Rieter

Piecing speed and piecing quality

Index

Piecing systems that perform the piecing process at high rotor speeds, i.e. at 80% to 100% of the normal spinning speed, ensure by virtue of the high spinning tension during yarn take-off that only strong piecings withstand the piecing process (Fig. 57). Piecing-up rotor speed during piecing is dictated by the raw material and yarn structure. The lower the piecing-up speed and thus the spinning tension, the greater the risk that weak piecings will also survive the piecing process and thus reach the package. A piecing that has only just survived the piecing process can prove very costly in downstream processing. The „integrated“ strength test imposed by high piecing-up speeds is therefore of advantage, since no monitoring system yet exists at the spinning position to examine piecing strength. However, quality control systems on a capacitive or optical basis do provide specific monitoring channels for examining piecing mass. If a piecing exceeds the (adjustable) limits for fiber mass or fiber thickness, the spinning process is immediately interrupted again. The robot draws the length of yarn with the excessively thick piecing off the package and extracts it. The piecing process is then repeated.

If high piecing-up speeds are the criterion for strong piecings, piecing at constant speeds is the precondition for high piecing uniformity in terms of thickness and length (Fig. 58). This is in contrast to systems on which the piecing process is performed while the rotor accelerates (Fig. 59). Since the rotor shaft is driven by friction via the tangential belt, it is impossible to avoid variations in speed between spinning positions, i.e. between piecing processes, due to variations in slippage between the tangential belt and the shaft, especially during acceleration of the rotor. These variations inevitably have a direct impact on mass and length, in the worst case also on piecing strength.

Fig. 60 shows the results of a series of measurements in which the tenacity and elongation of automated piecings are presented in comparison with the corresponding yarn values, expressed in percentages. With the exception of individual measurements, the fluctuation range of the piecings is almost the same as the values for the normal yarn. What is more, even the piecings with the lowest tenacity are well above the minimum piecing tenacity level of 60% required for downstream processing (compared to the average yarn tenacity).

Fig. 57 – Influence of piecing speed on spinning tension and thus on piecing tenacity

Fig. 58 – Automatic piecing at constant, high rotor speed

Fig. 59 – Automatic piecing during rotor acceleration

Fig. 60 – Tenacity and elongation of piecings compared to the corresponding yarn values