The practical case: The cartridge keeps failing
A customer from Baden-Württemberg used cartridge heaters with a diameter of 19 mm, a length of 1293 mm, 230 V and 3300 W in a heated assembly. The cartridges were purchased cheaply. The problem: They kept breaking down during operation.
The obvious explanation would have been: bad cartridge, wrong supplier, not enough quality. Technically, that was too short-sighted. Mr. Münch at the Lampertheim location not only checked the application based on the electrical data, but also based on the heat balance during installation.
The result: The cartridge was designed for a high heating rate. However, the decisive factor was not the wattage alone, but rather the question of whether the steel body could permanently absorb and transmit this heat.
The cartridge heater was electrically plausible. Thermally, it did not match the actual heat dissipation in the installation.
The mistake in thinking: more performance does not automatically mean better
In practice, heating output is often equated with heating speed. If you want an assembly to warm up more quickly, a more powerful cartridge is chosen. This can work if the surrounding material can also absorb the power.
That's exactly where the limit lies. A cartridge heater generates heat inside. This heat must be transferred into the steel body via the cartridge jacket. The steel body distributes them further into the tool or component. This heat flow is finite. It depends on thermal conductivity, contact area, fit, bore condition, target temperature and environment.
If the cartridge generates more heat than the installation can permanently dissipate, heat builds up in the cartridge. The temperature at the heating coil rises sharply. The resistance wire and the magnesium oxide insulation are subjected to thermal stress. The cartridge fails.
The physics: Every installation has a heat output that can be dissipated
The critical point is not an abstract material limit, but rather the heat balance of the specific installation situation. Each installation has a maximum heat output that can be permanently dissipated. If this is exceeded, the temperature in the cartridge heater rises more than in the component.
This is easy to miss in the machine. The temperature sensor often does not measure at the hottest point of the cartridge. The control sees the tool temperature or a measuring point in the component. The heating coil temperature inside the cartridge can be significantly higher.
That's why it's not enough to check voltage and wattage. A cartridge heater must fit into the thermal environment. Otherwise it is correct on the data sheet, but overloaded in operation.
The calculation: 3300 W versus 2200 W
For a cartridge with a diameter of 19 mm and a length of 1293 mm, the approximate surface load is as follows. To simplify the calculation, the entire jacket length is used. If the heated length is shorter, the value changes accordingly.
Hard facts from the case
π x 1.9 cm x 129.3 cm = approx. 772 cm²
3300 W / 772 cm² = approx. 4.3 W/cm²
2200 W / 772 cm² = approx. 2.9 W/cm²
The new 2200 W design reduces the calculated surface load from around 4.3 to around 2.9 W/cm². The case shows the technical point: the cartridge does not have to be as powerful as possible. It must be designed so that the installation can permanently dissipate heat.
The failures are therefore not explained by the number 3300 W alone, but by the relationship between power, installation and heat dissipation. What is crucial is how quickly this power can be coupled into the steel, whether the cartridge fits cleanly, whether there are local air gaps and how the control system manages the heating phase.
What needs to be checked when designing
A reliable design considers the cartridge and the installation together. These points are more important in practice than the isolated question of wattage:
What Mr. Münch correctly recognized in Lampertheim
The important technical achievement was not simply proposing a more powerful or more expensive cartridge. The crucial point was the consideration of the entire system at the Lampertheim competence location: cartridge heater, steel body, bore, contact surface, heating speed and control.
If an application repeatedly destroys cartridges, the cause must be found in the heat flow. A new cartridge with the same electrical data only solves the problem if the installation can also dissipate the heat.
This is exactly where the difference lies between replacing parts and designing. When replacing parts, a cartridge is replaced. When designing, it is checked whether the cartridge fits the real application.
What this means for purchasing and maintenance
When purchasing a cartridge heater, it is often a simple item: diameter, length, voltage, power, price. For maintenance purposes, it is a wearing part that must be available quickly. Technically, this view is not always sufficient.
When cartridges fail repeatedly, it's not just supplier and price that should be compared. The installation conditions must be checked. This includes bore condition, contact, heated length, control, heating phase and heat losses.
This also includes the design: While standard goods usually end up with diameters of 6.5, 8 or 10 mm, occasionally 16 mm, we manufacture cartridge heaters with significantly larger diameters up to 32 mm and beyond on request. cartridge heaters well over 1 meter long, adapted heating zones and suitable connections are also possible. In practice, cartridge heaters with a length of almost 4 meters have already been manufactured. This creates the cartridge that the installation requires, instead of a compromise from the catalog.
At Keller, Ihne & Tesch we don't just ask about wattage. What is crucial is what heat output the application really needs and what power the installation can permanently dissipate. For customers in Austria, Michael Hackl is the direct contact person for technical clarification on site, by telephone or via Microsoft Teams.
The right cartridge heater is not the strongest cartridge. The right cartridge is the one whose power can be dissipated cleanly in the specific installation.
Frequently asked questions
Is more watts automatically better for cartridge heaters?
No. Higher power can shorten the heating time. However, it is only of any use if the component can absorb and transmit the heat cleanly. If the heat dissipation is too weak, the temperature in the cartridge heater rises. The result is shorter service life, local overheating and, in the worst case, early failure.
What is the difference between power and surface loading?
The power describes the total electrical heating output of the cartridge heater in watts. The surface load relates this power to the heated surface area and is given in W/cm². It shows how much thermal stress the surface of the cartridge is exposed to.
Why can a cartridge heater fail despite low W/cm²?
Because the surface load is only a characteristic value. What is crucial is whether the heat is dissipated from the cartridge into the component. If the bore, fit, contact surface, material, sensor position or control do not fit, heat can build up locally. Then the cartridge overheats, even though the calculated W/cm² value looks uncritical.
What data does Keller, Ihne & Tesch need for an audit?
For a technical assessment, the diameter, length, heated length, voltage, power, target temperature, desired heating time, component material, hole tolerance, installation situation, sensor position and control are particularly important. The more precise this information is, the easier it is to assess whether performance and design match.
Cartridge heaters fail repeatedly?
Send us application data, installation situation and existing cartridge data. We check whether performance, heat dissipation and installation match. In Austria, Michael Hackl supports you directly.