Fig. 18.—Intermediate frame (bobbin and fly frame).
As regards twisting of the roving it must be distinctly understood that when the attenuated strand of cotton issues from the rollers of the first bobbin and fly frame, it has become so thin and weak that it can no longer withstand the requisite handling without being seriously damaged. Hence the introduction of "Twist," which is by far the most important strength-producing factor or principle entering into the composition of cotton roving and yarn.
Without twist there would be no cotton factories, no cotton goods; none of the splendid and gigantic buildings of one description or another which are found so plentifully intermingled with the dwellings and factories of large cotton manufacturing towns!
In a sense it is to this all-powerful factor of "twist" that all these buildings owe their existence, since it would be practically impossible to make a thread from cotton fibres without the assistance of "twist" to make the fibres adhere to each other. Hence there could be none of that wealth which has caused the erection of these buildings.
This is true in a double sense, since we have both the natural twist of the cotton fibres and the artificial twist introduced at the latter processes of cotton spinning, in order to make individual fibres and aggregations of fibres adhere to each other. What is termed the natural twist of the fibres may average in good cottons upwards of 180 twists per inch, while the twists per inch put into the finished threads of yarn from those fibres may vary, say, between 20 and 30 twists per inch.
In all the fly frames, therefore, this artificial twist is invariably and necessarily put into the roving. As the cotton leaves the front or delivery rollers, each strand descends to a bobbin of from 8 to 12 inches long, upon which it is wound by special mechanism. As in Arkwright's frame, this bobbin is placed loosely upon a vertical "spindle," and upon the latter is fitted a "flyer," whose duty it is to guide the cotton upon the bobbin.
The primary duty of the spindle is to insert the "twist" which has been shown to be so necessary to give sufficient strength to the roving.
Let any reader of this story hold a piece of soft stuff in one hand while with the other hand he rotates or twists the roving and he will have an idea of the method and effect of twisting (see [Fig. 19]).
Without going into minute details we may say that the practical effect is that, while the roving is held firmly by the rollers, it is twisted by means of its connection at the other end to the rotating bobbin, spindle and flyer. The twist runs right from the spindle along the 6 to 12 inches of cotton that may extend from the spindle top to the "nip" of the rollers, thus imparting the requisite strength to the roving as it issues from the rollers. The mechanism for revolving the spindles is by no means difficult to understand, simply consisting of a number of shafts and wheels revolved at a constant, definite and regulated speed per minute.