| 摘要 |
<p>PURPOSE: To avoid significant and permanent distortion under temperatures and pressures of a retort chamber by heating plastic blanks on a conveying means to a melting temperature enough to remove an internal stresses through a heating means. CONSTITUTION: Radiant heat emanating from heaters 40A, 40B of an oven 40 penetrate the top and bottom surfaces of each plastic blank 22. Because the blank 22 is almost completely exposed to heat except for the bottom peripheral edge, the temperature is uniform across such surfaces of the plastic blank 22. The dwell time of each tray 36 carrying the plastic blanks 22 through the oven 22 is sufficient to raise the temperature of each blank 22 to its melting point. The temperature inside the oven 40 is constantly sensed and controlled by a computerized system and the plastic blank 22 exiting the oven 40 is heated to the selected melting temperature. The internal stresses created in extruding the sheet of plastic material and remaining in the cut blanks 22 are relieved at this predetermined crystalline melting temperature.</p> |
