Silk yarn is classified in several ways based on the twist. A some of them are as follows:
In this the silk is produced by reeling together baves of several cocoons. It has no twist.
A silk yarn produced by twisting raw silk. The twist may be slight or exceed 3000 per meter.
To make a tram yarn, two or more raw silk threads are doubled and twisted slightly. Generally the twist is about 80 to 180 TPM ( Turns per meter)
This yarn is made by doubling several raw silk threads and twisting them to very high levels in the range of 2000 to 4000 TPM.
This silk yarn is formed by doubling two or more poil yarn and throwing them in a direction opposite to that of the individual yarn. The twist in the poil yarn will be about 700 TPM ‘Z’ and the doubled yarn will have about 950 TPM ‘S’.
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Steaming of Twisted Yarn
The twisted yarn has to be subjected to steaming in an autoclave. This process fixes the twist in the thread. Duration of steaming depends upon the depth of layers of threads in the bobbin and twist levels of the thread. Ten minutes is usually sufficient for organza while more highly twisted crepe require considerably more time of about 2 hours.