US 3496261 A
Description (OCR text may contain errors)
Feb. 17, 1970 w. G. PARR 3,496,261
DISTRIBUTION OF VISGOUS LIQUID SUBSTANCES IN PIPES Filed March 18, 1964 3 Sheets-Sheet 1 \jeciion 4.
Jecf/bn 2 J65 on I Inuenlor I fiW WW I Attorneys Feb. 17, 1970 w. e. PARR 3,496,261
DISTRIBUTION OF VISCOUS LIQUID SUBSTANCES IN PIPES Filed March 18, 1964 3 Sheets-Sheet 2 Feb. 17, 1970 w. G. PARR 3,49
DISTRIBUTION OF VISCOUS LIQUID SUBSTANCES IN PIPES 77/7[im'//uIslrwenlor WM Wwu A Home y;
United States Patent 3,496,261 DISTRIBUTION OF VISCOUS LIQUID SUBSTANCES IN PIPES William Geoffrey Parr, 20 Knoll Road, Abergavenny, England Filed Mar. 18, 1964, Ser. No. 352,786 Claims priority, application Great Britain, Mar. 22, 1963, 11,378/ 63 Int. Cl. B28]: 3/20, 3/00 US. Cl. 264176 13 Claims The present invention concerns improvements in or relating to the distribution of viscous liquid substances in pipes.
The invention will be described by reference to the distribution of molten polymer material in pipes to sundry means for spinning it into filaments; but it is to be understood that the invention is not so limited, and that it has application to the distribution of any viscous liquid substance in like circumstances and for like purposes.
In the melt-spinning of synthetic polymer material, Such as polyhexamethylene adipamide, it is of potential advantage from the points-of-view of productivity and of uniformity, and of actual advantage so far as concerns simplicity of machine design, that one melter, or polymeriser, shall supply a number of spinning heads.
It is possible for this to be done in a number of ways. Thus, each spinning head may be individually supplied by a pipe leading directly to it from the melter. Or, a number of spinning heads may be fed from each of one or more pipes, and such pipes may or may not circulate some of the polymer back into the melter. Whichever of the ways is employed, the molten polymer has to be supplied under a pressure suflicient to ensure its uniform flow in sufficient quantity down the pipe or pipes in question; and in this regard there are clear advantages, due to the lesser pressure required for a given transit time, and due to the simplicity of the pipework and the means for holding it at the required high temperature, in supplying a given number of spinning heads from a common pipe than in supplying them by individual pipes.
This invention, therefore, is concerned with the supply of viscous liquid material, such as the molten polymer material above referred to, to a number of positions by means of a single distribution pipe.
In order to attain the potential advantage of uniformity of operation afforded by a melt-spinning system in which one melter supplies a number of spinning heads, it is important to try and ensure that each spinning head is supplied with polymer that has taken the same average time to travel on its way from the melter. In other words, the mean transit times of the polymer streams to be extruded from each head shall be as near equal as possible. This follows from the fact that some melt-spinning materials, such as nylon, degrade and change their physical and chemical properties when kept at the high temperatures necessary to ensure fluidity. Thus, for uniform results, the supplies to different spinning positions must be, if not negligibly degraded, at least substantially equally degraded. When molten polymer flows down an ordinary pipe, the mean transit time of the polymer at each section is dependent on the length of pipe down which the polymer has travelled; the longer the flow path, the longer the mean transit time and the greater the degradation in the polymer at that section.
When a viscous liquid material, such as molten polymer material, flows down a pipe, the material near the axis of the advancing mass flows more quickly than that near the walls of the pipe itself; the flow is laminar, and in a cylindrical pipe has an axisymmetrical flow pattern.
The invention comprises a process for providing a vis- 3,496,261 Patented Feb. 17, 1970 ice cons liquid material under pressure from a source thereof along a pipe to a plurality of positions, e.g. spinning heads, in which process successive positions or groups of positions up to the final position or group of positions are supplied from stations along the pipe at each of which an outer annular portion containing the liquid required by its position or positions is withdrawn from the approaching stream and in which the final position or positions is or are supplied from the end of the pipe, the internal dimensions of the pipe along its length and the spacing of the stations being such that the mean times of transit of the liquid material from the inlet of the pipe to each of the positions are substantially equal.
Also, according to our invention, apparatus comprises liquid withdrawal means provided at a station or stations along a pipe through which pipe viscous liquid material is adapted to flow from a source of supply thereof, such means being adapted to withdraw from the approaching stream an outer annular portion containing the amount of liquid required at any such station for the supply of a position or group of positions, e.g. spinning heads, supplied from said station, the successive lengths and internal cross-sectional areas of the pipe between the inlet and the first of such stations, between any two such stations, and between the final such station and the downstream end of the pipe itself, being so selected, as by step-wise or gradual variations in the size of cross-section, that the mean times of transit of the liquid material from the inlet of the pipe to each of the positions are substantially equal. The mean times of transit referred to herein are the arithmetic means of the several times of transit.
Alternatively, the dimensions of the pipe may be chosen to give a set of different mean transit times.
The invention equally comprehends an arrangement whereby the direction of flow is reversed, moving from the several sources of supply to a common outlet.
When the pipe is used to supply spinning heads, the amounts withdrawn at the tapping stations are normally controlled by meter pumps, e.g. gear pumps, positioned upstream of each head.
The flow along the pipe being laminar, there will be no mixing between the streams, one within the other, flowing from the supply to the different tapping stations, or junctions. To achieve equal mean transit times, the dimensions of the pipe must be chosen so that each stream shall occupy a volume within the pipe proportional to its throughput. To obtain a particular set of mean transit times, the ratio of the volume occupied by each stream to its throughput must be equal to the desired mean transit time. To determine the volume occupied by a particular stream, the laws governing the flow of the particular material within the shape of pipe employed must be known. The calculation is greatly simplified when cylindrical pipes are used and axisymmetrical flow division ocurs; and even more so when it can be assumed that the flow is Newtonian, for then the outer fraction M of the pipe throughput occupies a fraction 1\ /I of the pipe volume. Such latter state of affairs exists in the case of the supply of molten polyhexamethylene adipamide (nylon 66) for melt-spinning.
For any given number of tappings along a pipe, it is a relatively simple matter to calculate the successively decreasing volumes of the complementary pipe sections re quired, assuming, for example, that the lengths of pipe between tappings should be equal.
At each tapping, the outer annual portion of material can then be extracted, leaving the remainder of it to continue its travel along the pipe, such usually being of reduced diameter, in the following section. In fact, tests have shown that up to 99% of the liquid material extracted at each of successive tappings is derived from their respective outer annuli.
Another important consequence of the invention is that, as none of the material flowing very slowly close to the Walls of the pipe has to travel further than the distance between two tapping stations, little will remain in the pipe for long enough to gel, which some polymeric materials have a tendency to do when kept in molten condition for any appreciable length of time. Certainly, there is a great improvement over the amount of longdwelling polymer that is present in a com-parable direct feed down an individual pipe.
If, for example, the pipe is required to distribute equal quantities of molten polymer material to each of four spinning heads with equal mean transit times, and the volume of section between the inlet and the first tapping station is V, then the volume of the section between the first and second stations will be 0.5V, that of the section between the second and third stations 031V, and that between the third station and the end of the pipe 0.19V. It can be calculated that, if the sections are themselves of equal length, and the final pump is at a given fixed distance from the supply, then the pressure required in a system as above described will be only a quarter that required to distribute the same material, with the same equal mean transit times, by means of individual pipes. Further, at each of the spinning heads of the system, there will be far less of the polymer material that has moved very slowly and hence has a significantly long transit time, than will be the case if individual pipes are used, achieving the same throughputs.
The invention will not be described with reference to the accompanying drawings in which FIGURE 1 is a diagram showing a molten synthetic polymer distribution pipe with four positions fed there from, according to the invention:
FIGURE 2 is a diagram showing the essential features of one embodiment of a twin-branch tapping station (or stripping junction) for use in the invention;
FIGURE 3 is a diagrammatic sectional view of one design of a singlebranch tapping station (or stripping junction) for use in the invention, in which division of the stream of liquid takes place upstream of the branch position;
FIGURE 4 is a diagrammatic sectional view of another design of a single-branch tapping station( or stripping junction) for use in the invention, in which division of the stream takes place downstream of the branch position;
FIGURE 5 is a diagrammatic sectional view of a design of a single-branch tapping station (or stripping junction) for use in the invention, which station incorporates an annual metering slot and a plenum chamber;
FIGURE 6 is a variant of the design of FIGURE 5, for a twin-branch tapping station (or stripping junction);
FIGURE 7 is a digram of a four branch tapping station (or stripping junction) for use in the invention;
FIGURE 8 is a graph of the distribution (or spread) of transit times of liquid at each of three positions, compared with that of liquid at the end of a pipe of volume equal to that occupied by any one of the streams leading to such positions.
In FIGURE 1, a polymer distribution manifold M leading from a source of supply, such as the melter or polymeriser of a melt-spinning unit (not shown) consists of a pipe having three step-wise reductions in diameter at tapping stations (or stripping junctions) T T and T The manifold is thus divided, as shown, into four sections along its length. At each of the steps-down in diameter, successive tapping stations T T and T strip from the approaching stream outer annuli of molten polymer each containing one quarter of the input to the pipe and direct them to positions (spinning heads) P P and P respectively. The residual core of molten polymer proceeds along the final (fourth) section of the manifold directly to position P The flows to the spinning heads are controlled by meter pumps G which are gang driven as indicated by the dashed line D. At each position, the volumetric flow, a, is the same, and is a quarter that of the input, 4a, of the manifold. The dotted lines within the manifold show the boundaries between the streams flowing to the respective positions.
In FIGURE 2, three branches B B and B are fed with equal volumetric flows from manifold M. The tapping station T is a simple twin-branch junction. This figure shows the upstream end portion of the smaller diameter pipe of branch B protruding concentrically backwardly into the downstream end portion of the manifold M. Such backward protrusion of the inner pipe, and the width of the annual gap between the two pipes, are important factors related to the stripping efficiency of the junction. The longer the protruding length of the inner pipe, the better the stripping eificiency; but, on the other hand, the longer the protruding length, the greater will be the spread of transit times for the liquid in the annular gap. Hence, a compromise is necessary, to achieve the optimum performance for the liquid in question, in the particular process.
In FIGURES 3 and 4, the tapping station T on manifold M is a single stripping junction, having branch pipe, B. In the design of FIGURE 3, division of the stream takes place upstream of the junction, as also shown in FIGURE 2, by virtue of the backward protrusion of the inner pipe of the stepped-down portion of the manifold within the larger-diameter upstream portion of the manifold. In the design of FIGURE 4, however, division of the stream takes place downstream of the branch, B, the outer annulus of the stream of liquid being reversed in direction before flowing down the branch pipe. Such downstream division of the stream may have advantages over the other method, in that the slower-moving liquid of the manifold, close to its walls, is directed into the centre of the branch pipe, and hence the spread of transit times at the outlet of the branch (e.g. a spinning head) is reduced; and in that the length of the last section of the manifold, where most of the pressure drop of the -entire manifold takes place, is reduced and hence the total pressure drop can be reduced or a lower mean transit time for the same pressure drop achieved.
FIGURES 5 and 6 illustrate the use of an annular metering slot at the tapping point leading to an annular plenum chamber, C. In the design of FIGURE 6, being an example of a multi-branch junction, the presence of a sufiiciently large plenum chamber would enable the asymetric arrangement of branch pipes B and B should this be desired.
In the four-branch junction shown in FIGURE 7, it is shown that branch pipes B B B and B are of equal diameter to that of manifold M, such that they more than cover the circumference of the manifold at the tapping station, T, which overlap is necessary if proper stripping of the entire outer annulus, as required, is to take place by means of the action of meter pumps extracting an equal flow in each of the branch pipes.
The graph of FIGURE 8 readily indicates the equivalence of the distributions of transit times of three outlet positions from a manifold constructed according to 'the invention, and compares these three curves with one for a simple pipe of equivalent volume. The unit of the abscissa is time t minutes, and that of the ordinate is the percentage of liquid with a transit time greater than t minutes.
The apparatus used for obtaining the values to be plotted for the curves of the manifold outlets Was one comprising three outlet positions, two such positions being fed from successive single-branch tapping stations along the length of the manifold and one position being fed directly from the end section of the manifold. The apparatus was designed to give equal mean transit times for the streams to the three outlet positions, when the flows from the three outlets were equal. A throughput of 30 cc./min. of viscous liquid material at each outlet was used in the tests. The volume occupied by each of the three streams of liquid was 237 cc. The dimensions of the three sections of the manifold were, respectively, from the input end:
1st section-1 inch diameter, 29% inch length 2nd section- A inch diameter, 28% inch length 3rd section- /2 inch diameter, 30 /8 inch length Simple stripping junctions, of the type illustrated in FIGURE 3 were employed, the inner lower-diameter tubes protruding concentrically into the larger-diameter tubes by some 2 inches.
Reading off from the graph, it can be calculated that the spread of transit times at each position fed from the manifold, between times t 100% and t 5%, is of the order of 8 minutes, whereas the spread of transit times for the simple pipe with an internal volume of 240 cc. is 14 minutes. It is also clear from the graph how a significantly large percentage of the liquid in the simple pipe is in transit over a long period of time, e.g. over 20 minutes in the process in question, compared with the almost negligible amounts in the three outlet positions.
In the case of molten polymeric material, for example molten polyhexamethylene adipamide, it may be desirable to homogenise the material both as supplied to the pipe and as supplied down the branch lines to the spinning heads. Such homogenising will be desirable when nonuniform degradation occurs in the melter or polymeriser supplying polymeric material to the manifold pipe, and it may be necessary in the branch lines so as to mix the laminae flowing into each line and thus to prevent unevenly degraded polymer from being supplied across the face of the spinneret with the consequent extrusion of poorer filaments from some holes than others. The type of tapping station shown in FIGURE 4 is conducive to this end.
On a melt-spinning machine, it may well be desirable to split the initial stream of polymer equally into two halves, each half then flowing along a manifold pipe. A simple T-junction will effect such equal division of the initial stream into the twin manifold.
Although we have specified above that the pipe is usually of progressively stepped-down diameter, and this is convenient since it is usual to wish to have the various sections of the pipe between tappings of equal length, it is not strictly necessary, according to our invention, for the pipe to be so proportioned. It is only essential that the volumes of the various sections between tappings shall be such as to give the equal mean transit times, or such other ratio of transit times as may be required. And hence, if the lengths of the various sections can be, and are, made unequal to the extent necessary to give the required volumes, the cross-section of the pipe can, in fact, be constant throughout the length of the pipe.
Although we have described the invention with respect to successive withdrawals from a pipe to supply a number of positions, it is within the scope of the invention, as declared hereinbefore, to reverse the procedure and to supply a pipe from a number of units of, e.g. molten polymer supply, so as to feed the molten polymer to a single spinning head or to a single pipe from which required amounts are then withdrawn for a plurality of spinning heads. In that case also, the respective volumes of the pipe sections may be so selected that the mean transit times of all the polymer streams are substantially equal, so as to reduce the variation of polymer characteristics across the face of the spinning head or the pipe outlet. Such a procedure may be useful in the spinning of large tows of a great number of filaments.
Finally, although we have specifically described and illustrated the supply of spinning heads fitted with meter pumps, it is to be understood that such a final position may comprise the source of supply itself, should it be desired completely to circulate a portion of the viscous liquid material.
1. In a process for melt spinning synthetic polymeric material, said process being of the type including providing viscous liquid synthetic polymeric material under pressure from a source thereof to the inlet of a pipe, providing a succession of stations along the pipe, providing a succession of spinning positions with at least one position correspoding to each station and with at least one of the last positions in the succession corresponding to the end of the pipe, collecting at each station an outer annular portion of the liquid material approaching the station, conducting the collected portion to each spinning position associated therewith in the amount required by the spinning position and conducting liquid material from the downstream end of the pipe to each spinning position associated therewith in the amount required by the spinning position, the improvement which comprises receiving the conducted liquid material into a meter pump at each spinning position, pumping the received liquid material to a spinning head associated with the spinning position, said pumping operation delivering liquid material to all of the spinning heads at the same flow rate and establishing substantial equality of residence times of the liquid material travelling from the inlet of the pipe to each spinning position solely by selection of the dimensions of the pipe along its length.
2. A process as in claim 1 wherein at least a portion of the liquid material flowing from the downstream end of the pipe is conducted back to the source of said material.
3. A process as in claim 1 including homogenising the liquid material being conducted from the pipe to the positions for the purpose of preventing unevenly degraded polymeric material from reaching the spinning heads.
4. A process as in claim 1 wherein said step of selecting the dimensions of the pipe includes selecting the successive lengths and internal cross-sectional areas of the pipe between the inlet end and the first of the stations, between successive stations, and between the final station and the downstream end of the pipe.
5. A manifold pipe for the distribution of molten synthetic polymer material to a plurality of spinning heads from a source of such material, said pipe having at least one stripping junction along its length from which at least one branch pipe leads to a spinning head and havig an end section leading directly to at least one spinning head, said stripping junction or junctions being adapted to direct an outer annular portion of the molten material from the approaching stream into said branch pipe or pipes, and each of said spinning heads being provided with a meter pump to control the amount of molten material supplied to each head, the dimensions of the manifold pipe along its length being such that the mean times of transit of the molten material from the inlet of the pipe to each of the spinning heads are substantially equal.
6. A manifold pipe as claimed in claim 5 in which the source of supply of molten synthetic polymer material is a melter of a melt-spinning unit.
7. A manifold pipe as claimed in claim 5 in which the source of supply of molten synthetic polymer material is a polymeriser.
8. A manifold pipe as claimed in claim 5 in which the meter pumps are gang-driven gear pumps.
9. A manifold pipe as claimed in claim 5 in which the stripping junction or each of the stripping junctions comprises an upstream end portion of a section of the pipe of smaller diameter protruding backwardly and concentrically into the downstream end portion of the immediately preceding section of the pipe of larger diameter.
7 10. A manifold pipe as claimed in claim 9 in which there is a single branch pipe leading from each stripping junction.
11. A manifold pipe as claimed in claim 5 in which the stripping junction or each of the stripping junctions 5 comprises an annular metering slot leading, into an annular plenum chamber.
12. A manifold pipe as claimed in claim 11 in which a plurality of branch pipes are asymmetrically spaced around and lead from the annular plenum chamber.
13. A manifold pipe as claimed in claim 5 in which the stripping junction or each of the stripping junctions comprises means for separating the outer annular portion of the stream downstream of a single branch pipe.
References Cited UNITED STATES PATENTS 699,079 4/1902 Coles 137S67 2,599,680 6/1952 Weeks 137567 X 3,000,053 9/1961 Hart.
3,034,526 5/1962 Roselle l371 3,103,942 9/1963 Sharp 1371 WILLIAM F. ODEA, Primary Examiner 10 DAVID R. MATTHEWS, Assistant Examiner US. Cl. X.R.
l88; 103-4; l379, 118, 561, S67