Understanding Common Thermal Processing Vocabulary
ITS offers a chance to build a better thermal processing vocabulary by providing
a partial list of thermal processing terminology with definitions.
Heat Treat Terms
Aging
The process of changing the properties of a metal or an alloy through
temperature changes.
Air/fuel ratio (a/f ratio)
The ratio of the air supply flow rate to the fuel supply flow rate when measured
under the same conditions. For gaseous fuels, usually the ratio of volumes in
the same units. For liquid and solid fuels, it may be expressed as a ratio of
weights in the same units, but it is often given in mixed units such as cubic
feet of air per pound of fuel
Annealing
The process of softening an object or changing other properties of the object
through cycles of heating and cooling.
Atmosphere (atm)
A mixture of gases (usually within a furnace). Also a unit of pressure equal to
14.7 lb/square inches or 760 millimeters (mm) of mercury.
Atmospheric Pressure
The amount of force the atmosphere exerts upon the earth's surface, measuring
14.7 psi at sea level.
Available Heat
The gross quantity of heat released within a combustion chamber minus both the
dry flue gas loss and the moisture loss. It represents the quantity of heat
remaining for useful purposes (and to balance losses to walls, openings, and
conveyors).
Basic Refractory
Refractory consisting essentially of magnesia, lime, chrome ore, or forsterite,
or mixtures of these (by contrast, acid refractory contain a substantial
proportion of free silica).
BTU (British Thermal Unit)
The amount of heat necessary to change the temperature of one pound of water by
one degree Fahrenheit.
Conduction
A form of heat transfer through the application of heat to a solid object
followed by the subsequent spread of the heat through the object.
Convection
Heat transfer between two objects, one of which is either a liquid or a gas.
During convection, the pull of gravity initiates fluid circulation, causing
heated molecules to rise and cool molecules to fall.
Curing
The process involving the solidification of a material through heating and
drying, in which the temperature of the cured object is maintained during the
process.
Demand
The load integrated over a specific interval of time.
Drying
The process of removing a solvent such as moisture from an object.
Effective Area of Furnace Openings
The area of an opening in an infinitely thin furnace wall that would permit a
radiation loss equal to that occurring through an actual
opening in a wall of finite thickness. The effective area is always less than
the actual area because some radiation always strikes the sides of the opening
and is reflected back into the furnace.
Efficiency
The percentage of gross Btu input that is realized as useful Btu output of a
furnace.
Heat Content
The sum total of latent and sensible heat stored in a substance minus that
contained at an arbitrary set of conditions chosen as the base or zero point.
It is usually designated h, in Btu per pound, but may also be expressed in such
units as Btu per gallon and Btu per cubic foot if the pressure and temperature
are specified.
Heat Transfer
The exchange between matter, or parts of the same matter, which always occurs
from warm to cool. Flow of heat by conduction, convection, or radiation.
Heat Treatment
The controlled heating and cooling of a material to achieve favorable mechanical
properties such as hardness, strength, and flexibility. The process of changing
properties in solid metals or alloys through heating and cooling applications.
Post Heating
Applying heat to an object after the manufacturing process, such as brazing,
welding or soldering.
Powder Coating
A dry finishing process that utilizes finely ground, electro statically charged
particles, which are sprayed onto a part to be coated. When placed in an oven,
the charged parts melt and fuse into a durable, even coating.
Preheated Air
Air heated prior to combustion, generally transferring energy from the hot flue
gases with a recuperation or regenerator
Preheating
The application of heat before the manufacturing process.
Process Heating
The supplication of heat to an object or material.
Quenching
The rapid cooling of a heated object. After solution treatment, it is important
to cool the work-piece quickly to preserve the proper crystalline
microstructure. This cooling is usually achieved by water immersion or water
sprays. Quenching operations must be carefully integrated with heat treatment
furnaces to avoid uncontrolled slow cooling.
Radiation
The movement of energy in the form of particles, rays or waves.
Radio Frequency
The creation of heat by the transfer of energy.
Refractory
Highly heat-resistant materials used to line furnaces, kilns, incinerators, and
boilers
Saturated Air
Air containing all the water vapor it can normally hold under existing
conditions.
Saturated Steam
Steam at the boiling point for water at the existing pressure.
Sensible Heat
Heat, for which the addition to or removal of will result in a temperature
change, as opposed to latent heat.
Sintering
The formation of large particles from a heap of small, fine particles through
the application of heat. In the sintering process, the temperature remains
below the melting point.
Solution Heat Treating
Cast, extruded, or forged pieces are heated to 850°F to 1050°F so that soluble alloying elements can diffuse evenly throughout the metal in
solid solution. Precise temperature control and timing are important. Larger
castings may require up to twenty hours of soaking while thin sheet may require
only a minute.
Stress Relieving
Reducing stress in a metal object by raising the temperature of the object and
maintaining the object's temperature for a specified amount of time.
Tempering Heating
Steel by different means to a given temperature and then cooling it, in order to
reduce the brittleness in the hardened steel.
Thermal Bonding
The application of heat to produce interlocking among fibers and fabrics.
Thermal conductance, C
The amount of heat transmitted by a material divided by the difference in
temperature of the material’s surfaces. Also known as conductance.
Thermal conductivity, k
The ability of a material to conduct heat, measured as the heat flow through a
square foot of cross sectional area and a one foot (or inch) thickness with 1°F of temperature difference across the
thickness. The refractory and insulation industries use the “inch thickness,” while most other industries use “foot thickness” to measure this material property.
Wall Loss
The heat loss from a furnace or tank through its walls.
