Length Measurement Instrument

WIRA 

 It involves a rotating shaft with a spiral groove machined in it. Once end of the fiber to be measured is gripped by a pair of tweezers whose point is then placed in the moving spiral. This has the effect of moving the tweezers to the right and so steadily drawing the fiber through the pressure plate. This ensures that the fiber is extended under a standard tension. A fine wire rests on the fiber and is arranged so that when the far end of the fiber passes under the wire it allows it to drop into a small cup of mercury and thus complete an electrical circuit. This causes the shaft to stop moving, so halting the tweezers, at this point the tweezers are then raised to lift the counter immediately above where it has stopped. The counters are arranged in 0.5 cm sections and each time one is lifted it adds a unit to the appropriate length group so contributing to a cumulative total. The advantage of the apparatus is that it gives a standard tension to the fibers, it involves less operator fatigue and it gives semi-automatic recording of the results to 0.5 cm intervals. The apparatus is claimed to be able to measure up to 500 fibers per hour However, the detector wire that is used to sense the end of the fiber is very delicate and it is difficult to set up.

Fiber Sorter Method

This is done by holding the fibers in one hand and extracting the fibers by their ends with the other hand. This first step produces a bundle of fiber ends together. The fibers are then taken from this bundle by hand a few a time starting with the longest fibers and are laid down next to one another in descending order of length. This produces a fiber diagram as show in fig.

As hand stapling requires experience, alternative methods of tuft measurement have evolved mostly involving similar methods of preparation:

1. Preparation of a fringe or tuft with all fibers aligned at one end.   

2. Withdrawal of fibers in order of decreasing length.

3. Preparation of a fiber diagram by laying fibers alongside one another in decreasing order of length with their lower ends in a line.

4. Analysis of the diagram.

 The Shirley comb sorter

1. The sorter shall be placed with the towards the operator and the top combs shall be lifted. The prepared sample shall be slightly twisted and placed in the lower combs, at the right-hand side of the sorter as it faces the operator, with a small tuft protruding.

2. By means of the grip all the loose fibers shall be removed from the protruding end until there is a straight edge. The loose fibers pulled out being placed between two glass slides. Later these shall be reincorporated in the original sample.

3. A tuft shall now be pulled from the sample, care being taken to grip the fibers as near the ends as possible. This shall be combed several times (combings being preserved) and transferred to the left-hand side of the sorter so that the co-terminous ends of the fibers are almost flush with the nearest comb B and the tuft is straight and at right angles to the combs. This tuft shall now be pressed into the combs means of the depressor.

4. This process shall be repeated until all the sample of lint is transferred to the left-hand side all combings etc. having been re-incorporated in the original sample.

5. The sorter shall now be turned round so that the front faces the operator and the longest hairs projected towards him (C).

6. The top combs shall be lowered and fitted in the rack so as to grip the tuft and prevent uncontrolled slipping of the fibers.

7. The lower combs shall be dropped successively until the tips of the longest fibers are seen.

8.  The fibers shall be pulled out in tufts of successively shorter lengths by means of the grip, the longest first the combs being successively dropped as required. The fibers shall be combed, straightened, and laid down on the velvet pad with the straight.