The Story of the Cotton Plant Part 9

It is at this stage that the bulk of the heavier impurities still found in the cotton are removed, as these fall through certain grids below the taker-in immediately they are loosened from the retaining fibres by the powerful teeth of the taker-in.

The great bulk of the cotton fibres, however, are retained by the teeth of the taker-in and carried round the under side to a point where they are exposed to the action of the central and most important part of every Carding Engine, viz., the main "cylinder." The licker-in contains about twenty-eight teeth per square inch, but the "cylinder" is the first of the parts that the cotton arrives at, previously referred to as being covered with a vast number of closely set steel wire teeth.

Just to convey an idea of this point to the uninitiated reader, it may be said that it is quite common to have on the "cylinder" as many as 600 steel wire teeth in one square inch. For a cylinder 40 inches wide and 50 inches diameter, this works out to the vast number of over 3,800,000 steel wire teeth on one cylinder, each tooth being about 1/4 inch long, and secured in a cloth or rubber foundation before the latter is wound round the cylinder.

The steel teeth of the cylinder strip the fibres from the taker-in and carry them in an upward direction, the surface speed of the cylinder being over 2000 feet per minute.

Placed over the cylinder, and extending for nearly one-half of its circ.u.mference, are what are technically known as the "flats."

These are narrow iron bars, each about 1-3/8 inches wide; each being covered with steel wire teeth in the same manner as the cylinder; and each extending right across the width of the cylinder, and resting on a suitable bearing termed the "bend."

They are formed into an endless chain containing about 108 "flats," but only about 44 of which are in actual work at one time; this endless chain of flats being given a slow movement of about 3 inches per minute.

Here it may be said that the various working parts are set as close as possible to each other without being in actual contact, the usual distance being about 1/143rd of an inch determined by a specially constructed gauge, in the hands of a skilled workman.

The steel teeth of the flats, being set very close to those of the cylinder, catch hold of and retain a portion of the short warty fibres and fine impurities that may be on the points of the cylinder teeth, the amount of this reaching about 3 per cent. of the cotton pa.s.sed through the machine. In addition to this the teeth of the flats work against those of the cylinder so as to exercise a combing action on the cotton fibres.

Having pa.s.sed the "flats," the cotton is deposited by the cylinder on what is termed the doffer. This is a cylindrical body, exactly similar to the main "cylinder" excepting that it is only about half the diameter, say 24 inches. Its steel wire teeth are set in the opposite way to those of the cylinder, and its surface speed is only about 75 feet per minute. These two circ.u.mstances acting together enable it to take the cotton fibres from the main cylinder.

The operations of carding may now be said to be practically performed, as the remaining operations have for their object the stripping, collecting, and guiding of the cotton into a form suitable for the next succeeding processes. The fleece of cotton is stripped from the doffer by the "Doffer Comb," which is a thin bar of steel, having a serrated under edge, and making about 1600 beats or strokes per minute. From this point cotton is collected into the form of a loose rope or "sliver," and pa.s.sed first through a trumpet-shaped mouth, and then through a pair of calender rollers about six inches wide and four inches in diameter.

Image: FIG. 16.--Lap, web, and sliver of cotton.

Finally, the sliver of cotton is carried upward, as shown in the ill.u.s.tration (Fig. 15), and pa.s.sed through special apparatus and deposited into the can, also shown. This latter is about 10 inches in diameter and 36 inches in length, and the whole arrangement for depositing the cotton suitably into the can is denominated the "Coiler."

In the next ill.u.s.tration (Fig. 16) are shown three forms in which the cotton is found before and after working by the Carding Engine. That to the left is the lap as it enters, the middle figure is part of the web as it comes from the doffer, and that to the right is part of a coil of cotton from the can.

Such is a brief description of the most important of the preparatory processes of cotton spinning. There are innumerable details involving technical knowledge which fall outside the province of this story.

=Drawing Frames.=--It is a very common thing for a new beginner in the study of cotton spinning to ask--what is the use of the drawing frame?

As a matter of fact, the unpractised eye cannot see any difference between the sliver or soft rope of cotton as it reaches, the drawing frame and as it leaves the frame.

The experienced eye of the practical man can, however, detect a wonderful difference.

It has been shown that the immediately preceding operation of carding--amongst other things--reduces the heavy lap into a comparatively thin light sliver; thus advancing with one great stride a long way toward the production of the long fine thread of yarn ready for the market.

No such difference can be perceived in the sliver at the drawing frame.

This machine is practically devoted to improving the thread finally made in two distinct and important ways.

1. The fibres of cotton in the sliver, as they leave the Carding Engine, are in a very crossed and entangled condition, not at all suited to the production of a strong yarn by the usual processes of cotton spinning.

The first duty of the drawing frame may be said, therefore, to be the laying of the fibres in parallel order to one another, by the action of the drawing rollers.

2. The sliver of cotton, as it leaves the card, is by no means sufficiently uniform in weight per yard for the production of a uniform and strong finished thread. It will easily be conceived by the readers of this story of the cotton plant that the strength of any thread is only that of its weakest portions.

Take a rope intended to hold a heavy weight suspended at its lower end, and a.s.sume it to be made of the best material and stoutest substance, but to contain one very weak place in it; this rope would practically be useless, because the strength of the rope would only be that of the weakest part.

The drawing machine in cotton spinning aims at removing the weak places in cotton thread, thus making the real strength of the thread vastly greater than it would otherwise be.

The method by which these important objects are attained may be briefly explained as follows:--

From four to eight, but most usually six, cans of sliver from the previous machine are placed behind the frame, and the ends of the slivers conducted over special mechanism within the range of action of four pairs of drawing rollers. This pa.s.sage of the cotton is shown very clearly in Fig. 17.

The top rollers are made of cast iron, covered with soft and highly finished leather made from sheepskins, the object of this being to cause the rollers to have a firm grip of the cotton fibres, without at the same time injuring them. The bottom rollers are of iron or steel, made with longitudinal flutes or grooves, in order to bite the cotton fibres firmly on the leathers of the top rollers. In order to a.s.sist the rollers in maintaining a firm grip of the fibres the top rollers are held down by somewhat heavy weights.

The action of the drawing rollers will be adequately discussed later in this story, when dealing with the inventions of Lewis Paul and Sir Richard Arkwright, and need not be enlarged upon at this stage.

It will be sufficient, therefore, to say that, a.s.suming that six slivers are put up together at the back of the frame, the "draft" or amount of drawing-out between the first and second pairs of rollers the cotton comes to, may be about 1.3, between the second and third pairs 1.8, and between the third and fourth pairs 2.6. These three multiplied together give a total draft of slightly over 6.

In other words, a.s.suming that 1 inch of cotton be pa.s.sed through the first pair of rollers, the second pair will immediately draw it out into 1.3 inches; the third pair will draw out the same portion of cotton into 1.3 1.8 inches = 2.34 inches, and the fourth or last pair of rollers will draw out the same portion of cotton into 2.34 2.6 inches = 6.084.

Image: FIG. 17.--Drawing frame showing eight slivers entering and one leaving the machine.

The six slivers put up at the back are therefore drawn out or attenuated to the dimensions of one by the rollers, and then at the delivery side of the machine the six slivers are united into one sliver, and arranged in beautiful order inside a can exactly as described for the Carding Engine.

Now it is in the doubling together and again drawing-out of the slivers of cotton that the two objects of making the fibres parallel and the slivers uniform are effected.

In the first place, even the uninitiated readers of this story may conceive that the combining of six slivers will naturally cause any extra thick or thin places in any of the individual slivers to become much reduced in extent by falling along with correct diameters of the other five slivers; and experience proves that such is the actual fact.

In this way the slivers, or soft untwisted ropes of cotton, are made uniform.

It is perhaps not so easy to see how it is that drawing rollers make the fibres of cotton parallel. As a matter of fact, it may be said that as each pair of rollers projects the fibres forward, the next pair of rollers takes hold of the fibres and draws their front extremities forward more rapidly than the other pair will let the back extremities of the same fibres pa.s.s forward. It is this action often repeated that draws the fibres straight, or in other words, reduces them to a condition in which they are parallel to each other.

It is the usual practice to pa.s.s each portion of cotton through three separate frames in this manner, in immediate and rapid succession. The "slivers" or ropes of cotton made at the front of the first drawing frame, would be placed in their cans behind a second drawing frame and the exact process just described would be repeated. The same identical process would usually be performed yet a third time in order to secure the required objects with what is considered a sufficient degree of perfection.

After this the cotton is usually deemed to be quite ready for the immediately succeeding process of "slubbing."

=Bobbin and Fly Frames.=--The series of machines now to be dealt with, are distinguished more for their complicated mechanism in putting twist into the attenuated cotton and in winding it upon bobbins in suitable form for the immediately succeeding process, than for the action of the parts upon the cotton so as to render it better fitted for the production of strong, fine yarn.

The manner in which these machines perform a part in the actual production of a thread or yarn is practically a repet.i.tion of the work of the drawing frame, with the great difference that the strand or thin rope of cotton leaves each machine of the series in a thinner and longer condition than when it arrived.

This attenuation of the cotton roving is indeed the chief desideratum that bobbin and fly frames aim at, although they a.s.sist in making the strand of cotton more uniform by carrying still further to a limited extent the doubling principle so extensively utilised at the drawing frames.

The basis of the operations are again the drawing rollers, brought to such a state of perfection by Richard Arkwright, and here it may be useful to remind the readers of this story how superior in this respect of general adaption Arkwright's method of spinning was to that of Hargreaves'. It will be remembered that the latter named inventor utilised a travelling carriage, for drawing the cotton finer, while the former performed the same work by drawing rollers.

Although the travelling carriage principle was at one time somewhat largely utilised in preparing the rovings for the final process of spinning, it has long since entirely given way before the superior merits and adaptability of the drawing roller principle; and it is now this latter method which is universally employed.

It usually takes three bobbin and fly frames to make up what may be called a "set," each portion of the cotton roving pa.s.sing through the three machines in succession. For low cla.s.ses of yarn only two of these machines may be used, while for the finest yarns there are sometimes four used to make up the "set."

Of course, all the readers of this story must understand that in an ordinary-sized cotton spinning mill there will be many sets of these machines, just as there will be a large number of "carding engines" and "drawing frames," and mules. Bale brakers, openers and scutchers are so very productive that only a limited number is required as compared with the other machines already named.

Those of our readers who have studied the details of Arkwright's spinning frame, described in another chapter in this book, and have understood those details, will have a clear comprehension of the action of the parts and leading mechanical principles concerned in the operations of a modern bobbin and fly frame. Certainly there are some of the most difficult problems of cotton spinning involved in the mechanism of these machines, but these points are so highly technical that it is not intended to introduce them here.

The "set" of machines just named are usually known by the names "Slubber," "Intermediate or Second Slubber," and "Roving" Frames.

Nearly all the operations and mechanisms involved in one are almost identical in the others, so that a description of one only in the set is necessary, merely explaining that the parts of each machine the cotton comes to in the latter two of the set are smaller and more finely set than the corresponding parts of the immediately preceding machine.

Taking the Intermediate frame as a basis, the operation may be described as follows:--The bobbins formed at the slubbing frame are put in the creel of the Intermediate, as shown in the photograph (Fig. 18), each bobbin resting on a wooden skewer or peg which will easily rotate.