Front Page | Johanson DMS, Inc. | Product Descriptions | Stock Heaters
Useful Formulas | Ordering Information | Therm. Cond. of Materials

Johanson DMS, Inc.

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Product Description page contents

Product Characteristics Chart
General Description
Stock Heater Temperatures
Silicone RTV Adhesives
Silicone Rubber

 

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CHARACTERISTICS
Thickness (In) Weight (Lb/sq. ft) Watts Category Watts Tolerance Voltages Available AC or DC Factory Test Voltage Types of heat conductors Multiple Circuits Availability
.005 -.015 .192 Commercial +/- 15% 0.5 -60 500 AC Conductive Ink Centertap only
.005 -.015 .192 Industrial +/- 10% 61 - 135 1250 AC Etched Foil Yes
.005 -.015 .192 Special +/- 5% 136 - 272 2000 AC Stamped Foil No
.005 -.015 .192 Precision +/- 2.5% 273 - 481 2500 AC Wire Wound Yes
 



General Description

This document not intended for preparing specifications.

Heater Construction The heater is normally comprised of two sheets of thin (.002 inch) polyester film with the heating element sandwiched in between. In many applications, a sheet of thin aluminum foil is added to the underside of the heater to improve the efficiency of heat transfer.

Heater Element Design The design of the heater element is accomplished with the assistance of computer programs which help the engineer to select the most thermally efficient configuration for the application. The circuit layout is established by reviewing all possible combinations of element width compared to spaces between to establish the maximum metal or conductive ink coverage. A sample printout is shown below:

HEAT CONDUCTOR = 48.90 MILS WIDE- 36% FOIL OR CONDUCTIVE INK COVERAGE- 130 MIL SPACES
HEAT CONDUCTOR = 52.97 MILS WIDE- 42% FOIL OR CONDUCTIVE INK COVERAGE- 104 MIL SPACES
HEAT CONDUCTOR = 57.05 MILS WIDE- 49% FOIL OR CONDUCTIVE INK COVERAGE- 83 MIL SPACES
HEAT CONDUCTOR = 61.12 MILS WIDE- 56% FOIL OR CONDUCTIVE INK COVERAGE- 64 MIL SPACES
HEAT CONDUCTOR = 65.20 MILS WIDE- 64% FOIL OR CONDUCTIVE INK COVERAGE- 49 MIL SPACES
HEAT CONDUCTOR = 69.27 MILS WIDE- 72% FOIL OR CONDUCTIVE INK COVERAGE- 34 MIL SPACES
HEAT CONDUCTOR = 73.34 MILS WIDE- 81% FOIL OR CONDUCTIVE INK COVERAGE- 22 MIL SPACES
HEAT CONDUCTOR = 77.42 MILS WIDE- 91% FOIL OR CONDUCTIVE INK COVERAGE- 10 MIL SPACES

The italicized selection above yields the best overall performance balanced with the least expensive manufacturing tolerances. Seventy two per cent of the effective heated area is covered by heat conductor, raising the cross-sectional heating efficiency. When the foil coverage is increased, the heater conducts heat away at a faster rate and does not have to rise to as high a temperature to accomplish the task. The element then does not have to expand and contract as much, thereby increasing life expectancy. Another consideration that is computer assisted is the selection of the shape of the loop. Shorter heated lengths mean that thermal expansion pressure can be relieved resulting in longer service life for high watt density elements.

Polyester, a semi-clear polyethylene terephthalate film, exhibits excellent electrical properties, high thermal durability, low moisture absorption, low shrinkage and exceptional cut-through resistance. It has a useful temperature range of -70C/-94F to + 150 C/+302F. One of the most important features of the polyester film is its ability to perform in humid or moisture laden environments. The dielectric strength of the film at 25 C is 14,000 volts per mil. Even at 150 C, the dielectric strength is 6000 Volts per mil. At a relative humidity of 80%, a 2 mil film still exhibits 5000 volts per mil. The thermal conductivity of the film is 1.07 BTU FT/SQ FT HR DEGREE F.

 

Methods of Connection

  • Solderable Tabs
  • 1/4 inch Spade Push-on Blade Terminals
  • Crimped, Soldered or Welded lead wire (Most Common)
  • Many other Styles Available

Acrylic Pressure Sensitive Adhesive # 1062 - (Maximum service temperature - 104C/220F). A twenty four hour waiting period (dwell time) should be observed after installation and before use to improve the bond strength.

 

IDENTIFICATION - Product Marking

Ink Stamp Marking - Least expensive, more commercial appearance.

Etched Foil Marking - Heaters can be marked along one of the unheated borders. The appearance of the marking is very sharp , well defined and permanent. Including the date of manufacture is not recommended unless only one production run is made, as a non-recurring set-up cost would be required to change the artwork for subsequent runs.

 

Bar Coding Containers for Shipment

Bar coding is available for marking on shipping containers in Code 39 (Interleaved 2 of 5), Code 128, UPC/EAN, Codabar, MSI, and ZIP (Postnet).

 



Stock Heater Temperatures

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The temperatures above were obtained by placing four stock heaters horizontally on a flat surface, on a one inch high wire form. The wire form allowed heat to circulate under and over the two major surfaces.

PLEASE NOTE ... Temperature controls must be used to limit the maximum operating temperature to 450F.

Applications
SHL (2.5W/IN2)
Gentle Heat
SHM (5W/IN2)
Moderate Heat
SHMH (7.5W/IN2)
High Heat
SHH (10W/IN2)
Very High Heat
Batteries

Exterior electrical equipment

Medical instruments

Mirror de-icing

Paraffin melting

Sensitive computer parts

Adhesive melters

Automatic doors

Book binding equipment

Electric motors

Food processing machines

Industrial antenna

Airborne equipment

Cardboard box sealing tape

Ink jet printing parts

Laboratory equipment

Pipe and tube heating

Plastic heat sealers

Process flow materials

Anti-icing devices

Heavy metal parts

Industrial process equipment

Press platens

Pressure vessels

Space & missle part

 



Use Of Silicone RTV Adhesives

(Room Temperature Vulcanized)

Silicone rubber heaters may be adhered by applying a one part room temperature curing adhesive to the underside of the part and mating it to the surface to be heated.

We recommend the following adhesives:

  • Dow Corning Silastic #732 (Translucent) with #1200 Primer
  • G.E. RTV 102 (White) with #SS4004, SS4044, or SS4179 Primer
  • G.E. RTV 103 (Black) with #SS4004, SS4044, or SS4179 Primer
  • G.E. RTV 106 (Red) with #SS4004, SS4044, or SS4179 Primer
  • G.E. RTV 108 (Translucent) with #SS4004, SS4044, or SS4179 Primer
  • G.E. RTV 109 (Aluminum) with #SS4004, SS4044, or SS4179 Primer

The adhesive is supplied in collapsible aluminum squeeze tubes, caulking cartridges, and in bulk containers. It is of a paste consistency and should be rapidly spread to a thickness of 15 to 50 mils.

Curing time is dependent on temperature, relative humidity, joint configuration, degree of confinement, sealant thickness and substrate porosity. Warm temperatures (not over 100 degrees F) and humid conditions will shorten the cure.

The heater should be firmly fixed in position and allowed to cure from 24 to 72 hours before use. Energizing the heater before a complete cure is accomplished may cause a failure of the bond line, as deep section cures require more time.

Adhesives and primers have a limited shelf life, and the containers should be marked with the last use date. Observation of shelf life is very important in obtaining proper bonds. Primer containers should not be left uncovered any longer than necessary, as the effectiveness is diminished after exposure to atmospheric moisture.

Adequate bond strength may be attained without the use of primer, but the use of it is strongly recommended.

 



Silicone Rubber

Service Life The service life of silicone rubber is defined by the following chart. The service life was determined when the elongation value dropped from an original value of 300% to 50%. Please bear in mind that test conditions cannot be compared to service conditions directly, but they serve as a guide to determining life expectancy.

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Silicone rubber is a good selection for use in flexible heaters, as it has many unique properties. Silicone belongs to a family of synthetic polymers which are partly organic and partly inorganic. They have a quartz-like polymer structure, being made up of alternating silicon and oxygen atoms rather than the carbon-to-carbon backbone which is a characteristic of the organic polymers.

Processing The heat-cured, or vulcanized vinyl/methyl silicone rubber is processed as gum stock, since it is a high viscosity, high molecular weight fluid polymer. Coloring agents are added to change the color from an off-white to a variety of others, the most popular being red. Red iron oxide is employed to impart the color, adding to the high temperature stability of the rubber. Resistance to fuel oil and certain greases may be improved by blending in fluorosilicone, but at a higher cost.

Mechanical A typical silicone rubber would exhibit a hardness of 60 Durometer (Shore A-2), a tensile strength of 950 psi, an elongation of 300% and a compression set of 33% after 22 hours at 350 F.

Temperature Limits Heaters made with silicone rubber can be expected to perform from -100 to +450 F, and the maximum short term service temperature can be extended as high as 500 F with the addition of certain heat stabilizing agents. Please consult the factory for details on additives.

Fluid Resistance Silicone rubber exhibits excellent resistance to moisture, sunlight and ozone. It has good resistance to bases such as ammonium and sodium hydroxide, and excellent resistance to salts such as sodium carbonate. Acid resistance depends on the acid, but generally acetic and low concentrations of hydrochloric and nitric have little or no effect. The use of silicone rubber in phosphoric or sulfuric environments is not recommended. Motor oils, transmission fluids, and mineral oil degrade the rubber, while brake fluid and gasoline have less of an effect. Silicone exhibits good resistance to acetone, ethyl alcohol and xylene, and fair to poor resistance to benzene, carbon tetrachloride and toluene.

Moisture Resistance The moisture resistance of silicone rubber heaters may be enhanced by selecting the proper configuration. Generally. fiberglass cloth is included in heater thickness selections as it dramatically improves tensile strength and tear resistance. Moisture can travel through the cross-sectional fibers of the glass, however, allowing deep penetration and reduction of electrical insulation resistance. Plies of fiberglass can be cut to less than full size, thereby interrupting the moisture path by allowing fiberglass-free silicone rubber to seal the edges.

Another potential leakage path for water is the location where the lead wires are installed. Teflon covered lead wire does not bond well, even if etched, to silicone rubber. Silicone rubber lead wire should be selected, as it bonds integrally to the rubber composition of the heater element. Silicone rubber lead wire is available with a fiberglass overbraid to impart abrasion resistance, but the glass overbraid should be trimmed short where it enters the heater connection area, again removing a moisture leak path.

Front Page | Johanson DMS, Inc | Product Descriptions | Stock Heaters
Useful Formulas | Ordering Information | Therm. Cond. of Materials