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Back Pressure: The resistance of the molten plastic material to forward flow. In molding, back pressure increases the temperature of the melt, and contributes to better mixing of colors and homogeneity of the material. However, as back pressure increases, so does cycle time.
Backflow: molten resin flows back out of the mold, returning to the runners.
Backing Plate: A plate used as a support for the mold cavity block, guide pins, bushings, etc.
Balanced Runner: A runner system designed to place all cavities at the same distance from the sprue.
Barrel: The section of a molding machine that contains the feed screw, also the section where resin heating and mixing occurs.
Binder: A resin or other material used to hold particles together. The binder is the continuous phase in a reinforced plastic, which provides mechanical strength or ensures uniform consistency, solidification, or adhesion to a surface coating. Typical binder materials include resin, glue, gum and asein.
Biocides & Fungicides: Additives that are used to inhibit the growth and colonization of fungus, bacteria, and other pests.
Black Specks: A specific kind of inclusion/contamination often associated with heat-degraded materials.
Blast Finishing: The process of removing flash from molded objects and/or dulling their surfaces, by impinging upon them with sufficient force to remove the flash.
Blister: An imperfection on the surface of a plastic article caused by a pocket of air or gas beneath the surface.
Blocking & Anticaking Agents: These additives are used to prevent the adhesion and agglomeration of ingredients within a resin compound.
Bloom (also know as Migration): An undesirable cloudy effect or whitish powdery deposit on the surface of a plastic article or to the surrounding environment caused by the exudation of an ingredient such as a lubricant, stabilizer pigment, plasticizer, or other non-bonded component.
Blow Molding: Method of fabrication in which a warm plastic hollow tube is placed between the two halves of a mold cavity and forced to assume the shape of that mold cavity by use of internal pressure. This process forms hollow articles such as bottles, tanks, etc.
Blowing & Foaming Agents: Additives for plastics or rubbers that generate inert gases within the resin matrix when heated. The resulting part construction will contain a cellular structure.

Blushing: The tendency of a plastic article to turn white or chalky in areas that are highly stressed.
Boss: A raised feature of a molded part designed to add strength, facilitate alignment during assembly or for attachment to another part.
Branching: The modification of the molecular structure of a polymer derived from the growth of a new polymer chain from an active site on an established chain, in a direction different from that of the original chain.
Breakdown Voltage: The voltage required, under specific conditions, to cause failure of an insulation material.
Brighteners: Are used to add smoother or brighter coatings or finishes.
Brittle Temperature: A measure for judging the relative merits of materials for low-temperature flexing or impact – i.e., the temperature at which materials rupture by impact under specified conditions.
Broken Mold Marks: Part surface defects caused by mold damage.
B-stage: This describes an intermediate stage of a thermoset resin reaction where the material will soften when heated and swells in the presence of certain liquids, but may not completely fuse or dissolve. The resin is usually supplied in this uncured state.
Bubbles: Air or gas pockets that have formed in the material of the component. Bubbles may vary in size.
Bulk Density: A measurement of mass per unit volume of materials (such as powders) that describes the effects of the particle packing density.
Bulk Factor: The ratio of the volume of any given mass of loose plastic material to the volume of the same mass of the material after molding.
Bulk-molding compounds (BMC): Bulk-molding compounds are used as a premix in composite manufacturing. A BMC consists of a mixture of resin, reinforcements, inert fillers, and other additives which form a puttylike preformed shape, rope or sheet.
Burned: Showing evidence of excessive heating during processing or use of a plastic, as evidenced by blistering, discoloration, distortion or destruction of the surface.

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