Why try to improve the blow-molding mold exhaust capacity?
When a container with the same volume is formed, the amount of air to be discharged from the blow mold is much larger than that from the injection mold.The volume of air to be discharged from the injection mold is equal to the flux of the cavity.For the blow mold, the volume of air to be excluded is equal to the volume of the mold cavity minus the volume after the billet has been blown out. The latter takes a large proportion, and there still seems to be a certain air clamp between the mold billet and the mold cavity, especially for the large volume of blowing products such as bucket tank and fuel tank.For example, the volume of the mold cavity is about 145L, and the volume of the instant billet is about 90L. In this way, about 55L air will be discharged in the final stage (about 2 ~ 3s) of the blow molding.In addition, the pressure inside the blow mold is very small (generally less than 1MPa) compared to the injection mold.Therefore, high requirements are required for the exhaust performance of the blow mold (especially the mold with cavity polishing).
If clip left cavity and air between the parison cannot fully or discharge as soon as possible, parison cannot blow up quickly and can't contact with the good cavity after blowing (especially the edges), can make the product defects such as surface roughness, dent, surface character, design is not clear, influence on the performance of the products appearance and the external shape, especially when the parison extrusion streaks or melt fracture occurs.Poor exhaust can also extend the cooling time of products, reduce their mechanical properties, resulting in uneven distribution of wall thickness.Therefore, we should try to improve the exhaust performance of the blow mold.