U.S. patent application number 13/747679 was filed with the patent office on 2013-10-03 for method and apparatus for imparting false twist to yarn before ring spinning.
This patent application is currently assigned to THE HONG KONG POLYTECHNIC UNIVERSITY. The applicant listed for this patent is THE HONG KONG POLYTECHNIC UNIVERSITY. Invention is credited to Jie Feng, Heng Guo, Tao Hua, Yunhui Jia, Xiao Ming Tao, Bin Gang Xu.
Application Number | 20130255217 13/747679 |
Document ID | / |
Family ID | 49233011 |
Filed Date | 2013-10-03 |
United States Patent
Application |
20130255217 |
Kind Code |
A1 |
Tao; Xiao Ming ; et
al. |
October 3, 2013 |
METHOD AND APPARATUS FOR IMPARTING FALSE TWIST TO YARN BEFORE RING
SPINNING
Abstract
A method and apparatus for imparting false twist to a short
staple yarn delivered from a nip of a pair of front drafting
rollers before ring spinning. Downstream of the nip, the twisted
yarn is drawn sequentially across first and second runs of
travelling endless belts, such that the yarn wraps about a first
convex surface of the first run, then passes between the first and
second runs, before wrapping about a second convex surface of the
second run. Friction between each of the first and second convex
surfaces and the yarn imparts the false twist in a common
direction. Maintaining a differential between first and second
linear speeds of the first and second runs, respectively, has been
found to reduce yarn defects, particularly the nep count.
Inventors: |
Tao; Xiao Ming; (Hong Kong,
CN) ; Xu; Bin Gang; (Hong Kong, CN) ; Hua;
Tao; (Hong Kong, CN) ; Feng; Jie; (Hong Kong,
CN) ; Guo; Heng; (Hong Kong, CN) ; Jia;
Yunhui; (Hong Kong, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
THE HONG KONG POLYTECHNIC UNIVERSITY |
Hong Kong |
|
CN |
|
|
Assignee: |
THE HONG KONG POLYTECHNIC
UNIVERSITY
Hong Kong
CN
|
Family ID: |
49233011 |
Appl. No.: |
13/747679 |
Filed: |
January 23, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61616198 |
Mar 27, 2012 |
|
|
|
Current U.S.
Class: |
57/284 |
Current CPC
Class: |
D01H 1/02 20130101; D01H
7/926 20130101; D01H 7/92 20130101 |
Class at
Publication: |
57/284 |
International
Class: |
D01H 7/92 20060101
D01H007/92 |
Claims
1. A method of imparting a false twist to a short staple yarn
delivered from a nip of two front drafting rollers, before ring
spinning of the yarn, the method comprising: drawing the yarn
sequentially across first and second runs of travelling endless
belts, such that the yarn sequentially exits from the nip and wraps
about a first convex surface of the first run, then passes between
the first and second runs, and thereafter wraps about a second
convex surface of the second run, whereby friction between the yarn
and each of the first and second convex surfaces applies a
respective torque to the yarn, each torque tending to twist the
yarn in a common direction, and maintaining the first and second
runs at different respective first and second linear speeds.
2. The method of claim 1 wherein both the first and second runs are
substantially parallel to the two front drafting rollers, and the
yarn is drawn transversely across the first and second runs, and
further including maintaining a substantially constant difference
between the first and second linear speeds of the first and second
runs when the two front drafting rollers are rotated at a constant
speed.
3. The method of claim 1 wherein the first and second convex
surfaces have the same radius of curvature.
4. The method of claim 3 wherein the endless belts are circular in
cross-section.
5. The method of claim 1 wherein the difference between the first
and second linear weeds of the first and second runs is maintained
such that a ratio of the first linear speed to a peripheral speed
of the two front drafting rollers is between 0.4 and 0.8, and a
ratio of the second linear speed to the peripheral speed of the
front drafting rollers is between 0.9 and 1.6.
6. The method of claim 1, including ring spinning the yarn after
imparting the false twist to the yarn and, during the ring
spinning, applying a twist to the yarn in the common direction of
the respective torques applied by the first and second runs.
7. The method of claim 1 wherein the first run is disposed below
the two front drafting rollers and the second run is disposed below
the first run.
8. An apparatus for imparting a false twist to a fibre bundle
delivered from the nip of a pair of front drafting rollers before
ring spinning the fibre bundle, the apparatus comprising: first and
second endless belts with first and second convex surfaces,
respectively, each of the first and second endless belts having a
respective linear run, the linear runs being substantially parallel
to one another such that the linear runs may be aligned parallel to
the pair of front drafting rollers, and drive means for driving the
first and second endless belts at respective, different first and
second speeds.
9. The apparatus of claim 8 wherein the drive means comprises a
controller operatively connected for controlling speeds of first
and second variable speed motors connected for driving the first
and second endless belts, respectively.
10. A ring spinning frame comprising the apparatus of claim 8
disposed between a drafting system and a take-up assembly.
Description
TECHNICAL FIELD
[0001] The present invention relates to yarn manufacture by ring
spinning, and more particularly to a method and apparatus for
imparting false twist to a yarn delivered from a nip of a pair of
front drafting rollers immediately before imparting real twist by
ring spinning.
BACKGROUND OF THE INVENTION
[0002] The characteristics of ring spun yarn are unmatched by the
products of other yarn spinning techniques which may be more
productive, so it is a technology that is unlikely to be superseded
in the near term. Much research has gone into ring spinning
technology and relatively modest improvements to the productivity
of a ring spinning frame can be very significant in a spinning mill
where many thousands of spindles are employed. Many different raw
material and machine-related factors directly influence both
productivity and quality, and sometimes improvements in one area
have consequences that necessitate a trade-off in another area. The
goal of spinning technologists might therefore be considered a
quest for an optimum balance between higher productivity and
desired quality.
[0003] U.S. Pat. No. 3,979,894 describes a five-belt false twisting
device for texturing filament yarn which, with its continuous
lengths of filament, has quite different structure and properties
to short staple ring spun yarn, and of course, it is not a ring
spun yarn. Moreover, in this old false twisting device the filament
yarn sequentially passes across parallel runs of five travelling
endless belts, wrapping about convex surfaces of each run before
passing between adjacent runs. Three of the belts turn in one
direction, while two turn in an opposite direction, the filament
yarn passing through the runs in a zig-zag manner such that
friction between each of the five runs and the filament yarn
imparts the false twist in a common direction. The belts are
matched and all five belts travel at the same speed, to avoid twist
variation that would lead to poor quality of the textured filament
yarns and instability of the yarn path.
[0004] With respect to ring spinning technology, a more relevant
apparatus is described in US2010/0024376, which teaches a
single-belt method for imparting false twist to a yarn delivered
from the nip of a pair of front drafting rollers immediately before
ring spinning. The yarn received from the drafting rollers is drawn
generally transversely and sequentially across first and second
parallel runs of a single belt, passing about the first run, then
between the runs, before passing about the second run. Friction
between the first and second runs and the yarn imparts the false
twist. The two runs of the belt move in opposite directions, but
the linear speeds of the two runs are the same. Compared to
conventional ring spinning, at a given production rate this
single-belt false twist method produces yarns having lower residual
torque which endows a resultant fabric with a softer handle, and it
also provides satisfactory strength and reduced hairiness. The
single belt can extend the length of a machine, making it a more
cost-effective investment than alternative technologies involving
heat treatment to reduce residual torque. However, it has been
found that this single-belt technology results in an increase in
yarn defects above the usual level--including the number of thick
places, thin places and neps. A sharp increase in the number of
neps is of particular concern, since neps can be a cause of ends
down in downstream processing and they may not take up dye like the
rest of the yarn, detracting from the appearance of the fabric.
Achieving satisfactory nep counts therefore necessitates relatively
higher maintenance costs to mitigate machine factors, such as wear,
that are known to contribute to nep formation. It will therefore be
understood, that a need exists for an improved false twist method
and apparatus that is able to at least maintain the above-mentioned
advantageous properties while reducing nep formation in ring
spinning of short staple yarns. It is an object of the invention to
address this need or, more generally, to provide an improved method
of imparting false twist to yarn between drafting and ring spinning
processes.
DISCLOSURE OF THE INVENTION
[0005] According to one aspect of the present invention there is
provided a method of imparting false twist to a short staple yarn
delivered from a nip of a pair of front drafting rollers before
ring spinning, the method comprising drawing the yarn sequentially
across first and second runs of travelling endless belts, such that
the yarn exits from the nip and wraps about a first convex surface
of the first run, then passes between the first and second runs,
before wrapping about a second convex surface of the second run,
whereby friction between each of the first and second convex
surfaces and the yarn imparts the false twist in a common
direction, and maintaining a differential between first and second
linear speeds of the first and second runs respectively.
[0006] Experimental results have shown that, by maintaining the
first and second runs at different speeds, a substantial reduction
in the number of neps produced is achieved when compared to the
single-belt false twisting method. It is to be understood that the
direction of runs does not alter the differential between their
linear speeds (hence the reference to speed--a scalar quantity),
and while the respective directions of movement of the runs are
preferably 180.degree. apart, both runs can of course be aligned at
other angles to one another so that both impart false twist to the
yarn in a common direction. Also, while the differential, or
non-zero difference in speeds, is preferably constant, it may be
varied dynamically.
[0007] Preferably both the first and second runs are substantially
parallel to the front drafting rollers and the yarn is drawn
transversely across the first and second runs, and the differential
is substantially constant when the front drafting rollers are
rotated at a constant speed.
[0008] Preferably the first and second convex surfaces have the
same radius of curvature, and most preferably the first and second
belts are circular in cross-section. The firsthand second convex
surfaces may subtend the same or different angles of wrap with the
yarn.
[0009] Preferably the differential is such that the ratio of the
first linear speed to a peripheral speed of the front drafting
rollers is between 0.4 and 0.8, and a ratio of the second linear
speed to the peripheral speed of the front drafting rollers is
between 0.9 and 1.6.
[0010] Preferably twist applied to the yarn during ring spinning is
in the same direction as the common direction of false twist.
[0011] Preferably the first run is disposed below the front
drafting rollers and the second run is disposed below the first
run. Preferably the first convex surface is aligned tangential to
both of the front drafting rollers.
[0012] In another aspect the invention comprises apparatus for
imparting false twist to a fibre bundle delivered from the nip of a
pair of front drafting rollers before ring spinning the fibre
bundle, the apparatus comprising first and second endless belts
with first and second convex surfaces respectively, each of the
first and second belts having a respective linear run, the linear
runs being substantially parallel to one another such that the
linear runs may be aligned parallel to the front drafting rollers,
and drive means for driving the first and second endless belts at
respective first and second different speeds.
[0013] Preferably the drive means comprises a controller
operatively connected for controlling the speed of first and second
variable speed motors connected for driving the first and second
endless belts respectively.
[0014] This invention provides a method and apparatus which is
effective and efficient in operational use, which reduces the nep
count, and which has an overall simple and modular design which
minimizes manufacturing costs and simplifies maintenance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Preferred forms of the present invention will now be
described by way of example with reference to the accompanying
drawings, wherein:
[0016] FIG. 1 is a schematic transverse section through a spinning
apparatus according to a first embodiment of the invention;
[0017] FIG. 2 is an enlarged schematic transverse section through
of the false twisting belt device like that of FIG. 1, but showing
an alternative geometry and wrap angles;
[0018] FIG. 3 is a schematic perspective view of the spinning
device of FIG. 1;
[0019] FIG. 4 is a schematic perspective view of a single-motor
variant of the spinning device of FIG. 1, and
[0020] FIG. 5 is a schematic transverse section through a spinning
apparatus according to a second embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] In machines 10a and 10b (shown in FIGS. 1 and 5
respectively) for spinning short staple fibres (those less than 2
inches or approximately 50 mm in length) the roving 11 (the
precursor to the yarn 13) is fed into a drafting system 12 where it
is drawn to its final count. The exemplary drafting system 12 is
shown at an angle of 45.degree. to the horizontal and may comprise
a six-roller, double-apron drafting system. After the resulting
thin ribbon of fibres leaves the delivery or front rollers 14,
false twist is applied by the upper and lower linear runs 15a, 16a
of two travelling endless belts 15, 16. The twist necessary for
imparting strength is provided, in a direction opposite the false
twist, by the take-up assembly 25 which also serves to draw the
yarn 13 across the upper and lower linear runs 15a, 16a. The
take-up assembly 25 is of conventional construction and includes
the bobbin 17 rotating at high speed on a spindle. In the process
each rotation of the traveller 18 on the spinning ring 19 produces
a twist in the yarn. The traveller 18 is pulled with the bobbin 17
via the yarn 13 attached to it.
[0022] The drafting system 12 may be of six-roller, double-apron
type illustrated, including three driven, bottom rollers 14a, 20a,
21a with top rollers 14b, 20b, 21b positioned above them, supported
and pressed against bottom rollers 14a, 20a, 21a. The main drafting
zone is provided with a guide unit consisting of rotating bottom
and top aprons 22a, 22b. The back roller 21a has a prescribed
rotational speed, and pinches the roving 11. The drawing speed of
the roving 11 is determined by the peripheral speed of back roller
21a. In a similar manner, the apron roller 20a draws out roving 11.
By adopting a drawing speed for apron roller 20a larger than the
drawing speed of back roller 21a, the fibres of the roving 11 slide
against each other and are formed into a fibre bundle finer than
the roving 11, being made, for example, 1.5 to 2 times longer. In a
similar manner, front roller 14a also draws out the fibre bundle
fed from apron roller 20a. Its drawing speed is set to be greater
than the drawing speed of apron roller 20a. For example, by setting
the drawing speed to be twenty times faster than that of apron
roller 20a, drafting will form a fibre bundle that is 20 times
longer than the original.
[0023] In the first embodiment of FIG. 1, the fibre bundle exits
from the nip 27 between the front rollers 14a, 14b and extends to
the point to which the twist is propagated from the belts 15, 16
(forming the so-called spinning triangle). Then yarn 13 passes
through the fixed pigtail or yarn guide 23 then wraps about a first
convex surface of the upper run 15a, then passes between the upper
and lower runs, before wrapping about a second convex surface of
the lower run 16a. The belts 15, 16 may be alike, having a circular
cross section of the same diameter, such that the convex surfaces
have the same radius of curvature. As shown in FIG. 2, the first
convex surface is subtended at the central axis of the upper run
15a by an angle of wrap 28a. The second convex surface is subtended
at the central axis of the lower run 16a by an angle of wrap 28b.
The angles of wrap 28a, 28b may vary between the upper and lower
runs 15a, 16a and for the geometry shown, where the upper and lower
runs 15a, 16a contact opposing sides of the tarn 13 and move in
opposite directions, the angles of wrap 28a, 28b may be
approximately 80-110.degree.. The yarn 13 may extend at the same
angle to the horizontal as the drafting system 12, passing between
the front rollers 14a, 14b and the upper run 15a, tangentially to
both the front rollers 14a, 14b and the convex surface of the upper
run 15a. The yarn 13 may pass generally in a line from the lower
run 16a to a fixed pigtail or yarn guide 30, before passing to the
take-up assembly 25. The yarn is then reverse twisted as a result
of the true twist propagated from the traveller 18, forming the
final yarn.
[0024] FIG. 3 shows the upper and lower runs 15a, 16a extending
linearly and parallel to one another between respective pairs of
pulleys 31/31, 32/32 mounted to rotate about upright axes at
opposite ends of the runs. The belts 15, 16 may be driven by
variable speed rotary motors driving the pulleys 31, 32, such as AC
motors 33, 34 with respective inverter-type speed controls 35, 36,
or DC servomotors or stepper motors (not shown). This allows the
belts 15, 16 to be driven at different speeds so as to maintain the
differential between the linear speeds of the upper and lower runs
15a, 16a. The upper and lower runs 15a, 16a preferably extend for
the full length of the machine (i.e. up to around 50 m in large
machines) so additional support pulleys or rollers 39 and guides 40
may be provided at intermediate positions to support the weight of
the belts 15, 16 and ensure their proper alignment.
[0025] As illustrated in FIG. 4, in a variation of the first
embodiment of FIGS. 1-3, instead of two different motors, a single
rotary motor 133 is provided for driving both belts 15, 16 via a
wheel 43 having a small diameter portion 43 about which the lower
belt 16 is wrapped, and a large diameter portion 44 about which the
upper belt 15 is wrapped. The motor 133 and wheel 43 may be
provided, along with other transmission, electrical and electronic
components in one of the end stocks 44 and the belts 15, 16 may
extend parallel to one another generally about the periphery of an
elongate frame member 45. In this manner the ratio of the diameters
of the portions 43, 44 defines the differential between the linear
speeds of the upper and lower runs 15a, 16a. The idler pulleys 31a
either side of the wheel 43 provide a direction change, so that the
upper and lower runs 15a, 16a move in opposite directions. By
moving on opposite directions, and engaging opposing sides of the
yarn, both the upper and lower linear runs 15a, 16a cooperate to
impart the false twist in a common direction.
[0026] As shown in FIG. 5, in the second embodiment the upper and
lower linear runs 15a, 16a may alternatively engage on the same
side of the yarn 13, in which case they are driven in the same
direction to impart the false twist in a common direction. As in
the first embodiment, the belts 15, 16 may be alike, having a
circular cross section of the same diameter, such that the convex
surfaces have the same radius of curvature. Alternatively, the
belts may have convex surfaces having different radius of curvature
which are in contact with the yarn. The first convex surface is
subtended at the central axis of the upper run 15a by an angle of
wrap (of approximately 5.degree.) which is smaller than the angle
of wrap subtended by the second convex surface at the central axis
of the lower run 16a (which may be of approximately 20). The yarn
13 may be deflected from the angle of 45.degree. to the horizontal
of the drafting system 12, having a larger angle of wrap about
front roller 14b than about front roller 14a.
[0027] Experimental results shown in the tables below demonstrate
that, compared to the single-belt method for imparting false twist
(as described in US2010/0024376) by maintaining the differential
such that the ratio of the first linear speed of the upper run 15a
to a peripheral speed of the front drafting rollers is 0.5, and the
ratio of the second linear speed of the lower run 16a to the
peripheral speed of the front drafting rollers is 1.0 a reduction
in neps to a level comparable to that of conventional ring spun
yarn (without the false twisting stage between drafting and
take-up) is achieved, while breaking strength is increased with
lower twist, hairiness (s3) is reduced and evenness is
substantially unaffected.
[0028] In each one of four sets of tests performed, a cotton yarn
of different yarn count was spun and the properties of the yarn
resulting from three different spinning methods were measured. The
results for each of the four sets of tests are presented in the
Tables 1-4 below.
[0029] Method/Apparatus 1--Conventional
[0030] The yarns were spun firstly on a conventional ring spinning
frame without false twisting.
[0031] Method/Apparatus 2--Single-Belt
[0032] In the second test the same conventional spinning frame was
modified to include a single-belt false twisting device as
described in US2010/0024376 between the drafting system 12 and
take-up assembly 25. A circular cross-section belt of 4 mm diameter
and made from polyurethane was maintained at a speed of 50% of the
peripheral speed of the front rollers 14a, 14b.
[0033] Method/Apparatus 3--Invention
[0034] In the third test the same spinning frame was modified to
include the two-belt differential speed arrangement described and
illustrated above with respect to the first embodiment of FIGS.
1-3. Two like circular cross-section belts of 4 mm diameter and
made from polyurethane were employed. The ratio of the first linear
speed of the upper run 15a to a peripheral speed of the front
drafting rollers was maintained at 0.5, and the ratio of the second
linear speed of the lower run 16a to the peripheral speed of the
front drafting rollers was maintained at 1.0.
TABLE-US-00001 TABLE 1 40 s yarn count and spindle speed of 16000
rev/minute. +200% Twist Breaking Method/ Evenness Neps (turns/
Strength S3 Apparatus CVm(%) (/1000 m) inch) (cN) (/10 m) 1 -
Conventional 12.79 33 25.5 291.5 151 2 - Single-belt 12.58 86 23
285.8 69 3 - Invention 12.76 39 23 286.2 65
TABLE-US-00002 TABLE 2 50 s yarn count and spindle speed of 16000
rev/minute +200% Twist Breaking Method/ Evenness Neps (turns/
Strength S3 Apparatus CVm(%) (/1000 m) inch) (cN) (/10 m) 1 -
Conventional 12.14 35 25 325.6 147 2 - Single-belt 12.34 107 21
305.1 118 3 - Invention 12.23 38 21 310.2 83
TABLE-US-00003 TABLE 3 80 s yarn count and spindle speed of 15000
rev/minute. +200% Twist Breaking Method/ Evenness Neps (turns/
Strength S3 Apparatus CVm(%) (/1000 m) inch) (cN) (/10 m) 1 -
Conventional 14.55 80 32.3 184 164 2 - Single-belt 15.17 452 27.4
176.2 102 3 - Invention 15.01 85 27.4 180.5 88
TABLE-US-00004 TABLE 4 100 s yarn count and spindle speed of 15000
rev/minute. +200% Twist Breaking Method/ Evenness Neps (turns/
Strength S3 Apparatus CVm(%) (/1000 m) inch) (cN) (/10 m) 1 -
Conventional 15.14 135 39 142.1 157 2 - Single-belt 15.91 676 33
135.8 99 3 - Invention 15.57 142 33 138.4 89
[0035] The optimum differential in speeds between the upper and
lower runs may vary depending upon the yarn being processed.
Further experimentation suggests that a worthwhile improvement,
compared to yarn produced by the single-belt method, can be
achieved by maintaining the differential such that the ratio of the
first linear speed to a peripheral speed of the front drafting
rollers is between 0.4 and 0.8, and a ratio of the second linear
speed to the peripheral speed of the front drafting rollers is
between 0.9 and 1.6.
[0036] While the significant reduction in the nep count achieved by
the invention was unexpected and the precise mechanism by which it
is achieved remains unclear, it is believed, without wishing to be
limited by theory, that the advantage of driving the upper run 15a
relatively slower than the lower run 16a may be two-fold. One
factor is the reduction the twist propagated toward the nip 27 that
may reduce the chance of wrapping by protruding fibre ends because
relative movement of the surface fibres and core fibres are
smaller. The second factor is the ability to reduce untwisting
after the upper run 15a, so as to reduce the possibilities for
loose fibres rubbing off the yarn surface. The combination of these
factors is believed to contribute to the significant reduction of
neps.
[0037] The frictional forces at the interface between the belts 15,
16 and the yarn 13 achieve the false twisting action, so the
factors influencing these frictional forces may be varied to allow
satisfactory false twist to be imparted to yarns of different
materials and yarn counts. The primary factors influencing friction
are yarn tension and belt material and surface finish. By
supporting the upper and lower runs 15a, 16a in pulleys which can
be axially displaced along upright axles, the spacing between the
runs, and between the upper run 15a and drafting rollers 14a, 14b,
can be readily adjusted, to vary the angle of wrap and therefore
the yarn tension. A coefficient of friction between the belts 15,
16 and the yarn 13 of between 0.5 and 0.8 is satisfactory, and this
may be readily achieved with commercially available reinforced or
unreinforced belts made of polyurethane, polyethylene, synthetic
rubber and polyester, or the like.
[0038] Compared to yarns produced by conventional ring spinning
without false twisting, the method of the invention allows yarns to
be spun with similar levels of defects, particularly neps, but with
higher tenacity, lower hairiness and a lower twist level. High
quality fabrics with a soft handle and smooth surface can be
produced from these yarns. Other advantages of the invention are
that the two belts 15, 16 can be economically installed and
maintained in a long machine. The provision of separately mounted
and tensioned belts makes the apparatus less susceptible belt
tension variations adversely affecting both runs simultaneously. A
reduction in ends down frequency in downstream processing can be
expected, owing to the reduced nep count.
[0039] Aspects of the present invention have been described by way
of example only and it should be appreciated that modifications and
additions may be made thereto without departing from the scope
thereof.
* * * * *