ovens may be either gas
infrared or electric infrared. We have the
unique ability to discuss both: Because we use both.
We have a wealth of infrared experience to assist
infrared ovens use electric infrared elements, or
sources. Electric infrared sources are heated by current
flowing through a resistance heating element. The
element and the material surrounding the element are
heated to an incandescent temperature. The following
descriptions highlight the most common sources for
electric infrared ovens.
lamps. Quartz lamps generally include a fused
quartz tube containing an inert gas and a coiled tungsten
filament held straight and away from the tube by tantalum
spacers. Standard lamps must be mounted horizontally,
or nearly so, to minimize filament sag and overheating
of the sealed ends. A modified design is available
for vertical mounting. Often called "T3s",
the source offers a temperature of 2,000 to 4,000°F
and a heat intensity of 5,000 to 30,000 BTUs per hour
per square foot. They typically appear yellow to white
during operation, heat up in 1 to 3 seconds, are not
very resistant to thermal or physical shock, and have
a typical radiant efficiency of 70 to 80%.
full voltage, they have an average life of 5,000 hours
and can withstand higher oven ambient temperatures
than bulbs or tubes. Thus, quartz lamps can be mounted
close to each other to provide high intensities. Reducing
voltage even slightly increases lamp service life
greatly. Quartz lamps are usually mounted on banks
of reflectors, which form the sidewalls of the oven.
Heat-up and cool-down times are short because of the
low filament mass. Quartz lamp ovens are insulated
to help keep lamp terminals and wiring cool. In some
very high intensity applications, air cooled reflectors,
water cooled reflectors, or both are used.
tube infrared sources. Quartz tube infrared sources
contain a coiled nickel-chrome wire lying unsupported
within a fused quartz tube. The use of quartz, being
more transparent to infrared rays than other materials,
allows higher heat intensities. Typically, the source
offers a temperature of 1,300 to 1,800°F and an
intensity of 2,000 to 7,500 BTUs per hour per square
foot. They typically appear red to orange during operation,
heat up in 20 to 60 seconds, are not very resistant
to thermal or physical shock, and have a typical radiant
efficiency of 70 to 80%.
quartz tubes are not sealed or filled with inert gas,
the oxidation temperature of the air limits the operating
temperature of the resistance wire. This also limits
how closely the tubes can be mounted in a curing oven
to achieve intense heating. Life expectancy depends
primarily on how close the element operating temperature
approaches its oxidation temperature. Although impact
or vibration can easily damage quartz-tube units,
they stand up relatively well to thermal shock. They
must usually be mounted horizontally or the internal
coil will sag and short circuit. Because the element
radiates in all directions, quartz tubes are usually
mounted in a fixture that contains a reflector.
sheathed elements. Metal sheath elements include
resistance heating wire embedded in an electrically
insulating ceramic material enclosed by a tube of
steel or alloy. Similar elements are used in the broilers
of electric ranges. The oxidation temperature of the
resistance wire embedded in the tube limits operating
temperatures. Metal sheath elements are rugged, have
excellent resistance to thermal shock, vibration and
impact, can be mounted in any position, and have longer
lives than vamps, tubes, or bulbs. Typically, the
source offers a temperature of 1,200 to 1,600°F
and an intensity of 2,000 to 6,000 BTUs per hour per
square foot. They typically appear red or have no
color during operation, heat up in 60 to 180 seconds,
are very resistant to thermal or physical shock, and
have a typical radiant efficiency of 60 to 75%. Higher
radiant efficiency is achieved when these elements
are shielded from direct airflow. Thermal storage
of the insulation and sheath yield long heat-up and
panels. Radiant panels contain resistance heating
wire grids, or ribbons, sandwiched between a thin
plate of electrical insulation on the radiating side
and thermal insulation on the back side. Low temperature
panels often use thin ceramic papers, boards, or steel
as the radiant surface. High temperature panels often
use alloy, quartz, or ceramic plates. Panels are generally
available in widths of 10 to 30 inches and lengths
of 12 to 96 inches. Typically, the source offers a
temperature of 1,200 to 1,600°F and a heat intensity
of 6,000 to 10,000 BTUs per hour per square foot.
They typically appear dull red or have no color during
operation, heat up in 60 to 300 seconds, are very
resistant to thermal or physical shock, and have a
typical radiant efficiency of 55 to 70%. The maximum
temperature the radiant surface can withstand or the
oxidation temperature of the resistance wire limit
operating temperatures. Because the entire surface
of the element serves as a radiator, no reflectors
are generally needed.
the entire surface emits infrared radiation, relatively
high infrared intensities can be achieved at lower
source temperatures compared with lamp or tube sources.
Panel elements generally cost more per KW than other
elements. Life expectancies are long, typically 5,000
to 10,000 hours, unless elements are overheated or
infrared ovens are common for an endless array of
coating and polymer applications as a result of the
degree of temperature control provided (no pun intended).
adhesive bonding, and preheating are ideal
applications. And all well designed electric infrared
ovens exhibit the following characteristics:
Vertical and horizontal zoning. To provide an effective,
flexible, and efficient application of electric
infrared heating to a specific process.
Precise layout and distribution of elements. To
incorporate shape factors, overcome an edge effect,
and provide greater flexibility.
Insulated reflective panels to reradiate heat. To
provide reradiation even when panels may be dirty.
Insulated element wiring to provide additional life.
To extend significantly the life of the infrared
Non-contact temperature sensors for control. To
provide the optimum in temperature control.
Rigid, non-vibrating structure. To lengthen the
life of the elements.
Custom control. To meet the specific needs of the
process and the operators.
Safety. Adherence to all NFPA, FM, IRI, and OSHA
standards and regulations.
also gas infrared ovens.