Note: Descriptions are shown in the official language in which they were submitted.
;;3,742-015
~ ~ $ ~3
Expree6 Mail: FB622002579
~l~OD A7iO APPARA'l'ilS FOR GAS ASSI:5Tel) I:HJRCTlON
MQLDI~ E~ING PRi~~5E CO}~ROL OF ~Nl!ECT C~l_ AND IIIIQLDING PRI~
STI~PPI~ IOLD~Q~QBILIT~
~a =IQlY
The present invention relates to gas assi6ted injection
molding and to a gas control 6yfitem for use in a Bas a6sisted iniection
molding system. Mcre particularly, the invention relate6 to a method
and apparatus for gas assisted injection molding which h~ the ability
to in~ect ~ shot of molten plastic into on in~ection mold, ahut off the
plastic flow, and in~ect a gas at a flrst predetermined and preci~ely
control pressure into the melt, elther almo6t lnstantaneou~ly or after a
delayed time. The pre6ent invention then has the ability to 6tep up
and/or step down and/or hold the Bas under pre6~ure in an Qlmost
infinite v~riety of patterns while the pla~tic i~ cooling in the mold,
fin311y drrivlng at R step down or controlled vent pres~ure when the
part i6 sufficiently cooled to be self-6upporting, followed by opening
the mold and removing the article.
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~eSCRI~TlQN OF 2~E P~I0~ A~
The history of injection molding as a manufacturing procesa
is relatively recent compared to 60me other manufscturing methods. In
the infancy of lnJection molding, article~ were generally proauced by
injectlng a molten plastic or resin material into a mold cavity, aDd
letting the material cool to form a molded article, at which time the
mold cavity wa6 opened and the article was relea6ed.
Afi the art of conventional injection molding advanced,
attempts were made to make larger and larger parts. It became evident
that there were many re6trictions on the ability of conventional
injection molding in 60me of the6e application6. Some restriction~
which were found were the impossibility to match, while molding a part,
different factor6 6uch a6 the presence of large, flat surface6, diverse
and heavy wall 6ection6 and exceptionally long flow6 with the need for
acceptable physical properties, good productivity and investment level6,
and an aesthetically pleagiDg surface fini6h.
These con6iderations were fo~md to be part~cularly relevant
in the electronic3 industry, where there was the need for enclosures for
television sets, computers, printers and the like in the homa
furnishlngs industry, where there wa~ a need for large parts for gArden
chairs and tables, bathroom furnishings, and the like. Also presenting
a problem were tools, handles and machinery components in general, and
in the automobile industry in particular. A particularly aggravating
problem was the tendency of sink mark~ to appear opposite large or thick
rib sections. This led those skilled in the art to devi~e a method and
apparatuG capable of generating a pres~ure inside the molded component
in addition to the injection pressure exerted by the m&chine at the
in~ection point.
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63,742-015 ~ 35 ~
One solution that proved satlsfactory for so0e injection
molded parts was the use of 6tructural foam6. Proces6es for fitructural
foam molding date back to the 1960s. In the 6tructural foam molding
proce66, a gas and polymer mixture is injected inside the pla6ticizing
barrel or the nozzle of the injection molding machil~e. Once injected,
the ga~ expands and form6 cavities which are generally closed cell6 in
which ga6 i6 entrapped. The structural foam in~ecting proces6 reduces
internal 6tresses and surface sink marks, and permits a reduction in the
weight of the material used. However, for some applications, it was
found that gas bubbleG could migrate to the surface and burst
therethrough, resulting in the unsuitability of the foam process for
certain parts. A1BO~ the cycle time i9 longer and special mold~ need to
be uaed. Therefore, the foam injection molding process remailled
unsatisfactory for many spplications, and those in the art continued
their search to find a satisfactory method of injection molding for use
on lnrge and/or complicated parts.
In order to solve the problemg in the in~ection molding art
which could not be solved with structural foam molding and other
methods, several in the art developed the proce6~ of gas assisted
ln~ection molding. In gas agsisted in~ection molding, unlike ~tructural
foam moldin~ the cavities formed in the molded component remain in
connection wlth the injection point of the gas. In such a process, the
mold is filled with molten plastic or synthetic res~n molding material
which, in many processe6, i6 leBB than the volume which is nece6sary to
fill the mold. The fllling of the mold is completed by the injection of
a gas into the molding material contained in the mold. This re~ult6 in
the formation of a cavity or cavities within the molding material. The
pressure of the injection gas compre6se6 or pack6 the melt againat the
mold walls during the curing state, resulting in the eliminfltion of 6ink
marks oppofiite thicker ~ections or ribs and the like.
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Many variations of the gas aggigted injection molding
proceg6 are present in the prior art. For example, U.S. Patent Number
4,106,617 requlrea a "aprue break" for venting the gag out of the part
before opening the mold. U.S. Patent Number 4,106,887 requires gas to
be injected through a needle valve within a runner which ig movably
mounted and engagable in the cavity Kate. U.S. Patent Number 4,140,672
provideg for the injection of viscou~ llquid which, at room temperature~
ig either a grease or solid.
U.S. Patent Number6 4,136,220 and 4,247,515 relate to the
formation of a structural web type material. U.S. Patent Number
4,498,860 relatea to a movable ram a6sociated with the cavity gate which
is used to cut off the 6prue. U.S. Patent Numberg 4,830,812 and
4,913,644 relate to cutting members within the mold body that are u~ed
to vent the pressurized gas. V.S. Patent Number 4,923,666 relate6 to a
method wherein the cavity ig fully packed with resin before gas
injection, and gag cavitie6 are formed only in areas in which there i8
6ignificant ghrinka8e.
U.S. Patent Number 4,923,677 requires a gas venting pa6sage
~eparAte from either the resin or gas injection pasgages. U.S. Patent
Number 4,943,407 require~ that gag injectlon be through the sprue
buahing. U.S. P~tent Number 4,944,910 require8 a simultaneous lnjection
of the resln and gag during the molding cycle, while U.S. Patent Number
4,948,547 requires that the injection ga~ i~ confined to the resln flow
path, and that lt does Dot enter the artlcle defining area. And
finally, U.S. Patent Number 5,0Z8,377 requireg a flow path at leaat
partially defined by a movable member where~n the pre~sure of the molten
pla~tic can be reduced in a controlled manner by moving the movable
member prior to ga6 injection.
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Also, variou6 type~ of control systems have been developed
in the prior art to control the prefi~ure of the injection gas. U.S.
Patent Number 4,824,732 requires a variable volume chamber for gas
storage and control. The gas i6 injected at a controlled rate by
reducing the volume of the variable volume chamber. U.S. Patent Number
4,855,094 require6 the lnjection of the gas at a predetermined pres~ure
no greater than the resln in~ection pre6sure. U.S. Patent Number
4,9~5,191 require6 that both the resin and the ga6 be injected
cimultaneou~ly for at lea6t a portion of the in~ection cycle. And U.S.
Patent Number 5,015,166 provides for a control ~ystem for ~upplying a
vsriable volume of a 8a~ art at a predetermined pres6ure and maintaining
that pre66ure at a aubstantially con~tant level. All of these patents
perform generally saticfactorily, but leave one or more problems in the
injection molding art. Thus, tho6e 6killed in the art continued their
6earch for a 6ati6factory gAS a~6isted injection molding method and
apparatu~.
Applicants have found, QS more fully explained in co-pending
Patent Applic~tion Serial Number 07/628,746, filed on December 17, 1990
and entitled "Method and Apparatus for GA8 Assiated In~ection Molding",
that ~tartin8 a flow of in~ection ga8 during the time that a flow of
molten material i~ ta~ing place hac caused the problem of clogging of
the ga6 sup~ly p~8ge8 due to the molten material entering and clogging
the supply pas~age during the lnitial injection of molten plastic. This
ha~ involved costly down time and complicated apparatus to try and
prevent the entry of the molten molding material into the gas ~upply
~ystem. In Patent Appl;cation Serial Number 07/628,746, which is
~pecifically incorporated herein by re~erence, lt i8 shown that ~t i~
po~sible to sequentially first introduce 8 moldlng material into the
mold cavity, and then 0hut off the 6upply of plastic. Thereafter,
pre~curlzed gas is introduced through the injection nozzle into the
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interior of the mold cavity, producing a 6ati~factory 601ution to Lhe
problems in the prior art.
Further work by the Applicants since the filing of Patent
Applicstion Serial Number 07/628,746 has shown that it is also pos6ible
to eliminate problem6 and to provide a higher quality part by providing
a method and apparatus which produces precise and careful control of the
presgure of the injection gas during injection into the part and during
the cooling process. The method and apparatu6 for preci6ion control of
the injection gas is preferably used in Applicants' system, wherein the
ga6 injection i~ not started until after the supply of molten resin or
plastic into the mold is stopped. It should be understood, however,
that such system can also be used to improve the perEormance of other
prior art gas assisted injection molding systems made by others.
SUMMAR~ QF Tn rN~NT~~
To solve the problems in the prior art, and to provide for
precise control of the pressure of the injection gas during injection~
and while within the molded part during the coolin~ proces6, a method
and epparatus for ga6 assi6ted injection molding i6 provided which will
fir6t inject a chot of molten plastic into a 6uitable mold, 6hut off the
plastic flow into the mold9 inject a suitable gas at a predetermined and
preclsely controlled pressure into the mold, immediately, or after a
delayed time, step up or step down the pres6ure in the mold in a finite
number of 8teps to arrive at a second predetermined and precisely
controlled pressure, hold the second predetermined pressure for a
desired time, repeat the 6ettin~ and holding of pressure as many times
as desired, step down the pressure to a final predetermined pressure,
and open the mold and remove the article.
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In a first embodiment of the invention, R method is provided
wherein a quantity of molten plsstic or other material i6 injected into
a mold, the flow of molten material is 6hut off, and a ga6 i6 injected
into the mold at a predetermined and precisely controlled presgure after
a delay time (Tl 2 O). The method continues by 6tepping down the
pressure over time to a second predetermined and preclsely controlled
pres6ure, which i6 held for ~ second time (Tz > O). A final 6tep down
of pres6ure to a final or controlled vent pres6ure is made, and the mold
iE opened and the article is removed.
In a second embodiment of the present invention, a method ig
provided whereby an smount of plastic less than is nece6sary to fill the
mold is injected lnto a mold cavity. The flow of plastic into the mold
is then 6hut off, after which a delay time may be introduced, if
desired. The method continues with an in3ection of gas at a
predetermined pres6ure, after which t!-e pressure of the gas may be
repeatedly ~ncreaeed and/or decreased in finite steps, determined by the
particular application, to produce a predetermined number of hold
pres6ures during the cool down cycle, terminating with a step down or
final vent pressure which i6 arrived at before the mold is opened and
the article removed.
In ¬her modlfication ~ the pre6ent invention, an
apparatus ls provided for injecting a molten molding material into a
mold cavity. Apparatus is provided to shut off the flow of material and
to in3ect a gas, preferably nitrogen, at a predetermlned and precisely
controlled pressure after a delsy time (Tl > 0~. Apparatus is further
provided to step down the pressure to a second predetermined and
precisely controlled pressure, and to hold the pressure in the part at
the second predetermined pre6sure for a time greater than or equal to
zero (T2 > O). The apparatus then has means to further step down the
pressure to atmosphere, and to open the mold and remove the article.
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In a 6tlll further modification of the present invention, a
source of gag or gas supply at a commercially available pre66ure i6
pas6ed through f~ ga6 booæter to increa6e its pre6sure to a pres6ure
higher than desired for the injection molding proce6s. The ga6 i6 then
filtered and p~s6ed through n conduit to a preasure regulator which ha6
a fixed volume ga6 re6ervoir immediately upstream therefrom. The
pres6ure regulator then lower6 the gas pressure to a desired lnjection
pre66ure and, at the appropriate time, the gas i8 pas6ed through a fast
operatiDg valve lnto the mold. The flow of gas iB then shut off. A
computer, including a programmable logic controller (PLC), connected to
the sy6tem, in addition to operating the other devices just de6cribed,
operates a back pre~sure regulator to step up and atep down the gas
pres6ure in the mold, as desired, until 6uch time as the part has
cooled, the pres6ure has been lowered to a final vent pre6sure, and the
mold is opened.
Thus, it is one of the objects of the present invention to
provide a method of ga6 as6i6ted injection molding where the pressure of
the injectlon gas can be closely controlled.
It is another ob~ect of the pre8ent invention to provide a
method and apparatus for gas essisted in~ection molding where the
pre6sure of the 8a~ in the mold during the mold cooling procea6 can be
closely controlled.
Another object of the present invention i6 to provide a
rnethod for gas a6sisted injectlon molding wherein a short shot of
pla6tic molding materlal i6 introduced into the interior of a mold
cavity, the flow of plastic molding material iB 6topped, a gas is
injected into the interlor of the mold cavit~r to form a cav~ty or
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63,742-015
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channel in the part being molded, and the pre~gure of the injectlon ga6
in the ga6 cavity is stepped up and/or held and/or stepped down, as
needed, to provide a fini6hed part of optimum quality.
A 6till further object of the present invention i6 to
provide a gn~ assi6ted in~ection molding proce66 where the clo6e control
of gas pre6sure in the part being molded will 6erve to reduce molding
stre6~ and warpage.
A still further object of the pre6ent inventlon ia to
provide a gas a6si~ted injection molding proceg6 whlch provlde improved
elimination of aink mark6.
A still further object of the preæent lnvention i6 to
provide an apparatu6 for ga6 assisted in~ection molding which will
inject a shot of molten plastic or synthetic re~in into the interior of
a mold cavity, cut off the flow of molten plastic or 6ynthetic re6in,
inject a gas into the interior of the molten plastlc or ~ynthetic re6in
to form a cavity or channel in the interior thereof, control the
prea6ure of the gas in6ide the part until 6uch tlme as the part ha6
cooled sufficently to be 6elf supporting, and then allow the mold to be
opened and the part relea6ed.
Another object oE the preaent invention i~ to provide an
-lmproved apparatu~ for injection mclding which will inject a 6hort ~hot
of molding material into the interior of a mold cavity, cut off the flow
of molding material, in~ect a gas at a first predetermned pressure into
the mold cavity thereby forming a ga~ cavlty within the part being
molded, and step up and/or 6tep down and/or hold the gas pres~ure in the
mold a~ needed, dependlng upon the particular application, to provlde a
molded part of optimum quality.
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5~
~ Further objectg and advantages of this lnvention will be
apparent from the following de6cription and appended claims, reference
being had to the accompanying drawing6 forming a part of the
specification, wherein like reference character6 des~gnate corresponding
part~ in the several views.
~RI~F D~S~RIPTI~ OF T~ D~ING~
Figure 1 is a flow chart showing the 6teps followed by the
proce66 or method of the pre6ent invention.
Figure 2 i6 an illu6trative graph 6howing the change6 of
pre6sure with re6pect to time used in the proces6 and apparatus of the
pre6ent invention.
Figure 3 is a diagrammatic view of an apparatus embodying
the present invention.
Figure 4 i6 a detailed 6chematic view of an apparatus
embodying the present invention.
Flgureu 5, 5A, 5B, and 6 illu6trate computer flow charts
6howing the stepa which can be used by the computer or control means
utilized in the present inventlon to control the procesa of the present
invention.
Figure 7 i8 a diagrammatic view ~howing speciflc portions of
the computer con601e, including the progr mmable logic controller, u3ed
in the operation of ths present invention.
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63,742-015
Figure 8 is a view 6howing the card arrangem~nt for the
programmable logic controller shown in Figure 7.
It is to be understood that the present invention is not
llmited in its application to the details of construction and
arrangement of parts illu6trated in the accompan7ing drawings, since the
invention is capable of other embodiments, and of being practiced or
carried out ~n variou6 way6 within the 6cope of the claim6. Also it is
to be under6tood tbat the phraseology and terminology employed herein 18
for the purpose of dezcrlption, and not of limltation.
D~T~IL~D DeS~BI~TI~N 0~ 1 ~
In the method of the pre~ent invention, a full or 6hort shot
of molten pla6tic is injected into the mold cavity. A short shot of
molten resin or plastlc is to be understood to be an mount less than
the volume of the mold cavity. Preferably an amount equal to about 60
to 90 volume percent oE the amount of plastic necessary to fill the mold
i6 injected. While a full shot (i.~Q~, the amount nece6sary to
completely fill the mold cavity) may be lnjected, as uaed ln 60me Ba6
66Gisted injection moldlng mschines, in the preferred embodiment of the
present invention, ~ 6hort shot i~ used.
Referring now to Figures 1 and 2, the step~ used in the
method of the present invention can be understood. It zhould be
under6tood that the numbers applied to the boxeg 6hown ln Figure l will
correspond to the numbers applied to certain portionz of the pres6ure
ver6ua time graph shown ln Figure 2. An injection molding apparatus of
a type well known in the art, which may be 6uch as u6ed in the in~ection
molding apparatus previously de6crlbed, or in Patent Appllcation Serial
Number 07/628,746, will inject a full shot (not ~hown) or a short shot
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of molten plastic (6tep 200) during the time zero to tl ~hown il~ the
graph of Figure 2. At time tl, the 6upply of plagtic or other molding
material is shut off (step 210). After the plastic flow is terminated
and following a delay time (Tl = (t2 - tl) in ~igure 2), a ga6 at a
desired injection preBsure i8 injected into the plaetic material in the
mold cavity (6tep 220). The delay time i8 generally in the range of
about 0 to 60 6econds. The gas pressure within the mold will increase
until time t3, at which point the gas pres6ure is equal to the fir~t
predetermined and preci6ely controlled pressure. The actual injection
duration (i e., t3 - t2 in Figure 2) i6 usually in the range of 0 to 60
6econd6 and more often in the range o~ just a few 6econd6.
Next, the pres6ure in~ide the mold cavity is stepped down or
lowered durine a time TSD (i~e., t4 - t3 in Figure 2) in a predetermined
6eries o~ steps to be more fully explained hereinafter (step 230). The
time TSD is also generally ln the range of 0 to 60 second6. At time t4,
the presaure i6 held at the second predetermined and preci6ely
controlled pressure for a time T2 (~lQ~, t5 - t4 in Figure 2) (6tep
240). At time t5, the gas pressure is stepped down to a final pressure
or controlled vent pres6ure (step 250), which is usually atmospheric
pre66ure or 61ightly above atmospheric pressure, after which the mold
can be opened and the article removed (step 260).
The apparatus to be described hereinafter is capable of, or
can readily be modified to be capable of, stepping down (or, if desired,
stepping up) the pressure in as many a6 100 steps or more using a ~eries
of timers in a programmable logic controller. More or less steps may be
used, depending upon the particular application, and the full capacity
of the apparatu6 does not have to be u~ed in every application.
Generally, it i~ preferred that the number of steps in which the
pressure is dropped is in the range of about 10 to 25 steps, and more
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63,7~2-015 ~ 5~
preferably about 20 steps. It i6 well within the acope of the present
invention to provide an apparatus which can provide for over 20 step~,
if needed or desired.
It should be under6tood that the pressure versus time graph
of Figure 2 is an illustrative example only, and that depending on the
specific application, many other pregsure/time relation6hips may be
suita~le and even preferred. For example, it iB posaible that the
pressure can be increased or 6tepped up for some step~ during the time
period TSD before beinB lowered in a atepwiae fashion to the aecond
predetermined pres~ure. Or, if desired, the pressure can be lowered in
a 6tepwise fashion from the second predetermined pressure to the final
venting pressure. As one gkilled in the art will realize, many otber
pressure/time patterna can be employed within the acope and spirit of
this invention.
It should be further under~tood that the method and
apparatus of the pre~ent invention are usable with any of the
aforementioned 8as ns6isted injection molding ~y6tems, wbether the
plastic i~ injected into the mold cavity through an injection pln,
~hrough a runner, or through a nozzle.
Also, the method and apparatu~ of the present inventlon are
usable whether or not the in~ection of the gas starta after the flow of
molding material i8 completely shut off, or while some of the moldine
material i6 ~till flowlng into the mold or mold cavity. Generally,
however, it i6 preferred that a gaa a~6~sted injectlon molding ~ystem i6
used where the plastic and the preasurized gas are both ~njected into
the mold cavity through a nozzle. It is also generally preferred that
the pre6surized eaa la injected after the flow of molding material ha~
been 6hut off. More preferred iB a gas assisted injection molding
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63,742-015 ~ 3~J~
system wherein the nozzle contains a valve mean6 for controlling the
flow of both pla6tic and pres6urized ga6. Suitsble nozzle6 with valve
means include tho6e described in U.S. ~atent Application Serial Number
07/628,746 filed on December 179 1930, U.S. Patent Application Serial
Number 07/714,117 filed on June 12, 1991, and U.S. Patent Application
Serial Number 07/714,118 filed on June 12, 1991, all of which are hereby
incorporated by reference. As one 6killed in the art will realize, the
ga6 control sy~tem of the present invention can also be used with other
gas delivery sy~tem6. One such other gas dellvery system is described
in U.S. Patent Application Serial Number 07/724,044 filed July 1, 1991,
which i6 hereby incorporated by reference. In thi6 la6t listed Patent
Application, the pressurized gas is introduced through either the nozzle
or the 6prue bu6hing using a cone-shaped checX valve which prevent6 the
flow of molding material back lnto the pressurized ga6 passageways.
Referrin8 now to Figure 3, a diagrammatic view of an
apparatus embodying the construction of the present invention is ~hown.
A 8a6 6upply or 60urce of injection gas 31 is placed in fluid
communication with a gas booster 33 to raise the pre6sure of
commercially available gaæ supplies to a pre6sure higher than a desired
ln~ection pre66ure. A ga6 booster 33, which may be such a6 the
AG~-62/152C ~a6 booster manufactured by Ha6kel Incorporated of Burbank,
California, will increase the injection ~a6 preg~ure ~rom the
co~mercinlly available pre66ure of the gas supply or source of in~ection
gas (i.e., about 500 to 2,500 p8i), to a 6ignificantly higher pressure,
preferably about 8,000 to 13,000 p6i, and more preferably about 12,000
to about 13,000 p6i.
Down6tream of the ga6 boo6ter 33 ig a fixed volume ga6
re6ervolr 39 which, in the preferred embodiments of the pre6ent
invention, ha6 a volume of approxlmately 10 to 100 cubic inchefi, and
prefersbly about 15 to 25 cubic inches, and mo6t preferably about 20
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63,742-015
cubic inches. The combination of the high pressures generatetl by the
gas booster 33 and the fixed volume reservolr 39 perform an important
function in the preferred embodiment of the present invention, a6 will
be explained in detail hereinaf ter in connection with the de6cription of
Figure 4. - ;
DownstreQm of the fixed volume re~ervoir 39 is a pressure
regulator 40 which may be the same as the ER serie~ of electronic
pre66ure regulators manufactured by the TestCom Corporation of Elk
River, Minnesota, or lts equivalent. The use of an electronic regulator
is preferred to Hllow computer control of the sy6tem. The purpose of
the pressure regulator i8 to reduce the pres6ure of the injection gas
from a pressure hlgher than a preferred or de0ired injection pressure to
the first predetermined or desired in~ection pres6ure. In the preferred
ambodiment of the lnvention, the pres6ure wlll be reduced from the
gas-boo6ted pre6sure of approximately 12,000 to 13,000 psi to the
preferred or desired injection pressure of about 1,000 to 6,û00 psi.
The actual injection pres6ure selected will depend, in large part, upon
the plastic u6ed, the mold cavity ~ize, and related parameter6; such a
selection of the appropriate injection pressure i~ within the skill in
the art of ga~ a6sisted in~ection molding.
A f irst pre66ure transducer 41 downætream and in f luid
communlcation with the pressure regulator 40 provides feedback to the
pres6ure regulator via computer 42 to enable the æystem pre66ure to be
maintained at the desired value. The pres6ure transducer 41, the
pressure regulAtor ~0, 6nd the computer 42 form n fir~t control loop
(LOOP 1) for controlling and ad~u6tlng the gas preæ6ure to the first
predetermined and preci6ely controlled pressure. This first
predetermined and preci~ely controlled pressure is the initial pressure
of the ga6 upon injection into the molten plaætic withln the mold 30.
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Important to the preferred embodiment of the method and
apparatu6 of the present invention i6 the Ea6t operating valve 44
located between and connected to the pressure regulator 40 and the mold
30. Since, ln the preferred embodiment of the invention, a method of
gA5 a6si6ted injection molding iB utili~ed where a short shot of-pla6tic
i6 fir6t injected into the mold, the plagtic flow into the mold is
6topped, and the pregsurized or injection ga6 i6 in~ection into the mold
cavity, the speed at which the gas reache6 the pre66ure nece66ary to
break into the hardening reBin iE important. In larger parts, or for
difficult to mold materials, if the break-through or preferred injection
pressure i6 not reached quickly, it may become difficult or impo6sible
to inject tbe ga6 into the plastic within the mold.
It i6~ therefore, preferred that the fast operating valve of
the pre6ent invention be fully opened from its normally clo6ed po6ition
in about l/lOth to 3/lOthc of a gecond ~or fa6ter). This require6
careful 6election of the valve for the present invention. One valve
which has been found to be especially 6atisfactory is the "SNO-TRI~"
Model SS-410~FP-C valve, which ig manufactured by the SNO-TRIR Company
of Cleveland, Ohio. Another suitable value is a Whitey Model
SS-H83P54-31C available from Whitey Company of ~ighland Heights, Ohio;
ba~ed on the manufacturer'6 fipeCifiCatiOn~, thiB YalVe iB alfiO expected
to be e~pecially sati8factory. The fa~t operating valve 44 should open
and very quickly 6upply fully pres6urized injection ga6 to the mold 30.
A second pre6sure transducer 46 is connected to, and in fluid
communication with, the fa6t operating valve 44 down6tream thereof, and
i8 electrically connected to the computer 42. A back pre6sure regulator
is also connected to, and in Eluid communication with, tlle fast
operating valve 44 and the mold 30. The back pres6ure regulator 45 i6
electrically connected to the pre6sure tranaducer 46 via the computer
42, thereby providing a second control loop (LOOP 2~ for control of the
-16-
63,742-015 ;~
gas pressure in the mold cavity after the flow of plastic or resin
molding material is stopped and the pres6urized gas has been injected.
Thus, the second control loop i6 used to control the pres6ure of the gas
within the mold during the pre~sure step down procedure, the holding
pressure procedure, and the venting procedure (steps 230, 240, and 250,
respectively, in Figure 2).
- ~eferring now to Figure 4, a scbematic dlagram
repre~entative of a preferred embodiment of the present invention i5
shown. This preferred embodiment compriseg four basic part~: (1) an
iniection molding Islachine 25, (2) a gas booster system 22, (3) a gas
injection consol 24, and (4) a computer ay6tem 42. The injection
molding machlne 25 has a plastic source, hopper, or source of molding
material 27, (~, thermoplastic, resin, or the like) communicating
with an injection rarn 50. Injection ram 50 plaaticizes, heats, or
otherwise tran6forms materials contained in the hopper or source of
plastic 27 into a molten resin or plastic molding ms-erial which is
trsnsmitted by conduit 51 to the mold 30 which contains a mold cavity
28. Pressurized gas of a predetermined pressure i6 in~ected lnto the
molten resln and the mold cavity 28 through eas inject~on point 60. The
prer6ure of the injected ~a6 is controlled as de~cribed in detall beloe".
A source of injection gas or gas supply 31, which may
consi~t of a plurality of gas cylinder6 (not shown) or a bulk gas
atorage system (not shown) i5 provided as part of the gas booster sy6tem
Z2. The injection gas preferably is nitrogen because it is inert and
relatively inexpen6ive, but other ga6es (e.g., air, argon, carbon
dioxide, Imd the like) may be used, if desired.
The gss supply 31 i6 in fluid communication9 through gas
valve 53, with a fir6t or inlet filter 32 for removlng impurltie6 ln the
-17~
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' : . .
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63,742-015
ga6 6team which might damage the ga6 booster 33. Conventional ga6
filter6 may be uaed (e.~., model number 28728-l manufactured by the
Haskell Manufacturing Company~. Gas filter 32 is connected to the inlet
29 of the gas boo6ter 33.
A 6upply of compressed air i6 used to drlve the gas booster
33. The compre66ed air 6upply 47, which may be building air 6upply or
directly from a compres60r, i6 connected through air filter 54, normally
open 6hut off valve 55, and regulator 56, to the gas boo~ter 33. Air
pre~6ure gage 57 allows the operator to ob6erve the alr pre6sure
delivered to the ga6 boo6ter.
The compre66ed alr 6upply 47 i6 al60 used to operate the
firat pilot 6witch 34 and the second pllot 6witch 35 by meanfi well known
in the art. Instruction6 for the connection of first pilot 6witch 34
and second pilot 6w~tch 35 are normally 6upplied by the manufacturer of
the ga6 boo6ter 33. In the preferred embodiment of the invention, the
fir6t pilot 6witch 34 i8 a decrea6ing pilot 6witch which will deactivate
the ga6 booster 33 if the pre6sure of the gas 8upply 31 to the boo6ter
fall6 below about S00 p6i. ~eactivation of the gas boo6ter 33 in 6uch
ca6es i6 designed to prevent damage to the gas boo~tsr. The fiecond
p~lot switch 35 is an lncrea~ing pllot 6witch which i6 set to vent
excess pres6ure lf the pressure of the ~as exltin~ the 8a6 booster ;s
greater than a ~et value.
The outlet 36 of the ga6 booster is connected to both the
6econd pilot switch 35, the pre6aure relief valve 37, the manual relief
valve 43, and the 6econd gas fllter 38. The preesure r~lief valve 37 i8
uaed, in combination with the 6econd pilot 6witch 35, to vent any exce66
pre06ure generated by the ga6 booster 33. A ~uitable prea6ure relief
valve 37 16 available from Haskell Manufacturlng Comyany afi model number
-18-
63,7~2-015 ~3~S~
15700-25. The relief valve 37 should automatically release exce6s
pre6sure from the 6ystem if the second pilot 6witch 35 fail~ to prevent
the gas booster 33 from gsnerating pre6sures in excess of the generally
preferred 12,000 to 13,000 psi range. In the preferred embodiment of
the pre6ent invention, the 6econd pilot 6witch 35 and the relief valve
37 are 6et at about 500 psi higher than the desired gaG boosted pressure
(e.g., if the ~a6 booster i~ to deliver a pre~sure of 13,000 p8i, the
~econd pilot switch 35 and the relief valve 37 would be set at 13,500
psi). The manual relief or bleed valve 43 i~ also provided as a safety
feature which allow6 the operator to quickly vent or depre~surize the
6y~tem in the event of a malfunction or to vent or depres6urize the
sy6tem eO perform maintenance.
The second filter or outlet filter 38 16 in fluid
communication downætream with the fixed volume reservoir 39. Downstream
of re6ervoir 39, the pre~sure regulator 40 reduces the pressure from the
ga6 booster 33 to a desired injection pressure of about lO00 to 6,000
psi. The pres~ure regulator 40 iB al60 connected by 6uitable electrical
connections to the electro pneumatic controller 58 which form~ part of
the pressure reeulator 40. First pressure transducer 41 ia provided
downstream of the pressure regulator 40, and ~n fluid communication
therewith. The first pre6sure tranaducer 41 is al~o electrically
connected to the programmable logic controller (PLC) 80 of the computer
or control means 42. A flrse control loop (LOOP 1) is establi6hed
between the PLC 80, the first pressure tranaducer 41, and the pressure
regulator 40 (and its electro pneumatic controller 58) to control the
pressure of the inJection gas to a predetermined and precisely
controlled o~ desired injection pres6ure. The electro pneumatic
controller 58 is cormected to and driven by a 60urce of low-pressure
nltrogen (generally about 170 p6i) for control purpo6es, as is well
known in the art.
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63,7~-015 ~ ~ $ ~
The preasure regulator 40 i6 connected to the fa6t operating
valve 44, 6uch ag the SN0-TRIK or Whitey fast operating valve6 described
above (or their equivalent), which will remain normally clG6ed until the
6y6tem is ready to inject gas into the mold 30. The fa6t operating
valve 44 is electrically colmected to the P~C 80 to receive a 6igual
therefrom st the appropriate in~ection time. When the signal 1B
received, the fa6t operating valve 44 open~ and injects, via gas line
~2, n quantity of pre6surized ga6 into the re6in or plastic contained in
mold cavity 28 until a ir6t predetermined and preci6ely controlled
pre~sure i6 reached. Since the fast operating valve 44 will remain open
until the desired pressure within the mold cavity 28 i~ reached, the
actual time the valve remait~s open (tt3 - t2~ in Figure 2) will vary
depending upon the application, and may even vary from cycle to cycle
becau6e of 6uch variable~ as temperature and preasure. It i~ generally
preferred that the gas line ~2 between the fa6t operating valve ~14 and
the injectlon point 60 be as short a6 po66ible to allow injection of the
pre6surized 8as a6 quickly as pos6ible. The desired pressure wlll be
initially programmed lnto the PLC 80 by the operator depending on the
application, and then will be controlled by the control means 4Z
thereafter.
The combination of the high pre6sure provided by the gas
booster 33 and the f~xed volume re6ervoir 39 should prevent, or ~t lea6t
minimize, 6ignificant gas pre~sure drop when the fa6t operating valve 44
opens. Aa noted sbove, the volume of the fixed volume reaervoir 39 i8
normally in the range of about approximately 10 to 100 cubic inche6, and
preferably about 15 to 25 cubic inche6, and most preferably about Z0
cubic inche~. The volume of the fixed volume ga6 reservoir 39 6hould be
large relative to the cumulative volume of the as60ciated gas line6 or
passagewaya between the ga6 booster 33 and the mold cavity 28 60 that,
for example, when the first control loop call6 for additional pre66ure
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:
63,742-015
or the fast operating valve 44 i8 opened, there i6 only a relatively
small chang~ in volume7 and therefore pre6sure, experienced by the
pressurized 8a6 in the fi~ed volume reservoir. Thus, as one skilled in
the art will realize, if the volume of the associated gas passage ways
is increased (e.~., by increasing the length of the pas6age ways ~etween
components~ or if a part with large volume gas channel6 i~ to be made,
it may be necessary to increase the volume of the fixed volume reservoir
39. Limiting the pre~6ure drop in thi6 manner will allow for pres~ure
control with only minimal "over shooting" or "under shooting" of the
"6et" or de6ired pre6sure.
The second pressure transducer 46 and the back pressure
regulator ~5 are connected to each other via the PLC 80 to ~orm a second
control loop (LOOP 2). Thi6 control loop control6 the preHsure in the
mold cavity 28 during the step down and pre6aure holding step6. This
control loop can also be used to increase the pre6sure, if de6ired, in
the mold cavity 28 (i.e., 6tepping up the pre6sure). If the pres~ure is
to be increa6ed, the computer 42 6ignAls the fa~t operatillg valve 44 to
open, thereby increa6ing the pressure ln gaR line 62. Thia 6econd
control loop is also used for controlled venting (250 in Figure 2). In
controlled venting, the pressurized gns i8 vented from the mold cavity
28, via g&6 pa~agew&y 62, through the back preBBure regulator 45.
Normally, the ga6 16 vented to atmo6pherlc pre6sure at the completion of
the molding cycle. In such a ca6e, the pres6ure within the plastic
molded part will be at atmo6pheric pressure. In 60me ca6e6, however, it
msy be de~irable to have re6idual ga~ pre6sure within the mold plastic
article. In such cases, the ga8 6hould be vented to the desired
re6idual pressure (ç~g~, 20 to 50 psi) u6ing the cecond control loop and
then, while holdin~ the de~ired pressure, in~ecting a ~mall quantity of
resin to "seal" the molded plastic part 80 it can retain a positive gaa
preH~ure when, after the "plastic seal" ha6 hardened, the molded part i8
removed from the mold.
.. . . ..
',
63,742-015
In order to begin the injection cycle lt i6 nece88ary,
primarily for 6afety rea60ns~ to determine whether the injection ram 50
ha6 come home and whether the safety 8ate 48 has closed. In accomplish
this, a ram proximity switch 81 i~ connected through first relay 83 to
the central proce66ing unit ~CPU) 79 of the computer 42. A gate cloged
proximity switch 82 18 connected through second relay 84 to CPU 79.
When relays 83 and 84 both ~end the appropriate signals to CPU 79 the
injection cycle can begin. The safety gate 48 is a plexigla6s or
6imilar shield that encloses the injection ram 50 and the mold 30 during
the actual injection process, thereby 6hielding and protecting the
operator in case of any sudden or ~mexpected pres~ure release or
blow-out during the injection molding cycle.
The computer or control means 42 include6 a power supply 86
connected to an operator interface terminal 87 which iB connected to the
CPU 79. In the preferred embodiment of the invention, the operator
interface terminal 87 i6 the mlniature operator lnterface terminal or
"MINI OIT" manufactured by GE Fanuc Automation North America, Inc. of
Charlotteaville, Virglnia. The operator interface terminnl 87 ig
connected via CPU 79 to the pro~rammable lo~ic controller 80, ~hich also
may be such as that made by GE Fanuc Automation North America. It 19
preferred that the operstor interface 87 i6 a "touch sen6itive" CRT unit
for ease of control, although other devices 6uch as hardware switches,
keyboards, and the llke can be u6ed. The arran8ement of the
programmable logic controller and various cards needed for the operatlon
of the control means i6 shown in Figures 7 and 8. If de61red, a printer
88 may be connected to the PLC 80 for prlnting out operator report6. As
tho6e skilled in the art will reallze, many commercially avallable
computer systems or computer components can be used as the control mean6
42.
-22-
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63,742-015 ~,S~3~
Referring now to Figures 5, 5A, 5B, and 6, there are shown
flow charts generally illu6trating computer software procedures which
can be used to operation the apparatu~ and method of the pre6eut
invention. A6 those skilled in the art wlll realize, many other
computer flowchart6 a6 well a6 many different computer programs or set6
of computer software instructions could be uaed to preform e66entially
the 6ame or very 6imilar 6tep6 illustrated in theee flow charts.
In an preferred embodiment there i~ provided an automatic
mode of operation and a manual mode of operation. The automatic mode i6
used for normal operation6. The manual mode i6 used for determlning
variou~ operat10nal parameters and for diagno6tics and 6y6tem
evaluation6 (~g~, clearing ga6 or plast~c lines aasociated with the
mold 30). In either mode of operation, the operator mu6t fir6t enable
the 6y6tem (block 280), and then enter ~block 290) the de6ired values
for injection pre~6ure and the duration OI' time at each pre66ure fox all
of the lndividual 6teps by which the injection or fir6t deslred and
preci6ely controlled pre6sure 18 stepped down to the second or
sub6equent predetermined desired pressure (auto mode~ or the gas
pressure (manual mode). The programmable logic controller 80 provide~
for the ~tepping down to the 6econd predetermlned and precisely
controlled pressure in a plurality of individual ateps (in a most
preferred embodiment, about 20 steps are used). As discus6ed above,
more or fewer than 20 6teps may be used if desired, and by virtue of the
fast opening valve 44, the pressure inside the mold cavity 28 may be
6tepped upwardly a~ well aa downwardly during the pres6ure 6tep down
cycle (i~Ç~, during time TSD in Figure 2).
Referrin8 now to Figure 5A, the enable subroutine (bloc~
280) 18 further descr1bed. Ualng a touch aensitive 6creen or CRT (i~
a preferred operator interface terminal 87) provided on tlle control
-23-
63,7~2-015 ~$ ~
means 42, the logo or enable 6creen will fir6t preaent itgelf to the
operator w~th a mes~sge "touch to proceed" (block 281). After
activating the "ennble" screen, a safety check screen will appear (block
282). The 6afety check6 will vary depending on the particular proceas
being u~ed. Generally the6e 6afety checks will involve an evaluation of
various temperatures and pre~sure~ throu~hout the injection molding
6yatem to determine if they are within acceptable limita. Both the
safety checka and the safe operating limit6 can be, if deaired, modified
by a computer programmer.
The operator will next be required to enter a ~ecurity code
or pas6word ~block 283). Normally two level6 of securlty are provided.
Level I, the lowest security level, simply allow~ the sy6tem to run
without the ability to modify or change the operational parametera.
Level II allow~, in addition to running the sy~tem, an operator to
modify an e~isting set of operational par~meters or to set up a new set
of operational parameters. If desired, additional security level6 could
be provided. An operator entering Level I 6ecurity automatically
bypas6e~ the "enter value~" subroutine (block 290) and proceed~ directly
to the selection of the approprlate mode of operatlon ~l.e., automatic
or manual operation). For Level I operation it is necesaary that the
valuea called for in the "enter values" subroutine have already been
entered and remained stored within the computer memory or on a machine
readable device ~uch as a computer disk or punched tape. For the Level
II operator, the "enter value" aubroutine can be bypasaed if the desired
operating parameters are already available in the ~ystem. (The flow
charts do not illu~trate bypassing the "enter value" subroutine in order
to simplify the flowchart6. Such conventional programming techniques
are well within the ~kill of the art.)
-24-
63,742-015 2q~3~
Operating parameters can be modified or entered initially
into the computer 6ystem through the "enter value" 6ubroutine 2gO by a
Level II operator. Three ~alues or parameters are required ln the auto
mode for each 6tep in the stepwl6e reduction of the pressure and for the
holding pre66ure indicated in Figure 2 by the numeral6 230 and 240,
respectively. (As oDe 6killed the art will reallze, the holding
pres6ure or ~tep 240 in Flgure 2 is of the same character as the step~
230 in that figure e~cept that the length of time at the holding
pre~sure 18 much longer. Similarly, the venting cycle 250 can also, if
de6~red, be treated a6 ju6t another step or other 6teps. Thu6, the
parameters a6sociated with the holding conditlon 240 will be of a
6imilar nuture and will be inputted in the same way a8 the parameter6
a660c~ated with the step~ 230. And 6imilarly for parameter6 a660ciated
with controlled venting 250.)
The three required values include (1) the step number (block
284), (2) the total time at pres6ure for each 6tep (block 285), and (3)
the pre66ure for each 6tep (block 286). The loop in the "enter value"
6ubroutine 290 will be repeated a6 many times a5 i8 nece6sary to 6et up
the proce6s (1~, for N total 4tep~ the loop will be repeated N
time6). For each 6tep, the operator will fir~t enter step number N
(block 284), then the time ~"atep time") that the pre~sure i5 to be held
for that step (block 285)9 and lastly, the pre6sure ("step pre~6ure")
for a part~cular step (block 284). The step number N i8 an integer
which identifie6 the order of the variou6 step3. A66uming there are
twenty step~, N will be equal, in turn as each data entry loop i6
completed, to 1, 2, 3 . . . 20. Data entry will contlnue through block
237 and lt6 associated loop back to block 284 until the appropriate data
ha6 been entered for all N step6.
-25-
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63,742-015
~3~
After completlon of data entry or lf the data entry
subroutine wa6 bypassed, the operator must 6elect between the auto mode
(blocks 300, 330, and 340 in Figure 5 and all of Figure 6) and the
manual mode (blocks 310, 350, 360, and 370 in Figure 5).
The auto mode of operatlon (block 300) ls used for normal
operation of the gas assisted injection molding 6y~tem and is
illustrated in Figure 6. After beginning the auto mode (block 330), it
mu6t fir6t be determined if the safety gate 48 i8 clo6ed (block 380).
If the 6afety gate is open, the auto mode cannot begin and the sy6tem
will exlt fro~n the auto mode (block 340). If the safety 8ate i6 clo6ed
(block 380), the injection cycle can begin (block 390) thereby beginning
the injection of the molten or plastic resin. Once the injection of
molten or plastic resin is complete (i.e, the injection ram is at the
home po6ition) (block 400), the injection cycle for injection of the
pressurized ga~ begins. Thus, two condition6 m~6t be met before
pressurized g~8 injection can begin: (1) safety gate i6 closed (block
380) and (2) in~ectlon of the molten or pla6tic resln iB complete (block
400). Although not shown on the flow chart, the gate closed proximity
switch 82 forms an interlocking sy6tem such that, if at any time during
the injection cycle (for elther recin or pres6urized ~as lnjectlon), the
~afety g~te 48 opens the i~jection cycle will abort and the sy6tem wlll
exit the auto mode (block 340). The ram pocition proximlty switch 81
does not form a 61milar interlocking system. Thus, once the re6in
injection is complete, the ram 50 can begin it's recovery ~nd prepare
for the next in~ection cycle, during the pressurized gas lnjectlon cycle.
Once the injection of molten or plastlc resin is complete (block
400), the pressurlzed gas injection cycle iB inltlated. Flrst the "step
reglster" 18 initialized (i.e., ~he step number N i6 ~et equal to 1)
(block 410). Then the "tlmer" is set equal to the "step tlme" for ~tep
.
.': ~ ' .
63,742-015 ~ f~
N (block 420) and the "auto pre6sure" 18 Bet equal to the "6tep
pre66ure" for step N (block 430) (for the first time through the loop --
block6 4Z0 to 480 -- N will equal 1). The "~tep time" and the "~tep
pre6fiure" for each 6tep N ure the value6 entered in the "enter values"
6ubroutine 290. If N equal6 1 (i~., the fir6t 6tep) (block 440), the
fast operating valve 44 i~ opened (block 450) to inJect ga6 into the
molten or pla6tic resin at the first predetermined and precisely
controlled pressure (equal to the "6tep pressure" for 6tep 1~. The fast
operating valve will automatically clo~e once the pres6ure reaches the
first predetermined prea6ure~ Although not shown in the flow chart, a
delay time Tl (see Figure 2~ between the completion of the injection of
the plastic (block 400) and the initial injection of pres6urized ga6
(block 450) can be in6erted if de6ired. After the ~ast operating valve
is opened (block 450), the pre6sure 16 held at the "6tep pressure" lsvel
for the "6tep time" duration (block 460). After holding at the de6ired
pre66ure for the de6ired time (block 460), the 6y6tem determines if the
pre66urized gas injection cycle i6 complete (block 470). lf Lhe cycle
ia not complete, the "6tep regi6ter" i~ incremented by 1 (i.e., N = N +
1) (block 480) and the æystem return6 to block 420 to begin the ga6
injection cycle once ~gain for the next step N. The ga6 injection cycle
repeat6 it6elf exactly as described for the fir~t cycle (N = 1) except
that block 460 (opening the fa6t operating valve) i6 bypa6sed. In other
word6, the "timer" and "auto pre~sure" value6 are 6et for the
appropriate step N (block6 420 and 430) and, ~ince N i~ not equal to ]
in block 440, the aystem proceed~ directly to block 460 where the "6tep
pre6sure" i6 maintalned for tlle "6tep time."
The ga~ in~ection cycle or loop (blocks 420 through 480) i6
repeated for the desired number of 6tep6 whereby the pre6sure in the
mold cavity is reduced to the second predetermined and preci6ely
controlled pre~sure (240 in Figure 2). Thi6 second predetermined and
-27-
:
63,742-015
precisely controlled pressure is usually -- but is not required to be --
the la~t 6tep in the cycle or loop In 60me in6tance6 it may be
de~irable to further reduce the pres6ure in a stepwi6e fa6hlon after the
6econd predetermilled and preclsely controlled pre66ure. In other word6,
the pre6sure can be further reduced in a stepwise fashion to the final
venting pressure u6ing thi6 8as in~ection cycle or loop. A~ one gkill
in the art will realized, thi~ gas in~ection cycle or loop can easily be
adjusted by varying the input values in the "enter values" subroutine
290 to obtain almost endle~s variations or patterns for stepping up or
stepping down the pressure in the mold cavity. As noted above, one such
psttern is ~hown in Figure 2. Once the ~a6 in~ection cycle or loop i8
compl&te (i~Ç~. the last step N ha6 been carrled out), the 6ystem will
exit the auto mode via block6 470 and 340.
IE the manual mode of operation tblock 310) is ~elected, an
operator can manually ln~ect gas at a single pressure level (i e., the
"manual pressure" of block 350). No reF.in is injected into the mold
cavity 28 during the manual mode of operatlon. As noted above, the
manual mode can be used for determining various operational parameter6
and for diagnoatics nnd system evaluations. Perhaps more importantly9
the manual mode can be used to clear plugged lines in or associated with
the mold 30 and mold cavity 28. The operator first ~ets the manual
pre~aure deslred (block 351) by entering thnt pressure via the touch
sensitive screen lnput device 87. (Although not shown in the flow
ch~rt, the computer software could ea~ily be modified BO thqt the manual
pressure could be entered via the "enter value" subroutine Z90.) Once
the manual presHure has been set, the operator, again u6ing the touch
sensitive screen lnput device 87, manually activates or opens th& fast
operating valve 9 thereby blowing pressurized ga~ at the manual pres~ure
into the mold cavity 28 (block 360). Ga6 is injected until the operator
deactivates or closes the fast operating valve ~block 370). After the
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63,7~12-0l5 2.`~,~$~
faet opening valve is clo6ed, the 6ystem exit6 from the manual mode.
This manual in~ection cycle can be repeated as often as desired or
needed to, for example, clear the lines.
After exiting either the auto mode (block 340) or the manual
mode (block 370j, the 6y6tem return6 to the main trunk line (Figure 5).
From thi6 point, the 6ystem can return to the auto mode (block 300) or
the manual mode (block 310) or the 6y6tem can be turned off (block
320). The Iy6tem can be 6tarted up or re-enabled through the "enable
sy6tem" gubroutine 280. A~ one 6killed in the art will realize, the
flow chart in Figure 5 could ea6ily be modified, if de6ired, go that,
for example, the "enter valueg" ~ubroutine 290 could be entered from the
auto mode (block 300) without having to turn the sy6tem off and then
back on. Many other variation6 could be made in the flow charts and the
6y6tem using conventional flowcharting and programming skills and
techniques to obtain a computer software package to operate and control
the ga6 control system of this invention.
-29-
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