High volume instrument

High volume instrument systems are based on the fibre bundle strength testing, ie, many fibres are checked at the same time and their average values determined. Traditional testing using micronaire, pressley, stelometre, and fibro graph are designed to determine average value for a large number of fibres, the so called fibre bundle tests. In HVI, the bundle testing method is automated. Here, the time for testing is less and so the number of samples that could be processed is increased, quite considerably. The influence of operator is reduced.

The HVI testing is attractive due to the classing of cotton and the laying down of a mix in the spinning mill. This HVI testing is suitable for the extensive quality control of all the bales processed in a spinning mill. The mill is in a position to determine its own quality level within a certain operating range. The time for testing per sample is 0.3 minutes. It is best applied to instituting optimum condition for raw material. About 180 samples per hour can be tested and that too with only 2 operators.

Principles of fibre testing using HVI

Sample preparation

The fibro gram method is preferred while preparing the sample for fibre length estimation. The sample has to be presented to the measuring zone by clamping the fibres at a random catch point. Here the fibro sampler is used.

The test specimen obtained using the fibro sampler/comb combination is a beard of fibres with individual fibres projecting to different length from the clamping point. In HVI, the strength testing is also done on the same beard of fibres with individual fibres projecting to different lengths from the clamping point.

In HVI, strength testing is also done on the same beard of fibres prepared for length measurement. While using the low volume instrument -fibro stelo for strength measurement, the sampling is done on the separate fibre bundles, of which 15 mm long is prepared after remounting the short fibres by combing. For micronaire testing, a sample of cotton weighing approximately 10 grams is used. For colour testing, random mass of fibres sufficient to cover the test window is used for measurement.

Measurement of different parameters using HVI & LVI

Length

Both the high volume instrument and the low volume instrument use an optical principle of determination of fibre length. A narrow rectangular beam of light is allowed to fall on the specimen beard. The attenuation of Iight through the specimen at different areas of the beard is measured and used to obtain the different span length values. In the HVI, the tip of the beard is scanned first and scanning gradually proceeds towards the clamp while in the LVI, the beard is scanned in the opposite direction. In both the instruments, the span length values are obtained by actual measurement.

Strength

In the LVI, the fibrostelo is used. This module uses the pendulum lever principle of loading the specimen to estimate the fibre strength characteristics. A random sample of cotton fibres is prepared, short fibres being removed by combing so that all the fibres in the test specimen extend all the way through the jaws.

Breaking tenacity in g/tex = (breaking load in kg/ sample weight in mg) x 15 mm.