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
