warp preparation for rope dyeing-II

Warp Preparation for Rope Dyeing-II

Oz tensioner: It consists of round cylinderical housing and is located at each running package in the creel. At the top and bottom of the housing is a small ceramic eyelet. Inside of the housing are two steel balls.The yarn is threaded up through the bottom eyelet, around the steel balls out through the top of the housing.

Tension is applied to the yarn as it passes around the steel balls inside of the housing.

Advantages: Tension at the front and back of the creel is constant. 2. Adjustments are never required. 3. It is almost maintenance free.

Disadvantages:
1. there is a limit to how much tension can be applied
2. Threading of tensioner is difficult
3. It is relatively expensive.

ELECTRONIC TENSIONER

1. Capastan Type
2. Rotating Disc Type

Capastan Type: There is a round capastan mounted on a precision shaft. This capastan is positioned onto the bearings which are located inside of a round DC coil. The yarn is wrapped around the outer surface of the capastan. The action of the yarn being pulled out of the creel by warper rotates capastan. If no voltage is applied to the DC coil, an EM field is created under the capastan. A hysterisis ring is attached to the inside of the capastan which reacts to this EM field and as such creates resistance to free rotation of the capastan. This resistance to rotation adds tension to the yarn on the capastan's outer surface. Varrying levels of DC voltages are applied to each tensioner in the creel and will provide equal tension to each in the rope.

Rotating Disc Type: Two disks are mounted in the vertical position onto a ceramic shaft. Behind the inside disk is a DC coil. When voltage is applied to the DC coil, an electromagnetic field is created. The outside disk is steel and is of course attached to the magnetic field which has been created. It pulls tightly against inner disk; again depending upon the strength of the EM field created by the DC coil, the yarn is threaded between the two disks. A 4 RPM AC motor mounted on each tensioiner, turn these disks to prevent thread cutting.

Advantage of Capstan types:
- No electric motor
- yarn is not distorted due to pinching action of disk
- less maintenance

As speed of ball warping is slow, mechanical tensioner are normally sufficient.

5. After that the yarn is then threaded through the eyebrows down the length of the creel. Here self threading type of ceramic eyelet is generally sufficient.

6. A stop motion device is required

a. The drop wire system
- It is located on each vertical row at the front of the creel bands.It is inexpensive with very short reaction and response time.However, it is exposed to dust, and if the end should break at or near the warper, there may be enough residual tension on the yarn, holding it up and preventing the drop wire from falling.

b. Photoelectric system
Instead of drop wire, this system uses a faller which is attached to a shutter inside of an airtight housing. Inside this housing is a photocell having a transmitter at one end of the housing and a receiver at the other end. A light beam is emitted to the receiver and an open electric circuit is maintained. When an end breaks, the faller drops and the attached shutter passes through the light beam, thus imitating the stop signer to the warper. it is reliable, comparatively inexpensive, easy to thread and maintenance free. However,it suffers from the same problem of residual tension.

c. Electric Motion Sensor
It is normally mounted on the balloon shield at the yarn package. This system actually measures the motion of the yarn as it exits the package. The yan balloons through a light beam housed in the balloon shield. As long as the light beam is constantly broken by the ballooning motion, the system remains open when the end breaks, the ballooning action stops and sensor signals the warper to stop. The circular motion of the yarn passing through the light sensor keeps the lenses clean. It is reliable, fast acting and self cleaning. However it is expensive.

7. The yarn exists the creel and is threaded through the lease stand. It houses a unique reed which allows each adjacent yarn end to be raised or lowered in order to create a shed through the yarn sheet. A lease string is inserted through this shed at given intervals ( 1000 m) in order to maintain control of the yarn during reopening at the long chain beamer. It can be manually or pneumetically operated.

warp preparation for rope dyeing-1

Warp Preparation Requirements for Rope Dyeing

Ball Warping: Equipment required to form the rope of yarn. It involves creeling multiple ends of yarn ( Between 350-500 ends) and collecting them into an untwisted rope for dyeing. the rope is wound onto a long cylinder called a log on a machine called as a ball warper.

Some Notes

1. Packages of yarn are preconditioned before ball warping
2. Packages are loaded into the creel ( larger lots- magine transefer creeL0 and smaller lots- swing gate or truck creel
3. Packages are placed on adapters. An adapter support the package of yarn and ensure that the package remains aligned to the tensioning devices. Wooden plug type adapter are most effective as they require least amount of exertion to remove the empty package.

Next Step is threading the tensioner located at each yarn package

1. Post and Disk tensioner. It has two posts mounted onto a flat base. two round disk are placed onto each post. The yarn is threaded between the disk and wrapped around the post. One of the parts is movable so that the angle of wrap can be varied. More tension can be added to the yarn by adding round weights onto the top disk.

Advantages are 1. Inexpnsive 2. does Marginally adequate job of maintaining yarn tension 3. Simple to thread up 4. Low maintenance requirements.

Disadvantages are 1. Yarn has a tendency to jump out from between the disks at the rear of the creel. 2. It is labour intensive- when different tension levels are required. 3. There is more frequency of cleaning up 4. It doesnt control tension well at higher speed.

2. The driven disk tensioner

It also uses twin disk arrangement, however the disks are supported from below- there are no posts. Tension is applied from above- there are weights or spring loaded.
A gear under each pair of disks is matched to another gear mounted on a continuous shaft which runs the length of the vertical tension post. This shaft is connected to a 4 rpm motor which rotates the disk.

Advantage of disk rotation are 1. Thread cutting prevention 2. Dampens out variation due to ballooning action of yarn. There is mor uniform tension 4. Less effor required to change tension levels.

Disadvantages are 1. It is more difficult to thread up, there is more maintenance due to electric motor used and at high speed the tension control is not well.

Rope Dyeing Vs. Sheet Dyeing

In rope Dyeing

Ball warp--> wash-Dye-Coil-->Beam-->Size-->Weave

In Sheet Dyeing

warp-->wash-dye-size-beam-->weave

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

Notes on Yarn for Rope Dyeing in Denim

Notes on Yarn for Rope Dyeing

* Yarn faces stress and stretch at ball warping, rope dyeing, rebeaming, sizing and loom shed so elongation of yarn should be more than stretch at (ball warping + Robe Dyeing+ Rebeaming + Sizing )= (2-3%) + Loom shed (about 5%)

* Tension at Ball warping should be less by 7-8% of single yarn strength.

* Strength CV should be within limits as it may give rise to weak points

* The tendency of yarn to migrate at rope dyeing can be countered by less micronaire of yarn ( should be around 3.8-4.2)

* More dropping of short fibers at long chain beaming is good

*The sensitivity settings for neps is set at +280 for rotor spun yarn and not +200 as in case of ring spun yarn. The reason for this is that the structure of rotor spun yarn is intrinsically different from that of conventional ring spun yarn. Neps in rotor yarn tend to be spun into the solid yarn body rather than remaining on the yarn surface, which is typical of ring spun yarns. Although embedded in the yarn core, these neps still represent a short mass defect and will therefore trigger the imperfection counter upon exceeding the preset value. However, compared to neps that are attached to the yarn surface, fully embedded neps are barely perceptible for the human eye. Thus, in order to balance the typical visual appearance of rotor spun yarn with the imperfection counts, +280 sensitivity setting is a common convention for rotor spun yarns.

Comparison of Ring Yarn with OE yarn at Ne 7