AMETEK Land - Industrial Heating - Process Thermal Imaging in the Modern Hot-Rolling Mill
Single-point radiation thermometers are installed at a distance, and they view the infrared radiation that is emitted by the target object. Their noncontact nature allows them to operate out of harm’s way. Because they don’t touch the surface, they can accurately measure moving objects, whereas thermocouples suffer from a frictional effect, generating heat and eroding the thermocouple. Pyrometers also feature extremely fast response speeds of a few milliseconds. This makes them very useful for measuring fastmoving strip or rod.
For furnace temperature-measurement applications, pyrometers measure the products in the furnace and not the furnace atmosphere. Noncontact pyrometers outlast contact sensors. They have very fast response speeds and are low maintenance. For some applications, a single-point pyrometer provides enough information for process control. In a hot-strip mill, a single-point pyrometer will measure a stripe (longitudinal profile) along the strip centerline.
With continuous, customer-driven requirements for higher-quality products, it is increasingly difficult to make premium-quality flat products with single-point temperature measurements.
Process Thermal Imaging
Two families of process thermal-imaging systems provide more complete temperature measurements in static and moving product environments.
2-D Thermal-Imaging Cameras
The first family of process thermal-imaging systems is based around 2-D thermal-imaging “cameras.” Their radiation detector consists of a matrix of tens of thousands of pixels, each of which is a noncontact temperature sensor. Its focal-plane array then looks through a filter and lens at the thermal scene. These process thermal imagers differ from portable thermal imagers in several important ways. Portable imagers use very low-power drain detectors. They sacrifice high-quality measurements to extend battery life in a portable imager. Process thermal imagers are built to operate in harsh industrial environments, providing years of continuous thermal imaging. Temperature-measurement accuracy across the entire scene is very important. Power use is not a design factor because they are powered by continuous power supplies. A process thermal imager is capable of viewing and measuring multiple targets in a scene simultaneously.
Figure 2 shows a process thermal imager measuring multiple strands at the exit of a caster. Fifteen areas of interest have been placed on the thermal image, and each is outputting a signal based on the peak temperature in each area.
Fig. 1. A single-point pyrometer measuring the centerline temperature of a hot strip.
Figure 3 shows the inside of a reheat furnace filled with pipes. By selecting the correct wavelength, the imager does not see the burners. At the top left of the roof, the image shows cold holes, which are the burners with the cold fuel entering. It also shows the heating effect on the furnace roof (yellow stripes), but the flames themselves are invisible. Once the correct pipe temperature is reached, the pipe is pushed from the furnace. Not only can the imager measure the product temperature, it also shows the temperature balance within the furnace.
Fig. 2. A five-strand caster exit area. Three temperaturemeasurement areas are located on each strand.
holes, which are the burners with the cold fuel entering. It also shows the heating effect on the furnace roof (yellow stripes), but the flames themselves are invisible. Once the correct pipe temperature is reached, the pipe is pushed from the furnace. Not only can the imager measure the product temperature, it also shows the temperature balance within the furnace.