The parison of Dalian hollow molding and injection molding is usually taken out after cooling. The parison is first stretched axially by mechanical method, and then in blow molding, the radial size of the parison is increased, and then stretched laterally, and then cooled rapidly below Tg. Entering the second stage of molding, that is, the mandrel and parison are quickly sent to the blow molding mold, the compressed air valve is opened, and the compressed air is blown through the mandrel.
Blow the parison still in the molten state to the shape of the mold cavity, open the mold after cooling in the mold, and take out the products. Due to its long chain structure and the flexibility of molecular chain, generally, when the polymer is placed at a certain temperature, from the action of external force, the formation of macromolecules undergoes a series of intermediate states to the equilibrium state suitable for external force, which is a relaxation process.
Because the relaxation time t * of the polymer is very short near the high elastic state or viscous flow temperature, if the deformation time T1 > > t * during molding, it can be obtained from formula (3). When the external force action time t = T1, it will be cooled below the glass transition temperature or crystallization temperature in a short time to freeze the deformation of the molded product. Because of its long chain structure and the flexibility of molecular chain.
Generally, when the polymer is placed at a certain temperature, from the action of external force, the formation and recombination of macromolecules undergo a series of intermediate states to the equilibrium state corresponding to the external force, which is a relaxation process. The change of deformation with time is that above the glass transition temperature of the polymer, the proportion of general elastic deformation in the total deformation is very small and can be ignored.
Dalian hollow molding