Soft materials do not glide well against each other. As long as only the pistons were made from an alunminium alloy, and one had found a solution for various thermal expansions, there were no problems with the cast iron cylinder blocks. After honing and buffing there were still sufficient criss-cross grooves to hold the oil ready for the lubrication of the piston on it's way to TDC.

Ever since cylinder blocks have been made of aluminium-silicon alloy, to reduce weight, cast iron sleeves were often inserted. Indeed, in this case, two materials which have very different properties as far as thermal expansion is concerned, are brought together. This results in tensions and a, depending on the temperature, varying air-gap which affects the heat transfer to the coolant negatively. It would be much better, to etch the aluminium away or to coat the pistons/cylinders. One method of doing this is the plasma coating.

The word 'plasma' appeared in 1920 as a description for a fourth physical state. It is only attainable at incredibly high temperatures. In this process the number of electrons in the atom are altered. The result is an electrically charged gas. With sufficient energy, this is possible with almost all substances.

The plasma-gas which streams into the water-cooled mixing jet is drawn to the anode where it emerges. The result is an electric arc with a temperature of over 10.000°C, which together with the coating powder (alloyed steel and molybdenum) and the conveying gas, is sprayed from an additional supply line and at a very speed, meeting the cylinder wall while still in a plastic state. Instead of ferrous metal, ceramic particles are also possible. After solidifying, a layer with a thickness of less than 1/00 of a mm is formfittingly joined to the initial material. While this was happening, the burner with the supply line has already turned further. Thus, in no time at all, the entire cylinder is coated and - as opposed to a dry cast iron sleeve - has hardly become any heavier at all.

In the case of plasma coated cylinders, the pretensioning of the piston rings can be reduced, which benefits the internal friction during the running-in phase. The final honing only produces small unconnected indentations where the oil is stored. All in all, the surface is smoother and hardly any mixed friction takes place during the running-in period. One process which can only be applied after honing, is the UV photon honing. In this case, the surface melts at a depth of 2 micrometers, nitrogen for the hardening penetrates and a structure is created, in which the oil is gathered, in more and smaller areas thus preventing it from being scraped off. The result is: The oil consumption, wear and tear and friction are reduced, the exhaust gases are less burdened.

Instead of honing the cast iron cylinder, the piston ring running area is processed with laser-light. The laser-pulsation causes exact points in the material to evaporate which also creates a plasma. Nitrogen is then added and a durable surface with an exactly defined roughness is developed.

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