Screw transfer

Fig. 8 a, b. Screw transfer elements, a Tight-fitting thread b loose-fitting thread... 

FIGURE 2.5 Drawing of a screw-transfer molding machine. (After Frados, J. ed. 1976. Plastics Engineering Handbook, 4th Ed., Van Nostrand Reinhold, New York.)... 

A typical arrangement for a direct screw-transfer injection-molding machine for thermosets is shown in Figure 2.16. The machine has two sections mounted on a common base. One section constitutes the plasticizing and injection unit, which includes the feed hopper, the heated barrel that en closes the screw, the hydraulic cylinder which pushes the screw forward to inject the plasticized material into the mold, and a motor to rotate the screw. The other section clamps and holds the mold halves together under pressure during the injection of the hot plastic melt into the mold. 

DOC dissolved organic compound DST direct screw transfer... 

A screw is an inclined plane wrapped around a cylinder. A screw transfers circular motion to a straight-line movement, either in or out, depending on the direction the screw is turned (Figure 10-3). Just like the inclined plane, the slope of the screw threads affects both the force required to turn the screw and the amount the screw travels on each turn. Examine the two screws in Figure 10-4. We can install the screw in (a) quickly because the slope of the inclined is very steep. The screw in (b) takes longer to install because of the gradual slope of the inclined plane. However, we can install the screw in (b) with very accurate regulation of the force it applies. The screw can also be used as a means to install a lid to a jar, as... 

Screw feeders are used to deliver product into extruders, roll presses, deaeration presses, and process machines, against a resisting pressure. They may also stimulate flow and secure feed through opening sizes much less than those over which the material will arch. Use of a horizontal screw transferring into a vertical down screw, allows a well-designed vee hopper with an extended slot to provide a good flow channel, while the final screw can deliver at pressure into roll press or extruder. De-aeration tactics, as described above, may also be appropriate. 

Intermediate bearing must not be fitted on to screws transferring... 

Automation of the transfer/plunger concept is accomplished by the addition of a hopper-fed screw plasticator, in a system called screw transfer, which can replace the preform and preheat operations and automatically load the pot in CM (and is used to load a CM mold cavity). Conventional screw injection molding (IM) is another so-called transfer system (Chapter... 

Refer to the following subject entries for additional information Screw Configurations, Screw Transfer Molding, Preplasticating Equipment, Injection Molding, and Sheet Extrusion,... 

Figure 1. Direct screw transfer molding machine.

This process can also be performed with a screw extruder. There are two ways of doing this. One, the screw-transfer method, uses a plasticating extruder, which not only replaces the preheat and preform portions of the cycle but also loads the pot. Another way of providing the material to be molded is to use a screw injection-molding unit. 

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