Modern Cotton Spinning Machinery, Its Principles and Construction

by Joseph Nasmith

Figs. 130 and 131.J.N.

(232) The bobbin L rests upon a flange of the bevel pinion M placed on the collar, and driven by the wheel N. The pinions are, as shown in Fig. [129], fixed in the “bobbin rail,” or, as in Fig. [130], carried on the top of a bearing sustained by the swivel joint. The upper flange of each pinion has formed on it oblong “snugs” or projections, which take into corresponding slots made in the bottom of the bobbins. The wheels N are keyed on the shafts O, which also extend the whole length of the machine, and are suitably borne by brackets fastened to the underside of the bobbin rail. Thus the latter sustains both the driving shafts and the bevel pinions which, as in the case of the spindles, are driven by wheels gearing at different sides of the centre.

(233) This mode of construction lends itself very easily to the formation of the bobbin or spool of roving, which, at its completion, is of the shape shown in Fig. [128], cylindrical with conical ends. In order to wrap the yarn upon the bobbin L it is necessary to give the latter not only a rotary but a vertical movement. It is, of course, possible to give this motion to the spindle and flyer and not to the bobbin, but this is not a convenient method in the case of machines like those under notice, for many reasons. The rail, therefore, which carries the bobbin pinions and bobbin, known as the “bobbin rail,” receives a vertical traverse to an extent which is determined by the class of material to be dealt with. This traverse is a reciprocal one, and is technically known as the “lift,” a machine being said to have a lift of so many inches according to the extent of the vertical movement of the bobbin rail. This varies from 10 or 12 inches in the case of the slubbing frame to 5 or 6 inches in the roving frame, and is obtained in a manner which will be presently described. While it is taking place the bobbins are slid upon the spindle, the presser eye continuing to revolve in the same horizontal plane. From this it follows that any yarn drawn through the eye by the rotation of the bobbin is of necessity wound upon a fresh portion of the surface of the latter. It only remains now to point out, before proceeding to deal with the machine in detail, that it has been shown the spindles and bobbins are driven independently, and may, if desired, rotate at various and different speeds; and that provision is also made for the maintenance of the vertical position of the spindles and flyers while permitting that of the bobbin to be altered. These, added to the regular delivery of sliver by means of the rollers, constitute the essential features of these machines, but the effective manipulation of them gives rise to a number of interesting mechanical problems.

(234) It has been pointed out that the action of the rollers in attenuating the sliver is identical with that of those in the drawing frame, so that no special description need be given of them. But these machines are the first in which the process of twisting is carried out, and the rollers form an important part of the mechanism for this purpose. In introducing twist into any strand or sliver it is necessary that one end of it should be held, while the other is also held and turned at a higher or lower speed. If this is done the strand will be twisted, and the amount of twist is strictly defined by the number of times it is turned. In actual working it is not practicable to continue so to twist the strand without at the same time submitting it to the action of the spindles continuously. Unless it was so delivered it would be broken because of the shortening which takes place during twisting, and it is therefore necessary to furnish a fresh portion of the sliver to the action of the twisting mechanism. For this reason the sliver, while being firmly held by the nip of the front rollers, is also delivered by them at a definite rate, which depends on their size and rate of revolution. Now, assuming that no such delivery takes place, and that a length of sliver of 10 inches is turned 100 times, there would be in each inch of it 10 turns or twists. Suppose, now, that another 10 inches was delivered and the same number of turns made, a similar result would be obtained. It does not matter whether the delivery is constant or intermittent, provided only that the ratio of the length delivered and the number of revolutions of the twisting mechanism remain the same. Intermittent delivery would, however, be very inconvenient in practice in producing rovings, and thus it is requisite to provide for a steady and regular delivery of yarn, as well as a uniform speed of the spindle and flyer. Granting the attainment of these conditions, it is easy to define the amount of twist put into any thread, it being in the same ratio as the number of revolutions made by the twisting mechanism during the delivery of one inch of sliver or roving. Twists are always defined as being so many “turns” per inch, and are arrived at in the way just indicated. As a matter of fact there is a little slip in the rollers, which does not, however, to any large extent modify the rule enunciated. The constants in a machine of this kind are therefore the rate of revolution of the spindles and front rollers; and, generally speaking, the amount of twist increases as the roving becomes finer. This can be attained by an increase of spindle speed or a decrease of that of the rollers, as will be readily understood, but considerations of a mechanical nature generally lead to the latter course being pursued. The spindle speeds in a slubbing intermediate, and roving frame, dealing with the same class of roving, would be approximately 700, 800, and 1,100 revolutions per minute. A table of productions, speeds, etc., is given on page 174, which will throw some light on this point.

(235) It has been already noticed that the bobbin receives a vertical traverse, while the spindle is vertically stationary, and that, in consequence, the yarn is wrapped upon the bobbin in spiral coils. The speed of this traverse is carefully regulated so that each layer is quite free from any overlap, while, at the same time, no space should be left between the coils. When the bobbin has wrapped round it for the whole of its length one layer of roving, its diameter is increased by an amount equal to double the thickness of the roving. Thus its circumference is enlarged, and every revolution it makes requires a longer length of material to cover the surface than it did when it was bare. This extra amount must either be fed to the bobbin, or its speed must be reduced, and as the rollers deliver at a constant rate, the latter is the course pursued. Further, the length of roving wrapped upon the bare bobbin during the whole lift is, of necessity, less than that which would be wrapped upon it after a layer has been wound on if the lift were constant. It is essential that the length of each complete layer should be as nearly as possible equal, and for this reason the traverse of the bobbin is shortened slightly after each of its reciprocal movements. The amount of the diminution in lift is in exact correspondence with the excess of length which would be taken up if it remained constant. The increase in the diameter of the spool has thus an important bearing on the lift, and it is of equal moment in relation to another function of the machine.

(236) A reference to Fig. [129] will show that the flyer and bobbin rotate round the same centre, and the roving delivered by the rollers is passed on to the bobbin through the presser eye, as pointed out. If it be assumed that the yarn passes on to the bobbin at some imaginary point in the circumference of the latter, and that this occupies during its rotation a definitely relative position to that of the flyer eye during its revolution in a concentric circle, it follows that no roving can pass from the flyer to the bobbin. A little thought will make this clear, but Fig. [132] will serve to illustrate it. In this figure, A is the spindle, B the circumference of the bobbin, and C the path of the flyer eye. Now, as A and C are attached in the manner previously described, they must of necessity revolve at the same speed. On the other hand, the rate of rotation of B is capable of variation by reason of its independent driving. Let D and E represent respectively the points at which the yarn leaves the flyer C find passes on to the bobbin B. It is obvious that if the relative position of D and E remain unchanged—that is, if they travel at equal speeds, so that the line between them is always alike—there can be no passage of roving from D to E; or, in other words, there can be no winding. But if the point E makes a complete revolution in less time than D does, or vice versâ, winding will take place. In the first case the quicker motion of E would result in the bobbin B taking up roving from D; and in the second the greater velocity of D would cause it to wrap the roving round the bobbin. To make this clear, suppose the lines A D and A E to represent radial lines drawn through the points D E at the commencement of winding, and that at the termination of say three revolutions, the position of these lines relatively is the same. It is perfectly clear that the line D E will have remained unaltered, and no passage of the roving will have occurred. But now assume that the flyer C had moved so much faster than the bobbin B, that the radial lines through D and E were in the position shown in Fig. [133]. It will at once be seen that C will have drawn forward a certain length of roving corresponding to its gain, and that the portion of its circumference between the point where the material from D passes on to it and the point E will be covered by the roving. In the event of B moving faster than C, the effect is identical with that described, although it is obtained in an entirely different way.

Figs. 132 and 133.J.N.

(237) This statement of the general principle is sufficient to show the conditions under which winding is successfully effected. The gain either of the bobbin or flyer upon the other is technically called the “lead,” and thus a frame is said to be constructed with a bobbin or flyer “lead.” The determination of the amount of lead is very simple, and is fixed by the speed of the rollers, it being manifestly impossible to take up more yarn than is delivered. It follows, therefore, that the excess of the surface speed of the bobbin or spool at any stage of its development must accurately correspond with that of the front rollers. If this condition be departed from, either by the lead given being too great or too little, the result will be broken yarn; in the first case by stretching, and in the second by the production of slack places which become entangled and broken. It may here be stated that it is now almost universally the practice to let the bobbin lead, as, with the flyer leading, a certain amount of stretch is put into the yarn, which is very injurious. This defect is especially noticeable in starting the frame, and it is entirely remedied by giving the lead to the bobbin.