Learn more about the integral components of our ceramic heating elements.
Technology / Details
Are you used to working with metals? You know all there is to know about the various alloys and their benefits? Perhaps you have extensive experience of the different metalworking processes? In your designs, you probably know exactly how you must interpret the individual metal components’ strength values?
But when you hear the word ‘ceramics’, you immediately think of plates and tiles? Then you’re just like many of our engineer colleagues who, after years of working as design engineers in machine and system construction, or in robotics, turned to technical ceramics.
Because technical ceramics, and in particular silicon nitride, which Bach RC uses for the production of fully ceramic heating elements, is admittedly still a really exotic material, which differs considerably from the above-mentioned plates and tiles.
Just as with the various metallic materials, with technical ceramics you need to pay attention to their special characteristics, in order to be able to utilise the full potential of this fascinating class of material.
We would therefore like to give you some tips, based on our practical experience.
Not our material! Silicon nitride, a material from the group of so-called ‘technical ceramics’, and which Bach RC uses for its fully ceramic heating elements, breaks only at bending loads of 400 N/mm2 and greater. This is a value that is comparable to the strength of typical steels.
Breaking is essentially ceramic materials’ main failure mechanism, because ceramics are hard, brittle materials, which only undergo elastic or plastic deformation to a very low extent. There are however considerable differences between different types of ceramics. Typical bending strength values for architectural ceramics (such as tiles) are around 50 N/mm2, whereas the bending strength of silicon nitride, as previously mentioned, is in the same range as that of steel.
But in contrast to most metallic materials, silicon nitride undergoes hardly any elastic deformation. This means that it does not gradually become apparent that the material is being used in a way that it is approaching its failure threshold. It is therefore always a good idea to precisely analyse the installation situation with regard to mechanical loads.
You can find information about optimum installation situations for various applications in our FAQ below. Our team of engineers would also be pleased to assist you.
On the contrary: at 2000 N/mm2, silicon nitride’s compressive strength is extremely high. A direct comparison of the Young’s modulus also demonstrates ceramic materials’ enormous potential. Silicon nitride has a Young’s modulus of 320 GPa, whereas that of typical construction steel is only 210 GPa.
In order to fully utilise this extremely high compressive strength, it is however important that the pressure load is not applied as a bending load or notched bar impact bend. In other words, the compressive forces must be applied to the ceramic material uniformly and without impact. Flat and parallel surfaces are particularly suitable for force transmission. To achieve this, the ceramic heating elements can be finished so that they exhibit exceptional degrees of flatness and parallelism. An even and flat support for the heating element being subjected to pressure should be used.
That’s not the case with our heating elements! After grinding, our silicon nitride ceramic enjoys the greatest dimensional accuracy and optimum surface properties: Precisely drilled holes and counterbores are just as possible as customer-specific external geometry. Degrees of flatness and parallelism can be achieved to the single-digit micrometer level. And the really special characteristic is this: at 3 * 10-6/K, silicon nitride’s thermal expansion is so low that the manufactured dimensions remain constant even at high temperatures: Typical steels expand at something like 18 * 10-6/K, therefore at a many times greater rate, meaning they therefore have a tendency to warp under temperature changes.
After sintering, where the individual powder particles are formed into a monolithic solid, the heating elements do indeed demonstrate a somewhat rough surface sinter skin (Ra approx. 5µm).
Unless otherwise is required, this sinter skin can then remain on the heating element’s surface (as is often the case with radiant heating elements). But the heating elements are usually ground smooth. Due to silicon nitride’s extreme hardness, they can only be ground using diamond tools. This process involves additional expenditure and effort, but brings great benefits for their use as heating elements.
No metallic heating filaments are used in our heating elements! For the electrical heating circuit, Bach RC’s technological core competence comes to the fore: Using a specially developed technology, the silicon nitride, which is actually highly electrically insulating, is so doped that it becomes electrically conductive.
In fully ceramic heating elements (so called because the heating conductor and insulator both have the same ceramic basis), the ceramic heating circuit is always enclosed by insulating material. The heating element’s shell is therefore electrically insulating, with the heating conductor being inside.
Many technical ceramics, including silicon nitride, demonstrate excellent insulating properties. With a specific electrical resistance of 1015 Ωcm, silicon nitride demonstrates insulating properties in the range of components used in high voltage technology, for example as insulators on high voltage lines. We utilise this property where it is important and beneficial - for the electrically insulating shell.
Silicon nitride, the technical ceramic from which Bach RC’s heating elements are made, is extremely resistant, even under adverse operating conditions. It is extremely resistant to oxidation, even at temperatures of up to 1000°C, and is resistant to many aggressive media. The ceramic heating conductor inside the heating element is adapted precisely to the insulating ceramic shell, especially with regard to its thermal expansion. This means that there is hardly any thermal stress in the heating elements. Direct heat transfer from the heating conductor to the shell is ensured, enabling extremely fast heating rates (up to 200 K/s) and extremely high surface power (up to 150 W/cm2) to be realized.
Thanks to its very low thermal expansion rate, this ceramic material is subject to hardly any failure, even at high temperatures: The excellent flatness and parallelism that we can achieve, even with large-sized heating elements, remains constant, even at high temperatures.
Silicon nitride’s low density keeps the ‘thermal mass’ low: Together with the high power density, we can therefore realize precise heating systems that can be heated extremely dynamically, and which also cool down again quickly.
Use of this fully ceramic technology creates the conditions for realizing our motto:
“Generating the heat where it is needed!”
Fully ceramic heating elements can be manufactured in a wide variety of different shapes. Basic geometric shapes such as cuboids or cylinders are just as possible to manufacture as extremely precisely produced, exceedingly complex geometries: Drill holes, fit tolerances, pockets, channels, grooves and surface structures can just as easily be integrated into the heating elements as multiple (ceramic) components can be assembled to form modules. The design possibilities are virtually limitless.
Due to the manufacturing technology used, there are however shapes that are especially suitable for the manufacturing process, the ceramic material itself and the functionality. These are predominantly plate-shaped components. We would be pleased to advise you on the optimal shape of the heating element for your application!
Bach RC’s ceramic heating elements are available in the widest variety of sizes: We can produce heated surfaces of just a few square millimetres, or heating plates from a piece with 400mm diameter. You can find a small selection of the available sizes and shapes on our website. Up to now, we have already manufactured over 1000 different heating element types. And in the event that your dream heating element isn’t among these 1000 types, we would be pleased to develop a customized design for you. Please just ask us about this!
Yes. Bach RC specializes in the manufacture of customer-specific heating elements - including small quantities and even single items. We are always seeking new challenges, uses and possible applications. Please contact us if you have any ‘exotic’ inquiries: Our heating elements can already be found in space and in the eternal ice, as well as in 3000m depth of the ocean and in devices for melting rock. We are confident that we can also find a creative solution for your requirements! Our engineers would be pleased to advise you on the possibilities!
We offer ceramic heating elements that can be operated at temperatures of up to 1000°C. Some types are however designed for operation at up to 500°C. You can learn more about the differences in design in ‘What is a ‘cold zone’?’ and ‘What is meant by a heated zone?’.
Silicon nitride demonstrates excellent oxidation resistance. Therefore, even at high temperatures, the heating reacts very slowly with atmospheric oxygen. This ensures a very long service life, even at high operating temperatures.
The ‘cold zone’ is an area of the heating element that has been designed so that heat output is lower. As a result, the heating element only heats up in this area to a lesser extent. The ‘cold zone’ is used for brazing the electrical contacts. The lower temperature in the ‘cold zone’ protects the contacts, as the braze material can only be heated to a maximum of 500°C.
Heating elements that can be operated at a temperature of higher than 500°C require a ‘cold zone’ for the electrical contacts.
When mounting the heating elements, please ensure that sufficient heat dissipation is guaranteed in the ‘cold zone’ area - especially directly near the brazed electrical contacts. For example, in this area, on no account should thermal insulation be applied to the heating element. ‘Cold’ when relating to the ‘cold zone’ is of course a relative term: In extreme cases, even the temperature of the ‘cold zone’ can reach up to 500°C.
The ‘heated zone’ is the part of the heating element that can be operated at up to the specified maximum operating temperature. The ‘heated zone’ directly adjoins the ‘cold zone’. The ‘heated zone’ is designed for the specified maximum temperature of the heating element (for example 800°C or 1000°C). Between the ‘cold’ and ‘heated’ zones, there is an area where there is a temperature gradient.
The high-temperature braze material used for the heating elements’ electrical contacts can only be used at a maximum temperature of 500°C. If the heating element doesn’t have a ‘cold zone’, the contacts are brazed in the ‘heated zone’, which means that the maximum temperature of 500°C applies to the entire heating element.
In order to measure the heating element’s temperature, we supply heating elements with integrated blind holes. Sheathed thermocouples or resistance temperature measuring sensors can be fitted in these holes. This enables you to measure the temperature directly in the heating element.
We offer various temperature control devices in order for you to control the heating elements’ temperature. These control devices range from basic target temperature setting, which the heating element then adheres to, right up to complex control instruments with programmable control of the heating rates and dwell times, multizone control, process visualisation and process logging. Integration into a higher-level PLC is also possible.
That is possible. We can design your heating element as a multizone heater, and also adapt suitable control technology for you. That way, it is possible to specifically compensate for heat loss in the surrounding environment (for example on the heating element’s mounting features), in order to achieve optimum temperature homogeneity, or to set precise temperature variations.
Yes. There are several possibilities for setting a precise temperature profile: One option is to adapt the shape and position of the heating circuit inside the element so that, during operation, the heating element achieves the desired temperature profile.
And if the temperature profile is supposed to be changed at different times, multiple heating zones can also be designated.
Fundamentally, the heating elements are designed not to be self-limiting. Separate temperature control is necessary for this.
Selected heating element types can be designed for precisely defined operating conditions, so that when operating at rated voltage, no additional temperature control is required, meaning they are self-limiting due to the increase of the electrical resistance with temperature as well as the convection and emission at their target temperature.
When a temperature measurement must be made on the heating element itself, we recommend you to install the temperature sensor in the middle of the ‘heated zone’. This ensures that the heating element’s highest temperature is measured.
But for some heating processes, it is often not the temperature of the heating element that is important, but that of the item being heated, such as a tool or material sample. The temperature measurement can therefore of course be taken some distance away from the heating element, in the respective component. In this event, please note: The further from the heating element the temperature is measured, the greater the difference that can occur between the measured temperature and the actual temperature of the heating element. For the heating element’s operational safety, ensure the maximum permitted temperature is not exceeded. In particular, the temperature of the brazed electrical contacts must not exceed 500°C.
We offer heating elements for all commonly used low voltages: 12V, 24V, 48V, 110V, 230V and 400V. In each case, the rated voltages should always be understood as the maximum rated voltages for the respective heating element. In other words, operation is also possible at a lower voltage.
Bach RC’s heating elements are fundamentally ohmic resistors, meaning that operation with either direct or alternating voltage is possible.
For information on the permitted amperages for individual heating elements, please see the operating manual of your heating element. You are also welcome to inquire with us in advance about permitted amperages.
Bach RC’s fully ceramic technology enables extremely high surface power of up to 150 W/cm² to be achieved. So large amounts of heat can also be achieved with very small heaters.
It is important for the long-term stable operation of the heating elements that the generated heat is passed to the object being heated or emitted into the surrounding air. If more heat is produced than can be dissipated, there is a risk of overheating. In such cases, the heat output must be reduced using a control device.
Therefore, the required heating power must be deduced from the application’s design and thermal conditions (see below ‘What heat output do I need for my heating element?’).
The electrical resistance results from the properties of the heating element itself, in particular the length, profile and the so-called specific electrical resistance of the material used for the heating circuit.
On the other hand, the power is determined by other factors that are independent of the heating element itself, in particular the applicable electrical voltage.
From an electrical point of view, in the specified operating voltage and operating frequency ranges, Bach RC’s heating elements behave like ohmic resistors. That is to say, their resistance values are independent of the operating voltage, amperage and frequency.
As a rule, Bach RC specifies the resistance value of its heating elements at room temperature (20°C), and always with a tolerance (usually ±25%).
As the heating elements’ temperature increases, their resistance also increases. The heating elements demonstrate what is known as PTC (Positive Temperature Coefficient) behavior. As the heating elements cool down, their resistance also reduces to the original value.
According to Ohm’s law, power P is calculated in watts [W] on the basis of the operating voltage U in volts [V] and the resistance R in ohms [Ω]: P =
R. The so-called ‘cold resistance’ (heating element at 20°C room temperature) is usually stated for the resistance value. As described above, as the temperature increases, so does the resistance. Heating power thereby reduces.
This question can also be expressed as: How much material of what type should be heated from what starting temperature to what end temperature within what timeframe under what environmental conditions? A very complex question…
There are various ways to find an answer to this:
Yes, it’s possible to roughly estimate the required heat output.
The most important parameters are of course those relating to the requirements of your planned application. To make an estimate, some fundamental questions must first be answered:
What is the starting temperature of the material that will be heated?
To what temperature is the material supposed to be heated to?
How long shall the heating process take?
What material will be heated?
What does the material weigh?
If you establish these values and enter them into the calculator, you will receive an initial indication of the heat output you require for your process.
It will become clear: If you can keep the mass that is supposed to be heated low, lower heat output is required. The thermal process will therefore be more energy-efficient, as well as more dynamic.
But one note of caution: This basic calculation only applies to the object or medium that you actually want to heat. It is based on 100% efficiency. However, in technical applications this is unfortunately not realizable. Because as soon as the temperature of an object or a medium differs from the ambient temperature, it begins to emit heat into its environment, or absorb heat from it.
With heating processes where the surrounding environment is mostly colder, heat is lost into the atmosphere (power dissipation), and so efficiency is reduced. If you do not want to increase the heating time, then heat output must be increased by the amount of dissipation.
How much heat is lost depends on the design in the respective process. The efficiency rates for different types of heat transfer shown below must only be understood as rough reference points. In real world conditions, and depending on circumstances, the actual values can differ greatly from these.
As a guide, we therefore usually recommend choosing significantly higher heat output than is actually required. This can usually be achieved by a simple adjustment of the resistance, and at no extra cost to you. You then have a racing car at your disposal for all circumstances, which you can also drive at walking speed.
Some basic considerations from the world of physics can help you with a rough initial estimate of the output required.
In order to warm a body or medium, it must be supplied with a certain amount of heat. The unit of measurement for heat energy is the joule [J].
The power is generally defined as ‘work per period of time’. For thermal processes, this general definition can be firmed up as ‘heat amount per period of time’, specified as joules per second or more commonly watts [W].
If, on the one hand, you know what amount of heat is required to heat a body or medium to a certain temperature, and on the other, how much time this heating process is permitted to take, then it is easy to calculate the required heat output.
To calculate the heat amount, you need both the mass [kg] of the body or medium to be heated and its specific heat capacity. The specific heat capacity is a material property that is mostly given in kJ/(kg*K). We have listed some values for frequently used materials in the calculator.
The time required for the heating process results from the requirements of your thermal process.
When putting heating elements into operation, their overall installation situation must be examined in detail once more, both from a thermal and electrical point of view. It is important to check that the heating element is firmly in place, and that it remains firmly in place even when there are high temperatures. It must not be possible for the thermal expansion of fixing materials to exercise too great a pressure, or bending, on the heating element.
You should establish exactly what temperatures the heating element will be exposed to, in order to prevent damage from overheating. You must pay particular attention that the heating elements’ brazed contact pads can only be operated at maximum 500°C. It must also be possible for the heating element to emit the generated heat safely into its surrounding environment, under all operating conditions.
The heating element’s electrical insulation must be designed so that it complies with applicable safety regulations.
Where present, any temperature sensors must also be inspected to ensure they are firmly in place and are functioning correctly.
Bach RC’s engineering team has extensive experience of structural design of the installation situations for our fully ceramic heating elements. We would be pleased to advise you and manufacture components for the installation of your heating elements.
The electrical connections are brazed to the heating elements using small ceramic contact pads. Braze fillet forms around these pads, which is where the operating voltage is present during operation.
As standard, nickel wire, usually with a diameter of 1mm, is brazed to the heating elements. Other wire materials and diameters are also possible. Extended and electrically insulated cables or connectors can be attached to these wires using various connection techniques (screw connection, spot welding, crimping). Bach RC keeps a wide range of extension options in its range.
We can supply heating elements with blind holes, so that sheathed thermocouples can be inserted. The holes’ diameters are chosen so that, at room temperature, the thermocouples are stuck inside into these holes. As the heating element heats up, the thermocouple’s steel sheath expands somewhat more than the hole. As a result, the thermocouple sits more tightly, and maintains excellent thermal contact to the heating element.
When using the heating element for contact heating, ensure there is uniform heat transfer from the heating element to the material being heated. Good heat transfer occurs where the contact surface between the heating element’s heated zone and the material being heated is as large as possible.
In the case of solid objects, you should also strive to ensure that the contact surfaces are as flat as possible. Please note that silicon nitride - in contrast to most metals - exhibits a very low degree of thermal expansion. As a result of their greater thermal expansion, many metals have a tendency to warp when heated. In turn, the contact surface to the heating element is also reduced, meaning considerable temperature gradients can occur.
When using the ceramic heating element as a radiant heater , adjusted emissions values for the material emitting the heat and the material being heated are decisive. The fully ceramic heating element is a long-wave infrared heater. Information about radiation emissions at 1000°C can be found here.
When using the heating element for the convective heating of gases, ensure that the gas’s convection takes heat from the heating element evenly, and that no critical temperature gradients can arise. The gas flow should be guided by suitable baffle plates or similar, and you should ensure that gas heated to a temperature of > 500°C is not fed over the electrical contacts’ brazed joints. The gas’s pressure and volume flow should be linked to the heating element’s electrical power by means of control technology, in order to ensure optimum heating of the gas and to prevent the heating element from overheating.