| 摘要 |
PURPOSE:To stably perform molding for a long time without generating a surface or internal flaw by once extruding a molten resin in the air to stretch and move the extrudate at specific stretching speed and subsequently holding the deflection rate thereof in a cooling medium to a specific value. CONSTITUTION:Polyoxymethylene supplied from a hopper 1 is melted and plasticized by an extruder 2 to be extruded from a heated double die 3 and the extrudate is once exposed to the air to be cooled in a cooling tank 7 filled with a cooling medium. As the fluid introduced from the orifice of an inner die, air is generally used and, as the cooling medium, water is generally used. The stretching speed of polyoxymethylene in the exposed part is set to the range of 150 - 600min<-1>. When the stretching speed is below 150min<-1>, the fluctuation of an outer diameter and surface unevenness are generated and, when the stretching speed exceeds 600min<-1>, the large fluctuation of an outer diameter is brought about to generate cutting. The deflection rate in the cooling medium is set to 80 or more. When the deflection rate is 80 or less, the shaking in the cooling medium becomes violent. |
