| 摘要 |
PURPOSE:To make the amount of contraction zero or very small and improve dimensional accuracy, by a method wherein the objective value of a pressure in a mold is set to a pressure, in which a specific volume of molten resin becomes equal to a specific volume under a normal pressure and a normal temperature or a softening temperature of the resin, and a resin passage is closed by this pressure after filling the resin. CONSTITUTION:The closing mechanism of a resin passage is provided between a nozzle 7 and a cylinder 18 while the closing mechanism is constitued of a needle 21 reciprocating in a needle valve 20 to open and close the resin passageway at the tip end of the nozzle 7, a piston rod 24 pivoting a lever 22, and a hydraulic cylinder 23. The objective value of a pressure in a mold is set to a pressure equal to a specific volume under a normal pressure and a normal temperature when molten resin is compressed by high-speed filling under adiabatic condition. When the resin passage is closed and the resin is cooled after the pressure in the mold has arrived at the pressure of the objective value, a necessary amount of resin under a normal temperature and a normal pressure is kept by the same volume, and the specific volume is not changed due to the cooling. Moreover, the resin passage is closed, therefore, the resin will never flow in a pressure keeping process and an excessive high pressure is not applied onto a gate, therefore, faulty size due to the strain of the gate or the like may be prevented.
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