Recycling process waste
As a consequence of the spinning, weaving and knitting of the cotton and short-staple fibre being carded, combed or open-end spun, working of regenerated fibre has sprung up where regenerated fibre is intended as knitting waste, sub-products derived from the spinning cycle (flying fibres), the waste, the scraps from weaving (cut selvedges and so on). Since the 1980′s, this type of fibre has been recycled thanks to the conventional carded spinning system: they were in fact worked in sets of two or three cards and then spun on conventional ring spinning frames). With the diffusion of open-end spinning frames, these fibres are now worked with the new technology that in just a few years has completely replaced conventional carded spinning.
The work stages of the cotton scraps have therefore become:
- unravelling of the hardest materials (knitted scraps, cut selvedges, flying fibres)
- beating of waste
- blending with virgin materials
- carding with a system dedicated to cotton fibres with the need to parallelise and open the fibres that are much shorter and opened to a much lesser degree with the lowest amount of waste possible.
- doubling and drawing (cotton drawframe). Essential for obtaining finer counts, this is inevitable in the case of coarser counts through the application of an autoleveller on the card and direct passage to the spinning frame.
The cards for regenerated cotton and for very dirty cotton must open and clean what cannot be opened in the preparation stage and must lead to the lowest percentage possible of waste, this type of fibre being extremely difficult to recycle a second time. As can be seen from the diagram attached (Figure 1), these cards are equipped with a preopening unit made up of a pre-carding cylinder (diameter 700 mm) with a series of fixed flats with ordinary clothing. It is the task of this cylinder to pre-card the fibres.
These cards have a main cylinder with a diameter wider than that of a conventional cotton card (1500 mm) which permits the application of a double set of flats (64 flats on drum entry side and 70 on delivery side) which permits a high carding action and improves the cleanliness of material on exit. The drum speed varies from 300 to 450 rpm, while the flats vary from 100 to 400 mm a minute. The speed of both the drum as well as the flats are variable to make developing the carding in function of the type of the materials used easier, bearing in mind that the fibres in this sector are very inhomogeneous. Machine aspiration is only employed to evacuate the dust that is generated during operation.
A single waste knife for coarse material is applied on entry to the licker-in cylinder. Flats fixed on the drum both on the entry as well as delivery make parallelisation of the fibres distributed on the drum easier and as a consequence permit them to be cleaned and opened. Once the material is carded, it is condensed on the combing machine and it is conveyed by two transversal belts (indispensable for this type of working) that transport the web coming out of the web doffer in a funnel.
For carding operations immediately preceding the open-end spinning stage, on each card a sliver autoleveller is applied which, acting on the delivery speed of the sliver, and eventually on the material entry speed, means the variations in count on the sliver can be reduced. In working materials involving passage through the drawframe (not possible with very short fibres or ones that are difficult to draw in a uniform manner) the evenness of the sliver fed to the spinning frame comes from both doubling the slivers from different cards as well as the autoleveller of the drawframe itself. The passage through one drawframe (when possible) also permits the doubling of slivers from different cards and guarantees on the final sliver a perfect homogeneity not possible in the case of a direct passage.
On the basis of these considerations, open-end spinning of regenerated fibre permits a yarn to be obtained that reaches a maximum count of Ne 5 in the case of direct spinning after carding and yarns up to a count of Ne 20 in the case of passage through the drawframe. When working with very dirty cottons and cotton waste, the card (having the structure that has been indicated) is equipped with additional aspiration points (under the licker-in cylinder and the main drum) so that it can
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