From four to eight, but most usually six, cans of sliver from the previous machine are placed behind the frame, and the ends of the slivers conducted over special mechanism within the range of action of four pairs of drawing rollers. This passage of the cotton is shown very clearly in [Fig. 17].
The top rollers are made of cast iron, covered with soft and highly finished leather made from sheepskins, the object of this being to cause the rollers to have a firm grip of the cotton fibres, without at the same time injuring them. The bottom rollers are of iron or steel, made with longitudinal flutes or grooves, in order to bite the cotton fibres firmly on the leathers of the top rollers. In order to assist the rollers in maintaining a firm grip of the fibres the top rollers are held down by somewhat heavy weights.
The action of the drawing rollers will be adequately discussed later in this story, when dealing with the inventions of Lewis Paul and Sir Richard Arkwright, and need not be enlarged upon at this stage.
It will be sufficient, therefore, to say that, assuming that six slivers are put up together at the back of the frame, the "draft" or amount of drawing-out between the first and second pairs of rollers the cotton comes to, may be about 1.3, between the second and third pairs 1.8, and between the third and fourth pairs 2.6. These three multiplied together give a total draft of slightly over 6.
In other words, assuming that 1 inch of cotton be passed through the first pair of rollers, the second pair will immediately draw it out into 1.3 inches; the third pair will draw out the same portion of cotton into 1.3 × 1.8 inches = 2.34 inches, and the fourth or last pair of rollers will draw out the same portion of cotton into 2.34 × 2.6 inches = 6.084.
Fig. 17.—Drawing frame showing eight slivers entering and one leaving the machine.
The six slivers put up at the back are therefore drawn out or attenuated to the dimensions of one by the rollers, and then at the delivery side of the machine the six slivers are united into one sliver, and arranged in beautiful order inside a can exactly as described for the Carding Engine.
Now it is in the doubling together and again drawing-out of the slivers of cotton that the two objects of making the fibres parallel and the slivers uniform are effected.