Pipe dies

Figure 17.12 Examples of different pipe die inline and crosshead designs...

Fig. 10 Tubing vacuum water-bath calibration and take-off (1) tubing/pipe die (2) molten tube extrudate (3) baffle (4) vacuum water tank (5) sizing ring (6) solidified tube and (7) puller.

PP/LCP ECP macromolecules stretched in a counter-rotating pipe die Haghighat et al., 1992... 

The metering section output must be the same as the flow rate through the die, as must the peak pressure p where the metering section meets the die. For a pipe die (Fig. 5.8), consisting of a channel of circumference b, height h and length L (or a set of such channels in series), the output, from Eqs (B.5) and (B.9) is... 

Vacuum tank calibration of rigid pipe used with water baths (a. pipe die, b. vacuum with discs, c. heated zone water baths and d. caterpillar take-off puller)... 

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 die n. An extrusion die whose lands form a circular annulus used in extrusion of plastic pipe or tubing. The outer shell of the die is usually called the die, the core is called the mandrel. Pipe dies may be side-fed or end-fed, and the mandrel may be supported by a trio of legs called a spider, or it may be supported from the rear of a side-fed die. It is easier to achieve circumferential uniformity of wall thickness with a spider die, but the splitting of the melt stream at the legs has sometimes caused weak welds because of insufficient knitting time before the pipe emerges and is chilled. 

Pipes are often extruded with in-line pipe dies see Fig. 9.20. 

Another method of improving circumferential orientation in tubing and pipe dies is by inducing relative motion between the tip and the die. This can be done by rotating the tip relative to a stationary die or by rotating the die relative to a stationary tip. It is even possible to rotate both the tip and the die separately and in different directions. With rotation of the tip and/or die there is a greater degree of control over the orientation of the extruded tube than with a spiral mandrel section. Obviously, this is at the expense of increased mechanical complexity. 

The flow channel of the die should be designed such that the plastic melt achieves a uniform velocity across the die exit. The shape of the land region of the die corresponds to the shape of the extruded product. An example of an in-line tube or pipe die is shown in Figure 17. The material flows into the die fi om the extruder then it flows around a torpedo. 

A pipe die is shown in Fig. 7.20. The polymer melt flow is separated into an annulus, enters the die land, and exits in tubular shape. It swells on exit and is drawn down to the correct diameter this is checked by means of a calibrator. The extruded (and still liquid) pipe enters the calibrator through the rubber seals (A in Fig. 7.21) and passes stainless steel guides (B). Within the calibrator, thermostatted water cools the pipe. In this calibrator, the wall thickness is gauged by ultrasonics an alarm is generated if the wall thickness falls above or below set values. Frequently, the pressure of water is below atmospheric, so that with atmospheric pressure in the tube, it is forced against sizing rings in the calibrator. 

Tubing Die A die with an annular opening used to extrude plastics tubing. The core (mandrel) of the die may be fitted with a water-cooled extension that aids in chilling the extrudate and bringing its internal diameter within tolerances. See also Pipe Die. 

A pipe die provides a carefully sized annular opening for the melt, which then is pulled through a long water trough where it cools. A common sheet die design is shown in Fig. 19.33. The melt from the extruder, which is... 

Why has this formulation been labeled as irrigation pipe or fence substrate. There are many similarities between the two products, and since PVC fence is currently considered a high growth market in North America, several former pipe makers have converted their operations from pipe to fence, even retaining the older pipe dies (square) fed into a rectangular or square final calibrator. 

The next example is more complicated and involves the flow of HOPE through a pipe die. It is important to minimize the temperature increase in a melt due to viscous dissipation. In this case the velocity profile may not be known a priori as it may be affected by the temperature distribution. 

Example 5.3. Nonisothermal Flow of HDPE Through a Pipe Die... 

---