Wear-Resistant Rotation Bushing of Sandvik HLX5T Rock Drill in Sweden

Longhole production drilling with the HLX5T places the rotation bushing in a loading condition that development drilling doesn't replicate: the drill string hangs 30–54 meters into the hole, and the combined weight of T51 rods in a 54-meter string reaches 180–220 kg. That hanging rod string weight applies a sustained downward force to the shank adapter, which transfers continuously through the rotation bushing to the drifter's front housing. The rotation bushing must maintain precise radial clearance to the shank adapter OD—the clearance that keeps the shank aligned with the percussion bore—under both this sustained weight load and the 50+ Hz percussion cycling simultaneously.

At Boliden's Garpenberg underground silver-zinc mine, where the HLX5T drills 25–35 meter longhole rings in the vein-hosted deposit, the rotation bushing's wear rate is 30–40% higher than at a development drifter because the long rod string's lateral deflection tendency—magnified by the bending flexibility of a 35-meter string—applies off-axis forces to the shank adapter that exceed those from a short development rod set. A shank adapter deflecting 0.5 mm off-axis at the bushing contact zone under a 35-meter string load concentrates bushing bore wear on the downward side, producing an oval wear pattern rather than uniform circumferential wear.

Rotation Bushing Wear Patterns in Longhole vs. Development Drilling

Garpenberg's HLX5T maintenance team uses an oval gauge rather than a single-point dial indicator to check bushing wear—measuring both vertical and horizontal diameters to catch the asymmetric wear from the long string weight. A bushing showing 0.20 mm vertical wear and 0.05 mm horizontal wear is already functionally degraded despite being within the nominal replacement limit on the horizontal axis. HOVOO supplies wear-resistant HLX5T rotation bushings with the bore geometry matched to the production drilling load profile. References at hovooseal.com.