Source:
1. Preliminary Remarks
This mode of operation is already very old and has hardlybeen 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 consequentlythe values of the most important yarn parameters.
2. The Drafting Process on the Ring Spinning Machine
2.1 The Break-Draft
The basic correlation for each individual staple lengthbetween the setting of the break-draft zone and of the break-draft of a ringframe drafting system is shown in Fig. 2.
A long break-draft zone with the smallest possible break-draftmust definitely be preferred. It reduces very clearly the wear of top rollercots and aprons and the load on the draft gearing, especially in the case oflong machines.
In addition, the total system is less prone to climaticmodifications, variations in fibre length and fluctuation in the draftingresistance of the roving.
2.2 The Main Draft
Both fields of friction are finally responsible for fibreguidance and the extent of regularity produced by the drafting process. The two fields of friction should not overlap, nor should their spheres of activity betoo far apart.
It is beneficial to the draft and degree of regularityachievable, if within a drafting zone the field of friction of the back rollerpair reaches as far as possible into the drafting zone to guide the fibres aslong as possible. The front field of friction should be short and strong sothat only the clamped fibres are drawn out of the fibre strand. This ideal ishowever restricted by relatively close limits in design as a result of thegeometrical conditions.
The high degree of parallelism of the fibres achieved by the preceding steps of drawing, doubling and imparting of twist on the roving frame has in turn the effect that the inter-fibre friction at the cradle clamping line is still high. The drafting force therefore rises considerably at first. It reaches its maximum when the first fibres start to move and static friction turns into kinetic friction. This process takes place in the main draft zone between the two aprons. As soon as all fibres are moving, the drafting force is decreasing again considerably. This condition is reached in the front area of both aprons up to the clamping line of the front roller pair. Inter-fibre friction is very low in this area (Fig. 4).
Fibres are therefore dispersing as a result of the drafting process. Such a thin formation of dispersed fibres can absorb only insufficient pressure from the front roller pair and is therefore unable to produce a sufficiently large field of friction.
The sector in which the inter-fibre friction of the fibre strand is at its minimum, has a length of at least 15 or 20 mm in current drafting system designs (Fig. 5).
This explains why this sector cannot contribute any more considerably to open undrafted bundles of fibres and to guide shorter fibres safely. As a rule, this disadvantage cannot be compensated by even closest cradle spacers and very soft top roller cots.
3. The ACP Quality Package
With an additional point of friction arranged in the sensitive sector of the main drafting zone, the aforesaid disadvantages can be eliminated. When the fibre strand, after leaving the double apron guidance, is deflected, the friction field produced by the front roller nipping line is increased and shifted in direction of the cradle opening (Fig. 6). Fibre orientation and extension are improved. Parallel fibres still adhering to each other (fibre packages) can now be shifted relatively to each other even in this sector. Consequently, drafting defects are reduced, and the overall regularity of the drafting process is improved. At the same time, the tendency of the fibre strand to spread is suppressed. Inter-fibre contact is increased, and finally this results in a better utilization of fibre substance and better yarn strength.
By shifting the front field of friction towards the cradle opening, the apron nip can be closer. For this reason, the correct cradle design is important for the interplay with the point of friction. Numerous trials have confirmed again and again that a cradle with flexible leading edge is of advantage in the combination with the bottom apron nose bars offered today, most of which have a steplike design. Such a cradle compensates the practically unavoidable length tolerance of aprons and permits closest apron nips without the dreaded stick-slip movements of the aprons. A vast amount of trials was required to define the correct position of the friction point in relation to the flexible leading edge of the cradle and to translate this solution into technical design (diameter, coefficient of friction of the surface). It had to be ensured in particular that for all yarn counts both fields of friction (Fig. 6) can be shifted as closely as possible towards each other without direct contact.
The result of the optimum combination of both - Active Cradle (AC) with flexible leading edge and an optimally arranged pin (P) - is the new ACP Quality Package by SUESSEN for ring spinning drafting systems.
As shown in Fig. 6, a fibre friction pin is arranged immediately at the cradle spacer of the Active Cradle.
The ACP Quality Package is presently available with the size of cradle spacers from 2 to 3 mm (in steps of 0.25 mm), and is principally suitable for yarns of combed cotton Ne 30 and finer. Assured industrial results for coarse yarns are not yet available.
ACP Solution types can be provided for Top Weighting Arms
- HP-A 310/320
- HP-GX 3010
- PK type
- P3.1 type
4. Spinning Results
The ACP Quality Package clearly improves the drafting process. The sector between the front cradle opening and the front roller nipping line, which has so far been critical, now contributes additionally to the drafting process in the main zone.
This substantially raises the quality level of almost all
yarn parameters which are influenced by the drafting process. No disadvantages
to the running properties of the ring spinning frame have been found. It has to
be pointed out, however that the correct cradle setting is of utmost
importance. The ACP Quality Package clearly reduces both frequent yarn defects
(IPI) and rare yarn faults (Classimat), so improvements can be registered in
all fault classes. Therefore the number of clearer cuts is substantially
reduced, maintaining the clearer settings.
The
optimized drafting process is further reflected by an improved mass irregularity
(Uster CV value) and results in an optimized utilization of fibre substance
(yarn strength). Improvements achievable in every individual case depend on
the raw material, staple length, roving twist and total draft.
Since the above-mentioned improvements are exclusively due to the improved drafting process, their influence on the quality of conventional ring-spun yarns, single EliTeYarns and EliTwistYarns is almost identical. Yarn hairiness is nearly unchanged by ACP.
Table 1 compares the spinning results of compact yarns from various spinning mills, once without and once with ACP.
5. Summary
On the traditional 3-roller double-apron drafting system of the cotton ring spinning frame, the drafting process in the main zone has not been optimal until now, because of the long distance between the two aprons and the front roller nipping line, which is caused by geometric constraints.
The ACP Quality Package by SUESSEN improves yarn quality very considerably due to enhanced inter-fibre friction in this sensible zone.
ACP Quality Package therefore becomes an indispensable spinning accessory in the drafting system of a modern ring spinning machine.
About the Author:
The author is the Head of Technics & Engineering RS, Suessen
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1 W. I. Budnikow, W. E. Sotikow and others: "Grundlagen des Spinnens", Vol. III, Fachbuchverlag Leipzig
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