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"Refers to a type of paper which has been treated with considerable size to resist moisture penetration. Opposite of ""slack sized""."


The presence of calcium or magnesium metal in water.


Refers to wood generally from broadleaf trees (oak, beech, etc.)


Broke or waste paper that accumulates and must be removed from various sections of the paper machine when there is a break or trouble on the machine.

Head (Total)

The pressure maintained in the head box, usually expressed as inches of water.


(1) The vessel used to properly distribute the fiber and fillers across the paper machine web. (2) On Fourdrinier machines: A large flow control chamber which receives the dilute paper stock of furnish from the stock preparation system and, by means of baffles and other flow evening devices, maintains sufficient agitation of the mixture to prevent flocculation of the fibers, spreads the flow evenly to the full width of the paper machine and provides delivery of stock to the Fourdrinier wire uniformly across its full width. The height of the liquid in an open head box or the air pressure in a closed head box provides the requisite speed of flow of the stock onto the Fourdrinier wire. The present design trend for high-speed machines is to enclose head boxes. (3) On cylinder machines: A flow-regulating device which controls the volume of stock flowing to the screens and mixing boxes upstream of the vats.

Heat Exchanger

A device used to cool a liquid (oil or condensate) in which the cooling water is turned into warm water, and is used at different locations. This in turn saves energy for cooling and the heating of water.

Herring Bone

A diagonally-slotted cover on a felt suction box.

High Density Storage

Tile pulp tower used for storage of unbleached pulp at 9 - 22% consistency.

High Velocity Dryer

A drier used for coated paper drying consisting of a large diameter drier drum enveloped from 180 to 270 degrees by an evaporating hood with forced convection of moisture-laden air through aerodynamically designed orifices.


The enclosure over the dryer sections.

Hot Extract Ph

A measure of the acid content of the sheet.

Hot Water

Water heated by the blow heat recovery system and/or heat exchangers with steam to be used in the bleach plant hood showers.

Hot Well

A tank used to create a barometric leg, or water seal, on a condenser to help produce a vacuum.


The moisture content of the air. Actual humidity is the number of droplets of moisture in the air at any given time. Relative humidity is the percentage of moisture relative to the maximum which air can retain at any given temperature without precipitation.


To swell the fibers and then partially break them down into fibrillate and mucilage or gel; any process of altering cellulose fibers to increase their ability to absorb water.

Hydraulic Headbox

A paper machine head box with no moving parts.


Used to dissolve paper or blocks of pulp by churning water.


The property of material which causes it to expand or contract when its moisture content is changed (as when the relative humidity of the surrounding atmosphere is changed). This property is of great importance where the dimensions of paper sheets and cards must remain constant.