The pre-carding is nothing but carding of odd/white/poor quality viscose component before it is being used on the bulk production line with the objective of improvement in yarn quality further by reduction of neps in the card sliver and subsequently in the final yarns.
The spinning of fiber-dyed PV yarns is highly complex in nature. Every month, spinners spin 60-70 shades, and each shade has 4 to 5 colors of polyester and viscose in proportions. Some of these shades have a small proportion of dark-colored viscose while all other shades are light in color; while some other shades have light-colored viscose with all other shades being dark. This small proportion of viscose forms neps that have to be removed during mending. Certain shades have so many neps that it is not possible physically to remove them during mending; such fabrics have then to be over-dyed, putting mills to considerable loss, then the pre-carding of these small proportions of viscose to solve this tricky problem is a must. The below table shows a comparison of results of pre-carded shades with regular shades, and the imperfections are lower by even less than 50% in pre-carded shades compared to regular non-pre-carded shades.
The study is conducted in 33Ne 65/35 PV blended yarns.
Comparison of Results Before and After Pre-Carding
Making Heavy Lap in Blow Room:
The carding of viscose requires different parameters in carding and Blow Room. Every time while pre-carding, one has to change settings before the start of viscose, which requires extra time. The viscose requires a larger lap weight to avoid lapping on doffer, web fall in carding, piecing difficulty in card, slipping of lap, etc. With larger laps, there is a reduction in the number of laps and saving in doffing time and no breaking of webs in the card. Hence the 18 to 20% heavy laps for pre-carded viscose in the blow room will work better in carding.
The spinning of fiber-dyed PV yarns is highly complex in nature. Every month, spinners spin 60-70 shades, and each shade has 4 to 5 colors of polyester and viscose in proportions. Some of these shades have a small proportion of dark-colored viscose while all other shades are light in color; while some other shades have light-colored viscose with all other shades being dark. This small proportion of viscose forms neps that have to be removed during mending. Certain shades have so many neps that it is not possible physically to remove them during mending; such fabrics have then to be over-dyed, putting mills to considerable loss, then the pre-carding of these small proportions of viscose to solve this tricky problem is a must. The below table shows a comparison of results of pre-carded shades with regular shades, and the imperfections are lower by even less than 50% in pre-carded shades compared to regular non-pre-carded shades.
The study is conducted in 33Ne 65/35 PV blended yarns.
Comparison of Results Before and After Pre-Carding
|
Yarn Imperfections |
Without Pre-Carding |
With Pre-Carding |
|
Results |
Results | |
|
U% |
10.56% |
10.23% |
|
Thin Places |
7.37 |
1.83 |
|
Thick Places |
35.55 |
14.63 |
|
Neps |
85.35 |
37.78 |
|
Total |
128.27 |
54.23 |
|
The reduction of neps is almost less than 50% after doing pre-carding in 65/35 blend.
| ||
The carding of viscose requires different parameters in carding and Blow Room. Every time while pre-carding, one has to change settings before the start of viscose, which requires extra time. The viscose requires a larger lap weight to avoid lapping on doffer, web fall in carding, piecing difficulty in card, slipping of lap, etc. With larger laps, there is a reduction in the number of laps and saving in doffing time and no breaking of webs in the card. Hence the 18 to 20% heavy laps for pre-carded viscose in the blow room will work better in carding.
The Lap Weight of Viscose for Pre-Carding
|
Specifications |
Lap size of PV Blend |
Viscose Lap Size |
Remarks |
|
Length (m) |
35m |
35m |
No Change |
|
Linear Density (g/m) |
350g/m |
414g/m |
64gm increase |
|
Weight (Kg) |
12.25kg |
14.49kg |
2.24Kgs increase |
|
The 18 to 20% heavy laps for pre-carded viscose in blow room will work better in carding. |
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Advantages of Pre-Carding:
- The reduction of neps in the yarn is less than 50% compared to normal yarn imperfections. The imperfections can be further reduced by increasing flat waste in carding.
- The fabric appearance will improve further. The re-mending / over dyeing will be reduced by adopting pre-carding technique. To begin with, start first odd/white/poor quality VSF shades going in full quantity of 35% in 65/35 blend. The mills going for modernization will have to develop pre-carding line with their existing old machines and procure new machines for bulk production. In days to come, the pre-carding will become regular practice due to increasing demand of quality yarns/fabrics and dyed viscose is from monopolistic supplier. In India, hardly or few mills are practicing this techniques only for the yarns going into premium quality fabrics.
Draw Backs of Pre-Carding:
- Increase in waste by 3 to 4% depending on the supplied quality of Viscose component to be pre-card. Hence increase of yarn cost by about Rs7 to 8 per kg of yarn. The use of pre-carded viscose is economical in high cost premium quality yarns/ fabrics, not advisable for bulk production.
- Separate pre-Carding line for viscose is required in addition to regular bulk production line, if pre-carding quantity is considerably high which needs huge capital investment in machineries, labors, electricity, humidification plant etc.
- The breakages observed are on higher side in ring frames in pre-carded shades and waste is also high in ring frame. This is because of treating viscose twice, over parallelization in carding and blow room.
- The breaking of pre-carded sliver is tedious, laborious and time consuming and huge man hours are required, also delay in delivery of pre-carded shades. The spinner will have option for sliver breaking either by machine or manually. The machine breaking is better for big quantity and quality of breaking is better in manual system, but needs huge time.
- The high speed cards have to be run at slow speed by 20 to 30% for pre-carding of material and shorten the preparatory capacity for regular production line, if pre-carding quantity is high. Hence loss in utilization of blow room and carding, if there is no separate line for pre-carding and quantity is also so big.
- The designer also has to develop shades alternatively by reducing % of odd/ white/ poor quality VSF or eliminating odd component shades from product mix.
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