Melt cooler for an extruder comprises cooled inner and outer tubes forming an intermediate melt flow chamber and barrier directs flow from inner chamber to intermediate chamber and back to inner chamber

摘要

A cooled inner tube(1) is surrounded by an outer tube(2) to form an intermediate chamber(18). The inner tube includes a barrier(7) which diverts melt flow from an inner chamber(17) on the inlet side of the cooler into bores(15) leading to the intermediate chamber. Radial bores(15) in the inner tube(1) between the intermediate chamber(18) and inner chamber(17) on the outlet side of the barrier(7) allow melt to flow back into the inner chamber from the intermediate chamber. Bore diameter is 4-15mm, preferably 6-12mm and more preferably 7-10mm. Bore spacing and spacing from channels is not less than1mm, preferably not less than2mm, more preferably 10mm and even more preferably equal to bore diameter. Helical coolant channels(3) extend around the outer and/or inner sides of the inner tube. Channel depth is 20-50mm, preferably 25-40mm and the cross-section is rectangular, with a breadth of 2-10mm, preferably 3-8mm and more preferably 4-7mm. Channel depth is not less than50%, preferably not less than60% and more preferably not less than70% of tube thickness. Flow cross-section for melt in the cooler deviates by not 20%, preferably not 10% and more preferably not 5% of inlet cross-section into the cooler. Flow cross-section of the inner chamber(17) on the inlet side reduces towards the barrier and on the outlet side increases from the barrier towards the outlet. Flow cross-section on the inlet side is reduced by a conical mandrel with a tip facing the incoming flow. Conversely on the outlet side the mandrel tapers to a tip at the outlet end. The mandrel is screwed and/or welded onto an internal collar of the inner tube which forms the flow barrier. The outer pipe is cooled Maximum external diameter of the cooler is 500mm, preferably 450mm, more preferably 400mm. Cooler length is not less than300mm, preferably 400mm and more preferably 1800mm with a most preferred length of not 1300mm. Several coolers can be arranged in series or parallel.