Controls for Normal Drilling

There are two ways to suppress dust generation or prevent the escape of the dust to the atmosphere. The two methods cannot be used at the same time as they are not compatible. One method to suppress the generation of dust is to inject water into the main air stream as it passes to the bit.

The water serves to conglomerate the dust particles into larger particles that may be treated as cuttings. The other method to suppress the dust is to contain the dust in the dust curtain enclosure then draw off the lighter particles and filter them out of the air before returning the air to the atmosphere. The filtering is done by a filter unit, which forces the dust laden air through filters where the dust is removed. In the filter system, the dust must remain dry as wet material will plug the filters.

NOTE: When the machine is equipped with a dry-type dust filter system, the air for cleaning the filters is drawn from the bailing air system. Air pressure to the dry-type dust filter must be maintained at 40 PSI (276 kPa) to insure proper cleaning of the filter elements.

DRILLING

VERTICAL DRILLING

Once the drill has been inspected and started, positioned, leveled, and the tool string assembled, it is now ready to begin drilling. There are two methods of drilling, vertical drilling and angle drilling. Vertical drilling is, as the name implies, drilling a vertical hole. Angle drilling is drilling the hole at some angle from vertical (up to 30 degrees). This section of the Operator’s Manual details the procedures involved in the drilling of vertical holes.

CONTROLS UTILIZED WHILE DRILLING

The actual drilling procedure involves three main sections:

1. Starting the hole (collaring). 2. Drilling the hole. 3. Cleaning or reaming the hole.

Many types of formations are found in mining areas. Formations that are drilled may range from a wet clay to solid taconite. Each formation, and the parts of the hole within each formation, requires drilling techniques, expressly for that formation. A hole drilled through fragmented limestone is not drilled the same way that a hole is drilled through consolidated taconite. For this reason it is important that the operator not only become familiar with the basic drilling procedures and the specific machine being operated, but that he also become familiar with the formation being drilled.

For the purpose of this section of the Operator’s Manual it is assumed that the hole will be drilled in a consolidated rock formation. This is probably the simplest formation to drill in. Special circumstances will be taken into account in the Drilling In Difficult Formations section of this manual. It is also assumed that the operator is familiar with the location and operation of all of the controls on the machine and that the machine is in good repair.

Controls for Normal Drilling

During the actual drilling the operator’s display terminal should be turned on and the operator display screen shown on the monitor. All of the drilling parameters noted in the following paragraphs will appear on the operator’s display screen.

NOTE: The bar graphs on the operator’s screen on the operator display terminal shows the condition of each of each functions. If a function operates beyond its normal operating range, especially for rotary current and hoist/pulldown force, the bar graph color will change from green to yellow or red when the graph valve raises into that particular range. For details, refer to the Operator Display Manual.

STARTING THE HOLE (COLLARING)

Since the first few feet of a hole are usually in unconsolidated material, the procedure for drilling through this material will be different than for the remainder of the hole. This procedure is commonly referred to as collaring the hole.

To begin, or collar the hole, proceed as follows:

1. Verify that the tool wrench and breakout wrench are retracted fully. Clear the drill deck of personnel and material which is not necessary for the drilling procedure (i.e. oil drums, tools, spare bits, etc.).

2. Place the operating mode selector switch in the DRILL position. Place the hoist/pulldown speed selector switch in the PULLDOWN position. Depress the drill/propel control ON pushbutton. Release the hoist brake and allow the tool string to lower so that the guide bushing is firmly seated in the hole in the drill deck. Make sure that the slots in the bushing align with the lugs on the drill deck. Reset the hoist brake.

3. Turn the rotary speed selector switch to LOW position. Turn the rotary rheostat clockwise until the rotary speed bar graph on the operator’s display terminal screen indicates that the tool string is turning at approximately 25 RPM.

4. Lower the dust curtains and turn on the dust control system. Place the main compressor vent/ drill switch in the DRILL position to supply bailing air to the bit.

NOTE: While the bit is passing through the unconsolidated material laying on the top of the formation, the pulldown speed sufficient to cause penetration of the bit is provided by turning the hoist/pulldown rheostat slightly in the pulldown direction.

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.

ENDING THE HOLE

Once the finished hole depth is reached normal drilling ceases. It is now necessary to ream the hole before preparing the drill to move to the next hole. Reaming the hole removes cuttings that have fallen to the bottom of the hole and also straightens and increases the diameter of the hole.

As the bit and tool string are cutting through the formation, the bit may tend to wander slightly. This wandering is due to the fact that the stabilizer cannot be exactly the same diameter of the bit or it would wear out quickly and create operation problems. The stabilizer tends to keep the bit on course, but it cannot keep the hole exactly straight. Reaming the hole straightens the hole and therefore increases the diameter of the hole slightly. Reaming the hole also removes any cuttings that are lodged in the hole. These cuttings must be removed or they will eventually fall to the bottom of the hole, reducing the drilling depth.

To complete the drilling procedure the hole is reamed as follows:

1. When the hole is drilled to the finished depth, leave the main air stream on and the rotary rheostat to the MINIMUM position and the motion activated. Return the hoist/pulldown rheostat to the “0” position and set the hoist brake. Allow the tool string to rotate and the air to bail the hole for a moment. This removes all of the cuttings in suspension from the hole.

2. Turn the hoist/pulldown speed selector switch to the LOW HOIST position and the hoist/ pulldown rheostat in the HOIST direction while simultaneously releasing the hoist brake. Slowly hoist the tool string out of the hole. If resistance is met, or if vibration increases, return the hoist/pulldown rheostat to “0” position and set the hoist brake. Allow the obstruction to be removed by the bit before continuing. If the hole is very crooked (indicating a worn stabilizer) it may be necessary to repeat this procedure of hoisting, then stopping and allowing the bit to clear, many times before reaching the top of the hole. This procedure straightens the hole and allows the tool string to be removed.

3. Once the tool string has been removed and the hole reamed, it must now be cleaned out. Reaming the hole loosens cuttings that have become lodged in the side of the hole. These cuttings, and most of the cuttings generated during reaming will fall to the bottom of the hole. This filling of the hole may reduce the actual depth of the hole significantly, so it is necessary to remove these cuttings from the hole. To do this, release the hoist brake and turn the hoist/ pulldown rheostat slowly in the pulldown mode.

Leave the air on and the tool string turning at 25-30 RPM. When the bit reaches the point where the cuttings have accumulated on the bottom of the hole, these cuttings will be forced out of the hole. When the cuttings have been cleaned out of the bottom of the hole, the bit will contact the undrilled formation at the bottom of the hole and stop penetrating. Once the flow of cuttings out of the hole stops and the tool string stops penetrating, the hole is clean.

4. After cleaning the hole the tool string may be raised to the top. Turning the hoist/pulldown rheostat control in the HOIST direction and the hoist/pulldown speed selector switch in the HOIST HIGH position will hoist the tool string.

ENDING THE HOLE (MULTIPLE PIPE SECTIONS)

Reaming the hole with multi-section tool strings is the same as reaming with single pipe section strings. The reaming procedure must be done in stages as the pipe sections are removed.

While removing the drill pipe the cuttings dislodged from the sides of the hole and the cuttings generated by reaming will fall to the bottom of the hole. To effectively clean the hole, it would be necessary to reassemble the tool string and lower it to the bottom of the hole. This is not desirable as it is time consuming. One method to eliminate the need to clean the hole is to overdrill the depth and allow cuttings to fill the hole to the desired finishing depth. Experience in this area will show how much to overdrill the hole. A good practice is to overdrill the hole by 1 to 2 feet (0.3 to 0.6 m) over the estimated finished hole depth. This way, if the estimate is wrong, the hole will be 1 to 2 feet (0.3 to 0.6 m) too deep. This can easily be corrected by a few shovels full of cutting thrown into the hole. Underestimating, on the other hand will require that the tool string be reassembled and the hole cleaned.

DRILLING DIFFICULT FORMATIONS

For the purpose of explanation, the drilling procedure given in the Drilling section of the manual assumes that drilling takes place in consistent, consolidated rock formation. Unfortunately, not all drilling is in this type of formation. This section of the Operator’s Manual will detail, in general, some typical drilling difficulties encountered.

The main cause of difficult drilling are unconsolidated material or wet sticky material. Unconsolidated material causes vibration far greater than experienced in consolidated formation, and if severe enough, may also decrease the bailing velocity of the main air stream. Wet, sticky material causes problems with cleaning the hole since the material may coat the hole and the drill pipe, increasing the air pressure above the working range. Wet material may also plug the bit orifices, freeze the bit cones, or compact into balls that refuse to be bailed out of the hole. The general procedure for drilling in difficult formations is the same as the procedure for drilling in good formations. The hole is collared, drilled, reamed, and cleaned using the standard operating procedures. Monitoring of the machine is, however, critical while drilling in difficult formations.

NOTE: Failure to closely monitor the machine and its bar graphs as shown on the operator’s display terminal operator’s display screen will result in damage to the machine or a stuck drill pipe.

UNCONSOLIDATED MATERIALS

Drilling unconsolidated materials may present two problems. The first, and most severe, is the vibration encountered if the penetration rate is too fast. As the bit rotates the cones pass over the material and the teeth or inserts chip away at the material being drilled. Unconsolidated material, however, has voids in it. When the bit passes over a void in the material it only contacts part of the bottom of the hole. As each roller passes through the void, the tool string moves down, as the roller falls into the void, and then back up as the roller climbs out. This continual up and down motion results in shock loads being transmitted from the bit, through the tool string, to the machine.

To drill through an unconsolidated formation it is necessary to reduce the load on the bit as it is passing over the voids. It is also helpful to isolate the shock loading to the tool string. This is accomplished by first reducing the pulldown speed. If reducing the pulldown speed does not reduce the vibration to the machine to an acceptable limit, it may even be necessary to hoist the bit above the void and then lower the bit a small amount at a time so as to chip away at the sides of the void a little at a time. Reduction of the rotary speed will also help reduce the vibration of the tool string. This is the last procedure that should be tried since if the pulldown speed is left high and the rotary speed diminished, the vibration will be just as severe, only at a different frequency.

Unconsolidated material presents another problem due to the fact that the voids in the material may allow the bailing air to escape through the sides of the hole, rather than passing along the drill pipe and exiting through the top of the hole. This loss of air reduces the volume of air available to bail the hole, causing the cuttings to fall to the bottom of the hole and be reground by the bit. This further reduces the penetration rate since these cuttings must be ground up by the bit and bailed out of the hole or they will plug the hole. Unconsolidated material may also cause the hole to cave in. This creates problems due to the sudden addition of material into the hole and the resultant loss of bailing velocity due to the increased diameter of the hole.

If unconsolidated material is causing the loss of bailing air volume or caving of the hole it is necessary to continually clean the hole as the recycled cuttings or the caved material will plug the hole. Closely monitor both the bailing air pressure and the flow of cuttings from the hole. If the air is being lost the air pressure will remain constant but the flow of cuttings will stop or drastically decrease while penetration does not decrease. Continue drilling for a few feet to try and get past the leak. If the bailing air pressure starts to rise, the hole is plugging. Immediately hoist the tool string until the pressure drops and allow the drill string to rotate for a few moments to clear itself. Then lower the tool string to the bottom of the hole and clean it out. It may be necessary to regrind the cuttings to make them small enough to seal the leak and be bailed out of the hole by reduced air volume. Once the hole is clean, repeat the hoisting and lowering procedure every 2 to 3 feet (0.3 to 0.6 m) to keep it so.

If the material tends to cave in from the sides of the hole, the tool string can become stuck in the hole quickly. If the caved material is small, it will fit between the cones of the roller and fall to the bottom of the hole. The hole can then be cleaned out using the same procedure as for a leaky hole. If the caved material is large it will be necessary to pull the tool string out of the hole and then redrill the caved material.

NOTE: Be very cautious when drilling in formations which tend to cave in easily, especially if the material caves in large blocks. Should the material that caves into the hole be too large to lift with the rotary drive unit or too hard to break with the top of the bit, the tool string will have to be abandoned in the hole.

Experience will dictate what procedure to follow when encountering material which tends to cave in. When the formation is unfamiliar always be cautious. Caution may result in lower production, but it could save a great amount of work and a complete tool string should the tool string become stuck. Always clean the hole often and monitor the air pressure constantly. If the air pressure starts to climb, hoist the tool string immediately — do not wait to see if the pressure will level off or not. By the time it is determined what the air pressure will be, the hole is plugged. Cleaning the hole often accomplishes two things.

First, it removes the caved in materials from the hole. Second, it loosens any potentially hazardous material and causes it to cave in while the stool string is being hoisted. If the hole caves in while in the hoist mode there is a better chance of recovering from the cave in.

If the hole should become plugged there are two ways to recover the tool string. Each method depends upon what type of material has plugged the hole. If the material that is plugging the hole is small (less than 6 inches [15.2 cm] square), it is possible to grind the material sufficiently to allow it to pass between the lobes of the bit and fall to the bottom of the hole. This condition can be observed if the bailing air pressure increases over normal working range. Large, chunky material will let the bailing air through, while fine material won’t. Also, when attempting to hoist out of the hole the tool string will not vibrate greatly, due to the small size of the material. Large material will cause the tool string to be shocked every time a lobe on the bit strikes the block.

To recover the tool string from a hole plugged with smaller material hoist the bit until it runs into the plug and stops hoisting. With rotary motion turning at approximately 50-60 RPM keep high hoist loading on the bit and allow the bit to work its way through the plug. Monitor the rotary motor loading (current) and reduce the hoist loading (force) to keep the load in the lower portion of the bar graph. Once the plug is passed, clean the hole and return to drilling. The main air pressure may or may not exceed the safety valve setting and cause the main air compressor to overheat. If the safety valve opens when the hole is plugged, continue to attempt to free the tool string. The safety valve will close when the plug has been removed. If the compressor overheats and shuts down continue to attempt to free the tool string without the compressor. Allow the compressor to cool for a few minutes and restart it. Continue this procedure until the tool string is free.

If the material plugging the hole is large it will be necessary to try and force the material back into position enough to let the bit go past, and then try and redrill through the plug. Large material is indicated when the tool string experiences severe vibration when being hoisted. To free the tool string apply maximum hoist power. If the plug does not clear itself within a few moments lower the tool string a few feet if possible and try again.

If the plug does not clear itself after repeated attempts at clearing it, there are two options available. The tool string can be abandoned immediately without further trial or an attempt to drill through the plug using the top of the bit can be made. In either case the hole being drilled will have to be abandoned. In the first case the cost of the abandoned tool string is known, while in the second case a gamble is being taken as the bit and stabilizer will almost certainly have to be scrapped and there is no guarantee that the rest of the drill pipe will be recovered. If it is decided to abandon the tool string, attempt to unscrew a section of pipe to recover some of the tool string. If this cannot be done, lower the tool string to the bottom of the hole and then, using a suitable burning torch, cut the drill pipe at ground level. It will be necessary to move over an existing hole to remove the stub of pipe from the rotary drive unit.

CAUTION: Before cutting the drill pipe verify that the main air compressor is shut down.

Burning the pipe with the main air compressor running may cause a fire or explosion as hot slag is introduced to the main air stream or may cause hot material to be blown back onto the torch operator.

If an attempt is to be made to free the drill string by drilling with the top of the bit, apply only enough hoist pressure to keep the vibration and rotary motor load levels in an acceptable range. Vary the hoist pressure by alternately placing the hoist/pulldown selector in the hoist and neutral positions. Vary the rotary speed to help reduce vibration. Drilling through a large block with the top of the bit can be a lengthy procedure and it is important to prevent damage to the rest of the machine. Once the tool string is free, check the bit and stabilizer as well as the drill pipe for damage. Replace components and move to a new location for the hole. Do not try and drill the same hole again as this will almost certainly cause the tool string to become stuck again.

WET OR STICKY FORMATIONS

Drilling in wet or sticky formations presents three possible problem areas. The three problems that may be encountered are coating of the hole and pipe with material, conglomeration of the material into pieces too large to remove with the bailing air stream and caving of the hole. Either of these problems may be present, or any combination of the three may be present at the same time.

Drilling in wet formations follows the same practices as drilling any other formation. Drilling wet formations, however, requires that particular attention be paid to the bailing air pressure and penetration rates. Wet formations are more susceptible to plugging the hole, but recovering the tool string from the plugged hole is easier than with unconsolidated material.