Tubular Heating Elements

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Highly versatile and economical, electric tubular heating elements are applied in virtually every conceivable type of heating application. These robust tubular heaters are a reliable thermal source used to heat a multitude of liquids, gases, and solids and can be applied straight or formed into complex formations.

Durex manufactured tubular heaters are also used for radiant heating in open air or vacuum atmospheres. The heating elements can be cast into or clamped onto metal to form heated parts. We offer a wide selection of standard designs, or tubular heating elements can be custom designed for your requirements. Durex Industries' application and design engineering team are available to assist in specifying the proper electric tubular heater configuration.

DESIGN FEATURES:

Advantages of Using a Tubular Heating Element

In addition to its versatility, other benefits of using a tubular heating element include:

Straight Heating Elements

Durex manufactures standard tubular heating elements for any application. Tubular heating elements are a versatile and economical heat source for a wide variety of industrial and commercial applications. Standard diameters are 0.260", 0.315", 0.375", 0.430", 0.475" and 0.496". Other special sizes are available. Depending on the diameter, lengths can be supplied up to 335". Standard sheath materials range from copper and steel to stainless steel and Incoloy® alloys. Special sheath materials may be available based on diameter and size of the element required. Standard terminations include a threaded stud, threaded bulkhead, screw lug, quick disconnect spade, ceramic-to-metal hermetic, molded rubber lead, conventional lead wire terminal assembly and more. Flexible lead wire extensions or other mounting options are available for specific applications.

Formed Heating Elements

Custom heating elements can be provided to any length, formed into virtually any configuration and sheathed in a variety of different materials to suit your application. Likewise, the connection/termination possibilities are limited only by your imagination and the availability of components. Standard terminations include a threaded stud, threaded bulkhead, screw lug, quick disconnect spade, ceramic-to-metal hermetic, molded rubber lead, conventional lead wire terminal assembly and more. Durex frequently fabricates custom tubular heaters in conjunction with an OEM's design staff, both for prototype and production.

Tubular Immersion Heating Elements

Tubular immersion heaters are commonly used in radiant and immersion heating applications such as infant incubators, where a formed tubular heating element warms the air flow and an immersion tubular heater assembly vaporizes water to provide humidity. These heater assemblies are also the preferred solution for laboratory sterilizers and environmental chambers.

Design Features:

Considerations when Selecting a Tubular Heating Element

When choosing which tubular heating element is right for your application, there are several factors one should consider before making a decision. Factors include:

Contact the Tubular Heating Experts at Durex Industries Today

At Durex Industries, we look forward to new designs and challenges. We have extensive experience applying tubular heating elements in challenging applications from cryogenic temperatures to over 1500F, from low or high-power densities, from benign or highly corrosive environments. Let’s get started on your next tubular heater element project today.

Tubular Heater Specifications & Options

Physical and Electrical Specs

Sheath Diameter +-0.005" (+-0.13mm) 0.260" (6.60mm) 0.315" (8.00mm) 0.375" (9.52mm) 0.430" (10.92mm) 0.475" (12.07mm) 0.496" (12.60mm)
Sheath Length Max. 404" (10,260mm) 370" (9398mm) 337" (8560mm) 329" (8356mm) 281" (7137mm) 263" (6680mm)
Maximum Voltage 250 480 480 600 600 600
Maximum Amperage 15 30 30 40 40 40
Wattage Tolerance Industry Standard +5% -10%
Resistance Tolerance Industry Standard +5% -10%

Length

Overall Sheath Length 11-20" 21-50" 51-80" 81-110" 111-140" 141-170" 171-200" 201"& up
Sheath Length ± 3/32" ± 1/8" ± 5/32" ± 3/16" ± 7/32" ± 1/4" ± 3/8" ± 1/2"
Heated Length ± 1/4" ± 1/2" 7/8" ± 1 1/8" ± 1 3/8" ± 1 5/8" ± 1 7/8" ± 2 3/8"
Minimum Unheated 1" 1 1/4" 1 1/2" 1 5/8" 1 3/4" 2" 2 1/4" 2 1/2"


Tubular Sheath, Temperature and Watt Density Guidelines

Heated Medium Process Temperature
°F (°C)
Sheath Material Max. Watt Density
W/in2 (W/cm2)
SOLIDS
Clamp on to Metal To 500 (260)
To 1000 (540)
Incoloy® 20 (3)
10 (1.5)
Milled Groove Molds To 500 (260)
To 1000 (540)
Incoloy® 60 (9)
30 (4.5)
Vacuum Platens To 650 (345)
To 1000 (540)
Aluminum, SS
Incoloy® or Inconel®
40 (6)
20 (3)
LIQUIDS
Clean Potable Water To 212 (100)
To 500 (260)
Copper
Incoloy®
60 - 90 (9 - 14)
30 - 40 (4.5 - 6)
De-I Water To 212 (100) 316SS 60 (9)
Process Water &
Very Diluted Corrosives
To 200 (95) 304SS or Incoloy® 48 (7.5)
Mild or Diluted Acids &
Alkalies
To 200 (95) Incoloy®, 316SS or
Inconel®
15-23 (2.3 - 3.5)
Oils (Depends on Type & Use) 50 - 600 (10-315) Steel 6 - 23 (1 - 3.5)
AIR
Ovens, Natural Convection To 700 (370)
To 1200 (650)
Incoloy® 30 (4.5)
10 (2.3)
Flowing Air @
Min. 500 fpm
To 800 (425)
To 1000 (650)
Incoloy® 30 (4.5)
23 (3.5)

Available Sheath Materials and Maximum Recommended Sheath Temperatures

Sheath Materials Maximum Temperature in Air °F (°C) Typical Applications
Standard Available Sheath Materials
Copper 350 (175) Clean, potable water heating
Aluminum 750 (400) Vacuum platens
Steel 750 (400) Oils, glycol, molten salts, non-corrosives
304SS 1200 (650) Improved corrosion resistance over steel
316SS 1200 (650) De-ionized water and some corrosives
Incoloy® 840 1600 (870) Improved corrosion resistance over steel and 304SS
Incoloy® 800 1600 (870) Improved resistance to chloride attack, other corrosives
Other Available Sheath Materials
321SS 1200 (650) Improved corrosion resistance over steel and 304SS
Incoloy® 825 1600 (870) Highly resistant to many acids, salts, and other media
Inconel® 600 1800 (980) Highly resistant to many acids, salts, and other media

Heater Mounting Options

TYPE R MOUNTING - Locator washers

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Heater Diameter A B
0.260" 3/4" Specify
0.315" 5/8" Specify
0.375" 3/4" Specify
0.430" 3/4" Specify
0.475" 3/4"
Specify

TYPE K MOUNTING - Mounting bracket

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Specify all required dimensions and tolerances.

TYPE F MOUNTING - Mounting flange

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Specify all required dimensions and tolerances.

TYPE B MOUNTING - Threaded bulkhead fittings

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Type Material
BB Brass
BS Steel
B4 304SS
Diameter Thread A B C
0.260" 1/2 - 20 3/4" 5/8" 3/4"
0.315" 1/2 - 20 3/4" 5/8" 3/4"
0.375" 5/8 - 18 15/16" 3/4" 7/8"
0.430" 5/8 - 18 15/16" 3/4" 7/8"
0.475" 3/4 - 20 1" 7/8" 1"

Tubular Heater Termination Options

TYPE S TERMINATION - Threaded stud terminal with a ceramic insulator.

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TYPE S1 TERMINATION - Threaded stud terminal with stacked mica.

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TYPE L TERMINATION - Screw lug terminal.

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Screw Size Diameter A W
#8-32 To 0.315" 7/8" 5/16"
#10-32 0.375" and above 1 1/16" 7/16"
Maximum 240V

TYPE L1 TERMINATION - Screw lug terminal 90°.

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Screw Size Diameter A W
#8-32 To 0.315" 7/8" 5/16"
#10-32 0.375" and above 1 1/16" 7/16"
Maximum 240V

TYPE D TERMINATION - Quick connect. Maximum 240V

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TYPE D1 TERMINATION - Quick connect 90°. Maximum 240V

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TYPE W TERMINATION - Leadwire terminal assembly.

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Type Insulation Max. Temperature Volts
WS Silicone 390°F (200°C) 600V
WF Fiberglass 480°F (250°C) 600V
WM Mica/Glass 840°F (450°C) 600V

Note: If protective armor cable (hose) is required, please consult factory.

Seal Options

TYPE G SEAL OPTION - Silicone Conformal Coating - General protection, porous, maximum temperature 220°F (105°C)

TYPE E SEAL OPTION - Epoxy Seal - Moisture and contamination resistant (better choice for long-term moisture resistance), low porosity, maximum temperature 450°F (230°C)

TYPE V SEAL OPTION - Silicone RTV - Moisture and contamination protection, porous, max. temperature 400°F (200°C)

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TYPE M SEAL OPTION - Silicone rubber over mold, max. temperature 300°F (150°F)

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Diameter A
0.260" 7/16"
0.315" 7/16"
0.430" 5/8"

TYPE PA SEAL OPTION - Potted adapter

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Potted protection tube ensures an integral bond between wire insulation, the seal, and protective sleeving that may be required.

Type PS is silicone RTV and silicone insulated lead wireType PP is epoxy coating and Fiberglass insulated lead wireType PT is epoxy coating and Teflon® insulated lead wire

TYPE HS SEAL OPTION - Ceramic to metal hermetic terminals, max. temperature 1000°F (540°C)

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Thread Size Diameter W
#8-32 0.260" 1 3/4"
#10-32 0.315" 1 7/8"
#1/4-28 0.430" 2 1/8"

Tubular Heater Construction Options

Unheated Length - The unheated length can be varied to suit application requirements. Longer unheated sections are often used to keep the termination area cool or to focus heat generation in a specific area of the part or media being heated.

Distributed Wattage - Durex tubular heaters can be tailor-made to vary the watt density along the length of the heater. This aids in temperature uniformity in-mold applications or to make up for heat losses close to the ends.

Sheath Treatment and Finish - For tubular heaters that will be field bent, please be sure to specify "full anneal" on the order. For pharmaceutical and other "clean" applications, a bright anneal finish can be supplied. Also available, depending on configuration, is sheath passivation which removes any free iron that may stain or rust the finish of the sheath.

Tubular Heater Bending Options

Tubular heating elements can be formed into 2-D and 3-D shapes to better suit application requirements. Ensure to allow for up to 10% dimensional increase due to thermal expansion and to provide adequate support to prevent heating element sagging due to high temperatures. If field bending of straight elements is necessary, contact Durex Industries for field bending guidelines prior to bending. Also, specify "full sheath anneal" to allow for field bending.

Bend Tolerances for Incoloy® and Stainless Steel Sheath Elements

Bend Data Reference Heater Diameter
0.260" 0.315" 0.375" 0.430" 0.475" 0.490"
Minimum Bend Radius Standard 0.437" 0.562" 0.687" 0.75" 0.812" 0.875"
Minimum Bend Radius w/Repressed Bend 0.375" 0.50" 0.562" 0.625" 0.687" 0.75"
Standard Bend Tolerances 1/8" 1/8" 1/8" 1/8" 1/8" 1/8"
Special Bend Tolerances 1/16" 1/16" 1/16" 1/16" 1/16" 1/16"
Precision Bend Tolerances w/Tooling 0.005" 0.005" 0.005" 0.005" 0.005" 0.005"

Note: Tighter bend radii possible for steel and copper sheath elements. Please consult Durex Industries for more information.

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Tubular Heater Application Guidelines

Heating Metal Parts

Below are the installation methods for heating metals in order of best to least effective.

Durex Industries recommends to "press fit" the tubular heating element into milled groove plates for extended heater life. Ensure that all heated portions of the heater are in contact with the part. Heat transfer cement should be used to promote heat transfer. If clamps are used, they should be closely spaced and not over tightened to ensure good heater-to-part contact. Allow for up to 10% length increase due to thermal expansion during heating.

Heating Liquids

To prevent overheating or fouling the heating element, ensure the heated portion of the tubular heater is immersed in liquids AT ALL TIMES. For optimal results, properly match the sheath material and heater watt density to the liquid application. Factory installed fittings or field installed compression fittings are used to mount and seal the tubular element against the tank wall. Refer to the Immersion, Circulation, and Over-The-Side Heater sections of our website or catalog for other liquid heating products.

Heating Air & Gases

Tubular heating elements are typically formed into a "U" hairpin or other formation, installed through wall openings and secured with lock washers, clips, threaded fittings, mounting bracket or flange. For optimal results, use an Incoloy® sheath and ensure reasonable watt densities are used. Allow for 10% length increase due to thermal expansion. For horizontal installations, provide supports at least every 18" of length to avoid element sagging due to high temperatures. Refer to the Circulation and Duct Heater sections of the website or catalog for forced air and gas heating.

Radiant Heating and Vacuums

Tubular heaters used for radiant heating typically use reflectors to direct heat energy toward the part being heated. This works well for warming, drying, and curing applications. However, when using heaters in a vacuum, the only heat transfer is through radiation, so reduce watt density by 20% to 30% versus air heating. Aluminum sheath, as well as Inconel® sheathed heaters are typically used with vacuum feedthrough assemblies. Durex Industries can test and measure vacuum leakage rates down to 8x10-8 SCCS He (3x10-6 Pa 1/s).

 

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Typical Tubular Heating Element Applications

  • Metal mold, die and platen heating
  • Medical and analytical device heating
  • Cast into metal parts and platens
  • Cut and seal heads on packaging equipment
  • Tank wall and pipe heating
  • Liquid immersion & circulation heaters
  • Furnace & oven heating
  • Comfort heating and freeze protection
  • Process air and gas heating
  • Thermoforming, curing, drying

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