Drilling Fundamentals
©Dr. B. C. Paul 2000
Note – The types of drilling machines discussed in these slides reflect the author’s
view of what is offered in the product literature of numerous manufacturers and is
common knowledge to the field and can be found in a variety of published sources no
one of which is by intention preferentially cited in these notes.
Drilling Blastholes
• Drills are mounted on rubber tires or
crawlers
• Have Mast Tower that can be raised to drill,
lowered to propel
• Drill moves into position
• Raises the Mast
• Lowers Jacks and Levels
• Adjust the Mast to Drilling Angle
Mast Height and Penetration
•
•
•
•
Masts Usually About 20 to 60 feet High
Drill Bit is Placed on the Business End
Have Drill Steels Above
Height of the Mast Determines the Length
of the Drill Steel
• When Steel is Extended a Carousel with 3
to 5 additional pipes rotates and lines up
another steel
Not So Good Old Days
• Old Days with limited drill distance would
drill horizontal holes and lift benches with
blast
– Fragmentation Usually Harder to Control
– Loading Holes More Challenging
• Most Holes Today are Vertical
Drill Penetration Mechanisms
• Hammer and Chisel Approach
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–
–
–
Sharp pointed bit is driven into rock
Bit Rotates Slightly
Air blows out cuttings
Bit comes down for another hammer
• Traditional Approach is Top Hammer - but
now hammering down the drill steel
• Alternate Approach is DTH - in past holes
too small - still provide some constraint
Other Mechanisms
• Auger Bits - Like Giant Drill Bit - limited to
very soft formations
• Rotary Bit
– Usually three cones to a bit
– Force Teeth into the rock causing spalling
– Air Blows Cuttings Out of Hole
• Drill Steels are Hollow - air blows down
between the tricones - 10% cools bearings
Dust Management
• Air Blows up Hole
– Sprayed Water in Past but made gummy and
freeze prone
– Now often use dry baghouse collection
• This system may not work well with wet cuttings
• One Challenges is to avoid wear on bits and
steels
• Systems often drop cuttings when drill
moves
The Really Hard Abrasive Stuff
• Stick Tungsten Carbide Inserts on Drilling
Tools
– Can get button bits
• Use Heating and Cooling to Make Rock
Self Destruct
– Jet Piercing Techniques
Powering a Drill
• Smaller Units have Diesel Engines
• Very Large Units have Extension Chords
• Often Power Transfer to drill shaft is
hydraulic
• Compressor is often second power
consideration
– Can give mixed diesel and electric
– Can make for auxiliary compressor units
Summary
• Drill By Percussive Action
– Top Hammer
– DTH
• Drill By Rotary Action
• Drill By Heating and Cooling