Molds parting lines

The type of molding machine available has an important influence upon the blow opening system used. Some machines, for instance, use needle blowing exclusively. Hollow needle insertion at the mold parting line is considered when a very small opening is required that may even need closing or if the hollow object must be blown up on the side, e.g., on carousels with a series of molds. 

The mold is cooled, usually by water, to solidify the plastic. When the plastic object has been cooled sufficiently to maintain its shape, the mold is opened, along the mold parting line, and the object is ejected. The cycle time in injection molding depends on the size of the molded part, as well as on the molding conditions and on the thermal and mechanical characteristics of the plastic being molded. In some case, the cycle time can be as short as two seconds. 

As is the case in molds for thermoforming, the design of injection molds must provide for venting to remove trapped air, which otherwise will mar the finish of the molded object, and may, in extreme cases, prevent accurate mold filling. The simplest way to accomplish this is to build vent holes into the mold parting line, where the core and the cavity come together. For large molded objects, this may be insufficient, and additional vents may be needed. 

The marks left from the removal of the flash serve as an easy means for identification of extrusion blow-molded containers. Usually this is easiest to see on the bottom of the container. It typically appears as a rough area along the mold parting line, centered in the middle of the bottom and running half or so of the distance to the heel of the bottle. It is also possible, on careful examination, to identify the roughness at the top of the finish, or on other areas where flash was trimmed. 

Mold parting line indented in part Blow-up air introduced prematurely Hooking parison Delay blow-up Reduce mold temperature... 

Cavity-retainer plate n. A plate in a mold that holds the cavities and forces. Such plates are at the mold parting line and usually contain the guide pins and bushings. 

H = maximum height of projection perpendicular to the mold parting line (see Fig. 8.30)... 

Parison sag (parison parting line and blow mold parting line do not overlap)... 

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