Laboratory Performance Test for Detergents in Continuous Wool Scouring

Wool scouring on a large scale involves feeding a continuous stream of loose wool successively through a line of bowls containing steeping, detergent, and rinsing solutions. After each bowl the wool passes through squeeze rolls which expel excess liquid. Scouring lines commonly have four or five bowls, of which the first is used for steeping, the second and third contain solutions of detergent and builders for scouring, and the last two may be rinse bowls. The immersion time of wool in any one bowl runs about 30 sec; the whole scouring operation is therefore done in about three minutes. Many details of equipment and operation are described in the American Wool Handbook (1). Comparative evaluation of detergent performance in plant scale test is complicated by several factors: 1. Raw wool is very heterogeneous as to dirt content from lot to lot and even from fleece to fleece. 2. The rate of wool fed through the washing line is variable. 3. The quality of labor is such as to render conduct of tests by plant personnel undesirable. Technical personnel must, therefore, be in attendence. 4. Plant requirements rather than the conduct of a scouring test take first consideration, and the latter is therefore subject to interruptions for routine cleaning, changes in wool mix, etc. The usual criterion for cleanliness of scoured wool is residual wool grease content, determined by solvent extraction. Random samples of wool extracted over a period of time provide data that conform to the normal law of variation. These data, if plotted on a tri-sigma control chart, would look like Fig. 1, Under a system of this type, the comparison of detergents can be made only by (1) determining the average level and variability of results under standard conditions, and (2) running the detergent under test for sufficient time to re-determine mean level and variability under this new condition.