DTH Drilling Care & Maintenance - Part One

DTH Drilling Care & Maintenance – Part One

January 21, 2018

General

Due to there are a lot of knowledge on care & maintenance, the whole content is divided into two parts- DTH Drilling Care & Maintenance – Part One and DTH Drilling Care & Maintenance – Part Two

Content

By nature of their design and way of usage, DTH Drilling Tools are self destructive, and  Our goal is to help customers to optimize their performance and make them last as long as possible!

Balanced system

  • The first steps to good performance and service life when drilling with DTH equipment is to have a balanced system – air supply, hammer and bit
  • The picture below left one is bad balanced system which will lead to low penetration rate, and right one is good balanced system with perfect penetration rate

 

 

 

 

Correct settings

  • Second step is to use correct settings in relation to the drilling situation
    • Percussion force
    • Feed force / weight on bit
    • Rotation

Causes of failures

  • The third step is good care and maintenance of the equipment to keep it working long and trouble free
  • This will avoid or delay the three main “natural” causes to hammer and bit failures to happen
    • Corrosion
    • Fatigue
    • Galling

 

 

 

 

Good practices

  • Scheduled maintenance is extremely important in preventing premature failures
  • Anew hammer should be disassembled, inspected an cleaned after the first eight (8) hours of drilling
  • Here after disassemble, inspected and cleaned every 100 hours of operation or 3 000 m (10 000 ft) of drilling
  • Wear limits
    • Follow recommendations in Operator’s Manual regarding wear limits for hammer key components
  • Regularlyinspect all parts for galling, cracks and burrs
    • Replace any parts which are cracked
    • Usea file or emery paper to remove any burrs
    • Any part which shows signs of galling also has a mating part with similar damage
  • If the piston is galled it should be replaced and a careful inspection is required inside the piston case
    • It is strongly recommended to hone or polish inside the piston case to smooth the galled surfaces

 

 

 

 

Corrosion

  • Corrosion “The deterioration of a substance because of a reaction with its environment” is a well known problem creator in a drillers world
  • Most environments encountered while drilling are considered to be corrosive
    • Water
    • Air
    • DrillingFoams
    • Sulphides
    • Chlorides

 

 

 

 

Fatigue

  • Metals will crack and break if they are subjected to high cyclic stresses
  • The mode of operation in percussive drilling is to use cyclic stresses to crush the rock, the cyclic stresses level depends on rock drillability
  • Energy levels during drilling are very close to the maximum stress that materials in hammer and bit components can take

 

 

 

 

Correlation of Corrosion and Fatigue

  • Below pictures is comparison of the schematic fatigue behaviors of steel for those part with corrosion and without corrosion. And the last three pictures in right is showing the process of how corrosion lead crack.

 

 

 

 

  • Final result the part is broken due to corrosion

 

 

 

 

Galling

  • Galling is a form of severe wear occurring between two sliding  Metal from one surface is “picked-up” by the other
  • Inside a hammer in DTH drilling rig there are several metal surfaces in motion that are in contact and galling can easily happen
  • Galling comes in most cases from poor lubrication or foreign material in the hammer
  • The easiest way to avoid galling is consequently to keep the hammer clean and well lubricated
  • The pictures blow showing the galling happened on hammer components

 

 

 

 

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