Wear-Resistant Piston of Atlas Copco RD22U in Finland

The RD22U's heavier piston—more mass, longer stroke, higher impact energy than the RD18U class—changes the fatigue arithmetic in Finnish hard-rock operations. At Agnico Eagle's Kittilä gold mine in Lapland, the gold-bearing schist transitions between quartzite-dominated zones at 180 MPa and softer phyllic alteration zones at 90–110 MPa within a single development round. Each transition zone puts the piston through a brief high-acceleration phase when the lighter formation offers reduced resistance on the return stroke, followed by the higher-resistance hard zone that absorbs the next blow fully. Those alternating partial and full return-wave reflections create a variable tensile-compressive stress cycle in the piston body—exactly the loading type that initiates fatigue cracks at surface irregularities.

The RD22U piston is manufactured from high-alloy tool steel with carburized surface treatment to 58–62 HRC at the strike face and guide diameters. That case depth—typically 0.8–1.2 mm—provides the hardness gradient that resists both abrasive wear at the piston guide surfaces and contact fatigue at the strike face. The Finnish requirement specific to variable-formation drilling is adequate toughness in the core steel below the carburized layer: a piston that's surface-hard but core-brittle fractures when the tensile wave from an unusually soft formation zone arrives with higher-than-expected amplitude.

Piston Wear Inspection at Finnish Service Intervals

Finnish maintenance teams at Kittilä check strike face mushrooming at every percussion seal change—a 3-minute measurement that catches piston degradation before the deformed geometry changes how the stress wave enters the rod string. A mushroomed face delivers the wave asymmetrically, producing hole deviation and asymmetric rod thread wear that aren't attributed to the piston until the pattern is obvious. HOVOO supplies RD22U wear-resistant pistons for Finnish hard-rock programs. References at hovooseal.com.