Optimal Design of Spiral die for Physical Foaming and blown film extrusion Process

• Main Authors: xein-min Chang, 張憲民
• Other Authors: Jiann-Shing Wu
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/94313729520286970079

碩士 === 國立交通大學 === 應用化學系所 === 92 === The purpose of the present study is to establish an analytical program for spiral die with physical foaming agent. First, we predict the viscosity of melt polymer with foaming agent mathematically, and establish the flow model by fluid dynamics. Applying the Sanchez-Lacombe equation, we can calculate the weight percentage of foaming agent in melt polymer at any pressure and temperature. As predicted, more foaming agent can be dissolved into melt polymer at a high pressure or low temperature. The parameters of spiral die include DEPTH, WCHAN, GIBC, HBC, NOSEC, θ and α. Second, we use the Tguchi method to search several optimal sets of die geometric parameters by assessing the flow uniformity(UNI) and mixing degree(MD) isothermally and create ANOVA tables. From ANOVA tables, we realize that the seven parameters can totally describe the flow situation in spiral die. At the same time, we find that whatever the number of channels is, the most relevant parameters with respect to MD are DEPTH,WCHAN and GIBC; with respect to UNI, WCHAN and NOSEC are the most relevant parameters; furthermore, with respect to pressure gradient, GIBC及ALFAR are the most relevant. During polymer foaming, if the local die pressure cannot reach the critical pressure, prefoaming occurs. Therefore, at the outlet of spiral die, we narrow down the channel depth to increase the local pressure, which is thus greater than critical pressure. Finally, with die lip being attached to spiral die, we examine the non-isothermal condition, so that an analytical program for spiral die with physical foaming agent can be established.