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.





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