Dust Control Handbook for Industrial Minerals Mining and Processing

that dust control efficiencies greatly increased from 0.2 to 0.6 gallons per minute (gpm), thenleveled off above this flow rate. However, once the flow rate approached 1.0 gpm at this site,operational problems were encountered such as the drill bit plugging and the drill steel rotationbinding due to the water causing the drill cuttings to become too heavy to be removed by thebailing air [USBM 1987]. Therefore, too little water reduces dust control efficiency while toomuch water creates operational problems. The amount of water needed would be dependentupon the surface drill type and the material being drilled.Figure 3.2. The air and water flow during drilling operation to demonstratewater flushing of the drill cuttings. The water flows through the center of thedrill steel and out the end of the drill bit to remove the cuttings from the drill hole.To provide for wet drilling, a water tank mounted on the drill is used to pump water into thebailing air, and the water droplets trap dust particles as they migrate up the annular space of thedrilled hole (the annulus is the open area of the drill hole between the drill steel and the wall ofthe drill hole), thus controlling the dust as the air bails the cuttings. The drill operator controlsthe water flow from the cab, and some cabs are equipped with a meter to indicate water flowrate.Advantages to Wet DrillingA potential advantage to the use of water in percussion drilling operations, besides better dustcontrol, is that the use of water may improve the penetration rate of percussion drilling forsurface mining. There is very little information on wet drilling effects on penetration rate, butsources have shown that the use of water while percussion drilling in underground mining canDrilling and Blasting 81