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Z94.12.6 Plastics

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HALOCARBON PLASTICS. Plastics based on resins made by the polymerization of monomers composed only of carbon and a halogen or halogens.

HARDENER. A substance or mixture of substances added to an adhesive to promote or control the curing reaction by taking part in it. The term is also used to designate a substance added to control the degree of hardness of the cured film. (See CATALYST.)

HAZE. Indefinite cloudy appearance within or on the surface of a plastic, not describable by the terms chalking, bloom.

HEAD BLOCK; RETAINER BOARD. A thick (3 to 5 in.) large piece of laminated lumber, usually with veneer crossing, used for bottom and top of a bale of plywood, during pressing and clamping.

HEATER-ADAPTER. That part of an extrusion die around which heating medium is held.

HEAT FORMING. (See THERMOFORMING.)

HIGH-DENSITY PLYWOOD. Plywood of special construction, made at high specific pressure, usually 500 psi and up. With the increase in pressure comes a corresponding increase in density, or specific gravity.

HIGH-FREQUENCY HEATING. The heating of materials by dielectric loss in a high-frequency electrostatic field. The material is exposed between electrodes, and by absorption of energy from the electrical field is heated quickly and uniformly throughout.

HOB. A master model used to sink the shape of a mold into a soft steel block.

HOBBING. A process of forming a mold by forcing a hob of the shape desired into a soft steel blank.

HOLD-DOWN GROOVE. A small groove cut into the side wall of the molding surface to assist in holding the molded article in that member while the mold opens.

HOMOPOLYMER/COPOLYMER. These terms are used frequently to differentiate between single and multiple monomers. For example, among acetal resins, Delrin is a homopolymer, whereas Celcon is a copolymer. Polypropylene is available in both molecular forms.

HOT-RUNNER MOLD. A mold in which the runners are insulated from the chilled cavities and are kept hot so the material can be used again.

HOT-SHORT. Inelastic, nonstretchable, and easily broken by tension when hot.

HUB. (See HOB.)

HUBBING. (See HOBBING.)

HYDROCARBON PLASTICS. Plastics based on resins composed of carbon and hydrogen alone.

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