March 11, 2008

Check Points for flawless dyeing in Cabinet Dyeing Machine

The following points may lead one to a flawless dyeing:

  1. Grieg yarn inspection - for oil stains, uneven twist, color variation is Grieg stage, Grieg yarn CSP, weight per bundle, hank weight, yarn count, moisture content of yarn - some of the tests, you can do it in your lab and for some of the textile tests, you have to get the report from an authorised textile lab.
  2. Proper dressing of hank yarn - this would be a manual operation. The yarn in hank form from bundles, have to be opened, beaten well on the beating poles to separate each yarn in to loose single thread. If the yarn hanks are not properly prepared, then there is every possibility of getting shade variations between the hanks with in a batch itself. After beating and making each strand parallel, the hank should be hanged on the stainless dye-sticks or poles.
  3. Cleanliness of the machine - Check the compartments of the dyeing machine. There should not be any stain of previous shade processed. Inspect thorugly and if necessary clean the machine once again before loading the greig yarn.
  4. Loading in to the cabinet dyeing machine - this operation requires minimum two operators. One should carry the poles from the trolley to the person standing near the machine. The loading of yarn should be done with all care, so that it would not get entangled on the side wall slides, or with other hanks.
  5. Water filling in to the machine - When you add the water in to the machine make sure, up to which level you should fill to reach the required volume of water. A best practice is to fill the water through a metering pump. Liquor ratio also plays an important role in reducing the batch to batch variation.
  6. Cabinet Dyeing Machine propeller wheel speed - The speed of the propeller determines, how much volume of water is being transferred per unit time. Higher the speed, faster the cycles. (High speed induces entanglements in the yarn hanks apart from enhancing the pilling.) If the belt connecting the motor is loose, then the speed will be less and the reverse impact will result.
  7. Calibrated thermometers - Dyeing is a chemical process, where the kinetic energy plays an important role. The ambient temperature recommended for each process has to be adhered without fail. The right temperature leads to right fixation and exhaustion as suggested by the dyestuff manufacturers. So keep the thermometer of cabinet dyeing machine frequently calibrated.
  8. Process Timings - Each operation is a chemical process, that needs to be done at proper temperature and for proper time. Higher and lower timings for each process creates again batch variations.
  9. Calculation mistakes of dyes and chemicals - please recheck your calculations for each dyestuff and chemical you are adding in to the bath. A third person checking is highly recommended.
  10. Check and calibrate your weight machines - Have the practice of checking your weight machine, at least once in a day. Calibrate with standard weight. Do not over or under weigh than what is specified in the weighing machine.
  11. Dyes and chemicals Weighment - appoint a separate person to inspect the weighments always. Weighing pans should be cleaned every time properly.
  12. Dissolving of dyestuff - this is a very important point, everybody is missing. Your lab to bulk reproduction mainly fails here. Use adequate quantity of water for dissolving the dyes and chemicals. Proper dilution during dissolution is very important. In case of vat and reactive dyes, temperature of dissolution is very important.
  13. Filtering of Dissolved dyes and chemicals - if it is a dyestuff, filter the dissolved dyestuff through a fine mesh like bolting cloth.
  14. Chemical parameters:

a) Physical and chemical properties of dyes and chemicals used to be tested (Quality Assurance) before using it in bulk production.

b) Water Quality - hardness, TDS, Iron and Copper Content - all these parameters should be tested before using the water for dyeing.

c) pH of processing at every stage - during bleaching, during bio-scouring, during peroxide killing, during dyeing, after dyeing, before fixing or softening treatment. Please read the article on the influence of pH in textile dyeing and textile finishing.

If all the check points are kept under control, one can dream on batch repetition

Cabinet Yarn Dyeing - Sequence of operations

Generally in cabinet yarn dyeing machine, cotton, acrylic, jute, flax and coarse natural fibers can be processed in hank form.

For Cotton yarn processing, the general sequence of operations are as below:

(1) Load the machine with yarn -> (2) Scouring and bleaching -> (3) Hot wash -> (4) Cold wash -> (5) Neutralization -> (6) Peroxide kill -> (7) Cold wash -> (8) Dyeing -> (9) Cold wash -> (10) Neutralization -> (11) Cold Wash -> (12) Soaping at boil -> (13) Hot wash -> (14) Cold Wash -> (15) Softening Treatment -> (16) Unload.

Out of the 16 operations, the (1) and (16), do not consume water. The other 14 operations mean, 14 times the machine has to be filled with fresh water. If for example, we dye a 100 kgs batch at 1:15 liquor ratio, then the water consumption will be 1500 liters per bath and for 14 baths, it will be 14 x 1500 = 21000 liters. That mean, for processing 1 kg of yarn, it requires 210 liters of water. This is a very high volume, in these days of water scarcity. So the following measures are being adopted in this industry.

  • Wherever possible, the dyeing units have started disposing off the old, high liquor ratio machines and buy new low liquor machines. Now 1:12 MLR cabinets are widely used everywhere in this industry. Straightaway 20% water saving is achieved.

  • Wherever possible, the dyeing masters have implemented reduced number of baths, with new auxiliary chemicals. For example, bio scouring and bio-peroxide killing is new emerging process, where you need not do separate cold and hot washes after scouring and there is no need for separate bath for residual peroxide removal. This process eliminates almost 3 baths with a saving of again a 20% water.

  • Using suitable good soaping of agents of anionic nature, one can easily acquire the soft feel and finish required by the end user. This also reduces one more bath.

This high volume of water consumption, not only adds to the water cost, but also to many other indirect costs like energy cost - steam to heat the water and power to pump in the water, extra dosage of dyes and chemicals to maintain the bath concentration and effluent treatment of excess water that is being let out.