Learn About Paper Drying

Paper Glossary

The Paper Glossary below is provided by the Paper Industry International Hall of Fame. Entries in the Glossary are grouped in the general order that paper is manufactured.

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.

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 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 Process

There are three main types of puling processes: Groundwood pulp; Chemical; and Chemi-mechanical.

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.