Plastic article or earthenware shaping or treating: apparatus – Control means responsive to or actuated by means sensing or... – Feed control of material en route to shaping area
Patent
1987-11-20
1989-07-11
Chiesa, Richard L.
Plastic article or earthenware shaping or treating: apparatus
Control means responsive to or actuated by means sensing or...
Feed control of material en route to shaping area
264 403, 425146, 425171, 425562, B29C 4577
Patent
active
048466514
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION
This invention relates to an injection molding machine arranged to charge molten resin in a mold cavity, and more particularly to an injection molding machine having a device for controlling the injection speed of the molten resin during the charging process thereof and a device for controlling dwell pressure application after the completion of charging of the molten resin.
BACKGROUND TECHNIQUE OF THE INVENTION
There has heretofore been known such an injection molding machine as disclosed, for example, in Japanese Patent Publication No. 57-59060 which is arranged to inject and charge the molten resin in a mold cavity from an injection nozzle by forwardly moving an injection screw mounted so as to be rotatively driven and reciprocated freely in a housing by the action of an injection cylinder located behind the base end of the screw.
Generally, in injection molding machines, it is necessary to control the injection speed of the molten resin to be charged into the mold cavity depending on the position of the injection screw.
The injection speed in the above-mentioned conventional injection molding machine is determined by the travel speed of the injection screw, that is, the speed of expansion of the injection cylinder, and therefore, in order to control the injection speed, there is no alternative to controlling the volume of hydraulic oil to be supplied into the expansible pressure chamber in the injection cylinder depending on the position of the injection screw to vary the speed of expansion of the injection cylinder as disclosed, for example, in Japanese Patent Application Laid-Open Specification No. 59-64337.
However, since there is a time-lag between the time the speed of expansion of the injection cylinder is changed and the time when the speed and flow rate of the molten resin passing through the injection nozzle and flowing into the mold cavity are varied, the injection speed cannot be controlled rapidly and with a high accuracy depending on the position of the injection screw.
Stated in more detail, since the molten resin itself has compressive properties, the travel speed of the injection screw does not always correspond to the injection speed of the molten resin from the injection nozzle. Therefore, there are instances where even though the speed of travel of the injection screw is controlled with a high accuracy, the accuracy of controlling the injection speed cannot be improved and such a control as to obtain a predetermined injection speed corresponding to the position of the injection screw cannot be achieved.
That is, when the injection screw forces the molten resin during, for example, the resin charging process, the pressure of the molten resin within the housing formed in the leading end of the injection screw is raised. Even if the forward movement of the injection screw is stopped in this condition, the compressed molten resin within the housing flows out from the injection nozzle into the mold cavity until its pressure has reduced to the level corresponding to the loading pressure within the mold, and as a result, there occurs some delay in response until the injection speed becomes zero.
Further, in case of rapidly accelerating the speed of travel of the injection screw from the condition wherein said speed has been changed over to thereby rapidly accelerate the injection speed, it is necessary to obtain momentarily the injection speed corresponding to the speed of travel of the injection screw. But, in order to meet this requirement, the pressure of the molten resin in the housing needs also to be increased correspondingly. As a matter of fact, however, there is some time lag until the pressure of the molten resin increases to such a level, and as a result, there is a corresponding delay in response until the injection speed is increased.
Stated concretely, in the case where a product whose shape varies steeply at two places as shown, for example, in FIG. 1 is produced by injection molding, in order to prevent the occurrence of surface imperfecti
Funabashi Tetsuji
Inaba Nobuaki
Kaminishi Masashi
Matsuda Kazuo
Tanaka Nobukazu
Chiesa Richard L.
Heitbrink Timothy W.
Kabushiki Kaisha Komatsu Seisakusho
Kananen Ronald P.
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