Wednesday, 5 November 2008

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%.


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

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