ISO 920:1976

Overview

ISO 920:1976 - "Wool - Determination of fibre length (barbe and hauteur) using a comb sorter" specifies a laboratory method for measuring wool fibre length distributions in worsted drawing slivers and rovings. The standard defines the two primary measures - barbe (mean fibre length from combing extractions) and hauteur (mean fibre length derived from mass proportions) - and describes sampling, specimen conditioning, the comb-sorting procedure, and calculation of mean lengths and their coefficients of variation. An annex describes the semi‑automatic Schlumberger (Type M.A.E.) analyser used for these determinations.

Key topics and requirements

• Scope and materials: Applicable to wool presented as worsted drawing slivers and rovings.
• Specimen preparation: 1 m samples, lightly twisted (~20 turns), ends aligned and conditioned 24 h in a normal atmosphere per ISO 139.
• Equipment:
  • Precision balance (1 mg resolution).
  • Comb sorter / comb analyser (field of combs with successively lowered pegs that define length classes).
  • Semi‑automatic Schlumberger analyser described in the annex (10 mm class intervals, lateral displacement, leather pullers and brush collector).
• Procedure:
  • Place a weighed mass (typically 500–4 000 mg) on the comb field, align fibre ends on the last comb and sequentially lower combs to peel off fibre fractions by increasing fineness.
  • Collect and weigh fibres from each length class separately.
  • Use the class mid‑lengths and class mass percentages to compute mean hauteur and barbe, plus their coefficients of variation.
• Calculations and reporting:
  • Standard provides tables and formulae (using totals denoted A, B, C from class data) to derive length values and CVs.
  • Results presentation includes class distributions, histograms or cumulative polygons and full test details.
• Reproducibility data:
  • Tabled method reproducibility is provided (e.g., reported method errors and percent figures for height and barbe and their CVs).

Practical applications and users

• Quality control in wool processing, worsted spinning and combing operations.
• Textile testing laboratories performing fibre characterisation for grading, blending and process optimisation.
• Research and development groups evaluating fibre length distributions for product performance.
• Buyers and sellers who need standardized, comparable fibre length data for specifications and trade.

Keywords: ISO 920:1976, wool fibre length, barbe and hauteur, comb sorter, Schlumberger analyser, worsted drawing slivers, rovings, textile testing, coefficient of variation.

Related standards

• ISO 139 - Textiles - Standard atmospheres for conditioning and testing (referenced for specimen conditioning).