Paper & Pulp Mill Glossary: The Ultimate Guide

You have probably noticed that Paper Mill has a significant amount of jargon as well as acronyms. As a result, this page contains a curated and organized list of the most essential terminology and meanings from the Pulp & Paper Mill Glossary.

Glossary of Pulp & Paper Machinery – Technical terms & concepts

ABRASION RESISTANCE:

The ability of a paper product to withstand abrasion. Measured by determining the degree and rate at which a sample loses weight under specific rubbing action of an abrading substance, such as an eraser.

ABSORBENCY:

Property of pulp, paper, and its constituents and products that permits the entrainment and retention of other materials it contacts, such as liquid, gaseous and solid substances.

AGITATOR:

A rotating device for mixing fluids and fluid suspension in a tank or chest.

APPARENT DENSITY:

Weight (mass) per unit volume of a sheet of paper is obtained by dividing the basis weight (or grammage) by the caliper (thickness).

BAFFLE:

A device that obstructs the flow of fluid, whether to aid mixing or restrict the flow rate.

BASIS WEIGHT OF A REAM OF PAPER:

Weight in pounds of a ream of paper, usually consisting of 480, 500, or 1000 sheets of a specified size, according to grade. In countries using the metric system, more commonly referred to as grammage and expressed as g/m2.

BEATER:

A large, longitudinally partitioned oval tub is used to mix and mechanically “work” pulp with other ingredients to make paper.

BIOLOGICAL OXYGEN DEMAND (BOD):

Amount of dissolved oxygen consumed in five days by biological processes breaking down organic matter in mill effluent.

BONDING STRENGTH:

An intralayer binding force in a multi-ply paperboard or laminate. Also refers to the degree of adherence of coating and film on a sheet and the inter-fiber binding force within a sheet.

BONE DRY OR OVER DTY:

Moisture-free conditions of pulp and paper. Usually determined by drying a known sample to a constant weight in a completely dry atmosphere at a temperature of 100°C to 105°C.

BREAST:

The point of the machine where the pulp suspension passes onto the paper machine wire.

BRIGHTNESS:

 The degree of the reflectivity of a sheet of pulp or paper for blue light is measured under specified standard conditions. (Also, though incorrectly, called whiteness).

BULK:

Compactness property of a sheet to its weight (whose value decreases as compactness increases). Bulk is calculated as caliper divided by grammage.

BURSTING STRENGTH:

Resistance of paper to rupture when pressure is applied to a side by a specified instrument. Also called burst, Mullen, and pop strength.

CALENDER / CALENDERS:

At the dry end of a paper machine, smooth-faced rolls smooth, level, polish and improve gloss. The rollers can be metal or composite (soft). Hardness affects how much paper or board is crushed. Equipment can be lined up at the end of the paper machine before reel-up or outside the machine.

CALENDER FINISHED:

Paper and paperboard passed through a calender to improve surface characteristics by application of pressure, friction, or moisture.

CALIPER:

The thickness of a sheet of paper or paperboard, measured under certain expressly stated conditions, expressed in units of thousandths of an inch (called “mils” when referring to paper and “points” when referring to paperboard)—in regions using metric measurement, usually measured in millionths of a meter (microns or µm). Also called thickness.

CARLOAD:

Quantity of paper shipped from mill in or on a freight car. Must exceed a freight classification zone minimum weight to qualify for carload freight rate.

CAST COATED PAPER:

Very high gloss coated paper and paperboard with surface characteristics produced by allowing the applied coating to harden while in contact with the surface of steam-heated, highly polished, chrome-plated drum.

CHEST:

 A vessel equipped with an agitating device for storing, collecting, mixing, and chemical treatment of pulp suspension. A large vessel fitted with an agitator for storing pulp stock.

CHIPPER:

 A machine that chips logs after de-barking.

CONSISTENCY REGULATOR:

A device for diluting pulp stuff to a steady, preset solids content.

CORRUGATED BOARD :

A pasted single or double-faced, multi-layered board is having a fluted bottom or middle layer.

CORRUGATING MEDIUM:

 Preboard to be converted to a corrugated board by passing it through a corrugating machine. (Sometimes abbreviated to CCM – Corrugated Case Medium).

COUCH PIT OR HOG PIT:

The paper-making machine has a tank with an agitator below it that is used to pick up couch broke. Also called a pig pit.

CROSS DIRECTION (CD):

Side to side direction of a paper machine or the paper sheet made on it, as opposed to machine direction, which runs from head to exit.

CUTTING PIPE:

Water jets used to trim the rough edge off the paper while it is being made on the machine (deckle edges).

COUCH:

 The point on a papermaking machine where the wet web leaves the wire before the presses.

CYLINDER MACHINE:

The machine makes paperboards. The forming cylinders are wrapped with wire, so fibers are picked up to form a web as they turn in a vat filled with stock solution, with water pouring out at the ends. The wet sheet is then transferred from the cylinder to felt for pressing and drying.

DIGESTER:

 Pressure vessels are used to chemically treat chips and other cellulosic fibrous materials such as straw, bagasse, rags, etc., under elevated temperature and pressure to separate fibres and produce pulp.

DIMENSIONAL STABILITY:

The ability of a sheet to maintain its original machine direction and cross direction dimensions with time and under variable moisture and relative humidity conditions.

DRYERS: Portion of a paper machine where water is removed from wet paper by passing it over rotating, steam heated, cylindrical, metal drums or by running it through a hot air stream.

ELONGATION OF PAPER:

 Physical property of a paper sheet that allows it to experience a certain degree of stretching.

FABRIC PRESS:

Paper machine wet press that uses a special multiple weave fabric belt sandwiched between the regular felt and the rubber covered roll, increasing the capacity to receive and remove water from the nip between the rolls.

FLOW BOX:

An open through with an adjustable slit along the length at the bottom (slice) and an inlet pipe of a manifold. Used to distribute the pulp suspension across the width of the papermaking machine.

FLUFF PULP:

Thick sheet or batt of wood pulp fibres manufactured in roll or bale form suitable for dry disintegration into individual fibres.

FURNISH:

Various pulps, dyes, additives and other chemicals blended together in stock preparation area of paper mill and fed to wet end of paper machine to make paper or paperboard. Also called stock.

GUILLOTINE:

A device for cutting or trimming piles of sheets of paper to the required size and with smooth edges.

HEAD BOX:

A device for applying and distributing stock onto the wire that keeps fibres from clogging together so that a consistent formulation can be achieved. Also known as a breast box or flow box.

HOOD:

 A hood covering the paper machine drying section and designed for moist air removal.

HYDRAPULPER:

 A metal tank fitted with an agitator rotor for disintegrating pulp and broke in water.

INTEGRATED MILL:

Mill manufacturing complex in which all pulp and papermaking operations are conducted at one site.

KRAFT PULP:

 Fibrous materials used in pulp, paper, and paperboard manufacturing, are produced by chemically reducing woodchips into their parts by cooking in a vessel under pressure using an alkaline cooking liquor, also called sulfate pulp.

KROFTA:

Name of equipment used for recovering fiber excess from backwater on an air flotation principle.

LACQUER:

Organic solution with volatile solvents is used for coating paper to give a high surface gloss, grease resistance, heat sealing, and improved surface appearance.

LAYBOY:

 Device at the end of a cutting machine for jogging sheets into a neat pile.

MACHINE DIRECTION (MD):

Direction from the wet end to the dry end of a paper machine or to a paper sheet parallel to its forward movement on a paper machine.

MECHANICAL PULP:

Pulp produced by reducing pulpwood logs and chips into their fibre components by the use or mechanical energy, via grinding stones, refiners etc.

MG CYLINDER:

Similar to a Yankee cylinder, usually more prominent in diameter, 23 feet, with lower steam pressure. It gives a smooth or glazed finish to one side of the sheet while leaving the other quite rough.

MOISTURE CONTENT (MC):

Percentage of water by its weight in paper, pulp, paperboard, chips, Etc., which will vary according to atmospheric conditions because of the ability of these types of materials to absorb or emit moisture.

MOTTLE:

A surface effect produced by the addition of heavily dyed fibres of a different colour in the stock furnish.

OPACITY:

The ability of substances such as paper, flue gases (smoke), and liquids to resist transmission of both diffuse and non-diffuse light through them. Prevents show through of dark printing in contact with the backside sheet of paper.

POROSITY:

Ability of fluids to pass into paper and paperboard, related to size, shape and distribution orientation or the pores in a sheet and the compactness of the fibers.

PRESS:

A wringer device situated in the machine after the wire and couch consist of a loaded top and bottom roll, through which the paper and felt pass. Water is squeezed out of the form into the felt.

PROFILE:

Cross machine visual display on the computer control system showing the actual variations from the target value.

PULP:

 Fibrous material is produced mechanically or chemically reducing plants into their parts from which pulp, paper, and paperboard sheets are formed after proper slushing treatment—also used for dissolving purposes (dissolving pulp or chemical cellulose) to make rayon (or viscose) and other synthetic products.

PULPER:

Machine that disintegrates fibrous raw material using water and mechanical agitation.

RAG CONTENT:

Paper containing from 25% to 75% cotton or rag fibres, including bond, ledger, and specialty papers.

REAM:

Stack or package of paper containing a number of sheets (usually 480, 500 or 520) designated as standard for that grade.

REFINER:

 A machine that modifies the fibre to the degree required by the final product. A series of metal blades rotate from a central shaft against static blades built inside the outer casing of a cone or disc.

REVERSE ROLLS:

Press rolls where the paper is fed through in the reverse direction from the normal flow of paper through the machine so that both sides of the paper have the same characteristics.

RIDING ROLL:

Roll mounted so that it rests under its own gravitational weight on the paper to control the tension, usually used during reeling operations.

SCREENS & STRAINERS:

A variety of devices for removing contraries from a pulp suspension by a filtering process, usually either pressure or vibratory.

SEMI CHEMICAL PULP:

Lower quality pulp made by cooking fibrous materials in a neutral sodium sulphite/sodium carbonate cooking liquor followed by a final separation of the fiber using unpressurised mechanical means.

SHEETER:

Machine for cutting the paper web into sheets.

SIZE PRESS:

Paper mill processing unit consisting of two usually rubber covered rolls located between two dry end sections of the paper machine. Applies size solution to the surface of the paper sheet.

STARCH:

 Type of carbohydrate adhesive and sizing material obtained primarily from corn, wheat, rice, tapioca, maize and potatoes. Produces a higher degree of rigidity in a sheet and improves the finish by causing the fibres to lie flat.

STOCK:

Fibrous mixture that is made into paper. May consist of one or more types of beaten or refined pulps, with or without suitable fillers, dyes, additives, and other chemicals. Also called furnish.

SUPERCALENDER:

 Auxiliary piece of papermaking equipment is used on some paper machines, to obtain a denser paper with a higher finish than paper obtained on a calender.

TEAR STRENGTH:

Resistance of a paper sheet to tearing, is usually measured by the force required to tear a strip under standardized conditions. (See Elmendorf test).

TENSILE STRENGTH OF PAPER:

Resistant property of a sheet to pull or stress produced by tension. Expressed as the force per unit width of a sample that is tested to the point of rupture.

THERMOMECHANICAL PULP (TMP) :

Pulp is made by pre-steaming chips and then reducing them into their fiber components during initial mechanical treatment in refiners under elevated temperature and pressure. Subsequent refining is done at atmospheric pressure.

WET MACHINE:

Paper machine consisting essentially of a wire covered cylinder rotating in a vat of pulp stock on which a mat of varying thickness is formed by drainage. These mats are removed either intermittently in thick sheets called laps or continuously.

YANKEE CYLINDER:

Cast iron cylinder, 8-18 feet in diameter and designed to handle steam pressures of up to 160 psi. Functions as a press roll and surface for creping.

YANKEE DRYER:

Type of steam heated paper dryer consisting of a large, revolving drum equipped with a felt to held the sheet in contact with its highly polished surface. Commonly used for drying tissue type papers.

Glossary of Pulp & Paper Making Procedures

AIR DRYING:

A method of drying the paper web on the paper machine by blowing air along the direction of the web.

BLEACHING:

 Chemical treatment to whiten, purify and stabilise the pulp normally carried out in several stages.

BLENDING:

 Blending of different pulps in a chest to determine the quality of the final product.

BREAKING:

 Process of returning sheets to liquid form.

CHEMICAL PULPING:

Process of dissolving and extracting the lignin in wood with help of chemical reactions.

COATING:

 Process by which paper or board is coated with an agent to improve its brightness and/or printing properties.

COOK:

Process of reacting fibre-containing materials, such as wood, rag, straw and bagasse, with suitable chemicals, usually under high temperature and pressure, to reduce them into parts so that acceptable fibres can be separated and made into pulp.

CREPING:

 Creping of paper on the paper machine using a large drying cylinder known as a Yankee.

DEFIBRATION:

 Separation of wood fibres by mechanical and/or chemical means.

DEFIBERING:

Term for pulping processes i.e. separating the fibres of pulp bales, broke or waste paper, in water by mechanical action.

DEINKING:

Removal or printing ink and impurities from recovered paper; to produce recycled fibre pulp with maximum whiteness by a floatation or washing process.

DRAINAGE:

Formation of a paper or board web on the wire by removing water at the paper machine wet end.

ELMENDORF TEST:

Test commonly used in paper mill laboratories to determine tear resistant property of paper. Also called tear test.

FINISHING:

Processing of paper after completion of papermaking operations, including supercalendering, slitting, rewinding, trimming, sorting, counting and packaging, prior to shipment from mill.

FLEXOGRAPHIC PRINTING:

 Rotary letterpress printing process using liquid ink. Solvent-based formulations made of aniline dyes and pigments (mixed with a binder) dry primarily by evaporation due to the solvent vehicle; water-based formulations have now become more common and are force-dried either by heat or irradiation (if the ink contains monomers that can be polymerized by UV-irradiation). Sometimes called aniline printing.

GLAZING:

 First calendering, in which paper is passed through a roll nip to give it a smoother surface.

GRAVURE PRINTING:

Intaglio printing process employing minute engraved “wells” and a liquid ink. Generally, deeply etched wells carry more ink than a raised surface, hence they print darker values. Shallow wells are used to print light values. A doctor blade wipes excess ink from the cylindrical printing surface. Rotogravure employs etched cylinders and web fed stock. Sheet fed gravure, as its name implies, involves individual sheet feeding.

OFF MACHINE COATING:

Process of applying coating material to a web of paper or paperboard in a location that is away from the machine on which it is made.

OFFSET PRINTING:

The indirect printing process is where an impression of type or a design on a flat plate or cylinder is transferred to a rubber blanketed cylinder from which it is impressed (“offset”) upon the surface to be printed.

PULPING:

Separation of the fibres in the raw material permits individual cellulose fibres to form a free suspension in water.

REFINING:

 Pulp and paper mill operations conducted of fibre suspensions to rub, brush, crush, fray or cut fibres as desired. Imparts such characteristics as increased capacity to absorb water and improved sheet formation.

SULPHATE PROCESS:

An alkaline pulp manufacturing process in which the active components of the liquor used to cook chips in a pressurised vessel are primarily sodium sulphide and sodium hydroxide, with sodium sulphate and lime being used to replenish these chemicals in recovery operations. Also called kraft process.

SULPHITE PROCESS:

An acid pulp manufacturing process in which chips are reduced to their component parts by cooking in a pressurised vessel using a liquor composed of calcium, sodium, magnesium, or ammonia salts of sulphurous acid.

Glossary of General Paper Mill Terms and Definitions

AIR DRY (a.d.):

Weight of moisture-free pulp or paper plus a nominal 10% moisture based on the traditional assumption that this amount of moisture exists when they come into equilibrium with the atmosphere.

ALUM:

Papermaking chemicals are commonly used for precipitating rosin size onto pulp fibers to impart water-resistant properties (when used for water treatment) to the paper. Also, used for pitch control. More correctly called aluminum sulphate.

ANTI-TARNISH PAPER:

Term originally applied to higher weight tissues used for wrapping silverware, but now used for all papers so prepared that they will not rust of discolor razor blades, needles, silverware etc.

BACKWATER:

Water used in the papermaking process, recycled to reduce the wastage of fresh water, and normally contains residual amounts of fibres and chemicals.

BACKS:

 The waste paper stock used to make the bottom ply of a sheet of board.

BASESTOCK:

 Paper or board to be further treated in various ways

BINDERS BOARD:

 Grey coloured, glazed board often used in the binding of hardcover books.

BISULPHITE PULP :

Pulp made by the bisulphite cooking process using bisulphite cooking liquor.

BOARD:

 Generic term for stiff paper, often consisting of several plies and with a grammage normally above 150g/m.

BOGUS:

Bogus refer to a product that is made from recycled fiber or an inferior pulp to imitate higher quality grades. There are bogus back liner, bogus bristol, bogus kraft, bogus wrapping etc. Gray bogus is used for packaging material, void fill, wipes, bedding, and a variety of other industrial and agricultural purposes. It is biodegradable.

BOND:

The name “bond” was initially given to a paper used for printing bonds and stock certificates. It is now used to refer to paper for letterheads and printing purposes. Important characteristics are finish, strength, freedom from fuzz, and rigidity.

BOOK PAPER:

A term used to refer to a variety of papers with similar physical properties and printing purposes in the graphic arts industry.

BRISTOL BORDS:

A fine quality cardboard made by pasting several sheets together, the middle sheets in it usually of inferior grade.

BROKE:
In general, it is a paper waste produced during Paper trimmings or damaged paper due to breaks on paper machine and in finishing operations. This is recyclable in pulp mills.

BROKE PIT:

A pit below the machine into which broke is disposed from the machine floor.

CAMBER:

 Greater diameter in the center of a papermaking roll, compared to the ends; this compensates for roll weight.

CARBONIZING PAPER:

Lightweight, uncoated paper made from unbleached chemical and/or mechanical pulps and surface coated with a carbon solvent or wax so that it takes up carbon inks and releases them under pressure, thereby duplicating the inked areas being printed.

CARBONLESS PAPER:

Copying paper that is treated or coated so it can be used without needing carbon coating or interleaved carbon paper.

CHEMICAL PULP:

The pulp is made from the process of extraction of cellulose from wood by dissolving the lignin that binds the cellulose.

CHEMICAL PULPING:

Mass of fibers resulting from reduction of wood or other fibrous raw material into component parts during cooking phases with various chemical liquors in processes such as sulphate, sulfite, soda and neutral sulfite semi-chemical process (NSCC).

CHEMICAL WOOD PULP:

Pulp is prepared from wood by either the kraft or other suitable digestion process.

CHEMITHERMOMECHANICAL PULP (CTMP):

Pulp made by a thermomechanical process in which woodchips are pre-treated with a chemical, usually sodium sulfite, either prior to or during pre-steaming, as an aid to subsequent mechanical processing in refiners.

CHIPBOARD:

Inferior quality, low density, solid or lined paperboard made primarily from recycled wastepaper stock and used in low strength applications.

COMBINATION BOARD:

A Multi layered, cylinder made paperboard having outer and inner layers made from different pulp stocks.

CONSTRUCTION PAPER:

Heavy type of paper used for watercolour and crayon artwork, made in various colours primarily from groundwood pulp. Used for Sheathing paper, roofing, floor covering, automotive, soundproofing, industrial, pipe covering, refrigerator, and similar felt Sheathing paper, roofing, floor covering, automotive, soundproofing, industrial, pipe covering, refrigerator, and similar felt.

EFFLUENT:

This waste backwater and rejected material from which fibre is recovered prior to discharge from the mill.

ELECTROSTATIC COPY PAPER:

Smooth finished, stable, medium weight bond paper made from chemical pulps. Generally treated with a zinc oxide coating material and used on dry type office copying machines.

FILLERS AND LOADINGS:

These are Minerals or compounds added to the stock to improve characteristics in the finished paper.

FINES:

These are Small fiber particles that pass through the wire of the papermaking machine.

FINE PAPERS:

These are High quality printing, writing, and cover papers having excellent surface characteristics for pen and ink writing.

FLUORESCENT PAPER:

White paper is made with synthetic dyes that produce a brighter appearance when irradiation by some light. Alternatively, this describes paper that is surface coated with colored, light-emitting dyestuff materials (which reflect white light as color). Primarily these materials absorb radiation in the UV region and re-emit in the visible, tending to give the paper a bluish tinge.

FOURDRINIER:

The name of the brothers who developed the first process for making paper on a continuous wire belt. Paper machines incorporating this principle are Fourdrinier machines and are still the most common form of paper machine in use today.

GROUNDWOOD PULP:

The slurry produced by mechanically abrading fibers from debarked logs through forced contact with the surface of a revolving grindstone is used extensively to make newsprint and publication grades.

HOTMELTS:

Plastic or wax coating materials in a molten state are applied to paper or paperboard sheets to produce a fluid-resistant surface with high gloss.

INDUSTRIAL PAPERS: This Paper is made for purposes such as industrial packaging, tissues, wrappings, impregnating, insulating, etc.

KRAFT:

A paper of high strength made from sulfate pulp. Kraft papers vary from unbleached Kraft used for wrapping purposes to fully bleached Kraft used for strong Bond and Ledger papers.

LEDGER PAPER:

Highly sized paper made from bleached chemical pulp. Used to make accounting and record books; also used with accounting machines.

LINERBOARD:

 Kraft paperboard, generally unbleached, is used to line or face corrugated core board (on both sides) to form shipping boxes and other containers.

MACHINE COATED:

Paper and paperboard that have a surface coating of adhesives and minerals applied while being made on the paper machine as an integral part of the papermaking operation.

MACHINE FINISH (MF):

The surface finish is produced on an uncoated sheet of paper as it is being made on the paper machine. It is usually accomplished with limited calendering on the machine calendar stacks.

MACHINE GLAZED (MG):

A high gloss surface finish is produced on the wire side of a sheet by passing it over a large diameter, highly polished, steam-heated roll as used on Yankee-type paper machine dryers.

NEWSPRINT:

A Grade of paper, combining high percentages of groundwood pulp, made especially for use in the printing of newspapers.

PAPER:

Homogeneous sheet of felted cellulose fibers, bound together by overlapping and by self-bonding (“hydrogen bonding”) or by the use of bonding agents and made in a variety of types.

PAPER STOCK:

Water slurry of various pulp fibers, dyes, additives, and chemicals is pumped to the paper machine for forming into a sheet.

SILVICHEMICAI:

Name of Chemical by-products of the wood pulping process and other chemicals derived from wood.

SOFTWOOD:  Wood obtained from evergreen, cone bearing species of trees, such as pines, spruces, hemlocks, etc., which are characterized by having needles.

WET STRENGTH PAPER:

Paper in which the fiber constituents and/or the sheet are chemically treated to enhance resistance to tear, rupture or disintegration after becoming saturated with liquids.