Coat Hanger Dies
“Large sheet dies are construction with two configurations: A ``T" type feed and a``coat hanger" type feed (Figure 5-39). Both die configurations consist of a large feed channel that directs melted plastics to the back edge of a deck surface. The deck reduces the flow and equalizes the pressure within the back of the die. As the pressure increases behind the deck, the plastic is forced over the deck and out through the die slit. The configuration of the ``T-type" die requires the plastics to travel a much greater distance to fill the end of the ``T". This reduces the pressure at the ends and increases the amount of residence time the plastics is in the die feed channel. The ``Coat-Hanger-type" overcomes this problem by extending the middle section of the die in the shape of a coat hanger. This construction equalizes the distance that the plastic melt must travel along the entire length of the die slit. With a properly designed coat hanger die all plastics experience the same residence time and the same pressure drop.” (Extrusion Dies, 11/3/2011)
Recent Journal Articles
Optimal geometry design of the coat-hanger die with uniform outlet velocity and minimal residence time
(2511–2516)Journal of Applied Polymer Science 123 #4 (2012)
Han and Wang of Donghua University, China, combined the orthogonal array design and the numerical simulation to optimize the geometry parameters of the coat-hanger die with uniform outlet velocity and minimal residence time. The outlet velocity and the residence time are obtained by simulating the three-dimensional nonisothermal polymer flow in the coat-hanger die, while the optimal geometry design is accomplished via the orthogonal array method. The results show that the effects of all the three parameters are significant for the outlet velocity. For the residence time, the manifold angle and the slot gap are the significant factors, while the effect of the land height is insignificant. The optimal geometry parameters of the coat-hanger die achieved in this study are that the manifold angle is 5°, the height land is 70 mm, and the slot gap is 3 mm. (RDC 11/2/2011)