Coat hanger design, manifolds

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. 

A basic problem with the coat hanger design is that it causes the distance from the lip exit to the back of the manifold to be longest at the... 

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. 

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]

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... 

Fig. 2 Comparing designs of T-type die (A) [(1) constant cross-section manifold (2) constant land length] to coat hanger-type die (B) [(1) manifold cross-section decreases as distance from centerline increases (2) land length becomes shorter farther from the centerline of the die].

Figure 5.42 Manifold designs (a) T manifold and (b) coat-hanger manifold. ...

In this chapter, we have described a novel design approach to correct flow nonuniformities caused by four types of production variations in a linearly tapered coat-hanger die. The theoretical approach is based on the onedimensional lubrication approximation and can be used to predict the taper function of an adjustable choker bar. Once a choker bar is constructed based on the prediction of the mathematical model, the flow nonuniformities can be properly eliminated by inserting this bar into the die. A choker bar can be tapered in different ways as indicated in Fig. 3. The shape displayed in Fig. 3a may be easier to machine and was selected for illustration. The four production variations we have considered include (i) enlarging the manifold, (ii) including the fluid inertial terms, (iii) varying the viscosity of the polymeric liquids, and (iv) narrowing the liquid film width to meet production requirements. All these four production variations can be properly handled, but if the fluid inertia becomes dominant, or the Reynolds number is not small, the present method may not be applicable. 

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