Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND DEVICE FOR ACTUATING A PRESS
Field of Invention
This invention relates to presses. In particular, this invention relates to
a press particularly suitable for use with an injection or extrusion molding
apparatus,
and a molding apparatus utilizing the press.
Background of the Invention
Presses have many uses, one of the most popular being to clamp mold
parts together in an injection molding apparatus. In a conventional injection
molding
apparatus a press section is disposed behind a plastic injection section. The
press
includes a moving platen which is forced toward a stationary platen by at
least one
actuator, usually a hydraulic cylinder mounted at the rear of the apparatus.
The
actuator bears against a stationary rear frame or "spider", which supports
upper and
lower pairs of guide bars that maintain the moving and stationary platens (and
thus the
mold parts) in precise alignment as the actuator forces the moving platen
toward the
stationary platen and into the clamping position.
Typically a hydraulic press is used in an injection molding apparatus,
due to the very high forces required to properly clamp the mold parts
together. In a
conventional hydraulic actuator the hydraulic cylinder must be longer than the
length
of a full stroke of the piston and must be oriented in the direction of the
stroke. Since
the injection molding apparatus occupies the space in front of the press, the
hydraulic
cylinder is conventionally mounted to the rear of the press and thus a large
clearance
is required behind the operative clamping portion of the press in order to
accommodate the cylinder.
Moreover, in a conventional hydraulic press the hydraulic cylinder
serves the sole purpose of actuating the moving platen, and separate guide
bars are
used to maintain the moving and stationary platens in precise alignment. The
use of
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separate structures for these purposes results in an expensive and heavy
apparatus
which makes poor use of available space.
It would accordingly be advantageous to provide a hydraulic press in
which the actuating cylinders can be reduced in length and contained within
the
operative clamping section of the press, to significantly reduce the space
requirements
of the overall apparatus and thus allow plastics fabricators to utilize
production
facilities more efficiently.
It would also be advantageous to provide a press which combines the
actuating and platen alignment functions of the press into the same structure,
to reduce
the weight and cost of the apparatus.
It would also be advantageous to provide a press that operates in two
directions, taking advantage of the reciprocating motion of the actuator, to
provide
two injection molding cycles within a single press cycle.
Summary of the Invention
The present invention overcomes these disadvantages and provides an
economical, lightweight and compact press and injection molding apparatus
utilizing
the press. The press of the invention may be used in virtually any application
in
which a conventional hydraulic press may be used, the press of the invention
being
particularly advantageously used with injection molding units in an injection
molding
apparatus.
The invention accomplishes this by providing a tandem press having a
moving frame comprising a moving platen moving in a reciprocating motion
between
stationary outer platens. The moving platen moves on a track between a first
clamping position in which the moving platen clamps a first mold mounted on
one
side of the press, and a second clamping position in which the moving platen
clamps a
second mold on the other side of the press. Because of the tandem design, as
one
mold is moved to a clamping position the other mold is being separated to
remove a
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molded article. The tandem press of the invention thus provides two complete
clamping cycles within one press cycle.
In the preferred embodiment the hydraulic; pistons actuating the
moving platen also serve as guide bars for maintaining the moving platen in
alignment
with the stationary platens. The tandem press of the invention thus avoids the
need
for separate guide bars by providing hydraulic actuating cylinders mounted on
the
stationary platens, the pistons for which serve both as guide bars to maintain
alignment between the platens and as actuators to move the moving platen
between
clamping positions. In the preferred embodiment the actuating cylinders
operate at a
relatively low force and high speed, and the moving platen is provided with
hydraulic
clamping cylinders operating at relatively high force to apply the required
clamping
force to the mold after the actuating cylinders have moved the moving platen
to the
clamping position.
The present invention thus provides an actuator for actuating opposed
first and second structures, the first and second structures being movable
between an
open position in which the first and second structures are spaced apart, and a
closed
position in which the first and second structures are disposed together,
comprising at
least one hydraulic actuating cylinder mounted to the first structure, having
an inner
end facing the second structure and an outer end, at least one hydraulic
clamping
cylinder mounted to the second structure, a piston extending out of both ends
of the
actuating cylinder, having a first portion providing a piston head disposed
within the
actuating cylinder and a second portion providing a piston head disposed
within the
clamping cylinder, and a piston lock for anchoring the piston, whereby the
actuating
cylinder can be actuated to move the first and second structures from the open
position to the closed position, and when the piston is anchored in the closed
position
the clamping cylinder can be actuated to apply a clamping force between the
first and
second structures.
The present invention further provides a method of clamping opposed
first and second structures movable between an open position in which the
first and
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second structures are spaced apart and a closed position in which the first
and second
structures are disposed together, by a piston extending out of ends of an
actuating
cylinder mounted to the first structure and having a first portion providing a
piston
head disposed within the actuating cylinder and a second portion providing a
piston
head disposed within a clamping cylinder mounted to the second structure, the
actuating cylinder having an inner end facing the second structure and an
outer end,
the method comprising the steps of actuating the actuating cylinder to draw
the second
structure toward the first structure, anchoring the piston, and actuating the
clamping
cylinder to clamp the second structure to the first structure.
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Brief Description of the Drawings
In drawings which illustrate by way of example only a preferred
embodiment of the invention,
Figure 1 is a perspective view of an injection molding apparatus
embodying a hydraulic press of the invention,
Figure 2 is a cross-sectional elevation of the press of the invention
illustrated in the injection molding apparatus of Figure 1,
Figures 3A to 3F are cross-sectional elevations of the press of Figure 2
showing the stages of operation of the press section,
Figure 4 is a cross-section of a clamping cylinder in the press of Figure
2,
Figure SA is a cross-section of an anchoring yoke in the press of Figure
2 showing the yoke in the anchoring position,
Figure SB is a cross-section of an anchoring yoke in the press of Figure
2 showing the yoke in the release position, and
Figure 6 is a an end elevation showing one preferred manner of
actuating the anchoring yokes.
Detailed Description of the Invention
Figure 1 illustrates an injection molding apparatus utilizing a preferred
embodiment of the press 20 of the invention. The injection molding units 2
shown in
Figure 1 are entirely conventional, having an injector pump (not shown) for
pressurizing a molten thermoplastic material through a screw/runner 4 for
injecting
the molten thermoplastic into a mold, and an ejector pin and platen (not
shown) for
ejecting the molded article from the mold. The operation and structural
details of the
injection molding units 2 will be well known to those skilled in the art, and
the
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invention is not intended to be limited to use with any particular type or
configuration
of injection molding unit 2.
The invention resides in a novel press 20, illustrated in detail in Figures
1 to SB. The press 20 of the invention is described in relation to a hydraulic
press
embodiment, which provides certain advantages that will become apparent from
the
description below. However, it will be appreciated by those skilled in the art
that the
press 20 of the invention utilizing other types of actuators, for example
electric motor
or screw-type actuators, may also be suitable.
In the preferred embodiment illustrated, the press 20 is preferably
supported on a base or pad 22, and includes a stationary frame and a moving
frame.
The press 20 is preferably laterally symmetrical and provides two molds 10a, l
Ob
each respectively comprising mold parts 11 a, 12a and 11 b, 12b. Mold 1 Oa is
mounted
into one side of the press 20, and mold l Ob is mounted into the other side of
the press
20. An injection molding apparatus 2 (shown schematically in phantom lines in
Figure 1 ) is preferably disposed at each end of the press 20 to inject
plastic into the
molds 10a, l Ob in conventional fashion. It will be appreciated that the press
20 of the
invention could also be operated with a single injection molding apparatus
operating
with a single mold l0a or l Ob, however there are benefits to operating the
press 20 in
tandem fashion to obtain two clamping cycles (i.e, injection molding cycles)
within a
single press cycle as described in the preferred embodiment.
The stationary frame comprises a first stationary platen 24a having a
working face 25a and a second stationary platen 24b having a working face 25b
disposed in opposition to the working face 25a. The moving frame comprises a
moving platen 26 disposed between the stationary outer platens 24a, 24b,
having a
first working face 26a and a second working face 26b on the opposite side
thereof.
The moving platen 26 is mounted on a track 32 and moves between two clamping
positions, a first clamping position in which the moving platen 26
compressively
clamps mold part 11 a mounted on face 26a of the moving platen 26 against a
mating
mold part 12a mounted on the working face 25a of the first stationary platen
24a, and
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a second clamping position in which the moving platen 26 compressively clamps
mold part 1 lb mounted on the opposite face 26b of the moving platen 26
against
mating mold part 12b mounted on the working face 25b of the second stationary
platen 24b. Because of the tandem design, as the mold part 11 b is moved
toward a
clamping position against mold part 12b mold part 11 a is separated from mold
part
12a, and vice versa. In the preferred embodiment the press 20 thus provides
two
complete clamping cycles in one press cycle.
In the preferred embodiment of the press 20 of the invention hydraulic
pistons SOa, SOb respectively actuated by hydraulic cylinders 40a, 40b serve
to
transfer the actuating force of the hydraulic fluid to the moving platen 26.
The pistons
SOa also act as guide bars to maintain the platens 24a and 26 in alignment
during the
process of clamping mold parts l la and 12a; likewise, the pistons SOb act as
guide
bars to maintain the platens 24b and 26 in alignment during the process of
clamping
mold parts 11 b and 12b.
In the preferred embodiment, to the outer face of each stationary platen
24a, 24b are respectively mounted four hydraulic cylinders 40a, 40b,
preferably
generally evenly spaced about the axial center of the press 20. The cylinders
40a, 40b
are bolted to the stationary platens 24a, 24b as by bolts 41. Each cylinder
40a, 40b
has a length slightly greater than the stroke length of the pistons SOa, SOb,
as defined
by the length of the path of travel of the moving platen 26 along the track
32.
The hydraulic actuating cylinders 40a, 40b are provided at each end
with an inner and outer head assembly 42a, 44a and 42b, 44b, respectively,
provided
with suitable bearings and seals. The outer head assembly 44a or 44b provides
an
hydraulic port 46a or 46b for pumping hydraulic fluid into and out of the
cylinders
40a, 40b. The piston SOa or SOb is slidably mounted within each cylinder 40a
or 40b,
respectively. (For ease of reference like parts on each side of the press 20
are referred
to herein using like reference numerals, with the suffix "a" to designate
parts on the
side of the press 20 containing mold 10a, shown at the left in the drawings,
and with
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the suffix "b" to designate parts on the side of the press 20 containing mold
1 Ob,
shown at the right in the drawings.)
Each piston SOa comprises a piston rod 52a which extends out of the
outer head assembly 44a to an outer end 54a, and extends through the inner
head
assembly 42a to a clamping end 56a which is secured to the moving platen 26 in
the
manner hereinafter described. The hydraulic head assemblies 42a and 44a retain
hydraulic fluid within the cylinder 40a while the piston rod 52a slides
through the
cylinder 40a to actuate the moving platen 26. The pistons SOa thus move
between a
retracted position in which the mold l0a is closed and the mold l Ob is fully
open, and
an extended position in which the mold l Ob is closed and the mold l0a is
fully open
as shown in Figures 2 and 3A.
Likewise, each piston SOb comprises a piston rod 52b extends out of
the outer head assembly 44b to an outer end 54b, and extends through the inner
head
assembly 42b to a clamping end 56b which is secured to the moving platen 26 in
the
manner hereinafter described. The pistons SOb thus move between a retracted
position in which the mold l Ob is closed and the mold l0a is fully open, and
an
extended position in which the mold l0a is closed and the mold l Ob is fully
open as
shown in Figure 3E.
The moving platen 26 is thus actuated along a path of travel defined by
the track 32 by the piston rods 52a, 52b, which in turn are driven by
hydraulic fluid
pumped into and out of the hydraulic actuating cylinders 40a, 40b during a
press
cycle. In the preferred embodiment each of the piston rods 52a, 52b
respectively
comprises a constricted portion 57a, 57b which provides a bearing surface 58a,
58b
where the diameter of the piston rod 52a, 52b increases. The bearing surface
58a or
58b is disposed within the respective hydraulic cylinder 40a or 40b and acts
as a
piston head; as hydraulic fluid is pumped into the cylinder 40a or 40b the
pressure on
the bearing surface 58a or 58b displaces the respective piston rod 52a or 52b
toward
the moving platen 26.
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This avoids the need for a separate piston head within the cylinder 40a
or 40b, with attendant cost advantages, and is sufficient for the relatively
low driving
force required to move the moving platen 26 to the clamping position. In the
preferred embodiment a much higher clamping force required is provided by
hydraulic clamping cylinders 60, described below. An embodiment of the
invention
actuated and clamped solely by the hydraulic actuating cylinders 40a, 40b is
also
feasible, in which case the cylinders 40a, 40b would also have to operate at
the higher
clamping force required to clamp the molds 10a, l Ob; in this case the piston
rods 52a,
52b could each be provided with a separate piston head disposed within the
actuating
cylinders 40a, 40b to provide the required clamping force, however it is
expected that
the duration of the press cycle would be considerably increased in this
embodiment.
As noted above, in the preferred embodiment the hydraulic actuating
cylinders 40a, 40b are small bore diameter high speed cylinders that are used
only to
move the moving platen 26 to the clamping positions. The clamping force is
supplied
by hydraulic clamping cylinders 60 mounted on the moving platen 26, which have
a
relatively larger bore diameter and thus provide a higher force than the
actuating
cylinders 40a, 40b. The inner ends 56a, 56b of the piston rods 52a, 52b are
disposed
through sealing flanges 64a, 64b and affixed to piston heads 62a, 62b which
may be
secured together (or formed as a single piston head 62) slidably contained
within the
cylinder 60. The purpose of the cylinders 60 is to apply a high clamping force
between the mold parts 11 a, 12a or 11 b, 12b in the final stage of the
clamping cycle,
and thus the clamping cylinders 60 are provided with a larger cross-section
than the
actuating cylinders 40a, 40b, and the piston heads 62a, 62b provide a
commensurately
larger surface area against which the hydraulic fluid acts to produce the
greater
clamping force. The cylinder 60 is mounted into the moving platen 26 and
provides
hydraulic ports 66a, 66b, respectively, for alternately actuating the piston
heads 62a,
62b as the moving platen 26 reaches the alternate clamping positions.
The outer end of each hydraulic actuating cylinder 40a or 40b is
provided with a movable spacer, in the preferred embodiment an anchoring yoke
70a
or 70b, the purpose of which is to anchor the pistons SOa, SOb into the
retracted
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position during the final stage of a clamping cycle. The outer ends S4a, S4b
of the
piston rods S2a, S2b are provided with an enlargement, for example anchoring
caps
S3a, S3b threadedly engaged to the outer ends S4a, S4b of the piston rods S2a,
S2b as
in the embodiment shown.
The yokes 70a, 70b each preferably comprise curved or hemi-
cylindrical portions 72a, 74a and 72b, 74b, respectively, which are actuated
by any
suitable actuator 80 such as a solenoid, or by any other suitable alternative
such as a
motor, pneumatic or hydraulic actuator or the like. In the preferred
embodiment the
actuator 80 actuates a reciprocating frame 81 comprising connecting rods 82
joined by
crossbars 84, as shown in Figure 6 (the actuator 80 and frame 81 have been
omitted
from Figures 1 to S for clarity). The frame 81 moves the yokes 70a, 70b
between an
anchoring position in which the yoke 70a or 70b is engaged about the piston
rod S2a
or S2b, respectively, and thus impinges into the path of the anchoring cap S3a
or S3b
to serve as a spacer which maintains the anchoring cap S3a or S3b at a fixed
spacing
from the hydraulic actuating cylinder 40a or 40b to anchor the piston SOa or
SOb in the
retracted position; and a release position in which the yoke 70a or 70b is
released
from the piston rod S2a or 52b and the anchoring cap 53a or S3b is free to
move
toward the hydraulic cylinder 40a or 40b so that the piston SOa or SOb can be
driven to
the extended position. For example, on the left-hand side of Figure 6 the
yokes 70a
axe shown in the anchoring position and on the right-hand side of Figure 6 the
yokes
70a are shown in the release position.
It will be appreciated that although the releasable spacer in the
preferred embodiment comprises a yoke 70a or 70b, the spacer functions to
space the
anchoring cap S3a or S3b from the cylinder 40a or 40b, respectively, and this
can be
accomplished by any other suitable means. Further, the manner in which yokes
70a,
70b are moved between the anchoring position and the release position can be
achieved many other ways, and the invention is not intended to be limited in
this
respect.
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The operation of the tandem embodiment of the press 20 of the
invention will now be described with reference to the preferred embodiment
illustrated, and particularly Figures 3A to 3F which show the various stages
in one
complete press cycle (two clamping cycles).
Figure 3A shows the press 20 with the mold l Ob in a fully clamped
condition and the mold l0a in a fully separated condition. The clamping
cylinders 60
are fully actuated to apply pressure against piston head 62b, and thus tension
the
piston SOb to provide the required clamping force between mold parts l lb and
12b. A
previously molded plastic article is being removed from separated mold parts
11 a and
12a.
To separate the mold parts l lb, 12b and begin the clamping cycle for
the mold parts 11 a, 12a, hydraulic pressure is released from the ports 66b of
the
clamping cylinders 60 to release the clamping force from the mold l Ob, which
in turn
releases the tension on the piston SOb, and the anchoring yokes 70b are
released to
free the outer ends 54b of the pistons SOb, as shown in Figure 3B. Hydraulic
fluid is
pumped into the ports 46b of actuating cylinders 40b, and as the hydraulic
fluid
intrudes into the gap 55 between the bearing surface 58b and the head assembly
44b
of each piston rod 52b (as best seen in Figure SA), the piston rods 52b are
forced out
of the cylinders 40b toward the stationary platen 24a, as shown in Figure 3C.
At first the piston heads 62a, 62b are forced to the opposite side of the
clamping cylinder 60. As hydraulic fluid continues to be pumped into the ports
46b
the pistons SOb are driven to the extended position, and the piston head 62a
in contact
with the end of the clamping cylinder 60 forces the moving platen 26 away from
the
stationary platen 24b and toward the stationary platen 24a to the clamping
position, as
shown in Figure 3D. This simultaneously separates the mold parts l lb, 12b and
closes the mold parts l la, 12a, and forces the pistons SOa to retract into
the cylinders
40a.
The yokes 70a are then closed to the anchoring position, as shown in
Figure 3E. This spaces the anchoring caps 53a from the actuating cylinders 40a
to
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anchor the outer ends 54a of the pistons SOa. In the preferred embodiment, the
anchoring caps 53a are spaced slightly from the yokes 70a at this stage (see
gap 57 in
Figure SA), so that the yokes 70a have room to close between the anchoring cap
53a
and the cylinder 40a.
Hydraulic fluid is then pumped into the ports 66a, drawing the
anchoring caps 53a snugly against the yokes 70a, which in the anchoring
position
prevent any substantial extension of the piston rods 52a. This is shown in
Figure 3F,
in which the anchoring cap 53a has been drawn fully against the yoke 70a and a
small
gap 59 can now be seen between the clamping cylinder 60 and the piston head
62a.
Since the anchoring caps 53a prevent the piston rods 52a from extending out of
the
cylinders 40a, so the piston heads 62a are effectively rendered stationary, as
hydraulic
fluid continues to be pumped into ports 64a the clamping cylinders 60 are
forced
toward the stationary platen 24a; since the clamping cylinders 60 are mounted
in the
moving platen 26, the moving platen is forced toward the stationary platen 24a
to thus
apply the clamping force to the mold 10a.
The mold l0a is now in the fully clamped position and the mold 24b is
in the fully separated position. A molded plastic article is removed from
separated
mold parts 1 lb and 12b.
To reverse the press 20 the steps described above are repeated in the
same order but in relation to the counterpart components on the other side of
the press
20: To separate the mold parts l la, 12a and begin the clamping cycle for the
mold
parts 1 lb, 12b, hydraulic pressure is released from the ports 64a of the
clamping
cylinders 60, releasing the clamping force from the mold 10a, and the
anchoring
yokes 70a are released from the outer end 54a of each piston SOa. Hydraulic
fluid is
pumped into the ports 46a of actuating cylinders 40a, first forcing the piston
heads
62a, 62b toward the stationary platen 24b as the piston rods 52a are forced
out of the
cylinders 40a, and ultimately driving the moving platen 26 away from the
stationary
platen 24a and toward the stationary platen 24b to the clamping position. This
simultaneously separates the mold parts 11 a, 12a and closes the mold parts 11
b, 12b,
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and retracts the pistons SOb into the cylinders 40b. The yokes 70b are closed
to the
anchoring position, anchoring the outer ends 54b of the pistons SOb. Hydraulic
fluid
is then pumped into the ports 66b in the clamping cylinders 60, drawing the
anchoring
caps 53b snugly against the yokes 70b and then, as the piston heads 62a, 62b
can no
longer move laterally, forcing the cylinders 60 and thus the moving platen 26
toward
the stationary platen 24a to the clamping position shown in Figure 3A.
The tandem embodiment of the invention as illustrated provides a
number of advantages. The ability to clamp molds 10a, l Ob on both sides of
the
moving platen 26, which itself effectively reduces the clamping cycle by half,
also
allows the stroke length of the pistons SOa, SOb to be shorter than in a
conventional
press 20. This reduces the clamping cycle even further and thus increases the
speed
and capacity of the press 20, but also allows the actuating cylinders 40a, 40b
to
occupy the space around the injection molding apparatus 2, requiring very
little
additional space for the overall apparatus.
Also, since the actuating cylinders 40a, 40b need only move the platen
they can be designed to operate at higher speeds than conventional high
pressure
actuating cylinders, so most of the clamping cycle occurs at high speed.
Moreover,
since the moving platen 26 does not have to slide along any guide bar
structure, the
design of the platen 26 and the hydraulic cylinders 40 is considerably
simplified, the
need for a spider is eliminated and the durability of the connections between
the
platens is substantially increased.
Preferred embodiments of the invention having been thus
described by way of example only, it will be apparent to those skilled in the
art that
certain modifications and adaptations may be made without departing from the
scope
of the invention, as set out in the appended claims. The invention is intended
to
include all such modifications and adaptations as fall within the scope of the
appended
claims.
