Die spider

Die spider n. In extrusion, the legs or webs supporting the die core within the head of an in-line pipe, tubing, or blown-film die. In many pipe dies, the spider legs are cored to permit application of air or water for cooling the mandrel. 

Pipe and Tubing. A typical die for extmding tubular products is shown in Figure 4. It is an in-line design, ie, the center of the extmded pipe is concentric with the extmder barrel. The extmdate is formed into a tube by the male and female die parts. The male die part is supported in the center by a spider mandrel. Melt flows around legs of the mandrel and meets on the downstream side. The position of the female die part can be adjusted with bolts adjustment is requited to obtain a tube with a uniform wall thickness. 

Fig. 4. Pipe or tubing die for in-line extmsion A, die body B, mandrel, pin, and male die part C, die, die bushing, and female part D, die-retaining ring E, die-retaining bolt F, die-centered bolt G, spider leg H, air hole I, seat for breaker plate J, ring for attachment to extmder and K, die land (15).

The theory of evolution provides answers to many questions pertaining to every day fife. For instance, why are we afraid of certain animals but not of others The simple answer is that some animals are more dangerous than others, i.e. certain types of spiders or snakes are very dangerous. Therefore, it makes sense that many people are afraid of these types of animals. People who like to play with spiders or snakes may have had a slightly lower reproduction rate because some of them died when playing with these animals. 

Plastic tube and tubular films are formed continuously by extruding a polymer through an annular die. The annular flow channel is formed by the outer die body and the die mandrel. A number of annular die designs are currently employed. In the first, the mandrel is supported mechanically onto the outer die body by a number of fins called spider legs Fig. 12.41 illustrates this type of die. The flow is axisymmetric, and the only serious problem encountered in the cross-machine direction uniformity of the extruded product is that of weld lines and streaks caused by the presence of the spider legs, which split the flow. 

Fig. 12.41 Typical spider-type tube or blown film die.

Even though these obstacles are far away from the die lip region, the polymer melt, at normal extrusion speeds, is unable to heal completely. That is, the macromolecules comprising the two layers that were split by the spider legs do not establish the entanglement level characteristic of the bulk at the prevailing shear rate and temperature. 

Skorzeny, an unrepentant Nazi, was the mastermind behind the Die Spinne (the Spider ) network that aided former SS and Nazi s to the safe-haven s in Latin America. 

Die design is critical because in foam extrusion the viscosity of the melt is so high that imperfections from the screw or from the die flow are easily transmitted to the output product. To prevent this, the entrance to the die is designed to have a restrictive flow passage to help heal the melt as it comes off the screw flights and through spiders, and to provide for uniform flow into the die body (Chapter 17). 

Tq eliminate spiders in the die and the inherent film weakness, the spiral mandrel die is used (Figure 17.11). This design usually is computer calculated since the flows and pressure drops are complicated. 

Figure 17.11 Examples of single layer blown film dies include side fed type (top left), bottom fed with spiders type (top center) and others are spiral fed types...

Processing can use spider dies, spiral mandrel dies, or basket-type dies that support the inner mandrel with a perforated sleeve through which the melt flows. Figure 17.12 provides examples of different die designs. 

Coextrusion can be performed with flat, tubular, and different shaped dies. The simplest application is to nest mandrels and support them with spiders or supply the plastic through circular manifolds and/or multiple ports. Up to 8-layer spiral mandrel blown film dies have been built that require eight separate spiral flow passages with the attendant problem of structural rigidity, interlayer temperature control, gauge control, and cleaning. Many techniques are available for coextrusion, some of them patented and available under license (Chapter 5). 

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