Maximising Loom efficiency at loom shed

Maximising Loom Efficiency at Loom Shed

Control of Stops:

The various stops can be classified as

1. Stops due to warp breaks and weft faults
2. Stops due to weft breaks
3. Stops due to shuttle changes
4. Stops due to mechanical failures

1. Stops due to warp breaks and warp faults

Given a quality of yarn, the end breaks during weaving are increased by
- Preparatory deficiencies such as uncleared yarn faults, unsized beams, excessively starched yarns etc.
- faulty loom settings
- defective loom parts and accessories
-unsatisfactory atmospheric conditions

The stops due to warp faults such as slack ends, sticky ends, cross ends, missing ends etc. are due to preparatory deficiencies.

2. Stops due to weft Breaks

Given the quality of yarn, breaks are mainly influenced by unwinding tension and package faults.

The unwinding tension in turn depends upon
- The condition of the surface of the pirn
- shape and dimension of the pirn
- condition of the shuttle accessories, such as shuttle tongue, shuttle jaw

3. Stops due to shuttle changes

4. Stops due to Mechanical Failures

The more common mechanical failures are: faulty working of the warp-stop-motion, weft-stop-motion, pirn transfer mechanical, fast read motion, bang off and shuttle trap.

5. Miscellaneous Stops

All other stops no caused by the earlier four categories such as stops due to beam gaiting, repairs, oiling and cleaning, and delays due to shortage of pirns, beam accessories are included here.

6. Quality of Yarn

It is proven that in mills where there is a consistently low warp breakage rate, the yarn CSP is higher and also the number of thin places is less than the certain minimum level.

7. Loom Performance

In order to determine whether the prevailing breakage rate is really different from the norm and to compare the effect of two treatments say two different size mixings, the appropriate tests are:
((O-N)^2)>=4 and ((A-B)^2)/(A+b) >=4
where O are observed breaks and N are norms for breaks. A and B are breaks with different treatments


Control of Loss of efficiency by Snap Reading

Snap reading is a technique that helps both in listing the various causes of loss in efficiency and in estimating the percentage loss due to each cause. For taking such reading, one walks down the loom alleys making the tally of looms that are stopped against a list of the causes of stoppage.

For example, in a shed of 800 looms, after taking 25 rounds of snap readings, if 4000 looms are found stopped, then the loss of loom efficiency is (4000x100)/(800x25) = 20%

If out of the stopped looms, 1600 looms are found stopeed due to end breaks and warp faults, the loss in efficiency due to this cause is 8%.

OPTIMUM LOOM ALLOCATION

Generally when we answer this question "How many looms per weaver", we should taken into account both operative and machine efficiencies simultaneously.

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.

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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.