Plastic article or earthenware shaping or treating: apparatus – Female mold and charger to supply fluent stock under... – With means to close mold
Reexamination Certificate
1999-03-05
2001-02-13
Mackey, James P. (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Female mold and charger to supply fluent stock under...
With means to close mold
C425S595000, C425S451200, C425S451700, C425S451900
Reexamination Certificate
active
06186770
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to clamping assemblies for injection molding, and, more particularly, to clamping assemblies for injection molding in which both closure of a mold and clamping during injection are achieved by relative rotation of complementary threaded elements.
A typical injection molding machine features a fixed platen and a complementary movable platen. The two platens are designed to come together so as to close between them a multi-part, typically a two-part, mold. With the two parts of the mold held firmly together, a molten plastic is injected under great pressure into the mold, thereby filling it. Once the plastic has cooled and hardened, the two parts of the mold are separated and the finished item is removed prior to repetition of the cycle.
This process requires two types of clamping displacement of the movable platen relative to the fixed platen. Firstly, the movable platen must provide an opening and closing function to allow removal of finished items and replacement of mold parts. This movement requires relatively small forces (typically not more than a few tons) but should occur as rapidly as possible to minimize wasted production time between injections. Secondly, during the injection process itself, very large clamping forces (with displacement of no more than a few millimeters) must be applied to prevent leakage from the mold under the high injection pressures used. Depending upon the size of machine and the particular application, clamping forces of tens or hundreds of tons may be required.
These two types of motion have commonly been achieved by use of a hydraulic piston or toggle mechanism located to the rear of the movable platen. However, the mechanical requirements to provide both the long range of movement and the large clamping forces required render these devices bulky. As a result, the clamping device frequently occupies more than 20% of the total length of the machine.
Various attempts have been made to arrive at a more compact clamping mechanism. One such attempt is disclosed in U.S. Pat. No. 5,776,516 to Armbrüster et al., which employs tiebars as clamping pins. A quick-locking mechanism fixes the effective length of the tiebars close to the movable platen and a set of short high-power pistons located on the fixed platen draws the tiebars to provide the required clamping force. Opening and closing movement is generated while the quick-locking mechanism is released by a separate low-power hydraulic piston adjacent to the platens.
Turning now briefly to clamping techniques known in other fields, there exist many clamping devices which are tightened by relative rotation of a threaded bolt and an internally threaded bushing. Such devices offer considerable advantages, providing large clamping forces from relatively low-power actuators such as electric or pneumatic motors. Devices of this type suffer, however, from problems associated with the large frictional losses inherent to conventional threaded connections, rendering them inferior for applications in which significant opening and closing movements are required frequently. For this and other reasons, clamping based on relative rotation of threaded elements has not been used for injection machine clamping applications.
There is therefore a need for a compact clamping assembly for injection molding machines which would employ relative rotation of complementary threaded elements to achieve both the opening/closing displacement and the required clamping forces between a movable platen and a fixed platen, providing a compact and efficient device.
SUMMARY OF THE INVENTION
The present invention is a clamping assembly for injection molding in which both an opening/closing displacement and clamping during injection are achieved by relative rotation of complementary threaded elements.
According to the teachings of the present invention there is provided, a clamping assembly for an injection molding apparatus comprising: (a) a base; (b) a first platen attached to the base; (c) a second platen slidingly associated with the base so as to be slidable towards and away from the first platen; (d) a plurality of tiebars mechanically linked to each of the first and second platens through a plurality of mechanical linkages; and (e) an actuation system associated with the plurality of tiebars and with at least one of the first and second platens and configured to generate movement of the second platen relative to the first platen, wherein at least a portion of each of the tiebars is threaded, and wherein the mechanical linkage between each of the tiebars and at least one of the first and second platens includes a threaded bushing engaged with the threaded portion, the actuation system being configured to generate relative rotation between each of the tiebars and a corresponding one of the threaded bushings.
According to a further feature of the present invention, the actuation system includes: (a) a first drive mechanism configured to generate relative rotation between each of the tiebars and a corresponding one of the threaded bushings so as to provide a first closing force directed to move the second platen towards the first platen; and (b) a second drive mechanism configured to apply a clamping torque between each of the tiebars and a corresponding one of the threaded bushings so as to generate a second closing force, the second closing force being at least an order of magnitude greater than the first closing force.
According to a further feature of the present invention, the first drive mechanism is configured to rotate the threaded bushings relative to the base.
According to an alternative feature of the present invention, the first drive mechanism is configured to rotate the tiebars relative to the base.
According to a further feature of the present invention, the first drive mechanism includes a mechanical link configured to maintain relative rotation between all of the tiebars and the corresponding ones of the threaded bushings substantially synchronous.
According to a further feature of the present invention, the mechanical link is implemented as at least one drive belt.
According to a further feature of the present invention, wherein the first drive mechanism includes a plurality of motors, each of the motors being mounted on one of the first and second platens and being connected in driving relation to generate relative rotation of one of the tiebars relative to a corresponding one of the threaded bushings.
According to a further feature of the present invention, the first drive mechanism further includes a control system for controlling the plurality of motors to generate substantially synchronous relative rotation between all of the tiebars and the corresponding threaded bushings so as to maintain parallel alignment of the first and second platens.
According to a further feature of the present invention, the first drive mechanism is configured to generate substantially synchronous relative rotation between all of the tiebars and the corresponding threaded bushings so as to maintain parallel alignment of the first and second platens.
According to a further feature of the present invention, the first drive mechanism is located adjacent to the first platen.
According to a further feature of the present invention, the second drive mechanism is located adjacent to the second platen.
According to an alternative feature of the present invention, both the first drive mechanism and the second drive mechanism are located adjacent to the second platen.
According to a further feature of the present invention, the second drive mechanism includes a plurality of lever arms.
According to a further feature of the present invention, the second drive mechanism further includes at least one actuator element, each actuator element being deployed to displace a first of the lever arms relative to a second of the lever arms.
According to a further feature of the present invention, each of the at least one actuator element is implemented as a pneumatic actuator element.
Accord
Friedman Mark M.
Mackey James P.
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