Once current starts flowing through an electrical conductor that has a comparatively high resistance, heat will be generated. By selecting a specific combination of base metal and add-on metals both the temperature level and the heating pattern can be controlled smartly enough for electrical conductors to be used in a wide range of heating applications.
At present, heating conductors are gaining increasing importance as environmentally friendly and energy-saving heat sources.
They lend themselves extremely well to all those applications that aim at a creating a real comfort zone with feel-good factor one enjoys indulging in. The heat generated by a conductor is quickly available and, even more importantly, serves a wide variety of specific purposes. Just take heating conductors used in bathrooms, fitted into clothes or heating up the seats in a vehicle – in all these different areas they provide an enjoyable temperature.
Applications for the automotive industry
As in car seats, heating patches glued or stitched onto non-woven fabrics are applied, which can be customized to the shape of the steering wheel and therefore neatly incorporated.
Heating patches glued or stitched onto non-woven fabrics for initial fitting or retrofitting.
Applications for housing technology
Water pipes are heated up to avert icing and a consequential rupture of the pipe. Chemical and industrial processes also invite trace heating and self-regulating applications.
It is mainly the following materials that can be used for manufacturing heating conductors:
- Bare copper
for temperatures up to 200 °C
- Copper-nickel alloys
for temperatures up to 500 °C
- LEONI Histral® R
copper-based alloys, which can be used for temperatures up to 500 °C, too. Due to their higher mechanical strength they also lend themselves well to any environment which is exposed to a high level of vibration or agitation.
- Nickel-chrome alloys
are extraordinarily hard and applied in temperatures ranging from approximately 500 °C to 1.000 °C
Heating conductors made of copper-based alloys (LEONI Histral®R) usually feature a final diameter of 0.5 mm to 0.05 mm, with deviating sizes also being available, of course. They are processed into strands with a wide variety of cross-sections.
“Flex Life“ is used as a synonym for fatigue strength in Germany. It characterizes the trait enabling a single-wire or bunch to counteract a continuous bending stress until the latter causes the wire to break (cf. our special feature on “Flex Life“).
Certain copper-based alloys – such as LEONI Histral® R15 – boast particularly good Flex Life values. Heating conductors consisting of these materials are exceptionally suitable for being used in an environment characterized by a high level of vibration and agitation as can be found in clothes or heating mats for car seats or carpeted floors.
The temperature coefficient indicates by how much the resistance increases when the temperature changes. Almost all metals are characterized by a positive temperature coefficient. In other words, the resistance goes up in all metals as a consequence of the temperature rising.
In heating conductors this indicator is of particular importance. The unidirectional behavior of temperature and resistance causes the heating conductor to cap itself, i.e. a certain temperature level cannot be exceeded. If the heating conductor has a low temperature coefficient, the output is basically plateauing when the temperature goes up. So the temperature will continue to rise until the physically feasible limit has been reached.
The heat-up time of a heating conductor depends on a whole string of factors:
- On the type of base metal used, e.g. copper, copper nickel, copper-based alloys or nickel chrome
- On the construction of the strand, i.e. how many single wires and which diameters are processed, and in what fashion they are stranded
- On the thickness and type of insulation material applied
Furthermore, other surrounding aspects play a role as well:
- Type of additional materials involved
- Thermal conductivity of these materials
- Length and laying density of heating conductors used
All these parameters may be varied at discretion, which ensures that an appropriate combination for any given purpose is available.