Although some of the larger silk mills have their own departments for this process, as a general rule it is done by independent concerns known as “throwsters”—who specialize in this particular operation. Machinery of a very complicated and accurate type is necessary, capable of operating at very high speed. It has been found that the investment called for to equip such a mill is too large in most cases to allow the manufacturers to incorporate this operation in their factories, particularly if it happens that the spindles are not fully employed during the whole of the year.
Throwing Machines
Organzine and Tram
There are two main classes of thrown silk—organzine and tram—the former has a heavy twist and is used for the warp; while the latter is given only a light twist and is used for filling. Within these two general types there are many special grades, according to the type of material for which they are to be used, such as crepe, chiffon, sewing thread, floss silk, embroidery silk, etc.
Soaking the Raw Silk
The raw silk as it comes to the throwing mill is done up in books of skeins and packed in bales, as described in a previous chapter. The skeins, after being weighed and examined, are first soaked for about twelve hours in warm soapy water, which softens the natural gum, after which they are thoroughly dried. This, of course, reduces the moisture content below the customary 11 per cent, which is later restored by natural absorption.
Winding
The first step in the actual throwing is the winding of the thread on bobbins. The skeins are put on swifts—a light type of reel—and wound at a very high rate of speed on the proper size of bobbin. It is here that the winding strength of the silk meets its severest test, for constant breaks during the winding involve considerable expense when speed is such an important factor.
Twisting