Coat hanger

The simplest molds consist of two parts one fixed and one moveable. We use such molds to fabricate items, such as disposable stadium cups, compact disks, and coat hangers, which have simple designs with no undercuts. As the complexity of the product increases, so must the complexity of the mold. The molds used to produce large items, such as dishwasher tubs and automobile bumpers, may consist of multiple moveable components and weigh several tons. Even apparently simple items, such as screw tops for bottles, require a complex ejection system that unscrews the product from part of the mold. In order to facilitate cooling, virtually all molds are designed with liquid cooling channels. 

He bought over HOOg of platinum/irldium from a number of suppliers. The wire was bent into coat hangers. 

Figure 5. Here, a coat hanger has been modified to support an aerosol monitoring cassette and sampling hose.

Flat Film Extrusion In flat film extrusion, the melt is extruded through a long slot in a T or coat hanger-type die, past the die lands. In this setup, the polymer melt is forced into the slot die at its center it reaches the slot opening by way of a manifold and over the lands. The principal advantages of film casting are substantial improvements in the film s transparency, freedom from haze, improved gloss, and other optical properties. 

Sheeting dies. One of the most widely used extrusion dies is the coat-hanger sheeting die. A sheeting die, such as the one depicted in Fig. 3.14, is formed by the following elements ... 

To generate a uniform extrudate geometry at the die lips, the geometry of the manifold must be specified appropriately. Figure 3.15 presents the schematic of a coat-hanger die with a pressure distribution that corresponds to a die that renders a uniform extrudate. It is important to mention that the flow through the manifold and the approach zone depend on the non-Newtonian properties of the polymer extruded. Hence, a die designed for one material does not necessarily work for another. 

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... 

Figure 6.12 Schematic diagram of a coat hanger sheeting die.

Perhaps a more common sheeting die is the so-called coat hanger die, presented in detail in Chapter 3. For a given manifold angle a we must determine the manifold radius profile, R(s), such that a uniform sheet or film is extruded through the die lips. 

A cross-head tubing die is equivalent to the coat hanger die by wrapping it around a cylinder as can be recognized in the schematic presented in Fig. 3.17. If we follow the same derivation but for a shear thinning power law melt, we get... 

Derive the die design equation (eqn. (6.50)) for a coat hanger die assuming a shear thinning power law viscosity model. 

Figure 12.29 presents the geometrical features of the coat-hanger die, on which the design equation will be developed. The manifold is a tubular, variable radius channel of curved axis /. The slit opening H is constant. The only geometric restriction is that the manifold be of a small curvature, so that the lubrication approximation can be applied in the manifold region. Also, for the same reason, dR(x)/dx [Pg.706]

Example 12.2 Coat Hanger Die Design We specify the coat hanger die manifold radius along the entire width of the die, if the manifold axis is straight and makes an angle a = 5° with the x coordinate (see Fig. 12.29). The slit opening is set at H — 0.05 cm, the half-width W = 100 cm, and the Power Law index of the polymer melt n — 0.5. 

Unlike the coat hanger flat film dies, no simple final film adjustment is possible by lip flexing. Consequently, the order of magnitude of thickness accuracy in tubular dies is 10% as compared to 5% in flat sheet and film dies. This larger margin of accuracy in blown film dies is compensated by die rotation, which permits the distribution of the thickness variation across the entire width of the product. 

In a 200 mm OPS line, the die is usually 1.0-1.3 m wide. These dies are generally of the coat hanger manifold design with separate choker bar and... 

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