In the insertion of yarns by air-jet, the yarn acceleration in the jet nozzle is one of the important factors. The present investigation is planned to discuss the yarn tension mechanism in nozzles as follows.
1) Air flow rate and its velocity in nozzles are measured experimentally.
2) The drag force acting on different kinds of yarns according to yarn structure and count is measured.
The yarn tension obtained is compared with the theoretical value based on the Reynolds number.
The results obtained were as follows.
1) An increase of the bore size of the induction nozzle provided in the jet nozzleincreases the air flow induced by driving flow. The maximum bore size was 3mm.
2) The induced flow rate reached a limited value despite of increasing the drivingpressure.
3) The applied tension on the yarn in a jet reached a limited value despite of increasing the length of the acceleration pipe. The tension had a maximum at 100 mm in length.
4) The yarn tension calculated from equations based on the isentropic flow of compressible fluid and the air drag in the nozzle were similar to those obtained experimentally.

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A lockstitch sewing machine for industrial use has been fitted with a rotary angular meter and a rotary encoder to determine feed length and feed velocity of the needle thread during sewing operation at the range from 250 to 4000 rpm. The needle thread was winded around a V-pulley, having 31 mm in diameter. The V-pulley was mounted between the angular meter axis and the encoder axis on the arm of the machine.
The sewing has been made by employing the spun thred of # 50 and continuous filament thread of # 50 under the constant tension required to pull out the thread through a shuttle spring and constant stroke of the check spring.
Records of feed length curves and feed velocity curves during the stitch cycle have been analysed and the results are summarised as follows :
1) The range of turning angle of the arm shaft required for feed of the needle thread increases with increasing the sewing speed. Thus, when the speeds are lower than ca. 1500 rpm for the use of continuous filament threads and ca. 2000 rpm for the use of spun threads, the needle thread is fed intermittently. When the speed are higher than the above speeds, feed motion of the threads is transformed continuously.
2) θ_v.maxhas been defined as the turning angle of the arm shaft at which the feed velocity of the needle thread had reached its maximum value.In most cases the value of θ_v.max increases with increasing the sewing speed.
3) The maximum feed velocity ΔV_maxof spun threads, at θ_v.max, are greater than those of continuous filament threads; The values of all threads are independent on sewing speeds, except 4000 rpm. Feed velocity at 4000 rpm reache : approximately constant value during the stitch cycle, and its value is larger than feed velocity below 3000 rpm.
4) Value of Δ V_max, at fabric feed scale of 4 is greater than that of scale of 2 in all threads.

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The effect of stitch length (lu) on the dimensional properties (Uc = Cu × lu, Uw = Wu × lu, Us= Cu × Wu×lu²Uc/Uw = Cu/Wu, and t/l, where lu is the total length in the SKC, Cu is courss/uint fabric length, Wu is wales /unit width the SKC is the smallest repeating unit of the structure, t is the fabric thickness, and l is the loop length), the porosity P (%), the air permeability V (cc/cm²/sec), the thermal retaining propertyH (%), the bending length L (mm), and the tensile breaking strength S (kgf) and elongation E (%) of the 1 X 1 rib fabric knitted from a cotton yarn (c30s/l) is investigated experimentally.
The results obtained are as follows :
(1) Us is approximately constant, but Uc, Uw, and Uc/Uw are dependent on 1/lu or the fabric tightness K (=n√T/lu, where n is the number of loops in the SKC and T is the yarn linear density in tex).
(2) t/l and the weight per unit area of fabric increase with the increase of 1/lu or K.
(3) The increase of lu increases P and V, but decreases H.
(4) L in each direction (the course (0°), bias (45°), and wale (90°) directions) decreases with the increase of lu. For all lu, L increases with the increase of the angle to the course direction.
(5) S in each direction (the course, 22.5°, 45°, 67.5°, and wale directions) decreases with the increase of lu. The strenght efficiency of fabric is about 40% in both the course and wale directions.
(6) The increase of lu increases E in the course, 22.5°, and 45° directions, but decreases E in the 67.5° and wale directions. For all lu, E decreases with the increase of the angle to the course direction.

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