barrel. The plastic in the barrel of the screw injection machine is helpful for plasticization due to the shear friction of the screw, so the overheating decomposition of the plastic is prevented, and the temperature of the front end of the barrel can be slightly lower than the middle section. When the injection volume of the plastic part is greater than 75% of the rated injection volume of the injection machine or the molding material is not preheated, the temperature of the rear section of the barrel should be 5~10℃ lower than that of the middle section and the front section.
The nozzle temperature is usually slightly lower than the maximum barrel temperature to prevent the melt from "drooling" at the nozzle. However, the temperature should not be too low to prevent the plastic from solidifying in the nozzle and blocking the nozzle or injecting the coagulant into the cavity to affect the quality of the plastic part. Although the nozzle temperature is low, when the plastic melt passes through the narrow nozzle, frictional heat will be generated, increasing the temperature of the melt entering the mold cavity. In production, the appropriate temperature is initially determined based on empirical data and actual conditions, and then adjusted through "air injection" of the melt and "intuitive analysis of plastic parts" to finally determine the appropriate barrel and nozzle.
In the injection moulding process parameter, the mold temperature refers to the temperature of the surface wall of the injection mold cavity in contact with the plastic part, which determines the filling ability of the melt, the cooling rate of the plastic part, and the internal and external quality of the molded plastic part. The choice of mold temperature is related to the variety of plastics, the shape and size of plastic parts and the requirements for use. The temperature of the injection mold is generally controlled by the cooling or heating medium at a constant temperature: when the mold temperature control requirements are not strict, it can be cooled by air without introducing any medium; in individual cases, resistance wires and resistance heating rods are also used. The mold is heated to maintain a constant temperature of the mold.