COOLING SECTIONS IN POLYOLEFIN PIPE EXTRUSION

Cooling equipment used in polyolefin pipe extrusion is designed purely empirically. There is but little information about the required lengths and the construction of calibrating and cooling sections. In particular, the application of a given set of figures to other pipe production lines through scaling-up or scaling-down, is impractical. Thick-walled polyolefin pipes, i. e. pipes for medium to high pressures, take very long to cool because of the poor thermal conductivity of polyolefins. The great temperature differences in the pipe wall during cooling result in thermal stresses being produced in the pipe. These internal stresses can be reduced by conditioning along the cooling section. High take-off speeds are desirable in the extrusion of small-bore polyolefin pipes. Here, the use of draw plates in a vacuum tank has proved successful for calibrating, combined with a vary thin film of water which is allowed to trickle on to the pipe before it enters the calibrating section. For figures see German Text.