Mandrel head

The Stedman-type column is shown in Fig. 11, 56, 25. The characteristic features are (i) the use of a fine stainless steel wire cloth formed into conical discs, and (ii) an accurately fitting Pyrex glass jacket, produced by shrinking Pyrex glass on mandrels to the required inside dimensions. Modifications incorporating a silvered vacuum jacket and an electrically-heated jacket are marketed. This column is said to possess high efficiency but is expensive. It is generally employed in conjunction with a total-condensation variable take-off still head. 

For rayon fiber based eomposites (Seetions 3 and 4) the fiber and powdered resins were mixed in a water slurry in approximately equal parts by mass. The isotropie piteh earbon fiber eomposites (Seetion 5) were manufaetured with less binder, typically a 4 1 mass ratio of fiber to binder being utilized. The slurry was transferred to a molding tank and the water drawn through a porous sereen under vacuum. In previous studies [2] it was established that a head of water must be maintained over the mold screen in order to prevent the formation of large voids, and thus to assure uniform properties. The fabrieation proeess allows the manufaeture of slab or tubular forms. In the latter case, the cylinders were molded over a perforated tubular mandrel covered with a fine mesh or screen. Moreover, it is possible to mold eontoured plates, and tubes, to near net shape via this synthesis route. 

A numerically controlled filament winder has been designed and constructed. The distance between the head-stock and tail-stock is six feet. Clearance between the centers emd the body of the winder is adjustable, but a specimen several feet in diameter could presently be fabricated. The mandrel and carriage are each driven by one horsepower, direct current motors with a maximum 2000 revolutions per minute. Three phase, 480 volt alternating current is transformed to a 90 volt, direct current power supply. A gear... 

To overcome weld line problems, the cross-head tubing die is often used. Here, the die design is similar to that of the coat-hanger die, but wrapped around a cylinder. This die is depicted in Fig. 3.17. Since the polymer melt must flow around the mandrel, the extruded... 

This is another ramification of incomplete response of polymers, because the experimental time is smaller than the relaxation time of the system of macromolecules. As expected, weld lines are mechanically weak and have optical properties that differ from those of the bulk, making them visible. Furthermore, they result in film or tube gauge nonuniformities, probably because of the different degree of swelling of the melt in the neighborhood of the weld line. They also induce cross-machine pressure nonuniformities. To overcome these problems, basic cross-head die designs (Fig. 12.42) have been devised in which the mandrel is mechanically attached to the die body in such a way that obstacles are not presented to the flow in the annular region. 

In the cross-head type of dies, the melt is split at the inlet to the manifold and recombines 180° from the inlet. Moreover, the flow is not axisymmetric, and fluid particles flowing around the mandrel have a longer distance to travel than those that do not. 

Fig. 14.23 Typical blow molding die A, choke adjusting nut B, mandrel adjustment C, feed throat D, choke screw E, die head F, plastic melt G, die barrel H, heater band /, choke ring J, centering screw K, clamp ring L, die heater M, die N, mandrel. [Reprinted by permission from J. D. Frankland, A High Speed Blow Molding Process, Trans. Soc. Rheol., 19, 371 (1975).]...

FIGURE 14-9 Schematic diagram of the die head and mandrel for a single screw extruder. 

The filling mandrels are comprised of a set of filling tips that are held within a protective air shower this is a small area within the filling machine that is typically fed with sterile filtered air. When the molds are beneath the air shower, the filling tips are lowered into the neck of the partially formed container and the containers are filled. The mandrels then return to the protective air shower, and the containers are sealed by a second mold set (head mold), which forms the neck and closure of the BFS containers. 

FIs. 1 3.36 Prototype pipe welding system showing external friction stir welded head and internal mandrel (inset). Courtesy of MegaStir, Inc. 

Fig. 2.8. A device for feeding a modifier to the extrusion head mandrel of the hose-film aggregate (1) extrusion head (2) mandrel (3) polymer hose (4, 5) and (24) tube and channels for compressed air (6) channel for inhibitor liquid (7) and (8) liquid levels over extrusion head mandrel and in the feeding chamber, respectively (9) Cl feeding chamber (10) and (12) valves (11) float (13) and (14) mains (15) and (16) magnetic distributors (17) pump (18), (19) and (22) taps (20) and (23) accumulator tanks (21) pressure valve...

The polyolefin melt is forced through an annular slot 3 of extrusion head 2 and is blown out into a hose. A solution of Cl that is easily volatile in PI is fed onto the site over the mandrel. The Cl solution dissolved in the varnish based on PVB, CEVA or cellulose acetobutyrate is forced to the surface of a diaphragm Table 2.11. The varnish is poured over the inner surface of the rising hose so as to avoid contact between the lower edge of the annular flow of varnish and the Cl layer. The varnish contacts the colloidal solution of polyolefine with Cl formed in the hose surface layer. Above the solidification line A-A the colloidal solution decomposes into phases and a jelly-like layer is formed. Just in this layer the inhibiting liquid is enclosed in the polymer matrix pores that are thermodynamically compatible with the varnish. The varnish diffuses into the pores and, on setting, forms on the inner hose surface an inhibited varnish coat embedded in the porous layer. 

The extrusion head [94] shown in Fig. 2.21 contains a unit for preparation of the inhibiting mixture that is made as a vortical tube. The polymer melt is fed from extruder 7 into annular slot 6 formed by mandrel 9 and nozzle 5, and is squeezed as a hose 3. The compressed air is fed into nozzle 10 of scroll 11, and into nozzle 15, and Cl is fed from tank 14 in a liquid or gaseous state. The compressed air and Cl are accelerated in the scroll over the spiral and form a swirl flow of a homogeneous mixture in duct 8. The peripheral layers of the flow become heated and the Cl (if it is a liquid) evaporates, whereas... 

Fig. 2.21. An extrusion head with a vortical unit for Cl feeding to the mandrel...

It is not always possible to elevate the liquid level fed to the extrusion head mandrel and escape high hydrostatic pressure (see Fig. 2.5e) lest the hose should rupture. To avoid this, the Cl is applied on the hose wall during rotation [98]. The liquid vortex formed this way promotes the required level of the liquid on the mandrel near the hose surface, making use of a minimum amount of Cl and changing the rotation velocity of the hose. The dynamic interaction of the hose and the Cl intensifies its diffusion into the polymer material, breaks the vapor jacket at the inhibitor-hose interface and facilitates the uniform distribution of Cl pressure, minimizing the probability of hose rupture. 

Forcing of Cl into the head die is a multifunctional operation leading to reduced friction of the melt against the die walls, in addition to improved orientation stretching and reinforcement of the film. The distinguishing feature of the employed extrusion head [100] (Fig. 2.24) is the presence of an annular chamber 6 in mandrel 4. The chamber communicates with Cl channel 8 and is shut off by a porous wall 5 from the side of channel 7 over which the polymer melt is fed from the extruder into the head. The outside surface (a) of the porous wall 5 and inner surface (b) of matrix 1 are made in the form of a cone whose apex faces the side opposite to the inlet to channel 7. 

The blown-film technique is widely used in the manufacture of polyethylene and other plastic films [14,15]. A typical setup is shown in Figure 2.23. In this case the molten polymer from the extruder head enters the die, where it flows round a mandrel and emerges through a ring-shaped opening in the form of a tube. The tube is expanded into a bubble of the required diameter by the pressure of internal air admitted through the center of the mandrel. The air contained in the bubble carmot escape because it is sealed by the die at one end and by the nip (or pinch) rolls at the other, so it acts like a permanent shaping mandrel once it has been injected. An even pressure of air is maintained to ensure urufoim thickness of the film bubble. 

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