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BACK-PRESSURE-RELIEF PORT. An opening from an extrusion die for escape of excess material.
BACKING PLATE. A plate which backs up the cavity blocks, guide pins, bushings, etc. (Sometimes called support plate.)
BACK TAPER. Reverse draft used in mold to prevent molded article from drawing freely. (See UNDERCUT.)
BAG MOLDING. A method of applying pressure during bonding or molding in which a flexible cover exerts pressure on the material being molded, through the application of air pressure or the drawing of a vacuum.
BAKELITE. The proprietary name for phenolic and other plastic materials produced by the Union Carbide Corp.
BLANKET. Veneers which have all been laid up on a flat table. The complete assembly is placed on or in the mold all at one time; useful only on simple curved surfaces to be molded by the flexible-bag process. Also used to denote a form of bag made of rubber in which the edges are sealed against the mold by clamps.
BLEEDING. (1) The flow of color from one region into an adjoining region. (2) In the manufacture of plywood, the escape of a portion of the steam-air mixture during cooking, to permit mixing of the steam and air and to maintain uniform temperature at all levels in the autoclave, when molding with flexible pressure.
BLIND HOLE. Hole that is not drilled entirely through.
BLIND-HOLE PARTIAL THREAD. Thread counterbored from the front for terminal or other assembly fit.
BLISTER. (1) Undesirable rounded elevation of the surface of a plastic, whose boundaries may be indefinitely outlined, somewhat resembling in shape a blister on the human skin. A blister may burst and become flattened. (2) An elevation of the surface of an adherend, somewhat resembling in shape a blister on the human skin; its boundaries may be indefinitely outlined and it may have burst and become flattened. A blister consists of trapped air, water, or solvent, and can be caused by insufficient adhesive, inadequate curing time, temperature, or pressure.
BLOCKING. An adhesion between touching layers of plastics, such as that which may develop under pressure during storage or use.
BLOOM. A visible exudation or efflorescence on the surface of a plastic. Bloom can be caused by lubricant, plasticizer, etc.
BOLSTER. Spacer or filler in a mold.
BOND. The attachment at an interface between an adhesive and an adherent. (2) To attach materials together by adhesives.
BUBBLE. Internal void or a trapped globule of air or other gas. (See JOINT.)
BULK DENSITY. The density of a molding material in loose form (granular, nodular, etc.) expressed as a ratio of weight to volume (e.g. g/cm3 or b/ft3).
BULK FACTOR. The ratio of the volume of the loose molding compound to the volume of the same quantity in a molded solid piece. Also the ratio of the density of the solid plastic object to the apparent density of the loose molding powder.
BURNED. Showing evidence of thermal decomposition through some discoloration, distortion, or destruction of the surface of the plastic.
BUTADIENE. A gas, insoluble in water but soluble in alcohol and ether, obtained from the cracking of petroleum and other methods. Butadiene is widely used in forming copolymers with styrene and other monomeric substances.
BUTADIENE STYRENE. A thermoplastic polymer used for film and sheet.
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