Chromalox DU-RAD-458 6.04 757 - Manual (Page 4)

OPERATION
CAUTION: For your own safety —
Before energizing this heater:
1. Be sure all electrical connections are tightly made.
2. Be sure that all conductors are properly insulated.
3. Be sure that terminal box cover has been properly replaced, and
that secondary insulation bushings have not been omitted.
Controlling Radiant Intensity —
Standard Radiant Heaters are built to operate at 40 watts per
sq. inch on the element sheath. When it is desired to reduce radi-
ant intensity, one or more of the following methods may be used.
1. INPUT CONTROLLERS. These motor-driven cycling devices
can be used to vary heater output capacity from 4 to 100%. They
are usually connected in holding coil circuit of magnetic contac-
tors. See Chromalox Radiant Heater Manual for further informa-
tion regarding Input Controllers and Contactors.
2. SOLID STATE THYRISTOR POWER CONTROLLERS.
For best non-contact control of radiant heat, a Series #6 Chromalox
Thyristor Power Controller with manual potentiometer setting is
recommended. Truly proportional output of from 0 – 100% can be
easily dialed-in to suit the particular product or process require-
ments. The Series #6 panels are pre-engineered, pre-packaged
assemblies in an enclosure with circuit disconnect provided and
ready for installation.
Maximum Ambient Temperatures —
Chromalox Radiant Heaters are not recommended for appli-
cations in ambient temperatures exceeding 450°F. Higher ambient
temperatures mean shorter heater life.
Maximum work temperature in a given time depends on sev-
eral factors: Reflectivity of work, specific heat of work, mass of
work, kW input and losses from oven, and time of exposure. As
work temperature increases, the work loses heat by radiation and
by convection to the surrounding ambient. Although it is a gener-
al principle of a Radiant Heater application that work temperature
conventionally exceeds ambient temperature, in cases where
extremely high work temperatures are desired, it is necessary to
enclose the heaters in order to increase the ambient. If evaporation
of a liquid is desired as a result of increasing work temperature, it
is necessary to provide ventilation air in order to carry away the
evaporated liquid. Under carefully engineered circumstances, a
maximum work temperature of 600°F may be attained.
Low Megohm Condition — The refractory material used in
electric heaters may absorb moisture during transit, storage or
when subject to humid environments that will reduce the cold
insulation resistance (low megohm). Low megohm may result in a
high leakage current to ground and nuisance trips of ground fault
protection equipment. Normally, the megohm value increases after
heat-up. Typical insulation values are 5 megohm or greater on
complete assemblies or 20 megohm on individual unsealed ele-
ments. It is recommended that heaters with 1 megohm or less be
dried out before applying full power. If dried properly, low
megohm will not effect heater life or efficiency.
To correct a low megohm condition, remove terminal enclo-
sure cover, gaskets, and terminal hardware. Bake heaters in an
oven at 300 to 350˚F for several hours or preferably overnight.
An alternate procedure is to cycle the heater in 10 to 15
minute periods at low voltage until megohm values are normal.
Sheath temperatures should not exceed 350˚F.
Note: Low megohm on heating elements with epoxy or her-
metic seals cannot be serviced in the field. Typical resistance val-
ues when sealed are 200 megohm or greater. Contact Chromalox
service center at number listed.
FIRE OR SHOCK HAZARD. Moisture accumulation
in the element refractory material, element over-
temperature or sheath corrosion can cause ground
fault to the element sheath, generating arcing and
molten metal. Install Ground Fault Protection to
prevent property damage.
ELECTRIC SHOCK HAZARD. Disconnect all power
before installing or servicing heater. Failure to do
so could result in personal injury or property dam-
age. Heater must be installed by a qualified person
in accordance with the National Electrical Code,
NFPA 70.
To Remove Heating Element —
1. End Elements
A. Remove element assembly mounting nut and bolt 18 and 16
and element support clips (see Figure 9) and slide element
assembly out of housing.
B. Disconnect heating element from electrical leads at both ends.
C. Remove screws from porcelain terminal blocks.
D. Remove element support clips and secondary insulating bush-
ings.
E. Lift out element.
2. Center Elements
A. Remove terminal box cover.
B. Disconnect heating element from electrical leads and remove
all hardware from terminals.
C. Remove screws 24 from secondary insulator retaining brack-
et and remove bracket 22 .
D. Remove secondary insulation bushings 23 .
E. Unclip element support clips 12 from housing. (See Fig. 10)
F. Lift out element.
G. Remove element support clips
12 , bushing retaining clip 14
and insulating bushings 13 from element.
To Install Element —
Observe instructions for removing element and proceed in
reverse order. Be sure to replace secondary insulating bushings.
Care of Reflectors —
Reflectors should be cleaned periodically. A mild soap and
water solution or fine cleaning powder is best although more dras-
tic means may be required if reflectors are badly soiled by chemi-
cal or other deposits. The reflector is aluminum. DO NOT use
alkali cleaners since alkalies will dull reflector. Mild non-alkaline
cleaners, such as used for scouring kitchen sinks, may be used.
Reflectors are replaceable and may be purchased from Chromalox.
MAINTENANCE
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