Fourdrinier Paper
Machine:
A papermaking
machine invented by the Frenchman, Nicolas Louis Robert in 1798, developed
in England by Brian Donkin for Henry and Sealy Fourdrinier, but not
placed into operation until 1804.
The Fourdrinier
Paper Machine was the first papermaking machine to make continuous
paper. Prior to this machine, paper was made in single separate sheets.
The first Fourdrinier
machine in the US was imported from England and erected in Saugerties,
New York, in 1827. The second was built in Connecticut by mechanic
George Spafford. He and his partner, James Phelps, completed the first
American-built fourdrinier in May 1829 and sold it to Amos Hubbard
at a cost of $2,426.
Instead of placing
the stock, or watery pulp, onto individual screens, the Fourdrinier
machine used a continuous screen, or wire, made of woven wires, that
moved like an endless belt. The stock was sprayed or dropped onto
the moving wire. The water was drained and sucked out through the
porous screen. The stock is usually about 3% solids when it is placed
on the wire and is about 7% solids by the time it gets to the end
of the wire.
At the end of
the wire, the stock is picked off the felt from above (at the couch
roll) by a felt which is moving at the same speed. Often, the stock
then goes through a series of rollers that squeeze and/or suck more
water out of the stock. This section is called the press section.
By the end of the press section, the stock is usually 40-50% solids.
The stock then
moves into the dryer section. The dryer section can be made up of
a series of dryer rolls or one large dryer. Dryers are basically can
heated from the inside by dry steam and from the outside by hot air.
The stock is usually about 95% solids by the time it comes off the
last dryers.
The original
Fourdrinier machines had to hang the paper in long sheets to dry.
Eventually, the paper was scraped off the dryer and wound onto the
dry end winder as part of the continuous process. Often, the paper
has to be rewound on rewinders to make the paper's thickness and grain
consistent
The process of
the wet end wire, placing stock on a continuously moving wire, was
the initial innovation of the Fourdrinier machine. This innovation
made today's high speed paper machines possible.
Pulping
Processes:
There are three
main types of puling processes: Groundwood pulp;
Chemical; and Chemi-mechanical.
The groundwood
pulping process grinds wood into pulp. Usually this involves taking
a log and pressing it against a rotating surface to grind off small
pieces. Typically a grinder is about 4 feet long. The groundwood pulp
is then often cooked to soften it.
The chemical
process involved cooking chips from a log in a hot bath of boiling
caustic.
The chemi-mechanical
process is a combination of the groundwood and chemical processes.
Freesheet:
A freesheet is
a sheet of paper that does not contain groundwood. It is generally
of a higher quality, a high density, and is less absorbent
Stock:
Stock is a mixture
of water and paper fiber. It can be made of wood pulp, cloth fiber,
or a mixture of any cellulose and fibrous material. Most paper is
made from wood pulp.
Furnish:
Furnish is another
way of referring to the stock mix that goes best with a specific product.
Hydrapulper:
A Hydrapulper,
originally known as the Cowles Pulper (invented by Edwin Cowles),
is a machine that rehydrates sheets of dry pulp, pulps up recycled
papers, and otherwise mixes and blends paper stock with water to create
the desired slush of pulp stock. It is used in almost every paper
mill.
Head Box:
The headbox is
the receptacle on the wet end of the paper machine in which the pulp,
or stock, is distributed onto the wire.
Full
Hydraulic Flow Boxes are head boxes that deliver stock uniformly
onto the wire on a consistent basis. The stock is "pumped"
into the head box under pressure.
Converflo
and Strat-Flo Headboxes are head box designs that enable
different layers of stock to be placed on the wire at the same time.
Using tapered flukes and baffles, they are able to lay down separate
layers of fibers of different lengths and strengths, creating a sheet
that, for example, has an outer layer that is smooth for printing
yet has an inner layer that is stronger for better paper strength.
Three layers could be formed so that the outer layers (top and bottom
layer) is made from hardwood fibers (which are shorter and more uniform)
and the inner layer is softwood (designed for strength).
The first materials
used to separate the layers of pulp slurry were made of very thin
Tevlar, which is currently used in bullet-proof vests. This enabled
a more precise movement of flexible separaters to create specific
pressure differences in order to control the basis weight of each
layer.
Clothing (wires,
felts, fabric):
There are two
main kinds of paper machine clothing: clothing for the wet and clothing
for the dry end.
The clothing
for the wet end is usually called the wire, because the first wires
were made of woven wire. One of the first innovations of the wire
was a staggered weave that eliminated the problems of wires hanging
up or freezing in the suction boxes. Another important early innovation
was the welded seam which replaced hand-woven seams. This eliminated
the visible line created each time the seam made it way around the
moving wire.
But wire is basically
an inflexible material. If stretched, bent, or frayed, the anomalies
remain in the wire and affect the look and consistency of the paper.
Wire is also not very resilient and the older wires often broke. In
the early machines, wires were often replaced daily, sometimes several
times a day.
The development
of monofilament forming fabric, or plastic thread wires which could
stretch and snap, made the higher speeds and increased productivity
possible of today's machines. A monofilament fabric usually lasts
at least several months before maintenance is required.
Dry end clothing
is usually made of felt. Felt is the fabric used to pick the wet stock
off the wire. It also acts as a blotter, soaking up water, in the
press section of the machine. The felt usually passes between a series
of press rolls which squeeze out more water. This kind of felt can
also be used in the multiple dryer section.
Twin Wire Formers:
As described
above, the sheet is formed on the wire from pulp slurry. In the beginning,
this was done with just one wire though which part of the water was
drained, by gravity and other means (suction boxes, drainage foils),
leaving a higher concentration of fiber. Subsequent developments included
the use of twin wires.
Instead of putting
the pulp slurry onto a single horizontal wire, the slurry flows from
the headbox through a slit bwteen two (downward) vertically moving
wires. These two wires form a nip. At the nip, suction is applied
to one wire so that the web (or "sheet") adheres to that
wire. That wire then moves forward to the press section of the paper
machine.
This innovation
enable papermachines to move at much higher speeds and to yield better
sheet formation. The Twinverform Paper Machine was the first machine
utilizing this innovation.
Pressure Forming:
Pressure forming
refers to a process in which the stock inside the head box is under
pressure to ensure an even distribution of stock onto the wire, affording
the operators the ability to adjust and change while the machine is
running, making a more consistent sheet, and also resulted in less
sheet breakage along the wire.
Couch Roll:
(Pronounced "kooch").
The couch roll is a vacuum roll under the wire, usually placed at
the end of the wire. The holes in the couch roll help suck out water
from the stock. A felt usually picks the stock off of the wire at
this point. The place at the end of the wire where the felt touches
the wire (where the couch roll is), is called the "nip."
Hydro Vario Roll:
A hydro vario
roll refers to a pressure controlled hydraulic process to control
the pressure between rolls, giving more control to the operators and
greatly reducing sheet breakage.
Nip:
The nip is the
place of intersection where one roll touches another. For example,
the place at the end of the wire where the stock is picked up by the
felt is a nip.
This place of
intersection is usually a line. But it is possible to extend the nip
by flattening out this place of intersection with a smaller series
of rollers, or belts. This is what is called an extended nip. By using
a belt at the nip, the nip can be extended by 6-10 inches, extending
the area of pressure against the roll so that more water can be squeezed
out.
Fabric Press:
A fabric press
uses absorbent felt to soak up moisture from the sheet in combination
with nips that squeeze the water out. The sheet cannot stay on the
felt long, so many rolls are combined in a series. The felt must be
squeezed dry again before it picks up a new section of sheet.
Drainage Foils:
Drainage foils
replaced rotating suction rolls, or "table rolls," which
were fairly inefficient. Drainage foils are tapered foils placed under
the wire at a slight angle so that when the wire runs over them at
high speeds, a suction is created and the water from the wet stock
is sucked through the wire into the foils.
Calender:
A calender refers
to the use of two rolls, or calenders, that squeeze paper in order
to smooth the surface.
Often a sheet
is run between a series of calenders that squeeze the sheet in several
directions, smoothing the surface in every possible direction.
Yankee Dryers:
Yankee dryers
are a single large dryer at the end of the paper machine. They are
used for making thin sheets, like toilet tissue and machine glazed
paper. The Yankee is really a large can heated to a very high temperature,
dry steam inside and air heated on the outside. It replaced many dryers
with a single, larger one, usually 300 inches wide and about 10 feet
in diameter. It can dry the sheet in those ten feet, cutting down
the length of the paper machine by 10-20 feet.
Blow-through Drying
Process:
There are two
kinds of drying systems: a hot surface (like the Yankee dryer); and
a system using dry steam or hot air that actually blows through the
wire. The blow through drying process enabled tissue products like
Charmin, because a thicker sheet can be dried in much less time using
this process.
St. Anne's Former:
The St. Anne's
Former, developed by Brian Attwood, is a way of applying stock to
the underside of the felt using a cylinder. Usually, a series of cylinders
apply several layers of stock, creating a multi-layered sheet. Once
all the necessary layers are applied, the felt rotates to the top
side of the wire and enters the pressure roll part of the machine.
This device enables
the creation of multi-layered paperboard. The multiple layers could
not be applied normally, from the top of the wire, because gravity
would begin to dismantle the lower layers.
Winders and Rewinders:
A paper machine
winder refers to the roll on to which the paper is wound when it comes
off the last dryer of the paper machine.
Rewinders rewind
the roll off the original winder. Because it is difficult to retain
perfect consistency of thickness and grain when the sheet is being
wound on directly off the machine onto the first winder, rewinding
the sheet can help even out stretches and crooked sheets and other
imperfections.
Coating:
Bill blade coating
refers to a way of coating paper and making that coating even and
consistent Coated paper cannot come in contact with any cylinders,
so it must be dried by hot air on the surface using a high speed air
flow. This initially formed ripples on the surface. Excess was sometimes
wiped off by a blade, skimming and smoothing the surface.
Tandem coating
refers to a two stage process that coats both sides of the paper sheet.
Coaters:
Coaters apply
separate coatings to paper after the paper sheet has been formed and
dried.
Coatings are
substances put on a finished sheet of paper. They are made in what
is called color kitchens. Coaters can make a paper protected or shining,
like magazine paper.
More than one
coater can be used. Sometimes an initial coat needs to be put on to
prepare the paper for a second coat, usually when the paper is porous
and the final coat is an expensive substance... then an initial coat
is used to prepare the paper so that less of the expensive coat is
necessary.
Pressure Rupturable
Materials:
A sheet can be
coated with a solution that includes pressure rupturable materials,
or tiny capsules that rupture when put under pressure. An example
is carbonless paper. One of the papers is coated with a material that
has a chemical captured inside tiny capsules that rupture when a pen
is drawn over them. A second sheet is then coated with a material
that reacts to that chemical by changing colors.
Rheology:
Rheology is the
science of studying the friction between liquids. In papermaking,
it is mainly used in studying the behavior of coatings.
Some of the questions
rheology helps to answer are: Will the coating adhere or fall off?
Will the coating be absorbed by the paper, requiring the paper to
be precoated with another material? Will the coating spread or dry
in the necessary time? Will one coating react with another coating
in an unwanted way?
Rotogravure:
Rotogravure is
a photomechanical process by which pictures are transferred onto a
cylinder so that the image (or typesetting) can be transferred to
a continuously moving sheet of paper.
Paperboard:
Paperboard is
a heavy layered paper, usually at least 100 lbs per ream or more.
It is intended to be a rigid, durable form of paper, often used in
packaging. Some examples include: cereal boxes, shoe boxes, paper
cups, file folders, noncorrugated liner board and packaging materials.
Waste paper:
Waste paper refers
to recycled paper that cannot be used as the surface of the sheet.
It is usually the inside layer of a 3 layer sheet.
Municipal Solid
Waste:
Municipal solid
wastes are the waste product collected as garbage, usually consisting
of 30% paper.
Secondary Paper:
Secondary paper
refers to any recycled fibers, waste papers, or other sources of pulp
and fiber that come from a previously created product or process.
"Virgin
fibers" refers to fibers that come directly from original pulping
processes.
Broke:
This term is
used to mean the discarded paper created when a break occurs in the
normally continuous papermaking process. The broke is usually recycled
in a Hydrapulper.
Broke is a kind
of secondary paper.
Savealls:
Savealls are
devices that save fibers for reuse from waste water, recovering useful
fibers and other materials.
Clarifiers:
Clarifiers remove
unwanted material. Sometimes these materials are reused in a different
part of the process, sometimes they are discarded.
There are two
main types of clarifiers: flotation and sedimentary Flotation clarifiers
often use very small bubbles, making the water milky, driving unwanted
materials upward with the bubbles. Sedimentary clarifiers either decant
the clear material off the top or they remove the heavier unwanted
materials in a centrifuge.
Classifiner:
A classifiner
sorts fibers into short, long, broken and unbroken classifications
and is able to separate them.
De-Inking:
Deinking refers
to the process of extracting the ink and coatings of printed papers
so that the undyed fibers can be used again as a secondary fiber source.
Effluent:
Effluent is the
liquid discharge or waste products of the papermaking process, usually
including a small amount of suspend solids and dissolved chemicals.
Effluent is usually discharged into rivers, since most modern mills
now have their own waste water treatment systems as part of the recycling
and end-process of their papermaking. If mills do not have their own
treatment plants, effluent is usually discharged to a municipal water
treatment facility.
Zero Discharge:
Zero discharge
means that no wastes are discharged, that everything is recycled and
no pollutants are being discharged into the environment.
Another term
for this is Totally Effluent Free (TEF).
Mini-Mill Concept:
As it's name
implies, the mini-mill refers to a smaller mill concept. The idea
is that a smaller mill can be made more self-sufficient and therefore
more economically efficient.
Spunbound technology:
A sheet that
is spunbound is made up of fibers that are randomly interlocking,
like cotton, but not woven. This results in a fluffy, woolly wad that
can still be rolled up in sheets, like insulation. The process also
creates disposable paper clothing like what is used in hospitals.
Differential-density
Sheet:
A differential-density
sheet is a sheet that changes in density, making it spongy or ridged.
Higher Caliper:
A sheet having
a higher caliper refers to a sheet's thickness. A higher caliper means
a thicker sheet.
Variance Component
Analysis:
Variance component
analysis refers to a system that analyzes how far off target a specific
sheet is and is able to adjust the machine or adjust the mix of stock
(change the recipe of the furnish).
Formation Measurement:
In order to tell
whether a sheet is uniform, it is inspected by placing a light source
underneath it and looking at the fibers and thickness. This was originally
done by hand (or by the human eye). Jaakko Poyry developed a machine
that was able to do this in a mechanized and consistent way.
Radioactive Tracing:
Radioactive tracing
is a way of tagging a fiber with a radioactive substance in order
to trace it as it goes through a specific process. This enables analyzers
to determine if fiber is accumulating in a specific area, how and
where it travels, if it splits, if the flow remains what is desired,
and is even able to follow fibers through the refining process.
This process
can also determine yield factors, such as how many of which fibers
make it to a certain layer of a sheet. It an also be used to analyze
fiber mixing in pulp chests.
Beta Radiography:
Beta radiography
is a technique for using beta rays to measure thickness, moisture,
evenness, density, and basis weight in paper.
Crystallography:
This is science
of analyzing crystalline structure of materials. In the paper industry,
it usually refers to the study of cellulose, which can have up to
a 20-40% crystalline structure.
High crystalline
structure means less swelling of the fibers.
Naval Cup:
A Naval Cup is
a collection device to collect rosin from pine trees. Rosin is used
in making paper less absorbent; for example, in writing paper, so
that ink won't feather. Rosin is also used with string instruments,
turpentine, and in many other industries.
Converting:
The converting
process is the step in papermaking that takes the sheet as it comes
off of the end of the paper machine and changes it into useable paper
items. Through rewinding, cutting, creping, embossing, printing, coating
and other process, the sheet is transformed into napkins, facial tissue,
placemats, packaging, etc.
Source: Paper
Industry International Hall of Fame, Inc., P.O.Box 9050, Appleton,
WI 54911-9050,2-2003, www.paperhall.org
