U.L. Recognized - E56973
C.S.A. Certified - 016386-0-000
Applications include but are not limited to:
Compressor Crankcase Heating, Copiers, Dies, Food Processing, Glue Pots, Heat Sealing, Hot
Melt Adhesive, Labeling, Medical Equipment, Packaging, Photographic Processing, Plastic
Molding, Platens, Wax Pots and Shoe Machinery.
Hotwatt manufactures a wide range of cartridge heating units for a variety of
size, sheath, leads, terminals, wattage and voltage can be adapted to your heating
Our most popular product is our Cartridge heaters. We make low to medium and high watt
Cartridge heaters. Cartridge heaters provide localized heat to restricted work areas
close thermal control. Dies, platens and a variety of other types of processing equipment
efficiently heated. Closely controlled work temperatures up to 1400° F (760 C) are
obtained by a
combination of heater location and proper wattage output.
Hotwatt can provide you with heating element manufactured to your specifications to
your application. Hotwatt stocks all material for the different diameter units listed in
Your order, specifying the wattage, voltage, diameter, length and lead type is readily and
fabricated from our inventory. In addition, many standard sizes are available from stock
Heaters: How they are made & Why they fail!
Are your heaters failing prematurely? The useful life of a cartridge heating element
is determined by how quickly the heat generated in the resistance wire can be dissipated
to the outside sheath. To accomplish a useful life of the heater, two methods of
manufacturing cartridge heaters are available; STANDARD cartridge heaters and SWAGED
cartridge heaters. Although both type heaters look identical, the internal construction is
are Cartridge heaters made?
STANDARD CARTRIDGE HEATERS
Nichrome wire heating coils are inserted in holes formed in ceramic tubes. Pure magnesium
oxide filler is vibrated into the holes housing the heating coils to allow maximum heat
transfer to the stainless steel sheath. The heater then has a heliarc welded end cap
inserted on the bottom of the heater and insulated leads are installed.
SWAGED CARTRIDGE HEATERS
Nichrome wire is wound around a ceramic core which situates it in close proximity to the
heater sheath. Pure magnesium oxide (MGO) is then vibrated in and the heater is swaged to
a specific diameter. This compresses the MGO so it becomes an improved conductor of heat
from the wire while maintaining its dielectric properties. This improves the heat transfer
rate and allows for higher watt densities to be used on swaged cartridge heaters. Swaged
heaters can operate at higher temperature and vibration applications with trouble free
Why do Cartridge heaters fail?
The most common cause of cartridge heater failure is an improper fit in the hole into
which it is inserted. If the heater cannot dissipate the heat being generated and produced
by contact with the sheath, the temperature inside the heater will continue to rise until
the heater fails.
2. MOISTURE and/or IMPURITIES
The MGO used in cartridge heaters is hydroscopic. Every time power to electric heaters is
eliminated, an internal vacuum occurs which draws in air from the surrounding area. If
moisture or impurities (oil, gas, etc.) are present, they can be drawn in to the heater,
and cause a short circuit resulting in a heater failure.
3. WATT DENSITY IS TOO HIGH!
If the watts/square inch is excessive, the heater will not be able to dissipate the heat
and the heater will fail.
4. INCORRECT VOLTAGE!
The wattage of any electric heater varies as the square of the voltage. If a 120 Volt
heater is powered on 240 Volts, the wattage will be 4 times greater than that for the same
120 Volt heater. Under normal conditions, this may result in heater failure.
We have cartridge heaters, round, square , and rectangular from 1/8 to 2 3/8
diameter and metric sizes from 6mm to 20mm. We have special features for lead
configuration and protection, end seals for adverse environmental situations, and sheath
materials from stainless steel to titanium.
maximum heat transfer and long life for high watt density heaters.
High watt density heaters require careful fit to insure optimum performance and long life.
Hotwatt recommends that installation holes not be drilled and reamed over .002 larger than
the nominal hole size required. The heaters are sized so that they never exceed .005 less
than the nominal diameter and always at least .001 under the nominal diameter for a slide
fit. These close fits insure rapid heat transfer from the heater and also help keep the
unit as cool as possible, which contributes to long life.
Rapid cycling of heaters from very low to very high temperatures shortens their life
considerably. It is recommended therefore, that care be taken to compute the correct
wattage for any given installation. Optimum wattage should result in a 50/50 off/on cycle.
For very high temperature operation (over 750°F), off/on control might well be replaced
by input voltage regulation through variable transformers or silicon rectifiers so that
great temperature fluctuations in the heater wire are minimized.
Location of temperature control point
When thermostats are used, the sensing element ought not to be placed further than
1/2" away from the heater wherever possible. Location further away could conceivably
cause the unit to run too hot and thereby shorten life.
Minimum wattage is based on 60 watts per square inch. Units with lower watt densities may
be manufactured for special conditions such as high temperature or vibration. Minimum
wattage available can be determined using the following formula and the values in Table 1:
History of cartridge heaters
Cartridge Types Usually
made inside a metal tube that looks like a bullet Cartridge; a possible source of its
name. Various types listed below.
Cartridges Original old standby made with ceramic supported wire insertion
into a metal tube filled with loose fill inorganic ceramic powder (usually magnesium
oxide). Cross sections can be round from 1/8 inch diameter to 2 inches diameter;
square, hexagon, triangular, etc. Cross sections are also available; length can be
from < 1 inch to > 4 feet.This is usually the first choice consideration for
OEMs and accounts for an estimated 20% of total electric heaters made. Power
density is < 100 watts per square inch and temperature up to 1200 degrees F are
* Compacted cartridges Developed
about 60 years ago, possible influenced by the good power density capacity of roll
compacted tubular, said units by nature of compacting the inorganic power tightly to the
resistance wire makes an excellent unit. Compared to un compacted units,
power density is much increased (< 500 watts per square inch) and temperatures can
approach 1800 degrees F. The requirement for higher quality tubing (to withstand
rolling/swaging compaction), precision fired crushable ceramic internal parts plus the
added compaction operation make this unit 1 ½ - 3 times standard cartridge cost.
They are available from most vendors in diameters from 1/8 inch to 1 inch and length from
1 inch to > 3 feet. A first choice for OEMs that need high power
density/temp. inside a small envelope.