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A round, hollow tube of molten plastic that is extruded from the head of the blow molding machine.

Parison Curtaining
The tendency for a parison to lose its tubular shape because of conditions in the extrusion process. Generally, the bottom of the parison tends to drape irregularly, causing the entire parison to lose its original shape, creating difficulties in molding the part.

Parison Melt Strength
Parison melt strength depends directly on the melt characteristics of the resin being extruded. The ability to extrude a parison of sufficient dimensions to produce the desired part depends on the melt strength of the parison. The larger and heavier the parison, the greater its melt strength requirements.

Parison Pinch Bars
Various methods are used to close or seal the bottom of the parison before mold closing or part inflation. The devices are called pinch bars and are usually spring loaded, or hydraulically or pneumatically actuated. They may be attached to the bottom of the mold or positioned directly under it.

A pinch-off is needed when the parison falls outside the cavity of the mold. It is the protruding edge separating the cavity from the flash pocket, and it compresses the flash to the point of severance. Inserted beryllium copper is preferred because the alloy has thermal conductivity equal to that of the aluminum alloy used in the mold. Steel pinches are used when pinch wear is critical - for example, when molding materials such as polycarbonates are used.

Parison Pre-Blowing
Introducing air pressure into the parison before closing the mold halves. This provides better distribution of wall thickness and prevents the parison wall from coming in contact before the inflation of the part.

Parison Programming
Varying the wall thicknesses in a parison to conform to the wall thickness requirements of a given part.

Parison Tail
The bottom portion of a parison that is severed by the lower pinch-offs and falls outside the mold.

The ability of a material to withstand continuous and permanent deformation by stresses exceeding the yield value of the material without rupture.

To render a material softer, more flexible and/or more moldable by the addition of a plasticizer.

A substance or material incorporated in a material (usually a plastic or an elastomer) to increase its flexibility, workability or extensibility. Some plasticizers have been known to have detrimental effects on certain types of plastic, end use testing is recommended.

An objectionable coating gradually formed on metal surfaces of molds during processing of plastics due to extraction and deposition of some ingredient such as pigment, lubricant, stabilizer or plasticizer.

The large metal plates the mold attaches to on a plastic molding machine.

PLC (Performance Level Categories)
As defined by UL: "In order to avoid an excessive level of implied precision and bias, material performances for several tests are recorded as PLC, based on the mean test results (rather than recording the exact numerical results)". PLC levels are assigned to electric properties, tested according to UL 746A

Polycarbonate Resin (PC)
A family of special types of polyesters in which groups of dihydric phenols are linked through carbonate linkages.

Polymer (Synthetic)
The product of a polymerization reaction. The product of polymerization of one monomer is called a homopolymer, monopolymer or simply a polymer. When two different monomers are polymerized simultaneously the product is called a copolymer. The term terpolymer is sometimes used for polymerization products of three monomers.

Polymer Chains
A linear polymer is a polymer in which the monomers are bound to each other in a straight chain without any branches. Branched polymers have branched connections of molecules.Copolymers are polymers with repeating molecular units from at least two different monomers. Two kinds of arrangements are possible: random and alternating, resulting in random copolymers and alternating copolymers.Such polymers are called block-copolymers, characterized by both monomers A and B forming the backbone chain of the polymer. They have repeating monomers in linearly connected blocks. Another possibility is the formation of a graft-copolymer, which is essentially a branched-chain structure. It has side chains composed of one type of monomer unit attached to the backbone or main chain from another monomer unit.

The process of converting a monomer or a mixture of monomers into a polymer. Addition polymerization is the stepwise addition of a simple repeated unit. Or, the reaction that yields a product that is an exact multiple of the original monomeric molecule. Condensation polymerization is the combination of functional molecules, leading to the formation of a polymer with the liberation of simple by-products, usually water.

Polymer Structure
A general term referring to the relative positions, arrangement in space, and freedom of motion of atoms in a polymer molecule.

The class of polymers made by polymerising relatively simple olefins.

Time, usually in hours, during which a two or three component product can be used after it is mixed. Sometimes measured in terms of time to gel and/or double in viscosity.

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