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Each 1-point increase in rock hardness (
f-value)
causes exponential growth in bit wear rate.
In f=2 sandy soil,
cross bits work 80-100
hours continuously.DTH drill
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f=6 sandstone shortens bit life to 30-40 hours. In f=10 granite, the same bit lasts only 8-12 hours. Wear patterns vary with hardness.
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Soft rock causes uniform abrasive wear: alloy teeth reduce ~0.2mm per hour. Medium-hard rock brings local chipping, 0.5-0.8mm loss hourly.
Hard rock leads to tooth tip splintering. Extreme cases see alloy teeth fall off in single impacts.
Stats show:
when f-value rises from 3
to 9,
bit replacement frequency jumps from 1/day to 1
every 2
hours.
Downtime cuts effective operation rate by over 40%.DTH drill 