Fig. 194.
(378) A glance at Fig. [188] will show that between the ring rail and the nip of the front rollers there is about ten inches of yarn, which, when it is being twisted, is held by the traveller and the rollers, and tends to fly outwards and assume a curved course, which from its shape is called a “balloon.” This is caused by the centrifugal action of the yarn and the resistance of the atmosphere, and leads, unless checked, to a serious loss of twist. In addition to this as the distance between the centres of the spindles is only 2 or 3 inches ordinarily, it is obvious that if this tendency is unchecked contiguous ends will come into contact and frequent breakages occur. The author was informed by Mr. Bernhardt that a careful trial made by him established the fact that, where the balloon is unchecked and allowed to attain its greatest size, the breakages are six and a half times as numerous as when its size is in some way limited. There are two methods of doing this, one by surrounding the spindle with a guard which prevents the balloon attaining more than a certain fixed maximum diameter, and the other by so adjusting the position of the thread board that the distance between the wire eye and the traveller is such that not more than a certain sized balloon can be formed. It is a well known fact that a balloon is absolutely essential to good spinning, as its centrifugal action enables a lighter traveller to be used, and the drag upon the yarn is thus reduced to a minimum. The use of a heavy traveller undoubtedly will check ballooning, but the yarn will suffer, and therefore a well formed but not excessive balloon is of advantage. Mr. Brooks employs a plate (L, Fig. [188]) pierced with a number of holes and mounted on pokers, which gradually rise higher as the bobbin fills, so that the balloon is checked by the hole in the plate. Other makers, such as Messrs. Platt Brothers and Co., Howard and Bullough, and Dobson and Barlow, employ forked wire guards which serve the same purpose as the plates referred to. Fig. [194] represents the appliance used by Mr. Bernhardt, which is very effective and is worth attention. Instead of depending upon a guard of the character referred to, the ballooning is checked by maintaining a defined distance between the guide eyes and the ring rail. It is clear that as the latter rises, if the guides are stationary, there will be a greater tendency to balloon when the rail is at its lowest position than when at its highest. More than that, the attainment of the full diameter of the cop is followed by more ballooning than when the building is just beginning, and it is therefore advisable to slightly shorten the distance between the guide and the point of the spindle. The guides are in this case mounted on a rod borne by and attached to vertical pokers A. The vertical position of A is determined by the cam C, which is slowly rotated as building proceeds. The shape of C is such that when spinning begins, the guide eye A is about an inch above the nose of the bobbin, but gradually falls until within 3⁄8 inch of the same point, after which it slowly rises until the relative positions at the commencement and finish are as indicated by the dotted and full lines. The rise begins as soon as the cop is formed of full diameter, and one important feature in this invention is that the vertical reciprocations of the guide eyes are independent of, less than, although simultaneous with, those of the ring rail. It is certainly remarkable how effective this contrivance is in checking ballooning, and this without submitting the yarn to any injurious rubbing action. The size of the balloon is accurately checked, while at the same time it is as large as can be permitted under the existing conditions. The inventor stated that the effect of this arrangement is that a bobbin of 6 inch lift can be employed, where in other cases not more than a 5 inch bobbin could be used. The extra length of yarn so wound on is of great service in subsequent processes, giving rise to other advantages which are well known.
(379) So far the mechanism employed has been designed to spin on bobbins placed on the spindles, but there is another branch of the subject to which reference must be made. Although the attempt to spin on bare spindles was made so far back as 1847, this special method of spinning is not even yet completely successful, though it is quite true that many efforts have been made which have attained partial success. It may perhaps help to the understanding of the difficulties of the case to remember that weft yarn is most urgently needed in the form of cops. Now, yarn which is used for weft has many less twists per inch put into it than warp yarn, and is in consequence much softer and more tender than the latter, breaking with less strain, and being altogether more difficult to spin. It is, therefore, under conditions which are the most unfavourable possible that the attempt to spin on the bare spindle in ring frames has to be made. In forming a cop, the diameter on which the yarn is wound is constantly changing, and the largest diameter is only a little smaller than the internal diameter of the ring, while the smallest will be about 3⁄16 of an inch. Now, it will be easily understood that the drag exercised by the yarn on the traveller will be greater when it is being wound on the larger diameter than when on the smaller, it being remembered that the spindle is always revolving at a regular rate, and consequently taking up more yarn per revolution on the body of the cop than on the spindle. Thus, if a regular rate of traverse of the ring rail were adopted it is clear that at one point the yarn would be taken up too rapidly, or too slowly at another. In the mule this difficulty is overcome by increasing the speed of the spindles when the yarn is being wound on the nose. It is not possible to adopt any such method in the case of ring spinning, and the solution has been attempted by the adoption of a mode of giving a very quick traverse at the beginning of its downward stroke to the ring rail, so that less yarn is wound on at that point. Of course this difficulty more or less exists even where spools and bobbins are used, but it is not so acute as when only the spindle is employed. The speed of the traveller varies continually, being greater when the yarn is being wound on the larger diameter and less when on the smaller. There is thus a greater resistance when winding is going on at the nose, and breakages occur more frequently at that point. In addition to this there is the difference existing in the way the pull is exerted on the traveller at both points, which will be readily understood by a reference to Fig. [197]. It will be seen that the direction of the draught of the yarn is in the first case from B to C, and is an angular or tangential one, whereas in the second case the pull is from A to C, and is almost radial. As the yarn in proceeding from the rollers to the bobbin is passed through the traveller, it will be clear that while the revolution of the spindle will in the first case draw the traveller round the ring in the direction of the arrow, in the second case it will exercise no tractive power, or at any rate very little, on the traveller, tending rather to pull it against the ring. As the point A is, however, constantly changing its position, a certain drag is given to the traveller, but it is a periodical one, for as soon as its position is altered the old conditions are again established. In this way the yarn is in a sense twitched or wrenched, and breakages occur in consequence. In addition to this difficulty there is another, arising from the different speeds at which the traveller runs, to which reference has been made. Owing to this difference more twist is put in when winding is going on at the largest diameter, and less when at the nose of the cop. Now, the latter place is where it is most wanted, owing to the increased drag, and as weft yarn is always more softly spun a decrease in the number of turns per inch is a fruitful source of breakage. The difference amounts to between one and two per cent, and constitutes really the chief difficulty to be overcome.
Fig. 197.J.N.
(380) As this subject is one of some interest a few words may be profitably expended on it. There is some confusion existing as to the way in which the loss in twist should be arrived at. On the one hand it is contended that the number of coils made in one lift of the ring rail should be counted, and the loss of twist calculated from that. On the other hand, it is urged that the coils laid in a double lift of the rail should be taken as a basis. This is the view held by Mr. Charles Lancaster, of Manchester, who has given a good deal of attention to the subject, and with whom the author is inclined to agree. To arrive at a conclusion it is necessary to ascertain the smallest and largest diameter of the surface of the bobbin, calculating therefrom their respective circumferences. The mean of the latter will give the average length of yarn wound per revolution, and the difference of the two the relative loss in twist. Mr. Lancaster put this matter very clearly, and the demonstration may be given in his own words: “To prove this calculation measure the length of a ‘draw’—i.e., the yarn deposited in one up or one down motion of the ring rail—and multiply by the number of turns per inch, count the number of coils in this layer of yarn (which represents the actual loss), and divide into total number of turns. Thus, if the up motion of the ring rail deposits 72 inches of 20’s yarn with 16·75 calculated turns per inch, then 72 x 16·75 = 1,206 ÷ 20 coils = 1·8 per cent of loss; and if the down motion deposits 178 inches of yarn with 16·75 calculated turns, then 178 x 16·75 = 2,981·5 ÷ 46 coils = 1·6 per cent, or an average of one up and one down motion of the ring rail of 1·7 per cent.”[A] Of course the finer the yarn spun the less the percentage of loss of twist.
(381) Whatever be the mode of calculation adopted, whether only the single or double lift be taken into account, the fact remains that there is a loss of twist, and that this is of most account when weft yarns are being spun. It being most desirable to spin these upon the bare spindle, so that they may be used in the shuttles, it will be seen that the subject is one of some importance. Various methods have been tried to overcome the difficulty, one mode being to take the yarn away from the nose of the cop as quickly as possible, but it has only been partially successful. Another, and more successful plan, is to form a special traveller, so arranged that the yarn in passing to the bobbin does not give a radial but a tangential pull to the traveller. The final form of traveller adopted by Mr. William Lancaster, who has tried a large number of shapes for this purpose, is arranged in this way, and to a certain extent frames made by him have been successfully used. The mode of construction adopted by Mr. Lancaster is shown in Figs. 198 and 199. In these the traveller is made at one end with an open fork, and at the other is C shaped, fitting the ring as shown in Fig. [199]. Referring to that figure it will be seen that the yarn is carried through the C shaped eye, and then round the foot of the open fork B to the spindle A. The result is that the point where the traveller rests on the spindle acts as a fulcrum, and the yarn exercises a pull on the end of the arm carrying the C, this portion of the traveller practically becoming a lever. In this way the direct radial pull upon the yarn is avoided, and the traveller is readily drawn round the ring. Its actual position on the cop is shown in Fig. [198], where B is the fork, A the yarn, and C the spindle. In this form a number of frames are working with considerable success.
(382) In Figs. [200] and [201] a special form of ring and traveller applied to a bare spindle is illustrated, these being made by Messrs. Platt Brothers and Co., Limited. The ring B has a groove A formed in it, in which a traveller D made of the shape shown is placed. The traveller has a loop or hook E near one extremity, and a second loop C nearer the centre. The yarn is first passed under the loop E, and then through C, thus giving a drag to the traveller at the point E, and causing it to travel round the groove. The loop C lies close up to the spindle when the yarn is at the nose of the cop, so that the yarn passes at once on to the former. The machine so constructed has been in use for some time, and it is found possible to stop it with the ring rail opposite the extreme point of the cop and re-start it without any considerable breakage of ends. In considering this portion of the subject past experience will form a base on which to found future efforts. A combination of a rapid traverse of the ring rail with some means of avoiding the direct pull of the yarn might be effective, but the subject is one for experimental work and not theorising.