CHAPTER III.GINNING AND MIXING MACHINES.
(24) When the cotton is ready for harvesting it is picked from the shrubs by hand. There have been many attempts to pick it by machinery, but these have not hitherto been very successful. After picking, it is subjected to the action of a machine called a “gin,” which is sometimes arranged to be worked by hand, but more often by power. In the latter case the machines are placed in a shed, and the cotton is brought there for treatment. The object of ginning is to remove from the cotton the seeds, which adhere closely to the fibre, and which have of late years acquired considerable value for oil-producing purposes. In order to remove them it is necessary that the fibre should be held in some way while it is submitted to a rubbing or scraping action, by which the seed is separated. To effectually perform this function great care is required, as otherwise a quantity of the seed is broken, and the fibres are rubbed up into “neps.” If either of these effects is produced additional labour is thrown on the spinner in his subsequent treatment, and it is therefore desirable to avoid such a manipulation of the machine as would lead to so undesirable a result.
(25) In Figs.1and2a single Macarthy gin is illustrated in part sectional side elevation and front elevation. This is a type which, in principle, is now largely adopted. It consists of a rollerA, rotated in the direction shown by the arrow, by means of a strap passing over a pulley fixed on the end of the roller shaft. The latter is square, and is passed through the centre of the roller, fitting a corresponding hole in the latter, and being carried by suitable bearings fixed on the machine frame. In constructing the rollerAthe following method is adopted. Wood segments are fitted together so as to form the complete cylinder, or the latter may be made in one piece. Having produced the body, it is fixed on the shaft, and is then turned quite round and parallel. Upon the surface so prepared a thick covering of walrus leatherBis fixed, in which spiral grooves are formed. The rough surface of the leather, as the roller is revolving, seizes the cotton fibres as they are fed along the tableF, which has a gridGat its inner end, a special feed being sometimes fitted. When the fibres are drawn in by the roller they are taken under a knife bladeC, which is fixed above the roller by means of the sets of clampsDandE. The clampsDbind the blade to its bearings, and those markedEare used to regulate its pressure on the rollerA. As the roller occasionally becomes hollow the wisdom of this procedure will be seen. A crank shaft is placed and driven from the shaft of the roller, and gives a rapid reciprocating motion to a connecting rodI, which has at its upper end a bladeH. The height of the bladeHis regulated by means of the adjustment of the connecting rod strap, to which it is jointed, and which can be packed to any desired amount. The blade is coupled to radius armsJ, adjustable by nuts at their outer ends, and oscillating on a rod fixed below the feed-table.
(26) As the fibres are drawn under the upper bladeC, the lower bladeHpushes up the seeds, which cannot pass between the roller and the bladeC. In this way the seeds are freed from the fibre, which is carried forwardand thrown off at the front of the machine, or it may be stripped by a fixed blade. The setting of the bladesCandHshould be arranged so that the necessary pressure is applied to the seeds to free them, but care must be taken that the lower blade does not rise so high as to crush them. It should also be set relatively to the roller, so as not to roll up the fibre by having close contact with either the roller or upper blade, while effectually removing the seeds. Other forms of ginning machines are made, including one in which rollers formed of a number of saws are employed, but their use is not so large as that of the Macarthy machine, which may be taken as typical.
(27) After the cotton is ginned, it is pressed in large hydraulic presses into bales of various sizes and weights, ranging from 400 to 600lbs. each. In this form it is imported into this country, and delivered to the mill-owners. The purchases of the material are made from samples of a few pounds taken from one or two bales of a lot of the same brand, and it is essential in purchasing that not only the “staple” but the condition in which the cotton is packed should be taken into account. In some seasons the percentage of moisture is much higher than in others, and in wet seasons a large weight of adherent sand is certain to be found. This, indeed, is the case always, but it is much greater after a bad season than when the weather is normal during picking. The question of the delivered condition of the fibre is a very sore one commercially, as it results in serious loss to the millowner, and there is little doubt that in many cases a fraudulent intermixture of sand is made.
Figs. 1, 2.J.N.
Figs. 1, 2.J.N.
Fig. 3.J.N.
Fig. 3.J.N.
Fig. 4.J.N.
Fig. 4.J.N.
(28) Whatever may be the condition in which the cotton is received, the first operation at the mill is to open out the bale and break it up into pieces of a convenient size. For many years this was conducted purely as a manual operation, but an arrangement which was made by Messrs. Platt Bros. and Co., in 1855, and has been working ever since, is shown in Fig.3. This consists of a lattice feed tableF, which delivers the cotton and brings it into the range of action of an opener cylinderC. The latter opened the material to a considerable extent,and threw it on to a second latticeH, by which it was delivered to a third one, and conveyed to the mixing stacks in a manner to be afterwards described. The operation is now almost always carried out by a machine known as a “bale breaker,” a perspective view of which, as made by Messrs. Platt Bros. and Co. Limited, is shown in Fig.4. It consists of a feed table, placed between the projecting framework, and is usually of the lattice type. The lattice feed apron consists of a number of narrow strips of wood fixed to two endless bands passing round rollers at each end of a longitudinal frame fixed to the machine. By suitably driving one or both of the rollers a continuous motion is obtained, and the wood strips being each free from the other no difficulty is experienced in forming an endless apron or feed table. The cotton is placed upon the table in large pieces or lumps, just as these are taken from the bale, and they are carried forward until they come into contact with the first pair of rollers. There areusually four pairs of rollers driven by means of the spur pinions shown in the illustrations. The first pair are provided with coarsely-pitched blunt teeth or spikes, which seize the cotton and pass it onward to the next pair, which are of similar construction. The last pair of rollers are usually made with coarse, longitudinal corrugations, or flutes, as shown in Fig.4, which deliver the cotton either on to the floor of the room, or on to lattice aprons arranged as hereafter noted. The top rollers are weighted by helical springs in the manner shown, and can easily yield if any obstruction or unusually large piece of material passes between them. The speed of the rollers increases rapidly, but there is a divergence of opinion as to the proportion of increase over the whole series. It will be well, therefore, at this point to state the conditions of the case fully.
(29) Before doing so, however, it is necessary to explain a term which even at this early stage is used, and which is a common one throughout the whole series of operations constituting spinning. The variation in the speed of the rollers of the bale breaker is known as its “draught.” In other words, an elongation or enlargement of the bulk of the cotton occurs in exact proportion to the velocity of the rollers. Thus, if the relative speed of the first and last of the series of rollers is as 1: 30, the draught of the machine is the same. In the case of the bale breaker the draught results merely in an increase in the bulk of the cotton, but subsequently it leads to an elongation of the sheet or sliver into which it is formed.
(30) It being highly desirable that the naturally open fleecy condition of the cotton shall be restored at the earliest moment, the question arises, What shall be the draught of the bale breaker rollers? Is it necessary to do more than break up the lumps of cotton into smaller pieces, which can be readily treated by the subsequent machines? To these questions different answers are given. On the one hand, it is contended that what is required is to reproduce the conditions of hand breaking, by which the cotton was pulled from the bales in small tufts ready for delivery to the opening machinery. Another practice advocated is to so pull the lumps into which the bale is broken up that the cotton when delivered is in an open fleecy condition. It would be preferred by spinners if they could obtain the cotton in the loosely packed condition in which it is received by the Indian spinners, for instance. As this cannot be done, owing to commercial and transit considerations, the question arises whether the first stage in the processes conducted in this country is not the right one to restore this condition.
(31) Between the two positions formulated there is a wide divergence, but, to the author, the latter appears to possess the balance of advantage. There can be no doubt that the preparation of the fibre cannot be commenced at too early a stage, and, as efficient cleansing is one of the first objects to be attained, it follows that the earlier the open condition of the cotton is reached the more readily can cleaning be effected. It must not be forgotten that care is necessary to avoid possible damage to the fibres, but, with rollers properly speeded, there appears to be no reason to expect such a result.
(32) In consequence of the divergent views held, the draught of a bale breaker varies considerably. In some cases it is only 2: 1, while in others it reaches 30: 1. The former is the rule adopted by Messrs. Crighton and Sons, who advocate the first course named, and the latter that adopted by Messrs. Lord Brothers, who prefer the second. Messrs. Platt Brothers and Company recommend a wise variation in this respect, proceeding upon theprinciple that different staples require different treatment. Thus one machine made by them has four rollers with a large draught, this being used for good staples, and producing as much as 90,000lbs. weight in 50 hours. In dealing with Surat cotton, which is more hardly pressed, two sets of rollers are used, followed by a beating cylinder by which the cotton is thoroughly broken up (Fig.8). In each case it is customary to attach lattices to the machine, by which the cotton is carried forward and deposited in the mixing bins (EFig.13). (See also Figs.6,7, and8). Another method is to treat Surat cotton by first passing it through breaker rollers, and thence through a Crighton cylinder, described in ChapterIV. The bale breaker may in this case be used either singly or as part of the combination.
(33) The rollers are made in two ways. They are cast in one piece and are mounted upon the shaft; or are built up from a number of discs threaded and fastened upon the shaft and bolted together. The latter is the preferable course, the breakage of a few teeth being easily remedied.
Fig. 5.J.N.
Fig. 5.J.N.
(34) Before proceeding further, reference may be made to Fig.5, which is a transverse section of the machine as made by Messrs. Dobson and Barlow. The top rollers of the machine, as ordinarily made, are provided with spring weighting, in order to permit them to rise if an unusually large piece of cotton is passed between them. If this enters at one side of the machine it will be at once seen that the roller will be raised at that side, and that its axis will be angularly disposed to that of the bottom roller. The two rollers will only be near each other at one side, and between them, across the whole of the width of the machine, will be a gradually increasing space through which lumps of cotton can pass unpulled. This is a defect of more or less magnitude, but is one which is ingeniously remedied in the machine shown in Fig.5. Only one line of rollers, markedU V Y Z, is used,by two of which the pulling is effected. Below these the noses of iron bars or levers,Q R, fulcrumed on knife edges, are placed. The bars are a few inches wide, and extend below the rollers over their entire width. The cotton passes over these “pedal” levers, which are weighted at their other end, and yield, as shown by the dotted lines, when an extra large piece of cotton passes. The weight is sufficient to enable the cotton to be held until it is pulled by the roller. It will be at once seen that only the pedals affected by the lump will be depressed, the remainder occupying their normal relative position to the roller, which is fixed by the stop shown. In this way the presence of a thick piece at one point in the width of the rollers does not affect the pulling at another point.
Fig. 6.J.N.
Fig. 6.J.N.
Fig. 7.J.N.
Fig. 7.J.N.
(35) The cotton being palled, it is necessary to mix it. This is effected by delivering it upon a second lattice,BFig.13, which can be made of any desired length, and by which the cotton can be delivered on to a third latticeCrunning transversely or in any other direction. Three such arrangements—the sketches supplied by Messrs. Platt Bros. and Company—are shown in Figs.6,7, and8, but there is practically no limit to them. By means of these devices as much as 90,000lbs. weight can be laid down per week by two workmen. To avoid the risk of fire, the flutes are so arranged as not to come into contact, but it is advisable to place the machine in a building removed, if possible, from the main structure.
(36) Having broken up the bale as described, the cotton is in a condition to be mixed. This operation is one of the most important in the economy of a cotton mill, and on its judicious and thorough accomplishment depends very often the production of a profit or loss. In order to obtain the best possible yarn the longest-stapled cotton should be used, and should be selected so that the fibres, when spun, are as nearly as possible of one length. By careful selection a practically perfect yarn can be produced, but it would naturally be a dear one. It is, however, possible to apply the same principle in the production of cheaper qualities of yarn. Briefly stated, the principle is, that to spin a good yarn it is necessary to use cotton in which the fibres are of approximately the same length. The longer the “staple” of the cotton the better the yarn; but, even when short staples are used, this selection is still essential to success. This does not necessarily mean that the same grade of cotton should be used exclusively, but, on the contrary, several can be mixed, provided that the staples are equal, even if they are not of the same commercial value, and differ in other characteristics. By a careful selection of cotton a mixture can be obtained from which a good even yarn of fair strength can be spun, the cost of which would be lower than it would be if a single good grade only was used.
Fig. 8.J.N.
Fig. 8.J.N.
(37) It is the practice in making a mixing to place round the breaker bales of the various grades which are to compose it. The attendant takes a layer from each bale in succession, and places it on the feed lattice of the bale breaker, by which it is broken and partially mixed, so that when stacked the elements of the mixing are well incorporated. The size of the stack depends very largely on the requirements of the spinner, but as most mills now are employed on a small range of counts, some of them on one or two, it is most usual to make a large one containing sufficient cotton to last for several weeks. By pursuing this course there is a very much better chance of getting a regular quality of yarn, which is essential to the commercial success of the mill. In taking cotton from the heap it is the best plan to begin at the top of the face and work downwards in a straight line, as by this procedure a uniform quantity of the different elements in the mixing is obtained. It is desirable to make a small stack of the same classes of cotton as the larger one is to be composed of, and in the same proportion. By passing this through the various machines a test can be made of its yarn producing qualities, and the mixture of the larger stack can be varied so as to remedy any defects discovered in the smaller one. It is impossible to lay down any definite rule as to mixings, the production of which is a matter of experience, and can only be arrived successfully at in that way. Not only must the strength and cost of the yarnbe considered, but also its colour, and it is for this reason essential that a thorough knowledge of the structure and characteristics of various growths should be acquired in addition to one of commercial values.
(38) It will be easily seen, when the operations of the various machines employed in cotton spinning are considered, how essential it is that the fibres in a mixing should be approximately equal in length. Unless this condition is observed there is likely to be a good deal of loss from fly in the carding engine, and the slivers in the drawing frame would tend to have the long fibres in the centre and the short ones on the surface, owing to the difficulty experienced in drawing different lengths with the same setting of rollers. These remarks are, of course, only relatively true, as it is possible to mix different staples economically, but the process is a difficult one. For instance, in the scutching room, laps, each consisting of cotton of different staples, can be fed simultaneously on the same lattice, and so produce a lap of the mixed staples. It is found to give the best results when the laps are made on the opener and mixed on the intermediate scutcher in the proportion required. By these means a better mixing is obtained than if the laps are put on the finishing scutchor only. Individual experience is the guide to a thorough comprehension of this department of spinning, and beyond enunciating these general principles no aid can be given to the student which is likely to be of value. The actual condition of even the same class of cotton, in different seasons, varies so largely that a mixture which is valuable one season is unsuitable in the next.