इस द रियरिंग आफ सिल्कवर्म फॉर द प्रोडक्शन ऑफ सिल्क
Answers
Answer:Silk fibres possess outstanding natural properties which rival the most advanced synthetic polymers. However, unlike synthetic polymers, the production of silk does not require harsh processing conditions (Mondal et al., 2007). One of the first operations in silk production is the reeling process (Sonthisombat and Speakman, 2004). Reeling is a vital link in converting the agricultural produce, cocoons, into an industrial output, yarn. Silk reeling consists of a number of activities: cocoon sorting, stifling, cooking, reeling, re-reeling and twisting. Silk reeling basically involves unwinding silk filaments from the cocoons and then reeling the ‘baves’ (silk fibres complete with their natural gum, sericin), followed by a process in which a number of cocoon baves are reeled together to produce a single thread on a fast moving reel (Das, 1992). Reeling forms a vital link in converting the agricultural produce, i.e. cocoons, into the industrial output of yarn. Raw silk reeling may be classified as:
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direct reeling on a standard sized reel;
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indirect reeling on small reels, and the transfer of reeled silk from small reels onto standard; and
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sized reels on a re-reeling machine.
The last technique is the most commonly used in modern silk reeling processes (Mahadevappa et al., 2001).
2.2.1 Cocoon sorting
This is a process of separating defective cocoons from good cocoons. The process also includes segregating cocoons according to their size. Defective cocoons may be classified as:
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double cocoons;
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pierced cocoons;
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urinated cocoons;
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flimsy cocoons;
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double cocoons;
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pointed or constricted cocoons;
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mould attacked cocoons and
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immature cocoons.
The process of sorting according to size is carried out by equipment known as riddling machines. The segregation of uniformly sized cocoons is of great importance as their size influences the cooking and reeling properties.
2.2.2 Cocoon stifling
The main purpose of stifling is to kill the pupa inside the cocoon to avoid its emergence as a moth, thereby preserving the continuity of the filament. This operation also dries the cocoons so they can be stored for a long period. The following methods are generally used in cocoon stifling:
(a)
Sun drying: The pupa is killed by prolonged exposure (2–3 days depending upon the intensity of sunlight) of freshly harvested cocoons to hot sun. The disadvantage of this process is that continuous exposure to sun hardens the cocoon shell, so affecting the reelability.
(b)
Steam stifling: The pupa is killed by exposing fresh cocoons to the action of steam for around 25 min. The process can be done by either basket steaming or chamber steaming.
(c)
Hot-air drying: This is the most effective method and produces good-quality cocoons such as bivoltine varieties. It facilitates the complete drying of cocoons and ease of storage.
Other methods of killing the pupa include the use of infra-red rays, cold air and poisonous gases.
2.2.3 Cocoon cooking
The object of cocoon cooking is to soften the sericin so that the cocoon shell is loosened, enabling the filament to unwind smoothly during reeling. Different methods of cooking may be used, such as open pan cooking, three-pan cooking, pressurized cooking and conveyor cooking.