Source: Indian Silk, Nov-2010

In India, eri silk is produced primarily by north-eastern states of Assam, Meghalaya, Nagaland etc. The filament from eri cocoon is discontinuous in length, and hence, can be used only for spinning.

Different techniques are available for manufacturing eri silk yarns like takuri (hand), CSTRI developed motorised-cum-pedal operated ring as well as flyer spinning machine, amber charka and mill spinning (Italian or Japanese technology). At present, in north-eastern states, takuri and CSTRI developed spinning techniques are quite popular. The Tamulpur Anchalik Gramdan Sangha (TAGS), Kumarikata, Bodoland Territorial Council (BTC), Assam (under KVIC) is producing eri silkyarn using amber charka technique. A study was conducted to assess the cost of production and quality level that can be achieved for manufacturing eri silk yarn by this process.

Manufacturing Of Eri Silk Yarn By Amber Charka Technique

Process sequence: Two methods are followed for eri spinning using amber charka after degumming and drying process i.e. without carding and with carding. The process sequence is provided in Flow chart.

These are manufactured and supplied by M/s. Khadi & Village Industries, Ahmedabad. Here, each set of one preparatory machine is sufficient for 6 nos. of amber charka. All machines are hand driven except carding which is motor operated. Roving machine used earlier in between tape draw frame and amber charka, was later withdrawn due to processing problems like undrafted output along with excessive end breaks.

Cost

The total cost of machineries is Rs.90,000/- exclusive of the cost of carding machine. TAGS is using Platts card (2 nos.) for production by the amber charka.

Comparison of processes: Higher production is obtained when carding machine is utilized. For 8 hours of working per day, the average output of amber charka (6 spindles) is 300 gm per machine in carding process, whereas in the other process, the production is 175 gm.

This is due to individual handling and better opening of eri fibre while using carding machine which helps in better drafting and reduced end breakage during spinning. After carding, the sliver is cut into 1" length by fibre cutter and processed through tape draw frame after hand opening. The sliver is then fed to amber charka for spinning. 1" length of the fibre helps in better drafting where 3 over 3 short staple drafting system (SKF-PK 225) is used. Similarly, in the process where carding is not used, the sliver-lap from fine fillet drum is cut into 1" staple and fed to tape draw frame before spinning on charka.


Two persons are engaged for degumming and 7 kg of eri cocoon can be degummed per day. Since, the carding machine is utilized partly in production process; the same manpower is utilized for hand opening to prepare the materials for feeding coarse fillet and tape draw frame. Degumming process: The degumming loss is estimated about 12%. Eri cocoon are wetted overnight in soap solution (1gpl) for about 12 hours before pressure cooking/boiling.


For one kg of eri cocoon used for the spinning process, degumming loss is 120g, waste generated in the spinning process is 50g and invisible losses are 30g. Hence, eri spun yarn realization is about 800g. Total cost of eri silk yarn for 800 g is Rs.688, the cost per kg of yarn works out to Rs.860. Wages: The minimum and maximum production of eri silk yarn is 2-3 kg per day. So the wages of artisans works out Rs.40 to 60 depending on the output.


Quality of Eri Silk Yarn


Usually eri spun silk yarns from 20 to 40 Nm are produced on the amber charka spinning process by double drawing in the tape draw frame through variation of feed. A 35 Nm eri silk yarn (single ply) was produced at TAGS for testing the amber charka spun yarn.

Observation


Although eri silk yarn from 20 to 40 Nm can be produced using amber charka technique, the following modifications are required in order to obtain better output and quality:


1. In preparatory process, eri silk fibre is cut into 1" length so that the same can be easily processed in amber charka using short staple drafting system (similar to cotton spinning). Due to drastic fibre length reduction, the spun silk yarn has low tensile strength and requires high twist which results in higher level of hairiness. Long staple worsted drafting system may be incorporated in amber charka along with modification in preparatory system, so that fibre length of the eri silk may be around 5". Using long staple drafting system in amber charka, the yarn quality can be improved to a great extent.


2. The amber charka has six spindles which is manually operated by a single person. Even in the event of single end break, the operator has to stop the machine to rejoin the same. So there is production loss for about 3 to 5 minutes in case of single end break. Also the human efficiency factor reduces during end of the day after long spinning operation. Either pedal operating (where electricity is not available) or motor driving system may be utilized in amber charka. This will help the operator to piece the yarn during end break without stopping the machine. Hence, production as well as the daily wages of artisans can be improved.


Conclusion


Eri spun yarn of count 20 to 40 Nm can be effectively produced by the amber charka process using a single carding machine along with two spinning assemblies. A single process sequence assembly with 6 amber charka spinning machines can produce up to 3 kg of eri spun yarn at Rs.860 per kg. The spun silk yarn has low tensile strength and higher level of hairiness. Modifications in these machines are essential for higher output and better quality of yarn, to be successively adopted for decentralized spun silk sectors.


About the Authors


The authors are with Regional Silk Technological Research Station, Khanapara, Guwahati except the last who is with CSTRI, Bangalore.