(269) In the roving machines the relative positions of the spindle and front rollers are fixed, but in the mule an important variation in this practice occurs. The carriage I receives by suitably arranged mechanism an alternate movement from and towards the roller B. During the period they are delivering roving it is drawn away from them until it has travelled about 63 inches, when its motion ceases. While this traverse is taking place the spindles are revolving, and twist is therefore being introduced into the roving. The cessation of the motion of the carriage is accompanied by a similar stoppage of the rollers and spindles, and there is then a number of lengths of yarn—each 63 inches—held in tension by them. This traverse of the carriage is called its “stretch” or “draw.”
(270) The yarn, as thus spun, requires winding upon the spindle, so as to form the cop, but before doing this it is necessary to free two or three turns which are wrapped on the spindle between its point and the point or “nose” of the cop. This operation is called “backing off.” In order to effect it the roller K has its motion reversed for a short time, so as to give the necessary backward rotation to the spindles. The slack yarn thus produced is taken up, first, by the ascent of the counter faller, and, second, by the descent of the winding faller. The former rises sufficiently to preserve the tension of the yarn as it is freed, and the latter is drawn down so as to assume a proper position to commence winding when the operation of backing off is completed.
(271) As soon as this stage is finished the inward traverse of the carriage I commences, an operation which is accompanied by the forward revolution of the spindles, which thus wrap or “wind” on to the cop the 63 inches of twisted yarn. The rollers during winding are, of course, stationary. By the time the carriage has again reached its innermost point the full length of yarn is wound, and during that period the faller has risen from the base of the upper cone of the cop to its nose. This ascent is a gradual one, and causes the yarn to be wound in finely pitched spiral coils upon the cop. With the termination of the inward traverse or “run” of the carriage winding ceases, the winding faller and counter faller wires are released, and the whole of the operations begin anew.
(272) It is now possible to define the various stages in the whole process of mule spinning. These are as follows:—
First. The period during which roving is being delivered and twisted. During it, the rollers are revolving at a defined speed; the carriage is being drawn outwards at a constant rate; the spindles are revolving rapidly at a velocity definitely relative to that of the front roller. During this period the faller and counter faller are held in the position shown in Fig. [148], being quite clear of the yarn.
Fig. 148.J.N.
Second. The period during which the movements just named are stopped. The roller driving gear is detached; the mechanism by which the carriage is drawn out is stopped; the spindles are stopped because of the transfer of the driving strap to the loose pulley and the consequent cessation of the motion of the driving band; and preparation for the engagement of the faller and counter-faller with the yarn takes place.
Third. This is the period of “backing-off.” During it the driving band is driven in the contrary direction to its normal one, and the spindles are reversed. The faller wire is drawn down, depressing the yarn; the yarn between the nose of the cop and spindle point is uncoiled; the counter faller rises and takes up the slack yarn; and the faller is “locked.”