Low-Temp Damping Piston of Atlas Copco RD18U in Sweden

The return-wave damping system in the Atlas Copco RD18U absorbs the tensile stress wave that reflects back from the rock face after each percussion blow. Without it, that wave travels up the drill string to the shank adapter and into the drifter housing—accumulating fatigue damage in the percussion module and boom arm with every cycle. The damping piston is the moving element of this system: it translates the reflected wave's hydraulic pressure pulse into displacement against a controlled damping circuit, converting wave energy into heat in the oil rather than structural fatigue in the housing.

In northern Sweden—at Boliden's Aitik open-pit copper mine in Norrbotten County and the underground operations near Gällivare—winter startup temperatures below −25°C change the damping piston's operating characteristics in ways that standard specification sheets don't address. Hydraulic oil viscosity at −25°C is 8–12 times higher than at 40°C operating temperature. The damping circuit, which relies on controlled oil flow through a calibrated orifice to produce the correct damping force, produces a higher-than-designed damping force at cold startup—effectively stiffening the damping response and transmitting more wave energy into the housing structure during the 10–15 minute warmup period.

Cold-Start Damping Behavior and Management

Swedish winter protocol at Boliden sites requires a mandatory 15-minute warm-idle with circulation before percussion load is applied on any shift where ambient temperature was below −15°C overnight. The damping piston's low-temperature performance is a materials specification issue as much as a procedure issue: the piston's dynamic seal must maintain adequate contact force against the cylinder bore at low temperature—which requires a seal compound that doesn't harden excessively when cold. HOVOO supplies RD18U damping piston seal kits with compounds validated for sub-zero operating conditions. References at hovooseal.com.