Study of processing of extruded structural foam. Part 1 - Celuka® process

The well known Celuka® process for the manufacture of extruded structural foams has been investigated. Experimental results indicate that to prevent a poor surface quality in the product, gap size of the die exit is critical and the curvature of the side walls of the calibrator must be small. By vacuuming the calibrator, product shrinkage can be significantly improved. To prevent voids from occurring inside the product, one of the following condition changes can be made: increase the concentration of blowing agent, increase the die temperature, increase the calibrator temperature, increase the screw speed, or lower the take off speed. An unstable extrusion output rate, inappropriate processing conditions, inaccurate control of the take off system, or an inaccurate alignment of the entire equipment may result in overflow, which subsequently causes an interruption to the process. Achieving a stable operation requires a take off speed within upper and lower bounds (an operation window) and precise control of both the extruder and the take off system. The operation window for the take off speed may be broadened under one of the following conditions: a higher blowing agent concentration, a higher die temperature, or a higher calibrator temperature.