Screw torpedo

Gravity-casting core pin, die-casting core pin, core, sleeve, and so on Fbrm e, extrusion die, extrusion screw, torpedo, cylinder sleeve, piston, nozzle, and so on... 

Fig. 9.39 Various mixing heads, (a) Torpedo extension, (b) Dulmage screw.

If the ultimate in protection is required, a membrane of metal less than 0.1 mm thick is left across the nozzle face and provides visible tamper-evidence. Sometimes a special double-ended cap is used, incorporating an integral piercing device. The tube is pierced by removing the cap, reversing it and screwing it back onto the tube until the inverted cone pierces the membrane. If the product is of the unit dose type a membrane tube is used without a cap or threaded portion, e.g. taper or torpedo ended tubes. In this case piercing of the nozzle must be carried out with a pin or similar device. Alternatively a break-off style tip can be used. 

The newest in this series of add-on mixing torpedoes is the Dynamic Melt Mixer, DMX. The device consists of a series of mixing modules inside a tubular housing. Two types of modules are available. Each module is made of two components a stationary ring fixed to the sleeve, and veined rotor keyed to an axial shaft either attached to the SSE screw or independently powered. Part of the rotor that does not enter the sleeve, provides the cutting action across the flow lines that induces the distributive action. The primarily distributive one consist of a stator and a rotor... 

FIGURE 5-13 The layout of an injection molding apparatus (a) driven by a ram (with torpedo), (b) driven by a screw... 

Figure 36-3. Processing via the elastoviscous state, (I) injection molding, (II) extrusion, (III) roll milling. The torpedo system shown for injection molding and previously exclusively used has more recently been replaced by screws or double screws.

With thermosets, the monomer or a prepolymer is actually extruded, whereby the main part of the curing reaction takes place in a heated compression chamber with pressures up to a few hundred bar. To prevent varying degrees of cure, an extruder with a torpedo is used instead of one with screws. The curing reaction of elastomers, however, is carried out in a separate process step after the extrusion. 

Figure 12-2. Processing via the elasto-viscous state (schematic). (I) Injection molding (with torpedo), (II) extrusion, (III) rolling or milling. In injection molding, the granulate is plasticized by heat and then injected into the mold by a torpedo (or with a screw). When the molded article is cold, the mold is removed and the article ejected. In extrusion, the heated material passes through a metal screen (filter) placed in front of the nozzle.

In extrusion, the preheated material is forced out of the extruder with a screw (Figure 12-2) or double screw and allowed to cool in a bath or in the air. Thermoplasts, elastomers, and thermosets are extruded. As a rule, thermosets are processed in torpedo-containing extruders. With thermosets, most of the curing reaction must occur in a heated pressure chamber. Pressures can approach several hundred bars. The rate of extrusion is lowest with thick-walled bodies. Tubes are extruded at rates of up to 10 m/min, films up to 150 m/min, and telephone-cable insulating material or fibers at up to 1000 m/min. In extrusion, the Barus effect (Section 11.3.1) and melt fracture (Section 7.6.1) may be observed. Tubes, films, ducts, cable insulation, and knot-free nets are produced by extrusion. 

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