In order to make a generation mechanism of interlaced yarn clear, an air jet was blown at a second to polyurethane yarn 400tex/3f, which was fixed to chucks at both ends, in an enlarged interlacer, and motion of each filament was photographed with a high speed video camera. Then we discussed twists, which create entanglements, by using an example of braids and a generation mechanism of entanglement from an example of filament motion photographed. The generation mechanisms of twist and entanglement obtained are as follows: (1) Filaments open at the cross-section of yarn duct positioning at the center axis of air jet nozzle: an opening part of interlaced yarn is generated. A twist is formed when a filament winds around another filament with this opening of filaments. Twists of different type, which are formed one after another, generate tangling parts at both sides of the opening part. (2) A high speed air jet collides with the yarn duct wall opposite to the air jet nozzle and flows along the wall in the direction of the exit of air jet nozzle to form a twin vortex. It would be a typical pattern of twist generation that a filament with this twin vortex winds around another filament, which stays at a relatively low speed near the wall opposite to the exit of air jet nozzle.

For the purpose of obtaining a design guideline of interlacer producing a high number of tangles, the numbers of tangles of interlaced yarns produced by slit-type interlacers with various sizes were measured. Furthermore, on the basis of numerical simulation result of airflow pattern in interlacers producing either the high number of tangles or the low one, a size effect of interlacer on the number of tangles was considered. Results obtained are as follows. (1) Three interlacers with different combinations of slit height and nozzle distance produced the high number of tangles in this experiment. The three interlacers have nearly the same yarn passage area. (2) The airflow forms a twin vortex, which changes relative positions between filaments (or filament groups) and generates entanglements. The size of vortex generating the high number of tangles would depend on the yarn fineness. As the airflow velocity of vortex is greater, the higher number of tangles would be produced. (3) An interlacer with a large characteristic force corresponding to opening and tangling force produced the interlaced yarn with high number of tangles in this analysis.

With the aim to clarify a generation mechanism of interlaced yarn, the yarn motion in a slit-type interlacer was analyzed by high-speed video images. Results obtained are as follows: (1) The running yarn in a closed state receives air jets and turns into a dispersion state where filaments separate from each other. With progress in time, the filaments reach the slit height and vicinity of the two air jet nozzles. Then, twin vortex from the two air jet nozzles produces relative motions of the dispersed filaments and/or filament groups at the yarn cross-section in the direction of the yarn axis, resulting in the twisting state of filaments. An opening part is composed of the dispersed filaments in this state and tangling parts are composed of entanglements accumulated at both ends of the opening part. The iteration of these three states (closed, dispersion and twisting) produces interlaced yarn. (2) It took the shortest time and yarn length to form the dispersion state, whereas the twisting state took the longest, and hence, opening parts are longer than tangling parts. (3) The yarn in a closed state showed circular motion along the air vortex at the yarn passage crosssection located at the two air jet nozzles. (4) The positions, where the dispersion state begins, were made clear.