Temperature Measurement in Induction Hardening Processes
The monitoring and the controlling of temperatures is one of the most important factors to guarantee the required product quality and profitability in induction hardening processes.
For these applications pyrometry allows a separate and accurate measurement and documentation of each components temperature.
In order to reach optimal hardness during the induction hardening process, the metal workpiece must be heated rapidly for a defined period of time over a multi-step temperature profile. The quality and mechanical properties of the resultant parts are significantly influenced by the temperature accuracy and stability before the part is quenched.
When hardening the surfaces of steel, cast steel or cast iron components, the following properties have to be achieved:
- The component has to attain the required hardness on all desired areas
- The desired or required hardness depth has to be achieved
- The component must not be damaged
- The distortion of the component should be minimal
- The process should be as short as possible
- The results have to be repeatable
The monitoring and the control of the temperature are essential in order to reach these targets. While too low temperatures lead to a too low hardness depth, too high temperatures may result in damage to the component. But also the duration of the inductively coupled energy, i.e. temperature, plays a significant role.
Our Solutions for Hardening Processes
The heating process and energy requirements can be optimized through the use of non-contact temperature measurement and adequate controllers. Infrared thermal imagers are capable of measuring a broad temperature profile to provide improved detail of thermal gradients across the workpiece, enabling further insight into the hardening process.
However, pyrometers provide accurate and precise temperature measurements at a single fixed point and enable the reproducibility that is critical in induction hardening processes. In addition, pyrometers are capable of very fast measurement speeds, which is required for the rapid thermal changes of the induction process.
The use of pyrometers, thermal imagers, and fast controllers for temperature monitoring and process control can increase the quality, accuracy, and repeatability of many heat treatment processes.
"Classic" measurement on components
The temperatures range between 300 and 1200 °C.
Use of pyrometers with a short wave spectral range recommended. Various pyrometers with different optics, spot sizes, and response times are available.
Preheating and run-in processes
For annealing temperature measurement after Induction hardening.
Various pyrometers with different optics, spot sizes and response times suitable for applications with temperatures from 50 °C.
Measurements in "difficult" environments
E.g. for objects with unknown or changing emissivity, measuring objects which are smaller than the pyrometers spot size, measuring objects which move during the measurement or measurements through steam, smoke or dust. The use of ratio-pyrometers is recommended, respectively required.
Applications for fiber optics pyrometers
The optical heads of fiber optics pyrometers can be used at ambient temperatures up to 250 C. They are unaffected by electromagnetic interferences, so that they can be used very close to the inductor. Their small design enables their use in locations that are difficult to access. They can be mounted very close to the measuring object. Optical fiber length up to 30 meters.
Control of induction generators
The induction process and the power of induction generators can e.g. be controlled using digital IMPAC pyrometers in combination with the extremely fast, digital, programmable PID controller PI 6000. This extremely fast controller (sampling time of only 250 µs) was especially designed for applications in which fast temperature measurement and control are required, e.g. in induction hardening processes.
IMPAC pyrometers excel in following aspects:
- Highest quality standards
- Fast response time (fast moving objects can be measured)
- Accurate measurements and broad measurement ranges
- Precise measurement with negative influences, e.g. water vapor or dust
- Full digital signal conditioning
- Ease of use
- Automatic process controls
Key Products for This application