Reciprocating screw plasticator

DeCapite, R., and C.S. Gudermuth, "The Vented Reciprocating Screw Plasticator", HPM Corporation, Mt. Gilead, Ohio 43338. 

A. DeCapite, R. Gudermuth, C. S. " fhe Vented Reciprocating Screw Plasticator" HPM Corporation Mt. Gilead, OH A3338. 

BMC is commercially available in different combinations of resins, predominandy TS polyesters, additives, and reinforcements. They meet a wide variety of end-use requirements in high-volume applications where fine finish, good dimensional stability, part complexity, and good overall mechanical properties are important. The most popular method of molding BMCs is compression. They can also be injection molded in much the same way as other RTS compounds using ram, ram-screw, and, certainly BMC mixes, conventional reciprocating screw plasticators. 

In the intermittent processes, single or multiple parisons are extruded using a reciprocating screw or ram accumulator. In the former system the screw moves forward to extrude the parisons and then screws back to prepare the charge of molten plastic for the next shot. In the other system the screw extruder supplies a constant output to an accumulator. A ram then pushes melt from the accumulator to produce a parison as required. 

It is usually done by computer controlled electronic weighing scales that supply precise amounts of each ingredient to a high intensity mixer. The still-dry, free-flowing blend is then charged to a feed hopper where it is screw fed into a continuous mixer such as an extruder and/or kneader. Under the action of a mixer s reciprocating screw in the confined volume of the mixer chamber, the blend begins to flux or masticate into the required plastic state. 

Albert (Aly) A. Kaufman, one of the early pioneers of extrusion, who established Prodex in New Jersey and later Kaufman S. A. in France, and introduced many innovations into extrusion practice, told one of the authors (Z.T.) that in one of the Annual Technical Conference (ANTEC) meetings long before in-line plasticating units came on board, he told the audience that the only way to get a uniform plasticized product is if the ram is replaced by a rotating and reciprocating screw. Aly never patented his innovative ideas because he believed that it is better to stay ahead of competition then to spend money and time on patents. 

Fig. 13.2 The injection molding cycle. [Reprinted by permission from R. C. Donovan, An Experimental Study of Plasticating in a Reciprocating-Screw Injection Molding Machine, Polym. Eng. Set, 11, 353 (1971).]...

Fig. 14.16 Schematic view of (a) continuous extrusion blow molding (b) reciprocating screw blow molding and (c) ram-accumulator blow molding. [Reprinted by permission from Modem Plastics Encyclopedia, McGraw-Hill, New York, 1976-1977.)...

Two-Stage" Injection Molding Machine. Instead of using a reciprocating screw to melt the plastic and to push the melt into the mold, the extruder screw may feed the molten plastic into a separate reservoir, and then a separate plunger can feed the melt into the mold. 

Injection molding is a cyclic discontinuous process used to form three-dimensional plastic parts (25. 26). Both thermoplastics and thermosets are injection molded. The process is shown schematically in Figure 11 for a reciprocating screw injection molder. This type of a machine has a screw rotating in a barrel similar to an extruder. However, here the melt flow is discontinuous and controlled via a check valve at the tip of the screw. Material is melted in the extruder, and the melt is accumulated in front of the screw tip until sufficient melt is at hand to fill the mold cavity (cavities). 

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