The majority of applications do not require maximum watt/in². Use a watt density only as high as needed. Take advantage of the
safety margin provided by using ratings less than the maximum allowed. Select space heaters for most even heat pattern rather
than the highest possible wattage per heater.
At medium Watt densities, general purpose drills are usually adequate for drilling holes. Typically, these
result in holes .003" to .008" over the nominal size of the drill, resulting in fits of .010" .015". Of
course, the tightest fit is desirable from a heat transfer standpoint, but somewhat looser fits aid in installing
and removing cartridge heaters, especially long ones. Holes drilled completely through the part are recommended to facilitate removal
of the heater. After drilling, clean or degrease the part to remove cutting lubricants.
At high Watt densities holes should be drilled and reamed, rather than just drilled to final diameter with a general purpose drill.
At high watt densities, a close fit is important. The fit is the difference between the minimum diameter of the heater and
maximum diameter of the hole. For example, at 1/2" diameter an OMEGALUX cartridge heater is actually .498" plus 000" minus
.005". If this heater is placed in a hole which has been drilled and reamed to a diameter of .503" - .493" = .010").
Temperature Controllers and Sensors for Cartridge Heaters
The sensor for the temperature control is also an important factor and should be placed between
the working surface of the part and the heaters. The temperature of the part approximately 1/2" away from the
heaters is used in selecting maximum allowable Watt density from the graph.
Control of power is an important consideration in high Watt density applications. On-off control is frequently utilized, but it can cause
wide excursions in the temperature of the heater and working parts. Thyristor power controls are valuable in extending the life of high
Watt density heaters, since they effectively eliminate on-off cycling.
There are a variety of temperature controllers and sensors one can use depending on the application. One of the more popular
sensor types for cartride heater applications are the surface mount temperature sensors. Thermocouple, RTD or Thermistors are available
with an adhesive backing or the ability to be cemented to the surface being heated. There also bolt on and magnetic surface mount type temperature
sensors available. Digital temperature controllers come in many different sizes with many output and input choices. Thermcouple and RTD inputs are the most
popular with a dc pulse output. DC pulse ouputs allow the user to go to a larger relay to switch the heater load and use proportional control versus on/off
control which can shorten the heater life.
Important Formula To Know: Determining Watt Density
The term "Watt density" refers to the heat flow rate or surface loading. It is the number of Watts per square inch of
heated surface area. For calcualation purposes, stock cartridge heaters have a 1/4" unheated length at each end. Thus, for a
1/2" x 12" heater rated 1000 Watts, the Watt density calculation would be as follows:
Watt Density = W / (Π x D x HL)
W= wattage = 1000 W
Π = pi (3.14)
D= diameter = 0.5 inch
HL = Heated Length = 11.5 inch
Watt Density = 1000/(3.14 x .5 x 11.5) = 55 W/in
Types of CartridgeHeaters
1/4" Diameter Cartridge Heaters OMEGALUX® CIR series high watt density cartridge heaters are manufactured to the highest
industry standards using only premium materials. They have been designed to last longer and outperform any other brand
cartridge heater in both laboratory and industrial applications. Their heavy duty construction provides high dielectric strength as well as
shock and vibration resistance.
1/2" Diameter Cartridge Heaters OMEGALUX® CIR series high watt density cartridge heaters are especially well suited for use in
applications involving molds, dies, platens, hot plates, and sealing operations.
3/8" Diameter Cartridge Heaters OMEGALUX® CIR series high watt density cartridge heaters are especially well suited for use in applications
involving molds, dies, platens, hot plates, and sealing operations. They are available in lengths from 1 to 24".
3/4" Diameter Cartridge Heaters OMEGALUX® CIR series high Watt density cartridge heaters are especially well suited for use in applications involving
molds, dies, platens, hot plates, and sealing operations. They are available in lengths from 2 1/4" to 48".
Heavy Duty Cartridge Heaters OMEGALUX® C Series heavy duty
cartridge heaters are especially suited
for use in applications involving hot
plates, molds, dies, platens and
Electric Stud Heaters CBH Series heaters are constructed of rugged metal sheathed tubular elements homogeneously combined with a
metal sleeve that has been accurately dimensioned to provide a proper clearance and ease of inserting into standard drill hole
sizes so large bolts or studs may be rapidly expanded and tightened with a wrench, providing ''shrink fit tightness" when cool.
Useful in assembly of large compressors, presses, turbines, die blocks, cylinders, engine heads, pressure vessels, etc. Quick heat-up
is important to avoid heat drain-away of surrounding metal. CBH heaters are generally used in sets to permit uniform tightening of mating parts.