In injection molding, temperature is an extremely important parameter. The temperature to be controlled mainly includes the temperature of the plastic melt and the mold temperature. The former temperature mainly affects the plasticization and flow of the plastic, and the latter temperature mainly affects the flow and cooling of the plastic.
1. The choice of melt temperature
The temperature of the plastic melt is controlled by the barrel, so the barrel temperature is related to the plasticization quality of the plastic. The selection of the barrel temperature is related to the characteristics of the plastic used. When selecting the barrel temperature, the main focus is to ensure that the plastic is well plasticized and can be injected smoothly without causing local degradation of the melt.
2. Selection of mold temperature
The temperature of the mold affects the flow behavior when the plastic melt is full, and affects the performance of the plastic product. The temperature of the mold actually determines the cooling rate of the melt. The faster the cooling rate, the faster the melt temperature decreases, which increases the viscosity and makes the flow difficult, resulting in an increase in injection pressure loss, a decrease in effective mold filling pressure, and even insufficient mold filling. Generally, the determination of the mold temperature should be based on comprehensive considerations such as the performance of the processed plastic, the performance requirements of the product, the shape and size of the product, and the process conditions of the molding process.
1. Injection pressure
Injection pressure is an important factor for melt filling and molding. It pushes the melt to the front end of the barrel and forces the melt to fill the mold cavity to form.
2. Injection pressure in the barrel
For the screw injection molding machine, through the rotation of the screw, the material is pushed forward while melting. The resistance in the barrel during injection mainly comes from the frictional resistance of the melt and the resistance at the nozzle. Due to the higher temperature at the front end of the barrel, the friction factor between the melt and the barrel is smaller, and the pressure drop caused is also smaller. But the plunger injection molding machine is different. The plunger not only pushes the melt forward, but also pushes the unmelted and semi-melted materials forward. The pressure drop caused by unmelted solid particles can reach 80% of the total pressure of the barrel. Therefore, the pressure loss of the plunger injection molding machine barrel is much greater than that of the screw type.