Watlow Flexible Shapes and Geometries Application Guide

W A T L O W

Flexible Heaters

Flexible Shapes
and Geometries

Flexible heaters from Watlow are
just what the name implies: thin,
bendable and shaped to fit your
equipment. You can use your
imagination to apply heat to the
most complex shapes and
geometries, without sacrificing
efficiency or dependability. With
Watlow’s customization capabilities,
you have the maximum amount of
freedom when designing your
equipment.

Excellent heat transfer results from
the heater’s thin design and its
direct bonding to the application.
Flexible heaters also provide fast
heatup and cool down rates,
uniform heat distribution and high
watt densities.

Features and Benefits

• Flat geometry permits holes,
notches and unusual shapes.

• Four material types and two
element styles are available for
wider flexibility in meeting your
requirements. See next page for
performance capabilities.

• Lightweight construction and
low thermal mass permit use in
applications that have limited
space or weight requirements.

• Heating elements as close as

0.003 inches (0.08 mm) from the
heated part respond to controls
with faster heat up and cool down.

• Uniformly spaced element
paths, placed within
(6 mm) of the heater perimeter,
distribute heat more evenly.

1

⁄4 inch

Wire-Wound
Element

• Same day shipment on stock units with orders
received by 11:00 a.m.CST.

Top Layer of Insulation
Sheath Material

Bottom Layer of Insulation
Sheath Material

Flexible Heaters

Etched Foil
Element

Applications

• Medical equipment such as blood
analyzers, respiratory therapy
units and hydrotherapy baths

• Satellite and communication
equipment

• Freeze protection for military
hardware, aircraft instrumentation,
hydraulic equipment, etc.

• Battery heating

• Semiconductor equipment

• Foodservice equipment

• Any application requiring a flexible
shape or design

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Flexible Heaters

Flexible Shapes
and Geometries

Applications and
Technical Data

Four Material Types

Silicone Rubber:

This rugged, moisture- and chemical­resistant material is easily bonded or
cemented to parts. Watlow silicone
rubber heaters can handle tempera­tures up to 500°F (260°C). Many
styles of these heaters are available
with UR®, cUR®and VDE
recognition. See page 171 for details.

Kapton®:

A thin, lightweight transparent
material from du Pont, Kapton®is
designed for extremely precise
heating requirements ranging from

-319° to 392°F (-195° to 200°C). It is
ideal for applications requiring low
outgassing in a vacuum, or
resistance to radiation, fungus and
chemicals. Many custom heaters can
be UR®and cUR®recognized.

Neoprene:

Neoprene resists weathering,
abrasion and chemicals. It can be
used economically in applications to
250°F (120°C), where high watt
densities are not needed.

HT Foil:

This mica-insulated, high
temperature foil is a semi-rigid
heater. Operating temperatures up to
1100°F (595°C) can be achieved.

See pages 169 to 182 and
189 to 194 for information
on silicone rubber,
Kapton®, neoprene, and
HT foil heaters.

Two Element Types

Watlow offers both wire-wound and
etched foil resistance elements.
These element types are available in

Wire-Wound Elements

Available on silicone rubber and
neoprene heaters, this element
style is created by spiraling fine
resistance wires around a fiberglass
cord. The element is then laid out in
a pattern designed specifically for
your application. The benefits of
wire-wound elements include:

• Excellent physical strength and
flexibility; repeated flexing of the
heater has no harmful effects on
its performance

• Good economy for small
production runs

• Conforms readily to curved
surfaces, including small
radius bends

Drum heaters and conduit bender
heaters are typical examples of
applications that use the wire­wound method. These heaters are
flexed repeatedly during use, but
due to their wiring, no internal
damage will occur.

most insulating materials, and
Watlow can recommend the type
best suited to your application.

Etched Foil Elements

This element type, created by acid
etching a circuit in nickel resistance
alloy foil, is available in silicone
rubber, Kapton
types. The etched foil element is
noted for its excellent circuit pattern
repeatability and superior heat
transfer, which results from greater
area coverage of the element. Other
benefits include:

• Delivers more heat and up to
twice the watt density of a wire­wound element, providing longer
heater life

• Most economical for large
production runs

• Complex heat distribution
patterns can be provided

The etched foil element style is
usually recommended for
applications requiring high
temperatures or watt densities, or
multiple zoning.

®

and HT foil heater

Kapton®is a registered trademark of
E.I. du Pont de Nemours & Company.

®

and cUR®are registered trademarks of

UR
Underwriter's Laboratories, Inc.

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W A T L O W

Flexible Heaters

Flexible Shapes
and Geometries

Options

Note: PSAS maximum six months storage

life before heater installation.

Note: Not recommended for Kapton

heaters.

®

Mounting Methods

Watlow offers various attachment
techniques, all designed for fast
installation. These include: three
types of adhesives; Watlow’s special
factory vulcanization process; and
mechanical fasteners.

Pressure Sensitive Adhesive
Surface (PSAS)

For speed, convenience and
economy of installation, specify
PSAS. Simply peel off the protective
backing and roll the heater in place
for an even bond to a clean, smooth
surface.

Field Applied Adhesive (RTV)

For a stronger bond, or when long
storage is probable, a room

temperature vulcanizing (RTV)
silicone adhesive is available from

stock within two days. Watlow offers
red RTV for temperatures up to 500°F
(260°C). White RTV is available from
adhesive suppliers for temperatures
up to 400°F (205°C). Watlow’s one-

Complete installation instructions are
available from Watlow. Ask for
technical letter #2, silicone rubber
heaters.

Note: PSAS is not recommended
for curved surfaces or for heaters
rated above 10 W/in2(0.8 W/cm2). It
should not be used for applications
exceeding 400°F (205°C) on silicone
rubber, 300°F (150°C) on Kapton
or 200°F (93°C) for neoprene.

part RTV is self-priming and can be
ordered in either 3 oz (90 ml) or
12 oz (355 ml) tubes. For larger
heaters requiring longer adhesive
working time, two-part RTV kits can
be purchased from adhesive
suppliers. These kits require primer on
the surface prior to application of the
adhesive.

®

Flexible Heaters

Silicone Contact Cement Kit

This two-part adhesive consists of a
resin and catalyst which are easily
mixed together and applied with a
paintbrush. Recommended usage is
for field cementing of silicone rubber
heaters to customer parts. Available

Factory Bonding

This attachment technique provides
a strong, void-free bond for excellent
heat transfer and extended heater
life. Watlow’s expertise in bonding
heaters to customer parts has
proven extremely successful.

Mechanical Fasteners

When a wire-wound flexible heater
must be detachable, any type of
fastener normally used with fabrics
can usually be built into the sheath
material of Watlow flexible heaters.
The most common types are
latch fasteners, boot hooks and

from stock, the cement kit will handle
temperatures to 350°F (175°C).
The resin is available in pint or quart
containers. To order, specify silicone
contact cement, and container size.

Bonding is recommended for
applications that reach maximum
temperatures of 500°F (260°C) on
silicone rubber and 300°F (150°C)
on Kapton®.

grommets. Other styles include snap
fasteners, springs, velcro style
fastener strips and lacing cord. The
grommets and boot hooks are
commonly used with tension springs
to compensate for slight variations in
part size.

165

Flexible Heaters

Flexible Shapes
and Geometries

Termination Styles

Watlow offers many types of leads
and terminations. Leads can project
from any position along the perimeter
of the unit. They will be centered

on the short side width of
rectangular heaters unless
specified otherwise.

Standard Leads —Type E Teflon

Leads shown exiting end of heater,
centered on short side.

®

Watlow’s standard leads are 12
inches (305 mm) long, white, Teflon
insulated, flexible, plated copper
wire. They are rated for 392°F
(200°C)/600 volts per MIL-W-16878,
Type E. The lead connections on or
at the heater are insulated with a
cap of sheath material, vulcanized to
the heater body. All custom flexible
heaters except HT foil will be
supplied with this lead type unless
otherwise specified.

®

HPN Cord and Plug Set

Molded leads are shown exiting edge of heater.
Capped leads are also available.

Silicone Insulated Leads

Leads shown exiting corner of heater.

®

Special Teflon

Leads shown exiting middle of heater.

Leads

For removable heaters, a six foot
(1.8 m) HPN (neoprene insulated)
cord and plug set provides conven­ience. It is rated for 194°F (90°C)/
300VÅ(ac). HPN cord without a plug
is also available in any length.

For a better moisture seal, specify

®

silicone insulated lead wires. This

UL
lead type is rated for 302°F (150°C)/
600VÅ(ac). Any lead length is avail­able. Note: Silicone rubber heaters
are not designed to be waterproof.
Excess exposure to moisture may
facilitate premature heater failure.

Teflon®leads, UL®style 1180 and
cUR®approved, are rated for 392°F
(200°C)/300 volts. Any length is
available. UL®Teflon®leads are
standard on stock rectangles.

Construction

Teflon®is a registered trademark of
E.I. du Pont de Nemours & Company.

166

Formed Heaters

Holes, Cutouts and Notches

Many three-dimensional shapes,
such as cylinders, cones and boxes,
can be factory formed. Semi-rigid
shapes can be self-gripping to the
part. Special tooling may be
required for some designs.

Watlow can provide flexible heaters
with special holes, cutouts and notch­es in nearly any position required for
your design. The resistance element
can be brought to within

1

⁄8 inch (3 mm)

of all edges. Standard spacing is

1

inch (6 mm) from all edges.

⁄4

W A T L O W

1

1

/

2

"

(38 mm)

1

3

/

4

"

(45 mm)

3

/

4

"

(19 mm )

Ref.

3

/

8

"

(10 mm)

T-10

1

1

/

2

"

(38 mm)

1

1

/

4

"

(32 mm)

3

/

4

"

(19 mm )

Ref.

11

/

16

"

(18 mm)

T-207

2

1

/

2

"

(64 mm)

3

/

4

"

(19 mm)

3

/

16

"

(5 mm)

Thermocouple

Flexible Heaters

Flexible Shapes
and Geometries

Temperature Sensors

Watlow offers several styles of
sensors for use with flexible heaters.
These sensors are available as
preset or adjustable thermostats,
thermocouples, thermistors, RTDs or
thermal fuses. They can be
integrally mounted (encapsulated
in silicone rubber) to sense the
temperature of either the part or the
heater sheath. The thermostats can
also be ordered separate from the
heater, allowing direct control of your
process temperature, if desired.

Pre-Set Thermostats

Several styles of non-adjustable,
pre-set thermostats are available
from Watlow. Thermostats separate
from the heater are encapsulated in
silicone rubber, and are available
with standard 12 inch (305 mm)
leads unless otherwise specified.

Note: Precise part temperature control with preset thermostats requires prototyping and
field testing.

Thermocouples, thermistors, RTDs
and thermal fuses are usually
mounted to the heater under a
vulcanized protective cap of
silicone rubber sheath material. This
drawing shows a typical mounting
style for a thermocouple.

Flexible Heaters

Pre-Set Thermostats (Non-Adjustable)

Thermostat Maximum Volts Temperature Settings

Model Watts AC Available °F (°C)

T-10 600/960 120/240 *125-300±10 (50-149±5) yes yes yes
T-207 1500 120/240 40/55±8 (4/13±4.4) yes yes yes

1500 120/240 60/75±8 (16/24±4.4) yes yes yes
1500 120/240 95/110±8 (35/43±4.4) yes yes yes
1500 120/240 145/160±8 (63/71±4.4) yes yes yes

Notes:

• When ordering a pre-set thermostat
separate from the heater, simply add the
prefix S to the model number.
(Example: ST-10) See next page.

• Snap action preset temperatures on the
T-207 are close/open settings.

• T-10 thermostats are manufactured for
specific preset temperatures. Available in
25˚F increments.

• Other temperature ranges and voltages
are available on special order. Minimum
quantities apply, so consult factory before
ordering.

Agency Approvals

UR cUR VDE

Adjustable Thermostats

The B-200 thermostat features a
maximum rating of 1500 watts at
120/240VÅ(ac). The following
temperature ranges are available:

• Model B-200-2:
100° to 500°F (40° to 260°C)

• Model B-200-3:
25° to 330°F (-5° to 165°C)

The B-200 thermostat can be
integrally mounted to the heater with
a bonded protective cap of
silicone rubber sheath material.

167

Flexible Heaters

Ref.

0.50

(13 mm)

1

(25 mm)

2.25

(57 mm)

0.50

(13 mm)

0.34

(9 mm)

0.218

(6 mm)

Dia. Typ.

1.75

(44 mm)

1.25

(32 mm)

0.50

(13 mm)

Flexible Shapes
and Geometries

Temperature Sensors

Continued

ST-207

ST-10

ST-207E

Separate Heater Accessories
Available From Stock

Pre-Set Thermostats Separate
From Heater

These are offered to allow direct
control of your process temperature,
so you’re not limited to controlling
only the heater temperature when
using stock heaters. Pre-set ther­mostats are encapsulated in silicone
rubber with standard 12 inch leads.

The same temperature ranges,
ratings and sizes are available on
these thermostats. When ordering,
add “S” prefix to the model number
to indicate “separate” item.
(Examples: ST-10 and ST-207)

Standard leads are 12 inch (305
mm) 18 ga. UL1180 black leads.

Notes: For direct control of air temperature
as is required in enclosure heating
applications, specify thermostat model
number ST-207E. This is a modified ST-207
mounted on 1⁄32
with the thermostat’s metal cap exposed to
sense air temperature.

inch thick G-10 circuit board

11

⁄16"

27⁄8

"

B-200

5

⁄8"

1

1

⁄2"

Adjustable Thermostats Separate
From Heater

The Model B-200 adjustable
thermostat can be ordered as a
separate item. The same model
numbers and temperature ranges

indicated under Adjustable
Thermostats are available. When
ordering, simply note that you want
the B-200 separate from the heater.

168