Rieter

General

Index

After an end down or package change the interrupted spinning process at the spinning position in question has to be re-started. In terms of spinning technology this entails overlapping a thread end that has been fed back with the fiber ring in the rotor groove. The quality of such a piecing is just as important as the quality of the yarn itself, since both determine its market value to a great extent. The quality of a piecing is defined essentially by:

  • the tenacity of the piecing expressed as a percentage of yarn tenacity;
  • the variation in tenacity between the piecings (CV% of piecing tenacity);
  • the thickness of the piecing (diameter or mass);
  • the length of the piecing;
  • the repeat accuracy of the piecing.

Every piecing with too much mass is regarded as disturbing in the final fabric and results in its devaluation; the longer the thick place, the more disturbing its appearance. Piecings that are too thick often display especially low tenacity as a result of having too little twist. This in turn causes problems in downstream processing. A high-quality yarn can suffer a drastic reduction in value due to defective piecings.

Piecings with high tenacity and virtually yarn-like appearance can only be produced by processor-controlled robotic systems, since the timing of the individual functional steps has to occur in the millisecond range. The piecings produced by means of controlled fiber feed and synchronized thread take-off are virtually invisible, both in the yarn and in the end product. The improvement in piecing quality when using processor-controlled operating robots instead of mechanically/electrically controlled robots is clearly apparent in Fig. 54. Repeat accuracy is provided by precise control of rotor speed and fiber flow. Piecing systems operating at high rotor speeds ensure that only piecings with high tenacity withstand the high spinning tension refer to section  Piecing speed and piecing quality.

The piecing process after ends down or quality stops (refer to section  Automatic piecing after ends down and quality stops) and the piecing process after package change (refer to section  Automatic piecing after package change) differ in principle in certain functional steps.

Fig. 54 – Piecing quality (Ne 30, Twist multiplier αe = 4.6, 100% Cotton); a) piecing quality with processor-controlled robotic systems; b) piecing quality with mechanically controlled operating robots