Note: Descriptions are shown in the official language in which they were submitted.
; 058
METHOD OF MAKING A TWIN-WALL INTERNALLY CORRUGATED PLASTIC
,
STRUCTURAL PART WITH SMOOTH NON-CELLULAR SKIN
AND APPARATUS THEREE7ORE
In the art of injection plastic molding utilizing mold members
defining a mold cnvity moldable thermoplastic resin compositions or materials have
heretofore been introduced into such molds for defining in the molded article a smooth
non-cellular skin and an internal foam body. Various problems have arisen in providing
a foam plastic structural part because of the need of finishing the exterior surface
thereof to render the same smooth and non-porous. In the use of blowing agents
10 heretofore and in the introduction of cellular plastic material into a mold, the
resulting part does not have in many cases a smooth, dense,solid outer surface due to
the passage of gaseous materials to the mold surfaces during the molding operation
resulting in pitting and irregularities formed in the surfaces. Costly hand finishing of
the part was often required.
Various unsuccessful attempts have been made heretofore to mold
foam plastic structural parts having smooth skins or surfaces and to commercialize
same in the industry. Typical of such efforts are the following United States patents
along with the prior art United States and foreign patents cited therein:
PATENT DATE INVENTOR
4,136,220 January 23, 1979 Olagoke Olabisi
4,140,672 Pebruary 20, 1979 Hiroshi Kataoka
4,201,742 May 6, 1980 3ames W. Hendry
An important feature of the present invention is to provide a method
and apparatus for making a twin-wall, internally corrugated plastic structural part
which has a smooth, dense, shiny, solid, fluid impermeable outer skin with the internal
or interior portion of the part being of low density and having generally elongated
hollow pockets or voids interconnected by smaller generally elongated narrow and
closed slits or tails which together form the internal corrugations and provide
structural strength to the part.
Another important feature is to provide a method of making a twin-
wall, internally corrugated plastic structural part provided with a smooth non-cellular
skin which comprises the steps of closing a mold within a suitable press having at least
I'
)58
a pair of mold members which define a sealed cavity, injecting a small amount of
thermoplastic resin composition, sometimes referred to as plastic material, through
one of the mold members into the mold cavity for impingement upon and dispersion
over the mold members thereby forming a generally continuous skin of predetermined
thickness throughout and over the surfaces of the mold members. A further step
includes thereafter successively injecting inert gas under pressure through one of the
mold members during continued injection of the plastic material into the cavity
thereby pressurizing the skin against the walls of the mold cavity and progressively
introducing the gas into the inwardly flowing plastic as it enters the cavity until the
10 cavity is filled with internal corrugations or a corrugated inner body integral with and
bonded to the skin.
A further feature includes the step of injecting the pressurized gas
intermittently thereby producing minute amounts of pressurized gas into the
continuously injected plastic material.
A still further feature of the molding process includes the provision
of injecting a small amount of heated plastic material into the mold cavity for forming
with the subsequent introduction of an inert gas a thin skin over the surfaces of the
mold members and successively injecting the inert gas under pressure, such as
nitrogen, through one of the mold members during the continued injection of the
20 plastic material into the mold cavity thereby pressurizing the skin against the walls of
the mold cavity and progressively corrugating the inwardly flowing plastic material as
it enters the cavity until the cavity is filled with an internal corrugated body integral
with and bonded to the skin of the part formed.
Another feature is to provide in the process the step of cooling the
mold members until the part is solidified and venting the cavity to atmosphere to
permit the escape of any pressure trapped in the mold cavity followed by the
successive repeat of the cycle of method steps for producing a series of such molded
articles or parts.
A further feature includes the intermittent introduction of
30 pressurized gas into the mold cavity during injection of plastic material thereinto and
wherein a valve mechanism or member is employed for controlling the intermittent
flow of minute amounts of pressurized gas into the continuously injected plastic
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3 2~20S8
material, incorporating a pneumatic or electrically operated oscillator for
intermittently opening and closing the valve member through a cycle OI 4 to 100 cycles
per second.
A still further feature includes the step of dispersing the pressurized
gas through one orifice or through a plurality of angularly related orifices of small
diameter in the range of .003 - .010 inches, approximately, wherein pressurized gas is
dispersed through the one orifice or is dispersed through the angularly related orifices
in a transverse plane laterally outward towards the interior walls of the mold members
throughout 360~.
Another feature in the present method and apparatus is to provide a
probe having a head and employing one orifice or a series of laterally directed
angularly related orifices therein delivering inert gas under pressure to the mold
cavity, and with an oscillator valve member controlling the intermittent flow of
pressurized gas into the mold cavity thereby introducing minute or small amounts of
pressurized gas into the continuously injected plastic material.
A further feature incorporates into the method and apparatus the
step of advancing the probe and its head with one or more orifices a short distance into
the mold cavity for introduction of the pressurized gas thereinto and for withdrawing
the probe from the mold cavity after the molded part has been formed.
According to the invention there is provided the method of making
a twin-wall, internally corrugated plastic structural part provided with a smooth non-
cellular skin comprising the steps of: closing a mold having at least a pair of mold
members defining a sealed cavity; injecting a small amount of plastic material through
one of the mold members into the mold cavity for impinging upon and dispersion over
said mold members thereby forming a generally continuous skin of predetermined
relatively thin thickness throughout and over the surfaces of said mold members; and
thereafter successively injecting an inert gas under pressure through one of the mold
members during continued injection of the plastic material into the cavity thereby
pressurizing and urging the skin against the walls of said mold cavity and progressively
30 commingling the inert gas under pressure and the inwardly flowing plastic material as
both enter the cavity, until the cavity and skin are filled with a body integral with and
bonded to said skin.
1C ~2058
Pigure 1 is a schematic fragmentary view of the basic mold apparatus
with mechanism for intermittently directing pressurized inert gss into the mold cavity
subsequent to the initial injection of plastic material thereinto and during continued
injection of the plastic material and gas into the mold cavity.
Figure 2 is a fragmentary section showing the mold members
defining the mold cavity, corresponding to Figure 1, illustrating the use of a fan gate
upon one of the mold members.
Figure 3 is a fragmentary plan view of a mold member on an
increased scale taken in the direction of arrows 3-3 of Figure 2.
Figure 4 is a sectional view on an increased scale taken on the line 4-
4 of Figure 1.
Pigure 5 is a fragmentary elevational view of the mold members, as
an example, as would be mounted upon a suitable press illustrating the injection of the
plastic material into the mold cavity and the apparatus for intermittent injection of
pressurized gas into the mold cavity.
Figure 6 is a fragmentary sectional view on an increased scale of part
of the apparatus shown in Figure 5.
Figure 6 A is a fragmentary sectional view of a modified valve
structure utilizing a single orifice and illustrated in a closed position.
Pigure 6 B is a fragmentary sectional view of the modified valve
structure of Figure 6 A but illustrated in an open position.
Figure 7 is a fragmentary section of a pair of mold members defining
a mold cavity and the illustration of a stationary probe having a plurality of orifices
together with a power operated oscillator assembly for intermittently opening and
closing the orifices for delivering pressurized gas intermittently into the mold cavity
during the injection of plasticized material.
Figure 8 is a fragmentary sectional view on an enlarged scale of the
head portion of the probe shown in Figure 7.
Figure 8 A is a frPgmentary sectional view of another modified valve
30 structure which may be used with a stationary probe or with a retractable probe.
Figure 9 is a fragmentary view of a modified mold apparatus utilizing
a retractable probe with the probe shown in a retracted position.
3L;~4~:0~8
Figure 10 is a fragmentary sectional view corresponding to Figure 9
illustrating the probe in an advanced position within the mold cavity.
Figure 11 is a sectional view similar to Figure 10 and illustrating the
advanced probe and mold member on an enlarged scale.
igure 12 is a fragmentary plan view of part of the apparatus and
il]ustrating the twin-wall, internally corrugated plastic structural part made according
to the novel method and apparatus.
Pigure 13 is a sectional view taken on the line 13-13 of Figure 12.
It will be understood that the above drawings illustrate merely
10 several preferred embodiments of the invention, that other embodiments illustrative of
the present method and apparatus are contemplated within the scope of the claims
hereafter set forth.
The twin-wall, intemally corrugated plastic structural part A
illustrated in Figures 12 and 13 is made in accordance with the teaching of this patent
application by utilizing the novel methods and the novel apparatuses disclosed herein.
Referring specifically to Figures 12 and 13, t}-le part A removed from
the mold, is in the form of a generally rectangular flat panel having an upper smooth,
dense, shiny, solid, thin-walled non-cellular top or upper skin or surface B, side
surfaces C, D, E a P and a bottom surface or skin G, all of which have physical
20 characteristics like surface B. No painting or finishing is required after the part is
formed thus providing much savings in labor, time and materials.
Figures 12 and 13 diagramatically illustrate a single manifold sprue S
in one mold member, not shown, for introducing the plastic material and a gas valve V
in the other mold member, not shown, for introducing intermittently the inert gas.
The conventional runner R and gate G' are also diagramatically shown for use with the
novel apparatus and for practicing the novel method.
The plastic structural part A when removed from the mold assembly
or apparatus as noted herein has a smooth dense, shiny, solid, fluid impermeable outer
skin, as represented by surfaces B, C, D, E, F and G which are bonded to the internal
30 or interior portion, body or zone of the part. The interior body is characterized herein
as an "internally corrugated" portion, body or zone. The term "foam" is not accurate
to describe the internal portion, body or zone of part A. As illustrated in Figures 12
~L~Z~20~
and 13, part A has many elongated hollow pockets or voids P of varying configurations
and in generally the same plane as shown in Figure 13, from which the pressure of gas
has escaped, and which are arranged in varying but random corrugated patterns
throughout the entire internal stFucture. The voids P are interconnected by smaller
but also elongated narrow and generally closed s1its or tails V', also in the same plane.
The voids P and slits V' are at atmospheric pressure, having had the pressure of the gas
vented prior to the setting of the solid plastic material which forms the plastic
structural part A.
Thus the term "corrugated" or "corrugating" refers to the internal or
10 interior zone or body of part A which has a series of randomly spaced but
interconnected voids or pockets P and to the closed slits or tails V' from which the gas
has been removed. The interior zone has a low density due to the pockets P and tails
V
The elongated voids or pockets P have a preferred length 'I" of
approximately 1/2 inch, a predefined width "w" of approximately 3/16 inch and a
preferred depth "d" of approximately 3/16 inch. The preferred length "t" of each tail
"v" is approximately 1/4 inch. The total volume of the voids or pockets P and the tails
V' is the range of 10% to 25% of the total volume of the molded structural part. The
spacing and size of the voids P and tails v' and therefore the density of the part is
20 dependent on the rate of delivery of the gas under pressure. It has been determined
that the faster the inert gas is introduced the smaller are the size of volume of the
pockets P and the closer the pockets P are together. Structural parts, produced
according to the teachings of this applica tion wl~en cut in half, display the
"corrugated" portion, body, or zone which is generally similar in appearance to a two
ply corrugated cardboard structure.
Referring to the drawings, Figures 1 through 4, a simplified form of
molding apparatus is generally designated at 11 including a movable mold member 13
and a stationary mold member 15 fragmentarily shown. Mold member 15 has a sprue
or bore 17 adapted to receive at 19 any thermoplastic resin composition, hereafter
30 referred to as plastic material, for injection into the sealed mold cavity 21 defined by
the mold members 13 and 15. The mold member 13 has centrally thereof and
concentric of the probe 31 an annular fan gate 23 secured to mold face 27 by a series
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of fasteners 25, Figures 2 and 3. The use of the fan gate 23 is optional and is not
necessary in practicing the novel method or in using the novel apparstus. Therefore
the fan gate 23 is illustrated in Figures 2 and 3 but not in Figure 1.
Within mold member 13 there is a radial bore 29 within which is
nested the elongated probe 31 having a mount nange 33 secured to the mold member13 by fasteners 35. The probe 31 has an axial fluid passage or bore 37 for receiving an
inert pressurized gas, such as nitrogen in the pressure range of 300 to 1500 psi. The
pressure range of the inert gas when introduced into Norel Styrene A.B.S. is 400 to 600
psi. Other inert gases which might be used are argon or helium. Their composition
must render them inert to the injected thermoplastic resin composition introduced as a
fluid or molten plastic at or through the sprue 19, Figure 1. It will be appreciated
that the pressure of the inert gas is higher than the pressure at which the plastic
material is introduced in the mold cavity.
Probe 31 at one end has a head 39 of reduced diameter relative to the
probe closing the passage 37 and having formed therein a series of right angularly
related or radial orifices 41. These are located at a central zone with respect to
cavity 21, Figure 1, 2 and 3. The orifices 41 are small, in the range of .003 to .010
inches, for laterally dispersing upon the interior of the mold cavity 21 in a transverse
plane minute quantities of inert pressurized gas during the molding process. It will be
appreciated that instead of using a plurality of orifices or holes 41, a single axially
extending orifice or hole in line with the injection sprue 17 could be used. Thus a
single orifice, as in figures 6 A and 6 B, would be at the end of and straight up from
passage 37 as viewed in Figure 1 along with an appropriate fan gate or gating structure
not shown.
Fitting 43 upon the outer end of probe 31is connected to a fluid pipe
or conduit 45 having a normally closed hand operated vent valve 47 and spaced
there*om a manually operable hand valve 49 with a gauge assembly 51, 53 designating
the pressure of inert gas such as nitrogen from pressurized gas source 55 as
schematically shown.
While the method steps will be hereunder set forth in greater detail,
figures 1 through 4 illustrate an apparatus by which the method could be carried out.
Subsequent to the injection of plastic material at the sprue 19 into the closed mold
cavity 21 for forming a skin upon the interior of the mold cavity 21, there is
~L242058
successively introduced into the mold cavity a stream of pressurized gas through the
orifices 41 applying uniform pressure to the plsstic skin formed upon the interior of
the mold cavity 21 and for producing an internal or interior corrugated zone or body
with the inwardly fed plastic material until the mold cavity 21 is filled therewith.
With the method and apparatus the probe 31 or head 39 is encapsulated or swallowed
by the plastic material at the beginning of the shot as represented by the puddle of
plastic P in Pigure 1 and elsewhere in the application. In the operation definedillustrated Pigure 1, the manual valve 49 provides a means by which pressurized gas
can be intermittently injected into the mold cavity 21 until the plastic material
injected thereinto through the sprue 19 has formed the corrugated core for the molded
part or product. In the molding process, after the pressurized gas supply is turned off
by the valve 49, the valve 47 is manually opened to vent the mold cavity 21 and the
molded part to atmosphere for relieving entrapped gases therein. It should be
appreciated from reviewing the above described method steps that a small amount of
plastic is first introduced into the mold cavity followed by jointly (a) continuing the
introduction of the plastic material, and (b) either continuosly or intermittently
introducing pressurized gas to form the corrugated zone or body of the twin-wallinternally corrugated plastic structural part.
A more sophisticated molding apparatus is designated by the numeral
57 in Figures 5 and 6 which includes movable mold member 13 and stationary mold
member lS defining therebetween, when closed, a sealed molding cavity 21 the same
as above described with respect to Figure 1. One of the mold members 13 has a mold
face 27 corresponding to Pigure 1 and a corresponding transverse bore 29 which
receives the probe 59, whose mount nange 33 is secured to mold member 13 by
fasteners 35. A fan gate, not shown, could be used with the apparatus of Figures 5 and
6 although it is not required and is therefore optional.
Probe 59 at one end has a tapered head 61 having a fluid outlet 63.
Alternately or in addition to the outlet 63 are a plurality or series of radially directed
right angularly related orifices 41, such as shown in Figure 4, for delivering pressurized
gas into the mold cavity 21. The plurality of orifices 41 may be located to extend
upwardly rather than radially when viewed in Figures 5 and 6.
058
A tapered seat 65 is formed within head l normally in registry with
the orifices 41. It should be understood that other configurations of valve heads and
valve seats may be used in place of the tapered configurations illustrated in Figures 5
and 6. As an example, a pointed end may be provided on the valve head which
cooperates with Q flat valve seat of the type shown in Figures 7-11 inclusive. Mold
member 13 is mounted upon and secured to travel plate or movable platen 67, Figure 5
forming a part of a conventional vertical or horizontal press. Mold member 15
underlies and is secured to the fixed support plate or platen 69, Figure 5 by the
fasteners 76. Guide rods 71 are secured as at 75 to the fixed support pl&te 69 and
10 guidably extend through the travel plate 67. Plate 67 has a central support 105 and a
clamp actuator 107 of a conventional construction, by which mold member 13 is
brought into snug sealing registry with mold member 15 and clamped together thereby
defining the sealed mold cavity 21.
Fragmentarily shown in Figure 5 is the nozzle 109 for the plastic
material 19 to be injected into cavity 21. The nozzel 109 is in cooperative registry
with sprue bushing 110 coaxial of sprue bore 17 within mold member 15. A reciprocal
material shut off pin 77, is fragmentarily shown as axially disposed within nozzle 109;
and in the position shown is blocking off the flow of plastic material 19 to the sprue
17. However, when the pin 77 is opened the head 61 is swallowed or encapsulated at
20 the beginning of the shot as represented by the plastic puddle P in Figures 5 and 6.
A plurality of interconnected holes or water or cooling channels ~9
are formed through the respective mold members 13 and 15 and are adapted to receive
cooling fluid for use during the cooling cycle of the method and after the molding of
the article within the mold cavity 21. Cooling fluids may be employed such as chilled
water, carbon dioxide, Freo~or other cooling fluids as is known in the art.
The mold members 13 and 15 are not normally pre-heated and are
operated at temperatures between 50 F to 100 F except where polycarbonate
material is utilized. In such a case the mold temperature is approximately 190 F to
240 F. The temperature of the mold members corresponds to the temperature used in
30 injection molding.
Nested within the travel plate or platen 67 centrally thereof is a
fitting 81 which has a bore 83, Figure 6 to guidably receive the oscillating valve rod
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89. The rod 89 at one end has, as an example, a tapered valve element 91 seated in
Figure 6 with respect to the tapered set 65 within the probe head 61 normally closing
off the orifices 41 in communication with mold cavity 21.
The fitting 81 has a counterbore 85 which is in communicationwith the
fluid chamber or passage 87 which extends axially ~sf the probe 59. The conduit 45 is
connected to a source of pressurized gas such as nitrogen at 55 as shown in Pigures 1
and 5 and includes a fitting member 43 which is connected to fitting 81 for delivering
pressurized gas into the counterbore 85 of the fitting 81 and into the communicating
passage or fluid chamber 87.
Vent pipe or conduit 95 normally communicating with atmosphere and
through some form of vent valve means such as shown at 47, Figure 5, is sdapted for
venting the passages 85, 87 at the completion of the molding of the twin-wall,
internally corrugated plastic structural part in order to permit the escape of
pressurized gas entrapped within mold cavity 21 or within the hollow pockets, voids
and slits of the molded part, as will be explained in connection with Figures 12 and 13.
This would occur, however, when the valve rod 89 is intermittently retracted from the
position shown in Figure 6 so that there is communication between the passage 87 and
the single orifice 63 or the series of orifices 41 to the interior of the mold cavity 21.
In the present method and as shown in Figures 5 and 6, pressurized
20 gas from source 55, conduit 45 and fitting 81 to the passages 85 and 87 is
intermittently directed through the orifices 41, under the control of the oscillatable
valve rod 89 connected to the oscillator 97. The oscillator 97 has a reciprocal element
which is secured to the valve rod 89 by which the valve rod 89 is reciprocated during
molding in a plurality of cycles such as four to one hundred cycles per second
approximately. In the molding process, and during the introduction of plastic material
within the mold cavity 21, minute amounts of pressurized gas are intermittently or
continuously injected into the plastic material to form the internal corrugated zone or
body of the part.
The present oscillator valve assembly, as one example, is available on
30 the market and may be purchased from Atkomatic Valve Company, Inc., located at 141
South Sherman Drive, Indianapolis, Indiana 46201. Specifically an Atkomatic 12000
serves, high pressure bronze solenoid valve which operates up to 3,000 psi may be used.
4~205~3
The oscillator 97 may be electrically, pneumatically or even
hydraulically operated with its primary function of effecting a plurality of oscillations
or intermittent movements of the valve rod 89 for opening and closing the orifices 41
in an intermittent manner during the molding process.
Figures 6 A and 6 B show a modified probe 61' having a bore or
passage 87' with an orfice 41' at the outer extremity of same of a size in the range of
.003 to .010 inch. A modified valve rod or member 89' has a pointed or tapered valve
element 91' which is seated in Figure 6 A with respect to the tapered seat 65' within
the probe head 61' to close orifice 41' from communication with the mold cavity.
When the valve member 89' is oscillated to open, the tapered valve
element 91' is moved away from the orifice 41' as shown in Figure 6 B to permit the
inert gas in passage 87', located in the modified probe 61' and surrounding the valve
member 89', to be injected into the mold cavity through the orfice 41'. Therefore in
certain application a single axially located orfice may be used along or in combination
with a plurality of angularily related orficies as explained previously. It should be
appreciated that a suitable fan gate or gating structure will be employed with the
modified valve structure of Figures 6 A and 6 B.
The flow rate of the plastic material is tailored to the number of
pumps or cycles required to inject it into the mold cavity 21. In addition the
20 relationship between the speed or rate of injection of the plastic material and the rate
of injection of the inert gas is important to insure that the inert gas does not out
distance the flow of the plastic material in the cavity. The plastic material has to
flow faster than the inert gas which in the apparatus and during the method is helping,
assisting and is thereby urging the plastic material to the extremities of the mold
cavity 21 to completely fill it. As noted previously the inert gas is introduced with the
plastic material to form the corrugated body or zone of the structural part either
preferably intermittently or continuously for some limited applications where
structural strength of the molded part is not critical.
A more sophisticated embodiment of the present invention is
30 illustrated by the mold apparatus 111, Figures 7 and 8, incorporating a stationary probe
113 corresponding to the stationary probe 59 of Figures 5 and 6.
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X~205~3 .
Without repeating in detail the construction of the mold apparatus,
there is included the mold members 13 and 15, fragmentarily shown, which when sealed
together closed as in Figure 7 define the mold cavity 21. As above described, the sprue
or bore 17 of the mold member 15 has injected thereinto as at 19, the preheated
moldable thermo plastic resin composition material hereafter referred to as plastic
material. No fan gate is employed in the mold cavity 21 although one could be used as
explained previously.
Probe 113 has a head 115 which projects beyond the mold face 27 so
that the single orifice 117 therein is centrally disposed substantially within the cavity
1021 for the purpose of intermittently injecting the pressurized inert gas into the mold
cavity 21. Also, an us an optional felture us shown in Figure 8, he'd 115 my employ
the axial outlet or orifice 117 through which some pressurized gas may be delivered to
the mold cavity 21 in conjunction with the series of radially directed orifices 41, when
the valve rod 121 has been retracted.from the position shown in Figures 7 and 8.The valve rod 121 has a tapered valve element 123 upon one end
adapted for cooperative sealing registry with the tapered valve seat 65 for normally
closing off the orifices 41 and aperture 117.
The oscillator assembly 97 includes an oscillator 125, Figure 7, which
is normally spring biased outwardly as by the coiled spring 127 normally maintaining
20the valve rod 121 and the valve element 123 seated with respect to orifices 41, Figure
8.
Probe 113 has a base 129 and an axial threaded shank 131 which is
threaded into mold member 13. Oscillator body 133 has an axial threaded boss 135which is threaded up into probe base 129 for securing the oscillator assembly 97 with
respect to mold member 13.
The oscillator assembly 97 may be pneumatic, electrically or
hydraulically operated as schematically shown by the element 137. Upon energization
thereof the oscillator 125 will reciprocate causing a simultaneous intermittent
reciprocal movement of the valve rod 121 for successively opening and closing the
30orifices 41 in the probe head 115.
In the mold apparatus 111, Figure 7, there is shown-a conventional
fluid control valve 139 which in the normaUy closed position of its valve spool 141
under the action of spring 143 vents to atmosphere as at the port 147. Energization of
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OS8
the solenoid 145 will move the valve spool 141 to its active position for directing the
flow of pressurized gas through the conduit 45 to the fitting 43 for communication
with fluid or gas chamber 119. Interposed in the conduit 45 connected to the source of
pressurized nitrogen or inert gas 55, Figure 7, is a normally open gas delay timer 149.
Also applied to the conduit 45 in communication therewith is the normally open gas
injection timer 151.
ln practicing the present method initially, the plastic material is
injected as at 19 into the sprue 17 of mold member 15 for injection into the mold
cavity 21 for impinging upon and dispersion over the mold members 13, 15 to thereby
10 form a generally continuous skin of a predetermined relatively thin thickness
throughout and over the surfaces of the mold members 13 and 15. The gas delay timer
149 times out admitt}ng the flow of gas through the conduit 45 and at the same time
the normally open gas injection timer 151 is activated for a predetermined interval for
thereafter shutting off the flow of pressurized gas into chamber 119 and successively
into the mold cavity 21.
The timing out of the gas injection timer 151 corresponds to the time
necessary for the plastic material injected at sprue 17 to fill the mold cavity. The
initial introduction of the pressurized gas assist in the formation of the skin upon the
molded part by urging the plastic material against the walls of the mold cavity.
20 Successively thereafter during the intermfttent injection of the pressurized gas and the
continuous injection of plastic material into the mold cavity, there is a commingling of
the plastic material with the pressurized gas as both plastic and gas are injected into
the mold cavity 21, progressively forming the internal corrugated zone or body of the
molded part which is integral with and bonded to the skin.
Thus, the gas injection timer 151 is preset to permit the continued
flow of pressurized gas intermittently under the control of the oscillator assembly 97
until the cavity 21 has been filled with plastic material completing the formation of
the molded part. Subsequently, as a part of the molding process the molded part is
cooled in the manner above described. After the mold part has become solidifed, a
30 further step is the venting of the mold cavity 21 by activating the oscillator and
reciprocating the valve rod 121.
At the moment that the cavity 21, has been filled with plastic
material completing the formation of the molded part, the flow of plastic material
42~58
into the mold is interrupted. Simultaneously the flow of pressurized gas is stopped.
- The solenoid 145 of the control valve 139 is held open to allow pressure to stay in the
cavity 21 for a period of time to permit the plastic to set up and to prevent collapse of
the twin-wall corrugated plastic structural part. The gas pressure is held on for thirty
to sixty seconds. After the expiration of the time the spring means 143 moves the
valve spool 145 to the position shown in Figure 7 venting the passage 119 to
atmosphere. SubsequenUy thereto, the valve rod 121 is intermittently retracted for a
short period to permit venting of the mold cavity 21 to atmosphere through the control
valve 139. This is for the purpose of permitting the escape of entrapped pressurized
10 gas within the mold cavity 21 and within the molded part. The valve rod 121 is
returned to the position shown in Figures 7 and 8 closing off the orifices. At that
time in a conventional operation of the press, the mold member 13, Figure 7 is
retracted with respect to the mold member 15 utilizing the actuator 107, Figure 5.
Simultaneously the ejector bar 101 and the connected ejector pins 103 are advanced
partly into the cavity 21 for separating the molded twin-wall corrugated structured
part from the mold members 13,15 and for removal from the mold so that the molding
cycle can be repeated in an automatic manner.
Figure 8 A shows a modified single valve and valve seat construction.
The valve element 121' is adapted to seat against a curved or rounded valve seat 122to
20 stop the flow of gas. It is intermittently opened like the other probes previously
described and permits gas to enter the slotted pocket or opening 124 which leads to a
plurality of orifices 126 located in the probe head. Gas enters the mold cavity through
the orifices 126.
The modified mold apparatus 153 which includes a retractable probe
113 is shown in Figures 9, 10 and 11, and without repetition includes much of the
structure above described with respect to Figures 7 and 8.
The function and operation of the reciprocal valve rod 121 in probe
113is nevertheless under the control of the oscillator assembly 97. The oscillator 125
is normally spring biased to the position shown in Figure 7 and is connected to the
valve element 121 for effecting a series of oscillations for opening and closing the
valve element 123 for intermittently directing pressurized inert gas, such as nitrogen,
into the mold chamber 21 during the injection thereinto of plastic material for forming
a molded structural part within cavity 21.
1~4~05f~
In the mold apparstus 153, there has been added thereto the function-
and apparatus by which the probe 113 is retractable such as to the position shown in
Figure 9 before the molding step. During molding the probe 113 will be advanced to the
position shown in Figure 10 with the orifices 41 exposed for lateral dispersion of
minute quantities of pressurized gas intermittently into the mold cavity 21. To the
extent that the mold apparatus 153 corresponds in structure to the mold apparatus 111,
Figure 7, the detail of this construction is not repeated.
Additionally, the mold apparatus 153 provides a means by which the
probe assembly, to which is connected the oscillator 97, is fed alternately inwardly and
10 outwardly. Bushing 155 underlies the mold member 13 and is threaded into a
corresponding bore 157. Reciprocal slide 159 has a head 161 at one end and at its
opposite end a threaded shank 163 which extends into bore 157 and has secured
thereover stop nut or support nut 165. The nut 165 is in registry with bushing 155 for
limiting downward movement of the slide 159.
Shoulder 161 in the retracted position is normally spaced from
bushing 155 a distance of 1/8 of an inch, approximately, which corresponds to the
amount of in and out movement 167, shown in Figure 9, of the slide 159 which is
axially connected to the probe 113 for movement in unison.
For the purpose of effecting the intermittent movements of the slide
20 159 mounting the probe 113 there is provided a power operated conventional cylinder
assembly 169, schematically shown, having a reciprocal piston rod 171, and secured to
the undersurface of the mold member 13 as by fasteners 173.
Control valve 175 in a conventional manner is connected to a source
of pressurized air; and a pair of conduits are connected to opposite ends of the cylinder
assembly 169 for effecting reciprocal movements of the piston rod 171 as desired.
Piston rod 171 at one end is connected to the clevis 179 from which projects one or a
pair of elongated cam bars 181 which are inclined upwardly at an acute angle and
which extend through corresponding cam slots 183 formed within the slide 159.
Accordingly, forward movement of the piston rod 171 causes the slide
30 159 and the connected valve rod 119 to retract such as to the position shown in Figure
9. When the piston rod 171 is retracted, under the control of the valve 175, the probe
head 115 on the probe body 113 will be elevated such as to the position shown in
Figures 10 and 11. Here the orifices 41 and outlet 117 are in communication with the
interior of the mold cavity 21 centrally thereof.
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~L242~8
While the valve rod 121 is intermittently reciprocated by the
oscillator assembly 97 resulting in a large number of oscillations during the period of
forming the molded plsstic corrugated product or part, the cylinder assembly 169 will
only be activated at the beginning of the molding cycle and retracted at the end of the
molding cycle. Thus, the reciprocation of the piston rod 171 is slow compared to the
oscillations of the valve rod 121 in the range of between 4 and 100 cycles per second.
The following method steps are involved in the present process
utilizing the apparatus shown in Figures 7 and 8.
1. The mold is closed by bringing together mold members 13 and 15 to
10 define the sealed molding cavity 21 utilizing the conventional apparatus shown in
Figure 5.
2. Open the fluid controlled valve 139 by energizing solenoid 145 so that
pressurized gas from the source 55 is directed through the normally open timers 149
and 151 into the probe chamber 119 at a preselected pressure such as would be
designated by the gauge shown at 51-53, Figure 1.
3. Start injecting plastic material at 19 through the sprue 17 within
mold member 15, Figure 7 and simultaneously start the gas delay timer 149.
4. This initial introduction of a little or small amount of plastic material
injected into the mold cavity 21 causes it to impinge upon and be dispersed over the
20 mold members and the surfaces thereof defining the cavity 21 thereby forming a
generally continuous skin of predetermined thickness throughout and over the surfaces
of the mold members. Almost simultaneously but after the small amount of plastic has
been introduced and after the gas delay timer 149 times out, the oscillator 97 is
energized causing the valve rod 121 to oscillate rapidly for opening and closing the
orifice 117, Figure 8. Oscillation is controlled electronically at a rate of between 4 to
100 cycles per second.
5. Simultaneously, with the proceeding step, the gas injection timer 151
is started.
6. When the gas injection timer 151 times out, the oscillator 97 is
30 deactivated to stop oscillation of the valve rod 121. At the same time, the solenoid of
the fluid control valve 139 is held open to allow the pressure of the gas to stay in the
cavity 21 for thirty to sixty seconds to permit the plastic to set and to thereby prevent
the collapse of the corrugated molded part. After the time has expired, the spring 143
--17--
'LZ~L~Orj8
automatically moves the valve spool 141 therein to the position shown in Figure 7
venting the pressurized gas. At the same time chamber 119 is vented to atmosphere as
at port 147. During the period that the chamber 119 is vented to atmosphere, the
valve rod 121 is intermittently retracted unseating the valve element 123 with respect
to the valve seat 65, Pigure 8 in order to vent the cavity 21 and the molded corrugated
part therein letting or permitting the entrapped pressurized gas escape to atmosphere
through port 147.
7. After complete venting, rod 121 is biased to the closed position shown
in Figures 7 and 8.
A conventional step that is now required is such sufîicient cooling of
the mold members as to assure that the molded part has congealed and is sufficiently
solid, after which the mold members are separated in a conventional manner and the
molded part ejected therefrom.
The molding steps involving the retractable probe 113 is similar in
many respects to the &bove steps of operation defined with respect to the stationary
probe. These process steps are as follows:
1. Close the mold members 13 and 15 defining the sealed cavity 21
therebetween in a convention manner.
2. Probe 113 and the connected head 115 are advanced from the position
20 shown in Figure 9 to the position shown in Figure 11. This is accomplished by
retracting the piston rod 171 from the position shown in Figure 9 causing an upward
movement of the slide 159 limited by the stop shoulder 161 with respect to the bushing
155. This advanced position is shown in Pigure 11 with the orifices 41 in
communication with the mold cavity 21, Figure 9.
3. Open the gas control valve 49 to pressurize the probe chamber 119
with pressurized gas at a preselected pressure.
4. Start injecting plastic material at 19 through the sprue 17 and
simultaneously start the gas delay timer 149. This means that at the beginning of the
molding cycle, the initially injected plastic material is injected in the mold cavity 21
30 and impinges upon and is dispersed over the mold members 13, 15 thereby forming a
generally continuous skin of predetermined relatively thin thickness throughout and
over the surfaces of the mold members.
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05~3
5. While the plastic material is continuing to be injected into the mold
cavity 21, the gas delay timer 149 times out as preset and the oscillator 97 is activated
and rapidly opens and closes the orifice 117 under the control of the oscillator
operated valve rod 121. The oscillator is controlled electronically at a rate of 4 to 1~0
cycles per second. Simultaneously with the proceeding step for starting the injecting
of plastic material, the gas injection timer 151 is started. This timer 151 is set for a
period which corresponds to the time needed for the mold cavity 21 to be filled with
the foamed material achieved by the intermixing of the continuously fed plastic
material with respect to the intermittently dispersed pressurized inert or nitrogen gas
10 within the mold cavity 21.
6. The successive alternate injecting of inert gas under pressure during
the continued injection of the plastic material into the cavity 21 first pressurizes the
plastic skin theretofore formed against the walls of the mold cavity and progressively
corrugates the inwardly flowing plastic material as it enters the cavity until the cavity
21 is filled with a corrugated body or zone integral with and bonded to the smooth
outer skin.
7. When the gas timer 151 times out, the oscillator 97 is deenergized
stopping oscillation of the valve rod 121. The fluid control valve 139 is held open to
allow the pressure of the gas to remain in the cavity 21 for thirty to sixty seconds to
20 permit the plastic to set and to thereby prevent the collapse of the twin-wall
corrugated molded part. After the time has expired the solenoid 145 is deenergized
and shuts off further supply of pressurized gas to the chamber 119 and at the same
time vents the gas within the chamber 119 to atmosphere as at port 147. At this time,
valve rod 121 is retracted a short distance under the control of the oscillator 97 so
that mold cavity 21 and the molded part therein is vented to atmosphere drawing
entrapped gas from the cavity 21 and from the molded part or article.
8. After completing venting, the rod 121 is automatically closed such as
to the position shown in Figure 11.
9. Probe 113 is retracted under the action of the cylinder assembly 169
30 which allows or permits the plastic material to seal the hole in the part left by the
retracted probe. The successive conventional steps include the cooling of the mold
members 13, 15 in order that the molded part be solidified. Thereafter one mold
member is retracted and the molded part ejected in a conventional manner so that the
apparatus is ready for a repeat cycle.
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~.24~:05B
It should be appreciated that a plurality of gas injecting probes may
be used to inject gas under pressure into the mold cavity or cavities. One gas probe is
used with each plastic injection sprue. The probe and sprue are normally mounted in
the mold assembly in opposed relationship as illustrated in the drawings. The teachings
of this application may be applied to multiple sprues and multiple gas probes used in a
single mold cavity or in multiple mold cavities as is known in the art.
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