Glossary of Blow Molding Terms

ACCUMULATOR:  A cylindrical reservoir that is fed melted resin from the extruder. The accumulator accepts a predetermined quantity of resin and then delivers this stored material to the die opening as required by a hydraulic ram pushed forward to deliver the parison as needed.

BACKING PLATE:  A plate used as a support for the molds and for fastening to the platens.

BLOW PIN:  Part of the head tooling used to form the parison. Usually a hollow tube through which air is blown into the mold.

BLOW PRESSURE:  The pressure of the air or blowing media necessary to expand the resin or material to be blown to conform to the cavity of the blowing mold.

BLOW-UP RATIO:  The ratio of the mold cavity diameter to the diameter of the parison or hollow form to be blown up.

CLAMP PRESSURE:  The pressure which is applied to the mold to keep it closed during a cycle.

COOLING CHANNELS:  Channels located within the body of a mold through which a cooling medium is circulated to control the mold surface temperature.

COOLING FIXTURE:  A device manufactured to hold a hot blow molded part in a fixed position until cool enough to retain it’s desired shape.

CYCLE:  The complete sequence of operations in a process to complete one set of parts. The cycle starts at a point in the operation and ends when this point is again reached.

DAYLIGHT OPENING:  The clearance between two mold halves or platens of a clamping press in the open position.

DENSITY:  Weight per unit volume of a resin usually expressed in grams per cubic centimeter.

DIE:  Any tool or arrangement of tools designed to shape or form materials to a desired configuration.

DIE GAP:  The distance between the mandrel and die in the blowing head. This clearance governs the thickness of the extruded parison, and thus the thickness of the walls of the finished part.

DIE SWELL RATIO:  The ratio of the outer parison diameter to the outer diameter of the die.

DRAFT:  The degree of taper of a side wall or the angle of clearance designed to facilitate removal of parts from a mold.

EJECTION: The removal of the finished item from the mold cavity.

HEAD:  The section of the blow molding machine immediately following the extruder. The head is comprised of the die and mandrel which forms the parison.

INJECTION RAM:  The ram or screw which applies pressure to the molten resin to force it through the tooling.

MANDREL:  The central portion or “core” of the tooling at the opening where the parison is formed.

MOLD:  The complete assembly that fits onto the platen area of a blow molding machine for receiving the hot parison and contains the expanded parison until it is cool enough to maintain the shape of the cavity in the mold assembly.

NEEDLE BLOW:  A sharp, rather small in diameter, blow pin that pierces the parison usually after the mold is closed.

PARISON:  The hollow plastic tube that is extruded from the heaad from which blown objects are made.

PINCH-OFF:  The area where plastic touches the mold that is not cavity. The pinch-off is later discarded.

PROGRAMMING:  A system on the blow molding machine to articulate the center mandrel in a linear fashion. This movement causes the parison to be thick or thin in the predetermined locations.

SHOT:  The completed resin used in a molding cycle to produce the finished part.

SHRINKAGE:  The measured difference found on a finished molded part verses the dimensions of the actual mold.

UNDERCUT:  A protrusion or indention in the mold that impedes withdrawal from the cavity.’

VENT:  A shallow channel or opening cut in the cavity to allow air or gases to escape from the mold at the parison is expanded to fill the cavity.

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