A certain amount of foaming agent and water vapor are retained in the beads pre expanded by EPS pre expand machine. When they are discharged from the machine, they condense into liquid, and the liquid foaming agent dissolves into polystyrene, so that the pressure in the bubble is quickly reduced, and there is negative pressure (partial vacuum) in the bubble. The beads are very soft and easy to deform. Therefore, during air supply, try not to make the wind pressure too large, the inner wall of the air duct should be as smooth as possible, and the bending radius should be as large as possible (reduce collision resistance). The pipeline should be a good conductor of electricity. The whole line must be grounded to avoid electrostatic ignition, and the transmission speed should not exceed 8m / s to avoid bead damage.
The beads just out of the EPS pre expander machine are wet. After being discharged from the pre expander machine, they absorb air and suddenly encounter cold, resulting in the condensation of foaming agent in the honeycomb cell and the formation of negative pressure in the cell. Therefore, the beads must be placed for a period of time after pre expander. On the one hand, they must be dried, and on the other hand, they must penetrate into the air to eliminate the negative pressure, so as to balance the internal pressure and external pressure in the cell, In order to avoid the collapse of the bubble hole and make the beads elastic.
The process of drying, cooling and stable cell pressure of EPS beads just out of EPS pre expander is called ripening. Ripening can improve the further expansion, fusibility between beads and elasticity of beads in the molding process, which is conducive to improving the quality of EPS products.
During the curing process, the beads are cooled by air, and the foaming agent and steam in the pores are condensed into liquid, resulting in negative pressure in the pores. At this time, air will penetrate into the interior of the bubble through the bubble membrane to balance the pressure in the bubble with the external pressure, which will make the pre expander sent beads elastic.
Ripening can be divided into natural ripening and pressure ripening. Under cool, dry and ventilated conditions, natural aeration is called natural ripening. It is called pressure curing to inflate the naturally matured pre expander released beads by adding gas (air and nitrogen) into a sealed container to make them have a certain pressure.
