| 摘要 |
<p>In the production of a tubular extruded section of thermoplastic material, the actual length of an extruded section at the end of the extrusion operation may be smaller or greater than the length of the extruded section which passed through the discharge orifice of the extrusion head during extrusion. If the wall thickness of the extruded section is varied during extrusion in accordance with a given program, inaccuracies in regard to distribution of the wall thickness over the length of the extruded section can be reduced by detecting the length of the extruded section which passes through the discharge orifice, and controlling the means for producing the programmed variation in wall thickness, in dependence on that discharge length. The same effect can be achieved by controlling the means for producing the programmed variation in wall thickness, in dependence on discharge speed and time. A higher degree of accuracy can be achieved by measuring the discharge length or discharge speed on the one hand and on the other hand the respective associated effective length of the extruded section, or the speed of movement of the free end of the extruded section, comparing those two detected values, and producing corrective variations in wall thickness in dependence on the result of the comparison operation.</p> |
