Hot Air Drier
Cocoons that are to be stored for long periods prior to reeling need to be dried to the optimum levels in order to achieve better quality of raw silk. This method achieves the major objective of hardening of the sericin uniformly in all layers of the cocoon shell, besides killing of the pupa and removal of the moisture. Further, optimal drying prevents fungus attack. These objectives cannot be achieved by the traditional steam stifling. Hot air drying can be achieved by employing a batch type hot air drier or a Ushnakoti.
CSTRI cocoon sorting table
Defective cocoons can be sorted out effectively using a cocoon-sorting table developed by CSTRI, which is of low cost and affordable. The rectangular shape sorting table consists of a hopper for feeding the cocoons on to the semi translucent glass top below which fluorescent tube lights are fixed. Defective cocoons are sorted out manually and good cocoons collected separately.
Use of pressing disc for open pan cooking:
In order to improve the cooking efficiency of the cocoons in open pan method of cooking, a small gadget namely the pressing disc has been developed by CSTRI and recommended. The methodology followed is:
- Put the cocoons in the open pan-cooking vessel at 85-90 °C and press them slightly using the pressing disc so that the cocoons are immersed in the water for about 60 seconds.
- Then press the cocoon to the bottom of cooking vessel and the cocoons are treated at 93-96 °C for about 60 to 120 seconds.
- Again the cocoons are brought back to the top surface of the open pan and cold water is sprinkled to reduce the temperature from 93 to 96 °C to 85-90 °C in about 60 seconds. Then the cocoons are brushed and taken for reeling.
CSTRI multifuel economic oven
CSTRI model multifuel economic oven is recommended for the reelers who do not have boilers for cooking purpose.
CSTRI Three pan cooking equipment
In order to cook the hot air dried bivoltine cocoons effectively three-pan cooking can be adopted. The procedure for three pan cooking (with water as media) is as follows.
- The cage with cocoons is immersed in first cooking pan at 50 -55 °C for about 45 – 60 seconds.
- The cage is transferred to second cooking pan, which is at 90 – 93°C for about 90 – 120 seconds.
- The cage is then dipped in third pan at 60 – 65 °C for about 45 – 60 seconds.
- The cage is then returned to the second pan at a boiling temperature of about 95-96 °C for 90 – 120 seconds.
- Steam supply is stopped and cold water is sprinkled on the cage for about 10 seconds.
- The cage is opened and the cocoons are transferred to the cooking pan. The floating cocoons are then pressed using perforated pressing plate for 30 seconds without steam and 30 – 45 seconds with steam.
- Steam supply to the pan is stopped and cold water is sprinkled gradually on the cocoons to reduce the temperature to 70 – 80 °C gradually.
- The cocoons are then brushed at 75 – 80 °C and transferred to reeling basin.
Circular pressurised cooking machine
For large scale reeling establishments it is advisable to adopt circular pressurised cooking technique for hot air dried bivoltine cocoons to achieve better productivity and quality raw silk. The methodology to be followed is as follows.
- The cooking vessel shall be filled with water up to half level mark.
- Dry cocoons are then filled up in the baskets.
- The water temperature is raised to 70 to 75 °C by passing steam.
- The cocoon baskets are immersed at 70 -75 °C for about 45 – 60 seconds.
- The baskets are raised above the water level and steamed by passing steam at 90 – 93°C for about 90 – 120 seconds.
- The baskets along with cocoons are immersed in water at 70 – 75 °C for about 60 – 90 seconds for low temperature permeation.
- After low permeation, the cocoons are raised above the water level and kept at about 80 °C. During the same period the water temperature will be raised to 97 °C.
- The cocoons are again steamed above water level at a boiling temperature of about 97 – 98 °C for 90 – 120 seconds to cook the cocoons.
- After cooking treatment the cocoons are immersed at 97 °C water and allowed to stand for 60 – 90 seconds.
- Then the steam valve will be closed and the lid will be opened.
- Cold water is sprinkled (Initially very gradually and later rapidly) to reduce the water temperature from 97 °C to 75 °C in about 4 – 6 minutes.
- The cocoons are taken from the baskets and stored at 40 °C water.
- The cooked cocoons are brushed at about 80 °C and transferred to reeling basin.
Cottage Basin Reeling Machine:
CSTRI has done following modification in the existing cottage basin:
- Modification of thread passage
- Introduction of Jetteboutte
- Replacing ordinary conventional rollers with Croissure pulleys
- Replacing wooden small reels with plastic reels.
- Replacing ordinary reeling button with improper hole size with ceramic button with appropriate hole size.
- Introducing side brushing mechanism and simple individual reel stop motion
CSTRI Multiend reeling machine
It is recommended to reel bivoltine cocoons on Multiend reeling machine in order to produce superior grade raw silk with following reeling parameters (6 & 7).
- Reel speed : 100 – 120 meters/min.,
- Croissure length : 8 cms for 20/22 denier.
- Reeling basin water temperature : 40 °C
- Good quality reeling button with appropriate hole size should be used.
CSTRI small reel vacuum permeation chamber
Wetting of raw silk on small reels before re-reeling is very essential for better re-reeling performance. This process softens the gum spots between the silk threads on the small reel and facilitates smooth unwinding. CSTRI has developed a small reel vacuum permeation chamber with capacity of 20 reels to achieve this objective. In the reel permeation chamber small reels are soaked in water with wetting agent using low pressure (vacuum up to 300 mm Hg to 400 mm Hg). Permeation is achieved by creating vacuum condition for 1-2 minutes and released. This cycle is repeated three times to achieve better reel permeation.
CSTRI closed type re-reeling machine
Silk reeled on the small reels are converted into standard size skeins in re-reeling machine. Re-reeling machine and its mechanical condition and re-reeling process parameters play a significant role on the production of quality silk, particularly winding performance of silk skeins.
CSTRI has standardized the specifications of closed type of re-reeling machine for production of quality silk. From the studies conducted at CSTRI following re-reeling process parameters are recommended.
Re-reeling speeds for different raw silk deniers as follows:
|Size||Speed of normal re-reeling machine|
|14 d||150 ± 10 rpm|
|21 d||160 ± 10 rpm|
|27 d||150 ± 10 rpm|
|42 d||130 ± 10 rpm|
Temperature and humidity to be maintained in the re-reeling section and re-reeling machine are as follows:
|In the re-reeling section||20 – 30°C||65 ± 5%|
|In the re-reeling machine||35 – 40°C||40 ± 5%|
Lacing of silk skeins
The silk skeins should be laced at six places using cotton thread in the form of figure “8” so that the coils of silk will be retained without entanglement.
In order to facilitate finding of ends of skeins during winding process it is essential to join and tie the top end and tail end together by extra lacing thread, which is inserted in the middle of the width of the skeins.
Cleaning of silk skeins
The re-reeled silk should be cleaned for gum spots and extraneous impurities gently by hand without damaging the silk threads. During lacing, cleaning, skeining and book making extra care should be taken to avoid end breakages in the skeins.
CSTRI Long skein book making machine
The laced silk in the form of hanks is made in to skeins. Care should be taken to avoid any break of silk threads during skeining. In order to avoid mishandling of raw silk and to keep the silk intact (without entanglements) it is recommended to practice long skeining and long skein book making. In order to popularise long skeining and long skein book making amongst reelers, CSTRI has developed a hand operated economical model long skeining and long skein book making equipment for Indian silk reeling units. In this method long skeins are made into 5 Kg. books.
Central Silk Technological Research Institute, Central Silk Board, Bangalore