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Tribology
Microwelding

"Microwelding" (MW) describes a particular form of damage to the piston ring or piston groove side that often occurs after only short operating times on cast iron top compression rings or the corresponding groove of aluminium pistons.
This form of damage is characterized by and derives its name from localized welding of material accompanied by breaking out and transference of material from the piston to the ring side, especially the bottom ring side. Examples of typical microwelding failures on piston groove and ring sides are shown in Fig. 18 and Fig. 19 [30].

If the ring with such damage is then restricted in its movement in the groove or even becomes jammed, this will affect the subsequent wear behaviour (e.g. flaring of the groove) and functional characteristics (increased blowby and oil consumption), in extreme cases to the point of engine failure.
There are many potential means of avoiding microwelding depending on the diverse tribological interactions between the component materials and surface finishes and the operating conditions in the engine [31]:

Microwelding can be reliably avoided above all if actions to the ring and piston are appropriately combined.


Fig. 18: Damaged Piston Groove at 25x; SEM micrograph


Fig. 19: Piston Ring Side Showing Welding of Aluminium, 100x

 

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