Abstract A simple model based on the lubrication approximation has been developed to analyze heat transfer of power‐law fluids inside an extrusion die. This model can effectively predict the influence of temperature variations and other production alterations on flow uniformity. The predictions of this model are compared with those based on three‐dimensional finite element simulation, and the agreement is satisfactory. The optimal design concept can be incorporated into this model so that a specially designed choker bar can be inserted into the extrusion die to reduce flow nonuniformities. The shape of the choker bar is initially suggested by the lubrication model; minor corrections through the three‐dimensional finite element simulation are then introduced so that a choker bar can be properly constructed to eliminate flow nonuniformities.
This chapter presents design formulas that can be used to construct tapered choker bars so that trial-and-error approaches can be eliminated and an extrusion die should be much more flexible to handle different production requirements. Owing to the complex geometry of extrusion dies, it is impractical to design dies based purely on trial-and-error approaches; mathematical modeling is usually required. Extrusion dies are necessary for the production of wide polymer and metal films or sheets and are also required to generate thin liquid layers for many coating operations. A liquid enters the interior of the die through the inlet tube; after filling the manifold, the liquid will move forward through the slot section and form a wide and thin liquid layer.
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