Printed Heaters for Non-planar surfaces

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Technology abstract

The german company developed a technique for printing heaters on any kind of surface. Direct printing of coatings and structures on flat and curved surfaces with electrical conductive material can be used for electrical resistance heaters. They can be applied as homogeneous large area coating, often based on graphene-Like material or as a layout of distinct heating tracks.

Technology Description

Printed resistance heaters have been manufactured for performance analysis onto space relevant flat and curved substrates. After application of coatings, the heating tracks are printed by aerosol jetting or dispensing technologies. The tracks are meanders with different distances of the parallel heating track sections and different number of slopes.
 
-Reliable, reproducible application procedure through automated process
-Reproducible, predetermined resistance values
-Operating temperature range adaptable to any needs
-Controlled, high reliability adhesion on various substrates (aluminium, titanium, -CFRP)
-Free design of heater path configuration (large, short meander)
-Printing of wire connection points
-Heating of surface geometries of any shape
-High heating power possible with low supply voltage
 
Possible applications:
-Heating of propellant lines (Ti-alloy tubes)
-Heating of curved surfaces (tanks, cylinders, etc.)
-Heater application on critical surfaces (CFRP structures, fibre wound spheres)
-Electrical grounding of electrically non-conductive parts (plastics, CFRP panels, etc.)

Innovations & Advantages

The concept of printing heaters on structural surfaces may replace the commonly used heater foil solution by avoiding some of their inherent limitations. In addition the printed conductive structures may be applied on non-conductive substrates, which improve the ability for equipment grounding, replacing the currently used grounding rail approach. With the same printing concept it is basically possible to print temperature sensors as well on any surfaces.
The benefits are free design of heater path configuration to tailor the operating temperature range to any needs, and reduced effort to integrate heaters and temperature sensors on surfaces such as structural panels and equipment housings, on propellant lines, on curved surfaces and on irregular surfaces (valves, brackets, etc.).
 

Further Information

Coatings
Typical surfaces of metal or CFRP need to be coated with an electrical insulation for direct printing of heaters or sensors. Highly cross-linked polysiloxane-like plasma coatings are possible over large and 3D surfaces areas. They adhere well on relevant substrates and are only few μm thin but the electrical insulation properties are found to be inhomogeneous and insufficient especially towards edges and borders. As expected, the electrical insulation properties of polyimide coatings are very good and reproducible up to 500 V.
These coatings prepared by fully imidized polyimide solution can be applied on large area by various technologies like spin-coating, dip-coating, and spraying or locally by jetting with a thickness of several μm. They adhere well on relevant metal substrates but are not suited for directly coating of carbon fibre based composites.A top coating of the printed heaters could be necessary as protection against mechanical damage during handling and integration. Furthermore, a top coating could be beneficial for better heater adhesion and abrasion resistance especially for very thin aerosol jetted heating tracks.Both evaluated coatings for electrical insulation can be used as top coating, plasma and polyimide.
Heater
Silver particle filled epoxy as well as nano-particulate silverinks have been used as heater material in this study, but other metals and alloys can be used in principle for this purpose. The final tracks show relating to length electrical resistances in the range from 10 to 1000 Ω/m which is comparable to commercial resistance wires, e.g. out of Ni or NiCr alloy. The commercial foilheaters have a total thickness of about 0.4mm including 0.1 mm foil backing which leads to unwanted high thermal gradients between heating structure and basic substrate. The applied polyimide coatings are less than 0.01 mm thick, therefor the build-Up of a significant minor thermal gradient is expected.

Current and Potential Domains of Application

Possible applications:
-Heating of propellant lines (Ti-alloy tubes)
-Heating of curved surfaces (tanks, cylinders, etc.)
-Heater application on critical surfaces (CFRP structures, fibre wound spheres)
-Electrical grounding of electrically non-conductive parts (plastics, CFRP panels, etc.)
 
-Reliable, reproducible application procedure through automated process
-Reproducible, predetermined resistance values
-Operating temperature range adaptable to any needs
-Controlled, high reliability adhesion on various substrates (aluminium, titanium, -CFRP)
-Free design of heater path configuration (large, short meander)
-Printing of wire connection points
-Heating of surface geometries of any shape
-High heating power possible with low supply voltage
-Reliable, reproducible application procedure through automated process
-Reproducible, predetermined resistance values
-Operating temperature range adaptable to any needs
-Controlled, high reliability adhesion on various substrates (aluminium, titanium, -CFRP)
-Free design of heater path configuration (large, short meander)
-Printing of wire connection points
-Heating of surface geometries of any shape
-High heating power possible with low supply voltage