The reeling of silk consists in the simultaneous unwinding of several cocoons, so that a single yarn can be obtained from the sum of several strands glued together. It is thanks to this process that the tenacity of the final yarn is good enough to be used.
In fact, the filament of a single cocoon is too thin and therefore it doesn’t have any practical application.
As the average counts size of the single thread is about 2,5/3,0 den and the thinnest raw silk quality counts produced is 9/11 den, at least 3/4 cocoons need to be reeled in one shot. For higher counts size, a proportionally higher number of cocoons are reeled.
Cocoons deflossing consists in removing the surrounding down of the external layers from each cocoon. This is done before the selection with special machinery.
This is an extremely important operation because it consists in dividing the dried cocoons in different categories, which are as homogeneous as possible in terms of quality. The selection is done by hand: the examined cocoons are placed on tables with low edges, around which employers sit. Thanks to the selection, it is also possible to get rid of those cocoons that are not suitable and therefore becomes leftovers: too small, stained, crushed, not-well-formed, double, calcined, mouldy, rusted, too soft, etc.
This operation comes before the brushing and it is used to soften the skin of the cocoon and to allow water to enter it. In this way, the unwinding of the single thread becomes possible.
Initially, dried cocoons are put into a steam boiler, in which vacuum is produced so that water can easily get inside. At this point, cocoons are full of water and are placed in particular baskets made of inox net where, dragged by a rack, go through the whole path diving the whole retting-pit. The difficulty of this passage mainly consists in being able to adjust and control the water temperature and the duration of the operation, in order to soften sericin both in the outer and inside layers of the cocoon’s bark. Of course, it is very important to always consider the specific peculiarities of the cocoons’ lot we are dealing with.
The brushing is necessary for the research of the thread head and it is performed into the “batteuse” machine.
The previously boiled cocoons are poured out into a tub full of water, which has a specific temperature set through steam. In a corner of the tub, rotating sorghum’s brushes are placed. The brushes perform a rotating movement into the water where cocoons are hovering. Thanks to this peculiar movement, cocoons head-ends are collected. Then, these are loaded into the basins that rotate around the reeling tubs by the brushing worker.
The brushed cocoons’ threads-ends are loaded into the basin and collected in carrier rods located at the edge of the basin, so that they are easily bound and ready to be reeled. At this point, the reeling worker takes a specific number of cocoons’ filaments, enough for the formation of a silk yarn of a given count size, then unites these threads and make them go through the hole of the spinning ring by the thread helical assembler. After the yarn has flown on the rollers for the formation of a light twisting, the silk is driven to the collecting spindle.
Once the filature has started, the bunch of cocoons needs to be fed continuously when they are exhausted or detach due to the break of the filament. In detail, the bunch of the cocoons is the group of cocoons that are being processed by the ring. This is controlled by a mechanical sensor that activate the lever that manages the continuous movement of the single threads from the tub to the spindle. When the yarn count is reducing, the reeling operator will favour the insertion of either a new or partially reeled cocoon. This depends on the composition of the bunch of cocoons. Usually this means that the reeling is done by mixed cocoons: some are new, some are partially reeled. The most common counts size for raw silk go from 13/15 denier, which is obtained with 2 new cocoons and 3 mixed ones, to 20/22 denier which is generally obtained with 4 new cocoons and 5 mixed ones.
The adjustment of the water temperature is a very important factor that has effects on the reeled yarn, because a too high temperature allows the water to have an excessive solvent action and, as a consequence, we obtain a hairy raw silk. On the other hand, a too low water temperature doesn’t allow to perfectly seal together the filament of each cocoon and, as a consequence, we obtain a silk with low cohesion.
The fake twist, “torta” or “tortiglia” in Italian, consists in a particular disposal of the raw silk thread. This is made by crossing the formatting silk yarn many times between two or more rollers, particularly in the lenght that goes from the yarn assembling to the reeling spindle.
The aims of the “torta” are many: first of all is necessary to remove most of the humidity from the yarn. The silk yarn, which goes out from the ceramic ring, is deeply soaked with water, a weight equal to the weight of the fiber. Thanks to the fake-twist, two third of this water is removed.
Moreover, the fake-twist has the power to seal the filaments steadily , so the cohesion of the yarn increases.
This feature is particularly important for raw silk yarns that are intended for special fine uses.
Finally, the fake-twist has a cleaning action on the yarn, so that many defects due to the filament and to the reeling process are removed. This occurs because, when defects are passing through, the fake-twist do break the yarn and the worker can remove the defective portion.
After the passage through the “torta”, the raw silk yarn itself is dried, sealed and cleaned.
For the last stage, after the yarn has passed through the fake-twist, it moves to the collecting spindle, where it wraps forming a bobbin, which will be later un-winded and packed in hanks.
The bobbins produced in the reeling machine are rehydrated in an autoclave before going to the final winding operation, so to smoothen the yarn and make it softer for further operations.
The bobbins are then positioned at the bottom, right above a container full of water and they are maintained humid through an occasional immersion in the water of the container.
The final winding in hanks occurs inside large, heated chests, at a temperature of about 40°, through steam piping, which usually power the whole productive process of the reeling mill.
The winding machine is composed of wheels with 6 wood arms, which are distant 60° from each other and are connected to the rotation axis through a spoke system. A couple of these rays can be shortened, so that the hanks can be removed easily when they had reached the desired weight.
Usually, the perimeter of the wheels is 150cm.
The hanks are removed from the wheels and placed in a specific room, called “Room of the silk”, where skeins are firstly examined in order to remove the most evident defects, then are tied, bent and packed.
The binding consists in leading a yarn through the hank and cross its ends 4 times, so that its length is divided in five equal parts. This is done so that the yarns of the hank are maintained correctly placed and therefore the subsequent unwinding will be easier. The bonds are 4/5 and can be white or coloured, to distinguish the counts size of the yarn. For the binding threads it is used a cotton or silk thread, as it is important that it can be broken barehand.
The tied hanks are bent either by hand or through a machinery called “tornello”.
Finally, they are packed through three stages. Firstly, they are packed in 5 kg packs, made of 24 – 28 hanks each. Then, they are placed in 30kg carton boxes or in 60kg bales made of heavy cotton canvas, which in turn will be packed in woven straw saddlebags.
The produced silk is usually divided in lot of 600KG each. Every single lot needs to be tested by a government agency, present in all the Chinese regions, which release the “Certificate for Raw Silk classification and conditioned weight”, recognized all over the world and fundamental for the export. For every single lot, the colour degree, the percentage of humidity (conventionally 11%) and the quality of the yarn are verified. For this reason, samples of small hanks, called baby skeins, are taken and used to be tested by the laboratories of the public agencies. At the end, the lots are classified basing on the obtained results. In particular, a score is given basing on a scale which can go until to 6A for the top qualities. Unfortunately, the Chinese classification method is not fully reliable, as a small quantity of silk is tested (few grams compared to the 600kg of the lot). In addition to this, the evaluation is made in a subjective way, the human eye, through the seriplane and black tables.
At last it is very important an accurate selection and reclassification of every lot. Through KEISOKKI CLASSIFAULT system a more accurate qualitative control can be made, and the requests made by the silk textile world, which are becoming more and more strict, can be satisfied. About this topic, please visit the production process of Torcitura di Dolzago.
Company specialized in the processing of silk yarns
Via Castello, 27/29
23843 Dolzago LC
TEL: (+39) 0341 451 320
FAX: (+39) 0341 451 404