Process Control in Drawing-in

Process Control in Drawing-in

The term drawing-in and warp tying refers to the operations involved in preparing the weaver's beam for the purpose of weaving fabrics on the loom.

The drawing-in process primarily consists of drawing ends from the weaver's beam through heald eyes of different harnesses and then through the dents of a reed in the order that is determined by the design of the fabric.

If a beam is to be worked with warp stop motion on the loom, specially when using closed drop-pins, the ends have to be drawn through these pins before drawing them through the heald eyes and reed dents.

conventionally drawing-in is carried out manually by two persons-one, the reacher for selecting and presenting the ends from the beam, and the other, the drawer for pulling ends through the drop-pins, heald eys and reed dents.

The main requirements of carrying out this process properly and efficiently are:

1. The operator should be aware of the principles of drawing-in and be trained to do the job speedily because any mistakes or delays in carrying out the process would prove to be costly.

2. The healds and reeds should be in good condition and of suitable specifications for ensuring that these are not the cause of warp breaks on the loom and of defects in the fabric.

3. The drawing of the beam should be done properly to avoid cross ends on the beam.

4. Suitable precautions should be taken to reduce the incidence of extra-ends and to compensate for the missing ends during the weaving of the loom.

CARE OF HEALDS AND REED

1. The healds and reed from the exhausted beam of the loom must be cleaned throughly to free them from fluff, size, rust etc. before using them for a new weaver's beam.

2. When warp tying is practiced, it should be ensured that the same set of healds and reed do not work on the loom for a long time, even if no apparent defect is noticed in them. This is because through cleaning of healds cannot be done on the loom itself and dirty healds are prone to give high warp breaks.

COMMON DEFECTS IN DRAWING-IN

1. Cross ends- To minimise the incidence of cross ends on the beam during weaving, the ends presented for drawing in or warp tying should be made to be parallel and in their respective positions as in the beam. Proper dressing of ends is, therefore, of great importance.

2. Extra Ends- some ends are generally cast out during drawing-in/warp tying to compensate for long missing ends on the weaver's beam.Whether to leave these ends or not should be governed by the method of cutting lappers at sizing.

If the lappers are cut and mended only after completion of a weaver's beam, there is no need of leaving extra-ends at drawing-in or warp tying. If however, the lappers are cut no sooner these are detected, the same ends should not be withdrawn or not taken for tying.

Process Control of Rope Dyeing for denim

1. Concentration of Hydrosulphite

It is measured by vatometer. It should be from 1.5 gpl to 2.5gpl , or by redox potential of dye bath which should be from -730 mV to -860 mV.

2. Caustic Soda or pH value

Should be from 11.5-12.5

3. Dye concentration in Dye bath

it is measured by spectrophotometer. It should be in g/l

Guidelines

High Indigo Concentration --> Shade is greener and lighter
Low Indigo Concentration --> Shade is dull and Red.

High pH or Caustic Concentration --> Redder and lighter
Low pH or caustic concentration --> greener and darker

Dipping Time

Longer the dipping time, better will be the penetration and lesser will be the ring dyeing effect. It varies from 15-22 seconds.

Squeeze Pressure
High pressure will lead to lower wet pick up and result in lesser color and better penetration. At rope dyeing, squeeze pressure is 5-10 tonnes, ie. wet pick up is as low as 60%. Hardness of squeeze roller is about 70-75 deg. shores. It sqeeze rolls are too hard then there are chances of slippage and uneven yarn tension.. If squeeze rollers are too soft then shading will occur. Surface of the squeeze rolls should be ground twice a year.

Airing Time

It should be 60-75 seconds. Longer airing time results in high tension on the yarn and subsequent processes will become difficult.

Drying

Insufficient or unevenly dried yarns will result in poor rebeaming

Calculation of Replenishing Dye feed/min

Conc. of stock vat is g/l= 90
range speed in yards/min=25
count = 7s
totoal ends = 4100

Wt of yarn dyed /min= (4100*25*1000)/(7*840*202)= 7924 gms
shade desired = 2%
Amount of dye to be replenished/min= 158.5 gms

Effect of pH

At pH of 10.5 to 11.5, there will be formation of more monophenolate ions, which lead to higher color yield, as strike rate of the dye to the yarn bundle is very high, and wash down activities will be very good.

At pH higher than this, dye penetration will be less and wash down characteristics are also poor.

Testing

1. Alkalanity in Dye Bath Liquor

Pipet 10.0 ml of vat liquor into 100ml of distilled water in a 150 ml beaker. place under continuous agitation and insert the electrodes of a pH meter caliberated at pH 7.0 with standard buffer solution.

Titrate with tenth normal HCl ( 0.1 HCl) to pH 7.0 (ml = A)

calculate
g/l of NaOH = A *0.40

2. Hydro in Dye bath Liquor

Add 2 ml of 37% HCHO to 150 ml beaker. Add 2 ml of dye range liquor . Add 6 ml of 25% glacial acetic acid solution prepared by diluting 1 part acid with 3 parts water. Add 2 ml of starch/KI indicator. Add ml of water. Titrate with 0.046 N ( prepared by diluting 460 ml of 0.1 N Iodine to one liter ) solution until the color changes from emarald green to bluish purple.

G/l of hydro= mo fo 0.046N of Iodine

Importance of High Concentration of Free Hydrosulphite

The clearest shades with minimum reddish streaks are observed at by relatively high conc. of hydrosulphite. On the other side, with lack of hydrosulphite, the leuco indigo is less dissolved and thereby adheres to a greater extent to the fibres. With lack of hydrosulphite furthermore, the amount of unreduced dyestuff by oxidation at the upper level of the liquor and through activiation of unfixed dyestuff, gets separated from the fibrous material would constantly rise as the reducing agent for creating leucoform would be missing. Under these circumstances a reddish bronze like shade results due to dispersion of not reduced dyestuff in the yarn. The min. proportion of hydrosulphite should be around 1.3 to 1.5 gpl in case of rope dyeing and 3-4 gpl in case of sheet dyeing. Also to avoid the lack of hydrosulphite or Indigo at certain places in the immersion, vat, the whole quantity of the liquor should be circulated 2-3 times every hour.

Reaction Time

At very short reaction time, an adequate liquor exchange ( i.e. the amount of chemicals consumed and replaced by fresh addition of reduced indigo) is not assured. This has a negative influence on dyeing and depth of dye penetration. In addition to this the time available for diffusion of dyestuff until oxidation commences is too short. To ensure an even and good depth of dye penetration by dyeing in several passages, the reaction time should be 20-30 sec. for each vat (eg. at a speed of 20m/min for a reaciton time of 10 seconds, the immersion path should be maximum 3.3 meters).

A reaction time exceeding 60 seconds should be avoided as the amount of dyestuff again get reduced and released may again supersede that of additionally take up dye stuff, resulting in higher shades.

Softening Agent: 8 g/lit

Drying: Rest humidity should be 30% and then sized.

Addition of chemicals

1. Red Tinge: reduce addition of NaOH, increase slightly Na2S2O3
2. Darkish Red: increase Hydro
3. Light Greenish: decrease Hydro
4. Dark Green: Increase Caustic

For further information you can read this article