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BACKGROUND OF THE INVENTION
Conventional air quench extrusion apparatus of `down-the-stack` type for
spinning polypropylene yarn is several stories high and usually requires
to be housed in at least a three story building. The extruder is located
on an upper floor, the air quench cabinets are located on the next lower
floor and may be six or seven feet in height, and below the air quench
cabinets are long inter-floor tubes which extend down to a third or fourth
floor. Below each inter-floor tube, which may be eighteen feet long,
denier control rollers are positioned for pulling the yarn down through
the `stack` with the denier of the undrawn yarn being determined by the
drawn-down of the filaments in the quenching zone.
Disadvantages of this type of apparatus are its height, so requiring a
special building, the complication of having operators on different
floors, and the cost to build and install it.
One story air quench extrusion apparatus for producing polypropylene yarn
are also known, but these have been found to have the disadvantage that
they tend to produce less uniform yarn. There tend to be undesirable
variations in denier from filament to filament and non-uniformily of
denier along the length of a filament. Such yarn is usually cut up into
staple fiber as it is not suitable, for example due to filament breaks
during drawing, to be used as a textile quality continuous filament yarn.
It is surmised that to reduce the height, or length, or air quench
extrusion apparatus for producing polypropylene yarn, the melt should be
extruded at lower temperatures than in conventional `down-the-stack`
apparatus, if the yarn is to be adequately and correctly cooled before it
reaches the denier control rollers. It is also surmised that the use of
lower temperatures normally contributes to denier irregularities and
spinning breaks.
SUMMARY OF THE INVENTION
The present invention is based on the theory that by extruding the yarn
into a hot zone before air quenching it, it is possible to extrude at
lower temperatures and reduce the filament denier irregularies and
spinning breaks that might otherwise occur. This theory is applied to
provide one story air quench extrusion apparatus that can make at least
some textile quality continuous filament polypropylene yarn. In a
preferred embodiment of the invention, this theory is used to shorten
conventional `down-the-stack` extrusion apparatus to enable it to fit in
one story of a building.
One aspect of the invention provides air quench extrusion apparatus having
a first zone into which at least one filament of polyolefin material is
extruded, said first zone being adapted to prevent substantial cooling of
the filament as it passes therethrough, a second zone disposed downstream
of said first zone, gas moving means for moving cooling gas, preferably
air, through said second zone to cool the filament, and denier control
means for pulling said filament out of said second zone, said denier
control means being disposed immediately adjacent said second zone. In
operation the temperature in said first zone should preferably be
maintained at or slightly below the temperature at which the filament is
extruded. The length of the path of said filament from extrusion to said
denier control means may be less than ten feet. Said first zone may be
less than two feet long, preferably less than eighteen inches long, and
may even be less than one foot long. The length of said second, or
quenching, zone may be less than six feet, and is desirably less than five
feet. Said denier control means may be less than eight feet below the
bottom of said first zone.
The length of said first zone may be less than one third that of the second
zone. Preferably the volume of said first zone should be small, for
example less than one tenth the volume of said second zone.
The first zone may be surrounded by a wall arranged to protect the filament
or filaments while passing therethrough from disturbance by outside air,
and air in said first zone may be substantially restricted from escaping
therefrom, thus enabling the temperature of the air in said first zone to
reach and remain close to the temperature of extrusion.
The invention also provides a method of producing filaments of polyolefin
material by air quench extrusion comprising extruding the filaments into a
first zone containing hot quiescent air, passing the filaments through a
quenching zone through which cooling air is blown to cool said filaments,
and contacting the cooled filaments with one or more denier control rolls
to pull the filaments out of said quenching zone at a controlled rate
causing the filaments to be drawn down in denier in said first zone; the
length of the path of the filaments from extrusion to contact by said
denier rolls being less than ten feet, thus enabling the process to be
carried out in a single story building.
A specific embodiment of the invention will now be described in greater
detail with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is side elevational view of an extrusion apparatus according to the
invention;
FIG. 2 is a plan view of the apparatus;
FIG. 3 is an end view of the apparatus on a larger scale;
FIG. 4 is a plan view of a distribution manifold of the apparatus;
FIG. 5 is a plan view of a spin block of the apparatus;
FIG. 6 is a stepped section, on a larger scale, on the line 6--6 of FIG. 5;
FIG. 7 is a diagrammatic section on the line 7--7 of FIG. 3 showing one
spinning position;
FIG. 8 is a diagrammatic section on the line 8--8 of FIG. 7, but on a
larger scale; and
FIG. 9 is a diagrammatic sectional view on the line 9--9 of FIG. 7 on the
same scale as FIG. 8.
An extruder 11 is supported on a framework 12 and has infeed hopper 13.
Although not shown, inside the extruder is a screw rotatable in a barrel
which is surrounded by band heaters as is well known in the art. The screw
is driven by a motor 14 via endless belts and a reduction gear box 15. At
the discharge end of the extruder 11 is mounted a screen shifter 16 which
is connected to a transfer tube 17 which in turn, after turning downwards,
is connected to a distribution manifold 18 (see FIGS. 2 and 4). the
distribution manifold 18 has four legs with passages 19, 20, 21 and 22
therethrough. The passages 19 and 20 are connected together at an orifice
23 in a flange 24. Similarly, the passages 21 and 22 are connected
together at an orifice 25 in the flange 24. The transfer tube 17 is
connected to the flange 24 via a distribution place (not shown) which
connects the bore of the transfer tube 17 with both the orifices 23 and
25. Flanges 26, 27 are connected to a spin block 28 with the passages 19,
20 registering with inlet passages 29, 30, respectively, in the spin block
28 (see FIG. 5). The passages 21, 22 similarly register with inlet
passages in a second spin block 31 which is the same as, but a mirror
image of, the spin block 28. In FIGS. 1, 2 and 3 the spin blocks 28 and 31
are shown enclosed by heat insulating covers.
The spin block 28 houses a metering pump 32 of the meshing gear wheel type
having three gear wheels and constructed to accept one infeed stream of
melt and divide it into two equal metered discharge streams. An inlet port
of the pump 32 registers with passage 30, and two discharge ports of the
pump 32 register with passages 33 and 34, respectively. The passage 33
registers with an inlet passage 35 in a spin pack 36 (see FIG. 6). The
passage 34 similarly registers with a spin pack 37. In like manner, a
second metering pump 38 is connected between the inlet passage 29 and two
more spin packs 39 and 40. FIG. 2 shows the four packs 36, 37, 39, and 40
covered by heat insulating covers 41, 42, 43, and 44, respectively. The
pack 36 has a cover plate 45, a body 46, a breaker plate 47, a spinnerette
48 and a lifting handle 49. Wire mesh screens are disposed above and below
the breaker plate which has passages 50 therethrough and the spinnerette
has capillaries 51 therethrough (see FIG. 8). A bolt 52 clamps the spin
pack 36 in place so that the passages 33 and 35 are in sealed register.
Packs 37, 39 and 40 are similarly constructed and held in place. A band
heater 53 surrounds spin block 28. Spin block 31 is similarly constructed
and contains four more spin packs which are fed from passages 21 and 22 in
the manifold 18.
The spin blocks 28 and 31 are supported by pillars 54 which also support
further structural members including a platform 55 on which are mounted
drive motors 56 and 57. The motor 56 drives the metering pumps 32 and 38
via a reduction gear box 58, right-angled gear boxes 59, 60 and drive
shafts 61 and 62. The gear box 60 is driven from the gear box 59 by a
shaft 63. The two metering pumps of spin block 31 are similarly driven by
the motor 57. For simplicity, the motors 56 and 57 have been omitted in
FIG. 3.
Below the eight spin packs are eight quench cabinets 64, each having a door
65 at the front and being supported by structural members. The door 65 is
constructed from slotted sheet metal (see FIG. 7) mounted in a frame 66
(see FIG. 8). The back of each quench cabinet is formed by wire mesh (see
FIG. 7) mounted in a frame 68. The wire mesh 67 of all the quench cabinets
is in communication with a plenum 69 which is connected by a duct 70 to a
blower 71. The blower 71 has an air inlet 72 covered by a filter 73 and is
driven by a motor 74.
Between the top of each quench cabinet and the spin block thereabove is a
shroud 75. Referring now to FIGS. 7, 8, and 9, the shroud has a flange 76
around its upper edge and is secured to the spin block 28 by bolts 77.
Around the lower edge of the shroud is a trough 78 directed inwardly. A
top cover 79 of the quench cabinet fits closely around the outside of the
trough 78. The shroud is rectangular in horizontal section and surround
the face of the spinnerette which is also rectangular (see FIG. 9). A
small spacer (not shown) is mounted on each bolt 77 between the flange 76
and the lower surface of the spin block 28 so that there is a minute
clearance between the flange 76 and the spin block sufficient to reduce
thermal conductivity from the spin block to the shroud 75. The front wall
of the shroud 75 may have a removable panel for ease of access to the
interior of the shroud and the face of the spinnerette 48.
The spinnerette has three groups 80, 81 and 82 of capillaries 51 for
producing three multi-filament yarns 84, 85 and 86. The three groups 80,
81 and 82 are spaced apart in a direction parallel to the longer sides of
the rectangle formed in horizontal section by the shroud 75. At the bottom
of the quench cabinet 64 are three finish applying guides 87 below which
is a denier control roll 88 to the discharge side of which is a pair of
nip rollers 89. As can be seen, the denier control roll 88 is disposed
immediately adjacent the quench cabinet 64 without the presence of an
inter-floor tube.
Each of the eight spinning positions are similarly constructed but with the
denier control rolls 88 being slightly staggered in the vertical direction
to keep the groups of yarns from different spinning positions separate
before they pass around and through the nip rollers 89.
All the various motors, drives, and heaters of the apparatus are controlled
from a control cabinet 90.
In operation, pellets of thermoplastic material, particularly
polypropylene, are fed via the hopper 13 into the extruder 11 where they
are melted and mixed. The resulting melt is fed by the screw of the
extruder through the screen shifter 16, where it is filtered, through the
transfer tube 17 to the manifold 18 where it divides into four streams
passing through the four passages 19, 20, 21 and 22. Each stream supplies
its respective metering pump which divides the stream into two equal
metered streams. Each metered stream is pumped to its respective spin pack
where it hydraulically splits and is extruded through the capillaries 51
into three groups of filaments to form three multi-filament yarns 84, 85
and 86. The yarns pass through the guides 87 which apply spin finish to
them before the three yarns come together and pass partly around the
denier control roll 88. The three yarns then pass around and through the
nipping rollers 89 which feed them to winders, at this point the three
yarns separate and each multi-filament yarn is fed to a separate winder.
The air inside the shroud 75 is trapped there and remains quiescent. This
air is heated by the metal above it, namely the face of the spinnerette
48, the lower end of the pack body 46 and part of the spin block 28, these
being heated by the spin block heater 53. The molten filaments leaving the
capillaries 51 also heat this air. In this way, the air inside the shroud
75 remains hot at a temperature close to, or just below, the temperature
of the melt being extruded and prevents substantial cooling of the
filaments as they pass therethrough. By extruding the filaments into the
hot zone inside the shroud 75, the draw-down of the molten filaments to
their undrawn denier before they solidify occurs at or closely adjacent
the face of the spinnerette, and can occur uniformly at lower melt
temperatures than if the molten filaments were extruded directly into a
quenching zone. Also, this draw-down occurs over a shorter distance. The
volume inside the shroud 75 is relatively small so that when extrusion is
started up, the air inside the shroud heats up quickly. The shroud is
relatively short but there is sufficient clearance between the yarns and
the trough 78 to prevent the yarns when they sway touching the inside edge
of the trough.
The outside of the shroud 75 is in contact with lower temperature air, and
the vapors, such as low molecular weight polymers or stabilizers, given
off by the filaments, while molten, condense on the inside surface of the
shroud 75 and are collected in the trough 78. This condensate is manually
cleaned out of the trough 78 periodically, for example when die facing or
changing spin packs.
Ambient air is drawn in through the filter 73 and blown by the blower 71
through the duct 70 into the plenum 69, then passing through the wire
meshes 67 transversely across the quench cabinets 64 from back to front,
and is exhausted to atmosphere through the slots in the doors 65. The wire
mesh 67 extends the full length of each quench cabinet and distributes
from the top to the bottom uniform flow of cooling air across the quench
cabinet and the yarns passing therethrough. In this way the yarns are
cooled in the quench cabinet. The three yarns 84, 85, 86 are spaced apart
across the quench cabinet in a direction at right angles to the direction
of air flow therethrough to prevent one yarn interfering with the cooling
of another. The main factor in the cooling of the yarns is the velocity of
the air as it passes over the yarns and not the temperature of the air.
However, if the temperature of the ambient air in the vicinity of the
filter 73 is high, for example over 90.degree. F., it may be desirable to
cool the air with refrigeration units before it is blown through the
quench cabinets.
By applying the spin finish to the yarns before they contact the denier
control roll 88, they are gripped better by the roll 88. The speed of the
roll 88 determines the undrawn denier of the yarns.
The dimensions of the shroud 75 are height 9 inches, width 12 inches, and
depth 7 inches. The face of the spinnerette 48 is 8 inches long by 4
inches wide. The height of the quench cabinets is 4 feet, and the bottom
of each quench cabinet is 1 feet 10 inches above the floor. The face of
the spinnerette is 6 feet 7 inches above the floor. This enables an
average height operator to reach the spinnerette face and any part of the
yarn path while standing on the floor. This is particularly advantageous
when extrusion is being started-up, for example after a spin pack change,
as the operator, while standing on the floor, can separate the three yarns
at each spinning position a short distance below the spinnerette and then
follow the separation through the guides 87 and from the nip rollers 89.
The overall height of the apparatus (including the hopper 13) is 10 feet 9
inches, the overall length (excluding winders) 19 feet, and the width 7
feet. Thus it can be seen that this is a compact extrusion apparatus that
can be installed in a single story building.
The extruder has a barrel diameter of 3 inches and a length over diameter
ratio of the barrel of 30:1.
The following is an example of the production of a polypropylene yarn with
the above extrusion apparatus. Polypropylene resin was used having a
narrow molecular weight distribution and a melt flow of 30. The
temperature profile of the extruder was set to give an extrusion
temperature of 400.degree. F. The metering pumps were set to produce each
metered stream at the rate of 24 pounds per hour with the extruder output
being 192 pounds per hour. Ambient air at 85.degree. F. was blown through
the quench cabinets at 100 feet per minute. The delivery speed of the
yarns from the denier control rolls 88 was 600 meters per minute. Each
yarn had 70 filaments and an undrawn denier of 900. When subsequently
drawn at a 3:1 draw ratio to 300 denier the final continuous filament yarn
was suitable for use as an upholstery filling yarn. It will be noticed
that although the length of the yarn path from the spinnerette to the
denier control roll is less than 7 feet, the speed of the extruded yarn is
surprisingly high.
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