Plastic molding process|Hardening characteristics of plastic molding
Plastic molding processThermosetting plastics are transformed into a plastic viscous flow state under heating and pressure during the forming process, and the fluidity increases to fill the cavity. At the same time, a condensation reaction occurs, the crosslinking density increases continuously, the fluidity decreases rapidly, and the melt gradually solidifies. . When designing the mold, for the materials with fast hardening speed and short flow state, attention should be paid to easy loading, loading and unloading inserts, and selecting reasonable forming conditions and operations to avoid premature hardening or insufficient hardening, resulting in poor forming of plastic parts.
The hardening speed can generally be analyzed from the holding time, which is related to the type of plastic, wall thickness, shape of plastic parts, and mold temperature. However, it is also affected by other factors, especially related to the preheating state. Appropriate preheating should be maintained under the condition that the plastic can exert the maximum fluidity, and the hardening speed should be improved as much as possible. Within the range), the hardening speed is accelerated, especially when the pre-rolled ingot is preheated at high frequency, the hardening speed is significantly accelerated. In addition, when the forming temperature is high and the pressing time is long, the hardening speed also increases. Therefore, the hardening speed can also be properly controlled by adjusting the preheating or forming conditions.
The hardening speed should also be suitable for the requirements of the forming method. For example, during injection and extrusion molding, the chemical reaction and hardening should be slow during plasticization and filling, and the flow state should be maintained for a long time. The bottom should harden quickly.