JPS6036931B2 - Film forming equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a valve arrangement for regulating the flow of molten polymer to an extrusion die in an apparatus for extruding thermoplastic materials.

More particularly, the present invention relates to techniques for regulating and balancing the flow of molten polymer flowing from a common supply manifold to each of a plurality of extrusion dies. It is common practice in the art of extruding thermoplastic materials to feed molten polymer from a single extruder to two or more extruder outlet orifices or dies.

An arrangement using this type of manifold to feed two extrusion dies is illustrated in FIG. The film removed from each die is fed to a separate production line that performs the appropriate series of mechanical forming operations.

It is important that the average thickness of the films on each production line be the same as each film on the other production lines fed from a single common extruder.

Further, the film thickness is constantly adjusted by making the speed of the nip roller (see 15 in FIG. 1) variable. That is, the flow rate of the semi-molten polymer immediately after exiting the orifice of the extrusion die is controlled as it is withdrawn from the die. If the flow rates of the two tatties are unbalanced (for example, due to slight mechanical differences between the dies), the speeds of the two films taken up by each nip roller will be unequal. The entire downstream series of line elements would have to be run at a different speed.

In many dual production lines of this type, the overall speed of operation (i.e. the overall speed at which one common extruder feeds both lines and produces film) is determined by the downstream components listed above. You will be subject to restrictions. in this case,
The overall speed of operation is limited by the faster of the two streams (as the constraining element's capacity will be maximized). This causes the slower stream to be slower than its maximum velocity, making compensation by increasing the throughput impossible. Equalizing the relative speeds of the two lines increases the total throughput, making it possible to maximize the production rate of both lines, and this equalization is achieved by using flow control valves to increase the total throughput of the polymer to the high-speed side of the manifold. This is possible by restricting the flow rate.

A typical flow control valve commonly used in the past is shown in FIG. Molten plastic material 203 fills the gap 20
1 and the pressure is lowered. This valve is adjusted by the adjusting device 20.
2, the gap 201
changes to change the resulting pressure drop. If there were two parallel valves as described above fed from a common manifold source, the flow rate through each of these valves would be approximately five times the size of the gap described above. Since this gap is typically on the order of a fraction of an inch, it can be seen that even a very small change in the gap size will result in a large change in flow rate. For example, if the gap is 0.1 inch, a minute change of 0.005 inch will cause the flow rate through the gap to change by approximately 2> cents, assuming the supply and discharge pressures remain unchanged. This is an extremely difficult problem even with precise flow control using conventional valves. The conventional valve device described above can be replaced with a common manifold.
Even if they were assembled in pairs (one for each die), they were not precise enough to accurately adjust the flow distribution within the manifold, and therefore accurate balancing of the flow rates could not be easily achieved.
Similarly, if two separate valves oppose each other, and each valve is sufficient to restrict the flow of polymer to the other die, frequent adjustments over a period of time can have the opposite effect. The effect on the overall flow restriction on one side of the flow channel in the lever manifold can be detrimental. Therefore, the entire flow system must be readjusted and rebalanced to restore proper flow again. The present invention relates to a manifold valve system for balancing the flow of molten polymer (eg, polyethylene) between two or more extrusion dies fed by the same extruder.

A common manifold supplies molten polymer to the multiple dies with multiple valves disposed in the flow channels within the manifold and flow control controlled by relative back pressure applied to the upstream portion of each extrusion die orifice in the flow channel. This is achieved by adjusting the pressure. In a preferred embodiment, molten polymer is introduced into the central portion of the manifold from a single conventional rotating screw extruder. The valve system consists of one elongated rod for each die, with one end of the rod tapered to provide a surface of minimal resistance to the flowing polymer.

The rods are inserted into the manifold on the upstream side of the die, facing each other and with one tapered end facing the inflow direction of the molten polymer, and each rod forms an annular cavity inside the manifold, through which the molten polymer flows and the rods are inserted into the manifold. 'Reach this adjacent die. In an embodiment, a first rod is inserted and secured into a manifold between a first die and an extruder to define a first annular cavity of constant length.

A second rod inserted into the manifold between the second die and the extruder forms a second annular cavity of variable length, which is adjustable. When the second rod is displaced, the length of the annular gap formed by the rod changes accordingly, causing the molten polymer flowing through the first annular gap of a fixed length to flow through the second annular gap. The back pressure of the molten polymer is varied. By increasing the length of the second annular gap (and thus also the relative backpressure), the flow rate of molten polymer into the second die relative to the first die can be reduced. Similarly, by reducing the length of the second annular gap, the resulting relative backpressure can be reduced, effectively increasing the molten polymer flow rate to the second die. In other embodiments, the first rod and the second rod are adjustable to form two variable length annular gaps.

In this case, a potentially higher sensitivity of the valve system is achieved, allowing the relative extrusion rates of the dies to be more finely "tuned" and the flow rates of the downstream production line reached evenly and highly. It can be matched. Another example includes multiple manifolds with two or more extrusion dies where valve members (or "rods") are positioned one above the other within the flow channel.

In the case of upper and lower valve members, they are located in the portion of the flow channel that branches from the central channel upstream of each extrusion die, with the tapered end of each rod facing downstream (as described above). direction) to minimize sudden changes in cutting speed or turbulence that could create stagnation areas in this flow. The advantage of the device of the invention is its high sensitivity.

The flow rate change to the die is much less variable in valve position than that of FIG. 3 for two reasons.

That is, firstly, the length of the annular gap is longer than its width, so even if the valve moves over a predetermined length, the dimensional change in the throttle will remain at a very small percentage, and secondly, the flow rate will change due to the pressure drop at the restrictor. It is proportional to the length of the three cases, but in the case of the valve shown in Figure 3, it is proportional to the fifth power of the air gap. Another advantage of the present invention is that the flow of molten polymer is not inconveniently stagnated by the adjustment of a series of valves. Embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

The distribution valve system according to the present invention is best understood from FIG. 4, which shows a cross-section of a manifold delivery system in an embodiment installed in a molten polymer extrusion apparatus.

Manifold 21 receives a single stream 20 of molten polymer from an extruder (not shown) and divides this stream into two substantially equal streams that feed paired extrusion dies 26, 30. . Valve members 24 and 28 are disposed at opposite ends of the flow channel 23 in the center of the manifold 21, and these valve members are arranged between the manifold inlet 22 and the extrusion dies 26 and 30, respectively, which are located approximately in the center. be done.

The valve members 24, 28 are elongated rods of small diameter relative to the diameter of the flow channels in which they are disposed, with one end portion of each valve member facing the manifold inlet 22 and directing the two incoming flows of molten polymer. The tapered profile minimizes fluid resistance in the molten fluid at the end of the rod and minimizes turbulence within the manifold. Each rod can form an annular restriction through which the molten polymer must pass before being extruded from each extrusion die. The length of one or both of these annular constrictions over which the valve operates is determined by operation. In the embodiment of FIG. 4, the valve member 24 is fixedly held at one end of the manifold 21 and immediately in front of the extrusion die 26, thus forming an annular constriction 25 of a predetermined fixed length and cross section. Ru.

Valve member 28 is disposed in the opposing weave portion of manifold 21 and immediately in front of extrusion die 30. This valve part 28 is fixedly held against the wall of the flow channel 23 but can move from side to side within the channel, and the cross section of the annular constricted part 29 thus formed is almost the same as that of the constricted part 25. However, the length is variable. Valve member 28 is retained through the wall of the manifold and is centered by sleeve 40 and mounting bracket 41. This bracket 41
is attached to the manifold by tightening screws 42. The sleeve 4 can be rotated 1800 times to block the main working channel 23A as shown by the broken line, so that if necessary, only one production line can be stopped without completely stopping the extruder. Designed. The ends of the rods 28 on the outside of the manifold are threaded, and the threads of this rod are engaged with the threads of a nut 43 whose movement from side to side is restrained by a bracket 41. A keyway 44 in the threaded portion of the rod with which the key 45 engages prevents rotation of the rod when the nut is rotated. By rotating the nut 43 by hand or by a motor drive unit (not shown), the rod 28
flows in and out of the flow channel 23, which allows the length of the annular constriction 29 to be variably adjusted. In this way, the back pressure exerted on the molten polymer stream 20' flowing toward the extrusion die 30 is adjustable. on the other hand,
Valve member 28 can be driven by a double acting hydraulic cylinder instead of the threaded nut mechanism described above. Extrusion equipment with two streams of molten polymer (shown and not)
is supplied to the manifold 21 by the inlet 2 in a pressurized state.
2.

The inlet 22 directs the molten polymer into the controlled flow channel 23 by splitting the incoming flow with a flow diverter 24' to direct a portion of the flow to each opposite end of the flow channel 23. A portion of the molten polymer flow is directed toward valve village 24 through annular constriction 25 and then through side channel 23B to extrusion die 26 at the end of manifold 21. Molten thermoplastic resin is produced using ordinary die 2.
A cylindrical film 27 is extruded from an annular extrusion orifice 6 (not shown). The remainder of the molten polymer flow passes through valve member 28 and annular constriction 29 before passing through side channel 23A and extrusion die 30 in the other side of the manifold. A portion of this molten polymer stream 20 is extruded as a cylindrical film 31 through an annular extrusion orifice (not shown) of a conventional extrusion die 30. The pressure drop of the molten polymer within the manifold flow channels depends on the size and length of the annulus it passes through before being extruded into the extrusion dies 2-6, 30. An annular constriction 25 of constant length and cross section produces a constant pressure drop for a given flow of molten polymer at a given temperature and pressure. Since the length of the annular constriction 29 is variable, the pressure drop across this constriction is also variable, and this pressure drop increases as the length of the annular constriction through which the molten polymer flows increases. Aperture part 2
9 (by increasing the length of the annular gap)
As the size increases, the flow rate of molten polymer through this constriction decreases compared to the flow rate at the constriction 25, and likewise as the pressure drop decreases (by shortening the length of the annular gap 29). The relative flow rate of molten polymer through this constriction will increase. By appropriately operating the valve 28 and thus varying the length of the annular constriction 29, the flow system can be "tuned" with high sensitivity to match the extrusion rate from the extrusion die 30 to the extrusion rate from the extrusion die 26. It can be balanced with. By "tuning" or equalizing the extrusion flow rate through each of these dies, both cylindrical films can be taken off at the same speed, and by simultaneously manipulating the speed of the nip rollers, the thickness of each film can be matched. be able to. In this way, the production speed can be increased through a multi-die production line to the point where the constraints on the speed are due to equipment downstream of any flow. The device described above also has the advantage of high adjustment precision.

If two valves are placed in parallel, fed from a common manifold source, and forced at equal downstream pressures, the flow rate through these two valves is approximately proportional to the length of the annulus.

If the initial length of the variable length annular gap is a few inches, its length can be varied considerably to fine tune the flow rate. For example, if the original length of the annulus is 6 inches, changing the length by just 0.194 inch will reduce the flow rate through this gap by approximately 10 mm for constant supply and discharge pressures.
% change. Therefore, the flow rate can be adjusted much more precisely than the previous variable Gillup type valve (Figure 3), in which the flow rate changes by 2 cents with a movement of 0.005 inch. The embodiments described above also have the advantage that fluid flow can be redistributed by operator adjustment of a single control.

No judgment is required to turn the knob. Moving the adjustable valve part to the right will decrease the average thickness of the left-hand product and, conversely, increase the average thickness of the right-hand product. Another embodiment of the invention includes a manifold as described above, but uses two adjustable valve members instead of one adjustable and one fixed member.

This embodiment has the advantage of not only operating over a wide range of pressure fluctuations, but also further improving the sensitivity of the control. A further embodiment of the invention is shown in FIG. 5, in which the valve mechanism is different from that shown in FIG.
28 and a corresponding annular restriction 129 are disposed horizontally within the main flow channel 123, but instead of the side channel 123A and the tapered end of the rod being placed in the extrusion die 1.
The structure is almost the same except that the three rivers are placed facing each other.

In the embodiments described above, the side-to-side displacement of the adjustable valve member allows the average film thickness to be set and adjusted in a conventional manner (i.e., by a downstream monitoring operator or by incorporating automatic film thickness detection equipment). The movement of the valve may be controlled to compensate for differences in the thickness of various extruded films.Although the present invention has been described for the extrusion of cylindrical films of thermoplastic materials, flat films, filaments, etc. It can be applied to various extrusion techniques such as extrusion of solid tubes, foamed plastic sheets and tubes.
In the same machine, the manifold has one supply source and two extrusion dies, but this is only for the convenience of illustration. Needless to say, it's good.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view of an apparatus with two subordinate cylindrical film extrusion dies attached to a manifold supplying molten polymer from a common source; FIG. A schematic perspective view of a secondary film technology that produces two films on the downstream side from an extrusion molded body, FIG. 3 is a cutaway cross-sectional view of a typical flow control valve commonly used in the prior art, and FIG. FIG. 5 is a cross-sectional view of an embodiment of a flow distribution valve system according to the invention incorporated into a manifold flow channel; FIG. 2o. ．． ．． Inflow of molten polymer, 21... manifold, 22... inlet, 23... flow channel, 2
3A, 23B... Outlet, 24, 28... Flow rate adjustment device (throttle, lord). FIG. l FIG. 2 FIG. 3 FIG. 4 FIG. 5

Claims (1)

Claims: 1. An apparatus for controlling the flow of molten polymer from a source, comprising a manifold having an inlet, an internal flow channel, and two or more outlets, the apparatus comprising: a flow regulating device disposed upstream of the outlet adjacent to the outlet and comprising a plurality of elongated rods having a diameter smaller than the diameter of the flow channel, at least one of the rods being displaceable in the axial direction within the channel; A film forming device characterized by: 2. The device according to claim 1, wherein one of the rods of the flow rate adjustment device is fixed; 3. The device according to claim 2, wherein both rods of the flow rate adjustment device are displaceable in the axial direction. what is being done. 4. In the device according to claims 1 to 3, the end portion of each flow regulating device is tapered toward the inlet. 5. The apparatus according to claims 1 to 3, wherein the end portion of the rod of each flow regulating device is tapered toward the adjacent outlet.