1.Characteristics of diamond drill
1.1 Strength and Thermal Stability of Diamond Bits
Diamond has the characteristics of high hardness, high strength and high thermal conductivity, but it has the disadvantages of brittleness and poor thermal stability. It is easy to be broken by impact, and easy to oxidize and graphitize under high temperature conditions. Temperature has a great influence on the strength of diamond, and the strength of diamond decreases with increasing temperature. When the diamond drill is heated to 300 ℃ in the air, it starts to oxidize. At 800 ℃, the weight starts to decrease and the color of the crystal changes. When the temperature reaches 900 ℃, the diamond quality changes significantly, showing looseness and easy to break. It burns cleanly and forms carbon dioxide after burning.
1.2 Adaptability of diamond drill
The adaptability of the diamond bit to the formation is very strong. As long as the corresponding drill bit is selected according to different formations, the long life and high efficiency of the diamond drill bit can be achieved. When the rock is in the 8-9 grade, it is more suitable to use a pregnant setting or electroplated drill bit with a hardness of HRC34-42 and a diamond size of 60-100. However, when encountering relatively hard granite veins or quartz veins, this kind of bit is not suitable. A bit with softer carcass hardness and finer diamond grain size should be used.
2. The main problems in diamond bit drilling
2.1 Burnout of diamond drill bits
Burnout is the most serious problem in diamond bit drilling. Severely burning the drill can completely burn the drill bit carcass, or even completely burn or burn out the drill’s steel body, reamer, inner tube short joint or core pipe, or burn the drilling tool and core together, causing a stuck accident. Processing is very difficult. After a severe burnout, the entire bit will be scrapped. Some diamond drill bits only cause drill burn accidents with only a few centimeters or meters of footage, and the loss is very large. Lightly burnt drill bits can still be used, but the strength of the drill bit will decrease significantly. The diamond drill bit wears a few or a dozen wires per round, and the life of the drill bit will decrease by about 60%.
2.2 Abnormal wear of diamond drill bits
Abnormal wear is mainly caused by foreign bodies or hard rock particles in the pores, partly due to light burning. When the diamond drill bit is drilled, the central part of the carcass has poor heat dissipation conditions, poor cooling of the diamond, and easy to cause local light burn, resulting in reduced diamond strength and increased wear, which will cause slotting. Once the groove is formed, the rock powder in the groove is not easy to be discharged, the diamond is difficult to cool, and the graphitization phenomenon is aggravated, causing the drill to be scrapped. In recent years, slotting phenomenon has often occurred in the use of impregnated diamond drill bits, and grooves have often appeared on the drill carcass, which shortens the service life of the drill bit.
3.Diamond Bit Burnout and Cause Analysis of Abnormal Wear
3.1 Reasons for drilling methods
Diamond diamond bits generally need to be at a higher speed to fully function. If the speed of the vertical shaft is too high, the pump volume cannot meet the requirements, and the insufficient supply of flushing liquid will cause the drill to burn lightly and increase the wear of the drill. In addition, in weak or broken formations, the pressure is too large, so that the diamond cuts into the rock too deeply, blocking the circulation of the water body, the rock powder cannot be removed in time, the water circulation conditions are deteriorated, and the drill bit cannot be effectively cooled, and the burnout will occur.
3.2 Reasons for water circulation
The flushing fluid plays the role of removing rock dust and cooling the drill bit during the drilling process. Keeping the waterway unobstructed is very important for the performance of the drill bit. If the inner and outer diameter of the diamond drill bit is too worn, the drill nozzle will become smaller, which will affect the cooling effect on the drill bit. Sometimes the drill bit is too large in diameter, the core is thick, or the outer diameter is too small, and the annular gap between the drill bit and the hole wall will be reduced. Cooling effect of rinsing fluid on the drill. In addition, the water pipe of the drill pipe or double pipe joint is blocked or the drill pipe is not tightly connected due to the wear of the threaded fastener, which will cause insufficient supply of flushing fluid at the bottom of the hole and cause the drill to burn lightly. When you drill down, drill the bit to the end. The bite’s nozzle is blocked by rock powder under the impact of falling impact. It will rush to drill before the hole returns, and it will also cause the bit to cool down and burn out.
4. Experience of using diamond drill
4.1 Install the machinery correctly and design the drilling structure reasonably
Small-diameter diamond drilling generally has high rotation speed and large torque, so the rig installation should be round, level and stable. The machinery installation site should be flat and firm, and the center of the crane, vertical shaft, and drilling should be on a straight line. When drilling, the inclination of the drilled hole should be controlled. The large bending of the drilled hole will cause the diamond drill to vibrate violently and affect the service life of the drill.
Reasonable drilling structure design is very important for the effectiveness of the drill. Generally, when drilling in a weathered layer, the lower three layers of casing should be adopted, and the three layers of casing should be layered to protect the drilling rig. It is only stable and stable under high-speed rotation to obtain good results.
4.2 Reasonable choice of diamond drill bits
At present, there are many types of diamond drill bits, and different types of drill bits have different characteristics, so when drilling, the drill bits should be reasonably selected according to the changes in the formation lithology. The distribution of sandstone in our province is relatively common, and most of them have four types of weathering zones: full, strong, weak, and micro. In full and strong weathering layers, diamond drill bits are generally not suitable. Ordinary or needle-shaped hard alloy heads are more suitable; in weak weathering layers, 3. Micro weathered layers and fresh rock layers should be drilled with artificial impregnated diamonds.
In addition, diamond drills with different carcass hardness and grain size should be selected according to the drillability, abrasiveness, and integrity of the rock in order to obtain better results. For example, in the drilling of 10 to 11 grade granite, diamond drill bits with a hardness of HRC 36 to 38 should be used, and the diamond grain size should be 80 to 100 mesh. In this way, the diamond drill bits can achieve higher drilling efficiency and drill bit life. If the choice of diamond bit is not adapted to the formation conditions, it will cause problems such as bit slippage, increased wear, low drilling efficiency and short bit life.
4.3 Reasonable drilling parameters
① Vertical shaft speed: Diamond drilling should be maintained at a certain vertical shaft speed to achieve high drilling efficiency. However, it can’t be considered that the higher the speed, the better, the speed is too high, and the burnout will occur if the water supply cannot keep up; although the table efficiency is improved, the drill life is significantly reduced. At present, the vertical shaft speed is generally not required to exceed 1000 r / min during drilling, and normal drilling is usually 500 to 800 r / min. In practice, when starting drilling each time, the initial rotation speed is preferably 200-300r / min. After a few minutes of running-in, the rotation speed is increased to the normal rotation speed, which can improve the drilling efficiency and extend the life of the drill.
② Drilling pressure: The pressure should be appropriate and uniform, and it should not be too large or too small. Excessive drilling pressure, too much diamond cut into the rock, will block the waterway, cause poor cooling of the diamond, and lead to burnout. Generally, the initial pressure is 1 to 2 kN, and the normal pressure is generally 4 to 8 kN. When drilling into broken rock formations or soft broken rock bands, the rotation speed should be appropriately reduced, the pressure should be reduced, and the water delivery volume should be increased. Because the pressure is too large and the diamond is cut into the rock too deeply, it will cause water blocking and affect the cooling of the diamond bit. .
③ Pumping volume: The pumping volume must be uniform and continuous during diamond drilling. Reasonably grasp the pumping volume and pumping pressure. Generally the pump volume should be controlled between 30 ～ 50L / min, and the pump volume should be adjusted in time according to the drilling speed of the rock formation. Adjust the size of the drill bit in time to ensure that the return flow rate of the flushing liquid is greater than 0.3m / s, so as to effectively cool the drill bit, remove rock dust and keep the hole clean. When drilling, when the distance from the bottom of the hole is more than 0.5m, the pump should be turned on and rinsed. After the hole returns to the water, it can be gently pressed and swept to the end.