METHODE DE METROLOGIE DU RETRECISSEMENT ET DU CREPAGE DES FILES

METHOD FOR MEASURING YARN SHRINKAGE AND CRIMP DEVELOPMENT

Abrégé anglais

TITLE
METHOD FOR MEASURING YARN
SHRINKAGE AND CRIMP DEVELOPMENT
ABSTRACT OF THE DISCLOSURE
A method for measuring continuously shrinkage
and crimp development in a long continuous sample of
yarn involves the steps providing a zero-tension loop,
applying a standard tension, then developing crimp in a
single downward pass through a hot air chamber providing
a second zero-tension loop and thereafter retensioning
it. The shrinkage and crimp development is calculated
from differential speeds of rolls advancing the yarn.
C-2083A

Revendications

The embodiments of the invention in which an
exclusive property or privilege is claimed are defined as
follows:
In a method for measuring continuously
shrinkage and crimp development in yarns which develop
crimp upon heating under low tension and wherein the yarn
is advanced by driven rolls from a yarn source to a first
tension zone, through a heating zone to a second tension
zone and then through an elongation zone, whereby shrink-
age and crimp development are determined in a measuring
system from ratios of driven roll speeds; the improvement
comprising: advancing said yarn downwardly in a free-
hanging loop as it passes from said source to said first
tension zone while maintaining zero tension in the yarn
of said loop by noncontacting means sensing the length
of the free-hanging loop and in turn controlling the
speed of the driven rolls near the yarn source whereby
tension differences in the yarn due to removing the yarn
from the source are isolated from the measuring system,
passing the yarn downward through said heating zone into
a second free-hanging loop while maintaining zero tension
in the yarn in said second loop by a second noncontacting
means sensing the length of the second free-hanging loop
and in turn controlling the speed of driven rolls in the
second tension zone whereby the yarn is able to retract
completely prior to entering the elongation zone, and
cooling the yarn while passing upward to the second
tension zone.

Description

li44647
TITLE
METHOD FOR MEASURING YARN
SHRINKAGE AND CRIMP DEVELOPMENT
TECHNICAL FIELD
This invention concerns a method for measuring
continuously shrinkage and crimp development of a run-
ning yarn sample.
BACKGROUND OF THE INYENTION
Automatic-instruments for measuring certain
properties of yarns automatically on the run are known.
However, properties such as shrinkage and crimp develop-
ment in yarns which develop crimp upon heating at low
tension are qllite sensitive to the tension under which
such crimp is developed and measured. A considerable
amount of the shrinkage or crimp development in such
yarns becomes evident only at very low tensions, such as
are encountered in a pile carpet when the fabric is dyed
at elevated temperature where the pile yarn may be under
zero tension while being agitated in the dye bath. The
conventional method of forming skeins and measuring
their length before and after crimp development during
zero-tension tumbling allows for full retraction, but
this method is not continuous or automatic.
Automatic instruments used for measuring shrink-
age or crimp development in such yarns, such as described
by M. J. Denton in USP 3,72~,137 and by C. M. Langkammerer
in Chemiefasern _ , 41-49(1971) Jan., have kept the yarn
under controlled low tension during heating and measur-
ing of properties. In such cases the yarn is unable to
develop the same amount of shrinkage or crimp which the
yarn undergoes in normal fabric processing, and there-
fore the measurement does not reflect conditions of
actual use. Variations in yarn properties which may
cause undesirable appearance, such as configurational
dye streaks in fabrics, thus may not be detected when
DC-20~3A

1~4~647
such properties are measured with an instrument which
maintains substantial tension on the yarn. This is
particularly true of yarns which have a low degree of
shrinkage or crimp and which are desired for high-luster
5 fabrics.
The traditional way of beginning a measurement
is to place the yarn under a standard tension using one
of a variety of known tensioning devices, as described
for example in USP 3,726,137 to Denton and 3,762,220 to
10 Gusack. However, such tensioners are usually affected by
variations in tensio~ caused by varying drag on the yarn
as it comes off a package, tension being low when the
yarn is feedlng from the near end of the package and
higher as it feeds from the farther end. Yarn defects
1~ may cause tension plucks as yarn slides over them. Such
tension variations may be magnified by conventional ten-
sioning systems, or at least are not eliminated by them.
SUMMARY OF THE INYENTION
An improved method of measurement of yarn
20 shrinkage and crimp development has now been developed
to obtain reliable bulk and other useful yarn data which
permits use of long continuous sample length at increased
yarn speed with excellent precision. The method involves
the steps of advancing the yarn from a source through a
25 tension zone, a heating zone and an elongation zone in a
system that regulates the speed of the rolls advancing
~he yarn through the above-mentioned zones. Property
measurements are determined from the ratio of roll speeds
as will be detailed later. The improvement involves
30 maintaining the yarn in a zero-tension zone by means of
a free-hanging loop as it passes from the source to the
tension zone and passing the yarn downward through the
heating zone into another zero-tension zone by means of
a second free-hang~ng loop prior to entering the
35 elongation zone.

~144647
BRIEF DESCRIPTION OF THE DRAWING
The drawing is a schematic diagram of the
method of this in~ention.
DETAILED DESCRTPTION OF THE PREFERRED EMBODIMENT
Referring to the drawing, yarn 10 is taken
from package 12 by driven rolls 14 with associated nip
roll 15 to prevent slippage of the yarn. Yarn 10 then
passes downward in a free-hanging loop and up to driven
10 rolls 16 with associated nip roll 17. Rolls 16 are
driven at constant speed, and the length of the loop
between rolls 14 and 16 is controlled by a noncontacting
control system 18 such as photoelectric cells to sense
the position of the loop, which in turn controls the
15 speed of rolls 14 to maintain the length of the loop
between an upper and lower limit. The yarn then passes
over pulleys 20 and 21 having low friction bearings,
between which is positioned tensioner pully 19 hanging
on the loop of yarn and having weight 22 to provide a
20 standardized tension such as 0.1 grams per denier.
Different values of weight 22 are provided for different
deniers of yarn. An optlcal system (not shown) senses
the position of pulley 19 and controls the speed of
roll 23 to maintain pulley 19 at the desired position.
25 Yarn 10 then passes over free-running roll 24 and enters
heating chamber 26 supplied with hot air ~from a source
not illustrated) at accurately regulated temperature and
flow rate. As the yarn passes downward through heating
chamber 26, hot air flows outwardly through both yarn
30 entrance 25 and yarn exit 27 to prevent ambient air from
entering the chamber. The flow rate of the hot air is
adjusted to maintain a slight tension on the yarn within
chamber 26 due to fluid drag as the hot air exits. This
outward flow also removes the cold air which is entrained
35 with the yarn entering at entrance 25 and prevents

1144647
ambient air from entering upward at exit 27 through
convection. Yarn lQ leaving exit 27 proceeds downward
in a second free-hanging loop then upward to driven
rolls 28 which are controlled by a noncontacting device
5 30, for example photoelectric cells, to maintain the
loop length within an upper and lower limit. The yarn
cools to approximately ambient temperature during its
travel from exit 27 to rolls 28. Yarn 10 then passes
over free-running pulleys 32 and 34 between which is
10 positioned tensioner pulley 36 with weight 38, the
position of which is controlled by a system (not shown)
which senses the position of pulley 36 and controls the
speed of rolls 40. Yarn 10 then enters aspirator 42
which deposits it in a waste container such as 44.
The free-hanging loop between rolls 14 and 16
isolates the measuring system from tension differences
due to removing yarn from package 12. This also elimi-
nates any elasticity effects so that the tension applied
by tensioner pulley 19 and weight 22 will provide a more
20 accurate base for measuring subsequent behavior of the
yarn. The heating of the yarn in chamber 26 takes
place under only the weight of the yarn loop and the
slight drag produced by the outflowing hot air, but
this yarn is then able to retract completely while still
25 hot as it leaves exit 27 and approaches zero tension at
the bottom of the second free-hanging loop where even
the effect of its own weight is minimized.
The speeds of rolls 16, 23, 28 and 40 are
obtained by photoelectric devices which count the teeth
30 of a gear attached to each roll shaft. These pulses
are fed into a computer which calculates one or more
properties and displays the results on a panel and/or
prints the results through a teletype or similar devices
(not shown). Three typical measurements which may be
35 made are:

il4464'7
(1) ~ Bulk Crimp Elongation =
(speed of rolls 40)-(speed of rolls 28) x 100
~speed o ro s 28
(2) % Residual Crimp Elongation =
(speed of rolls 23)-(speed of rolls 16) x 10
~spee o ro s
(3) ~ Fiber Shrinkage =
(speed of rolls 23)-(speed of rolls 40) x 100
(speed of rolls 23)
For most purposes the measurement reported is
the average value for a preset length of sample. How-
ever, the computer may also be programmed to report
variations of a property within the given sample length.
The hot air within heating chamber 26 is pref-
15 erably dry because the addition of moisture in the form
of steam is more difficult to control accurately and may
cause condensation problems outside the chamber. The
flow rate of hot air through and out of heating chamber
26 should be no less than that required to maintain an
20 outward flow of hot air at both yarn entrance 25 and
yarn exit 27. Higher flows may be desirable for opening
large yarn bundles to thoroughly heat all filaments and
provide sufficient agitation for all filaments to develop
crimp. However, high flow rates also impose more tension
25 on the yarn during the heating process. Flow rates
should not exceed a value which reduces the measured
crimp elongation and shrinkage significantly.
The various zero-tension and high-tension
zones on the instrument both before and after bulking
30 can.acco~moda~e additional detecting devices to measure
luster, denier, denier uniformity, initial modulus and
so forth.
The improved instrument of the invention is
able to measure crimp and shrinkage parameters over the
35 full range of commercial interest including the low

1144647
values which are most difficult. The faster analysis
time means that more or longer samples may be measured
to give more accurate averages or alternately that
variations along the end of a yarn may be determined
5 quickly.
The measurement error of the present device
has been found to be only about 10 to 1 5D/D of the total
variance compared to 60-70DID measurement error for the
skein method.