Injection molding method and apparatus with magnetic mold clamping

A method for clamping a pair of molds, which comprises the steps of:

• (a) moving two platens relatively towards each other;
• (b) stopping both of the platens in a position where a minute gap is produced between abutting surfaces of both of the molds;
• (c) pouring a raw molding material into the molds;
• (d) after a preset time period has elapsed from initiation of said step (c), producing a magnetic attracting force between both of the platens by magnetic attracting force generating means to thereby produce a predetermined mold clamping force between the two molds.

A mold clamping device

• in an infection molding machine, comprising:
• a first platen for retaining a first mold therein and a second platen for retaining a second mold therein, said first and second platens being arranged on a table on which an injection device is mounted;
• a platen feeding means for moving said first and second platens relative to each other on said table;
• a magnetic attracting force generating means, comprising an electromagnetic coil, arranged in at least one of said first and second platens, said electromagnetic coil being arranged so as to enclose the periphery of at least one of the first and second molds;
• and
• a magnetic attracting force controlling means for controlling the magnetic attracting force of said magnetic attracting force generating means;
• wherein a groove member comprising magnetic material having a great maximum magnetic flux is embedded in at least one of the first platen and second platen, the opening side of said groove member being directed towards the surface of the opposing platen, and said electromagnetic coil is arranged within said groove member.

A mold clamping device in an infection molding machine, comprising:

• a first platen for retaining a first mold therein and a second platen for retaining a second mold therein, said first and second platens being arranged on a table on which an injection device is mounted;
• a platen feeding means for moving said first and second platens relative to each other on said table;
• a magnetic attracting force generating means, comprising an electromagnetic coil, arranged in at least one of said first and second platens, said electromagnetic coil being arranged so as to enclose the periphery of at least one of the first and second molds;
• a magnetic attracting force controlling means for controlling the magnetic attracting force of said magnetic attracting force generating means;
• and
• guide means, provided on said table, for slidably moving at least one of said first and second platens;
• wherein said electromagnetic coil is attached to an adjusting member mounted on one of the first platen and second platen for movement in the same direction as that of the guide means.

A mold clamping device in an injection molding machine, comprising:

• a first platen for retaining a first mold therein and a second platen for retaining a second mold therein, said first and second platens being arranged on a table on which an injection device is mounted;
• a platen feeding means for moving said first and second platens relative to each other on said table;
• a magnetic attracting force generating means arranged in at least one of said first and second platens;
• and
• a magnetic attracting force controlling means for controlling the magnetic attracting force of said magnetic attracting force generating means;
• wherein striking pins, which are movable forward and backward with respect to the opposite surface of one of the first and the second platen, are mounted on any one of the first and second platens for biasing against one of said first platen and second platen to open said mold clamping device, each of said striking pins having a front portion having a first diameter and a middle portion having a second diameter, said second diameter being greater than said first diameter.