In order to make air-jet spinning possible, 2 quite difficult tasks have to be solved in the zone between the drafting system and entering the spindle.
- separation of free fiber ends
- prevention of false twist formation
The fiber feed channel and the spindle are surrounded by a housing (Fig. 36). The air vortex near the spindle entry generates a certain vacuum, which results in an air flow through this channel. This air flow transports the fibers from the drafting unit to the spindle entry.
For generating free fiber ends, the correct choice of distance L (Fig. 35) is very important. This distance should be slightly shorter than the average length of the fibers being processed. This enables the transport air in the fiber feed channel to separate fiber ends from the main fiber flow. It is evident that the longer the distance L, the more free fiber ends become available. L is therefore an important process parameter. It is of course possible that during this process of fiber end separation, entire – mainly shorter – fibers are extracted from the main fiber flow. These fibers have no chance of being integrated in the yarn. They bypass the spindle and are lost. In air-jet spinning, the fiber loss (relatively short fibers) is therefore relatively high (5 to 10%). The higher the short fiber content in the sliver, the higher the ratio of fiber waste.
By the action of the vortex, the fiber ends eventually whirl around the spindle tip and are thus twisted around the twistless yarn core and transformed into a twisted yarn surface or cover fibers. This occurs at the spindle tip. The twist of these surface fibers generates a certain torque in the yarn being formed. This torque has the tendency to twist the fiber bundle between drafting unit and spindle. Twist of this kind must be avoided in order not to interfere with the generation of the necessary free fiber ends. This can be solved by means of a twist stop. For this purpose Murata uses a needle (Fig. 35), which detours the fiber bundle before entering the spindle, thereby acting as an efficient twist stop.
Once inside the spindle tip, the yarn formation process is finished, and the yarn can be taken off and wound onto a package.