_MAKING PAPER BY MACHINERY._
The Fourdrinier Machine.--Bertrams' Large Paper
Machine.--Stuff Chests.--Strainers.--Revolving Strainer
and Knotter.--Self-cleansing Strainer.--Roeckner's Pulp
Strainers.--The Machine Wire and its Accessories.--Conical
Pulp Saver.--The Dandy Roll.--Water Marking.--De la Rue's
Improvements in Water-marks.--Suction Boxes.--Couch Rolls.--
Press Rolls.--Drying Cylinders.--Smoothing Rolls.--Single
Cylinder Machine.
=The Fourdrinier Machine.=--It is just ninety years since Louis
Robert, a Frenchman, devised a machine for making a continuous
web of paper on an endless wire-cloth, to which rotary motion was
applied, thus producing a sheet of paper of indefinite length.
The idea was subsequently improved upon by Messrs. Fourdrinier,
who adopted and improved upon M. Robert's machine, and with the
valuable aid of Mr. Bryan Donkin, a young and gifted machinist,
in the employ of Mr. Hall, engineer, of Dartford, constructed a
self-acting machine, or working model, in 1803, which, from its
effectiveness and general excellency of workmanship, created
at the time a profound sensation. This machine was erected at
Frogmore, Hertfordshire; and in 1804 a second machine was made
and put up at Two-Waters, Herts, which was completely successful,
and the manufacture of continuous paper became one of the most
useful and important inventions of the age. From that period the
"Fourdrinier," with some important improvements introduced by Mr.
Donkin, gradually, but surely, became established as an absolutely
indispensable machine in every paper-mill all over the world.
Although the machine has been still further improved from time to
time, those of recent construction differ but little in principle
from the original machine. An illustration of the machine is shown
in Fig. 25, the detailed parts of which are expressed on the
engraving.
=Bertrams' Large Paper Machine.=--The principal aim in the
construction of the paper-making machine has been to imitate, and
in some particulars to improve, the operations involved in the
art of making paper by hand, but apart from the greater width
and length of paper which can be produced by the machine, the
increased rapidity of its powers of production are so great that
one machine can turn out as much paper in three minutes as could
be accomplished by the older system in as many weeks. The drawing
represents the modern paper-machine as manufactured by Bertrams,
Limited, who supplied one of these machines to Mr. Edward Lloyd,
for the _Daily Chronicle_ Mill, at Sittingbourne, which runs a
wire 40 feet long by 126 inches wide, this being, we believe, the
largest and widest paper-machine in the world. It is provided with
20 cylinders, chilled calenders, double-drum reeling motion, with
slitting appliance for preparing webs to go direct to the printer's
office without the assistance of a re-reeling machine, and is
driven by a pair of coupled condensing steam-engines. On our recent
visit to Mr. Lloyd's mill we were much struck with the excellent
working of this splendid machine.
In the illustration, as will be seen, there are two sets of
drying cylinders, while small cylinders, or felt drying-rolls,
from 16 to 24 inches in diameter, are introduced to the felts of
the cylinders, before the smoothing-rolls, which discharge the
moisture with which the felts are impregnated from the damp paper,
whereby a considerable saving in felts is effected. Messrs. Bertram
state that the highest speed yet attained has been by their own
machinery, and is 270 feet of paper per minute.
[Illustration: Fig. 25.]
The progress of the pulp after it leaves the beating-engines for
conversion into paper may be described as follows:--The valve at
the bottom of the beating-engine is opened, when the pulp flows
through a pipe into the stuff-chests, which are generally situated
below the level of the engines. The beaters are then rinsed with
clean water to remove any pulp that may still cling to them, the
rinsing water passing also into the stuff-chests.
=Stuff-chests.=--These are large vessels of a cylindrical form, so
that the pulp may have no corners to lodge in, and are generally
made of wood, though sometimes they are made of cast-iron plates
bolted together. The chests are of various dimensions, according
to the requirements of the mill, being usually about 12 feet in
diameter and 6 feet deep, having a capacity for 1,000 to 1,200
lbs. of stuff. To keep the pulp well mixed in the stuff-chest,
of which two are usually employed for each machine, a vertical
shaft, carrying two horizontal arms, each extending nearly across
the interior of the chest, are provided, which are only allowed
to revolve at a moderate speed, that is, about two or three
revolutions per minute, otherwise the pulp would be liable to work
up into knots, and thus form a defective paper. Motion being given
to the shaft, the rotating arms keep the pulp and water uniformly
mixed, at the same time preventing the pulp from sinking to the
bottom of the stuff-chest.
The pulp is next transferred to a regulating box, or "supply box,"
by means of a pump called the _stuff-pump_. The regulating-box,
which has the effect of keeping a regular supply of pulp in the
machine, is provided with two overflow pipes, which carry back to
the stuff-chests any superfluous pulp that may have entered them,
by which the stuff in the regulating-box is kept at a uniform
level, while the machine is supplied with a regular and uniform
quantity of the diluted pulp. The stuff-pump conveys the pulp
through a valve in the bottom of the regulating-box in a greater
quantity than is actually required, the superfluity returning
to the stuff-chests by the overflow pipes; thus the supply-box,
being always kept full, furnishes a regular and uniform supply
of pulp to the sand-tables, or sand-traps as they are sometimes
called. _Sand-tables_ are large wooden troughs, varying in size at
different mills, but Mr. Dunbar gives the following proportions for
a first-class sand-trap; namely, 14 feet long by 8 feet wide, and 8
inches deep. The bottom of the trap is covered with felt, sometimes
old first-press felt being used, and is divided into several
compartments by thin bars of lead or iron, or strips of wood, which
keep the felt in position, and also retain any particles of sand
or other heavy solid matter that may be accidentally present in
the pulp. For the purpose of diluting the pulp for the machine,
there is, attached to the inlet of the sand-traps, a box with
two supply-taps, one for the delivery of pulp, and the other for
water; and these being turned on, the pulp and water flow over the
sand-traps, and the diluted pulp then falls into the strainers,
which, while allowing the fine pulp to pass freely, keep back all
lumps of twisted fibre, and particles of unboiled fibre, which
latter, if not removed, would appear as specks on the surface of
the finished paper.
=The Strainers= are formed of brass or bronze plates, in which are
cut a very large number of narrow slits, which gradually widen
downward, so as to prevent the pulp from lodging. Each plate has
about 510 slits, and several plates, connected together by bolts,
constitutes the complete strainer. When in use, the strainer
receives a jogging motion, which is communicated to it by means of
small ratchet wheels keyed on shafts passing beneath the machine;
this causes the fibres to pass more freely through the slits. There
are many different forms of strainers, which have been the subject
of numerous patents. It will be sufficient, however, to give one or
two examples of improved strainers which have been more recently
adopted by manufacturers.
[Illustration: Fig. 26.]
=Revolving Strainer and Knotter.=--The revolving strainer, which
was invented by the late senior partner in the firm of Messrs. G.
and W. Bertram (now Bertrams, Limited), has since been extensively
adopted, and the present firm have introduced a patent knotter
in conjunction with the apparatus, the complete arrangement of
which is shown in Fig. 26. The standard size for these revolving
strainers is 7 feet long by 18⅜ inches wide on each side of the
four surfaces. The vats are of cast iron, and the apparatus is
supplied with driving gear, bellows, regulating boxes and spouts,
as necessary. The firm also supply these strainers with White's
patent discs, and Annandale and Watson's arrangement. A A are two
revolving strainers, as applied to the paper-machine, showing
gearing for strainers and bellows. B is the patent knotter as used
for two strainers. C is the counter-shaft overhead. D D is the back
shaft of the machine, and E E the wire of the paper-machine.
[Illustration: Fig. 27.]
=Self-cleansing Strainer.=--The same firm also introduced this
form of strainer, an illustration of which is given in Fig. 27. The
action of the strainer is described as follows:--
The pulp flows on to the strainer at A, and passes away through
the pipes B B. At C is a valve for the discharge of waste pulp.
The strainer plates have an inclination of about 1 inch in the
direction of their length, and in those which are nearest to A,
where the pulp enters, the slits are wider, the knots being pushed
forward by the energy of the flow. The vacuum pumps, D D, are
worked from the shaft E. The tubes F F are for supplying water to
the plates, by which the coarser particles of the pulp are pushed
forward, and the slits are thus kept clean. The strainer will pass
from 18 to 20 tons of the finest paper per week.
[Illustration: Fig. 28.]
[Illustration: Fig. 29.]
=Roeckner's Pulp Strainers.=--This invention consists in
constructing boxes, with one or both ends open, forming the
strainers, fixed, or to slide in or out, so as to be readily
cleaned. One or more fans are fitted in these boxes, and are put in
motion from the outside, so as to cause what is called "suction"
through the strainers. One or a number of such boxes are fixed
into a vat, the open ends discharging the pulp which has passed
through the strainers to the paper-machine, and can be so arranged
that all the fans are worked on one shaft. The vat may be divided
into compartments, so that the stuff flows from one to the other.
Instead of boxes, the strainers may be formed of tubes, in which
suitable slits or perforations have been provided. The tubes will
be perfectly closed at one end, and the strained pulp, after
passing through them, will be delivered to the paper-machine from
their open ends, which may fit into a ring, so that when cleaning
is required they may be easily lifted out or in. The suction is
provided inside these tubes by the fans, which are oscillated by
suitable gear from the outside of the vat. The strainers may,
instead of being stationary, be attached to the fans and oscillate
with them, in which case the open ends would have to be attached
to the vat by an indiarubber or cloth ring, or the strainers may
oscillate whilst the fans are stationary. Any number of these
strainers may be fixed into vats, disposed vertically or otherwise.
In the vat A, Fig. 28, which receives the pulp to be strained,
are several tubes, _p p p_, with one end open, having slits in
them similar to strainer plates. Inside of these are two, three,
or more plates, _f f f_, Fig. 29, running the full length of the
tube fixed to the shafts, _s s s_, and to the sides of the tubes,
which serve as fans, besides giving strength to the tubes. The
shafts _s s s_ are carried in bearings at each end, and have each
one end projecting through, upon which are keyed levers, _h h
h_, which, being connected to a rod _r_, worked by an eccentric,
_e_, at the end, gives an oscillating motion to the tubes and
fans. Any number of tubes may be in the vat, and may either work
separately or divided. With several tubes it is preferable to have
them arranged as shown in the drawing by division plate _d_, so
that the accumulated "knots," &c., may flow finally into the end
compartment (which will form an auxiliary strainer), and may be
mixed with more water, so that the fine pulp still contained in
the stuff can flow away through the slits and the knots, &c., be
taken out when necessary. The tubes should be placed so far apart
that a workman can get his hand between. The closed ends work free
in the stuff, while the open ends run through indiarubber sheet or
other material, fitted so well to the tube that the fibre can only
get through the slits of the tube to flow on to the paper-machine
through the channel at side by the sluice _v_. The arrows indicate
the direction of the flow of pulp.
[Illustration: Fig. 30.]
Mr. Dunbar says, "the straining power necessary to pass and clean
pulp in an efficient manner for 25 tons of finished paper per week
is two revolving strainers, consisting of four rows of plates, or 7
feet by 18 inches of straining surface on each of the four sides,
the plates being cut No. 2½ Watson's gauge."
After passing through the strainers the pulp should be absolutely
free from knots or objectionable particles of any kind, and in a
proper condition for conversion into paper.
=The Machine Wire and its Accessories.=--On leaving the strainers
the pulp passes into a vat, in which is a horizontal agitator,
which causes the pulp and water to become well mixed, and ready to
flow on to the endless wire-cloth of the machine. The wire-cloth is
made of exceedingly fine wire, the meshes ranging from 60 threads
and upwards to the inch, there being sometimes as many as 1,900
holes per square inch, but the meshes usually employed run from
2,000 to 6,000 per square inch. The ends of the cloth are united by
being sewn with very fine wire. The width of the wire-cloth varies
considerably, the greatest width being, we believe, that supplied
for the large machine at Mr. Edward Lloyd's mill at Sittingbourne,
which is 126 inches. The length of the wire-cloth is generally from
35 to 40 feet, the latter being considered preferable. Beneath the
wire is placed a shallow box called the "save-all," which receives
the water as it flows through the wire cloth from the pulp. In
order to effect a further saving of pulp which escapes through the
meshes of the wire-cloth, a machine called a "pulp-saver" is used
at some mills, through which the backwater, as it leaves the box or
save-all referred to, is passed.
The wire-cloth is supported by a series of brass tube rolls, which
are so placed as to render the layer of pulp on the wire absolutely
uniform, by which a regular thickness of the finished paper is
ensured. The wire is attached to a malleable iron frame, having a
sole-plate of cast iron, and carries a brass or copper breast-roll,
18 inches in diameter, a guide-roll 7 inches in diameter, and four
brass or copper rolls 5 inches in diameter under the wire, with
shafts extending through the rolls, and furnished with brass bushes
and brackets, and a self-acting guide upon the 7-inch guide-roll.
The tube-rolls or "carrying tubes" are carried upon brass bearings.
Attached to the sole-plate of the wire framing are three cast-iron
stands on each side for supporting the save-all beneath the wire.
To regulate the width of the paper there is on the top of the wire
a set of brass "deckles," carried on a brass frame passing over the
first suction box, of which there are two, and supported on the
wire frame by iron studs fixed in the frame. At each end of the
deckle-frame is a pulley for carrying the deckle-strap, with three
similar pulleys for expanding it. The deckle-frame is furnished
with two endless straps of india-rubber, these straps keeping the
pulp to the width required for forming ledges at the sides of the
web.
[Illustration: Fig. 31.]
=The Conical Pulp-saver=, which is shown in Fig. 31, was invented
by the late Mr. George Bertram and Mr. Paisley, and is manufactured
by Bertrams, Limited. Its use is to extract fibres from the washing
water before going into the river or otherwise. For the water
from the drum-washer, washing and beating engines, and for the
water from the paper-making machine, save-all, &c., it has proved
itself of great utility. It is simple in construction, small in
cost, takes up little room, and is easily repaired. When placed to
receive the washings from the beaters or paper-machine, the pulp
saved, if kept clean, can always be re-used. A is a conical drum
which is covered with wire-cloth, and it is made to revolve slowly
by suitable gearing. The water enters by the pipe B, which is
perforated, as shown, and passes through the meshes of the gauze,
while the pulp gradually finds its way to the wider end of the
drum, where it escapes into the box C, and can be conveyed again to
the beating-engines.
[Illustration: Fig. 32.]
[Illustration: Fig. 33.]
=The Dandy-roll.=--When it is required to produce a design or name,
termed a _water-mark_, upon the paper, this is done by means of a
roll called the _dandy-roll_, which consists of a skeleton roll
covered with wire-cloth, upon which the design is worked by means
of very fine wire. If the paper is required to be alike on both
sides, without any specific pattern or name upon it, the roll is
simply covered with wire-cloth, the impressions from which upon the
moist pulp correspond with those of the machine-wire on the under
surface. By this means paper known as "wove" paper is produced. A
dandy-roll of this character is shown in Fig. 32. "Laid" paper,
as it is termed, is distinguished by a dandy-roll having a series
of equidistant transverse wires on the upper surface of the wire
cylinder, as shown in Fig. 33, the effect of which is to produce
parallel lines on the paper, caused by the pulp being thinner where
the moist paper is impressed by the raised wires, which renders the
lines more transparent than the rest of the paper. The dandy-roll,
which is usually about 7 inches in diameter, corresponds in length
to the width of wire on which it rests, and is placed over the
wire-cloth between the suction-boxes. The journals of the roll
turn in slits in two vertical stands, one behind the machine frame
and the other in front of it. The roll, however, rests with its
whole weight on the wire, and revolves by the progressive motion
of the wire. The stands which support the roll prevent it from
being influenced by the lateral motion of the wire. By thus running
over the surface of the pulp when the wire is in motion, this roll
presses out a considerable quantity of water, at the same time
rendering the paper closer and finer in texture. Dandy-rolls of
various lengths, and bearing different designs or patterns, are
kept at the paper-mills, and great care is exercised to preserve
them from injury.
=Water-Marking.=--Dr. Ure describes the following processes
for producing a design for a line water-mark:--1. The design
is engraved on some yielding surface in the same way as on a
copper-plate, and afterwards, by immersing the plate in a solution
of copper sulphate, and producing an electrotype in the usual
way, by which all the interstices become so filled up as to give
a casting of pure copper. This casting, on being removed from the
sulphate bath, is ready for attaching to the wire gauze of the
dandy-roll. 2. The design is first engraved on a steel die, the
parts required to give the greatest effect being cut deepest; the
die, after being hardened, is forced by a steam hammer into some
yielding material, such as copper, and all of this metal which
remains above the plain surface of the steel is subsequently
removed by suitable means; the portion representing the design
being left untouched would then be attached to the wire-gauze
as before. Light and shade can be communicated to the mark by a
modification of the above process, for which purpose an electrotype
of the raised surface of a design is first taken, and afterwards
a second electrotype from this latter, which consequently will be
identical with the original surface. These two are then mounted
on lead or gutta-percha, and employed as dies to give impression
to fine copper-wire gauze, which is then employed as a mould. Thus
absolute uniformity, such as could not be attained by the old
system of stitching wires together, is now attained in bank-notes
by the adoption of the above method. It may be mentioned that when
the moulds were formed by stitching the fine wires together to
form a design, no less than 1,056 wires, with 67,584 twists, and
involving some hundreds of thousands of stitches, were required to
form a pair of £5 note moulds, and it was obviously impossible that
the designs should remain absolutely identical.
Sometimes water-marks are produced by depressing the surface of the
dandy-roll in the form of a design, which causes the paper to be
thicker where the design is than in the rest of the sheet of paper.
This modification was invented by Dr. De la Rue.
=De La Rue's Improvements in Water-marks.=--By one method, patented
in 1869, dandy-rolls, having a surface of embossed wire-gauze,
are used; the indentations in the gauze are inwards, causing a
thickening of the paper where they are brought in contact with
it. These thickenings correspond in form to the configuration of
the design or water-mark. The inventor has also affixed wire to
the surface of such dandy-rolls so as to form projections, in
order to thin the paper where the projections come in contact with
it, by which means light lines are obtained in the water-mark,
strengthening the effect of the thickened opaque design.
[Illustration: Fig. 34.]
By another patent, dated May, 1884, No. 8348, the inventor forms
the surface of the dandy-roll of wire-gauze embossed in such a
manner that parts of the surface of the gauze, corresponding to
the configuration of the design of the water-mark, are raised,
and project out from the general surface, and other parts
corresponding to the line shading of the design are depressed
below the level of the general surface. The accompanying drawing,
Fig. 34, shows diagrammatically, and greatly enlarged, a section
of a portion of the surface of a dandy-roll made in accordance
with this invention. _a_ represents the section of a ridge or
projection raised on the surface of the gauze; _b_ represents the
section of a groove or depression in the wire-gauze, which, with
other similar grooves, serves to produce an opaque shading to the
design. _c_ is an auxiliary ridge or projection, serving to define
the shading line, and to intensify it by driving the pulp into
the groove or depression _b_. Further effects may be obtained by
attaching wires to the dandy-roll, either in the usual way, where
the surface is unembossed, or upon the raised parts _a_, which
give the configuration to the water-mark. In place of forming the
ridges or projections _a_, which produce the configuration of the
water-mark, by raising portions of the wire-gauze above the general
surface, they may be formed by sewing on suitably shaped slips
of wire-gauze, or of sheet metal perforated all over with fine
holes, on to the surface of the gauze which is embossed with the
grooves _b_, but it is much to be preferred that both the ridges
_a_ and the grooves _b_ should be produced by embossing the gauze.
Water-marks may also be produced by placing sheets of finished
paper in contact with plates of copper or zinc, bearing a design in
relief, and submitting them to heavy pressure.
[Illustration: Fig. 35.]
=Suction-Boxes.=--These boxes, which are fitted under the wire,
are made of wood, and are open at the top, the edges being lined
with vulcanite. The ends of the boxes are movable, so that they
may be adjusted to suit the width of the paper required; they are
also provided with air-cocks for regulating the vacuum, which is
obtained by means of two sets of vacuum pumps, having three 6-inch
barrels to each set: a vacuum pump of this form is shown in Fig.
35. As the wire travels over these boxes, the action of the pumps
draws the wire upon them with sufficient pressure to render them
air-tight; by this means a large portion of the water which the
pulp still retains at this point becomes extracted, thereby giving
to it such a degree of consistency that it can stand the pressure
of the couch-rolls without injury. The backwater extracted by the
suction-boxes, as also that collected in the save-all, is added to
a fresh supply of pulp before it flows on to the sand-tables.
=Couch-Rolls.=--At the extreme end of the wire-cloth from the
breast-roll, and inside the wire, is the under couch-roll, from
which the wire receives its motion. This roll, which is of brass,
is usually about 14 inches in diameter, is carried upon a cast-iron
framing with brass bearings, and is ground to a working joint with
the top roll, which is also of brass, and 20 inches in diameter.
Both these rolls are covered with a seamless coating of woollen
felt. The upper roll rests upon the lower one, and the wire-cloth,
and the web of paper upon it, pass between the rolls, receiving
gentle pressure, by which the paper becomes deprived of more water,
rendering it still more compact. It is at this stage that the web
of paper leaves the wire-cloth, and passes on to a continuously
revolving and endless web of woollen felt, termed the "wet felt,"
from the moist condition of the paper. This felt, which is carried
on wooden rollers, is about 20 feet long, and is manufactured with
considerable care.
=The Press-Rolls.=--The paper now passes on to the _first
press-rolls_, which deprive it of a still further quantity of
water, and put it in a condition to bear gentle handling without
injury. The upper roll is fitted with a contrivance termed the
"doctor," which keeps the roll clean by removing fragments of paper
that may have become attached to it. The doctor is furnished with
a knife which passes along the entire length of the roll, pressing
against it from end to end. These rolls are generally of iron,
jacketed with brass, the under one being 14 inches in diameter, and
the top roll 16 inches. Sometimes this roll is made of fine-grained
cast-iron. When the roll is of iron the doctor blade is steel; but
when this roll is brass the knife is of the same material. The
under surface of the paper, which has been in contact with the
felt, and necessarily being in a moist condition, receives more or
less an impression from the felt over which it travelled, while the
upper surface, on the other hand, will have been rendered smooth
by the pressure of the top roll of the first press. To modify
this, and to render both surfaces of the paper as nearly uniform
as possible, the paper passes through another set of rolls, termed
the _second press-rolls_, in which the paper becomes reversed,
which is effected by causing it to enter at the back of the rolls,
which rotate in a reverse direction to those of the first press, by
which the under or wire side of the paper comes in contact with
the top roll of the press. By this arrangement the underside of
the paper is rendered equally smooth with the upper surface. The
second set of press-rolls is provided with an endless felt of its
own, which is usually both stronger and thicker than that used in
connection with the first press-rolls. In some mills each set of
press-rolls is provided with a doctor, to prevent the web of paper
from adhering to the metal. Sometimes the doctor knives are made
from vulcanite, a material which would seem specially suited for a
purpose of this kind. From this point the paper passes to the first
set of drying cylinders.
=The Drying Cylinders.=--The invention of the steam drying cylinder
is due to Mr. T. B. Crompton, who, in the year 1821, obtained a
patent for this useful addition to the paper-machine. Since that
period, however, the system of drying the paper by steam-heat has
been brought to a high state of perfection; not only this, but
the number of cylinders has gradually increased, while the heat
to which they are raised has proportionately decreased, and as
a consequence the size, which is injuriously affected by rapid
drying, is gradually deprived of its moisture, and thus renders
the paper closer and stronger, while at the same time a very rapid
speed can be maintained. The drying cylinders in the machine shown
in the engraving are 4 feet in diameter and 12 in number, being
arranged in two groups of 8 and 4 cylinders respectively, and in
the aggregate present a very large drying surface, it being very
important that the operation should be effected gradually, more
especially at its earlier stages. There is a passage between the
second press-roll and the cylinders, through which the machine-men
can pass from one side of the machine to the other. The first two
or three of the first section of cylinders are only moderately
heated, and having no felt on them, allow the moisture from the
paper to escape freely. The next five cylinders, however, are
provided with felts, which press the paper against the heated
surfaces, by which it becomes smooth and flattened, thus putting it
into a proper condition for passing between the _smoothing-rolls_.
The cylinders are heated by steam, and are generally of decreasing
diameter, to allow for the shrinking of the paper during the drying.
=Smoothing-Rolls.=--These consist of highly polished cast-iron
rolls, heated by steam. The paper being in a somewhat moist
condition when it passes through these rolls, they have the effect
of producing a fine smooth surface.
The paper next passes over the last four drying cylinders, all
being provided with felts, to keep the paper closely pressed
against their heating surfaces, by which the remaining moisture
becomes expelled and the paper rendered perfectly dry. The paper
now passes through the calender rolls, and is then wound on to
reels at the extreme end of the machinery. The operation of
calendering will be treated in the next chapter.
[Illustration: Fig. 36.]
=Single Cylinder Machine.=--For the manufacture of thin papers,
as also for papers which are required to be glazed on one side
only, a single cylinder machine, called the Yankee machine, has
been introduced, a representation of which is shown in Fig. 36.
It is constructed on the same principle as the larger Fourdrinier
machine up to the couching-rolls, when the paper leaves the
wire-cloth and passes on to an endless felt running round the top
couch-roll, and passes from thence to a large drying cylinder,
which is about 10 feet in diameter and heated by steam, the surface
of which is highly polished, giving to the surface of the paper
in contact with it a high gloss. There is attached to the machine
an arrangement for washing the felt for the purpose of cooling
and opening it out after passing through a cold press-roll and
the hot drying cylinder. This machine, as manufactured by Messrs.
Bentley and Jackson, for cap, skip, and thin papers, consists of
a rocking frame, and wrought-iron side bars, fitted with brass
bearings, the necessary brass and copper tube-rolls, couch-rolls,
with driving shaft, stands and pulley; self-acting wire guide,
brass deckle sides and pulleys, brass slice, vacuum boxes, pipes
and cocks; wet felt frame, with the necessary water pipes and
cocks, and carriages to carry the couch-rolls and felt-rolls; the
necessary wet felt-rolls and a felt washing apparatus; one bottom
press-roll carried by brass steps, and fitted with compound levers
and weight; one large cast-iron drying cylinder about 10 feet in
diameter, and fitted with a central shaft, steam admission and
water delivery nozzles, two water lifters and pipes, a manhole and
vacuum valve, a large spur driving wheel, spur pinion, driving
shaft and pulley; massive cast-iron framework, with pedestals to
carry the cylinder; traversing steel doctor and frames; copper
leading roll and carriages, a pair of reeling stands fitted with
brass steps, friction pulleys and plates, regulating screws, etc.;
a wooden platform and iron guard rail, all carried by strong
cast-iron framing; the necessary pulp and backwater pumps, shake,
knotter, stuff chests, service cistern, pipes and valves, shafting,
pedestals, change wheels, pulleys, &c. These machines can be
obtained of any desired width.