Pitching molten iron particles against a surface at high speed – this is known as arc wire spraying. Daimler AG uses this thermal process for coating the contact faces of light-alloy cylinders in the engine block, thus ensuring particularly low-friction operation. This technology dispenses with cylinder liners, which are normally used to produce a resilient cylinder contact surface.
In arc wire spraying, two live metal wires are brought into contact to produce an electrical short circuit. The intense heat thereby generated causes the ends of the wires to melt; the molten metal is atomised and sprayed by means of a gas stream. The accelerated metal particles finally form a thin coating on the cylinder contact surface.
The Daimler engineers have brought arc wire spraying to series maturity. Friction and wear in the engine can thus be considerably reduced. By dispensing with the cylinder liners, this technology not only saves space, but also cuts weight by seven to twelve percent. A further advantage is the thermal behaviour of the coating: it more readily dissipates heat in the combustion chamber, thus making cooling more efficient.