Mean Fibre Diameter is one of the more important parameters of wool.

It determines what end product can be made from the wool. The handle and visual appearance of the overall product is affected by the fineness of the wool.

Price differentials exist for different mean fibre diameter ranges.

AIRFLOW METHOD

This is the traditional method for mean fibre diameter measurement.

Approximately 10g is removed from each sub sample and combined into one sample. A Shirley Analyser is used to card the sample. This removes any Vegetable Matter and remaining dirt, untangling the fibre to produce an open web. The sample is conditioned to the point of equilibrium in a standard atmosphere of 20 degrees and 65% RH.

Two specimens of 2,5g each are weighed and measured in duplicate on two Airflow instruments using the principle of constant air pressure to a fixed mass of wool in a standard volume chamber to determine the air flow through the specimen.

LASERSCAN

Approximately 10g is removed from each subsample and combined into one sample. The sample is conditioned to a point of equilibrium in a standard atmosphere of 20 degrees and 65% relative humidity.

Fibre snippets are taken from a sample by a mini–coring device and placed in the Laserscan. The diameter of the fibre snippets, suspended in liquid solution, are measured as they pass through a laser beam.

At least four measurements are performed per test using two or more instruments.

Optical Fibre Diameter Analyser (OFDA)

The OFDA is essentially an automatic microscope set above a moving clean glass slide containing fibre snippets. The instrument magnifies and captures images of the individual fibres using a video camera, where after it identifies and measures each fibre.

The sample is conditioned as per IWTO specifications.

The sample is minicored and the snippets fall directly onto the glass slide. The slide is placed on the stage of the OFDA and the snippets are measured. At least four measurements are performed per test.