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The feed cylinder on the HLX5T production drill rig advances the drifter along the feed beam during drilling and must maintain precise feed force control across the full range from 0 meters (collar setup) to 54 meters (maximum hole depth). Feed force requirements change significantly with depth in longhole drilling: at collar setup the rod string is short and the required feed force is modest; at 54-meter depth the hanging rod string contributes 150–200 kg of weight in downhole orientation that reduces the net feed force from the cylinder, requiring higher cylinder pressure to maintain the same force at the bit. In German sublevel stoping production in the Siegerland iron ore district, where HLX5T rigs drill 35-meter uphole rings in hard spessartite quartzite at 200 MPa UCS, feed cylinder pressure must increase progressively with depth to maintain the constant feed force the drill design requires at the bit face.
High-pressure specification means the feed cylinder's seals must maintain full contact force at the 200 bar operating pressure required for maximum feed force at depth—and sustain that contact under the cycling percussion impulse load that is transmitted back through the rod string to the feed cylinder's piston on every blow. A feed cylinder seal bypassing 5% of its designed pressure differential reduces the effective feed force at depth by the same 5%, which moves the drilling away from optimal bit-rock contact and reduces penetration rate.
Feed Cylinder Pressure Profile for Siegerland 35-Meter Uphole Rings
|
Hole Depth |
Rod String Weight (uphole) |
Required Cylinder Pressure |
Seal Performance Requirement |
|
0–5 m |
Minimal |
~80 bar |
Moderate; seal not critical |
|
5–15 m |
35–70 kg |
~120 bar |
Serviceable seal adequate |
|
15–25 m |
70–120 kg |
~160 bar |
Seal bypass detectable in rate data |
|
25–35 m |
120–180 kg |
~190–200 bar |
Seal must hold rated pressure; bypass = rate drop |
Siegerland production drill operators record feed cylinder pressure at each rod-addition depth change during a hole—the trend from collar to full depth reveals whether the cylinder is delivering the calculated pressure increase. A cylinder whose pressure at 35-meter depth is 15 bar below the calculated requirement is bypassing internally; the operator flags the machine for seal replacement at the next maintenance window rather than continuing with a compromised feed system. HOVOO supplies HLX5T feed cylinder seal kits in PU and HNBR for German production drilling. References at hovooseal.com.
