Overview
ISO 2646:1974 specifies a laboratory method for measuring the length distribution of wool fibres processed on the worsted system using a fibre diagram machine. The test produces a graphical estimate of the cumulative fibre-length distribution (known as hauteur) for combed slivers. The method is focused on combed slivers (worsted tops) and includes apparatus, specimen preparation, test procedure, calibration and result calculation. A key limitation: slivers containing two or more fibre types with different dielectric properties (e.g., wool blended with polyester) may yield inaccurate length distributions.
Key topics and requirements
- Scope: Applies to combed slivers processed on the worsted system; not fully reliable for mixed-fibre slivers with different dielectric constants.
- Apparatus: Essential components include a transparent recording table (overall width 22.9 cm), input platform with velvet strip, R.F. bridge electrode system and tuned amplifier, optical system producing a recording image, tension clip (1.5–3 g), small brush, and recording paper graduated in millimetres.
- Specimens and conditioning:
- Prepare and test multiple specimens (typically four) from one sliver sample.
- Condition specimens in the standard atmospheres defined by ISO 139 before testing.
- Preparation and test procedure:
- Squaring sliver, sealing a band of fibre ends to plastic strips using a heating sealing unit, and punching a hole 23.8 mm from the aligned ends.
- Feeding the sealed draw through the electrode guard, adjusting the recording image (V-point), and rotating the instrument to record cumulative distributions.
- Data and calculations:
- Read length ordinates corresponding to 5%, 15%, … 95% (ten values) for each specimen; the mean of these values is the specimen hauteur.
- Calculate average hauteur across specimens, determine the coefficient of variation (CV) of hauteur, and derive the related parameter ("average barbe") as prescribed by the standard.
- Calibration:
- Use reference sliver and a plastic test tape (example dimensions given in the annex) to verify instrument and technique (WIRA fibre diagram machine described).
Open preview (PDF)Wool — Measurement of the length of fibres processed on the worsted system, using a fibre diagram machine
