(13) As the question of driving is a somewhat important one a few remarks may be made on it. There is no doubt that toothed gearing properly constructed forms the most economical method, the loss of power in transmission not exceeding 21⁄2 per cent. In constructing wheels for this purpose care should be taken that the tooth is not too long, 5⁄8ths of the pitch being a sufficient length. Next to toothed wheels for economy belts may be placed. The loss in transmission varies, if the belts are properly applied, from three to five per cent. A good speed for leather belts is 3,000 feet per minute if they are single, and 4,000 feet if double. Rope driving is the least economical of the three methods, this arising from a variety of causes. Chief among these is the difficulty of maintaining an equal diameter in every rope of the series, which leads to a difference in their driving power, owing to their unequal engagement with the V grooves. Another cause of this loss of power is found in the fact that they jam in the grooves and have to be forcibly extracted as the pulleys revolve. The following rules laid down by Mr. Alexander Rea in a discussion, at a meeting of the Manchester Association of Engineers, on the subject of the comparative merits of the three systems of driving, are worth reproducing.
“The ropes should not be too large in diameter; it is much safer to use 25 13⁄4 inch ropes than 20 2 inch diameter ropes. The tension in the several ropes should be kept as low as possible. The power should be subdivided to different points. The centres of the several shafts should be kept well apart. The pulleys should be large in diameter. The best speed for the ropes is from 4,000 to 6,000 feet per minute. Care should be taken in turning the V groove pulleys; the best angle for these is now found to be 45 degrees.”
(14) As this subject of rope driving is an interesting one, it is worth noting that Mr. George Goodfellow, of Hyde, who has had a wide experience in this matter, confirms the advice as to small diameter of ropes. In the same discussion he stated that he did not now use larger diameters than 13⁄4 inch, and had ropes running successfully, the diameter of which was only 11⁄4 inches. Mr. James Hartley also bore out this experience. By the reduction of ropes from 2 inches to 11⁄4 inches diameter the friction diagram from the engine had been materially reduced, indicating a saving of power. Mr. J. H. Ratcliffe, of Dukinfield, has recently revived a method by which, instead of using a series of ropes, he uses one only, this being endless, and being wrapped spirally on the pulleys. At one point the slack is taken up by a compensating apparatus, so that the whole of the coils are tight back and front instead of having one side slack and bellying. For this arrangement Mr. Ratcliffe claims that it materially reduces the friction diagram, inasmuch as there is no necessity to drag the rope forcibly out of the grooves at each revolution. It is not necessary for a detailed examination of this subject to be made, but the hints given will probably prove useful to many readers.
(15) It is essential, owing to the peculiar structure of the cotton fibre, to which reference will be made in the next chapter, that the rooms in which spinning is conducted should be heated to a certain temperature. Closely allied to this question is that of humidification. It is not only essential to have heat, but that must be accompanied by a certain amount of moisture, a point which is often neglected. Spinning rooms are often heated to over 90° F., which is quite unnecessary, and is, moreover, detrimental to good work. At such a temperature much of the natural moisture of the cotton is extracted, and the fibre becomes harsh and brittle. A temperature of from 75° to 80° F., with a humidity of about 75 percent, is absolutely the best condition for spinning. The question is an important one, and deserves greater consideration at the hands of spinners. The artificial heat required is now obtained by the use of wrought-iron steam pipes, through which high-pressure steam is passed. The radiation from these is much greater than from cast-iron pipes of larger diameter filled with low-pressure steam.
(16) Having thus briefly glanced at some of the chief features of modern practice, it is now only necessary to say that the utmost cleanliness is absolutely essential to good working. The manipulation of the cotton is now so largely automatically performed that there is much less difficulty in keeping a mill clean than formerly. It should be the aim of every spinner to diminish the handling of the material as much as possible, and students of this subject should remember that it is never too early to begin to deal with the cotton so as to prepare it for subsequent treatment. Efficient purification at an early stage is a great help towards economical and efficient spinning. In conclusion, it may be remarked that one of the worst faults in studying a subject of this sort is any kind of crystallised thought. The conditions of work vary from day to day, and there are wise variations in procedure which can easily be discovered by the observant mind. This watchful attitude is the proper one to cultivate, and the succeeding pages are written in the hope that they will lead some reader to a deeper and closer observation of the facts which are discoverable in the actual work of construction or spinning.
CHAPTER II.
THE STRUCTURE OF COTTON.
(17) The cotton plant is indigenous to many tropical countries, in which it is often found in a wild state. The product of the wild plant is, however, quite unsuitable for manufacturing purposes, and, even in cases where cotton is produced by cultivation, the value of the fibre varies very largely. Into the question of the growth and structure of the fibre it is not necessary to go in detail, as this is a subject which has a literature of its own. The student who is desirous of obtaining a thorough knowledge of the subject can find it fully treated in the “Structure of the Cotton Fibre,” by Dr. Bowman, and in a recent work by Mr. Hugh Monie, jun., of Glasgow. It will suffice for present purposes to state briefly the characteristics of cotton, which are of essential importance in its subsequent treatment mechanically. The cotton fibre is a hollow tube of cellular construction, and is of an oval or flattened cylindrical shape. Ripe or fully matured fibres of the best cotton are convoluted or spirally twisted on their axis, and the edge of such a fibre presents a corrugated appearance. The regularity of the convolutions, or twists, is greatest in the highest class of cotton, and reaches its lowest point in the poorer grades. One important effect of such a formation is that each fibre naturally tends to coil round its neighbour, and thus lends itself to spinning. The outer sheath of each fibre is apparently continuous, and the diameter is greater at the end which is attached to the seed. The diameter of the fibre varies from 1⁄1562 of an inch in the case of Sea Island cotton, to 1⁄1185 of an inch in Indian cotton. In length a similar variation is observable, reaching a mean of 1·8 inch in Sea Island, and being as low as 0·8 inch in Indian cotton. The length of the fibres in any particular class of cotton is known as the “staple,” and this is one of the chief commercial merits of the better kinds. The strength of cotton fibres varies very materially, and on the authority of Mr. Charles O’Neill, of Manchester, the order in which the various classes ought to be placed is as follows:—Surat (Comptah), New Orleans, Queensland, Surat (Dhollerah), Pernambuco, Egyptian, Maranham, Upland, Sea Island. It does not necessarily follow that the possession of greater strength by one class of fibre over another involves an advantage, for the greatest strength is possessed by a fibre which is the most deficient in regularity of the convolute form and length, which are much more important than strength. Again, the diameter of Comptah cotton is much greater than that of longer stapled varieties, and this is important in determining the value to be placed upon the strength. Viewed in this light, Egyptian cotton is the strongest, and this fact, in conjunction with certain other qualities to which attention will afterwards be called, renders it of high value. It only remains to be said that a waxy covering is found on the outside of each fibre, which requires to be softened by heat during spinning so that the flexibility of the fibre may be fully maintained. Where it is intended to dye fabrics it is necessary to remove the whole or the greater part of this wax, and so permit the dye to penetrate the fibre. Having briefly indicated the chief characteristics of the cotton fibre, a detailed account of some of the principal varieties may now be given.