Plastic and nonmetallic article shaping or treating: processes – With severing – removing material from preform mechanically,... – Flash or sprue removal type
Reexamination Certificate
1998-07-09
2001-07-10
Ortiz, Angela (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With severing, removing material from preform mechanically,...
Flash or sprue removal type
C264S328900, C264S328150
Reexamination Certificate
active
06258306
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to mold gates for controlling the flow of molten plastic into a cavity of a mold for injection molding of plastic parts, as for example, plastic buckets. In typical commercial operations, multiple molding chambers are provided so that several molded products can be produced in a single molding cycle. Normally, each such molding chamber will have its own mold gate to control the flow of molding compound into a molding cavity or chamber.
Prior art mold gates customarily have mechanisms for opening or closing down the size of a flow area to a central hole which leads to a mold cavity. However, while adjustment of the flow area leading to a round opening communicating with the mold cavity may serve to regulate such flow, the final opening is fixed in size so that such regulation is limited.
SUMMARY OF THE INVENTION
By this invention, a simple, quick-adjusting, reliable, variable-sized mold gate system is provided. This allows the injection molder to fill a mold cavity in such a manner and within a cycle time as to accomplish three objectives simultaneously, preferably without the movement of mechanical valve parts in the gate while the mold is operating. First, it becomes possible to fill the mold cavity to produce a part of predetermined wall thickness, length of flow, and plastic material rheology at temperatures and pressures that do not degrade the plastic material in the molding process. Secondly, it becomes possible to “pack out” the part without creating internal stresses in the molded part. Third, plastic in the gate and the plastic of the molded part wall freezes simultaneously.
One object of the present invention is to provide an improved mechanism for adjusting a mold gate in order to increase or reduce the flow rate of the molten plastic into the mold cavity. In accordance with one embodiment of the invention, such adjustment is achieved manually by use of a hand tool when the mold is open at the parting line. Such an adjustment feature is desirable where a very large number of cavities and mold gates are utilized, for example; with a mold having forty-eight (48) cavities and corresponding gates.
Another embodiment of the present invention permits adjustment of a mold gate from outside the mold so that such adjustments can be made without opening the mold. In accordance with one design, such outside gate adjustment mechanism is used when sixteen mold cavities and gates are utilized.
An objective of the invention is to provide an adjustable mold gate which will adjust the size of a final, annular opening through which molten plastic flows into the mold cavity so that the opening is not a constant as in prior designs. Another objective is to provide a mold gate which can be adjusted so that by the time the molten plastic in the mold cavity has hardened by an amount sufficient to eject the part, the plastic in the area of the mold gate will also be sufficiently hardened so that the length of a mold cycle need not be extended in order to await hardening of the plastic in the mold gate area.
In particular, with an embodiment of the invention the mold gate opening comprises the annular passage defined by an outer diameter and an inner diameter, between which the annular passage is defined for the flow of molten plastic. For a given area of gate opening, such an annular passage will permit molten plastic to cool more rapidly than where the mold opening comprises a round hole, because in the latter case the resulting round piece of plastic, which must harden in the gate area before the next cycle can begin, will not cool rapidly in the middle of such a piece. In contrast, an annular ring of plastic in the mold gate area will cool more rapidly so as to avoid the need to extend the mold cycle simply to permit cooling of the plastic in the gate area.
Another important object of the present invention is to provide a nozzle insert with a plastic runner extending therethrough, the insert having radially expandable end portions so that under high pressure from the molten plastic the insert will expand radially against other mold elements to effect improved sealing against leakage of the molding compound.
By this invention, a mold gate is provided for controlling the flow of molten plastic to a mold cavity for injection molding of plastic parts. By this invention, an outer mold gate member is provided, having a central opening at an inner end through which molten plastic flows to a mold cavity. A hot probe is centrally disposed adjacent to the central opening, to define an annular passage between the hot probe and wall of the central opening. The hot probe is longitudinally adjustable relative to the outer mold gate member to vary the area of the annular passage. Furthermore, apparatus is provided for longitudinally adjusting the position of the hot probe, to adjust the area of the annular passage at the discretion of the user, and thereby to control the flow of molten plastic to the mold cavity. By this invention, the outer mold gate member may carry cooling water lines to facilitate the cooling of plastic adjacent the hot probe and in the mold cavity.
Preferably, the hot probe is seated in a rotatable inner mold gate unit, to be rotatable along with the inner gate unit and to be also longitudinally movable relative to the outer mold gate member. The longitudinal movement may be provided by the hot probe being threadedly engaged with a stationery inner bushing. Thus, rotation of the inner mold gate unit and the hot probe together causes the hot probe to move longitudinally, as guided by the threaded interengagement with the inner bushing. Thus, the area of the annular passage into the mold cavity can be varied on a moment-by-moment basis, if desired, by rotating the inner mold gate unit, a portion of which may be accessible to permit such rotation by an engaging gear or the like.
The cooling water lines adjacent the hot probe and the annular passage facilitate rapid cooling in that area, so that it becomes possible for molding compound in the annular passage to freeze simultaneously with the molding compound in the mold cavity, so that no metal parts are needed to close the mold gate between shots. The frozen plastic serves as a plug to seal the molten molding compound in between shots. Then, when a new shot is desired, the rush of hot molding compound will break through the plug provided by the tiny amount of frozen molding compound, remelting it as the mold cavity is once again refilled, to repeat the process.
Thus, molding of plastic parts can take place by passing molten plastic through a mold gate into a mold cavity, and allowing the plastic to cool. This method comprises the steps of: passing liquid molding compound through the mold gate in an annular flow path to fill the mold cavity; allowing the plastic material in the mold cavity and the mold gate to solidify by cooling; and removing the newly molded plastic part from the mold cavity, including the step of severing the plastic in the mold gate, and ejecting the part without closing the gate with a metal gate-closing member. The severing process may be done in tension, or in shear, as may be desired.
Specifically, a method of injection molding of plastic parts by flowing molten plastic through a mold gate into a mold cavity is provided. The method comprises the steps of: (a) providing an opening in the mold gate leading to the mold cavity to conduct molten plastic thereto; (b) aligning a hot probe member adjacent to the opening, the hot probe member being movable between variable positions to convert the opening into an annular opening of varying area depending upon the position of the hot probe member; (c) adjusting the position of the hot probe member to a specific, desired position; (d) molding a plastic part under molding parameters whereby the plastic part is fully formed in the mold cavity. The parameters include the usual molding parameters of temperature, molding pressure, setting time, and the like. However, the position of the hot probe member and the speci
Banner & Witcoff , Ltd.
Ortiz Angela
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