2 IDENTIFICATION OF CONTAMINANT SALE LOTS
SUMMARY A trial incorporating the testing of commercial core samples has provided further evidence of wool contamination arising from crossbreeding Merinos with Damara fat tail rams. The trial has also highlighted limitations of the CSIRO Dark Fibre Detector for this purpose in terms of both its subjectivity and the operator time required for a test. Core samples from bales of fleece wool from Merino ewes known to have reared Merino lambs (5 lots), or to have reared Damara crossbred lambs (14 lots), or to have been mated to Damara rams but failed to rear a lamb (6 lots), were tested for pigmented and for medullated fibres by 3 laboratory methods. The tests were performed at AWTA Ltd and SARDI. The wool from the 3 different farm management practices had significantly different (P<0.005) concentrations of pigmented and medullated fibre. The ewes rearing the Merino lambs showed the lowest contamination, those rearing the Damara crossbred lambs showed the greatest contamination, and the remaining 6 lots showed intermediate concentrations of pigmented and medullated fibre. The 2 laboratories were not significantly different (P≥0.05) in their reported concentrations of medullated fibres and of the darkest (CSIRO darkness levels 6 to 8) pigmented fibres. However, for the pale-pigmented fibres (CSIRO darkness levels 4 and 5) and the total pigmented fibre concentration there were differences between the laboratories.
Merino wool contamination from rearing of Damara crossbred lambs
Recent importations and promotion of Damara sheep has raised concerns and debate about potential for Merino wool contamination. This project examined Merino ewe wool contamination arising from the mating of Damara rams and rearing of Damara crossbred lambs. Shirley-blended core samples from 3 commercial greasy wool sale lots known to involve Merino ewes shorn with Damara crossbred lambs at foot (2 lots), or shorn 3 weeks after weaning, were assessed. Contaminant fibres were above commercial expectations for Merino wool and present in every core sample measured. There was no significant difference found between these sale lots. From an experimental flock, composites of fleece samples were carded and the effects of mating or rearing alone assessed. No detectable increase of pigmented or heavily medullated fibres, above very low background levels, were detected among the Merino ewes mated to Damara rams (1 ram per 65 ewes). However, high concentrations of contaminant fibres were found in the Merino ewe wool at weaning of their Damara crossbred lambs and also 3.5 months after weaning; with reduced levels post-weaning. The management strategy of restricting wool exposure to mating effects alone may offer advantage but delaying shearing of ewes after weaning to reduce the contaminant fibre burden was, in this case, not sufficient to overcome potential concerns for wool processing. However, in view of the many potential contributing factors, actual contamination may vary widely between cases and require the advancement of presale measurement to gain buyer confidence and accurate appraisals.
Determination of Optimal Ball-Burnishing Parameters for Plastic Injection Moulding Steel
The objective of this study is to determine the optimal plane ball-burnishing parameters for plastic injection moulding steel PDS5 on a machining centre by utilising the Taguchi’s orthogonal array method. The design and manufacture of a burnishing tool are described. Four burnishing parameters, namely the ball material, burnishing speed, burnishing force and feed, were selected as the experimental factors in Taguchi’s design of experiments to determine the optimal burnishing parameters which have the dominant influence on surface roughness. The optimal burnishing parameters were found after carrying out the experiments specified by Taguchi’s L18 orthogonal table, by the analysis of variation, and by a full factorial experiment. The optimal plane burnishing parameters for the plastic injection moulding steel PDS5 were a combination of a tungsten carbide ball, a burnishing speed of 200 mm/min, a burnishing force of 300 N and a feed of 40 μm. The surface roughness Ra of the specimen can be improved from about 1 μm to 0.07 μm by using the optimal burnishing parameters for plane burnishing.