Mechanism for closing and opening injection molds

Claim 2

In an injection molding machine comprising a frame, a substantially stationary platen on said frame adapted to support a first mold portion, a set of tie bars having forward ends anchored to said stationary platen, and a movable platen slidable along said tie bars and adapted to support a second mold portion, the combination therewith of mechanism for reciprocating said movable platen on said tie bars between an advanced position of mold closure and a retracted position of mold opening, said mechanism comprising: a lead screw parallel to said tie bars, said lead screw having a rear end remote from said platen for axial reciprocation therewith; a nut threadedly engaging said rear end of the lead screw, said nut being rotatably mounted on said frame with freedom of limited axial displacement relative thereto; reversible drive means for rotating said nut to advance and retract said lead screw together with said movable platen; and actuating means operable by fluid pressure, upon deactivation of said drive means in said advanced position of said movable platen, to bear upon said nut in a forward direction for clamping said mold portions tightly between said platens, said actuating means including a cylinder mounted on said frame rearwardly of said tie bars, a piston disposed rearwardly of said nut and movable within said cylinder in axial direction of said lead screw, said piston and said nut being provided with confronting contact surfaces, and biasing means tending to maintain said contact surfaces axially separated by a small clearance, said clearance being reduced by continuing rotation of said nut upon arrestation of said lead screw in said advanced position.

Claim 3

The combination defined in claim 1 wherein said drive means includes a rotatable but axially fixed collar on said frame coaxial with said nut and keyed thereto on the side remote from said piston, and transmission means for imparting rotation to said collar.

Claim 4

The combination defined in claim 1 wherein said actuating means comprises a cylinder mounted on said frame, a piston movable within said cylinder in axial direction of said lead screw, said piston and said nut being provided with confronting contact surfaces, and biasing means tending to maintain said contact surfaces axially separated by a small clearance, said clearance being reduced by continuing rotation of said nut upon arrestation of said lead screw in said advanced position.

Claim 5

The combination defined in claim 1, further comprising resilient loading means bearing upon said piston for limiting the width of said clearance.

Claim 6

The combination defined in claim 1 wherein said actuating means includes first valve means responsive to arrival of said movable platen in said advanced position for admitting pressure fluid to a rear face of said piston substantially concurrently with deactivation of said drive means, second valve means for admitting pressure fluid to a front face of said piston substantially concurrently with reactivation of said drive means at the beginning of a retraction stroke, and switch means for disabling said second valve means upon the reestablishment of said clearance during said retraction stroke.

Claim 7

The combination defined in claim 5 wherein said switch means is disposed in said clearance for operation by one of said contact surfaces.

Claim 8

The combination defined in claim 1 wherein said cylinder has a body surrounding said piston and a forward extension enveloping said nut, said drive means being mounted at least in part on said extension.

Claim 9

The combination defined in claim 7 wherein said tie bars have rear ends secured to said extension forwardly of said body, said cylinder and said stationary platen being positioned on said frame with freedom of limited relative axial displacement permitting elastic stretching of said tie bars.

Claim 10

The combination defined in claim 8, further comprising an axially shiftable plate on said tie bars between said extension and said movable platen, an array of ejector members extending forwardly from said plate toward said movable platen for penetration thereof, and operating means for said ejector means carried by said movable platen and coupled with said plate.

Claim 11

The combination defined in claim 7 wherein said body has a radius greater than the distance of any of said tie bars from the lead screw axis.

Claim 12

The combination defined in claim 1 wherein said drive means is provided with speed control means for slowing the advance of said movable platen in a terminal phase of its forward stroke.

Claim 13

In an injection molding machine comprising a frame, a substantially stationary platen on said frame adapted to support a first mold portion, a set of tie bars having forward ends anchored to said stationary platen, and a movable platen slidable along said tie bars and adapted to support a second mold portion, the combination therewith of mechanism for reciprocating said movable platen on said tie bars between an advanced position of mold closure and a retracted position of mold opening, said mechanism comprising: a lead screw parallel to said tie bars, said lead screw havinG a rear end remote from said platens and a front end nonrotatably secured to said movable platen for axial reciprocation therewith; a nut member threadedly engaging said lead screw, said nut member being rotatably mounted on said frame with freedom of limited axial displacement relative thereto; reversible drive means for rotating said nut member to advance and retract said lead screw together with said movable platen; actuating means operable by fluid pressure, upon deactivation of said drive means in said advanced position of said movable platen, to bear upon said nut member in a forward direction for clamping said mold portions tightly between said platens, said actuating means including a cylinder mounted on said frame, a piston member movable within said cylinder in axial direction of said lead screw, said piston and nut members being provided with confronting contact surfaces, and biasing means tending to maintain said contact surfaces axially separated by a small clearance, said clearance being reduced by continuing rotation of said nut upon arrestation of said lead screw in said advanced position; switch means on one of said members responsive to the proximity of the other of said members for generating a signal indicating a substantial reduction of said clearance; and fluid pressure means controlled by said switch means upon reversal of said drive means in said advanced position for restoring said clearance preparatorily to retraction of said lead screw.

Claim 14

In an injection molding machine comprising a frame, a substantially stationary platen on said frame adapted to support a first mold portion, a set of tie bars having forward ends anchored to said stationary platen, and a movable platen slidable along said tie bars and adapted to support a second mold portion, the combination therewith of mechanism for reciprocating said movable platen on said tie bars between an advanced position of mold closure and a retracted position of mold opening, said mechanism comprising: a lead screw parallel to said tie bars, said lead screw havinG a rear end remote from said platens and a front end nonrotatably secured to said movable platen for axial reciprocation therewith; a nut member threadedly engaging said lead screw, said nut member being rotatably mounted on said frame with freedom of limited axial displacement relative thereto; reversible drive means for rotating said nut member to advance and retract said lead screw together with said movable platen; actuating means operable by fluid pressure, upon deactivation of said drive means in said advanced position of said movable platen, to bear upon said nut member in a forward direction for clamping said mold portions tightly between said platens, said actuating means including a cylinder mounted on said frame, a piston member movable within said cylinder in axial direction of said lead screw, said piston and nut members being provided with confronting contact surfaces, and biasing means tending to maintain said contact surfaces axially separated by a small clearance, said clearance being reduced by continuing rotation of said nut upon arrestation of said lead screw in said advanced position; switch means on one of said members responsive to the proximity of the other of said members for generating a signal indicating a substantial reduction of said clearance; and fluid pressure means controlled by said switch means upon reversal of said drive means in said advanced position for restoring said clearance preparatorily to retraction of said lead screw.