CHAPTER XI
THREAD AND COTTON FINISHING
=Thread.= In general a twisted strand of cotton, flax, wool, silk, etc., spun out to considerable length, is called thread. In a specific sense, thread is a compound cord consisting of two or more yarns firmly united by twisting. Thread is used in some kinds of weaving, but its principal use is for sewing, for which purpose it is composed of either silk, cotton, or flax. Thread made of silk is technically known as sewing silk; that made of flax is known as linen thread; while cotton thread intended for sewing is commonly called spool cotton. These distinctions, while generally observed by trade, are not always maintained by the public.
The spool cotton of to-day is of a different grade from that made before the sewing machine came into general use. The early thread was but three cord, and contained such a large number of knots, thin places, etc., that it could not be worked satisfactorily on the machines, so manufacturers were called upon to produce a thread that would be of the same thickness in every twist. This was effected by making the thread of six cords instead of three, thereby producing a smoother and more uniform strand.
=Manufacturing Processes.= The raw cotton for the manufacture of thread must be of long staple. If the fiber is short the thread made of it will be weak, and hence unsuited for the purposes required of it. Ordinary cotton is not adapted to the manufacture of the better grades of spool cotton on account of the shortness of its fiber. Egyptian and Sea Island cotton are used because they have a much longer fiber and are softer in texture. The raw cotton comes to the factory packed in great bales, and is usually stored away for some months before it is used. The first step in the conversion of the bale of cotton into thread consists in giving the fiber a thorough cleaning. This is accomplished by feeding it to a series of pickers which pull the matted locks and wads to shreds, beat out the dirt and seeds, and roll the cotton in the form of batting upon cylinders until it issues from the finisher lap machines as a downy roll or lap.
The lap of cotton then goes to the carding rooms, where it is combed into parallel fibers by means of a revolving cylinder covered with fine wire teeth, sometimes 90,000 of them to the square foot. On leaving the carding machines the lap has become a gossamer-like web thirty-nine inches broad. This web is next passed through a small "eye" which condenses it into a narrow band about an inch in width, known as the sliver. By this time the fiber has been so drawn out that one yard of the original lap has become 360 yards of the sliver. The sliver now looks almost perfect, but if it were spun it would not make good thread. It is necessary to lay every fiber as nearly parallel as possible, so that there will be an equal number of fibers in the strand per inch. Besides this, the remaining dirt and short fibers must be removed and the knots and kinks in the fibers straightened out. To accomplish these objects the cotton must be "combed." First, the slivers are passed through several sets of rollers, each set moving faster than the preceding, so that the strands are drawn out fine and thin. In this condition the cotton passes to a doubling frame, and from thence to the lapping frame, a device combining six laps into one and drawing the whole out into one fine, delicate, ropy lap.
The comber now takes the lap and combs out all the impurities and short fibers, at a sacrifice of about one-fifth of the material; next, it combines six of these fluffy combed rolls of fiber into one. A number of these rolls are then drawn out by another machine twelve times as long as they were before and twisted together on a slubbing frame. This last drawing reduces the roll to about the thickness of zephyr yarn. After being further doubled and twisted, the yarn, or roll, is ready for the mule spinner, which accomplishes by means of hundreds of spindles and wheels what the housewife once did with her spinning wheel. The mule, however, does the work of more than 1,000 hand spinners and takes up much less space. On this machine 900 spindles take the yarn from 1,800 bobbins, and by means of accelerating rollers and a carriage draw out and twist it to the proper fineness for the size of thread wanted. Having passed through the complex processes of cleansing, combing, drawing, and spinning, the cotton is now in the form of yarn of various sizes, and the real work of thread making, which is a distinct art from yarn making, begins.
The thread-making process is briefly as follows: The yarn is doubled and twisted; then three of such yarns are twisted together, which give the six-fold combination for six-cord thread. For a three-cord thread three yarns are twisted together. After the twisting is completed the thread is reeled into skeins having a continuous length of 4,000 to 12,000 yards, according to the size, and is then sent to the examining department where it is rigidly inspected. Every strand is looked over, and any found to be defective are laid aside, so that when the thread is put on the market it shall be as perfect as care and skill can make it.
At this stage of the work the skeins of thread are of the pale cream color common to all unbleached cotton goods, and are technically known as "in the gray." They therefore have to be bleached pure white or dyed in fast colors. The skeins, whether intended for white or colored thread, are first placed in large, steam-tight iron tanks and boiled. Here the thread remains subjected to a furious boiling for six or seven hours; when removed it is perfectly clean, but still retains the brownish gray color of unbleached cotton. It then goes into a bath of chloride of lime and is bleached as white as snow. The skeins are next drawn through an acid solution to neutralize the chloride. Another boiling, another bleaching, a bath of soapsuds, and the final rinsing, complete the cleansing and whitening process. Those skeins intended for colored threads are taken to the dyeing room and placed in tanks filled with suitably prepared dyeing solutions.
From the bleaching and dyeing departments the skeins of thread go back to the mill to be wound on the bobbins, and from the bobbins finally on the small wooden spools. The automatic winding machines can be regulated to wind any given number of yards. The small spools are fastened on pivots, the thread from the bobbins fastened on the spools, and the machines set in motion. At the required number of yards the spools stop revolving. The ordinary spool of cotton thread contains 200 yards, and when this has been wound on, the thread is cut with a knife by an attendant, who also cuts the little nick in the rim of the spool and fastens therein the end of the thread. Thread mills commonly print their own labels, and these are affixed to the spools by special machinery with remarkable rapidity. From the labeling machine the spools go to an inspector, who examines each one for imperfections, and any that are found faulty are discarded. When packed in pasteboard boxes or in cabinets the thread is ready for market.
=Thread Numbers.= Spool cotton for ordinary use is made in sizes ranging from No. 8 coarse to No. 200 fine. In cotton yarn numbering, the fineness of the spun strand is denoted by the number of hanks, each containing 840 yards, which are required to weigh one pound, as illustrated in the following table:
When 1 hank of cotton yarn ( 840 yds.) weigh 1 lb. it is No. 1 " 10 " " " " ( 8,400 yds.) " " " " 10 " 16 " " " " (13,440 yds.) " " " " 16 " 30 " " " " (25,200 yds.) " " " " 30 " 50 " " " " (42,000 yds.) " " " " 50 " 100 " " " " (84,000 yds.) " " " " 100
The early manufactured thread was three cord, and took its number from the size of the yarn from which it was made. No. 60 yarn made No. 60 thread, though in point of fact the actual caliber of No. 60 thread would equal No. 20 yarn, being three No. 60 strands combined together. When the sewing machine came into the market as the great consumer of thread, spool cotton had to be made a smoother and more even product than had previously been necessary for hand needles. This was accomplished by using six strands instead of three, the yarns being twice as fine. As thread numbers were already established, they were not altered for the new article, and consequently at the present time No. 60 six-cord, for example, and No. 60 three-cord are identical in size, though in reality No. 60 six-cord is formed of No. 120 yarns. It is relatively smoother, more even, and stronger than the three-cord grade. All sizes of six-cord threads are made of six strands, each of the latter being twice as fine as the number of the thread as designated by the label. Three-cord spool cotton is made of three strands of yarn, each of the same number as the thread.
=Sizing.= In textile manufacturing, sizing is the process of strengthening warp yarns by coating them with a preparation of starch, flour, etc., in order that they may withstand the weaving process without chafing or breaking. The operation of sizing is also often resorted to in finishing certain classes of cotton and linen fabrics, which are sized or dressed with various mixtures in order to create an appearance of weight and strength where these qualities do not exist, or, if present, only in a small degree. The object in sizing warp yarn before weaving is to enable that process to be performed with the minimum of threads breaking. Judicious sizing adds to the strength of the yarn by filling up the spaces between the fibers, and by binding the loose ends on the outside of the thread to the main part. In order to accomplish this a number of ingredients are used in the size preparation, as no single material used alone gives satisfactory results. The filling up of the minute spaces in the yarns and the adhesion of the fibers produce a smooth thread with sufficient hardness to resist the continual chafing of the shuttles, reeds, and harnesses during the process of weaving. Flour and starch in a liquid state are used for this purpose, but owing to the liability to mildew, flour is not so much used as starch. Both of these materials, however, make the yarn brittle, and other ingredients are combined with them to overcome the brittleness. For a softener on heavy weight goods nothing has been found superior to good beef tallow. On light-weight goods the softener giving the most general satisfaction is paraffin.
When properly made the size preparation is a smooth mass of uniform consistence, free from lumps of any kind, and from all sediment and odor. Starch--the principal material which gives body to any size--requires the most careful treatment. It is first mixed with cold water into a smooth, creamy milk, which is slowly poured into the necessary quantity of boiling water until a clear, uniform paste is formed. Then the softeners are added, such as soaps, oils, and animal fats; next a small amount of gelatine or glue is stirred in and some form of preservative, usually chloride of zinc or salicylic acid. The mass is then thoroughly stirred in tilted jacketed kettles with mechanical stirrers. The size may be applied to the yarn either hot or cold. When applied hot it penetrates into the interior, filling up every space between the fibers, binding all together, and forming a hard coating on the surface of the thread. A thorough washing or steaming serves to remove all the size from the woven fabric.
=Cotton Finishing.= Cotton fabrics, like other textiles, after leaving the loom must be subjected to various finishing processes so as to bring them into commercial condition. On piece-dyed goods part of the finishing is done before and part after the dyeing process. Each class of fabrics has definite finishing processes. In some cases weighting materials are added to the fabric so as to hide more or less its actual construction. Cotton fabrics just from the loom present a soft and open structure, more so than other textiles. Therefore it is necessary to use proper finishing materials and processes which will fill up the openings or interstices as produced in the fabric by the interlacing of warp and filling, and at the same time give to the fabric a certain amount of stiffness. Of course this finish will disappear during wear or washing, it having been imparted to the fabric to bring the latter into a salable condition.
Cotton fabrics after weaving may be subjected to the following sub-processes of finishing:
Inspecting, Burling and Trimming, Bleaching, Washing, Scutching, Drying.
After the cloth leaves the loom it is brushed; then it passes over to the inspection table in an upward receding direction, so that the eye of the operator can readily detect imperfections. The ends of two or more pieces as coming from the loom are sewed into a string for convenient handling in the bleaching.
=Bleaching.= The object of bleaching is to free the cotton from its natural color. The ancient method of bleaching by exposure to the action of the sun's rays and frequent wetting has been superseded by a more complicated process involving the use of various chemicals. Pieces of cloth are tacked together (sewed) to form one continuous piece of from three to one thousand yards in length. The cloth is next passed over hot cylinders or a row of small gas jets to remove all the fine, loose down from the surface. The goods are then washed and allowed to remain in a wet condition for a few hours, after which they are passed through milk of lime under heavy pressure, followed by rinsing in clear water. The goods are next "scoured" in water acidulated with hydrochloric acid, and boiled in a solution of soda, then washed as before in clear water. Next they are chlorined by being laid in a stone cistern containing a solution of chloride of lime and allowed to remain a few hours. This operation requires great care in the preparation of the chloride of lime, for if the smallest particle of undissolved bleaching powder is allowed to come in contact with and remain upon the cloth it is liable to produce holes. The goods are then boiled for four or five hours in a solution of carbonate of soda, after which they are washed. They are again chlorined as before and washed. The long strips are finally scoured in hydrochloric acid, washed, and well squeezed between metal rollers covered with cloth. After squeezing and drying, the cloth, if required for printing, needs no further operation, but if intended to be marketed in a white state, it must be finished, that is, starched or calendered.
=Starching.= The starch is applied to the cloth by means of rollers which dip into a vat containing the solution, while other rollers remove the excess. Sometimes the cloth is artificially weighted with fine clay or gypsum, the object being to render the cloth solid in appearance.
=Calendering.= The cloth is now put through the calendering machine, the object of which is to give a perfectly smooth and even surface, and sometimes a superficial glaze; the common domestic smoothing iron may be regarded as a form of a calendering utensil. The cloth is first passed between the cylinders of a machine two, three, or four times, according to the finish desired. The calender finishes may be classed as dull, luster, glazed, watered or moire, and embossed. The calender always flattens and imparts a luster to the cloth passed through it. With considerable pressure between smooth rollers a soft, silky luster is given by equal flattening of all the threads. By passing two folds of the cloth at the same time between the rollers the threads of one make an impression upon the other, and give a wiry appearance. The iron rollers are sometimes made hollow for the purpose of admitting steam or gas in order to give a glaze finish. Embossing is produced by passing the cloth under heated metal rollers upon which are engraved suitable patterns, the effect of which is the reproduction of the pattern upon the surface of the cloth.
=Mercerizing.= This is a process of treating cotton yarn or fabrics with caustic soda and sulphuric acid whereby they are made stronger and heavier, and given a silky luster and feel. The luster produced upon cotton is due to two causes, the change in the structure of the fiber, and the removing of the outer skin of the fiber. The swelling of the fiber makes it rounder, so that the rays of light as they fall upon the surface are reflected instead of being absorbed. The quality and degree of luster of mercerized cotton fabrics depends largely upon the grade of cotton used. The long-staple Egyptian and Sea Island cotton, so twisted as to leave the fibers as nearly loose and parallel as possible, show the best results. If the yarn is singed the result is a further improvement. Yarns and fabrics constructed of the ordinary grades of cotton cannot be mercerized to advantage. The cost of producing high-grade mercerized yarn is about three times that of an unmercerized yarn of the same count, spun from the commoner qualities of cotton.
Mercerized yarn is employed in almost every conceivable manner, not only in the manufacture of half-silk and half-wool fabrics, and in lustrous all-cotton tissues, but also in the production of figures and stripes of cotton goods having non-lustrous grounds. Mercerized yarn used in connection with silk is difficult to detect except by an expert eye.
=Characteristics of a good piece of Cotton Cloth.= A perfect cotton fiber has little convolutions in it which give the strong twist and spring to a good thread. In this respect the Sea Island cotton is the best. There are five things requisite for cotton cloth to be good, viz.:
1. The cloth must be made of good fiber, that is ripe and long.
2. The fiber must be carefully prepared. All the processes must be well performed--for the very fine thread fiber must be combed to remove poor fiber. The combing, however, is not always done.
3. The warp and woof threads must be in good proportion.
4. The cloth must be soft, so that it will not crease easily.
5. It must be carefully bleached--the chemicals used must not be strong.