NORMAL DRILLING

5. Release the hoist brake and allow the drill bit to contact the ground. Monitor the vibration coming from the tool string. To reduce vibration slow the rotary speed with the rotary rheostat. Keep the vibration to a minimum. As the vibration lessens, increase the rotary speed and the pulldown speed while monitoring the rotary current bar graph and the air pressure bar graph on the operator’s display terminal screen.

The objective is to penetrate the formation as fast as possible without damaging the machine or plugging the hole with cuttings. Monitoring the rotary current, and keeping the load in the lower portion of the bar graph (green) will eliminate damage to the rotary motor. Reducing the load on the motor is accomplished by reducing the pulldown force on the bit. Reducing the pulldown force will, in most instances, accomplish this. In some cases it may even be necessary to hoist the tool string slightly to reduce the loading. Monitoring the air pressure graph will indicate the condition of the hole. If penetration is too fast and the bailing air cannot remove the cuttings as fast as they are generated, the hole will plug and the air pressure will rise. Varying the penetration rate will vary the air pressure. Keep the air pressure in the normal working range (30 PSI for machines with water injection and 40 PSI for machines with dry-type dust control) by increasing or reducing the penetration rate. Keep the vibration levels to a minimum by varying the rotary speed and the pulldown force.

6. When the bit passes through the fragmented material (approximately 3-5 ft [0.9-1.5 M]) and into the consolidated material underneath, the vibration and loading will reduce drastically. When this occurs, the hole has been collared and normal drilling may commence.

NORMAL DRILLING

After the bit has passed through the unconsolidated material at the top of the hole, it is no longer necessary to reduce the load on the bit to reduce vibration and rotary motor loading. More rapid penetration and increased pulldown force may now be used to complete the hole as fast as possible with minimum vibration. This is the normal drilling condition for the machine.

Normal drilling follows the same guidelines as collaring the hole. Penetration is increased to the maximum determined by the rotary motor load, the vibration of the tool string, and the air pressure. By keeping the penetration at or slightly below the optimum, the hole can be completed in the shortest possible time.

To begin normal drilling proceed as follows:

1. When normal drilling is desired it is necessary to add pressure to the bit in addition to the deadweight of the tool string and rotary/pulldown unit. This pressure is furnished with the electric motor and pulldown gearbox. To activate the pulldown motor, turn the hoist/pulldown rheostat in the pulldown direction as required for maximum drill rate and pulldown force. Turning the control in the pulldown direction will increase the pressure on the bit by calling for a desired pulldown speed.

Apply enough pulldown force to allow the bit inserts to chip the material being drilled, rather than pulverizing it. If the pulldown force is not sufficient enough, the bit will ride over the top of the material being drilled and will not create chips. This condition can be observed by monitoring the cuttings. If the cuttings are finely pulverized material, the pulldown force is not enough. Another cause of poor cutting is a worn bit. If pulldown force is high, but the cuttings are fine and penetration is slow, change the bit.

2. Monitor the rotary motor load (current) and adjust the pulldown force to keep the bar graph in the lower (green) portion of the graph. It is permissible for the load to increase momentarily into the yellow, but continuous running in the yellow or red portions will cause rotary motor damage.

3. Monitor the vibration of the tool string and the machine. Keep the vibration to a minimum by varying the pulldown speed and the rotary speed. If vibration increases, reduce the rotary speed first. If this does not reduce the vibration to an acceptable level, reduce the pulldown speed until the vibration is acceptable.

NOTE: Excessive or prolonged vibration of the tool string and machine will cause eventual damage to the machine.

Monitor the air pressure. Keep the pressure in normal working range to eliminate compressor overheating. Pressures above normal working range (30 PSI [206.85 kpa] for machines with water injection and 40 PSI [275.8 kpa] for machines with dry-type dust control) indicate that the hole is starting to plug with cuttings. Stop the pulldown by returning the hoist/pulldown rheostat to the “0” position. Set the hoist brake. Wait a moment and if the pressure starts to decrease, let the hole clear before returning to drilling. If the pressure does not start to decrease it will be necessary to hoist the tool string to clear the hole. To do this release the hoist brake and turn the hoist/pulldown selector switch to the LOW position and the hoist/pulldown rheostat in the hoist direction. Hoist the tool string until the hole is cleared. Leave the rotary motion activated since this will help clear the hole. If the pressure is noticed slowly rising during drilling, reducing the penetration rate momentarily may eliminate the need to cease pulldown and hoist the tool string.

4. Continue normal drilling until the hole is at the desired depth. It may be necessary to add drill pipe to complete the hole. Refer to the appropriate sections in this manual for the procedures necessary for adding drill pipe.

The operator’s display screen on the operator’s display terminal will show the hole depth in feet.

5. Once the finished hole depth is reached it is necessary to clean or ream the hole before it is completed.