Note: Descriptions are shown in the official language in which they were submitted.
10~ 78
This in~ention relates to a ~alve system for the control
of the flow of molten polymer to extrusion dles ln an
apparatus for the extrusion of thermoplastic materlal. It
ls especlally concerned with regulating and balanclng the
flow of molten polymer from a common feed manl~old to each
of multiple extrusion dies.
.... . . ... ..
It ls common practlce ln the thermoplastic extrusion
art to supply molten polymer from a single extruder to two
or more extruslon outlet orifices or d~es. Such an arrange-
ment, ln which a manifold is used to feed two extruslon dies,
ls lllustrated ln FIGURE 1 of the drawlngs.
The fllm belng taken off of each of these respectlve
dles ls fed to a separate prod~ctlon llne made up o~ the
approprlate sequence of mechanlcal forming operatlons. It is
lmportant that the fllm in each such line be the same ln
terms of average thlckness as the fllm ln each of the other
llnes belng supplied by the single common extruder, and thls
ls normally ad~usted by ~arylng the speed of the n~p rollers
(see 15 of FIGURE 1), thereby controlllng the rate at whlch
the still seml-molten polymer immedlately ad3acent to the
extrusion dle or~ce ~s drawn away from the die.
In the event that the flow from the two dles ls
une~ual (e.g~ because of small mechanlcal d~fferences ~etween
the dies), then the rates at wh~ch the two films are drawn
.- ~
105'~;78
off by thelr respectlve nlp rollers are also unequal and
consequently the entlre serles o~ llne components downstream
from each palr of nip rollers are running at dl~erent rates.
On many such dual productlon llnes,the overall speed Or the
operatlon (l.e. the total rate Or fllm productlon from the
slngle common extruder ~eedlng both lines) 18 llmlted by one
of these downstream components. In such a case, the speed
Or the overall operation ls restrlcted by the faster o~ the
two streams (slnce lts llmitlng component will be functloning
at maxlmum càpacity), so that the slower stream runs at less
than its maxlmum speed and the rate of extrus~on cannot be
increased to compensate. It ls deslrable to equalize the
ielatlve speeds o~ the two llnes, enabllng the overall rate
Or extrusion to be increased to maximize the rate of production
on both llnes, and such an equalizatlon is made posslble by
utlllzlng a flow control valve to restrlct the polymer flow
to the ~aster ~1de of the manifold.
A typical flow control valve that has commonly been
used in the prior art ls shown in ~IGURE 3. Molten thermo-
plastlc materlal 203 ls caused to flow through gap 201,
where it is sub~ected to a pressure drop. As the valve is
ad~usted by moving restrlctor 202, gap 201 is changed and
the resulting pressure drop ls-changed accordlngly. I~
there are two such valves ln parallel, fed from a common
2~ manl~old source and dlscharglng into ldentlcal downstream
pressures, the flow rate through each of the two valves
--3--
109~;78
will be proportional to approximately the fifth power o~ the
slze of the gap. Slnce this gap is usually a small fractlon
of an inch, it may be seen that a very small change in the
size Or thls gap wlll result in an undeslrably large change
ln flow rate. For example, i~ the gap is 0.1 inch, and it
is changed by a very small amount such as 0.005 inches, there
will be a resultlng change ln flow through the gap of approxi-
mately 28 percent, provided that the supply and discharge
pressures remaln unchanged. Any precise flow rate control
wlth such valves 18, at best, extremely dif~icult. It may
be seen that prlor art valvlng means such as that descrlbed
above, when used in a pair (one for each dle) on a common
manlfold, cannot readlly be used for the purpose of accurately
balanclng the flow since they are not sufflciently preclse to
.permit accurate ad~ustment of flow dlstrlbutiop wlthln the
manlfold. Also, since there are two separate ~al~es to contend
wlth and elther one ls capable of ~ully restrlcting the flow
of poly.mer to lts ad~acent dle, numerous ad~ustments over
a perlod of time may result ln the lnadvertent and undeslrable
total restrlction of one slde of the flow channel ln the
manlfold, necessltatlng the laborlous task of read~ustlng
and rebalanclng the entlre system ln order to get that side
flowlng properly once agaln.
, . ,:, . , = . . . . . . .
The present invention is directed to a manlfold valve
system whlch ~alances the flow of molten the~moplastlc resin
(e.g. polyethylene~ between two or more d~es which are being
-4-
1090{;78
s~pplled wlth molten resin by the same extruder. The valves
are located ln a ~low channel wlthin the common man~old whlch
reed~ the molten polymer to the multlple dies, and the ~low
control ls accomplished by means o~ adJustlng the relatl~e
back pre~sure exerted on the polymer wlthln that portlon of ;
the ~low channel which precedes each extruslon die orl~lce.
In the pre~erred em~odiment, the molten polymer ls lntroduced lnto
the central portion o~ the man~old ~rom a sln~lè conventlonal
rotatlng screw extruder.
The ~alve system comprises one elongated rod ~or
each dle, the rods being tapered at one end portlon to present
a surface which of~ers minim~l resistance to the flowlng polymer
stream. The rods are ~nserted lnto the manifold, each ad~acent
to and preceding one o~ the dies and wlth lts tapered end
portlon dlrected lnto the flowlng stream o~ molten resin,
such that each rod creates wlthln the manl~old an annular
space through whlch the molten resin must ~low 1~ lt ls to
reach the die ad~acent to that rod.
The present invention, therefore, provides apparatus
for controlling the flow of molten polymer
from a feed source to two or more extrusion die orifices, comprising:
(a) a manifold having an inlet port, a flow channel
co~unicating wlth the inlet port)and two or more
extrusion die outlets, and
(b) a plur~lity of separate flow res~rictors in the flow
channel adjacent to and preceding each of the extrus~on
die orifices in the direction of pol~er flow, each flow
B
1090~;78
restrictor comprising an elongated rod of reduced
diameter relative to the diameter of the flow channel
in which it is positioned, thereby forming a restr$cted,
elongabed annual channel of constant cross ~ection through which the mDlten polymer
must flow in order to pass from the lnlet port to the
extrusion die orifice, at least one of the rots being
axially displaceable in the channel so ~s to permit ehe
length of the annular channel to be ~ar~ed, 50 as to control
the flow of molten polymer to the die orifices.
B
1090~;78
In one embodlment a first rod is inserted into the
manlfold between a first dle and the extruder and is held
ln flxed posltlon to create a rirst annular space Or fixed
length. A second rod, which ls inserted into the manifold
between a second die and the extruder, is adJu~table to
provide a second annular space Or varying length. Lateral
displacement Or thls second rod wlll cause a corresponding
change in the length Or the annular space created by such
rod, thereby causing a change in the back-pressure created
by the molten polymer ~lowlng through this second annular
space relatlve to that created by the molten polymer flowlng
through the first annular space of fixed length. By lncreaslng
the length of the second annular space (and hence the relative
back-pressure created thereby), the operator can decrease
the amount Or molten polymer flowing to the second die
relative to the first die. Similarly, by decreasing the
length o~ the second annular space the operator can decrease
the relative bac~-pressure caused thereby and effectively
increase the amount of polymer flowing to the second dle.
In another embodiment both the first rod and the
second rod are adJustable to provide annular spaces of varying
length. In such an embodiment as this the potentlal
sensltlvlty of the valving system ~s increased and the
operator can more finely "tune" the relative extrusion
rates of the dies to achieve an e~en higher degree of
matching of the speeds of the related downstream production
lines.
--6--
~O~ ;7~
Other alternate embodiments include manifolds havlng
mounted thereon more than two extruslon dies and systems in
whlch the valve members (l.e. the "rods"~ are mounted
vertlcally ln the flow channel. Tn embodiments whereln the
valve members are vertlcally mounted, they are posltloned
in the portions o~ the flow channel whlch branch O~r 0
the central channel prlor to each extruslon die and the
tapered end portlon Or each rod is dlrected downstream
(as opposed to belng directed lnto the ~lowing stream as
descrlbed above) to minlmize any turbulence or sudden
reductlon in shear rate which could cause the formatlon of
stagnant areas ln the flowlng polymer stream.
One advantage to the system of the present lnventlon
1s lts sensitlvity. The flow to the die changes much less
for a given change ln valve posltlon in the pres.ent design
as compared to the deslgn of FIGURE 3 for two reasons:
~ first, the length of the annular space is larger than its
wldth, so a glven number of lnches of movement of the val~e
constltutes a smaller percentage change ln the slze of the
restrlction; and second, for a glven pressure drop across
the restrlction the flow is proportional to the cube of the
length, whereas ln the valve of FIGURE 3 lt was proportional
to the flfth power o~ the gap.
Another advantage of the system of the present
invention lies ln the fact that the flow of the molten polymer
cann~t be inadvertent7y stopped through a series of valve
ad~ustments.
~U90~;7~
Other obJects and advantages of the present invention
wlll be apparent upon an examination of the detailed descriptlon
given below.
In the drawings:
FIGURE 1 ls a schematlc lllustratlon Or two conventlonal
tubular film extrusion dles mounted on a manlfold whlch
supplies them wlth molten polymer ~rom a single common
source.
FIGURE 2 ls a schematlc illustration o~ a prlor art
technlque whereby two downstream llnes are red rllm from a
slngle relatively lar~e tubular extrudate.
FIGURE 3 is a rragmentary view, ln cross sectlon,
Or a typical rlow control valve that ls commonly used ln
the prior art.
FIGURE 4 ls a schematic illustratlon, ln cross
sectton, Or an embodlment Or the rlow distribution valve
~y~tem Or the present lnventlon mounted wlthin the manirold
flow channel.
~ IGURE 5 ls a rragmentary cross sectlon of a manlfold
showing the val~e member mounted vertically ln the flow
channel.
~, ,
~ 10~ 7 ~
Understandlng Or the dlstrlbutlon valve system o~ ~he
present lnventlon can best be ~acilltated by reference to FIGuRE
4 o~ the drawings, which ls a cross-sectlonal representatlon o~
a manl~old feed system employlng an embodlment Or thls lnventlon
which might typlcally be mounted on a conventlonal extruslon
apparatus ror the extruslon Or molten polymer. The manirold
21 ls adapted to accept a single stream 20 o~ molten polymer
~rom the extruslon apparatus (not shown) and to dlvlde lt lnto
two substantlally equal streams which are ~ed to palred extruslon
dles 26 and 30.
Mounted ln the opposing end portlons o~ central flow
channel 23 Or manlrold 21 are valve members 24 and 28, whlch are
posltioned between the su~stantlally centrally located mani~old
inlet port 22 and the extruslon dles 26 and 30, respectlvely.
Valve membors 24 and 28 are elongated rods of reduced dlameter,
relative to the dlameter o~ the ~low channel in which they are
posltloned, each having one end portion whlch ls dlrected toward
the manl~old lnlet port 22 and which ls tapered to present a
streamline contour to the incoming molten polymer stream 20 so
as to minlmize the reslstance o~ the end o~ the rod to the move-
ment o~ the molten fluid and to create a minlmum o~ turbulence
wlthin the manlfol~. Each o~ the rods create an annular
restrlction through which the molten polymer m~st pass before
belng extruded through the respective extrusion dles. It is by
means of manlpulation o~ the length Q~ one or both ol' these
annular restrictions that the valve operates.
1090~i78
In the embodiment depicted in FIGURE 4, valve member 24
18 held in ~lxed posltlon in one end portion of manirold 21 and
immediately preceding extrusion die 26, such that it creates
an annular restrictlon 25 o~ predetermined ~ixed length and
cross section. Val~e member 28 is posltioned in the opposing
end portlon of the manlrold 21, immediately preceding extrusion
dle 30. It ls held ln rixed positlon relati~e to the walls o~
rlow channel 23 but is capable of lateral movement therein,
such that an annular restrlction 29 is created, restriction 29
being of substantially the same cross-sectional dimension as
restriction 25 but of variable length.
Valve member 28 extends through the wall of the mani~old
and ls held in place and allgned by means of slee~e 40 and
mounting bracket 41, the bracket belng attached to the manifold
by means Or tension screws 42. Sleeve 40 may be designed such
that lt can be rotated 180 to completely close o~ slde channel
23A rrom the main flow channel 23, as shown by the broken llne
representation, so that one production line may be stopped
if required wlthout completely stopping the extruder. The
end portlon of rod 28 whlch ls outslde the manl~old ls threaded
and the threads on the rod are engaged by the threads ln a nut
43 whlch ls restralned ~rom lateral movement by bracket 41.
A keyway 44 ln the threaded section o~ the rod, engaged by a
~ey 45, prevents the rota~ion o~ the rod when the nut is rotated.
By turnlng nut ~3, elther by hand or by an attached motor drl~e
(not shown), rod 28 is made to mo~e elther ln or out o~ the
--10--
109~78
flow channel 23, thereby controllably varylng the length of
annular restriction 29. This, in turn, has the effect of
controllably varylng the back pressure exerted on molten
polymer stream 20 as lt flows toward extruslon die 30.
Alternately, valve member 28 may be actuated by means Or a
double-actlng hydraulic cylinder ln place Or the threaded
nut mechanism.
Molten polymer stream 20 ls supplied to manifold 21
by the extruslon apparatus (not shown) and enters inlet port
22 under pressure. Inlet port 22 dlrects the ~olten polymer
to control flow channel 23 where flow diverter 24 divldes the
entering stream, dlrecting a portlon of lt to each of the
opposlte ends of flow channel 23. One portlon of the molten
polymer stream is directed toward valve member 24, passes through
the annular restriction 25, and then through side channel 233
to extrusion die 26 whlch 18 mounted at the end Or manifold 21.
The molten thermoplastlc resln ls subsequently expressed ln
the form of tubular fllm 27 through the annular extruslon orlflce
(not shown) of conventlonal dle 26. The remalning portion of
the molten polymer stream ls directed toward valve member 28
and passes through the annular restrlctlon 29, then through side
channel 23A to extrusion dle 30 mounted at the other end of
manifold 21. This portlon of the molten resln stream 20 is
subsequently expressed through the annu}ar extrusion ortflce
(not shown~ of conventional extrusion die 30 in the form of
tubular film 31.
lV9t~;7~
The pressure drop of the molten polymer withln the
manlfold flow channel 23 wlll be dependent upon the slze and
length o~ the annulus through whlch it travels before belng
expressed lnto the extruslon dles 26 and 30. Annular restrlctlon
25, belng of ~lxed length and cross section, will bring about
a ~lxed pressure drop for a given molten polymer stream havlng
a given temperature and pressure. Slnce annular restrlction 29
ls o~ ~ariable length it follows that the pressure drop across
that restrlctlon ls llkewlse varlable, the pressure drop
increaslng for increaslng length Or annular restriction through
which the molten polymer must flow. As the pressure drop across
restriction 29 is increased (by increaslng the length o~ the
annular space) the rate of flow of the molten polymer through
that restrlction ls reduced relative to the rate o~ rlow
through restriction 25, and simllarly as the pressure drop ls
decreased (by decreasing the length of annular space 29) the
relatlve rate o~ flow o~ the molten polymer through that
restriction is increased. ~y approprlate manipulatlon of valve
member 28, and hence the length of annular restrictlon 29, lt
ls possible to "tune" the system wlth a high degree of sensitivity
and to ad~ust the rate o~ extrusion through extruslon die 30
to match the rate o~ extruslon through extrusion dle 26.
m is "tuning" or balancing of the extrusion rates through the
respectl~e dies enables one to draw o~f both tubular fllms at
2~ the same rate while s~multaneously matching thelr respective
thlc~nesses by manipulation of the nip roller speeds.
-12-
10!~)678
Thls ln turn enables the manu~acturer to realize an increased
productlon rate from a multlple-die line in that he can now
run both streams at the speed limlt imposed by the llmitatlons
o~ thelr respectlve downstream equipment.
Such a system has the advantage of precl~lon Or ad~ust-
ment. If there are two valves as descrlbed, ln parallel and
~ed ~rom a common manifold source and discharging into identical
downstream pressures, the ~low rate through the two valves ls
proportlonal to approximately the third power of the length
of the annulus. When the lnltlal length o~ the Yariable
annular space is in the order o~ several lnches, it ls posslble
to make a substantlal change ln that length to achieve a ~lne
adJustment ln ~low rate. For example, 1~ the inltlal length
o~ the annulus is 6 inches, and lt ls changed by a substantial
amount, such as 0.194 inches, there will be a resultlng change
ln the rate of ~low through that space Or approximately 10
percent, provlded the supply and discharge pressures remain
unchanged. Thls permlts a much more precise ad~ustment than
was posslble with the varlable-gap prlor art valve (see FIGURE
3) in whlch a movement o~ 0.005 inch produced a 28 percent
change ln flow rate.
The above-descrlbed embodlment has a further advantage
~n that there ls a single control whlch ls used by the operator
to redlstrlbute the ~-ow. No declslon ls requ~red on hts part
as to which knob to turn. Movln~ the ad~ustable valve member
to the right decreases the average thickness of the product on
the le~t and lncreases thickness on the rlght, and conversely.
~09~)678
Another embodiment of the present inventlon involves
a manl~old as descrlbed above, but utillzlng two ad~ustable
valve members lnstead Or one ad~ustable and one flxed member.
Such an embodlment would have the advantage Or even greater
sensltlvlty of control, as well as the ablllty to operate
over a wlder range of pressure drop varlation.
Stlll another embodlment of the valve system o~ the
present lnventlon ls lllustrated ln FIGU~E 5, whereln the valve
mechanlsm ls the same ln all respects as that shown in FIGURE 4
except that lnstead of rod 128 and assoclated annular restrlction
129 belng positioned horizontally ln the maln ~low channel 123,
it ls posltioned ln slde channel 123A and the tapered end
portlon of the rod ls dlrected toward extruslon dle 130.
In any of the aforementloned embodlments, the lateral
dlsplacement Or the ad~ustable valve member may be inltiated
and controlled ln the conYentlonal manner (l.e. by an operator
who is monitorlng the average fllm thickness somewhere down
stream~, or by means o~ automatic fllm thickness detectlon
devlce whlch ls adapted to control the movement of the valve
to compensate for any dlfferential ln the gauge o~ the various
extruded fllms.
Although the present lnventlon has been described with
reference to the extruslon o~ tubular ~ilms of thermopla~tic
materlal, it has appllcablllty to other extruslon technlques,
such as the extrus~on of flat fl}ms, fllaments, solld tubes,
and ~oamed plasttc sheets and tubes. Slmllarly, references
- -14-
-- 109~i78
ln the specirlcatlon and drawlngs to manlfolds havlng a slngle
reed source and two extruslon dies mounted thereon are lntended
to be merely lllustratlve Or the concept disclosed hereln, it
belng readlly apparent to those skllled ln the art that a
slngle manl~old can be designed to handle any number Or such
extruslon dles or reed sources.
It ls to be understood that other modiricatlon~ and
varlations Or the present inventlon may be made without depart-
ing ~rom the splrit and scope Or this disclosure, as those
skllled in the art wlll readily understand. Such modirlcations
and variatlons are to be consldered as coming within the purview
and scope o~ the appended claims.
15-
