Our technicians and drilling specialists are on call to help you solve your support pack and drilling issues. Here are a few of the common problems we encounter, what they mean for your project, and how to handle them.
- Carbide Pop Out – When the piston strikes the bit without the bit being tight against the bottom of the hole, inertia can force the buttons to pop out of the sockets.
- Bit Shank Failure – If the bit is not held firmly against the bottom of the hole excessive longitudinal movement between the bit splines and the chuck splines can generate extreme temperatures. This can cause a transfer of metal between the bit and chuck commonly known as cold welding. Once heat damage has occurred, failure is inevitable.
- Residual Stress Failures – If the hammer is not held firm against the formation, the energy generated by the piston cannot be transmitted correctly and a large portion will remain in the piston. These energy vibrations can initiate failures in many different ways including piston, feed tube and/or loosen connections.
Best Practices for Drilling
In a wet hole or unconsolidated material, it will be necessary to push (thrust) the hammer slowly to sufficiently clean the hole as the hammer is advanced. Care should be taken to limit the power developed by the hammer when drilling in these conditions. When the edge of a boulder is encountered and rotation becomes erratic or stalls, pull the hammer off enough to clear the edge of the boulder and slowly push back up to the edge until it is drilled off. Repeat the process until the rotation becomes smooth. When a solid formation is encountered, the rotation will stabilize and the hammer will sound strong and smooth. Stay alert to the possibility that the solid formation may be a large boulder with loose material below. As soon as the hammer sound changes or the rotation torque fluctuates, pull the hammer and bit off bottom. Keep the rotation slow (20 to 30 rpm’s) and thrust back up to bottom carefully to continue drilling.
It is good practice to monitor the hole flushing. It may be necessary to pull the hammer off bottom periodically to flush the hole until all the cuttings have been removed. Maintain rotation during this procedure.
Drilling with water only will develop mud rings and hinder hole cleaning. These mud rings can become severe enough to cause hammers and bits to become stuck in the hole. Proper mixing of the required poly/foam is important.
Bit inspection should be done after every bore. When the carbides have wear flats that are ½ the diameter of the insert they are subjected to severe radial forces. Although carbide inserts can withstand extreme longitudinal loading, they are easily fractured when subjected to sever radial loading. In addition, when the carbide inserts are severely worn, drilling speed is reduced dramatically. After the bit has experienced carbide insert failures, further drilling allows the steel bit to erode quickly. It is not particularly evident when only one insert is broken, but when more than one insert are broken is when the steel matrix of the bit is damaged beyond repair.
Using Foam and Polymers
Drilling with foam and polymer has many advantages and will improve drilling in certain ground conditions. Some benefits include:
- Ability to clean the hole with low annular velocity. Using a quality foam with the correct mixture may allow for sufficient hole cleaning with the annular velocity as low as 150 feet (46 m) per minute.
- Utilizing a strong foam/polymer mixture, low stability formations can be drilled with minimal borehole erosion. This mixture reduces the need for high annular velocity and will suspend the cutting during rod changes. The polymer foam will form a filter cake on the borehole wall, reduce hole collapse and inhibit swelling of clays.
- Foam injections also aids when drilling in boreholes where water intrusion creates high back pressures. The foam mixture will reduce the head pressure lowering the peak unloading pressure and operating pressure.
- Light mixture creates large ‘bubble bath’ bubbles
- Heavy mixture creates ‘shaving cream’ bubbles
- A heavy foam mixture will create the best cutting carrying capabilities and low quality foams will have a tendency to break down quickly in the hole allowing cuttings to fall out of the solution.
- When finished drilling with foam, you need to rinse all drilling tools with clean water and lubricate them properly. Prolonged exposure to the atmosphere creates a corrosive reaction between the steel and the foam. Corrosion stress risers are a common cause of drilling tool failures.
The polymer/foam mix we recommend is environmentally friendly. You will pump between 1 to 2 gallons per minute of the polymer/foam mixture to assist airflow in cleaning the pilot hole.