Source: www.suessen.com

1. Preliminary Remarks

Today, the well-known 3-roller double-apron drafting systems of ring spinning frames permit to draft rovings up to a total draft of 80 and more under optimum conditions. The task of the break-draft zone is to introduce the sliding process of the fibres of the twisted roving. In the subsequent main draft zone, the fibre strand is guided between the top and the bottom aprons and drafted to the desired final count of the yarn.

This mode of operation is already very old and has hardly been modified in the last decades.

With the ACP Quality Package by SUESSEN it is now possible, however, to improve the drafting process in the main draft zone and consequently the values of the most important yarn parameters.

2. The Drafting Process on the Ring Spinning Machine

2.1 The Break-Draft

The purpose of the break-draft zone is to prepare the main draft. The fibres in the roving are stretched and extended up to a degree which allows them to shift in the main zone immediately after leaving the cradle clamping line.

The basic correlation for each individual staple length between the setting of the break-draft zone and of the break-draft of a ring frame drafting system is shown in Fig. 2.

A long break-draft zone with the smallest possible break-draft must definitely be preferred. It reduces very clearly the wear of top roller cots and aprons and the load on the draft gearing, especially in the case of long machines.

In addition, the total system is less prone to climatic modifications, variations in fibre length and fluctuation in the drafting resistance of the roving.

2.2 The Main Draft

As a basic principle, each of the two pairs of rollers in a drafting zone produces a zone of fibre friction by pressure¹. The fibre condensation caused by this pressure does not only have a vertical effect, but spreads from both sides into the fibre strand (Fig. 3).

Both fields of friction are finally responsible for fibre guidance and the extent of regularity produced by the drafting process. The two fields of friction should not overlap, nor should their spheres of activity be too far apart.

It is beneficial to the draft and degree of regularity achievable, if within a drafting zone the field of friction of the back roller pair reaches as far as possible into the drafting zone to guide the fibres as long as possible. The front field of friction should be short and strong so that only the clamped fibres are drawn out of the fibre strand. This ideal is however restricted by relatively close limits in design as a result of the geometrical conditions.