Common challenges
- Probably the most common area of dissatisfaction arises when a measurement of diameter in the spinning mill is higher than the greasy wool or top specifications. There is a typical error of 0.2 to 0.3µm on a single test, the diameter of the top averages about 0.15µm coarser than the greasy wool, and the full test method requires that the wool be oven-dried and re-conditioned before testing as the regain history has an effect. The spinning mill should measure a number of samples using a properly calibrated instrument following the full test method. If the average level is then above specification the mill should be concerned because of the importance of diameter.
- Many mills put tight limits on the specified greasy or top properties but do not appreciate that this means that the cost of the top may be significantly higher. The average CVD of Australian tops is approximately D/2 + 10.5, so that the average CVD is 21% for a 21µm wool. Specifying a lower value of CVD than the average will mean that the topmaker could become severely limited in the choice of wool lots to purchase. An astute mill could allow higher CVD if D is low and vice-versa. Tight limits on CVH, e.g. 40 < CVH% < 45, also severely limit the wools that can be blended in a consignment and the topmaker will have to pay significantly more for the wool.
- Nep levels of the top are difficult to measure and consistency between visual assessments is difficult to achieve. The spinner can afford to be relaxed about nep levels if the top is going to be re-combed because combing is highly effective at removing neps.
- Top is sold at a specified regain (% moisture) but this does not mean that the wool will have this regain when it arrives in the mill. Sliver will fairly rapidly take up or lose moisture to the surrounding air and a relative humidity of 65% or more is recommended for good processing of pure wool.
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