Hot as hell

Gustav in VR-gear

Some warm winds blew in today’s investigation when we finally got to use some hot steel! Wow! Yes, you assumed correctly, we will try to measure the temperature of the steel when forging. Our blacksmith has the day in honor brought to us a forge since we were going to meet a measurement-guru from Termisk Systemteknik. Mr. Guru (who usually goes by the name of Claes Nelsson) brought some nice heat cameras with him to show us their almost magical properties. These heat cameras are sensing IR to measure the temperature. However, they need to have a few reference points as calibration of the temperature of the steel to give a correct measurement and visualization, so old SP has lent out their amazing self-built thermocouple data-logger together with a few thermocouples. Thank you!

Let’s start! The first critical point of measuring the temperature was to attach the heating element to the steel. How would we do this? Our blacksmith came as a rescuer and tempered his steel by cutting a score in it, which we then could use to attach the thermocouple to it. We needed to do this to measure the emissivity of the steel.

Emissivity of metals is a difficult area, which is currently being researched. All materials will emit electromagnetic radiation when heated, and this radiation varies with the temperature of the material. Further there is something called a black body. A black body is quite simply a physical body that is perfectly black, and thus will absorb all incoming radiation and not reflect anything. When such a body is heated it will, just like any other physical body, emit radiation in the form of electromagnetic waves, and this is then called “black body radiation”. But in reality there is no such thing as a perfectly black body. This is where the emissivity comes in handy. Because the emissivity is simply a material property that is used to describe how close a certain material is to having the properties of a black body, in the form of a fractional number between 0 and 1. And thanks to the physicist Max Planck there is an equation called Planck’s Radiation law, that describes the frequency distribution of electromagnetic waves that are emitted from a black body at a certain temperature in temperature equilibrium. So why is this important to us then? Well, because if we know the emissivity of a material AND the distribution of electromagnetic waves coming from that same material, we can then find the temperature using an IR-camera. And this time the emissivity was calculated by actually measuring the temperature using the thermocouples, something which was then fed into the software of the IR-camera to find the correct emissivity that made the readings on the screen of the IR-camera match our measurements.

So why did we go through all this trouble to measure the temperature of the steel? It is significant for us to measure the temperature and try to find a solution to how it should be visualized, as the temperature is an important parameter in the forge exercising. Unfortunately, we did not get convinced that this method was the right way for us as the results were too uncertain. A few problems that struck us when we used these cameras was that it did not give a constant value, and it was also a bit too expensive.

Today, a lot of things also happened in addition to testing the heat cameras. An attempt was made to program a algorithm to measure brightness using a regular camera (and thus somehow being able to extract the temperature from that reading), and we continued the work with the depth camera. We took a few steps forward and the journey progresses.

And from all of us to all of you a very merry christmas!

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