Plastic molding properties
(continuation 5)
(四) Curing performance
During the molding process, thermosetting plastics are transformed into a viscous fluid state under the action of heat and pressure, and the fluidity increases to fill the mold cavity. At the same time, condensation reactions occur and the cross-linking density continues to increase. The fluidity decreases rapidly and the melt gradually solidifies. When designing the mold, for materials that harden quickly and maintain a short flow state, it is reasonable to make the loading and unloading of inserts easier and avoid molding defects caused by premature or insufficient curing. Conditions and operations. Plastic parts.
The curing speed can usually be analyzed based on the holding time related to the plastic type, wall thickness, plastic part geometry and mold temperature. However, other factors also come into play, especially those related to preheating conditions. Proper preheating can maintain conditions that allow the plastic to exhibit maximum fluidity, and generally requires higher preheating temperatures and faster curing rates. Longer (within the tolerance range) will result in faster curing speeds, especially when the pre-pressed ingot material is preheated at high frequency. In addition, the higher the molding temperature and the longer the pressing time, the faster the curing speed. Therefore, the curing speed can be properly controlled by adjusting the preheating and molding conditions.
The curing speed must also meet the requirements of the molding method. For example, injection molding and extrusion molding require slow solidification during the plasticization and filling process. However, the fluid state in the cavity is maintained for a long time. After filling, high temperature and pressure are applied to harden it immediately.