Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Shaping against forming surface
Reexamination Certificate
2001-04-10
2003-02-18
Silbaugh, Jan H. (Department: 1722)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Shaping against forming surface
C425S443000, C425S556000
Reexamination Certificate
active
06521165
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to injection molding molds. More specifically, this invention relates to the stripping of molded parts from an injection mold featuring core lock wedges on a core portion thereof.
BACKGROUND OF THE INVENTION
Injection molding basically involves the injection of a molten material, such as a plastic into a space defined between a core and a cavity of an injection mold. The core is typically an outward projection from a core portion of the mold. The cavity is typically a recess extending into a cavity portion of the mold. After injection the molten material is allowed to cool and solidify subsequent to which the core portion and cavity portion of the mold are separated in a longitudinal direction. As cooling and solidification of the part is generally accompanied by some shrinkage, the part usually shrinks onto the core from which it has to be removed or “stripped”.
Various methods and apparatus are used for stripping parts, the selection of which depends upon practical considerations such as the configuration of the part to be stripped and space available. A stripping assembly which is often desired for thin wall containers and other cup shaped parts is called a stripper plate. A stripper plate, as the name suggests is a plate which lies against the core portion during molding, extends about each core, and engages an outer edge or lip of the molded part. The stripper plate may in fact define a portion of a mold face of the core. This initial position is referred to herein as the “molding position”.
The stripper plate is axially movable relative to the core by any suitable actuator connected thereto, such as a pressurized fluid displaceable piston or a linkage arm. As the stripper plate is urged away from the core portion, it presses against the part (usually a lip of the part) and urges the part off of the core. Stripper plates are desirable because they are relatively inexpensive (compared for example to pin ejection systems), reliable (compared to air ejection systems) and require minimal height and minimal changeover times.
A problem encountered with thin wall containers, particularly with relatively large ones, is a tendency of the outer edge of the cavity to flex laterally outwardly in response to the pressure of the molten material being injected, thereby causing the wall of the part to be unduly thick toward its outer edges. One way to combat this flex of the cavity is with “core lock wedges”. Core lock wedges are protrusions which extend about the core and abut against an outer perimeter of the cavity to prevent radial outward movement of the outer end of the cavity. A single “wedge” may be used which extends continuously about the cavity in which case the mold is referred to as having a “ring lock core”. The present invention relates to wedge lock cores in which a plurality of spaced apart wedges are provided.
FIG. 1A
is a perspective view of a prior art wedge lock core on a core part which is illustrated generally by reference
20
. The core part
20
has a core
22
extending from a core face
24
. Disposed about the core
22
and also extending from the core face
24
are four core lock wedges
26
. Although four are shown in this illustrative example, it will be understood by persons skilled in such structures that other numbers are possible.
FIG. 1B
is a section on line
2
—
2
of
FIG. 1A
additionally showing a cavity part
30
of a mold (the cavity part
30
does not appear in FIG.
1
). The cavity part
30
has a cavity
32
extending therefrom with an outer end
34
distal the cavity part
30
.
FIG. 1B
illustrates the core
32
and the cavity
22
in a molding configuration in which the core lock wedges
26
engage the outer ends
34
of the core
30
to resist outward lateral movement in the direction of arrows
36
.
Until the present invention, a problem associated with wedge lock cores has been the inability to use a stripper plate. The presence of the core lock wedges
26
interferes with placing a stripper plate on the core face
24
and accordingly, the stripper plate is replaced with a stripper ring.
FIG. 1C
is a sectional view corresponding to
FIG. 1B
of a prior art stripper ring
40
. The stripper ring
40
extends between the core
22
and the core lock wedges
26
. As the stripper ring
40
does not extend to edges
28
of the core part
20
, its actuation cannot be from adjacent the edges
28
as with a conventional stripper plate. Accordingly, the prior art solution has been to provide an ejector box
50
behind the core part
20
and connect the stripper ring
40
to an ejector plate
52
with ejector rods
54
. The ejector plate
52
and in turn the ejector rods
54
and stripper ring
40
are moved by ejector cylinders
56
also connected to the ejector plate
52
.
While the use of an ejector box
50
provides a workable arrangement, it has the disadvantage that the ejector box adds significantly to the height of the mold and accordingly, reduces the number of levels that may be provided in a stack mold.
An object of the present invention is to provide a stripper plate assembly actuatable without an ejector box for use with a wedge lock core.
SUMMARY OF THE INVENTION
A stripper assembly is provided for stripping a mold part from a core, extending from a core part of an injection mold where the core part has core lock which is disposed thereabout for engaging a corresponding mold cavity and resisting outward movement of an outer edge of the mold cavity. The core wedges are spaced apart to provide an opening between adjacent ends of the adjacent wedges.
The stripper assembly includes a stripper plate extending about a base of the core to engage a part formed on the core and is longitudinally moveable relative to the core by an actuator connected to the stripper plate, between a molding configuration in which the part is formed on the core and a stripping configuration for removing the part from the core.
The stripper plate has actuator attachment range extending through the openings between the core lock wedges to provide for attachment of the actuator thereto. The actuator is disposed laterally outwardly of the adjacent ends of the core lock wedges to move the stripper plate between the molding and stripping configurations with the core part being mounted directly to a respective part of an injection molding machine.
The actuator may include a fluid pressure response of piston slidably mounted within a bore extending into the core part adjacent at least one of the actuator attachment regions, with the piston being connected to the stripper plate.
The actuator may include two or more such pistons, each of the pistons being associated with a different one of the actuator attachment regions.
The stripper plate may have one of the actuator attachment regions at each corner thereof and respective of the pistons associated therewith. The actuator attachment regions may extend laterally beyond the confines of the injection mold and the actuator may include at least one lever arm acting between the stripper plate and the core part of the injection mold to move the stripper plate away from the core part in response to the injection mold moving from its molding to a stripping configuration.
The actuator may include two such lever arms, each of which is associated with a different one of the actuator attachment regions.
The stripper plate may have one of the actuator attachment regions at each corner thereof and a respect of the lever arms associated with each of the actuator attachment regions.
The stripper plate may include an inner plate adjacent, the core part and an outer plate adjacent the inner plate. The stripper plate is moveable by the actuator in a first stage wherein the inner and outer plates move together and further moveable by the actuator in a second stage, wherein the outer plate is moved away from the inner plate.
The first and second plates may act as an outer end of the cavity associated with the core for the forming of an outer edge of the molded part between the inner an
Gowling Lafleur Henderson LLP
Luk Emmanuel
Silbaugh Jan H.
Stackteck Systems Limited
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