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Dalton Watt-Flex Cartridge Heaters - The Revolutionary* Split-Sheath Cartridge Heater

Dalton Diff-Therm Vacuum Diffusion Pump Heaters
Chromaloxฎ CH Infinite Control Mechanism
Chromalox VCF Percentage Timing Input Controller
Fenwal 17000 Series Cartridge Style Thermoswitch
Payne Engineering 18TBP SCR Power Controls

We are an authorized distributor for Dalton Electric Heating Co., Inc.

We are an authorized distributor for Dalton Electric Heating Company, Inc. manufacturer of the Split-Sheath Cartridge Heater and Diff-Therm Diffusion Pump Heaters.

The Revolutionary Watt-Flex
Split-Sheath Cartridge Heater

  • Maximizes Heat Transfer
  • Reduces Maintenance Costs
  • Reduces the Cost of Process Heating

Hot Tip or
Cool Tip Option
Watt-Flex Cartridge Heaters run more
efficiently, use less power and last
up to 5 times longer than conventional
cartridge heaters.



A single continuous heating
coil ensures a uniform
temperature profile.
No sections to burn out as
in conventional cartridge heaters.

  Split-sheath expands to maximize heat transfer and
contracts when cold for easy removal from bore.

Ideal for use in oversized
bores. Eliminates need
for tight fits, tight
tolerance bores.


Watt-Flex's tightly compacted MgO dielectric accommodates higher watt densities - up to
50% higher warrantable heat densities than conventional heaters.

External Thermocouple Option- a Watt-Flex exclusive-provides more accurate temperature at the point of heat transfer to host metal.

Through the patented split-sheath design and highly specialized manufacturing techniques, Dalton Watt-Flex cartridge heaters reduce your total cost of process heating by an average of 40% over other heaters.

Dalton Electric's Watt-Flex Cartridge Heaters use a unique, patented split-sheath design that expand when energized to maximize heat transfer through greater contact with the wall of the bore. Better heat transfer means less power is consumed to maintain the set point temperature, reducing operating costs.

The Watt-Flex heater construction eliminates ceramic cores typically found in conventional cartridge heaters. Dalton has developed and highly-specialized manufacturing techniques to compact high-grade MgO dielectric to its near theoretical maximum around the heater coil, which increases dielectric strength and heat transfer away from the coil which results in significantly longer heater life.

Watt-Flex cartridge heaters last up to 5 times longer than conventional heaters with less downtime for heater replacements and lower maintenance costs. Watt-Flex heaters contract when de-energized, eliminating bore seizure and the need for expensive drill-outs.

Maximize Heat Transfer

The unique split-sheath design of the Watt-Flex Cartridge Heater allows the independent, bilateral expansion of each half of the heater outward against the walls of the surrounding bore.

The result is greatly improved heat transfer under normal fit conditions of .005" to .007", assuring superior heat transfer, more uniform process heat, greater efficiency, and reduced consumption of electricity. If bores are oversized from previous use and drill-outs, the bilateral sheath expansion will maximize heater-to-bore contact for the most efficient conduction heating.

  Conventional Cartridge Heater   Watt-Flex Heater Energized   Watt-Flex Heater De-energized
Limited to ordinary thermal expansion, cannot compensate for oversized bores.   The unique bi-lateral expansion of an energized Watt-Flex cartridge heater produces superior metal-to-metal contact with the surrounding bore, thereby maximizing heat transfer.   When de-energized, the Watt-Flex heater contracts for easy removal from bore.
Watt Flex Cartridge Heaters Last Longer

Cartridge heater life is directly related to its internal operating temperature.
Watt-Flex cartridge heaters run substantially cooler and have a more uniform temperature profile than conventional heaters.

The result is Watt-Flex heaters that last up to 5 times longer, have less downtime and lower operating costs than conventional cartridge heaters.

Efficient Heat Transfer

  • The high purity MgO dielectric in Watt-Flex heaters is compacted to extreme density, ensuring maximum heat transfer away from the core to the heater sheath.
  • As the energized split-sheath expands, it creates intimate contact with the bore wall, efficiently transferring heater sheath to the host metal.

Conventional ceramic core cartridge heaters (shown below) use multiple
heating cores that can independently burn out, causing a cold section on the
sheath. And voids of coil at core junctions produce cold sections on the
heater profile.

Conventional Cartridge Heater Weaknesses: cold spots, indepndent sections to burn out.
Conventional Cartridge Heater

Unlike conventional ceramic heaters, Watt-Flex heaters use a continuous heating coil to achieve a more uniform temperature profile. With Watt-Flex heaters, there are no independent heating element sections to burn out. Watt-Flex heaters are either totally on or totally off.

Watt-Flex Cartridge Heater uses  coil, and split sheath design , and  so they last longer than conventional heaters.
Watt-Flex Cartridge Heater
Watt-Flex Cartridge Heaters Eliminate Bore Seizure
The patented split-sheath design of the Watt-Flex cartridge heater reduces your heater change-out costs by preventing heater bore seizure.

Dalton Electric will replace, free of charge, any Watt-Flex Heater that cannot be withdrawn from the bore.

What causes conventional heaters to warp and bind?
  In conventional cylindrical heaters, temperature can vary from one side of the heater diameter to the other. These differentials are caused by heat deflection within a close fitting bore, and are the most frequent cause of heater warping and binding during removal.   Conventional cartridge heaters can warp and bind up in the bore because of temperature differentials from one side of heater to the other.
How the Watt-Flex Split-Sheath prevents bore seizure:
With the Watt-Flex heaters' unique split-sheath design, each half of the heater expands and contracts independently. Dalton's Watt Flex Cartridge heaters use a unique, patented split-sheath design  with bi-lateral expansion.  When energized the heater contacts the bore wall;  when de-energized, it contracts for warranted easy removal.
  When energized, the heater expands to make intimate contact with the bore wall. When de-energized the sheath contracts for ease of removal:

Watt-Flex cartridge heater split-sheaths (end view) expand bi-laterally to make contact with bore walls,  contract when cool for easy removal.

Dalton Electric's standard warranty covers the removal of Watt-Flex Heaters from bores, provided that the bore fit is a minimum of 0.005" and there is no bore contamination to cause seizure.

Watt-Flex Temperature Profiles

Unlike conventional cartridge heaters, Watt-Flex heaters use a continuous heating coil that allows for a more uniform temperature profile.

By varying the watt-density, Watt-Flex heaters can also be configured for customized temperature profiles with varying zones of heat along the heater.

Uniform Temperature Profile

Uniform sheath temperature is vital when molding heat-sensitive plastics where the temperature window between gate freeze-off and material degradation is very narrow. The test results below highlight the superior temperature profile along the length of a torpedo probe heated by a Watt-Flex heater.

Customized Temperature Profile

By varying the watt-density, the temperature profile may be custom matched to your specific requirements.

For example, certain applications such as those requiring temperatures higher at the tip of a molding probe than along the sheath can be accomplished with Watt-Flex heaters, but not with conventional cartridge heaters. Or, watt density can be varied to compensate for
process heat loss."

Higher Watt Density and Temperatures

Watt Flex heaters produce up to 50% higher warrantable watt-densities than conventional heaters and can operate at much higher temperatures.

The Watt-Flex Cartridge Heater is a high-quality tubular heating element bent back on itself and swaged into a cylindrical format. Dalton manufactures heaters using only high-purity magnesium oxide, nickel chromium resistance wire and stainless steel terminals.

Special filling methods and equipment compact the magnesium oxide inside and around the resistor coil to extreme density. Swaging further compacts the magnesium oxide to virtually maximum density, which yields high dielectric strength and efficient internal heat conduction. Unlike conventional heaters, Watt-Flex cartridge heaters have no ceramic core that can crack during swaging.

Watt-Flex Cartridge Heaters run more efficiently, use less power, last longer and are much simpler and faster to replace than conventional cartridge heaters.

Watt-Flex Cartridge Heaters
Ideal for Use in Oversized Bores
The unique bi-lateral expansion of Watt-Flex cartridge heaters eliminates the need for tight fits and makes them well-suited for use in oversized bores where conventional cartridge heaters cannot be used effectively.

Cartridge heater fit is measured as the difference between the inside diameter (I.D.) of the bore and the outside dimension (O.D.) of the heater.

The suggested fit for a Watt-Flex Cartridge Heater is .007" greater than the nominal Watt-Flex heater sheath diameter.

For example, the ideal bore diameter for a 1/2" diameter Watt-Flex heater would be 0.502 --> 0.505". At the maximum tolerance dimension of heater and the minimum bore diameter, the heater would have a 0.005" fit, allowing ease of insertion and removal.

Generally, smaller diameter heaters benefit from a tighter fit and fit can be loosened for larger diameters.


Bi-lateral Expansion

eliminates tight fits.


Watt-Flex Heaters - Hot Tip or Cool Tip Options

Watt-Flex heaters use a continuous coil construction that can be designed to deliver either full or reduced power at the tip to suit your process heating application.

Used in injection molding heat probes, for example, the Watt-Flex Hot Tip option can minimize undesirable gate freeze-off.

Conventional heater designs prohibit heated tips.

  Conventional cartridge heaters  prohibit heated tip.




Watt-Flex heaters, however, can be constructed for hot or cool tips by either concentrating or stretching the continuous coil inside the densely compacted MgO dielectric.

  Watt-Flex cartridge heater cross-section shows concentrated heating coils that produce full power at heater tip; Hot-Tip Option.




  Watt-Flex Heater cross-section shows cool-tip option.


External Thermocouples - an Exclusive Watt-Flex Option

Watt-Flex split-sheath cartridge heaters can be manufactured with a groove along the exterior of the cartridge to accommodate a needle-type thermocouple for more accurate temperature sensing and control.

Watt-Flex cartridge heater with external thermocouple for monitoring heat at the precise point of heat transfer.
Watt-Flex external thermocouples outperform internal monitors used in conventional heaters. With Watt-Flex heaters, you can:
Measure temperature at the precise point of heat transfer.
Unlike conventional heaters with internal thermocouples that measure internal heater coil temperature, Watt-Flex external thermocouples measure more precisely at the point where heat transfers from the heater to the host metal.
Monitor temperature at any point along the heater.
Dalton Watt-Flex heaters give you the flexibility to monitor heat at any point along the heater, instead of at pre-defined fixed points with internal monitors in conventional heaters.
Replace heater or thermocouple independently.
With Watt-Flex external thermocouples, you can replace either the heater or the thermocouple independently, without having to replace an operational component as with conventional heater designs.
Thermocouple Specifications

Maximum lengths:

15" maximum for grooved heaters with 1/4" or 3/8" diameter heaters.
7" maximum for grooved heaters with 1/2" diameter heaters.

Longer heaters using 1/2" diameter or larger heaters, can be center- grooved between the legs to any depth between 6" to 15".


Type J with 48" leads.
Type K with 48" leads.

Needle diameters:

0.040" for 1/4" diameter heaters and all center grooves.
0.062" for side-grooved 3/8" and 1/2" diameter heaters.

Watt-Flex Cartridge Heater Standard Dimensions

All Watt-Flex cartridge heaters are built-to-order to match your heating and size requirements. Available sizes for cartridges are listed below.

Watt-Flex heaters eliminate the need for a tight fit. When selecting the right diameter for the bore in your application, keep in mind that the recommended fit for a Watt-Flex diameter is .007" larger than the nominal diameters shown.

For custom sizes and special heating applications, call and talk to one of our heating specialists at (978) 356-9844.

We have designed and built high-watt heaters for use across a wide variety of industries and process heating applications such as molds and dies, plastics, package sealing, and liquids in automotive, plastics, composites, aerospace, food service, and more.

Table: Watt-Flex Cartridge Heater Dimensions
Nominal Diameters (1) Standard Cold Section at Terminal End Min - Max (2) Lengths
1/4” 0.245” 5/16” 1 1/4”- 22”
3/8” 0.370” 3/8” 1 1/2” - 36”
1/2” 0.495” 5/8” 2” - 50"
5/8” 0.620” 5/8” 2 1/2” - 72”
11/16” 0.683” 5/8” 3 1/2” - 64”
3/4” 0.745” 5/8” 3 1/2” - 90”
1" 0.9925" 10” - 60”
  8.0 mm  7.875 mm  8.000 mm 38 - 660 mm
10.0 mm  9.875 mm  9.500 mm 38 - 915 mm
12.0 mm 11.875 mm 15.875 mm   50 - 1140 mm
12.5 mm 12.375 mm 15.875 mm   50 - 1140 mm
15.0 mm 14.875 mm 15.875 mm   65 - 1250 mm
16.0 mm 15.875 mm 15.875 mm   65 - 1525 mm
20.0 mm 19.875 mm 15.875 mm 100 - 1525 mm
(1) Tolerances: ฑ.002" ( 1/4" to 3/4"); ฑ.0025 (1"); ฑ.05mm (8mm-20mm)
(2) Tolerances: ฑ 3% with 3/32"minimum; ฑ2% above 20 " (500 mm)

Watt-Flex Replaceable Immersion Heaters

Clean and safe.
Heater never comes into contact with tank contents.

Easily replaced without draining the vat or tank.
Watt-Flex heater contracts when de-energized
for easy removal.

Stainless-steel sheath accommodates
standard diameter flanged
Watt-Flex cartridge heaters
from 5" to 72" lengths.
Solid Construction. Stainless steel
sheath with a welded end cap and
NPT fitting that screws into and becomes a permanent part of the tank or vat to be heated.
Easy Heater Change Out

The flanged Watt-Flex cartridge heater is secured to the NPT fitting with two screws.

To replace the immersion heater, simply remove the screws, and slide out the de-energized heater.

Immersion Heater Specifications

Both the Watt-Flex Cartridge Heaters and Immersion Heaters are manufactured to customer specified lengths.

Immersion Heater
Cartridge Heater
Sheath O.D.
NPT Fitting
5/8" 3/4" 1/2" 5" - 45"
7/8" 1" 3/4" 8" - 72"

Watt-Flex Cartridge Heater Modifications and Accessories

Watt-Flex cartridge heaters are built-to-order to meet your electric process heating application. A variety of heater modifications and accessories are available for:

Abrasion Protection Heater Mounting Accessories
Lead Modifications High Temperature Modifications
Contaminant Protection Distributed Wattage

Designing a challenging new heating application?

With over 20 years of experience in the manufacture of cartridge heaters, Dalton Electric has the engineering expertise and production capabilities to design and produce modified, special, or custom heaters for your most challenging requirements.


Abrasion Protection

Watt-Flex headers shield lead wires and insulators from abrasion damage caused by machine cycling, severe environment and rough handling.

High-quality stainless steel construction provides long-lasting protection even in the most rugged industrial environments.

Stainless Steel Braid - flexible, with tighter bend radius plus the strength of braided strands of high-quality stainless steel.

Stainless Steel BX - interlocking hose provides greater strength and abrasion protection than braid, and a slight economic advantage.

Straight and Right Angle Headers

Abrasion protection headers for Watt-Flex cartridge heaters include stainless steel straight or right angle headers; stainless steel braid or flexible conduit.
Straight and Right Angle Headers

Watt-Flex cartridge heater abrasion protection header dimensions

Straight and Right Angle Headers

Header O.D.
Hose O.D.
11/32" *
1 1/8"
(* 3/8" diameter right angle header with high-temperature leads has 1/2" hose O.D.)

Lead Modifications

Standard Temperature Leads - TGGT insulation (Teflon tape primary, glass servings, woven glass braid, Teflon coated) over stranded Grade "A" nickel wire.
(< 480o F / 250o C).

Standard Temperature Teflon Leads - Extruded PFA over stranded Grade "A" nickel wire. (< 480o F / 250o C)

High Temperature Leads - Fiberglass insulation (threaded glass servings primary, treated glass braid) over stranded Grade "A" nickel wire. (< 840o F / 450o C).

Fiberglass or Rubber Sleeving - Rubber sleeving provides excellent insulation value for low temperature process heating applications (< 450o F / 230o C). Fiberglass woven glass strands provide good insulation for use in high temperature process heating applications.

Quick Disconnect - a modular plug or terminal junction in the wire for ease of heater disconnection.

Threaded post terminals - useful when wire must be occasionally disconnected and/or replaced. Often used in conjunction with a bussbar.

Integral Ground Wire - attached to the heater, meant for termination to ground on the machine.

Extra Length Leads - available in any length. For wires longer than 10 feet (3 meters), a quick connect or male/female connector plug assembly can be used to reduce heater cost.

Stainless Steel Clip Support
- displaces and reinforces the point of wire flexure away from the heater terminal connection. Useful for applications where there is repeated flexing (packaging and sealing).

Watt-Flex cartridge  heaters can be fitted with Fiberglass (high temp) or Rubber (low temp) insulating sleeves.
Fiberglass or Silicon Rubber Sleeving


Threaded post terminals are useful when wires must be disconnected occasionally.
Threaded Post Terminal

Post Terminal
thread dimensions
Cartridge Heater Post Terminal Thread Dimensions
Watt-Flex O.D.
Terminal Thread
3/8" to 3/4"
(0.1368"diameter with 32 threads/inch)
1/2 to 1"
(0.2894" diameter with 24 threads/ inch)

Watt-Flex cartridge heater  stainless steel clip  support used as an anti-flex device.  90 degree angle also available.
Stainless Steel Clip anti-flex support

Dimensions shown  for Watt-Flex cartidge heater clip supports.

Contaminant Protection

A protective contaminant barrier inserted into the terminal cavity can protect the cartridge heating element from moisture, dirt and other contaminants that can damage the heating element.

RTV Potting - RTV (Room Temperature Vulcanized) rubber provides an excellent moisture barrier for low temperature process heating applications (< 450o F / 230o C).

Ceramic Potting - provides good contaminant protection, but is not a complete moisture barrier. Ceramic material supports very high temperature process heating and is rated to 2000+ oF / 1090 oC.


Cartridge  Heater with RTV potting provides excellent moisture protection for  low temperature process heat applications.
RTV Potting for contaminant protection

Mounting Modifications

Dalton Electric heating engineers can develop mounting apparatus for any heating application. A sampling of standard accessories are listed below.

  • Stainless Steel Flange
  • Puller End Plug
  • Mounting Bracket
  • NPT Fitting
  • In Line Diodes
  • Threaded Extraction Collars
  • Solid Pin Connectors
  • Ground Wire

watt-flex cartridge heater  with stainless steel mounting flange.
At Top: Stainless Steel Flanged Heater
At Bottom: Puller End Plug

Stainless Steel Flange - available in sizes shown at left, the stainless steel flange acts as a mechanical stop at the edge of the heater well.

Mounting Bracket - an "L" shaped bracket welded to the sheath to act as an insertion stop or for mechanically securing the heater at the edge of the heat sink.

Puller End Plug - used for heater extraction in applications where the terminal end of the heater is not accessible. Interior thread attaches the puller plug to the heater tip.

NPT Fitting - used with Watt-Flex replaceable immersion heaters for heating liquids in vats or tanks.

Flanged cartridge heater dimensions
Stainless Steel Flange Dimensions
Watt-Flex O.D.
.080"R on 1" BC
.080"R on 1" BC
.080"R on 1" BC
.080"R on 1" BC
1 1/2"
.080"R on 1 1/4" BC
.080"R on 1 1/2" BC

High Temperature Modifications

  • Extra Cold Section at End
  • Ceramic Beads
Extra Cold Section at End - when the heater extends out of the bore (through insulation, for example) an extra cold section added to the cartridge heater ensures that the heated section is fully enclosed by the heat sink. The cold terminal end is usually produced by adding a longer terminal pin so no heat is produced. Longer cold sections are created by stretching the continuous coil resistance wire to limited heat production.

Ceramic Bead Insulation -- Placed over insulated lead wire to protect beyond temperature rating of insulation. Withstands temperatures to 2000ฐ F / 1090 ฐC.

Distributed Wattage

Watt-Flex heaters can be designed with zones of varying watt density, allowing you to put a specific amount of heat exactly where you need it.

Distributed wattage is ideal for applications where higher temperatures are required at certain points to offset radiant heat loss such as at the ends of a sealing bar or at the tip of the molding probe. Distributed watt density along  heater profile.

Process Heating Engineering Data
and Application Design Considerations

The following reference information can assist you in the selection of Watt-Flex heaters for new process heating designs. For a consultation on any heating application, call our heating engineers at 978-356-9844.

  Heating Metal Parts
  Calculate Process Heating Wattage Requirements
  Physical Properties of Materials Table
  Heating Liquids

Heating Metal Parts

The required wattage for a metal heating application is equal to the sum of watts required for material heat up plus watt loss during heat-up, plus a 20% safety margin added for contingencies.

To calculate the heater capacity needed to produce a required level of heat, find the thermal values in the Physical Properties of Materials Table and plug them into the following equations:


Wattage Loss Rates  Chart:  This chart shows rates at which convection watt loss as function of surface temparature.  It is  used to calculate wattage requirements for  process heating of metals.

Calculation of Required Wattage

C = (A + B)*1.2

where A = Watts for material heat-up
where B = Watts Heat Loss during heat-up
where C = Total Watts Required
  A = [Weight of Material (lbs.)] x [Specific Heat] x [Temperature Rise (F)]
    3.412 x Heat up Time (hours)
  B = [Watt Loss per sq. in.] x [Area (Sq.In)]

Physical Properties of Materials


Specific Heat

Heat of Fusion
Lowest melting point
Thermal conductivity
Thermal Expansion
 inches per inch per  oF x 10-6
Aluminum 1100
Aluminum 2024
Aluminum 3003
4.7 - 6.0 
.3 -> 2.4 
Inconel 600
Iron, Cast
Iron, wrought
Lead, solid
Lead, melted
Monel 400
Nickel 200
(80% Ni, 20% Cr)
(50%Pb, 50%Sn)
Steel, mild carbon 
Steel, stainless 304 
Steel, stainless 430 
Tin, solid 
Tin, melted 
Type Metal
(85% Pb, 15% Sb)
9.4 - 22

Heating Liquids

Consideration should be given to the following factors when heating liquids with Watt-Flex Cartridge heaters.

  • Locate heater wells in an unrestricted space in the main body of the liquid.
  • The heated section of the well should be covered by liquids at all times.
  • In metal-melting applications, explosions can result unless pressure is vented during melting phase of heat-up.
  • Certain watt-density limits exist in immersion applications. Please consult the factory for technical assistance.

This page is Copyright ฉ 1997-2004 Dalton Electric Co., Inc. All Rights Reserved. Used with permission of Dalton Electric Co., Inc.

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We are a Distributor of Industrial, Commercial and Residential Heaters and Controls. Always consult manufacturers installation instructions for proper installation of the products or systems shown on this website. ยฉ Copyright 1999-2019 Mor Electric Heating Assoc., Inc.

5880 Alpine Ave. NW - Comstock Park, MI 49321  USA
Tel 616-784-1121 - 800-442-2581 - Fax 616-784-7775

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