General
In chapterDTH Drilling Care & Maintenance – Part One, we introduced following topics:
- A balanced system
- Correct drilling parameters
- Most commoncausesofproductfailures
- Corrosion
- Fatigue
- Galling
In this chapter, the discussion will be continued and following items will be explained:
- Lubrication
- Hammer disassembly
- Drill pipes
Lubrication
- Correct lubricationduring DTH drillingis extremelyimportant
- Inadequate lubricationisamajorcause ofhammerwearandfailure
- Excessive lubricationslowsdownthe pistonandmakesstartupdifficult
- Use rock drill oil only
- Modern drill rigs are provided with automatic lubrication equipment injecting oilintotheairstreamsupplied from thecompressor
- Rate oflubricationisafunctionof hammer air consumption, which dependsonoperatingpressure, and choke size beingused
- Joints liketopanddriversubs,pinand boxthreadsshallhaveagoodlayerof threadlubricant
- This willpreventcorrosionandgalling and insure ease of breakout at disassembly
- Thread lubricantshallcontainatleast 40% metalparticles
Corrosioncontrol
- Hammer storage
- Clean andlubricateallcomponentswith rockdrilloilandthreadlubricantbefore storage
- When using foam
- After usageclean&oilbyblowingdry lubricatedairthroughthesystemupon completionofeachholeorwhennotin use for threehours
- Water injection or in wetholes
- Never leavehammerinholeunder. Inspectandserviceevery100hours
- Periodically test water
- pH factorabove7
- No chlorides or sulfides
- At frequent intervals
- Re-coat topanddriversubwiththread lubricant
The gap
- When thedriversubhasbeenscrewedintothe pistoncasewithguidesleeveandretainerring installed,agapmustbevisiblewherethepiston case and driver subjoin
- The sizeofthegapisnotcriticalbutitshouldnot belessthan0,5mm(0.02”)andnotmorethan 1.0 mm(0.04”)
- When thegapisatthelowerlevelitistimeto changethepistonretainer If hammer operationcontinueswithnogap,thereisahigh risk of componentfailures
Hammer Disassembly
- Usethecorrecttoolsintherightspotstodisassemblehammers Clampingoverthreadareaswillmakedisassemblingverydifficult
- 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 surethatdrillpipesareclean beforeaddingthemtothedrillstring
- Use compressedairtocleantheinterior
- All contamination indrillpipeswillend up in thehammer
- Never use bent drill pipes
- Inspect thelowerconnectioninthetop subtomakesurethethreadsareingood condition
- Ifyou areputtingonanewstringorasignificant numberofnewdrillrods,anewtopsub is recommended
- Remove threadprotectors,cleanoffand inspecttheconnectionsfordamage
- Apply a good quality thread grease
- Make suretheinsideofthepipeisclean, evenifthepipeisnew
- Make andbreaktheconnectionsslowly a couple oftimes
- If resistancetomakeandbreakistoo highbackoffandinspectforthread damageandrigalignment
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