European Journal of Scientific Research - EuroJournals

Blast-Hole Cuttings: An Indicator of Drill Bit Wear in Quarries 722
of fines (Morley, 1944 and Hetenyi, 1966). Blast-hole cuttings are debris, chippings or caving flushed
by compressed air rock is attacked mechanically.
In addition, to effectively remove the blast-hole cuttings, annular space should be about 17% of
the cross-sectional area of the blast-hole. If the percentage of the annular space is less than 17% then
for every 1% reduction in this percentage the bailing velocity must be increased by 2% (Gokhale,
2004). An estimated correlation factor on account of insufficient annular space is given as:
aa = (1+ 0.02) [17-A] (1)
Where A is the percentage of annular space for combination of bit and drill rods to be used in
actual drilling (if A is more than 17% then aa should be given a value 1).
Beste (2004) observed that it is difficult to get an overview of wear mechanisms of the rock
drill bit. Shah and Wong (1997) were of the view that the contact geometry between tungsten-carbide
insert and rock is complex. Wear of rock drill bit is a constant phenomenon in hard rock drilling which
cannot be avoided; this may be a severe factor of cost for effective management of quarries, hence, a
reasonable measurement and prediction would be desirable. Moreover, when the drilling time increases
as well as low penetration rate, one can infer that the button of the bit is likely to be dull or worn and of
course this can lead to regrinding of blast-hole cuttings.
Therefore, utilization of energy to achieve penetration, under normal condition depends on
drillability of the rock; a certain amount of energy will be dissipated by rock breakage. It was
discovered through research that when bit button is blunt after very few impacts the hammer will
become useless because of plastic deformation. The bit which has the shortest span of all the three
main components will last in the order of 120 million cycles and the main cause of the failure is wear
(Chiang and Elias, 2000) and as the bit buttons wear out more fines are likely to be generated. The
objective of this paper therefore, are to use blast-hole cuttings as a measure of bit wear rate as well
correlate the weight retained at 75µm sieve size in order to establish their relationship.
Materials and Method
The materials for this work includes: blast-hole cuttings collected from 45 holes from three Nigeria
quarries and drill bit
Method
The grain size of 45 blast-holes drill cuttings collected from three selected quarries were determined
using standard method of America Society for Testing and Materials (ASTM) D 2487 and sieve of the
following mesh sizes: 850 µm, 600µm, 425µm, 300µm, 212µm, 150µm, 75µm, and 63µm were used
the results are presented in Table 1-45 and The wear of the gauge buttons were measured at regular
interval this correlated with weight retained on 75µm sieve size.
Result and Discussion
Tables 1-46 present the size distribution of the blast-hole cutting, it is observe that as number of hole
drill and wear increases the weight blast-hole cuttings retained on 850 µm decreases the weight of
blast-hole cuttings retained on the 75µm sieve size increases. All these point to the fact that it is likely
that as bit button is blunt, regrinding of blast-hole occurs.
Figure 1 shows the correlation between bit gauge button wear rate and weight of blast-hole
cuttings retained on 75µm sieve size cuttings from Geovertrag Quarry, Ado-Ekiti. The polynomial
relationship between Gauge button wear rate and weight of blast-hole cuttings retained on 75µm sieve
size is expressed by equation 2 which is an equation of order 2 and R 2 = 0.957.
Gw = -3E-05wt 2 + 0.003x - 0.099, R² = 0.957 (2)
Where Gw is gauge wear rate and wt is the weight of blast-hole cuttings retained on 75µm
sieve size. Figure 2 presents the correlation between bit gauge button wear rate and weight of blast-