Rieter

The dimensions of the spinning triangle (width and length)

Index

(see also: W. Klein, Spinning Geometry and its Significance, International Textile Bulletin, Zurich, 1993)

The dimensions of the triangle and their influence on spinning are derived hereafter by some statements in an uncomplicated scheme, starting with the width of the triangle.
With a given outlet width of W, length (L) of the spinning triangle determines in turn the spinning width (WS), which – unfortunately – is always smaller than W. Due to the difference between W and WS, the edge fibers leaving the drafting system are not caught by the spinning triangle and therefore not incorporated into the yarn. These fibers are lost by forming fly and fluff or they are attached to the outside of the yarn already formed in an uncontrolled manner, thus increasing hairiness. The greater the difference between W and WS, the higher the loss of fibers, the greater the hairiness, and also the adverse impact on yarn structure. Width WS should therefore be as close as possible to W. On the other hand, the length of the spinning triangle depends mainly on the twist according to the following correlation: since twist always rises to a state where tie-in angle η at tie-in point E and fiber disposition angle κ in the yarn are equal, high yarn twist results in a short (L1), but low yarn twist in a longer spinning triangle (L2). This means that the greater length (L2) increases the size of the “spinning triangle” weak point and thus the ends down rate. To keep the ends down rate at the same level as for high-twist yarns, the yarn manufacturer is forced to reduce yarn tension by lowering spindle speed (e.g. when spinning knitting yarns).

Not only yarn twist but also machine design affects the length of the spinning triangle through wrapping angle λ (Fig. 85) of the fiber strand at the front roller. The wider this angle, the longer the spinning triangle with all its advantages and disadvantages. However, two additional advantages of the deflection at the front roller are worth mentioning; firstly the extra guidance of the fibers by supporting the fibers without clamping them, and secondly the reduction of the abrupt bending-off of the edge fibers. Being supported over a small surface area at the front roller up to lift-off line H, the fibers are gathered-in curving from the edge and tied in firmly and regularly. Fiber loss is also reduced (Fig. 86).

Of course, when discussing the advantages of a longer spinning triangle it is always assumed that most of the fibers in the fiber strand are longer than the spinning triangle. This is mostly the case, as the length of the spinning triangle varies according to the machine design (inclination of the drafting system α, height IG between lappet F and front roller etc.) of different manufacturers in a range between 2.5 and 7 mm only (Fig. 82).

Fig. 84 – Spinning triangle – influence of the twist

Fig. 85 – Reflection arc at the front roller

Fig. 86 – Spinning triangle delivery angle of the fibers