Expandable Bead Molding

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ANTTBIOTTCS - BETA-LACTAMS - PENICILLINS AND OTTiERS] (Vol 3) Expanded bead molding... 

Expandable bead molding 10 Extruding 7 Extrusion blowing 7... 

With regard to methods of fabrication, all processes in Table 1.1 that are applicable to unfilled, unmodified thermoplastics can also be used for discontinuous systems (with the exception of expandable bead molding). In addition to thermoforming, hot stamping of reinforced thermoplastic sheets mostly containing randomly oriented continuous or discontinuous fibers is used for the production of large semistructural parts. Fillers can also be used in the thermoset processes in Table 1.1, often in combination with the primary continuous fiber reinforcement. The content and inherent properties of the additive, as well as its physical/chemical interactions with the matrix, are important parameters controlling the processability of the composite. 

Polystyrene. There are five basic types of polystyrene foams produced in a wide range of densities and employed in a wide variety of applications (1) extruded polystyrene board (2) extruded polystyrene sheet (3) expanded bead molding (4) injection-molded structural foam and (5) expanded polystyrene loose-fill packaging. 

Mechanical Properties and Structural Performance. As a result of the manufacturing process, some cellular plastics have an elongated cell shape and thus exhibit anisotropy in mechanical, thermal, and expansion properties (35,36). Efforts are underway to develop manufacturing techniques that reduce such anisotropy and its effects. In general, higher strengths occur for the paraHel-to-rise direction than in the perpendicular-to-rise orientation. Properties of these materials show variabiUty due to specimen form and position in the bulk material and to uncertainty in the axes with respect to direction of foam rise. Expanded and molded bead products exhibit Httie anisotropy. 

Patent Number US 6077875 A1 20000620 FOAMED AND EXPANDED BEADS OF POLYPROPYLENE RESIN FOR MOLDING... 

Expanded polystyrene bead molding products account fur the largest portion of the drinking cup market and arc used in fabricating a variety of other products including packaging materials, insulation board, and ice chests. The insulation value, Ihe moisture resistance, and physical properties arc inferior to extruded boardsinck. but Ihe material cost is much less. 

Tihis chapter describes the manufacture of expandable beads in the copolymer 1-butene-sulfur dioxide by suspension polymerization. The processing and properties of expandable beads and of molded articles are examined briefly. 

Close temperature control is required to obtain reproducible results, because the expansion of the polystyrene is a function of temperature. The polystyrene microspheres may be pre-expanded by steam or radiant heat and then added to the mold, heated in advance to a convenient temperature, such as 60°C. The mixed epoxy resin is then poured over the pre-expanded beads and allowed to cure. In this case, a limited amount of further expansion will occur as a result of exotherm or cure temperature to permit complete mold fill (10). A typical formulation is shown below ... 

Further expansion and fusion of the pre-expanded beads by heat within the shaping confines of a mold. 

MIL-P-19644C Plastic Molding Material (Polystyrene Foam, Expanded Bead), 10 July 1970, 15 pp (FSC 9330) (OS). Int amend 1 was issued 1 AprU 91, 3 pp (SA)... 

Expandable polystyrene beads are often molded in two separate steps (1) Preexpansion or prefoaming of the expandable beads by heat, and (2) further expansion and fusion of the preexpanded beads by heat in the enclosed space of a shaping mold. 

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