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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-
723 Z.O. Opafunso and B. Adebayo hole cuttings retained at 75µm sieve size cuttings from Johnson Quarry, Akure. The power relationship between Gauge button wear rate and weight of blast-hole cuttings retained at 75µm sieve size is expressed by equation 3 Gw = 3E-09wt 3.418 R² = 0.777 (3) Where Gw is gauge wear rate and wt is the weight of blast-hole cuttings retained at 75µm sieve size. Figure 3 shows the correlation between bit gauge button wear rate and weight of blast-hole cuttings retained at 75µm sieve size cuttings from Sonel Boneh Quarry, Ibadan. The polynomial relationship between Gauge button wear rate and weight of blast-hole cuttings retained on 75µm sieve size is expressed by equation 4 which is an equation of order 3 and R 2 = 0.729. Gw = -1E-06wt 3 +0.000wt 2 - 0.021wt + 0.544, R² = 0.729 (4) Where Gw is gauge wear rate and wt is the weight of blast-hole cuttings retained on 75µm sieve size. Figure 1: Plot of Wear Rate against Weight of Blast-hole Cuttings Retained for Geovertrag Quarry, Ado – Ekiti.
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