- 1 Importance Of Length Measurement
- 1.1 Properties/Parameters Tested
- 1.2 Instrument(s) Used For Testing
- 1.3 Sample Preparation
- 1.4 Procedure
- 1.5 Calculation & Expression Of Results
- 1.6 Uses Of Fiber Length Testing
- 1.7 Related
Importance Of Length Measurement
- Fiber Length is one of the most important aspects to decide fiber quality.
- Fiber length decides the cost of raw material.
- It is required for most of the settings i.e. roller setting, beater setting, etc.
- Depending upon the count of the yarn to be spun length of the fiber is selected.
Related Standards: IS 233 (Part 2): 1978, ASTM : D – 1440 -96 – Array method, D – 1447-89 – fibrograph.
- Maximum Length.
- Effective Length.
- Mean Length.
- Upper Quartile.
- Percent Short fibers.
Instrument(s) Used For Testing
Working Principle Of Instrument
This instrument works on end aligned principle. The fibers are arranged in the descending order of fiber length which forms an array diagram of which various properties related to fiber length are determined.
Specifications of the Instrument
- Top comb – 3
- Bottom comb – 12
- Velvet pad
- Plastic scale
The instrument is used to prepare the fiber array. It consists of two sets of horizontal combs, an upper and a lower set.
- Top comb – Teeth only at one end, can be removed.
- Bottom comb – Fixed at one end and can be dropped at another end by a knob.
- Depressor – To press fibers in the bottom comb.
- Tweezer – To pull fibers from the comb.
- Velvet pad – To arrange fibers in order.
- Plastic Scale – To trace baer sorter diagram.
- Preliminary adjustments- Nil
Divide the sample into 4 quarters. Take 16 small tufts from each corner at random of size 20mg. Each tuft is halved four times, discarded alternately with right and left hands and 16 parts are produced from each quarter. Combine into a new tuft and divide into 4 parts. Obtain 4 new Tufts and take a quarter from each to make the final sample.
20mg of fiber
- Clean all the combs of the comb sorter before testing.
- Take about 20 mg of the fiber to be tested.
- Make the fibers straight and parallel by drawing and doubling several times by the hand
(This is done by holding the specimen with the thumb and the forefinger of each hand and then drawing and doubling).
- Slightly twist the straightened specimen to hold the fibers more firmly.
- Place the comb sorter in a suitable position such that the first of the bottom combs, which can be dropped in succession, faces the operator.
- Lift the upper combs, and lay the representative fiber sample towards the right and across the lower bed of combs.
- Press the fiber into the combs with the depressor.
- Remove the projecting fibers with the grip and make the fiber end to align with the first comb.
- Grip a small tuft from the straightened edge of the fiber and comb it several times across the needles of the upper comb to remove the loose fibers.
- Transfer the combed tuft to the left-hand side needles and press it with the rake so that it is gripped by the first row of combs.
- Transfer all the fibers present at the right side to the left side as above.
- Turn the sorter round through 180 degrees.
- Lower the upper combs.
- Drop a sufficient number of lower combs and raise the corresponding number of upper combs until the ends of the longest fibers project about 0.5 cm.
- Using the grip, pull out small tufts of successively shorter lengths.
- Comb and straighten the fibers in each tuft, and lay them side–by–side on the velvet pad such that the free ends of the tufts lie along a straight base line.
- A continuous array of uniform density is produced by skillfully using the teasing needle and a forefinger to arrange each tuft perpendicular to the base line and joining up with the previous one.
- Successive top and bottom combs are moved as shorter and shorter fibers are pulled out and joined into the pattern.
- The last few tufts should be very carefully arranged so that no short fibers are lost. It should also be ensured that the pattern is of uniform density throughout as the ultimate evaluation is based on this assumption.
- Trace the outline of the fiber array on a sheet of transparent material.
Calculation & Expression Of Results
Effective length = LL’
%mean length = (area of OAB / length of OB)
Dispersion = (NL’ / LL’) × 100
%of short fibers = (RB/OB)×100
Modern Instruments Available To Test Fiber Length
fiber length and Strength-HVI.
Uses Of Fiber Length Testing
Eg: For testing cotton sample for suitability for spinning a count for finding FQI value of the cotton sample.