E. J. Bevan

The pulp as it comes from the beaters is now ready to be made into paper. We will first consider briefly the manufacture of hand-made paper.

It is made on a mould of wire-cloth, with a movable frame of wood, called the “deckle,” fitting on to the outside of the mould and extending slightly above its surface.

The wire-cloth is generally supported by a much coarser wire-cloth, or by pieces of thick wire, and these again by wedge-shaped pieces of wood, the thin end being next to the wire.

To form a sheet of paper the workman dips the mould, with the “deckle” in position, into a vat containing the prepared pulp diluted with water, lifting up just so much as will make a sheet of the necessary thickness. As soon as the 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 of paper. The felting or intertwining is assisted by lateral motion in every direction given to the frame by the workman. The movable deckle is then removed, and the mould, with the sheet of paper, given to another workman, called the “coucher,” who turns it over and presses it against the felt, by this means transferring the sheet from the wire to the felt. In the meantime the “vat-man” is engaged in the formation of another sheet with a second mould.

The Fourdrinier Paper Machine. Plate I.

A number of the sheets thus formed are piled together, alternately with pieces of felt, and when a sufficient number {145} have been obtained, the whole is subjected to strong pressure, to expel the water. The felts are then removed, and the sheets again pressed.

They are then sized, if required, by dipping them into a solution of gelatine: again slightly pressed, and hung up on lines or poles to dry. Such paper is called loft-dried.

When dry the sheets of paper are calendered. (See Chapter XI.)

The making of paper by hand involves considerable dexterity on the part of the workman; on account of the expensive labour necessary, in comparison with paper-machines, it is comparatively little practised in the present day; certain kinds of paper, however, such as bank-notes, various drawing papers, and printing papers intended for the production of very elaborate editions are always made in this way.

Any pattern or name required on the paper is obtained by means of a raised pattern on the wire-cloth mould: consequently, less pulp lodges there, and the paper is proportionally thinner, thus showing the exact counterpart of the pattern. Such devices are known as “water-marks.” (See also p. 156.)

The Paper Machine.

—The paper machine of the present day, with all its ingenious improvements, differs but little in principle from that originally constructed by Fourdrinier. It consists essentially of an endless mould of wire-cloth, on to which the prepared pulp flows, and on which a continuous sheet of paper is formed. The sheet of paper then passes through a series of rollers and over a number of heated cylinders, where it is completely dried.

A modern Fourdrinier paper machine is shown in plan and side elevation in Plates I. and II.

The pulp, after leaving the beaters, passes into a large vessel called the stuff-chest, of which there are one or more to each machine. As soon as the beater is empty, water is run in to thoroughly rinse out the remaining pulp, the washings also going into the stuff-chests. These may be {146} made either of wood or iron, and should be provided with arms fixed on a vertical shaft, made to revolve by suitable gearing. The arms are for the purpose of keeping the pulp thoroughly mixed, and should only work at a moderate speed, otherwise they are liable to cause the fibres to form into small knots or lumps. The pulp is drawn from the stuff-chests by means of the pump A, and is discharged into a regulating-box (not shown). The object of this box is to keep a regular and constant supply of pulp on the machine. It consists of a cylindrical vessel, having two overflow-pipes near the top, and a discharge-pipe near the bottom. The pulp is pumped in through a ball-valve in the bottom, in larger quantity than is actually needed, the excess flowing away back into the stuff-chests, through the two overflow-pipes. By this means, the box is always kept full, and therefore the stream of pulp issuing out of the bottom pipe is always under the same pressure. It flows from this pipe, the quantity being regulated by means of a cock, according to the thickness of paper required, directly on to the sand-tables. These may be of various sizes and shapes, but should be so large that the pulp takes some little time to travel over them. They consist of long shallow troughs, generally of a sinuous form. The bottoms are sometimes covered with woollen felt, or with thin strips of wood placed across the direction of the flow of the pulp, and at a slight angle. These serve to retain any particles, such as sand and dirt, that may have escaped removal in the previous treatment of the pulp, and that are heavy enough to have sunk down during the passage of the pulp along the sand-tables. In some mills, where great care is exercised, the pulp is caused to flow over sand-tables 200 yards in length. As the pulp, when it leaves the stuff-chests, does not contain sufficient water for the purpose of making paper, it is mixed, where it enters the sand-tables, with a quantity of water from the “save-all” (see p. 154), flowing from the box B placed at a higher level.

In some mills, instead of being pumped into the {147} regulating-box, the pulp flows into a small vessel below the stuff-chest, and is lifted on to the sand-tables by means of buckets fastened on the circumference of a wheel.

The pulp, after leaving the sand-tables, passes on to the strainers. These consist of strong brass or bronze plates, having a large number of very fine V-shaped slits cut in them, the narrowest end being on the outside.

Strainers.

—The strainers are for the purpose of removing from the pulp all lumps formed by the intertwining of the fibres, and all pieces of unboiled fibre, which, if allowed to pass on, would show in the paper as inequalities in the surface, or as dark specks. The slits are made narrow at the top, and gradually increasing in width, so as to prevent them from getting choked up. These slits allow only the individual fibres to pass through, and their width varies according to the quality of the paper. They are from 2 to 3 in. long, and they vary in width from ·007 to ·05 in. They are put at distances of about ¹?/?₄ in. apart. Several plates, each containing about 500 slits, are bolted together, and form a strainer. The whole strainer receives a violent shaking motion, to assist the passage of the fibres through the slits. In the machine represented, two of these strainers are shown at C. The shaking motion is produced by the ratchet-wheel or cams a acting on the hammer b. An improved form, called the “revolving strainer,” has of late years been introduced. The pulp generally passes first through one of these, and then through the ordinary or “flat” strainers, as they are called. A revolving strainer is shown at D. It consists of a rectangular box, the sides of which are formed of plates perforated with slits. Inside this box, a slight vacuum is formed by means of an indiarubber bellows worked by a crank on the shaft d. The vacuum is intended to serve the purpose of the shake in the ordinary form. The box revolves slowly inside a vat containing the pulp, and the strained pulp flows into the box D¹, and thence on to the flat strainers.

FIG. 45.

Various patents have been taken out from time to time for {148} flat strainers worked by means of a vacuum underneath the plates caused by the motion of discs of indiarubber or thin metal. Fig. 45 shows in plan a set of strainers, as manufactured by Messrs. G. & W. Bertram, similar to those in Plate II., but illustrated somewhat more in detail.

The pulp first passes through the flat strainer B, and from thence to the two revolving strainers A. From these it flows along the shoots placed at the side on to the paper-machine at E.

FIG. 46.

Fig. 46 gives a view of a patent flat vacuum strainer made by the same firm, which may also be used for cleaning straw or esparto previous to its passage over a presse-pÂte. The pulp flows on to the strainer at a, and passes away by {149} the cast-iron pipes f. The valve g is for running off waste pulp. The plates are placed at a slope of about 1 in. in their length; those nearest the supply of pulp are provided with coarser slits, as the impetus carries the knots forward. The vacuum pumps are worked by the rods d from the shaft e. By means of the tubes c water can be directed on to the plates, whereby the coarser particles of fibre are carried forward, and the slits are kept clean. The plates can be removed in a few minutes.

Figs. 47 and 48 show in side and end elevation, Messrs. Masson, Scott, & Bertram’s patent self-cleaning strainer. The novelty consists in an arrangement by means of which the upper surface of the plates are continually freed from those portions of the pulp which cannot pass through the slits.

The scrapers d are made of vulcanised indiarubber, and are continually carried forward by an endless chain; the knots, &c., collect in a heap at the end of a strainer. The {150} pulp flows on at a, and passes away through the pipe b. The pumps are driven from the shaft e.

FIG. 47.

FIG. 48.

Messrs. C. H. & F. L. Roeckner’s patent strainer (No. 7932, 1885) consists of a series of cylindrical tubes, open at one end and perforated with slits. They are placed in a vat into which the pulp flows. Inside the cylinders are placed two, three, or more plates, fixed to the shafts on which the cylinders are supported, and extending to the circumference. These plates form a kind of fan, which, together with the cylinders, are caused to oscillate by means of a rod and cranks. This oscillating motion serves to draw the fibres through the slits, and at the same time to keep the outsides of the cylinders clean. The cylinders are easily removable.

After a time, the slits in the plates get too large, owing to the plate having been worn away by the constant friction of the fibres, and as they are very expensive, various attempts have been made to invent plans for partially closing them again. Hammering will effect this, but is liable to break the plates. Annandale of Beltonford has introduced a method of closing the plates, by means of heavy pressure acting on small steel rollers moving on each side of the slit, in which is placed a small sheet of metal the exact thickness of the width desired. {151}

Another method of closing the plates consists in filling them up by means of electrically deposited copper or other metal. They can then be recut in the usual way.

In the case of revolving strainers, all that cannot pass through the slits falls to the bottom of the vat, in connection with which it is customary to have an auxiliary strainer, or “patent knotter,” as it is called, shown at E. All fibre that passes through this one, which is of the ordinary flat kind with shaking motion, goes into a box near E', called the “low box” for “save-all” water (see p. 154).

The pulp, after passing through the strainers, should be perfectly free from knots and impurities, and in a fit condition for making paper. In the machine shown, it passes from the last strainer directly on to the wire, its flow being regulated by a movable gate e. In some cases, however, it first flows into a small vat, in the centre of which revolves a rod carrying paddles, with the object of keeping the pulp well stirred up. It is carried right on to the wire by means of the apron, a piece of canvas, oil-cloth, or sheet rubber, one end of which is fastened to the breast-board e', the other end resting on, and covering the wire to the extent of about 15 in. The edges of the apron are rolled up to prevent the pulp from overflowing. After leaving the apron, it passes under a gate, or “slicer,” as it is sometimes called, made of two pieces of brass, overlapping each other in the centre, and bolted together. It is made thus to enable it to be lengthened or shortened according to the width of the paper; its height from the wire-cloth can be altered by means of screws, and should be equal at all points, in order to ensure a uniformly thick sheet of paper. The ends of the two pieces forming the slicer are fastened to the frame f or “deckle,” as it is called, and this again is carried by two or more rods stretching right across the wire, and fastened by small upright supports on both sides to the frame g. The deckle-frame also carries the grooved pulleys h, along which the deckle-straps i, endless square bands of indiarubber, move. {152}

FIG. 49.

The object of the deckle-straps is to regulate the width of the paper; they form, together with the wire-cloth, a kind of mould into which the pulp flows, thus corresponding to the mould used in hand-made paper-making. The width of the paper can be altered by shifting the position of the frame f, and also the deckle-straps, which are carried on it as described, the pulleys h being so arranged that they slide along the rods on which they revolve. In order to alter the width of the paper it is necessary to stop the flow of pulp on to the wire, and it not only con­sumes a con­si­der­able amount of time, but gen­eral­ly neces­si­tates a partial cleaning up of the machine. Various at­tempts have, therefore, been made to devise an ar­range­ment whereby the change can be effected while the paper is being made. Several {153} con­tri­vances have late­ly been in­tro­duced, all similar to the one shown in Figs. 49 and 50.

In it the frame f carrying the deckle-strap is made to slide along the rods e by means of the small wheel b, and by a similar arrangement on the opposite side and geared with it. The movable apron l, Fig. 49, is wound round the spindle g, and is kept taut by the cords m connected with the springs n. As the deckles approach each other, the excess of apron is wound up, when they are separated it unwinds again. The flow of pulp is regulated by two slices a a, which are kept in position by the screws h. The whole arrangement is securely bolted to the frame of the machine; c (Fig. 50) represents the breast-roll, and corresponds to F, Plates I. and II.

FIG. 50.

The thickness of the paper is regulated by altering the supply of pulp to the wire-cloth, and by the speed at which the machine is working. This speed may vary from about 60 feet to as high as 270 feet per minute.

The “wire” is an endless cloth made of very fine wire, the fineness depending much on the quality of the paper required. The mesh varies from 60 to 70 and even more threads to the inch. It is not woven endless, but is joined by very careful sewing with wire. Its width varies considerably, some {154} being made as wide as 126 inches; the length is generally 35–40 ft. It is carried by the breast-roll F, the lower couch-roll G, and the small rolls f ', and by a large number of small rolls f . The latter and the breast-roll are supported by the frame g, while the small rolls f ' are supported by brackets attached to it. The course of the wire is indicated by the arrows. The frame g works on two pivots g', and receives a shaking motion from side to side from the rod j, in connection with a crank worked by two conical drums H. The supports g are also pivoted at their lower ends to allow for the shaking motion. This shaking motion is given for the purpose of weaving or intertwining the fibres. One or more of the rolls f ' can be moved up or down on the support which carries it, for the purpose of stretching the wire. There is usually a large number of the small rolls f , as it has been found by experience that, probably owing to capillary attraction, they, cause the water to leave the pulp. Though a large quantity of water thus passes through the wire-cloth, it is necessary to assist it by artificial means. This is done by means of the suction-boxes I connected by pipes with the vacuum-pumps I'.

This part of the machine, which is called the “wet-end,” is placed at a slight slope of about 1 in. in its entire length, the lowest end being nearest the strainers.

Underneath the wire-cloth is placed a box called the “save-all” K, connected with the box E'. The water that passes through the wire-cloth contains a considerable quantity of very fine fibres, together with size, alum, clay, and colouring materials, that have passed through the wire, and which would be lost but for the arrangement now universally adopted. It flows into the box E', and is pumped, together with the pulp that has passed through the knotter E (see p. 151), into the high box B, whence the mixed stuff flows on the sand-tables, to be again used to dilute fresh pulp from the stuff-chests. The following numbers will give some idea of the nature and amount of fibre, &c., which passes through. {155} The paper was made from esparto and straw, sized with rosin and starch. It contained 12 per cent. of clay.

	Grains per Gallon of Waste Water.
Fibre	34·37
Clay	37·10
Starch	1·40

It is almost impossible to utilise the whole of the back-water passing through the wire-cloth in the way described. In some mills a portion of this water is made to pass through a “pulp-saver,” such as is shown in Figs. 51 and 52. It consists of a conical drum A, the circumference of which is covered with wire-cloth, and it is caused to revolve slowly by suitable gearing. The water enters by the pipe B, and passes through the meshes of the wire-cloth, the pulp gradually finding its way to the wider end, where it is discharged into the box C. It can then be returned to the beaters.

This pulp-saver can also be used for recovering the fibre from other waste water, such as the wash water from the washing and beating-engines; or it can be used for freeing bleached pulp from water in cases where drainage or hydraulic pressure is not resorted to.

If any pattern or name is required on the paper, it is produced by means of a light skeleton roll, called a “dandy-roll,” covered with raised wires in the form of the desired pattern, {156} placed between the suction-boxes, and pressing lightly on the still moist paper. The paper is thinned where the wire pattern presses, and thus a mark (water-mark) is produced. The other side of the paper has a mark corresponding to the wire-cloth; by using a dandy-roll covered with wire-cloth, the two sides can be obtained alike, such paper going by the name of “wove.”

Paper in which a series of parallel lines are produced is called a “laid” paper.

Some water-marks are produced by means of a dandy-roll in which the pattern is formed by depressions in the surface. The paper is thus thicker where the pattern is formed than in the ground-work. De la Rue (Patent No. 8348, 1884) has patented the use of dandy-rolls so formed as to produce upon the paper the effects both of thickening and thinning.

Imitation water-marks can be produced on the finished paper by subjecting it to pressure in contact with plates on which the design has been produced in relief. In this way very beautiful results can be obtained. (See Patent No. 13,455, 1884.)

It sometimes happens that the wire-cloth slips slightly to one side. This can be obviated by the machine-man shifting, by means of screws, one of the rolls provided for the purpose with a movable journal, until its axis is at a slight angle to that of the other rolls. An automatic apparatus has been invented for this purpose. Two brass plates are fixed, one on each side of the wire-cloth, to a long rod, connected by suitable machinery with the screws working the movable journal, so that, as the wire presses against one or the other of these plates, the roll is shifted so as to correct this.

The paper, which, even after passing the suction-boxes, is still very wet, passes with the wire-cloth between the couch-rolls GG'. These are hollow copper or brass cylinders, covered with a tightly-fitting endless jacket of felt. They may also be made of wood (sycamore or mahogany) or of iron or iron and brass combined. The pressure of the upper couch-roll upon the lower can be regulated by means of {157} screws or levers. They serve to press out water from the paper, and to detach the paper from the wire-cloth. By dexterous manipulation on the part of the machine-men, the paper is transferred to the endless felt, travelling over the rolls k in the direction of the arrows. It is known as the “wet felt,” from the condition of the paper at this stage. In its passage along this felt, the paper passes between two iron rolls K, called the first press-rolls, with the object of having the water squeezed or pressed out of it. These rolls are sometimes covered with a thin brass case, and the top one is provided with an arrangement called the “doctor,” in order to keep it clean, and free from pieces of paper that may have stuck to it. The lower press roll is sometimes covered with an indiarubber jacket. The “doctor” is a kind of knife placed along the whole length of the roll, and pressing against it at every point. The pressure on the rolls can be regulated by means of levers, or, as in the illustration, by the screw k'. It will be readily seen that the under side of the paper that has been next to the felt will, in its still moist condition, have taken to some extent an impression from the felt, while the upper side will have been made comparatively smooth by the pressure against the top roll of the 1st press. In order to make both sides of the paper as nearly as possible alike, it is passed through another set of rolls L, called the 2nd press. This time it is reversed, and enters at the back of the rolls; thus the other side of the paper is next the metal, being taken through by the felt (called the “2nd press felt”) travelling on the small rolls l, the paper, after leaving the wet felt, and before being taken on to the 2nd press felt, travels over the rolls l'. The 2nd press felt is necessary, because the paper is too tender to withstand, unsupported, the pressure of the rolls.

The paper, after passing the 2nd press rolls, travels over the drying-cylinders M, the number of which varies somewhat. In the machine shown, there are in all eight cylinders. Sometimes as many as twelve are employed. Between the {158} 2nd press rolls and the cylinders, a passage S allows easy access to the other side of the machine. The paper generally passes alone over the first two, which are only slightly heated; afterwards it is led over the others by means of felts, as shown. The arrangements shown at R are for the purpose of stretching the felts. The cylinders are heated by means of steam, and are generally divided into two sets, between which is a pair of chilled-iron, highly-polished rolls N, called “smoothers,” the function of which is sufficiently explained by their name. They are also heated by means of steam. The cylinders are usually made of slightly decreasing diameter, in order to allow for the shrinking of the paper on drying. Messrs. G. & W. Bertram introduce into some of their machines one or two small drying cylinders, over which the 2nd press felt travels, the object being to drive off some of the moisture absorbed from the paper. This contrivance is said to give excellent results, and to ensure a considerable saving in felts. The arrangement is shown in Fig. 53. It is especially useful in machines running at a high speed, or in those having limited drying power. After leaving the cylinders, the paper should be quite dry; it is then led through the calenders, of which there are in some machines {159} as many as three sets, though only one is shown. These are similar to the smoothing-rolls, just described. Pressure is applied by the screws O', or by levers and weights. The friction of the hot calenders on the dry paper develops a large quantity of electricity, which occasionally discharges itself in bright sparks.

It is the practice in some mills to cool the paper before passing it through the calenders. This is effected by passing it over a copper cylinder, through which a stream of cold water runs.

The degree of smoothness or “finish” that can be given to the paper by the calenders, depends to a large extent upon the degree of moisture which it contains. As it leaves the last cylinder it is perfectly dry, that is to say, it contains only that amount of water which cellulose, from whatever source, always carries. This amount varies slightly with the nature of the cellulose, and with the plant from which it has been isolated, and also with the state of the atmosphere, it being greater on damp days. It would be impossible so to regulate the drying action of the cylinders that the requisite amount of water should always be left in the paper; it is therefore better to dry it as thoroughly as possible, and then to add the water, by artificial means, just before it passes through the calenders. This method, moreover, has the advantage of damping only the surface of the paper.

Fig. 54 shows a damping arrangement as manufactured by Messrs. James Bertram & Son. The paper on leaving the last drying cylinder passes on to two copper cylinders c, filled with cold water. Steam passes through the pipe a, and issues through a number of fine holes in a pipe running at right angles to the direction in which the paper is travelling, and near to it. The steam condenses on the paper and on the surface of the cylinders, from which the paper absorbs it. The supply can be regulated by the cocks shown in the drawing. The troughs d carry off any excess of condensed water.

Amongst other methods proposed is one by Annandale; it {160} consists in breaking up jets of water into a very fine spray by means of a blast of air.

The finished paper, after passing through the calenders, is wound on the reels P. The gearing by which the whole machine is driven is shown in Plate II.

It sometimes happens that, owing to the increased tension due to the contraction of the paper in drying, the paper breaks. It is therefore necessary to alter the speed of some of the cylinders to compensate for this. A rough expedient which is largely adopted, consists in attaching, by means of a mixture of rosin and tallow, a piece of felt to one or other of the pulleys (Plate II.), and thus altering its speed.

To the filtered solution of gelatine, which should be, if properly prepared, of a pale colour, a quantity of alum solution is added. The effect of alum upon gelatine is very remarkable. If added slowly it will be found gradually to render it stiff until at a certain point the mass will become almost solid; a further addition renders it fluid again. It is in this state ready to be used for sizing purposes. The amount of alum necessary to produce this effect is about 20 per cent. of the weight of the raw material. The alum is also useful in preventing the decomposition of the gelatine, but its chief characteristic is to render the gelatine a more efficient sizing material. There is no doubt that, besides its action upon the gelatine itself, it has a considerable effect upon cellulose. It is of the greatest importance that the alum or the sulphate of alumina, which can be substituted, should not contain any free acid. This is especially necessary in the case of papers made from rags, in the bleaching of which an acid has been used; one effect of which is to remove all basic substances derived from the boiling or bleaching processes. In the case of esparto and similar fibres, a considerable quantity of such substances are present in the pulp, the result being that the free acid of alum is to a large extent neutralised, and its injurious effects prevented.

The effect of the free acid is seen in the weakening of the paper and the destruction of metal surfaces with which it comes in contact. The effect of acid upon cellulose will be found more fully described in p. 12.

Many paper-makers add to the gelatine a certain quantity of soap, the effect of which is to render the paper capable of taking a high finish. The soaps employed should be white and firm, and should be free from rosin. Some soap-makers prepare a special soap for paper-making. They are usually made from tallow, or a mixture of this with a small quantity of coconut oil.

If a solution of soap be added to one of alum, a double decomposition immediately occurs, the fatty acid being thrown down in combination with the alumina, and the soda {164} combining with the sulphuric acid. If, however, the soap solution be previously mixed with a solution of gelatine, no precipitation takes place, the mixture forming an emulsion having somewhat the appearance of thin milk.

Various attempts have from time to time been made to size paper in the engine with gelatine, by precipitating it in the pulp after the manner of rosin sizing, but as yet no successful method has been devised.

It resembles the Fourdrinier machine as far as the couch-rolls A and B. The paper is taken off the wire-cloth on to an endless felt running round the upper couch-roll A, and travelling in the direction of the arrows. It is taken from the felt on to the large drying-cylinder C, of about 10 feet diameter, heated with steam. It is carefully turned and polished so as to impart a high gloss to the surface of the paper with which it is in contact. Calender-rolls are sometimes supplied in addition.

The arrangement shown at D is for the purpose of washing the felt. This is necessary to cool and open it out after passing between the cold press-roll E and the hot cylinder. {165}

The paper, after passing over the greater part of the surface of the cylinder, is sufficiently dried, and it is then wound off at F.

A machine of a very dif­fer­ent con­struc­tion from the or­di­nary form is shown in Fig. 57. The pulp, after passing through the strainer A, enters the vat B, in the centre of which a large drum or cylinder C revolves. This cylinder is covered with fine wire-cloth, and on it the paper is made. As it revolves, the fibres attach themselves to the wire, and the water passes through the meshes, being assisted by means of a pump. The sheet of paper thus formed is taken on to the endless felt passing round the couch-roll D, and travels along with it to the large drying-cylinder E, heated by steam. It leaves the felt at F, and is then taken on to the cylinder, after travelling round which it is sufficiently dried, and is then wound off as at G. The felt on its return journey passes through the washer H, where it is cleaned and freed from adhering particles by the scraper I. It is squeezed free from excess of {166} water by the rolls K. Paper made on such a machine is weaker than that made in the ordinary way, because it has not been found possible to give a shaking motion to the cylinder, and thus the fibres are only imperfectly felted.

A modification of this machine is used for making millboards, the difference being that it has no drying-cylinder. The felt carrying the paper passes between a pair of press-rolls, which squeeze out the water. The sheet of paper is then allowed to wind round the top press-roll until of the required thickness. When this happens, it is cut off the roll by a knife. The thick sheets so produced are dried either in the open air or in a room heated for the purpose. (See p. 108, Fig. 31.)