Analysis of Button Bit Wear and Performance of Down-The-Hole Hammer Drill

Abstract

This work investigates bit button wear and performance of Down-The-Hole Hammer (DTH) drill in Navachab Gold Mine, Namibia. Rock samples obtained were tested in the laboratory for chemical composition, equivalent quartz content and compressive strength.  Schmidt hammer was used to determine the rebound hardness values of the selected rocks. The specific energy was determined by using empirical equation. The length of insert buttons on the surface of the drill bits were measured by using digital vernier caliper at regular intervals as drilling operation progressed and wear rates were correlated with the rock properties. Silica content varied from 71.34 – 71.83% and 83.25 – 83.56% for oxidised  and non-oxidised  schist respectively. The equivalent quartz content was estimated to 72.30% for oxidised  schist and 64.20% for non-oxidised  schist. The highest wear rate was experienced on the non-oxidised schist having equivalent quartz content of 72.30%. This revealed that wear of rock drill bit is influenced by rock properties.  Uniaxial compressive strength varied from 123 to 194 MPa.  The strength characteristics of these rocks varied from medium to high strength. Rebound hardness values from the L-Type schmidt hammer ranged from 42 to 58 for oxidised  and non-oxidised  schist. Rebound hardness values obtained from N-Type schmidt hammer varied from 50 to 58 for oxidised  and non-oxidised  schist. The specific energy varied from 6.0 MJ/m³ for oxidised  schist to 12.5 MJ/m³ for non-oxidised  schist. Moreso, wear rate varied from 0.0284 - 0.1045 mm/m for oxidised  and non oxidised  schist respectively. The result of correlation matrix revealed that uniaxial compressive strength, equivalent quartz content and silica content are dominant rock properties affecting wear rate of bit button of DTH drill.