U.S. patent number 3,648,451 [Application Number 05/011,719] was granted by the patent office on 1972-03-14 for novel yarn and process.
This patent grant is currently assigned to Monsanto Company. Invention is credited to Myrne R. Riley.
United States Patent |
3,648,451 |
Riley |
March 14, 1972 |
NOVEL YARN AND PROCESS
Abstract
A fluid vortex spinning process for yarn in which a dispersion
of high-modulus refractory fibers and lower modulus fibers in a
viscous carrier liquid as a flowing stream is rotated about its
axis to produce a composite staple fiber yarn of axially aligned
high-modulus refractory fibers intermixed with and intertwined by
lower modulus fibers and the composite yarns so produced.
Inventors: |
Riley; Myrne R. (Rolla,
MO) |
Assignee: |
Monsanto Company (St. Louis,
MO)
|
Family
ID: |
21751688 |
Appl.
No.: |
05/011,719 |
Filed: |
February 16, 1970 |
Current U.S.
Class: |
57/255;
57/403 |
Current CPC
Class: |
D02G
3/16 (20130101); D01H 4/34 (20130101); D10B
2101/16 (20130101); D10B 2101/06 (20130101) |
Current International
Class: |
D01H
4/34 (20060101); D01H 4/00 (20060101); D02g
003/04 (); D02g 003/18 (); D01d 005/06 () |
Field of
Search: |
;57/58.89,14BL,156,157,34,12 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Watkins; Donald E.
Claims
I claim:
1. A process of fluid vortex spinning which comprises forming a
dispersion of discrete high modulus refractory staple fibers and
lower modulus staple fibers in a viscous carrier liquid having a
viscosity of from 30 to about 20,000 poise, establishing a flowing
stream of said liquid dispersion through a passage whose end
portion at least is straight, rotating about its axis the terminal
portion of said stream thereby to produce a yarn, and separating
the carrier liquid from the yarn so produced.
2. The process of fluid vortex spinning of claim 1 wherein the high
modulus refractory fibers have a staple length of from one-fourth
inch to about 1.5 inches.
3. The process of fluid vortex spinning of claim 1 wherein the high
modulus refractory fibers are glass.
4. The process of fluid vortex spinning of claim 1 wherein the high
modulus refractory fibers are whisker fibers.
5. The process of fluid vortex spinning of claim 1 wherein the high
modulus refractory fibers are silicon carbide whisker fibers.
6. The process of fluid vortex spinning of claim 1 wherein the
lower modulus fibers have a staple length of from three-eighths
inch to about 1.5 inches.
7. The process of fluid vortex spinning of claim 1 wherein the
lower modulus fibers are synthetic cellulosic or polymeric staple
fibers.
8. The process of fluid vortex spinning of claim 1 wherein the
lower modulus fibers are acrylic staple fibers.
9. The process of fluid vortex spinning of claim 1 wherein the
lower modulus fibers are cellulosic staple fibers.
10. The process of fluid vortex spinning of claim 1 wherein the
carrier liquid is corn syrup.
11. A composite staple fiber yarn of high modulus refractory fibers
and lower modulus fibers, which yarn comprises axially aligned high
modulus refractory staple fibers intermixed with and intertwined by
lower modulus staple fibers.
12. The composite staple fiber yarn of claim 11 wherein the high
modulus refractory fibers have a staple length of from about
one-fourth inch to about 1.5 inches.
13. The composite staple fiber yarn of claim 11 wherein the high
modulus refractory fibers are whisker fibers.
14. The composite staple fiber yarn of claim 11 wherein the high
modulus refractory fibers are glass.
15. The composite staple fiber yarn of claim 11 wherein the high
modulus refractory fibers are silicon carbide whisker fibers.
16. The composite staple fiber yarn of claim 11 wherein the lower
modulus fibers have a staple length of from three-eighths inch to
about 1.5 inches.
17. The composite staple fiber yarn of claim 11 wherein the lower
modulus fibers are synthetic cellulosic or polymeric fibers.
18. The composite staple fiber yarns of claim 11 wherein the lower
modulus fibers are cellulosic fibers.
19. The composite staple fiber yarn of claim 11 wherein the lower
modulus fibers are acrylic fibers.
Description
The invention described herein was made in the course of or under a
contract or subcontract thereunder with the U.S. Department of
Defense, Office of Naval Research.
BACKGROUND OF THE INVENTION
The field of the invention is that of yarns of low and high modulus
staple fibers suited for use in the preparation of reinforced
composites and the process of preparing such yarns with axial
alignment of the high modulus fibers.
Reinforced composites produced generally by molding a matrix
material have been reinforced with a variety of high modulus fibers
and filaments for increased strength and stiffness. But the
greatest increases are only realized when the high modulus
reinforcing fibers or filaments are aligned in the direction in
which the greatest strength and stiffness are desired. When
continuous high modulus filaments are employed this can generally
be achieved by known methods. However, when high modulus staple
fibers are to be employed their alignment in the desired direction
or directions is much more difficult. It is particularly difficult
when employing the very brittle and fragile whisker fibers of
silicon carbide and other metal carbides and nitrides, graphite and
the like. In fact short of fully aligning such whisker fibers by
laborious hand operations and then infusing the arrangement with a
setting liquid to fix the whiskers in their alignment no fully
successful method for their use as aligned reinforcing fibers has
been developed.
It would be very desirable if such high modulus staple fibers and
particularly whisker fibers could be aligned in a continuous yarn
which yarn could then be employed directly in producing a molding
lay-up for later infusion with a moldable matrix material,
resinous, metallic or ceramic, or in which the lay-up produced
could be charred and the carrier fibers volatilized so that the
fired lay-up could then be infused with the desired matrix
material. Such a yarn has been produced by the present
invention.
Although conventional textile processes cannot be used to produce
such yarns, it was previously known to produce yarns from one or
more textile type fibers of generally low modulus by various
methods generally described as open-end spinning where a yarn is
produced from staple fibers directly. Open-end spinning processes
employ several different modes of collecting and assembling fibers
including a fluid vortex, twisting by a mechanical rotating element
from a collecting zone, overlapping of tufts of fibers on a
collecting drum and twisting them as withdrawn, and collection on a
rotating collecting surface and twisting onto a seed yarn as in
so-called "pot spinners." None of these methods are adapted to
handle short, stiff or fragile high modulus fibers since most of
them require well crimped fibers of relatively low modulus. The
fluid vortex spinning systems have not employed sufficiently strong
hydrodynamic forces to handle such short, stiff or fragile
uncrimped fibers.
One such fluid vortex system employing liquids such as water as a
fluid has been described in which yarns of low modulus crimped
textile type fibers could be produced by means of the vortex
produced in a two-part tube with a rotating terminal portion.
However, such processes are unsuccessful when attempts are made to
spin yarns comprised of high modulus short, stiff or fragile fibers
as well as textile type fibers.
It has now been found that blended yarns of low and high modulus
fibers including high modulus fibers of whisker type and in which
the high modulus fibers are controlled in axial alignment can be
produced by a fluid vortex method. The yarns are suited for use in
preparing preforms for infusion by liquid or molten matrices and
thereafter for molding or otherwise forming to form reinforced
composite structures of increased strength and stiffness in
controlled desired directions. A fluid vortex method has been found
by which such yarn can be produced which is subject to control in
the alignment of the high modulus fibers and for the production of
multicomponent yarns which previously could not be produced either
by conventional textile processes or the so called open-end
spinning technique.
BRIEF DESCRIPTION OF THE INVENTION
The present invention embraces a process of fluid vortex spinning
of yarns comprising forming a dispersion of discrete high modulus
refractory fibers and low modulus fibers in a viscous carrier
liquid, establishing a flowing stream of said liquid dispersion
through a passage whose end portion at least is straight, rotating
about its axis the terminal portion of said stream thereby to
produce a yarn, and separating the carrier liquid from the yarn so
produced.
It also embraces a yarn product comprising a composite yarn of
aligned high modulus refractory fibers and wrapped low modulus
fibers in yarn form which can be used as reinforcing agent in
composite matrices. The viscous carrier liquid used is a liquid in
which the two types of fibers are dispersable and which is
sufficiently viscous to produce relatively high hydrodynamic forces
in the flowing and rotating stream formed.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic drawing of certain apparatus suitable for
carrying out the process of the invention.
FIG. 2 is an enlarged sectional view of that portion of the
apparatus of FIG. 1 from points A to B of FIG. 1 with fluid
effluent pot shown.
DETAILED DESCRIPTION OF INVENTION
The present invention is of a novel yarn structure and a process
for producing such yarn by fluid vortex spinning. Basically the
process comprises forming a dispersion of discrete high modulus
refractory fibers and low modulus fibers in a viscous carrier
liquid, establishing a flowing stream of said liquid dispersion
through a passage whose end portion at least is straight, rotating
about its axis the terminal portion of said stream to produce a
yarn, and separating the carrier liquid from the yarn so
produced.
The fibers utilized in the process and forming the yarn are of two
general types, high modulus refractory fibers and low modulus
fibers. The high modulus fibers are all those of high strength and
stiffness useful as reinforcing fibers in composites with resinous,
metallic, ceramic or other moldable matrices. They include staple
fibers of glass, metal such as boron, steel, aluminum and the like,
graphite and high temperature resistant polymers such as aromatic
polyamides and other resins as well as those occurring generally in
the form of "whiskers" such as silica, silicon carbide, silicon
nitride, and the carbides and nitrides of other metals of very high
stiffness and strength. In general the staple fibers most useful
are those of lengths from about one-fourth to 1.5 inch or somewhat
longer. Likewise the whisker fibers of lengths of about one-fourth
to 1 inch or greater are most useful. Fibers and whiskers of
lengths less than the internal diameter of the passage leading to
the rotating portion of the apparatus can be employed, but will
generally not be as well aligned with the axis of the resulting
yarn, but more generally dispersed at all radii throughout same and
at more or less random angles of incidence to such axis. Hence, the
yarns produced therefrom afford less control of the strength and
stiffness in a given desired direction of composites made
therefrom.
The low modulus fibers may generally comprise any staple fiber of
textile type which is of a length that will not plug the passage of
the apparatus used. The preferred lengths of such low modulus
fibers range from about three-eighths to 11/2 inch or longer and
generally it is preferred to use low modulus fibers somewhat longer
than the high modulus fibers used. Such low modulus fibers will
normally possess aspect ratios ranging from about 100 to 1,000 or
greater. The diameter of the low modulus fibers is not critical but
may embrace any size generally useful in the production of
textiles. Large diameter filaments are useful but are not preferred
because of the increase in size of the yarn and the lower volume
percent of high modulus fibers in the resulting yarn. The low
modulus fibers can be crimped or uncrimped.
The viscous carrier liquids which can be used are any in which the
fibers are dispersible, are chemically inert thereto, and which
will produce relatively high hydrodynamic forces in the flowing and
rotating stream form. Fluids with viscosities of from about 30 to
about 20,000 poise or higher can be used. Preferably fluids of from
about 50 to 2,000 poise are used. Also it is desirable to employ
liquids which are easily separated from the yarns produced and such
are preferred. Many viscous liquids can be employed including
glycerol, and polyglycols of high molecular weight, silicone oils
of suitable viscosities, polymeric carboxylic acid esters of
suitable viscosities, sugar solutions such as glucose, sucrose and
the like, corn syrups of various viscosities, mineral oils of
various viscosities such as white mineral oil, vegetable oils such
as peanut oil, rape oil, castor oil and epoxidized corn oil, soya
oil and the like and other liquids and mixtures thereof falling
within the above viscosity range. The sugar and corn syrups and
polyglycols are particularly preferred because of the ease with
which they can be washed from the yarn product with water only. The
viscosity of the viscous liquid can be controlled by varying the
dilution varying the temperature or by blending different liquids
or different viscosities of the same liquid to obtain intermediate
viscosities.
The dispersion of the staple fibers in the viscous carrier liquid
may be accomplished in any convenient manner, such as by stirring,
kneading or other form of agitation or by blending an already
prepared master batch in a miscible liquid or the same liquid. With
the high modulus fibers employed it is generally sufficient to
simply stir the fibers which have been deposited on the surface or
in the carrier liquid for a short time at a few hundred r.p.m. to
substantially disperse the fibers in a relatively homogenous
manner. Likewise the same procedure can be employed with a low
modulus or textile type fiber. However, with some of the longer
fibers, particularly the longer low modulus fibers, the use of a
rotating stirrer whether round or in other form frequently results
in a balling up of the longer fibers between the stirrer and the
walls of the vessel containing the dispersion. When this happens
such balls of fiber have to be removed from the dispersion and
additional fiber added to make up the desired concentration. A
convenient method for dispersing fragile fibers and such longer
fibers is to deposit groups of the fibers on the surface of the
viscous liquid and thereafter knead them by repeated vertical
working of a stirring rod or cylinder so that these fibers
gradually disperse downward into the viscous liquid. This avoids
any balling up effect from rotational dispersion. If desired,
dispersing aids such as wetting agents or other form of dispersant
may be added to the fibers or the liquids to assist in obtaining
relatively homogenous dispersions thereof.
With reference to the drawing an apparatus for carrying out the
process is schematically illustrated in FIG. 1 thereof. Basically
such apparatus consists of a pressure vessel or tank 1 for
receiving the dispersion 2 of fibers in the viscous carrier liquid
and which is fitted with an exit conduit or tube 3. This tube may
conveniently be adapted with a flared or funnel shaped lower end to
assist in entraining the dispersed fibers with the carrier liquid.
It will likewise be supplied with a source of gas pressure 4 and a
gauge 5 to determine the pressure applied. The exit conduit or tube
3 which is desirably fitted with a valve 6 to control flow
therethrough, is not necessarily a straight conduit as shown but
may take any position except that the latter portion thereof where
it joins a rotating conduit tube 8 should be straight. The rotating
tube 8 mounted in flexible sleeves and mounts is supplied with a
pulley 9 adapted to be driven by a motor 11 with a pulley 12
through a belt, cable, chain or V-belt drive and the speed of the
motor controlled by controller 13. The rotating conduit or tube is
thus adapted for rotation at speeds varying from 100 to 4,000 to
5,000 r.p.m. Yarn 10 formed therein is taken up on a reel 14 which
is preferably perforated and desirably traverses a snubber roll 15
prior to its final take-up.
The details of the rotating tube assembly are shown in FIG. 2 of
the drawing. Reference is made to FIG. 2 showing the end portion of
the fixed tube 7 and the entirety of the rotating tube 8 and the
manner of their mounting and sealing. Fixed tube 7 is pressed
through flexible sleeves 20 and 20' preferably of Teflon or other
sealing materials and the seals 20 and 20' in turn mounted in
mounts 21 and 21'. The mounts are in turn fixed to a frame 34 which
serves to fix same. The rotating tube 8 is likewise carried in
seals 23 and 23' of Teflon or other sealing material which in turn
are mounted in bearings 24 and 24' carried by mounts 25 and 25'. At
approximately the middle of the rotating tube 8 seal 23" is carried
within a pulley 9 adapted for rotation of the tube. In order that a
good seal against the fixed tube is maintained the abutting end of
the rotating tube 8 is supplied with a rotating seal 28 of Teflon
or even more elastic sealing material and a spring 27 which rests
on metallic plate 26 carried by the mount 25. A reciprocal plate 22
carried by mount 21' serves to fix and stabilize the Teflon seal
20' of the fixed tube so that constant spring biasing pressure is
maintained at the abutted sealed junction 16 of the fixed tube 7
with the rotating tube 8. At the opposite or free end of the
rotating tube 8 there is placed an oil seal 29 within mount 30
serving to prevent the effluent carrier liquid from running back
down the rotating tube. The mount 30 serves to separate from the
top bearing mount 25' the effluent pot 31 fitted about the exit end
of the rotating tube 8. This pot 31 is supplied with an exit
conduit 32 to a receptacle, not shown, for the separated carrier
fluid. In order to prevent the yarn 10 exiting from the rotating
tube 8 from catching and wrapping about the end of the tube, the
exit end of the rotating tube is supplied with a stationary cap 33
with an exit aperture just smaller or equal to the internal
diameter of the rotating tube 8.
The apparatus described above was employed in all of the examples
of the process and to produce the yarn of the invention. Other
equivalent apparatus of somewhat different design could likewise be
employed in the present process. This form of the apparatus was
illustrated as vertically arranged which was done to minimize the
gravitational effects on the spinning process and the viscous
liquid employed. However this is not essential in carrying out the
process and any other arrangement of the relative parts of the
apparatus could likewise be employed including horizontal
disposition.
The process of the present invention will hereinafter be described
with reference to the apparatus described above for convenience but
it is understood that some variations would be adopted when other
similar apparatus of different arrangement were employed. The
process is carried out by means of charging the pressure vessel 1
with a dispersion 2 of both high modulus and low modulus fibers in
the highly viscous carrier liquid. The spinning is initiated by
pressuring the pressure vessel 1 by means of gas pressure inlet 4
to establish a flowing stream of the liquid dispersion 2 through
the fixed tube 3 and, upon opening of valve 6, through the rotating
tube 8. The rotating tube 8 is rotated by means of motor 11 and
associated controller 13 through pulleys 12 and 9 at a speed
correlated with the flow induced by pressuring the vessel 1.
Generally spinning has been successful at speeds of from 800 to
3,000 to 4,000 r.p.m. Higher rotational speeds are desirable and
can be effected in equipment designed to sustain such rotational
forces.
The dispersion 2 of high and low modulus fibers in viscous carrier
liquid is caused to flow through the fixed tube 3 and by
establishing such flow both types of fibers are axially aligned
across the flowing stream of viscous fluid. It is essential that
laminar flow in the stream be maintained so that areas of
turbulence will not be developed since these will adversely affect
the axial alignment of the fibers within the dispersion. Contrary
to the teachings in some of the prior art processes, in the viscous
fluids employed and the distances traversed through tube 3 there is
little or no progression of fibers to the axis of the flowing
stream and fibers aligned with the axis are found at all radii of
the stream.
Near the interface 16 with the rotating tube 8 a vortex in the
flowing stream of viscous fluid is formed and the hydrodynamic
forces induced thereby cause the condensation of the entrained
fibers into a yarn. This yarn 10 near the vortex is comprised of
axially aligned high modulus fibers distributed across the diameter
of the yarn and intertwined loosely by the low modulus fibers of
the dispersion. The helix angle and amount of twist of the low
modulus fibers increases during progression through the remaining
portion of the rotating tube 8. There is no sharp demarcation
between the two types of fibers due to their more or less general
occurrence throughout the dispersion 2 and the yarns 10 consist of
an intermingling of high modulus and low modulus fibers. However,
due to their greater stiffness the high modulus fibers tend to
maintain their axial alignment while the low modulus fibers are
more readily twisted about them. Some high modulus fibers occur at
the periphery of the yarn bundle, but when their lengths are longer
than the internal diameter of the fixed tube 7 they are generally
in axial alignment and demonstrate relatively low angles of
incidence with the axis of the yarn 10.
In spinning the viscous carrier liquid in most part separates from
the yarn as it exits from the end of the rotating tube and such
fluid is trapped by the effluent pot 31 and directed by conduit 32
to a receptacle, not shown. The stationary cap 33 with its opening
no larger than the internal diameter of the rotating tube 8
prevents the raw yarn catching thereon and wrapping about the end
of the rotating tube. Additional small amounts of the viscous fluid
will be thrown or drained off the yarn during its passage about the
snubbing roll 15 and its take-up on the take-up reel 14. This
take-up reel 14 is desirably a perforated reel, generally metal,
which is adapted for draining away entrained viscous fluid and for
subsequent thorough washing of the yarn taken up for removal of the
final amounts of entrained fluid. The speed of the take-up reel is
generally controlled to match that of production and exit of the
yarn produced by the rotating tube assembly so as not to apply
unusual forces to the yarn during its formation. The flow rate from
the receptacle 1 is likewise adapted to maintain this yarn velocity
constant.
In the apparatus described above the conduit or tube 3 from the
receptacle 1 to the valve 6 comprised a 3/8 -inch tube. The valve
was fitted with a reducer to one-fourth inch size so as to receive
the 6-mm. tube fitted thereto. The internal diameter of the fixed
tube 7 and of the rotating tube 8 were 4 mm. and the relative
lengths thereof were 4 inches of fixed tube 7 and 6 inches of
rotating tube 8. These sizes however are not limitations on the
apparatus in general but were used for convenience in the apparatus
assembled. Larger and somewhat smaller tubes can be successfully
employed in the apparatus described above with suitable adaptations
in the sizes of seals and motor drives
The yarns of this invention produced by the process described above
demonstrate a high degree of alignment of the high modulus fibers
with an intertwining of the low modulus fibers about the high
modulus fibers. These high modulus fibers are at varying radii
within the yarn although aligned axially therein. Such yarns are
produced from crimped or uncrimped textile length low modulus
fibers and straight, stiff high modulus fibers including whisker
fibers. In all of the yarns produced the degree of alignment is
such that the yarns are very suited for use as reinforcing members
for composite matrices both directly in the case of some of the low
modulus fibers employed and after charring and burn-out of the low
modulus fibers in other cases. Not only do the yarns afford a much
easier physical form for producing lay-ups and preforms for
subsequent infusion with matrix materials, but they also afford a
higher degree of alignment of the reinforcing high modulus fibers
than is obtainable by other textile, mechanical or production
means. Thus such yarns meet a real need in the art of producing
fiber reinforced composites in a more efficacious manner and at
reduced cost.
The present invention will be more fully comprehended from the
examples which follow.
EXAMPLE 1
A slurry or dispersion of fibers in corn syrup was prepared from 8
grams of glass fiber 0.57 mil diameter and chopped to a staple
length of one-half inch which had been fired at 600.degree. C. for
23 minutes to remove the size added to 1,400 ml. of a corn syrup
with a viscosity of approximately 130 poise at room temperature.
These fibers were dispersed by rotating a 2 -inch diameter Teflon
cylinder at 300 r.p.m. for 20 minutes. The dispersion was
essentially complete and quite homogenous. Thereafter the
dispersion of glass fibers in corn syrup was heated to 60.degree.
C. in a heating mantle and the low modulus fibers dispersed
therein. The low modulus fibers were bicomponent acrylic fibers of
0.7 mil average diameter cut to three-fourths inch staple length.
They were dispersed by gradually placing groups of fibers on the
surface of the heated corn syrup and stroking them into the syrup
by a vertical motion with a glass rod. When addition was completed
a brief stirring with the 2 -inch diameter Teflon cylinder evenly
dispersed the low modulus fibers without causing balling. The
dispersion of both types of fibers appeared to be homogenous. The
dispersion was cooled to room temperature for spinning.
The dispersion prepared as above was spun into yarn employing the
apparatus described herein, which consisted of a 3/8 -inch exit
conduit from the slurry receptacle, a 4 -inch fixed section of
6-mm. tube and a 6 -inch rotating section of 6-mm. tube, both tubes
having an internal diameter of approximately 4 mm. Spinning of yarn
through the apparatus was initiated by pressuring the vessel
containing the dispersion to 20 p.s.i. and opening the valve. The
take-up reel was driven at a rate of 0.66 inch per second and the
rotating tube driven at a rotation of 2,000 r.p.m. When flow of the
corn syrup dispersion appeared at the effluent cup, probing of the
cup with a stirring rod picked up the yarn and it was lead over the
snubbing roll and to the take-up reel. Continuous spinning was
established and a 7-foot sample of yarn was spun. Qualitative
inspection of the yarn under a microscope revealed excellent axial
alignment of the glass fibers throughout the yarn with the low
modulus fibers intertwined thereabout at a low helix angle. The
yarn produced was suitable for use in molding reinforced
composites. A 1/4.times.4.times.0.06-inch sample of a curable
epoxide resin and curing agent containing such yarn as
reinforcement has good flexural strength and modulus in the
direction of lay of the yarn demonstrating effective reinforcement
by the yarn.
EXAMPLE 2
In this example an additional composite yarn employing silicon
carbide "whisker" fibers was prepared employing the same apparatus
as described hereinbefore. In the same manner as detailed in
Example 1 above 0.7 gram of dark green "long" silicon carbide
whiskers which had been harvested from a random ball of such
whiskers and of average length of approximately one-half inch were
placed in tufts in a 1,000 ml. of corn syrup of viscosity of
approximately 130 poise. Rotation of the 2 -inch Teflon cylinder at
about 350 r.p.m. easily dispersed the whiskers. Thereafter 7 grams
of the bicomponent acrylic fibers employed in Example 1 were
dispersed by the vertical kneading procedure there described while
the corn syrup dispersion was heated to 60.degree. C. Thereafter
the dispersion was cooled to room temperature and spun.
The yarn was spun in the same apparatus described above. Flow was
initiated by pressuring the vessel containing the dispersion of
fibers at 17 p.s.i., driving the rotating tube at 1,800 r.p.m. and
driving the take-up reel at 0.66 inch per second. A yarn was
produced upon initiation of flow and continuous yarn production
ensued for a total take-up of 80 feet of composite yarn. Upon
microscopic examination of the yarn it was found that all the
whisker fibers longer than the internal diameter of the fixed and
rotating tubes, approximately 4 mm., were aligned axially in the
yarn and intertwined with the low modulus acrylic fibers which were
at a low helix angle. Some breakage of the long carbide whisker
fibers occurred and those short fibers shorter than the internal
diameter of the rotating tube were found to be dispersed at random
angles throughout the yarn. The yarn was quite suitable for use in
preparing molding lay-ups and in reinforcing molded composite
samples.
This example demonstrates the efficacy of the present process for
the production of yarns of carbide and other whisker type fibers in
a form which facilitates their alignment and use in producing
directionally reinforced composites.
EXAMPLE 3
This example illustrates the utility of cellulosic fibers as low
modulus fibers in the present process. Rayon fibers of 0.36 mil
diameter cut to three-fourths inch staple length are employed to
form a yarn with the same 1/2-inch glass staple fibers of Example
1. The dispersion of 4 grams of the glass fibers and 7 grams of
rayon fibers in 1,400 ml. of corn syrup of 100 poise viscosity is
prepared as in Example 1. When spun through the apparatus described
above with fixed and rotating tubes of 6 mm. internal diameter at a
pressure of 20 p.s.i. on the dispersion, the rotating tube driven
at 1,650 r.p.m. and the yarn take-up reel driven at a speed of 0.8
in./sec. a yarn with no breaks is secured with continuous spinning
until the dispersion is exhausted. A uniform yarn is produced with
the glass fibers axially aligned and intertwined by the rayon
fibers.
It will be understood that the foregoing details of apparatus and
process of the invention are given by way of example only and that
modifications can be made to suit the requirements of various
fibers and viscous fluids without departing from the scope of the
invention as defined by the claims.
* * * * *