B - Polymer Processing Glossary of Terms

Back draft - A slight undercut or tapered area in a mold tending to prevent removal of the molded part.
Back plate - A plate used as a support for the cavity blocks, guide pins, bushing, etc. Sometimes called support plate.
Back pressure - Pressure exerted by the injection unit's cylinder against the screw as it recovers or plasticates. Used to increase the melt homogeneity. Increases melt temperature.
Baffle - A plug or other device inserted in a flow channel to divert cooling medium to a desired path.
Balanced runner - A runner system designed to place all cavities at the same distance from the sprue.
Ball check valve - An anti-back flow valve which prevents the plastic melt from flowing back over the screw during injection.
Band heaters - Electrical heaters surrounding the barrel and nozzle of the injection unit.
Bar chart - Histogram
Barrel (extruder) - Hollow tube in which plastic is gradually heated and melted. Inside the barrel is a helical screw which compresses and moves the plastic from the feed throat (hopper end) to the injection nozzle (mold end). Outside the barrel are band heaters.
Barrier - A layer of material designed to limit migration or infiltration of undesirable elements through the plastic or limit the loss of desirable elements through the plastic.
Barrier properties - Material; permeability characteristics which limit the migration or permeability of elements.
Blueing off - A mold making term for the process of checking the accuracy of mating of two surfaces by applying a thin coating of Prussian Blue on one surface, pressing the coated surface against the other surface, and observing the areas of intimate contact where the blue color has been transferred.
Boost (1st Stage Pressure) - Pressure exerted on melt to fill the mold cavities.
Burned - Showing evidence of excessive heating during processing or use of a plastic, as evidenced by blistering, discoloration, distortion or destruction of the surface.
Bushing - The outer ring of any type of circular tube or pipe die which forms the outer surface of the tube or pipe.

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