Screw Injection Molding Machine

Fig. 13. Injection molding machine A, hydiaulic motoi foi turning the screw B, hydraulic cylinder and piston allowing the screw to reciprocate about three diameters C, hopper D, injection cylinder (a single-screw extmder) E, no22le F, fixed platen G, tie rods H, mold I, movable platen , hydraulic cylinder and piston used to move the movable platen and supply the force needed to keep the mold closed and K, machine base.

Figure 20 A horizontal reciprocating screw injection molding machine.

To ensure consistency, the two critical areas for control specific to injection molding are shot size control and temperature control on the injection system, i.e., screw portion for the reciprocating screw machines, and both the screw and ram sections for the screw/ram machines. As mentioned previously, for temperature and cure control, the use of microprocessor controls has significantly improved the performance of injection molding machines, including control of the shot size. 

The standard injection molding machine used had a screw diameter of 30 mm and the aspect ratio of 23.70. The barrel temperature profile was 270, 280, 290, and 295°C. The mold temperature was about 90°C. The injection molded tensile samples were processed according to the CAMPUS specification (Computer Aided Materials Preselection by Uniform Standards) [24] and DIN 53455 Form 3. To obtain the different flow conditions, four groups of samples were injection molded by varying melt... 

In the case of polyolefins the dispersing performance of single-screw extruders and injection molding machines is not sufficiently to undertake high-quality coloration (fibers, film, tape) with powder pigments or pigment mixtures. 

Processing and Application. Polystyrene and the other thermoplastics would not have been able to enter on their triumphal march if the manufacturers of processing equipment had not been able to provide efficient fabrication methods. A decisive factor was that between 1950 and 1960 the injection molding machine with a screw preplasticizer was developed and extrusion through slit dies to give sheeting or film followed by thermoforming was evolved. 

The plasticator on an injection-molding machine is a specialized plasticating single-screw extruder. The plasticator has two main differences there is a nonreturn valve on the tip of the screw, and the screw retracts as molten material accumulates between the nonreturn valve and the end of the barrel. Pressure is maintained on the accumulated material by a constant force applied to the shank of the screw via the drive system. This force is typically measured as a pressure applied to the shank and is referred to as the back pressure. During the injection step of the process, the screw is forced forward, the nonreturn valve closes, and the material is injected into the mold. Additional information on the injection-molding process can be obtained elsewhere [Ij. 

Journal of Injection Molding Technology 5,No.3, Sept.2001,p.l52-9 MICROCELLULAR FOAM PROCESSING IN RECIPROCATING-SCREW INJECTION MOLDING MACHINES Jingyi Xu Pierick D Trexel Inc. 

Injection molding is not new. A patent was issued in 1872 for an injection-molding machine for camphor-plasticized CN, celluloid. Almost all of the machines used today are reciprocating or two-stage screw types. Both types employ a reciprocating Archimedean-like screw similar to that of a screw extruder. A few are of the plunger type. 

Two systems have been used in injection molding machines to melt and inject the polymer. The most commonly used types use a reciprocating screw, which has many... 

An injection molding machine is operated by hydraulic power and equipped with an dectric motor and hydraulic pump. The maximum hydraulic oil pressure is ca 14 MPa (2000 psi). A hydraulic cylinder opens and closes the mold and holds the mold dosed during injection another cylinder forces the screw forward, thereby injecting the mdt into the mold. A separate hydraulic motor turns the screw to plasticate, homogenize, and pressurize the mdt. Control of these movements is a combined function of the hydraulic and electrical systems (35—37). 

William Willert filed a patent on the in-line, now more commonly known as the reciprocating screw injection molding machine in 1952. In 1953 Reed Prentice Corp. was the first to use Willert s invention, building a 600-ton machine. The patent was issued in 1956. By the end of the decade almost all the injection molding machines being built were of the reciprocating screw type. 

Fig. 11.30 Effect of preheating 50% by weight E-glass fiber-filled polyamide pulltruded pellets on fiber lengths at the screw tip of a 300-ton 23.86-oz reciprocating injection molding machine. [Reprinted by permission from C. G. Gogos, C. K. Yoon, and J. Brizzolara, Injection Molding Process Development for Long Fiber Reinforced Thermoplastics, SPE ANTEC Tech. Papers, 40, 384 (1994).]...

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).]...

S. D. Lipshitz, R. Lavie, and Z. Tadmor, A Melting Model for Reciprocating Screw Injection Molding Machines, Polym. Eng. Set, 14, 553 (1974). 

HPM and Johnson Plastics Machinery report that they can use vented extruders, and vented screw plasticators on injection molding machines, to eliminate the pre-drying step required by many plastics, and thus reduce processing costs 5-20% ( y. 

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