The Dyeing of Woollen Fabrics

by Franklin Beech

Nos. 1 and 2 are prepared from Yorkshire grease. The unsaponifiable matter in these is purely natural, it will be seen it varies within wide limits. Nos. 3 and 4 are made from the oleic acid of the candle factories, and the unsaponifiable matter is due to their containing mineral oil which has been added to them.

So far as regards the object for which the wool is oiled, the mineral oils will answer almost as well as the fatty oils and with most satisfactory results from an economical point of view, for they are much cheaper. But this is not the only point to be considered. The oil has to be got out of the wool before the latter can be dyed. Now while the fatty oils can be easily removed, by treatment with soap, and they can be recovered along with the fat of the soap, mineral oils cannot be entirely removed from the wool, what remains in will interfere very much with the satisfactory dyeing of the wool, and what is got out finding its way into the covered wool grease, spoils this for soap making and other uses, so that on the whole what is gained in lessened cost of oiling is lost by the increased liability to defects in dyeing and consequently depreciation in value of the wool, and to decrease in value of the recovered grease.

The amount of oil used varies from 7 per cent. with the best wools to 15 per cent. with shoddy wools. The scouring agents generally used are the same as those used in loose wool scouring, namely, carbonate of soda for coarse woollen yarns, soap and soda for medium yarns, and soap and ammonia for fine yarns. Prior to treating the yarns it is best to allow them to steep in hot water at about 170° F. for twenty minutes, then to allow them to cool. The actual scouring is often done in large wooden tubs, across which rods can be put on which to hang the hanks of yarn, and in which are placed steam pipes for heating up the bath. The best temperature to treat the yarn at is about 150° F.; too high a temperature must be avoided, as with increased heat the tendency to felt is materially augmented, and felting must be avoided. The hanks are treated for about twenty minutes in the liquor, and are then wrung out, drained, and again treated in new scouring liquor for the same length of time. After rinsing in cold water they are dried and finished.

When the oiled wool has been spun into yarns, whether worsted or woollen, and passes into the hands of the dyer, it is necessary to remove from it all the oil before any dyeing operations can be satisfactorily carried out. This oil is removed by the use of soap and weak alkaline liquors, using these at about 110° to 120° F. The most common way is to have the liquor in a rectangular wooden tank, and hang the hank of yarn in by sticks resting on the edges of the tank; from time to time the hanks are turned over until all the oil has been washed out, then they are wrung out and passed into a tank of clean water to wash out the soap, after which the yarn is ready for dyeing.

When the yarn is of such a character that it is liable to curl up, shrink and become entangled, it is necessary that it be stretched while it is being treated with the soap liquor; this is effected by a stretching apparatus consisting of two sets of rollers connected together by a screw attachment, so that the distance between the two sets of rollers can be varied. The hanks are hung between each pair of rollers, and can be stretched tightly as may be required.

For pressing out the surplus liquor from the hanks of yarn a pair of squeezing rollers is used.

Scouring Woollen Piece Goods.--Very often before weaving the yarns are not scoured to remove the oil they contain, as the weaving is more conveniently done with oily yarn than with a scoured yarn. Before dyeing the oil must be taken out of the pieces, and this can be conveniently done by scouring in a washing machine such as is shown in figures 7 and 8, using soap and soda liquors as before, and following up with a good rinse with water.

The soap liquors used in scouring yarns and pieces become charged with oil, and they should be kept, and the oil recovered from them together with the fatty matter of the soap, by treatment with sulphuric acid. By subjecting the grease or fatty matter so obtained to a boil with caustic soda soap is obtained which may be again used in scouring wool.