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SANDWICH MOLDING. A molding process in which two different materials are injected consecutively into a mold cavity to produce products having surfaces of one plastic with desirable characteristics and a core of another material with its desired characteristics.
SARAN PLASTICS. Plastics based on resins made by the polymerization of binylidene chloride or copolymerization of binylidene chloride with not more than an equal weight of other unsaturated compounds.
SEALING DIAMETER. Portion of the insert which is free of knurl and is allowed to enter into the mold to prevent the flow of material.
SECONDARY GLUING. The process of gluing together wood and plywood parts in assembling wood products, such as aircraft. Contrasted with primary gluing, when veneers are glued into plywood. (See ASSEMBLY: IN PLASTICS SECTION 12-70.)
SET. To convert a liquid resin or adhesive into a solid state by curing, by evaporation of solvent or suspending medium, or by gelling.
SHEET. A piece of plastic sheeting produced as an individual piece rather than in a continuous length, or cut as individual pieces from a continuous length. (See SHEETING, FILM.)
SHEETING. A form of plastic in which the thickness is very small in proportion to length and width, and in which the plastic is present as a continuous phase throughout, with or without filler. (See FILM.)
SHEET MOLDING COMPOUND (SMC). A combination of polyester resin, filler, and reinforcement rolled into a sheet form. Thermoplastic resin often is added to obtain a surface with desired characteristics.
SHELF LIFE. The length of time over which a product will remain fit for use during storage under specific conditions (especially temperature).
SHIM. In the manufacture of plywood, a long narrow patch glued into the panel, or into the lumber core.
SILICONE. One of a family of polymeric materials in which the recurring chemical group contains silicon and oxygen atoms as links in the main chain. Silicons are derived from silica (sand) and methyl chloride.
SILICONE PLASTICS. Plastics based on resins in which the main polymer chain consists of alternating silicon and oxygen atoms, with carbon-containing side groups.
SIZING. The process of applying a material on a surface in order to fill pores and thus reduce the absorption of the subsequently applied adhesive or coating, or to otherwise modify the surface properties of the substrate to improve adhesion. Also, the material used for this purpose. The latter is sometimes called size.
SLEEVE EJECTOR. Busing-type knockout.
SLIDING PLATE. (See DUPLICATE CAVITY-PLATE.)
SLIP JOINT. The method of laying up veneers in flexible-bag molding, wherein the edges are beveled and allowed to overlap part or all of the scarfed area.
SOFTENING RANGE. The range of temperatures in which a plastic changes from a rigid to a soft state. Actual values will depend on the method of test. Sometimes erroneously referred to as softening point.
SOLID-PILED. Sometimes called dead-piled or bulked-down. Plywood fresh from clamps or hot press is piled on a solid, flat base, without stickers, and weighted down while reaching normal temperature and moisture content.
SOLVATION. The process of swelling, gelling, or solution of a resin by a solvent or plasticizer as a result of mutual attraction.
SOLVENCY. Solvent action, or strength of solvent action
SPLIT CAVITY. Cavity made in section.
SPLIT-CAVITY BLOCKS. Blocks which when assembled contain a cavity for molding articles having undercuts.
SPRAY-UP. The term for a number of techniques in which a spray gun is used as the processing tool.
SPREAD. The quantity of adhesive per unit joint area applied to an adherend. It is preferably expressed in pounds of liquid or solid adhesive per thousand square feet of joint area. Single spread refers to application of adhesive to only one adherend of a joint. Double spread refers to application of adhesive to both adherends of a joint.
SPRUE. (1) The primary feed channel that runs from the outer face of an injection or transfer mold to the mold gate in a single-cavity mold or to the runners in a multiple-cavity mold. (2) The piece formed in a primary feed channel or sprue.
SPRUE BUSHING. In an injection mold, a hardened steel insert which contains the tapered sprue hole and has a suitable seat for making close contact with the nozzle of the injection cylinder.
SPRUE-PULLER. A pin having a Z-shaped slot undercut in its end, by means of which it serves to pull the sprue out of the sprue bushing.
STIR-IN RESIN. A vinyl resin which does not require grinding to effect dispersion in a plastisol or an organosol.
STOP BUTTONS. Multiple island limiting travel of ejector mechanism when returned to molding position.
STRESS-CRACK. External or internal crack in a plastic caused by tensile stresses greater than that of its short-time mechanical strength. The development of such cracks is frequently accelerated by the environment to which the plastic is exposed. The stresses which cause cracking may be present internally or externally or may be combinations of these stresses. The appearance of a network of fine cracks is called crazing.
STRETCH FORMING. A plastics sheet forming technique in which the heated thermoplastic sheet is stretched over a mold and then cooled.
STRIPPER PLATE. A plate which strips the molded article from mold pin, force or cores.
STRIPPING FORK. Tool, usually of brass or laminated sheet, used to remove articles from the mold (also called comb).
STRUCTURAL FOAM. This product has a rigid cellular core and a solid integral skin.
STYRENE ACRYLONITRILE (SAN). A thermoplastic copolymer with good stiffness, along with good resistance to chemicals, scratching, and stress cracking.
STYRENE PLASTICS. Plastics based on resins made by the polymerization of styrene or copolymerization of styrene with other unsaturated compounds.
STYRENE RUBBER PLASTICS. Plastics consisting of at least 50 percent of a styrene plastic combined with rubbers and other compounding ingredients.
SUPPORT POST OR PILLAR. Post used to resist deflection under pressure.
SYNDIOTACTIC. Alternating placement of the group on either side of the chain with respect to the carbon-carbon backbone plane.
SYNERSIS. The contraction of a gel. This is usually evidenced by the separation of a liquid. (See GEL.)
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