General

In chapter DTH Drilling Care & Maintenance – Part One, we introduced following topics:

  • A balanced system
  • Correct drilling parameters
  • Most common causes of product failures
    • Corrosion
    • Fatigue
    • Galling

In this chapter, the discussion will be continued and following items will be explained:

  • Lubrication
  • Hammer disassembly
  • Drill pipes

Lubrication

  • Correct lubrication during DTH drilling is extremely important
  • Inadequate lubrication is a major cause of hammer wear and failure
  • Excessive lubrication slows down the piston and makes start up difficult
  • Use rock drill oil only
  • Modern drill rigs are provided with automatic lubrication equipment injecting oil into the air stream supplied from the compressor
  • Rate of lubrication is a function of hammer air consumption, which depends  on  operating pressure, and choke size being  used
  • Joints like top and driver subs, pin and box threads shall have a good layer of thread lubricant
  • This will prevent corrosion and galling and insure ease of breakout at disassembly
  • Thread lubricant shall contain at least 40% metal particles

Corrosion control

  • Hammer storage
    • Clean and lubricate all components with rock drill oil and thread lubricant before storage
  • When using foam
    • After usage clean & oil by blowing dry lubricated air through the system upon completion of each hole or when not in use for three hours
  • Water injection or in wetholes
    • Never leave hammer in hole under. Inspect and service every 100 hours
  • Periodically test water
    • pH factor above 7
    • No chlorides or sulfides

 

 

 

 

  • At frequent intervals
    • Re-coat top and driver sub with thread lubricant

The gap

  • When the driver sub has been screwed into the piston case with guide sleeve and retainer ring installed, a gap must be visible where the piston case and driver sub join
  • The size of the gap is not critical but it should not be less than 0,5 mm (0.02”) and not more than 1.0 mm (0.04”)
  • When the gap is at the lower level it is time to change the piston retainer  If hammer operation continues with no gap, there is a high risk of component failures

 

 

 

 

Hammer Disassembly

  • Use the correct tools in the right spots to disassemble hammers Clamping over thread areas will make disassembling very difficult
  • The hammer disassembly procedure and proper tools are shown in below and the fourth picture in right is showing the damaged hammer by un-proper hammer disassembly tools and procedure.

 

 

 

 

Drill pipes

  • Make sure that drill pipes are clean before adding them to the drill string
  • Use compressed air to clean the interior
  • All contamination in drill pipes will end up in the hammer
  • Never use bent drill pipes

 

  • Inspect the lower connection in the top sub to make sure the threads are in good condition
  • If you are putting on a new string or a significant number of new drill rods, a new top sub is recommended
  • Remove thread protectors, clean off and inspect the connections for damage
  • Apply a good quality thread grease
  • Make sure the inside of the pipe is clean, even if the pipe is new
  • Make and break the connections slowly a couple of times
  • If resistance to make and break is too high back off and inspect for thread damage and rig alignment

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