Part 5 (1/2)
The matted pulp, now having sufficient body, pa.s.ses on between two rolls covered with felt which deliver the web of damp paper upon an endless belt of moist felt, while the ”wire” pa.s.ses under and back to continue a fresh supply. The paper is as yet too fragile to travel alone, and the web felt carries it between two metal rolls called the first press-rolls. These squeeze out more water, give a greater degree of compactness to the fibers, smooth the upper surface, and finally deliver the web of paper to a second felt ap.r.o.n which carries it under and to the back of the second press-rolls. In this way the under surface comes to the top, and is in its turn subjected to the smoothing process. A delicate sc.r.a.per or blade, the length of the press-rolls, is so placed on each roll that should the endless web from any cause be broken, the blade may operate with sufficient force to prevent the wet paper from clinging to the rolls and winding about them. From this point the paper travels alone, having become firm and strong enough to sustain its own weight; pa.s.sing above the second press-rolls, it resumes its onward journey around the drying cylinders, pa.s.sing over and under and over and under. The drying cylinders are hollow and heated by steam, their temperature being regulated according to requirements. These driers, made from iron or steel, are usually from three to four feet in diameter and vary in length according to the width of the machine. There are from twelve to fifty of these cylinders, their number depending upon the character and weight of the paper to be produced, very heavy sheets requiring many more drying cylinders than sheets of lighter weight.
Strange, almost phenomenal, conditions come about in the transformation from filmy pulp to finished paper. A sheet which, though formed, is at the first press-roll too fragile to carry its own weight, becomes possessed of a final strength and power that is almost incredible. The myriad of minute fibers composing the sheet, upon drying uniformly, possesses great aggregate strength. A sheet of paper yields readily to tearing, but the same sheet, when a perfectly even tension is applied, will demonstrate that it is possessed of wonderful resisting power. In evidence may be cited an instance that seems almost beyond belief.
Through some curious mishap a web of heavy paper, in fact, bristol board, which had been thoroughly formed, was suddenly superheated and then cooled while still on the driers. This was caused by a difference in temperature of the driers and resulted in the sudden contraction of the web of bristol; the strain on the machine was so great that not only were the driving-cogs broken on two of the driers around which the paper was at the moment pa.s.sing, but the driers themselves were actually lifted out of place, showing a resisting power in the paper of at least several tons. The paper now pa.s.ses to the upright stack of rolls which are known as ”calenders.” The word is derived from calendra; a corruption of cylindrus, a roller or cylinder. They are simply rollers revolving in contact, and heated from the interior by steam. These calenders are used for giving to the paper a smooth and even surface, and are also employed in the smoothing and finis.h.i.+ng of cloth. The speed with which the paper pa.s.ses through these cylinders is remarkable, from one hundred to five hundred feet running through and over the machine in a minute; and in some of the most recent mills the web is as wide as one hundred and fifty-six inches (thirteen feet); this is very nearly double the average machine width of a very few years ago, while the speed has increased in proportionate ratio; only a few years ago the maximum speed was from two hundred and fifty to three hundred feet per minute; at this writing (1900) there are machines in operation which run as high as five hundred feet per minute. But great as has been the increase in the production of paper, the demand has kept pace steadily. The wonderful product of the rag-bag holds an invincible position in the world's economy.
For machine-finished book and print papers, as well as for other cheaper grades, the process ends with the calenders, after which the paper is slit into required widths by disc-knives which are revolving, and so cut continuously. Paper intended for web newspaper presses is taken off in continuous rolls of the widths required, varying from seventeen to seventy-six inches, according to the size of the paper to be printed.
These reels contain from fifteen to twenty-five thousand lineal feet of paper, or from three to five miles. The amount of paper used in disseminating the news of the day is enormous; sometimes one or two mills are required to manufacture the supply for a single metropolitan daily, while one New York newspaper claims to have used four hundred and fifty tons of paper in one Christmas edition, which is about four times the amount of its regular daily consumption.
After having been slit into the proper widths by the revolving knives, ordinary flat and book papers are cut into sheets by a straight knife revolving at proper intervals on a horizontal drum. The paper, in sheets, is carried by a travelling ap.r.o.n to a receiving table at the end of the machine, where the sheets as they fall are carefully examined by experts, usually women, who remove any that may be imperfect.
The entire length of a paper machine, from the screens to the calenders, is about one hundred and twenty-five feet, while the height varies, the average being about ten feet. The machines, while necessarily of the finest adjustment, are ponderous and heavy, weighing in some cases as much as four hundred tons, this being the weight of the machine itself, exclusive of its foundations. The machine-room is of necessity well lighted and thoroughly ventilated, and should be kept clean throughout, as cleanliness is an essential factor in the making of good paper. While the same general process applies to all cla.s.ses of paper made, the particular character of any paper that is to be produced determines exactly the details of the process through which it shall pa.s.s and regulates the deviations to be made from the general operations in order to secure special results. For example, some papers are wanted with a rough or ”antique” finish, as it is called; in such cases calendering is omitted. Another special process is that by which the paper is made with a ragged or ”deckel-edge;” this result is obtained in some mills by playing a stream of water upon the edge of the pulp, crus.h.i.+ng and thinning it, and thus giving it a jagged appearance. At the present time this ”deckel-edge” paper is being quite extensively used in high-cla.s.s bookwork. In the case of writing papers, as has already been stated in the description of the beating engines, a vegetable sizing made from resinous matter is introduced into the paper pulp while it is still in solution, and mixes with it thoroughly, thus filling more or less completely the pores of the pulp fibers. This is found sufficient for all ordinary book-papers, for papers that are to be printed upon in the usual way, and for the cheapest grades of writing-paper, where the requirements are not very exacting and where a curtailment of expense is necessary. For the higher grades of writing-paper, however, a distinctly separate and additional process is required. These papers while on the machine in web form are pa.s.sed through a vat which is called the size-tub, and which is filled with a liquid sizing made of gelatine from clippings of the horns, hides, and hoofs of cattle, this gelatine or glue being mixed with dissolved alum and made fluid in the vat. Papers which are treated in this way are known as ”animal,” or ”tub-sized.”
We have duly described machine-dried papers, but these higher grades of writing-papers are dried by what is known as the loft, or pole-dried process. Such paper is permitted to dry very slowly in a loft specially constructed for the purpose, where it is hung on poles several days, during which time the loft is kept at a temperature of about 100 Fahrenheit.
Another detail of considerable importance is that of the ”finish” or surface of the paper. When paper with a particularly high or glossy surface is desired, it is subjected to a separate process, after leaving the paper machine, known as supercalendering.
”Supercalendering” is effected by pa.s.sing the web through a stack of rolls which are similar to the machine calenders already described.
These rolls are composed of metal cylinders, alternating with rolls made of solidified paper or cotton, turned exactly true, the top and bottom rolls being of metal and heavier than the others; a stack of supercalenders is necessarily composed of an odd number of rolls, as seven, nine, or eleven. The paper pa.s.ses and repa.s.ses through these calenders until the requisite degree of smoothness and polish has been acquired. The friction in this machine produces so much electricity that ground wires are often used to carry it off in order that the paper may not become so highly charged as to attract dust or cause the sheets to cling together. When the fine polish has been imparted, the rolls of paper go to the cutting machines, which are automatic in action, cutting regular sheets of the required length as the paper is fed to them in a continuous web. In the manufacture of some high grades of paper, such as linens and bonds, where an especially fine, smooth surface is required, the sheets after being cut are arranged in piles of from twelve to fifteen sheets, plates of zinc are inserted alternately between them, and they are subjected to powerful hydraulic pressure. This process is termed ”plating,” and is, of course, very much more expensive than the process of supercalendering described above.
From the cutters, the sheets are carried to the inspectors, who are seated in a row along an extended board table before two divisions with part.i.tions ten or twelve inches high, affording s.p.a.ces for the sheets before and after sorting. The work of inspection is performed by women, who detect almost instantly any blemish or imperfection in the finished product as it pa.s.ses through their hands. If the paper is to be ruled for writing purposes, it is then taken to the ruling machines, where it is pa.s.sed under revolving discs or pens, set at regular intervals. These convey the ruling ink to the paper as it pa.s.ses on through the machine, and thus form true and continuous lines. If the paper is to be folded after ruling, as in the case of fine note-papers, the sheets pa.s.s on from the ruling machine to the folding machines, which are entirely automatic in their action. The paper is stacked at the back of the first folding guide and is fed in by the action of small rubber rollers which loosen each sheet from the one beneath, and push it forward until it is caught by the folding apparatus. Man's mechanical ingenuity has given to the machines of his invention something that seems almost like human intelligence, and in the case of the folding machine, the action is so regular and perfect that there seems to be no need of an attendant, save to furnish a constant supply of sheets. The folding completed, cutting machines are again brought into requisition, to cut and trim the sheets to the size of folded note or letter-paper, which is the final operation before they are sent out into the world on their mission of usefulness.
The finished paper may or may not have pa.s.sed through the ruling and folding process, but in either case it goes from the cutters to the wrappers and packers, and then to the s.h.i.+pping-clerks, all of whom perform the duties indicated by their names. The wonderful transformation wrought by the magic wand of science and human invention is complete, and what came into the factory as great bales of offensive rags, disgusting to sight and smell, goes forth as delicate, beautiful, perfected paper, redeemed from filth, and glorified into a high and n.o.ble use. Purity and beauty have come from what was foul and unwholesome; the highly useful has been summoned forth from the seemingly useless; a product that is one of the essential factors in the world's progress, and that promises to serve an ever-increasing purpose, has been developed from a material that apparently held not the slightest promise. Well might the _Boston News Letter_ of 1769 exclaim in quaint old rhyme:
Rags are as beauties which concealed lie, But when in paper, charming to the eye!
Pray save your rags, new beauties to discover, For of paper truly every one's a lover; By the pen and press such knowledge is displayed As would not exist if paper was not made.
And well may man pride himself on this achievement, this marvelous transformation, which represents the fruitage of centuries of striving and endeavor!
Up to this point the reference has been almost entirely to paper made from rags, but radical improvements have been made, caused by the introduction of wood pulp, and these are of such importance that the account would not be complete without some mention of them. These changes are mainly in the methods of manipulating the wood to obtain the pulp, for when that is ready, the process from and including the ”washers” and ”beaters,” is very similar to that already described. All papers, whether made from rags or wood, depend upon vegetable fiber for their substance and fundamental base, and it is found that the different fibers used in paper-making, when finally subdued, do not differ, in fact, whether obtained from rags or from the tree growing in the forest.
In the latter case the raw wood is subjected to chemical treatment which destroys all resinous and foreign matters, leaving merely the cellular tissue, which, it is found, does not differ in substance from the cell tissue obtained after treating rags. In either case this cellular tissue, through the treatment to which the raw material is subjected, becomes perfectly plastic or moldable, and while the paper made from one differs slightly in certain characteristics from the paper made from the other, they are nevertheless very similar, and it might be safe to predict that further perfecting of processes will eventually make them practically alike.
The woods used for this purpose are princ.i.p.ally poplar and spruce, and there are three cla.s.ses of the wood pulp: (1) mechanical wood, (2) soda process wood, and (3) sulphite wood pulp. The first method was invented in Germany in 1844. The logs are hewn in the forest, roughly barked, and s.h.i.+pped to the factory, where the first operation is to cut them up by steam saws into blocks about two feet in length. Any bark that may still cling to the log is removed by a rapidly revolving corrugated wheel of steel, while the larger blocks are split by a steam splitter. The next stage of their journey takes these blocks to a great millstone set perpendicularly instead of horizontally. Here a very strong and ingenious machine receives one block at a time, and with an automatically elastic pressure holds it sidewise against the millstone, which, like the mills of the G.o.ds, ”grinds exceeding fine,” and with the aid of constantly flowing water rapidly reduces these blocks to a pulpy form. This pulp is carried into tanks, from which it is pa.s.sed between rollers, which leave it in thick, damp sheets, which are folded up evenly for s.h.i.+pment, or for storage for future use. If a paper-mill is operated in connection with the pulp-mill, the wood pulp is not necessarily rolled out in sheets, but is pumped directly from the tanks to the beaters.
In the preparation of pulp by the other processes, the blocks are first thrown into a chipping machine with great wheels, the short, slanting knives of which quickly cut the blocks into small chips.
In the soda process, invented by M. Meliner in France in 1865, the chips from spruce and poplar logs are boiled under pressure in a strong solution of caustic soda.
When sulphite wood pulp is to be prepared, the chips are conveyed from the chipper into hoppers in the upper part of the building. Here they are thrown into great upright iron boilers or digesters charged with lime-water and fed with the fumes of sulphur which is burned for the purpose in a furnace adjoining the building and which thus forms acid sulphide of lime. The sulphite process was originally invented by a celebrated Philadelphia chemist, but was perfected in Europe.
The ”cooking,” or boiling, to which the wood is subjected in both the soda and sulphite processes, effects a complete separation of all resinous and foreign substances from the fine and true cell tissue, or cellulose, which is left a pure fiber, ready for use as described. In the case of all fibers, whether rag or wood, painstaking work counts, and the excellence of the paper is largely dependent upon the time and care given to the reduction of the pulp from the original raw material.
Chemical wood pulp of the best quality makes an excellent product, and is largely used for both print and book paper; it is frequently mixed with rag pulp, making a paper that can scarcely be distinguished from that made entirely from fine rags, though it is not of the proper firmness for the best flat or writing papers. All ordinary newspapers, as well as some of the cheaper grades of book and wrapping paper, are made entirely from wood, the sulphite or soda process supplying the fiber, and ground wood being used as a filler. In the average newspaper of to-day's issue, twenty-five per cent of sulphite fiber is sufficient to carry seventy-five per cent of the ground wood filler. The value of the idea is an economical one entirely, as the ground wood employed costs less than any other of the component parts of a print-paper sheet.
The cylinder machine, to which reference was made earlier in the chapter, was patented in 1809 by a prominent paper-maker of England, Mr.
John d.i.c.kinson. In this machine, a cylinder covered with wire cloth revolves with its lower portion dipping into a vat of pulp, while by suction a partial vacuum is maintained in the cylinder, causing the pulp to cling to the wire until it is conveyed to a covered cylinder, which takes it up and carries it forward in a manner similar to the system already described. This machine is employed in making straw-board and other heavy and cheap grades of paper.
Generous Mother Nature, who supplies man's wants in such bountiful fas.h.i.+on, has furnished on her plains and in her forests an abundance of material that may be transformed into this fine product of human ingenuity. Esparto, a Spanish gra.s.s grown in South Africa, has entered largely into the making of print-paper in England. Mixed with rags it makes an excellent product, but the chemicals required to free it from resin and gritty silica are expensive, while the cost of importation has rendered its use in America impractical. Flax, hemp, manila, jute and straw, and of course old paper that has been once used, are extensively employed in this manufacture, the process beginning with the chemical treatment and boiling that are found necessary in the manipulation of rags. The successful use of these materials has met demands that would not otherwise have been supplied. As a result, the price has been so cheapened that the demand for paper has greatly increased, and its use has been extended to many and various purposes.
Many additional items of interest might be described in connection with the methods of manufacturing paper, but as this work is intended for the general reader, rather than for the manufacturer, those wis.h.i.+ng further information are referred to technical works on the subject.