Metal can hardened strongly by mechanical processing. Sometimes the sheet metal becomes very hard during the shaping work and gets to too hard for the planned deformation.
In this case, in our example it ÂŽs an aluminum sheet, the metal is getting annealed. During the annealing, the sheet metal is softened.
Because aluminum is only glowing at a very high temperature range, black soot is applied as an indicator to it. The soot is applied in a thin layer on the surface with an acetylene flame. With a hotter flame, which is achieved by the addition of oxygen, the sheet is heated now strongly. The soot layer disappears after heating the aluminum. That the heat does not melt through the aluminum, the flame moves through quickly back and forth in a fast motion, After a while you can see very clearly, how the soot slowly disappears. The aluminum sheet is continuously „annealed“ at the end. Now it needs to cool down slowly. But be careful, because after the tempering the sheet metal is extremely hot.
If you pick the sheet after it has cooled off, youÂŽll realize immediately the sheet has become very soft. Now, the sheet metal is tapped on the leather shot bag with a round hammer. It deforms significantly stronger than a metal sheet, which was not previously been annealed. It is so soft that the shape on a flat anvil can be smoothed with a hammer. But by tapping the metal, the metal will be hardening again.