JPS614646B

PURPOSE:To obtain a polyester pipe molded by extrusion which is superior in dimensional accuracy through keeping film heat transfer coefficient and residence time of the surface of pipe in the water within a specified scope at quenching the pipe in the water below specified temperature. CONSTITUTION:After extrusion from a pipe die 3, polyester over 0.7 in ultimate viscosity with polyethylene terephtalate as the main constituent is formed into a pipe through a molding die 6. Then, it is quenched in the water below 15 deg.C in a vacuum forming tank 5 and a cooling water tank 8 under the conditions that film heat transfer coefficient of the surface of pipe in the water is more than 200 Kcal/m hr deg.C and residence time satisfies a formula t>=10X (-35)X(+50) (t being residence seconds and x pipe wall thickness in mm). For prevention of drawdown at the same time, fusion viscosity of polyester at the outlet of a pipe die 3 is kept more than 7,000 poise, and also for prevention of the pipe from being crystallized to whitening, fusion temperature at one portion at least on an extruding machine is kept more than 270 deg.C.