Foam extrusion

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Foam extrusion Process for producing plastic sheet of cellular construction. Either a chemical or a gaseous blowing agent is introduced into the polymer melt while the melt is being prepared in the extruder barrel. As the plastic melt exits the die, it expands a predetermined amount, forming a cellular wall.

Machine and method

A foam extrusion machine and method in which extrudate is extruded into a sealed chamber which may be subjected to pressure variation such as a vacuum with the controlled shaping of the plastic being obtained by power driven rolls within the chamber downstream of the die. Because of the harsh environmental conditions within the chamber it is desirable that the shaping or forming rolls be driven by an externally powered source which will therefore be not subject to the pressure, vacuum, or other deliterious conditions found within the chamber. Moreover, because of the external position of the drive with regard to the chamber, the entire system need not then be shut down in order to open the chamber and make the required adjustments or repairs. The chamber is preferably the upper end of a barometric leg into which the extrudate passes. The upper end of the chamber is closed by one or more bulkheads which are movable toward and away from the upper end of the chamber. The present invention utilizes DC drive motors on the exterior of the bulkheads and of course the chamber to drive the shaping rolls which are downstream of the die. With this arrangement, both torque and speed may be closely controlled and of course the chamber does not require to be opened to make adjustments, replacements or repairs to the power system.