Slasher/Sheet Dyeing | Process Sequence in Indigo Slasher/Sheet Dyeing | Advantages and Disadvantages of Slasher/Sheet Dyeing

Slasher / Sheet Dyeing:
In continuous slasher / sheet dyeing and sizing machine, direct warping beams are used, instead of ball warping logs in case of Indigo rope dyeing system. The Slasher Dyeing machine is capable of handling Ne count form 9/s to 30/s (OE and Slub both). At the back end of the slasher / sheet dyeing range, the direct warping beams are creeled. The yarns sheet from each beam is pulled over and combined with the yarns from the other beams so that multiple sheets of yarns can be made.

Creeling of direct warping beam in Sheet dyeing machine
In sheet dyeing range, the total No of required ends for a weavers beam are dyed, dried, sized and dried simultaneously. The back direct warping beam contains 380- 420 ends, similar to rope, but the ends are distributed evenly over the width of the flanges and the end lay parallel to each other.

This continuous slasher dyeing range eliminates a few intermediate processes of the rope dyeing, such as re-beaming, sizing. The yarn sheet from the back beam passes through wash boxes, where it is treated with caustic and subsequently washed with normal water. After squeezing the excess water; the yarn sheet passes through Dye baths and skied for oxidation as in the case of rope dyeing. This develops the indigo coating on the yarn. After dyeing, the dyed yarn is washed by passing through 3-4 wash boxes and finally squeezed before allowing it to pass through drying cylinders. The dyed yarn then enters into the sow box, where it is sized. Subsequently the yarn sheet is dried.

The yarn sheets then passes through a set of stainless steel split rods, which separate them into individual sheets, equivalent to the number of section beams in the creel. After passing through the split rods, the yarn sheets are collected into single sheet and passed through a expansion comb at the head stock, which separate individual yarns. The expansion comb can be adjusted to the desired loom beam width. Slasher dyeing range typically consists of 1-2 wetting vats, 4-8 dye baths and 3-4 rinsing troughs. The immersion and oxidation times lie between 10-20s or 45-60s.

Process Sequence in Indigo Slasher / Sheet Dyeing:
The passage of flow of yarns in slasher dyeing is shown below-

Pretreatment

Washing

Dyeing

Washing

Drying

Sizing

Drying

Pre-treatment:
Pre-treatment process in sheet dyeing consists of treatment of the cotton yarn sheet with caustic and wetting agent. Pre-wetting is carried out in order to get proper dyeing of the sheet. Pre-wetting is carried out with a Wetting agent, at room temperature. In some cases, if well penetration of the dye is required, the yarns are treated with strong caustic soda solution followed by hot wash and cold wash treatment prior to dyeing. The pH of the bath is 11.8-12

Washing :
Cold washing is carried out at room temperature.

Dyeing (Indigo blue dye):

The dyeing is carried out in 4 to 8 dye boxes. The dyeing is carried out with;
Typical dipping time of sheet in each tank is 15secs and oxidation time is about 90secs.

Washing:
The dyed yarn sheet is subsequently in order to remove the unfix dye from the yarn surface. However the number of washing tank may vary. Typical wash type is: cold wash at room temperature and hot wash at temperature of 70ÂșC.

Drying:
The dyed yarn sheet is dried by passing it through drying hot cylinders.

Accumulator:
The function of accumulator is to store the extra yarn sheet when the machine is stopped or at the time of size beam doffing, so the dyeing cannot be stop.

Sizing:
The yarns are sized in order to achieve the required strength.

Drying:
The dyed sheet is dried by passing through drying cylinders.

Advantages of Slasher / Sheet Dyeing:
Slasher dyeing ranges have a number of advantages. Slasher dyeing range produce sized beam directly which is ready to use in weaving. Sheet Dyeing method has the following advantages:
  1. Slasher dyeing is more comfortable for producing lightweight denims.
  2. These machines require less floor space,
  3. Enable smaller production runs,
  4. Have a quicker turn over time,
  5. The technology is less capital intensive and the machinery cost is less;
  6. The cost of production is less
  7. Other type of dye can be use to dye the cotton in this range. Hence the slasher dyeing technique can produce a wide variety of colors other than indigo blue.
  8. Rope opening is avoided, as in the case of rope dyeing.
  9. The immersion and oxidation times are much shorter than rope dyeing.
Disadvantages are:
  1. In Sheet dyeing, their is a problem of center to selvedge shade variation.
  2. The hydrosulphite consumption is much higher owing to the greater surface 

1 comments:

raheel barula said...

i have read your article and find it appealing , though i want to ask you that can you explain the reason of center to selvedge shade variation?

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