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attached to the tension sensor and another end is fixed on the
eyelet. The yarn segment between the guide-eye and eyelet
forms a ballooning curve while the eyelet is rotating and this
segment is defined as the yarn-length in the balloon. The
yarn-length in the balloon increases while the arm, on which
the tension sensor is fixed, moves downward (Figure 2). When
the arm goes to the lower limit, the yarn-length between
guide-eye and eyelet reaches the “maximum” value. The
yarn-length in balloon decreases while the arm moves upward
until it reaches the upper limit. The arm speed is set at 200
mm/min. When the eyelet starts rotating, the yarn segment
between the guide-eye and rotating eyelet will form a
ballooning curve and generate tension in the ballooning
yarn. The tension signal at the guide-eye is digitised by the
computer data acquisition system.
Materials
We have used three different types of yarns with various
counts and hairiness for the experiments. Therefore, we can
examine the effects of yarn thickness and hairiness on the
yarn tension. Table 1 gives the details of the yarn characteristics.
For the hairiness results listed in Table 1, we tested the
yarns at a speed of 400 m/min for a minimum of 3.5 minutes
(or 1,400 m of yarn length) using the Uster Tester 4.
For yarn tension measurement, we ‘spun’ the yarns at
different ‘twisting’ speeds on the ballooning rig, with the
balloon height varying from 120 mm to 360 mm. We
measured the yarn rotating speed with a digital tachometer
during the tests, and used a digital camera with video
capability to capture the balloon shape.
Results and Discussion
Effects of Yarn-length in Balloon on Balloon Shape
Figure 3 shows the effect of yarn-length in balloon, for the
70.1 tex two-fold wool yarn, on the balloon shapes at a
balloon height of 300 mm and a rotating speed of 4200 rpm.
When the ratio of yarn-length in balloon to balloon-height
(Rl/h) is 1.03, 1.10, 1.20, 1.35 and 1.65, the balloon has 1, 2,
3, 4 and 5 loops respectively.
When the yarn-length in balloon is close to the “minimum”
value of (where h is the balloon height and a is the
ring radius), the balloon is almost in the axial plane (a plane
that contains ballooning yarn and passes the centre line of
the balloon rig), as shown in Figure 3(a). When the yarnlength
in balloon is increased, the axial plane will twist some
radians due to the air drag on the ballooning yarn and yarn
hairs. For ease of statement, we call the twist angle of the
ballooning yarn at the rotating eyelet relative to the guideeye
as the offset-angle [radian]. Figures 3(a)-(e) correspond
to an offset-angle of around 0.4π, 1.5π, 2.5π, 3.3π and 4.4π,
respectively. As the yarn-length in balloon is continuously
increased, the offset-angle increases further, and then the
yarn in the balloon will usually form knots and break at the
rotating speed under consideration.