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Bible Encyclopedias
Paper Manufacture
1911 Encyclopedia Britannica
or MANUFACTURE In the modern sense " paper " may best be described as a more or less thin tissue composed of any fibrous material, whose individual fibres, first separated by mechanical action, are then deposited and felted together on wire cloth while suspended in water (see Fibres). The main constituent in the structure of all plants is the fibre or cellulose which forms the casing or walls of the different cells; it is the woody portion of the plant freed from all foreign substances, and forms, so to speak, the skeleton of vegetable fibre to the amount of 75 to 78%. Its forms and combinations are extremely varied, but it always consists of the same chemical elements, carbon, hydrogen and oxygen, and in the same proportions. It is the object of the paper-maker to eliminate the glutinous, resinous, siliceous and other intercellular matters and to produce the fibre as pure and as strong as possible. Linen and cotton rags, having already undergone a process of manufacture, consist of almost pure fibres with the addition of fatty and colouring matters which can be got rid of by simple boiling under a low pressure of steam with a weak alkaline solution; but the substitutes for rags, esparto, wood, straw, &c., being used as they come from the soil, contain all the intercellular matter in its original form, which has to be dissolved by strong chemical treatment under a high temperature. The vegetable fibre or cellulose, being of a tougher and stronger nature, is untouched by the action of caustic soda (which is the chemical generally employed for the purpose), unless the treatment be carried too far, whilst animal fibres or other organic matters are rendered soluble or destroyed by it. The cellulose, after its resolution by chemical treatment, is still impregnated with insoluble colouring matters, which have to be eliminated or destroyed by treatment with a solution of chlorine or bleachingpowder. The object of the paper-maker in treating any one particular fibre is to carry the action of the dissolving and bleaching agents just so far as to obtain the fibre as free from impurities and as white in colour as is desired. The usefulness of a plant for a good white paper depends upon the strength and elasticity of its fibres, upon the proportion of cellular tissue contained in them„and upon the ease with which this can be freed from the encrusting and intercellular matters. Although experiments had previously been made with many fibrous materials, paper was made in Europe, until the middle of the 19th century, almost entirely from rags, either linen or cotton. At that period other fibres began to be adopted as substitutes, due in part, no doubt, to insufficient supply of rags for the increasing consumption of paper, and to the consequent rise in price. The most important of these substitutes are esparto-grass, wood and straw, and these, together with flax (linen), hemp, jute and cotton rags, form the principal raw material for the manufacture of paper.
Paper was first entirely made by hand, sheet by sheet, but in 1798 the invention of the paper machine by Louis Robert, a clerk in the employ of Messrs Didot, of the Essonne Paper Mills in France, gave a new impetus to the industry. The invention was introduced into England by Henry Fourdrinier (1766-1854), the proprietor of a mill at Dartford in Kent. He secured the assistance of Bryan Donkin (1768-1855), an engineer, and after much toil and perseverance, attended with great expense, for which he received no recompense, succeeded in 1803 in erecting a machine at Frogmore, Herts, which worked comparatively well. This machine, by the subsequent improvements of Dickinson, Causon, Crompton and others, has been brought to the state of perfection in which it now stands. It embraces a multitude of most ingenious and delicate operations, and produces in a few minutes, and in one continuous process from the prepared pulp, sheets of paper ready for use. Machine-made paper has now gradually supplanted that made by hand for all except special purposes, such as bank-note, ledger, drawing and other high-class papers - in one word, in cases where great -durability is the chief requisite.
The various uses to which paper is put in the present day are multitudinous, but the main classes may be grouped into four: (i) writing and drawing papers; (2) printing and newspapers; (3) wrapping papers; (4) tissue and cigarette papers.
The process of paper manufacture consists of two main divisions: (i) the treatment of the raw material, including cleaning, dusting, boiling, washing, bleaching and reducing to pulp; (2) the methods by which the prepared pulp or fibres are converted into paper ready for the market; this is paper-making proper, and includes the operations of beating, sizing, colouring, making the sheet or web, surfacing, cutting, &c.
Rags arrive at the mill from the rag merchants, either roughly sorted into grades or mixed in quality and material, and the first process is to free them from sand, dust and other im purities. To effect this they are usually passed in bulk through an ordinary revolving duster. They are then sorted into grades, and cut to a workable size about four inches square. For the best work, hand-cutting, done by women, is still preferred, but it is expensive and good machines have now been designed for this purpose. After further thrashing and dusting, the rags are ready for boiling, the object of which is not only to get rid of the dirt still remaining in them and to remove some of the colouring matter, but also to decompose a particular glutinous substance which would impair the flexibilit y of the fibres and render them too harsh and stiff for readily making into paper. Various forms of vessels are used for boiling, but usually they are made to revolve by means of suitable gearing, and are either cylindrical or spherical (fig. I).
FIG. I. - Revolving Spherical Rag Boiler.
In these the rags are boiled with an alkaline solution under a low steam pressure for six to twelve hours. The next step is that of washing and " breaking in," which takes place in an engine called the " breaker." This (fig. 2) is an oblong shallow vessel or trough with rounded ends and dished bottom, usually about 13 ft. long by 6 ft. wide, by about 2 ft. 6 in. in depth, but the size varies greatly. It is partly divided along the centre by a partition or " mid-feather," and furnished with a heavy cast-iron roll fitted round its circumference with knives or bars of steel in bunches or clumps. Underneath the roll and fixed in the bottom of the trough is the " plate," consisting of a number of parallel steel bars bedded in a wooden frame. The roll can be raised or lowered on the plate so as to increase or diminish, as desired, the cutting action of the bars and plate on the material. The duty of the roll is to cut and tease out the rags, and also to act as a lifter to cause the stuff to circulate round the trough. The breaker is half filled with water and packed with the boiled rags; an ample supply of clean water is run into the engine for washing the rags, the dirty water being withdrawn by the " drum-washer," a hollow cylinder fitted with buckets and covered with fine wire-cloth. During the washing process the roll is gradually lowered on the plate to tease out the rags into their original fibres; this operation takes from two to four hours. As soon as all signs of the textile nature of the material are destroyed, the washing water is turned off, the drum-washer lifted, and a solution of chlorine or bleach is run in to bring the pulp up to the degree of whiteness desired, after which the rag " halfstuff," as it is now called, is emptied into steeps or drainers, where it is stored ready for use.
In treating esparto (the use of which for paper-making is almost confined to Great Britain) the object is to free it from all encrusting and intercellular matter. To effect this it is digested E with a strong solution of caustic soda under a high temperature, in boilers which are almost invariably stationary. The most usual form is that known as Sinclair's patent (fig. 3). This boiler is constructed of wrought-iron or steel plates, and holds from 22 to 3 tons of grass. It is charged through the opening at the top A, and the boiled material taken out from a door B at the side; the grass rests on a false bottom of perforated plates C, through which the liquor drains, and by means of two " vomiting " pipes, D, D, at the sides of the boiler, Connecting the space at the bottom with a similar space a the top, a continuous circulation of steam and liquor is maintained through the grass. The steam pressure is kept up to 30 to 40 lb per sq. in. for three or four hours; then the strong liquor or lye, which contains all the resinous and intercellular matters dissolved by the action of the caustic soda, is run off and stored in tanks for subsequent recovery of the soda, while the grass is taken to the "potcher " or washing engine. In construction and working this is similar to the breaking engine used for rags; in it the grass is reduced to pulp, and washed for about twenty minutes to free it from the traces of soda liquor remaining Plan FIG. 2. - Rag-breaking Engine.
after the partial washing in the boiler. As soon as the wash water is running clear it is shut off, and the necessary quantity of a solution of bleaching powder or chlorine (averaging about 6 to 8% on the raw material) is run into the potcher, and the contents are heated by steam to a temperature of about 90° F. After about four to six hours the bleaching is complete, the drum-washer is let down, fresh water run into the potcher, and the grass washed to free it from all traces of chlorine, an operation generally assisted by the use of a little antichlor or hyposulphite of soda. The esparto, as shipped in bales from the Spanish or African fields, is mixed with roots, weeds and other impurities; and as most of these do not boil or bleach as rapidly as the esparto they would, if not taken out of the pulp, show up in the finished paper as specks and spots. To get rid of them the esparto pulp when washed and bleached is run from the potcher into storage chests, from which it is pumped over a long, narrow serpentine settling table or " sand-table," made of wood and fitted with divisions, or " weirs," behind which the heavy impurities or weeds fall to the bottom and are caught. The pulp is next passed over what is known as a " presse-pate " (fig. 4) or " half-stuff " machine, very similar to the wet end of a paper machine, consisting of strainers fitted with coarse-cut strainer plates, a short wire and a pair of couch and press rolls. The pulp is drawn by suction through the strainers, which keep back the finer impurities that have passed the sand-table, and then flows on to the wire-cloth in the form of a thick web of pulp. After passing through the couch and press rolls, the pulp leaves the machine with about 70% of moisture, and is ready for the beating engine, the first operation of paper-making proper. This is the usual process, though various modifications are introduced in different mills and for different purposes.
Most kinds of straw can be ultilized for making into paper, the varieties generally used being rye, oat, wheat and barley; of these, the two former are the most important, as they give the largest yield in fibre. Germany and France are the two principal users of straw, which closely resembles esparto in its chemical constitution, and is reduced to a pulp by a somewhat similar process.
Scandinavia, Germany, the United States and Canada are the countries which mainly use wood as a material for paper-making, Elevation owing to their possession of large forest areas. They also export large quantities of wood-pulp to other countries. In Europe the Scotch fir ( Pinus sylvestris ), the spruce (Picea excelsa ), the poplar (Populus alba ) and the aspen (Populus tremula ), are the timbers principally employed; and in America the black spruce (Picea nigra ), the hemlock (Tsuga canadensis ), the poplar (Populus grandidentata ) and the aspen (Populus tremuloides). Two kinds of wood-pulp are used for paper manufacture, one prepared mechanically and the other chemically. The former is obtained by disintegrating the wood entirely by machinery without the use of chemicals, and is, as may readily be understood, a very inferior pulp. In the manufacture of chemical wood-pulp, very great about seven or eight hours, in a similar manner to esparto and straw, though it requires much severer treatment. The steam pressure varies from 90 lb to as much as 150 lb per sq. in., and the amount of soda required is about 16% of Na O, estimated on the barked and cleaned wood. The essential feature of the sulphite process is the employment of a solution of sulphurous acid combined with a certain amount of base, either magnesia or lime. As the acid reaction of the bisulphite solution would attack any exposed ironwork with which it comes in contact, the boilers in all cases should be lined with lead. The type of boiler employed varies according to the process adopted. The principal patents connected with the sulphite process are those of Tilghman, Ekman, sas FIG. 3. - Sinclair Esparto Boiler.
advances have been made since 1880, and wood-pulp has grown to be one of the most important fibres for paper-making purposes. Two methods are in use, known respectively as the soda or alkaline process, and the sulphite or acid process, according as soda or sulphur (or rather sulphurous acid) forms the base of the reagent employed. Trees of medium age are usually selected, varying from seventy to eighty years' growth and running from 8 to 12 in. in diameter. They are felled in winter and reach the mill in logs about 4 ft. long. After being freed from bark and the knots taken out by machinery, the logs are cut into small cubical chips about to in. in size by a revolving cutter. s The chips are then bruised by being passed between two heavy iron rolls to allow the boiling solution thoroughly to penetrate them, and are conveyed to the boilers over a screen of coarse wire-cloth, which separates out the fine sawdust as well as any dirt or sand. In the soda process the wood is boiled in large revolving or upright stationary boilers for Francke, Ritter-Kellner, Mitscherlich, and Partington. The subsequent operations, in both the acid and alkaline processes of washing, bleaching and straining the pulp, are all very similar to those described for esparto. Wood-pulp produced by the sulphite process differs in a marked degree from that made by the soda process; the fibre in the former case is harsher and stronger, and papers made from it are characterized by their hardness and transparency, whereas those made from soda pulp are softer and more mellow, corresponding in some way to the difference between linen and cotton fibres. Each class of pulp is largely used, both alone and mixed with other materials.
Within recent years important modifications and improvements have been adopted in the preparation of esparto and wood ,halfstuff with a view to reduce the cost of manufacture and save waste of material. From the boiler to the beater the process becomes a continuous one, so that the prepared pulp requires practically no ¦ ???... ?'_'o ???: ?iia?a a? ? FIG. 4. - " Presse -Pate," or Half-stuff Machine.
handling till it is made into finished paper at the end of the machine; this effects a considerable saving in cost of labour and reduces the waste of material incidental to a series of disconnected operations. From the potcher or breaking engine the esparto or wood pulp is discharged, by means of a patent circulator or pump, into the first of a series of upright bleaching towers. These towers (fig. 5) are built up of wrought-iron rods and a special kind of cement. They are usually about 16 ft. high in the parallel by 82 ft. in diameter; the bottom of the tower is conical and connected to a powerful circulator or pump, which discharges the pulp into the top of the tower and causes thereby a continuous circulation and a thorough mixing of the pulp and bleach. A special Feet ` form of concentrator is fixed pi? g t ? 9 =,o on the top of the first tower, which reduces the water in the pulp as it leaves the i ? potcher to the minimum quantity necessary for perfect circulation in the tower; --- by this means a considerable Beater Fi ,, saving is effected in the quantity of bleach required.
After the necessary concentratio { tor, the bleachin l gliquor is added and thecirculatorq the foot of the tower ut in motion. A two-way valve in the discharge pipe allows the pulp to pass on to tower No. 2, and so on through the series. The circulator in each tower is only put in working for a short time once ?l?Il i?lY in every hour and there is never more than one circu- - lator working in the series at one time. There is no manual L. 7 1 ! labour in working the process, perfect cleanliness, and a great saving in power over ???' the old process. Each tower - will hold about two tons of dry pulp. When the pulp is fully bleached in the last " - tower of the series, fresh e ,,
water is run into it, and a '?? second concentrator, similar 8. r, to the one on the first tower,, ?. -
is put in motion and. washes e' out all t2ace s o of th0e b urin to in „? /). These concentrators effect '? ?, also another purpose, taking to some extent the place of the presse-pate machine for other impurities. ites roots, d weeds and ,(From the last tower and concentrator the bleached pulp is pumped through a line of pipes to the beaters, valves being fixed in the line of pipes to discharge into whichever beater is desired. These beaters are constructed in .tower-form like the bleach ,...3.T__,...--;: =; ers, the roll and plate being fixed on the top of the tower and the circulation effected in the same way as in the bleachers. Fig. 5 shows plan and elevation of such an arrangement of beaters and bleachers arranged in series.
The beaters are made to hold each about 1500 lb of dry paper and a series of four of these can make from 55 to 60 tons of paper per week.
Fibres like jute, hemp, manila, &c., are chiefly used for the manufacture of coarse papers where strength is of more importance than appearance, such as wrapping-papers, paper for telegraphforms, &c. The boiling processes for them are similar to those used for esparto and straw.
The alkaline liquors in which rags, esparto and other papermaking materials had been boiled were formerly run into the nearest water-course; but now, partly because it is insisted upon in England by the Rivers Pollution Acts, and partly because the recovery of the soda can be Recovery. made remunerative, all these liquors are preserved and the soda they contain utilized. One of the best and most economical of the simple recovery plants is that invented by Porion, a French distiller, and named after him. This consists of an evaporating chamber A, on the floor of which a few inches of the liquid to be evaporated rest. By the action of fanners B, B revolving at a high speed and dipping into the liquid, it is thrown up in a fine spray through which the heated gases pass to the chimney. After being concentrated in the eva p orating chamber the liquid flows into the incinerating furnaces C,C, where the remaining water is driven off by the heat of the fire D, and the mass afterwards ignited to drive off the carbonaceous matter. A considerable feature in this evaporator is Menzies and Davis's patent smell chamber E, a chamber filled with masonry in which the strongly-smelling gases from the incinerating furnace are allowed to remain at a red heat for a short time. After being recovered, the soda, in the form of crude carbonate, is lixiviated and re-causticized by boiling with milk of lime.
Porion's method is open, however, to the objection that the whole of the sulphur in the coal employed for the furnaces finds its way into the recovered soda, and forms sulphur compounds, thus reducing the value of the ash for boiling purposes; in addition, a considerable amount of soda is volatilized during the evaporation. By the application of the system of multiple-effect evaporation to the recovery of waste liquors these drawbacks disappear, and an important change has been made in the soda-recovery plant of the paper-mill. This system of multiple-effect evaporation, originally introduced by M. Rillieux, was perfected by the invention of Homer T. Yaryan, of Toledo, Ohio, U.S.A. This type may here be taken for description, though other types of evaporator are now also employed, notably the ordinary vertical tube multiple effect evaporator as used for concentrating sugar liquors. The Yaryan evaporator was originally applied in the United States to the concentration of the waste alkaline liquors of paper-mills; it then came into extensive use for the manufacture and refining of sugar, the production of glucose and a variety of other purposes. The principle of multiple-effect evaporation is to utilize the latent heat of a vapour given off from a liquid under a certain pressure to vaporize a further quantity of the liquid under a pressure maintained by mechanical means below that of the first. The essential feature which distinguishes the Yaryan evaporator consists in the boiling of the liquor to be treated while it is passing through a series of tubes, which constitute a coil and are heated externally by steam or vapour. The quantity of liquor entering the coil is so controlled that it is only permitted partially to fill the tubes, and thus leaves room for the instantaneous liberation of the vapour and its free escape.' As the liquor descends from tube to tube it becomes concentrated and reduced in volume until it ultimately passes into a ” separator," where it impinges on a plate or disk, which causes a complete separation of the vapour and liquid; each then passes on to the next " effect," the liquid through the second coil of tubes and the vapour to the chamber enclosing them. This combination of a series of tubes, or coil, and separator constitutes a vessel or " effect," and the evaporator consists of a series, usually three or more, of these vessels, one above the other (fig. 7). The vital feature, it will be understood, is therefore that the latent heat of the original steam, after performiig its function in the first effect, is passed on to the second and then to the third or more effects, in each of which an equal amount of work is done before passing to the final condenser,. where a vacuum is maintained. Thus, if the total temperature be divided three times, the result is a triple-effect, if four times, a quadruple-effect. Taking an evaporation of io lb of water per pound of coal, a single-effect apparatus will evaporate to lb of water, a ' In England, it should be stated, it is found that both for paper liquors and other liquors equally good evaporation results are obtained and the tubes kept cleaner by keeping them under a head of liquor, i.e. the liquor is fed into the bottom row of tubes and has to ascend row by row to the top row, from which it flows to the separator.
I//// /iI//i ,/ /I /i%?H%iN ////////H/////////// . %///.
/, / H/ / // /// / / / / H / / / / // / / / // / / // /H/ / FIG. 6. - Porion Evaporator.
Masson, Scott and Co., Ltd.
F IG 5. - Esparto Bleaching and Beating Plant.
0 double-effect zo Ib, a triple-effect 30 lb, and so on. 1 The liquor to be concentrated is pumped from the storage tanks to the top or first effect of the Yaryan apparatus through a series of multiple-effect heaters, corresponding to the number of effects in the machine, by means of which the liquor is heated to as near the boiling point as possible of the liquor in the tubes of the first effect.
The Mirrlees Watson Co., Ltd.
FIG. 7. - The Yaryan Patent Multiple Effect Evaporator.
Live steam is introduced into the chamber surrounding the tubes of the first effect, and from the separator of the last effect the concentrated liquor is pumped tO the incinerator.
Any form of incinerating hearth can be used in conjunction with the multiple-effect evaporator, but one very suitable to the continuous work of, and the high degree of concentration produced by, the Yaryan machine is that known as the Warren rotary furnace. This consists of a revolving iron cylinder lined with brick, about 12 ft. long by ro ft. in diameter. The lining being 6 in. thicker at the inlet 2 than at the discharge, the interior of the furnace is conical in form so that the ash gradually works forward and is eventually discharged fully burnt into trucks for storage, or on a travelling band, and so carried automatically to the dissolving or lixiviating tanks. The strong liquor runs in at one end in a slow continuous stream; by the rotation of the hearth the burning mass is carried up the sides and drops through the flame again to the bottom, much in the same manner as rags do in a revolving duster. In this way all the labour required to stir the ash of the ordinary hearth is dispensed with, and the burning material comes continuously in close contact with the flame, a complete and thorough combustion being the result. The fire-box is situated at the delivery end of the furnace, and is mounted on trucks 3 so that it can be run back when cleaning or repairing the brickwork. The waste heat is utilized in raising steam in a steam boiler set behind the furnace, and often in keeping the thick liquor hot after leaving the evaporator and before entering the rotary furnace.
Paper-making proper from prepared pulp, whether of rags, esparto, wood or other raw material, may be said to; begin with the operation technically known as " beating " which is 1 The figures given here are theoretical rather than actual. In practice a double effect is not capable of evaporating twice as much with I lb of coal as a single-effect, owing to loss of efficiency through radiation, &c.
2 This was the original Warren principle, but has largely been abandoned in favour of a parallel brick lining throughout; the ash gradually works forward and is discharged as described.
3 A later method is to build the fire-box on the descending side of the rotary furnace, while a specially constructed door and ash discharge shoot are provided at the ascending side, which gives access to the inside of the furnace and provides all the other essentials without the loss of heat which resulted from the portable fire-box, due to leakage between the box and the rotary furnace proper.
carried out in one of the various forms of beating engine or " Hollander." The object of the beater is to reduce the fibres to suitable lengths and also to beat or bruise them info a stiff pulp of sufficient consistency to absorb and carry the water necessary to felt them together on the wire Masson, Scott & Co., Ltd.
FIG. 8. - Taylor's Patent Beater.
cloth of the paper-machine. This operation is one of the most important and most delicate processes in the manufacture, requiring experience, skill and careful manipulation. Not only does every class of fibre demand its own special treatment, but this treatment has to be modified and varied in each case to suit the qualities and substances of the papers to be made from it.
Although there are now in use a great many forms of beating engine, they are all, more or less, modifications of the original Hollander, which in its essential details differs little from the breaking engine already described. There are usually more bars in the roll and plate than in the breaker; the bars of the plate are set at a slight angle to the fly-bars of the roll to act as shears in a similar manner to a pair of scissors. Bars and plates of bronze are frequently used for the higher grades of paper to avoid rust and dirt and to produce a softer and less violent action on the fibres. The time required for the beating process varies from 3 to 4 hours up to to and 12 and even more. Beating engines fitted with mechanical circulation by pumps or otherwise have been extensively adopted, more particularly for working esparto and the other substitutes for rags. Fig. 8 shows one of these beaters, known as the Taylor beater; the roll and plate are fixed above the trough of the beater, which has no partition or mid-feather, and from the lower end a powerful circulator or pump circulates the pulp through the beater and discharges it through a pipe in a continuous stream in front of the roll. In the pipe is fixed a two-way valve, so that when the beating operation is complete the finished pulp can be run into the stuff-chests of the paper machine. The advantages of this form of beater are that a quicker and more thorough circulation of the pulp takes place than when the roll has to do the double duty of making the pulp travel and beating it up at the same time, and thus tends to reduce the time of the operation. Also more bars can be fixed in the roll, increasing its effect on the pulp, and less power is required than when the roll revolves in the middle of the stuff as in the ordinary form of beater.
Beating engines of quite a different construction are now largely used in American mills, and also to some extent in Great Britain. These are known as " refiners," and the most important forms are the Jordan and Kingsland beaters (so called from the names of the inventors), or modifications of them.
The first (fig. 9) consists of a conical plug or roll fixed on a shaft and revolving at a high rate of speed within an outer casing of corresponding shape; both the plug and the casing are furnished with steel bars parallel with the shaft, but set at slightly different angles, taking the place of the bars in the roll and plate of the ordinary beater. This conical plug or roll can be moved in either direction parallel to its axis and by this means the cutting action of the two sets of bars can be increased or reduced. The pulp flows into the top of the beater at the smaller end of the cone through a box provided with an arrangement for regulating the flow and passes out through an opening in the casing at the other end. The roll or plug revolves at from 350 to 400 revolutions per minute, and requires a power to drive it of from 25 to 40 h.p., FIG. 9. - Jordan Beater.
according to the work to be done, and one engine is capable of passing as much as woo lb weight of dry pulp per hour. The Kingsland beater consists of a circular box or casing, on both inside faces of which are fixed a number of knives or bars of steel or bronze; inside the case is a revolving disk of metal fitted on both sides with corresponding and similar bars. The contact between the revolving and stationary bars can be regulated, as in the Jordan engine, to give the required amount of beating action on the pulp. The refiner is essentially a finishing process as an adjunct to the beating process proper. The advantages to be derived from its use are a considerable saving in the time occupied in beating and the production of a more uniform and evenly divided pulp, particularly where a mixture of different fibres is used. By the use of the refiner the time occupied in the beater can be reduced by nearly one-half, the half-beaten pulp passing through the refiner from the beater on its way to the paper-machine. It is not, however, generally employed for the best kinds of paper.
During the operation of beating various materials and chemicals are added to the pulp for the purposes of sizing, loading, colouring, &c. Papers for writing and most of those for printing purposes must be rendered non-absorbent of ink or other liquid applied to them. To effect 'this some form of animal or vegetable size or glue must be applied to the paper, either as a coating on the finished web or sheet, or mixed with the pulp in the beating engine. The former, called " tub-sizing " will be described later; the latter which is known as " engine-sizing " consists in filling up the interstices of the fibres with a chemical precipitate of finely-divided resin, which, when dried and heated on the cylinders of the papermachine, possesses the property of being with difficulty wetted with water. Except in the very best qualities of paper, it is usual to add to the pulp a certain quantity of cheap loading material, such as china-clay or kaolin, or pearl-hardening, a chemically precipitated form of sulphate of lime. The addition of such loading material to a moderate extent, say to to 15%, is not entirely in the nature of an adulterant, as it serves to close up the pores of the paper, and for ordinary writing, printing and lithographic papers renders the material softer, enabling it to take a much better and more even surface or glaze. But if added in excess it is detrimental to the strength and hardness of the sheet. Most materials, however well bleached, have a more or less yellowish tinge; to produce the desired white shade in the paper certain quantities of red and blue in the form of pigments or dyes must be added to the pulp. The blues usually employed are ultramarine, smalts and the aniline blues, while the red dyes are generally preparations of either cochineal or the aniline dyes. Other colours are required in the manufacture of papers of different tints, and with one or two exceptions they must be mixed with the pulp in the beater.
There are two distinct processes of producing the finished paper from the pulp, known respectively as " hand-made " and " machine-made." The expense of manufacture of hand-made paper and the consequent high price render it too costly for ordinary use; the entire process on the machine occupies a few minutes, while in the ordinary state of the weather it could not be done by hand in less than a week.
A brief description of the hand-made process will suffice and it will at the same time facilitate the right comprehension of the machine process. Only the finest qualities of rags are used for hand-made paper; and the preparation of the half-stuff is the same as that already described under treatment of rags. The pulp after being prepared in the beating engine is run into large chests from which the vat is supplied; before reaching this it is strained as on the paper-machine (see below). The sheet of paper is made on a mould of fine wire-cloth with a removable frame of wood to keep the pulp from running off, extending slightly above the surface of the mould, called the " deckel." To form the sheet, the paper-maker dips the mould into a vat (see fig. io) containing the prepared pulp, lifting up just so much as will make a sheet of the required thickness; as soon as the FIG II - Mould and Deckel for hand-made paper.
mould is removed from the vat, the water begins to drain through the wire-cloth and to leave the fibres on the surface in the form of a coherent sheet, the felting or intertwining being assisted by a lateral motion or " shake " given to the mould by the workman; the movable deckel is then taken off, and the mould is given to another workman, called the " coucher," who turns it over and presses it against a felt, by this means transferring or " couching " the sheet from the wire to the felt. A number of the sheets thus formed are piled one above another alternately with pieces of felt, and the whole is subjected to strong pressure to expel the water; the felts are then removed and the sheets are again pressed and dried, when they are ready for sizing. Any pattern or name required in the sheet is obtained by making the wire-cloth mould in such a way that it is slightly raised in those parts where the pattern is needed (fig. 11); consequently less pulp lodges there and the paper is proportionately thinner, thus showing the exact counterpart of the pattern on the mould; such are known as " watermarks." The expense of manufacturing paper in this way is very much greater than by machinery; but the gain in strength, partly owing to the time allowed to the fibres to knit together, and partly to the free expansion and contraction permitted them in drying, still maintains a steady demand for this class of paper.
The paper-machine (fig. 12) consists essentially of an endless mould of fine wire-cloth on which the pulp flows and on which a continuous sheet of paper is formed; the sheet then passes through a series of press rolls and over a number of steam-heated cylinders until it is dry. From the beating engines, the pulp is emptied Paper-maker r??h ..
FIG. IO.
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-- - _? ? = ?=?_?;---=?-? ? ?m 1111 into storage tanks or stuff-chests, fitted with revolving arms or agitators; from these the pulp is pumped into a long upright supply box at a higher level, called the stuff box, which communicates with the sand trap or table by means of a regulating valve. With the pulp a certain amount of water is allowed to flow on to the sand trap so as to dilute it sufficiently to form on the wire-cloth of WET face of a rapidly-revolving disk driven by a pair of speed-cones, so that the speed of the shake can be altered. The object of this shake is to interlace the fibres together, but it also assists in keeping the water from passing through the wire too rapidly before the paper has been properly formed. Most machines have two suctionboxes with the " dandy-roll " revolving between them on the top END = .A a a ?
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the paper-machine. The sand trap consists of an elevated table in which is sunk a shallow serpentine channel lined on the bottom with rough felt and divided throughout its length by a number of small strips of wood, behind which the impurities collect as the pulp flows over them on its way to the strainers.
The strainers are made of plates of brass or some hard and durable composition with fine parallel slits cut in them, through which the fibres pass, all knots and improperly divided portions Straining. remaining behind; the pulp is made to pass through them by the rapid vibration of the plates themselves or by a strong suction underneath them, or sometimes by a combination of the two. From the strainers the pulp flows into a long wooden box or trough, of the same width as the paper machine, called the " breast-box," and thence on to the wire-cloth. The wire consists of a continuous woven brass cloth, supported horizontally by small brass rolls, called " tube-rolls," carried on a Forming frame; it is usually 40 to 50 ft. long and is stretched tight over two rolls, one at each end of the frame, called respectively the " breast-roll " and the " lower-couch roll." The ordinary gauge for the wire-cloth is 66 meshes to the inch for writings and printings; finer wires are sometimes used, however, up to 80 to the inch; for lower grades the mesh is coarser. The water, mixed with the pulp, flows from the wire-cloth by gravitation along the lines of contact between it and the tube-rolls; this water, which contains a considerable percentage of fibre, especially from finely beaten pulps, drops into a flat copper or wooden tray, from which it flows into a tank and is pumped up with the water for diluting the pulp so that none of it shall be wasted. From the tube-rolls the wire conveys the pulp over a pair of suction-boxes for extracting the remaining water from the web. The width of the web of paper is determined by two continuous straps of vulcanized rubber about i 2 in. square, one on each side of the wire, called the " deckel-straps "; the distance between these straps can be increased or diminished; they serve to guide the pulp from the FIG. 13. - llandy - roll.
moment it spreads on the wire until it arrives at the first suctionbox, where the web is sufficiently dry to retain its edges. The Shake. frame of the machine from the breast-roll to the first suction-box is hung on a pair of strong hinges, and is capable of a slight horizontal motion imparted by a horizontal connecting-rod, one end of which is eccentrically keyed on to the of the pulp (so called because it can be made to give to the paper any desired water-marking). The " dandy-roll " (fig. 13) is a light skeleton cylinder covered with wire-cloth on which small pieces of wire are soldered representing the watermark marking to be reproduced in the paper. From the last suctionbox the half-dried sheet of pulp passes between the couch-rolls," so called from the corresponding operation of couching in hand-made paper, which, by pressing out most of the remaining moisture, impart sufficient consistency to the paper to, enable it to leave the wire; both rolls are covered with a felt jacket,. and the top one is provided with levers and weights to increase or diminish the pressure on the web. The paper is now fully formed, and is next carried by means of endless felts between two and sometimes three pairs of press-rolls and Drying. to extract the remaining moisture, and to obliterate as much as. possible the impression of the wire-cloth from the under-side of the web. The web of paper is finally dried by passing it over a series of hollow steam-heated drying cylinders driven one from the other by gearing. The slower and more gradual the drying process. the better, as the change on the fibres of the web due to the rapid contraction in drying is thereby not so excessive, and the heat required at one time is not so great nor so likely to damage the quality of the paper; the heating surface should therefore be as. large as possible, and a great number of cylinders is required now that the machines are driven at high speeds. The cylinders are so placed that both surfaces of the web are alternately in contact with the heating surface. All the cylinders, except the first two or three with which the moist paper comes in contact and where the greatest evaporation occurs, are encased by continuous travelling felts. The drying cylinders are generally divided into two sets between which is placed a pair of highly polished chilled iron rolls heated by steam, called " nip-rolls," or " smoothers," the purpose of which is to flatten or smooth the surface of the paper while in a partially dry condition. Before being reeled up at the end of the machine the web of paper is passed through two or more sets of " calenders," according to the degree Surfacing. of surface or smoothness required. These calenders consist of a vertical sack of chilled iron rolls, generally five in number, revolving one upon another, and one or more of which are bored and heated by steam; pressure can be applied to the stack as required by means of levers and screws. The web of paper is now wound up. in long reels at the end of the machine.
Paper-machines are now usually driven by two separate steam engines. The first,"running at a constant speed, drives the strainers, pumps, shake motion, &c., while the second, working the papermachine, varies in speed according to the rate at which it requires Ile stuff - - box ? gig Sand-table Strainer Wire-`----- -
---s tst. Press Rolls to be driven. The power consumed by the two engines will average from 40 to loo h.p. The drying cylinders of the paper-machine form a convenient and economical condenser for the two steamengines, and it is customary to exhaust the driving engine into the drying cylinders and utilize the latent heat in the steam for drying the paper, supplementing the supply when necessary with live steam. The speed of the machine has frequently to be altered while in motion. An alteration of a few feet per minute can be effected by changing the driving-speed of the steam-engine governor; for a greater change the machine must be stopped and other drivingwheels substituted. Arrangements are made in the driving-gear by which the various parts of the machine can be slightly altered in speed relatively to one another, to allow for the varying contraction or expansion of the paper web for different kinds and thicknesses of paper. The average speed of a paper-machine on fine writing-papers of medium weight is from 60 to 90 ft. per minute, but for printing-papers, newspapers, &c., the machine is driven from 120 up to as much as 300 and 400 ft. per minute. The width of machines varies greatly in different mills, from about 60 in. to as much as 150 in. wide. Mills running on higher classes of papers as a rule use narrow machines, as these make a closer and more even sheet of paper than wider ones. On fine writing-papers an average machine will make from 20 to 40 tons per week, while for common printing and newspapers the weekly output will amount to 50 to 70 tons.
All hand-made papers, and many of the best classes of machinemade papers, instead of being sized in the beater with a preparation - of resin are what is called " tub-sized," that is, coated with a solution of gelatin. Such papers, when machine made, are reeled off the machine straight from the drying cylinders in the rough state. The web is then led slowly through a tub or vat containing a heated solution of animal glue or gelatin mixed with a certain amount of alum; after passing through a pair of brass rolls to squeeze out the superfluous size, the web is reeled up again and allowed to remain for some time for the size to set. The paper is then led by means of continuous travelling tapes over a long series of open skeleton drums, about 4 ft. in diameter, inside J. Milne & Son, Ltd.' FIG. 14. - Super-calender.' The bottom roll and the 3rd, 6th, 8th and 10th rolls, all reckoned from the bottom, are made of highly polished chilled cast-iron; the others of highly compressed paper.
which revolve fans for creating a circulation of hot air; rows of steam-pipes underneath the line of drums furnish the heat for drying. Slow and gradual drying is essential to this process to get the full benefit of the sizing properties of the gelatin. In hand-made papers, the sheets are passed by handfuls of three or five on an endless felt through the gelatin solution and between a pair of rolls, and then slowly dried on rope lines or " tribbles " in a steam-heated and well-ventilated loft.
The cheaper kinds of paper are glazed on the paper-machine in the calenders as before described. For the better class or very highly-glazed papers and those that are tub-sized, a subsequent glazing process is required; this is effected Surfacing. by sheet or plate-glazing and by super-calendering or web-glazing. The plate-glazing process is adopted mainly for the best grades of writing-papers, as it gives a smoother, higher and more permanent gloss than has yet been imitated by the roll-calender. In this method each sheet is placed by hand between two zinc or copper plates until a pile of sheets and plates has been formed sufficient to make a handful for passing through the glazing-rolls; this handful of about two quires or 48 sheets of paper, is then passed backwards and forwards between two chilled-iron rolls gearing together. A considerable pressure can be brought to bear upon the top roll by levers and weights, or by a pair of screws; the pressure on the rolls, and the number of times the handful is passed through, are varied according to the amount of gloss required on the paper. The super-calender (see fig. 14) is used to imitate the plate-glazed surface, partly as a matter of economy in cost, but principally for the high surfaces required on papers for books and periodicals to show up wood-cuts and photographic illustrations. It usually consists of a stack of chilled cast-iron rolls, alternating with rolls of compressed cotton or paper so that the web at each nip is between cotton and iron; it will be seen from the illustration that there are two cotton rolls together in the stack for the purpose of reversing the action on the paper and so making both sides alike; pressure is applied to the rolls at the top by compound levers and weights or screws. A very high surface can be quickly given to paper by friction with the assistance of heat; the process is known as " burnishing," and is used mostly for envelope papers and wrappings where one surface only of the web is required to be glazed. It is produced by the friction of a chilled-iron roll on one of cotton or paper, the ratio of the revolutions being as 4 to 5; steam is admitted to the burnishing iron roll.
At the end of the 19th century a large and increasing demand sprang up for papers embossed with a special pattern, such as linen-finish, &c.; these are used principally for fancy writingpapers, programmes, menu-cards, &c. This embossing is effected usually on the plate-glazing machine, in the case of linen and similar finishes by enclosing each sheet of paper between two pieces of linen or other suitable material to give the desired texture or pattern on the surface of the sheet. Each sheet of paper with its two pieces of cloth is placed between zinc plates and passed backwards and forwards between the rolls of the machine as in plate-glazing.
| ?"? Mot a 11, il | Except for special purposes, such for example as for use in a continuous printing-machine, paper is usually sent from the mill in the form of sheets. A number of reels of paper is hung on spindles between two upright frames to feed the cutting-machine (see fig. 15); the various webs of paper are drawn forward together through two small rollers, and ripped into widths of the required size by means of a number of pairs of circular knives or " slitters "; they then pass between another pair of rollers, and over a long dead-knife fixed across the cutting-machine, on which they are cut into sheets by another transverse knife fastened to a revolving drum and acting with the dead-knife like a large pair of shears. The cut sheets then fall upon an endless travelling felt, from which they are stacked in piles by boys. It is often necessary, as in the case of water-marked papers, that the sheets should be cut with great exactness so that the designs shall appear IItIIIIIIII?I IIII f° James Bertram & Son, Ltd. FIG. 15. - Reel Paper Cutter. in the centre of the sheet; the ordinary cutter cannot be relied upon for this purpose and in its place a machine called a " singlesheet cutter " is used. In this cutter only one web of paper is cut at a time; between the circular slitters and the transverse knives is placed a measuring-drum, which receives an oscillating motion and can be adjusted by suitable mechanism to draw the exact amount of paper forward for the length of sheet required.  All that now remains to be done before the paper is ready for the market is overhauling or sheeting. This operation consists in sorting out all speckled, spotted or damaged sheets, or sheets of different shades of colour, &c.; this entails considerable time and expense as each sheet ., has to be passed in review separately.. This sorting is usually performed by women. Papers are as a rule sorted into three different qualities, known in the trade respectively as " perfect," " retree " and " broke "; the best of the defective sheets form the second quality " retree," a term derived from the French word retirer (to draw out), and are sold at a reduced price; sheets that are torn or damaged or too badly marked to pass for the third quality " broke," are returned to the mill to be repulped as waste paper. Paper is sold in sheets of different sizes and is "made up into reams containing from 480 to 516 sheets; these sizes correspond to different trade names, such for example as foolscap, post, demy, royal, &c.; the following are the ordinary sizes: - With the enormously increased production of paper and the great reduction in price within recent years, it has been found that the " science " of paper-making has scarcely advanced with the same rapid strides as the art itself. Although a sheet of paper made to-day differs little as a fabric from the papers of earlier epochs, the introduction of new and cheaper forms of vegetable fibres and the auxiliary methods of treating them have caused a great change in the quality, strength and lasting power of the manufactured article. 4The undue introduction of excessive quantities of mechanical or ground wood-pulp in the period1870-1880into the cheaper qualities of printing-papers, particularly in Germany, first drew attention to this matter, since it was noticed that books printed on paper in which much of this material had been used soon began to discolour and turn brown where exposed to the air or light, and after a time the paper became brittle. This important question began to be scientifically investigated in Germany about the year 1885 by the Imperial Testing Institution in Berlin. A scheme of testing papers has been formulated and officially adopted by which the chemical and physical properties of different papers are compared and brought to numerical expression. The result of these investigations has been the fixing of certain standards of quality for papers intended for different purposes. These qualities are grouped and defined under such heads as the following: Strength, expressed in terms of the weight or strain which the paper will support. Elasticity and texture, measured by elongation under strain and resistance to crumpling or rubbing. Bulk, expressed in the precise terms of specific gravity or weight per unit of volume. Of not less importance are the qualities which belong to paper as a chemical substance or mixture, which are: its actual composition; (2) the liability to change under whatever conditions of storage and use it may be subjected to. For all papers to be used for any permanent purpose these physical and chemical qualities must ultimately rank as regulating the consumption and production of papers. In England and Wales in 1907 there were 207 mills, using 409 machines and 99 vats for hand-made paper; in Scotland, 59 mills and III machines; in Ireland, 7 mills and II machines. A rough estimate of the amount of capital embarked in the industry may be formed on the basis that average mills would represent from £20,000 to £30,000 and upwards per machine. The table at foot of page shows the amounts and values of the British imports and exports of paper and paper-making materials in 1907.
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