Percussion drilling is frequently adopted in advancing boring performed for forward exploration and drainage in the construction of road and railway tunnels. It is also used to make blastholes for mine development and mountain tunnel construction. Drilling efficiency declines with progressing wear of drill bit. In the present study, the effect of rock abrasiveness of granite on the tip wear on percussion bit is examined through laboratory drilling tests. Percussion drill bits equipped with cemented tungsten carbide (WC-Co) and polycrystalline diamond compact (PDC) tips were used in the test. Three types of Japanese granite (Sori granite, Inada granite and Takine granite) were employed as the drilling medium. The height loss of gage tips were measured every drilled length of about 6 m. The effects of some mechanical properties, e.g., unconfined compressive strength and indirect tensile strength, and some abrasivity indexes, e.g., CAI (CERCHAR Abrasivity Index) and Schimazek F value, on the increasing ratio of the height loss of tips to drilled length are discussed.
Percussion drilling is frequently adopted in advancing boring performed for forward exploration and drainage in the construction of road and railway tunnels and also used in making blastholes for mine development. The maximum rate of penetration (ROP) reaches 50–100 cm/min or higher in the percussion drilling of hard rock such as granite (Okubo et al., 1992), indicating that percussion drilling is a very efficient drilling technique.
Percussion bits are conventionally equipped with cobalt (Co)-containing cemented tungsten carbide (WC-Co) tips. Recently, percussion bits with polycrystalline diamond compact (PDC) tips have been put to practical use. Hereafter, these bits are respectively called WC-Co and PDC percussion bits. PDC is superior to WC-Co in terms of wear resistance. Therefore, PDC percussion bits are considered to exhibit better drilling performance (long bit life) than WC-Co percussion bits.
The wear of tips on a percussion bit is thought to be affected by the mechanical properties or abrasivity indexes of drilled rock. In this study, percussion drilling tests on hard and highly abrasive granite were performed in a laboratory using PDC and WC-Co percussion bits to evaluate the influence of the mechanical properties and abrasivity indexes of drilled rock on the tip wear. The test result contains some published data (Miyazaki et al., 2016).
