CA1090678A - Flow distribution valve - Google Patents

Abstract

ABSTRACT

A valve system for control of polymer flow from a common feed manifold to each of multiple extrusion dies. The valve system comprises one or more fixed rod valves, each of which creates an annular restriction of fixed length in the manifold, and one or more adjustable rod valves, each of which creates an annular restriction of varible length in the manifold or all adjustable rods creating multiple annular restrictions of variable length, for effecting flow control.

Description

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 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 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.

~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 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.

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 -- 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.

Claims (5)

WE CLAIM:

1. 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 communicating with the inlet port and two or more extrusion die outlets, and (b) a plurality of separate flow restrictors in the flow channel adjacent to and preceding each of the extrusion die orifices in the direction of polymer flow, each flow restrictor comprising an elongated rod of reduced diameter relative to the diameter of the flow channel in which it is positioned, thereby forming a restricted, elongated annual channel of constant cross section through which the molten polymer must flow in order to pass from the inlet port to the extrusion die orifice, at least one of the rods being axially displaceable in the channel so as to permit the length of the annular channel to be varied, so as to control the flow of molten polymer to the die orifices.

2. Apparatus according to Claim 1 which includes: two extrusion die outlets in communication with the flow channel, and two flow restrictor rods in the flow channel, one adjacent to and preceding each extrusion die outlet in the direction of polymer flow, one of the flow restrictor rods being held in a fixed position in the channel to create a restrictor elongated, annular channel of fixed length, the second of said flow restrictor rods being axially displaceable in the flow channel to create a restricted, elongated annular channel of variable length.

3. Apparatus according to Claim 1 which includes: two extrusion die outlets in communication with the flow channel, ant two flow restrictor rods in the flow channel, one adjacent to and preceding each extrusion die outlet in the direction of polymer flow, both the rods being axially displaceable in the flow channel to create a restricted elongated annular flow channel of variable length.

4. Apparatus according to Claim 1 in which each flow restrictor rod is tapered at one end, the tapered end portion being directed towards the inlet port in the flowing stream of molten polymer.

5. Apparatus according to Claim 1 in which each flow restrictor rod is tapered at one end, the tapered end portion being directed downstream towards the adjacent extrusion die orifice in the flowing stream of molten polymer.