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complementary colour and thus the impression contained in the pulp as impurities, settle of white is presented to the eye ; this process behind these ribs. is known as “ tinting” of papers.
The pulp still contains fibre bundles which After bleaching and dyeing the pulp is have escaped the action of the knives and also ready to be conducted to that part of the mill small knots consisting of felted fibres, as well in which its conversion into paper actually as other impurities, which, if allowed to pass takes place.
along to the paper machine would show as From the beater it is allowed to flow into “specks." To free the pulp, as far as posthe stuff chest (a, Figs. 21 and 22), a large sible, from these impurities, it is necessary vessel made of wood or built in bricks and to pass it through one or more “ strainers,” cement, provided with either a vertical or a c (Figs. 21 and 22). The operation of horizontal stirring arrangement. The quantity | “ straining” is accomplished by the aid of of pulp which comes from the stuff chest and brass plates provided with very fine V-shaped which is required to produce a paper of certain slits which are narrower at the top and are thickness and at a certain speed has to be wider towards the other side of the plate. carefully regulated. To achieve this the pulp These slits which vary in width for the different is generally first pumped to the so-called qualities of pulp are, however, only just wide “regulating box," from which a continuous enough to allow the single fibres to pass stream under a constant pressure is conducted through whilst all the coarser particles are reto the paper machine.
tained on the top of the plate. A number of Another arrangement in very common use, these plates securely bolted together form a especially in Continental mills, has been strainer. By means of rapidly revolving ratched devised for regulating the flow of pulp from the wheels, which support the axle of the strainer, chest to the sand tables and is the following: - a shaking motion is produced which greatly The horizontal stirring arrangement in the assists the passage of the pulp through the stuff chest is provided at one end with a cir slits. A strainer in which the plates are bolted cular rim which carries on its circumference a together so as to form a flat surface is called a series of small beakers or buckets. During | “flat strainer.” The other types in which their downward journey these beakers are the plates form a rectangular box or a slowly filled by tipping into the pulp. On reaching revolvirg cylinder, are termed “revolving the highest position the pulp is discharged strainers.” into a channel connected with the sand tables ; Flat strainers have been introduced in this channel may be widened or narrowed which the passage of the pulp is consideraccording to the amount of pulp required, the ably accelerated by a vacuum produced excess of pulp flowing back into the stuff underneath the strainer plate. chest.
Automatic cleansing devices, consisting of Special pulp regulators, consisting of two or endless bands provided with india-rubber three pumps, as well as arrangements in | scrapers or brushes which move over the surwhich the flow of pulp is regulated directly face of the plates and carry away the knots, from, and in accordance with, the speed of the are also in use with flat strainers. In other paper machine, are used in some mills.
self-cleansing strainers the knots are carried In the manufacture of heavily-sized, loaded along with the pulp into channels from which and coloured papers, it is essential to the pro- | they are conducted to “patent knotters." duction of uniformity of shade and quality to | The rotating strainer invented by Wandel use the so-called “back water” for the (Fig. 23), consists of a revolving cylinder (a) thinning down of the pulp in place of fresh placed horizontally in a trough; this cylinder water. The mixing is usually accomplished is formed of a number of plates bolted securely in a small mixing chest placed above the together the narrower parts of the slits being level of the sand tables to which pulp and on the inside. The pulp enters through the back water are conducted ; the pulp then hollow journals (6), and finds its way through travels over the “ sand tables" (6, Figs. 21 the slits into the trough, whilst knots and and 22), which consist of shallow troughs other inpurities are lifted by ribs between varying in length considerably according to the plates inside the cylinder whence they the quality of paper made on the machine. ultimately fall into, and are conducted away Ribs are fixed cross-ways on the bottom of through, a channel (c) situated above the these troughs and during their passage over channel through which the pulp enters. A the sand tables heavy particles, such as sand, spurt pipe (d) fixed above the cylinder directs
a stream of fresh water against the plates, thus containing a small drumwasher, by aid of preventing choking of the slits.
which water is removed and unnecessary After its passage through the strainers the dilution of the stuff in the vat avoided. From pulp is ready for conversion into paper. Up this the pulp flows in a continuous stream into to this point the series of processes through the vat, which is a rectangular vessel usually which pass the raw materials both for paper | made of hard wood; settling of the fibres in
made by hand and by machine, are iden- , the vat is prevented by the use of a stirring tical, with the sole exception of the sizing arrangement and a uniform temperature is of the pulp in the engine. We may therefore maintained by means of a steam-heated closed at this stage conveniently consider the older of coil. The sheet of paper is actually made the two methods of making paper, namely, upon an appliance called the “ mould;" the the so-called “hand process.” The pulp, as mould consists of two parts, the framework, it leaves the strainer, is conducted to a box made of wood, over which is evenly stretched
a piece of fine wire gauze supported by coarser having been deposited. By using wires of wires, and the “ deckle," a narrow frame varying thickness, and also by sewing on to which fits closely on to the top of the wire | the mould patterns produced by pressing very gauze screen. The deckle serves the purpose flexible wire gauze between steel dies, most of preventing the pulp from flowing away over elaborate water-marks may be produced. the sides of the mould ; the amount of pulp No size having been used with the pulp, the removed from the vat, and therefore the thick sheets, as they come from the drying-rooms, ness of the finished paper, are, to a certain are absorbent, and therefore unsuited for extent, determined by the height of the deckle. writing and for some printing purposes; the
The workman who handles the mould is next operation through which hand-made paper called “the vatman”; he takes from the vat has to pass is the so-called “tub sizing," and the quantity of pulp required to form a sheet of is accomplished by passing the sheets through paper by dipping the mould into the pulp and , a solution of glue or gelatine. This is generally lifting it out whilst holding it horizontally. As done by hand, although some mills are prothe water passes away through the sieve the vided with special sizing machines in which the vatman gives the mould a peculiar shaking sheets travel through the size on endless motion by means of which felting or inter bands. twining of the fibres is ensured; the strength The glue, as used in the tub sizing, is either of the resulting paper depends to a very con prepared in the mill by treating clippings of siderable extent upon the skill with which this hides, bones, horn, &c., with water, thus expart of the process is performed.
tracting the gelatine ; or very pure gelatine, As soon as the water has drained sufficiently which dissolves readily in water, is bought and the mould is passed by the vatman to the used by the paper-maker. A certain amount “ coucher," who, after the deckle has been re- of alum is always added to the gelatine solumoved, presses the wet sheet on to a felt. The tion in the manufacture of highly-finished mould is then removed and the sheet of paper papers and soap is frequently used in concovered with another felt. Paper and felts are junction with the tub size. thus placed carefully alternately one on the The sheets are freed from excess of size by other until a so-called “felt post” has been | pressing in screw or hydraulic presses; they obtained; this is then removed to a press by are then separated and conveyed to the drying means of which a large portion of the water is chamber for the final drying. Hand-made slowly pressed out. The sheets having obtained papers are finished either by repeated pressing sufficient strength by the treatment are sepa- | in hydraulic presses, by calendering, or by rated from the felts and placed one on the top plate glazing. of the other and are once more taken to the presses ; the felt marks are thus removed and the surface of the paper is considerably improved.
Miscellaneous. In the case of some papers this pressing is repeated, the sheets being separated and again placed in contact between each operation.
MOTORS.* The pressed papers are next conveyed to the Speed in locomotion appeared to be the first drying-room where they are placed on ropes, consideration, whether as regards mails, passengers, usually made of cow-hair, and slowly dried. A or goods; and three or four classes of machines mould, the covering gauze of which consists appeared to be ambitious to drive pedestrians, horseof wires of uniform thickness placed at equal
men, and horse-drawn vehicles off the road. The distances lengthways and crossways, is called
first practical steam carriage was used by Trevithick
in the year 1802. The points of importance in con. a “wove mould.” If the wires are arranged closely together in the one direction but are
nection with traction engines and their trailers are
their speed, weight, and width. Mr. E. R. Calthrop, placed further apart in the other direction,
M.Inst.C.E., one of the founders of the Liverpool the mould is termed a “laid mould.” Papers
Self-propelled Traffic Association, was opposed to made on the two kinds of moulds are called
any weight restriction, but it was to be remembered “ wove” and “ laid” papers respectively.
that the momentum of heavily laden waggons drawn Water-marks are produced by wires sewn
by a powersul traction engine at the maximum speed on the top of the wire on the mould. The
• Extracted from the Presidential Address by Mr. Charles paper is thinner and therefore more trans
Hawksley to the Engineering Section of the British Asso parent at these parts, owing to fewer fibres | ciation at Southpoit.