The Dyeing of Woollen Fabrics Part 3

Articles of all kinds can be bleached by simply placing them in a weak solution of the peroxide, leaving them there for a short time, then taking out and exposing to the air for some time. The best plan of applying peroxide of hydrogen is the following: Prepare the bleaching bath by mixing 1 part of peroxide with 4 parts of water. The strength can be varied; for those goods that only require a very slight bleach the proportions may be 1 to 12, while for dark goods the proportions first given may be used. This bath must be used in either a wooden or earthenware vessel. Metals of all kinds must be avoided, as they lead to a decomposition of the peroxide, and therefore a loss of material.

To the bath so prepared just enough ammonia should be added to make it alkaline, a condition that may be ascertained by using a red litmus paper, which must just turn blue. Into the bath so prepared the well-scoured goods are entered and worked well, so that they become thoroughly saturated. They are then lightly wrung and exposed to the air for some hours, but must not be allowed to get dry, because only so long as they are moist is the bleaching going on; if they get dry the goods should be re-entered into the bath and again exposed to the air.

If one treatment is not sufficient the process should be repeated. The peroxide bath is not exhausted, and only requires new material to (p. 036) be added to it in sufficient quant.i.ty to enable the goods to be readily and easily worked in the liquor. Any degree of whiteness may be obtained with a sufficient number of workings. No further treatment is necessary. It is found in practice that an alkaline bath gives the best results.

Another plan of preparing the bleaching bath is to prepare a bath with peroxide and water as before, then add to a sufficient quant.i.ty of a solution of silicate of soda 4 parts of water to 1 of silicate of soda at 100 Tw., to make the bath alkaline. Into this bath the goods are entered and are then exposed to the air as before, after which they may be pa.s.sed through a weak bath of sulphurous acid, being next well washed in water and dried.

The advantage of bleaching with peroxide is that, as it leaves only water in the goods as the result of action, there is no danger of their becoming tendered by an after development of acid due to defective washing, as is the case with the sulphur bleach. The goods never alter in colour afterwards, because there is nothing left in that will change colour. Some bleachers add a little magnesia to the bath, but this is not at all necessary.

#Bleaching with Peroxide of Soda.#--Peroxide of soda has come to the front of late for bleaching wool. With it a stronger bleaching bath can be made, while the product itself is more stable than peroxide of hydrogen, only it is needful to keep it in tightly closed metal vessels, free from any possibility of coming in contact with water or organic matter of any kind, or accidents may happen. In order to bleach 100 lb. of wool, a bath of water is prepared, and to this is added 6 lb. of sulphuric acid and then slowly 4 lb. of peroxide of sodium in small quant.i.ties at a time. Make the bath slightly alkaline by adding ammonia. Heat the bath to 150 F., enter the wool and allow to remain five to six hours, then rinse well and dry. If the (p. 037) colour does not come out sufficiently white repeat the process.

THE CHLORINATION OF WOOL.

The employment of chlorine in wool dyeing and wool printing has of late years received an impetus in directions previously little thought of. The addition of a little chlorine to the decoction of logwood has been recommended as increasing the dyeing power of the wool. Treating the wool with chlorine has a material influence in increasing its capacity for taking dye-stuffs, and although but little attention has been paid to this circ.u.mstance by wool dyers, yet among wool printers it has come largely into use, and enables them to produce fuller and faster shades than would otherwise be possible.

The method involves the treatment of the wool first with an acid, then with a solution of a hypochlorite. The staple becomes soft and supple and a.s.sumes a silky character; in dyeing it shows a greater affinity for the dyes than it did previously. Although not deteriorated in strength, it almost entirely loses its felting properties. On account of this feature the process cannot be adopted for wool which has to be fulled, but it is of service where felting of the goods is to be avoided, for worsteds, underwear, woollen and half woollen hosiery, etc., in which the felting property that occurs on washing is rather objectionable.

By the chloring of the wool the intensity of the shade dyed is increased to such a degree that when dyeing with Acid black, Naphthol black, Naphthol green, Nigrosine, Fast blue, Water blue, and some others dyed in an acid bath, but little more than half the dye used on unchlored wool is required, while with Induline, more even and intense shades are obtained than is otherwise possible.

The operation of chlorination can be done either in one or two (p. 038) baths. The choice depends upon circ.u.mstances and the judgment of the dyer. The process by the two-bath method, with subsequent dyeing in the second or separate bath is (for 100 lb. of wool), as follows. The first bath contains, for light cloths, yarn, etc., from 3 to 4 lb.

sulphuric acid, 168 Tw., and for heavier cloths and felt, where the penetration and equalisation of the colour is difficult, from 8 lb. to 10 lb. of acid. Generally speaking, a temperature of 170 to 175 F.

is sufficient, although for heavy wool and for wool with poor dyeing qualities it is well to use the bath at the boil. The treatment lasts for half an hour, in which time the acid is almost completely absorbed.

The second bath contains a clear solution of 10 lb. bleaching powder, which solution is prepared as follows. Dry bleaching powder of the best quality is stirred in a wooden vat with 70 gallons of water, the ma.s.s is allowed to stand, the clear, supernatant liquor is run into the vat and the sediment stirred up and again allowed to settle, the clear liquor being run off as before, and 5 gallons more water is run in. The clear liquors of these three treatments are then mixed together to form the chloring bath. Special care should be taken that no undissolved particles of the bleaching powder should be left in, for if these settle on the wool they result in too great a development of chlorine, which injures the wool.

The goods after being in the acid bath are entered in this chlorine bath at a temperature of 70 F., which is then raised to the boil. If the acid bath has been strong, or been used at the boil, it is perhaps best to rinse the goods before entering into the chlorine bath. The hypochlorous acid disappears so completely from this bath that it may at once be used as the dye-bath, for which purpose it is only necessary to lift the goods, add the required amount of dye-stuff, re-enter the goods and work until the bath is exhausted, which generally happens when acid dyes are used. If a separate dye-bath be preferred, this is (p. 039) made and used as is ordinarily done.

To perform all the operations in one bath the acid bath is made with from 3 to 4 lb. sulphuric acid, and the wool is treated therein for thirty minutes at 170 F., until all the acid has been absorbed. Then the bath is allowed to cool down to 70 or 80 F., the clear bleaching powder solution is added, the goods are re-entered, and the bath is heated to the boil. When all the chlorine has disappeared add the dye-stuff, and dye as directed above.

In printing on wool the chlorination of the wool is a most important preliminary operation. For this purpose the cloth is pa.s.sed for fifteen minutes at 170 F. through a bath containing 3/4 oz. sulphuric acid per gallon of water. Then it is pa.s.sed through a cold bath of 3/4 oz. bleaching powder per gallon of water, after which the cloth is rinsed and dried and is then ready for printing.

Another method of chloring the wool is to pa.s.s the goods through a bath made with 100 gallons of water, 2 gallons hydrochloric acid and 2 gallons bleaching powder solution of 16 Tw. As some chlorine is given off it is best to use this in a well-ventilated place.

CHAPTER III. (p. 040)

DYEING MACHINERY AND DYEING MANIPULATIONS.

Wool is dyed in a variety of forms, raw, loose wool; partly manufactured fibre in the form of slubbing or sliver; spun fibres or yarns, in hanks or skeins and in warps, and lastly in the form of woven pieces. These different forms necessitate the employment of different forms of machinery and different modes of handling, it is evident to the least un.o.bservant that it would be quite impossible to subject slubbing or sliver to the same treatment as yarn or cloth, otherwise the slubbing would be destroyed and rendered valueless.

In the early days all dyeing was done by hand in the simplest possible contrivances, but during the last quarter of a century there has been a great development in the quant.i.ty of dyeing that has been done, and this has really necessitated the application of machinery, for hand work could not possibly cope with the amount of dyeing now done.

Consequently there has been devised during the past two decades a great variety of machines for dyeing every description of textile fabrics, some have not been found a practical success for a variety of reasons and have gone out of use, others have been successful and are in use in dye-works.

#Hand Dyeing.#--Dyeing by hand is carried on in the simplest possible appliances, much depends upon whether the work can be done at the ordinary temperature or at the boil. Figure 10 shows round and oval tubs and a rectangular vat much in use in dye-houses. These are (p. 041) made of wood, but copper dye-vats are also made, these may be used for all kinds of material--loose fibre, yarns or cloth. In the case of loose fibre this is stirred about either with poles or with rakes, care being taken to turn every part over and over and open out the ma.s.ses of fibre as much as possible in order to avoid matting or clotting together. In the case of yarns or skeins, these are hung on sticks resting on the edges of the tub or vat. These sticks are best made of hickory, but ash or beech or any hard wood that can be worked smooth and which does not swell much when treated with water may be used. The usual method of working is to hang the skein on the stick, spreading it out as much as possible, then immerse the yarn in the liquor, lift it up and down two or three times to fully wet out the yarn, then turn the yarn over on the stick and repeat the dipping processes, then allow to steep in the dye-liquor. This is done with all the batch of yarn that is to be dyed at a time. When all the yarn has been entered into the dye-bath, the first stickful is lifted out, the yarn turned over and re-entered in the dye-liquor; this operation is carried out with all the sticks of yarn until the wool has become dyed of the required depth. In the case of long rectangular vats it is customary for two men, one on each side of the vat, to turn the yarns, each man taking charge of the yarn which is nearest to him.

[Ill.u.s.tration: Fig. 10.--Dyeing-tubs and Vat.]

Woven goods may be dyed in the tub or vat, the pieces being drawn in and out by poles, but the results are not altogether satisfactory, (p. 042) and it is preferable to use machines for dyeing piece goods.

[Ill.u.s.tration: Fig. 11.--Dye-vat with Steam-pipe.]

Plain tubs or vats, such as those shown in figure 10, are used for dyeing and otherwise treating goods in the cold, or at a lukewarm heat, when the supply of hot water can be drawn from a separate boiler. When, however, it is necessary to work at the boil, then the vat must be fitted with a steam coil. This is best laid along the bottom in a serpentine form. Above the pipe should be an open lattice-work bottom, which, while it permits the free circulation of boiling water in the vat, prevents the material being dyed from coming in contact with the steam pipe. This is important if uniform shades are to be dyed, for any excessive heating of any portion of the bath leads to stains being produced on the material in that part of the bath. Figure 11 shows a vat fitted with a steam pipe. That portion (p. 043) of the steam pipe which pa.s.ses down at the end of the vat is in a small compartment boxed off from the main body of the vat, so that no part of the material which is being dyed can come in contact with it.

A closed steam coil will, on the whole, give the best results, as then no weakening of the dye-liquor can take place through dilution by the condensation of the steam. Many dye-vats are, however, fitted with perforated, or as they are called, open steam coils, in which case there is, perhaps, better circulation of the liquor in the dye-vat, but as some of the steam must condense there is a little dilution of it.

DYEING MACHINES.

Dye-tubs and vats, such as those described above, have been largely superseded by machines in which the handling or working of the materials being dyed is effected by mechanical means. There have been a large number of dyeing machines invented, some of these have not been found to be very practical, and so they have gone out of use.

s.p.a.ce will not admit of a detailed account of every kind of machine, but only of those which are in constant use in dye-works.

#Dyeing Loose or Raw Wool and Cotton.#--Few machines have been designed for this purpose, and about the only successful one is

_Delahunty's Dyeing Machine._--This is ill.u.s.trated in figure 12. It consists of a drum made of lattice work which can revolve inside an outer wooden casing. The interior of the revolving drum is fitted with hooks or fingers, whose action is to keep the material open. One segment of the drum is made to open so that the loose cotton or wool to be dyed can be inserted. By suitable gearing the drum can be revolved, and the dye-liquor, which is in the lower half of the wooden casing, penetrates through the lattice work of the drum, and dyes (p. 044) the material contained in it. The construction of the machine is well shown in the drawing, while the mode of working is obvious from it and the description just given. The machine is very successful, and well adapted for dyeing loose or raw wool and cotton. The material may be scoured, bleached, dyed or otherwise treated in this machine.

[Ill.u.s.tration: Fig. 12.--Delahunty's Dyeing Machine.]

The Obermaier Machine, presently to be described, may also be used for dyeing loose cotton or wool.

[Ill.u.s.tration: Fig. 13.--Obermaier Dyeing Machine.]

#Dyeing Slubbing, Sliver or Carded Wool.#--It is found in practice that the dyeing of loose wool is not altogether satisfactory, the impurities they naturally contain interfere with the purity of the (p. 045) shade they will take. Then again the dyes and mordants used in dyeing them are found to have some action on the wire of the carding engine through which they are pa.s.sed; at any rate, a card does not last as long when working dyed wools as when used on undyed cotton or wool fibres. Yet for the production of certain fancy yarns for weaving some special cla.s.ses of fabrics it is desirable to dye the wool before it is spun into thread. The best plan is undoubtedly to dye the fibre after it has been carded and partly spun into what is known as slubbing, or sliver. All the impurities have been removed, the wool fibres are laid straight, and so it becomes much easier to dye. On the other hand, as it is necessary to keep the sliver or slubbing straight and level, no working about in the dye-liquors can be allowed to take place, and so such must be dyed in specially constructed machines, and one of the best of these is the

_Obermaier Dyeing Machine_, which is ill.u.s.trated in figure 13.--In (p. 046) the Obermaier apparatus dye-vat, A, is placed a cage consisting of an inner perforated metal cylinder, C, and an outer perforated metal cylinder, D; between these two is placed the material to be dyed. C is in contact with the suction end of a centrifugal pump, P, the delivery end of which discharges into the dye-vat A. The working of the machine is as follows: the slubbing or sliver is placed in the s.p.a.ce between C and D rather tightly, so that it will not move about. Then the inner cage is placed in the dye-vat as shown. The vat is filled with the dye-liquor, which can be heated up by a steam pipe. The pump is set in motion, the dye-liquor is drawn from A to C, and in so doing pa.s.ses through the material packed in B and dyes it. The circulation of the liquor is carried on as long as experience shows to be necessary. The dye-liquor is run off, hot water is run in to wash the dyed material, and the pump is kept running for some time to ensure thorough rinsing, then the water is run off, and by keeping the pump running and air going through a certain amount of drying can be effected. This machine works very well, and with a little experience constant results can (p. 047) be obtained. The slubbing or sliver may be scoured, bleached, rinsed, dyed, washed, soaped, or otherwise treated without removing it from the machine, which is a most decided advantage.

[Ill.u.s.tration: Fig. 14.--Read Holliday's Yarn-dyeing Machine.]

#Yarn Dyeing Machines.#--In figure 14 is given an ill.u.s.tration of a machine for dyeing yarn in the hank form, made by Messrs. Read Holliday & Sons, of Huddersfield. The ill.u.s.tration gives a very good idea of the machine. It consists of a wooden dye-vat, which can be heated by steam pipes in the usual way. Extending over the vat are a number of reels or bobbins, these are best made of wood or enamelled iron. These reels are in connection with suitable gearing, so that they can be revolved. There is also an arrangement by means of which the reels can be lifted bodily in and out of the dye-vat for the purpose of taking on and off the hanks of yarn. A reel will hold about 2 lb. of yarn. The working of the machine is simple. The vat is filled with the requisite dye-liquor. The reels which are lifted out of the vat are then charged with the yarn, which has been previously wetted out. They are then set in revolution and dropped into the dye-vat, and kept there until it is seen that the yarn has acquired the desired shade. The reels are lifted out and the hanks removed when the machine is ready for another lot of yarn.

There are several makers of hank-dyeing machines of this type, and as a rule they work very well. The only source of trouble is a slight tendency for the yarn on one reel if hung loosely of becoming entangled with the yarn on other reels. This is to some extent obviated by hanging in the bottom of the hank a roller, which acts as a weight and keeps the yarn stretched and so prevents it flying about.

To some makes of these machines a hank wringer is attached.

[Ill.u.s.tration: Fig. 15.--Klauder-Weldon Dyeing Machine.]

_Klauder-Weldon Hank-dyeing Machine._--This is ill.u.s.trated in (p. 048) figure 15, which shows the latest form. It consists of a half-cylindrical dye-vat built of wood. On a central axis is built two discs or rod carriers, which can revolve in the dye-vat, the revolution being given by suitable gearing which is shown at the side of the machine. On the outer edge of the discs are clips for carrying rods on which one end of the hanks of yarn is hung, while the other end is placed on a similar rod carrier near the axle. The revolution of the discs carries the yarn through the dye-liquor contained in the lower semi-cylindrical part of the machine previously alluded to. (p. 049) At a certain point in every revolution of the discs the rods carrying the yarns are turned a little; this causes the yarn to move on the rods, and this motion helps to bring about greater evenness of dyeing.

The most modern form of this machine is provided with an arrangement by means of which the whole batch of yarn can be lifted out of the dye-liquor. Arrangements are made by which from time to time fresh quant.i.ties of dyes can be added if required to bring up the dyed yarn to any desired shade. This machine works well and gives good results.

Beyond the necessary labour in charging and discharging, and a little attention from time to time as the operation proceeds, to see if the dyeing is coming up to shade, the machine requires little attention.

Many other forms of hank-dyeing machine have been devised. There is Corron's, in which an ordinary rectangular dye-vat is used. Round this is a framework which carries a lifting and falling arrangement that travels to and fro along the vat. The hanks of yarn are hung on rods of a special construction designed to open them out in a manner as nearly approaching hand work as is possible. The machine works in this way. The lifting arrangement is at one end of the vat, the hanks are hung on the rods and placed in the vat. Then the lifter is set in motion and moves along the vat; as it does so it lifts up each rod full of yarn, turns it over, opening out the yarn in so doing, then it drops it again in the vat. When it has travelled to the end of the vat it returns, packing up the rods of yarn in so doing, and this motion is kept up until the dyeing is completed. This machine is very ingenious.

A type of machine which has been made by several makers consists of an ordinary rectangular dye-vat surrounded with a framework carrying a number of sets of endless chains, the links of which carry fingers.

The hanks of yarn are hung on rods at one end of which is a tooth (p. 050) wheel that when in position fits into a rack on the side of the vat.

The action of the machine is this, the hanks are hung on the rods and placed at the entrance end of the vat, by the moving of the chains it is carried along the vat and at the same time revolves, thus turning over the yarn, which hangs in the dye-liquor; when it reaches the opposite end of the vat, the rod full of yarn is lifted out, carried upwards and then towards the other end of the vat when it is again dropped into the dye-vat to go through the same cycle of movements which is continued until the yarn is properly dyed.

#Piece Dyeing Machines.#--Wherever it is possible it is far more preferable to dye textile fabrics in the form of woven pieces rather than in the yarn from which they are woven. During the process of weaving it is quite impossible to avoid the material getting dirty and somewhat greasy, and the operations of scouring necessary to remove this dirt and grease has an impairing action on the colour if dyed yarns have been used in weaving it. This is avoided when the pieces are woven first and dyed afterwards, and this can always be done when the cloths are dyed in one colour only. Of course when the goods are fancy goods containing several colours they have to be woven from dyed yarns.