Wear of Hard-Metals in Rock Drilling: A Survey of the Literature

Abstract

The literature concerning the wear of tungsten carbide-cobalt alloys used as tool bits in rock drilling is surveyed.The possible mechanisms of rock breakage and of tool wear are briefly discussed. 'Year takes place as a result of shock impact or impact-fatigue spalling, by abrasion-mainly from the quartz grains in the rock, and also by thermal fatigue. The mechanism that dominates in any given conditions depends on the method of drilling and on the strength and abrasiveness of the rock. For rotarypercussive drilling, impact-fatigue wear and abrasion operate simultaneously, though essentially independently.Published data on the relations between the wear of We-Co alloys in rock drilling and their structure and properties are critically discussed. It appears that the resistance to impact wear is a direct function of the bulk compressive or transverse rupture strength and is related to the WC grain size and the Co mean free path.It is directly proportional to the blow energy in percussion.The results indicate that abrasion of'VC-Co alloys by quartz is more complicated than abrasion of 'simpler' metals by either hard or relatively soft abrasives.The wear in abrasion during running-in is quite high and becomes greater with larger 'VC grain size, while the steady-state wear rate becomes less. The abrasion-resistance increases with rise in hardness and with decrease in WC grain size and cobalt content, but not in a simple fashion. It is proposed that abrasive wear takes place both by microfracture at the point of abrasive/metal contact and by preferential removal of cobalt. The former factor dominates for hard, brittle alloys and when the abrasive grains have a high resistance to fracture.The latter dominates for softer, more cobalt-rich alloys and when the abrasives are friable.The considerable need for further research on all aspects of the wear behaviour of these alloys is stressed.THE need for improved rock-excavation and drilling methods is rapidly growing. This need is created by the demand for utilization of ores of lower and lower grade, for drilling increasing footages of exploratory holes or wells, for large-scale excavation work, and for general improvement in the efficiency of rock-removal methods.Wear of the tool bit is a major factor in determining the energy requirements and the penetration rate in drilling and usually dictates the choice of drilling method for a given type of rock. It is the purpose of this paper to survey published information on the relationship between drilling variables and wear and the influence of structure and * "Manuscript

Critical Analysis of Wear Mechanisms in Cemented Carbide

“…Researchers have investigated severe cracking and crushing in CC drill buttons used for rock drilling ( Ref 20,32,[49][50][51]. Similar pattern of cracking has been observed for the CC tip of conical picks which were used in coal cutting through continuous miner machine.…”

Wear of Hardmetals

“…Very high intermittent contact stresses are generated in applications such as percussive drilling (Larsen-Basse, 1973;Montgomery, 1968). These stresses aggravate the wear that takes place through mechanisms such as fracture and spallation of individual or small clusters of WC grains.…”

“…Much of the early work was concerned with the forensic examination of WC-Co components used in mining and mineral extraction applications; this was combined with laboratory-based testing, and attempts to develop some understanding of the mechanisms of wear that occur in abrasion and erosion (Bailey & Perrott, 1974;Blombery, Perrott, & Robinson, 1974a;Blombery, Perrott, & Robinson, 1974b;Conrad, McCabe, & Sargent, 1981;Dahlin, 1962;Dawihl & Frisch, 1968;Jonsson, 1976;Larsen-Basse & Koyanagi, 1979;Larsen-Basse, 1973;Larsen-Basse, 1981a, 1981bLarsen-Basse, 1983, 1985bLarsen-Basse, Perrott, & Robinson, 1974;Larsen-Basse, Shishido, & Tanouye, 1974;Latin, 1961;Montgomery, 1968;Montgomery, 1969;Osburn, 1969;Precht, Viswanadham, & Venables, 1981;Stjernberg, Fischer, & Hugoson, 1975;Wright, Shetty, & Clauer, 1983;Yardley, Johnson, & Kenny, 1981). Often these studies were combined with evaluation of the microstructure and mechanical performance of the materials, so that information on how the wear resistance alters with changes in material makeup could be gathered.…”

MICROSTRUCTURAL STUDY OF FAILURE PHENOMENA IN WC 94%-Co 6% HARD METAL ALLOY TIPS OF RADIAL PICKS

“…In case of percussive drilling, the wear pattern is caused by mainly fatigue whereas cracks and abrasion are the failure modes in case of rotary drilling [28,42]. LarsenBasse (1973,1985) has stated that Microspalling, Abrasion wear, WC grain pull out, Extrusion of binder metal and Reptile skin are common wear mechanism in the WC-Co [28,29]. Beste et al (2008) have concluded that corrosive degradation and oxidation are responsible for erosion of binder content in drill bits.…”