Among the mechanical properties of rock, the compressive capacity is the strongest, and the tensile, shearing and bending resistance is much worse. However, the underground Drilling Machine
is difficult to directly stretch and shear the rock directly due to the limitation of the working space. bending. This requires the use of a Drill Bit
to convert the pressure and torque provided by the equipment into tensile, shearing, and bending of the rock. In order for the drill bit to be effectively drilled into the rock formation, the problem should be solved in the following five aspects.
1. Drill structure and cloth teeth: The bit structure and the cloth teeth determine the free surface of the shape, the size of the free surface, and the free surface. As can be seen from Figure 4, Figure 5 and Figure 6 below, the drill in the early stage provides a free surface for later drilling.
The drill bit that was drilled in advance created the free surface of the rock mass for the next drill bit. After the rock mass is stressed, the unconstrained free surface provides space for the operation of small rock blocks. From Figure 4, the pressure on the tool has been transformed into shear force, tensile force or bending moment, and the rock mass is under the action of these forces. Peel off from the large rock mass. The alternate operation of two or more drill bits can provide free faces to each other (Fig. 6), which greatly improves the drilling efficiency, thereby improving the rock breaking ability and reducing the excessive power demand for the host. For the incoming rock, the different rock formation properties should be matched with the drill bit. The structure of the drill bit, the shape of the cutter on the drill bit (chops, teeth, etc.) and the arrangement (dense, spatial angle) should be based on the strength of the rock mass. The degree of development of the joints, the inclination angle of the joints, the void ratio, the structural spacing, the cohesive force of the shear strength of the rock mass and the friction angle are set in a targeted manner, and the universal working bit does not exist.
2. The movement of cuttings: The cuttings have a hindrance to the drilling of the drill bit in the hole, the resistance of the cuttings is small, and the equipment capacity is used for effective work. With a drill bit, a rock-in-tube drill, a slag bucket and other drill bits to match the drill hole, the principle of screw conveyor is generally used to convey and guide the movement and discharge of the slag chip. It is less labor-intensive to drill the bit with smooth flow of slag.
3, the failure form of the tooth: the tooth is a tool directly acting on the rock. There are four main failure modes in use: First, the friction heat is too large, and the contact surface between the tooth and the rock layer is softened (or even melted) layer by layer. The pressure and friction flow; secondly, the wear resistance is poor; thirdly, the drill teeth working on one drill bit are less and overloaded; and the impact load is excessively broken. Others are hard alloys, hard alloys and unqualified welds. The pick-up of overheating and softening is a poor thermal strength of the carcass material; a large furrow appears on the carcass, indicating that the hardness of the carcass is much lower than the hardness of the abrasive; the visible furrow appears in the hard alloy, which is too soft for the hard alloy; The reason for the loss of cemented carbide is that the brazing quality is poor; a few teeth overloading operations are irregular teeth of the drill bit. At present, the biggest cause of tooth failure is that the tooth quality is too poor. Firstly, the pick-up produced by professional manufacturers has a low market share. Non-professional manufacturers basically do not understand what performance of the teeth can meet the requirements of use; secondly, the user buys the teeth when the figure is cheap. , regardless of cost performance.
4, the use of several types of drills: the purpose of the combination of several drills is to provide a free surface that facilitates rock fragmentation. After the rock is broken, the broken rock is taken out. This involves two problems. First, the structural interaction of the drill bit provides the possibility of facilitating the free surface of the rock. Second, the drilling depth of each drill is mastered. The most commonly used drill bit matching mode for rotary drilling bit into rock is suitable for hard rock (15≤Ra≤200MPa): cone spiral drill bit + rock-socketed drill + hard rock sand bucket + other tools (such as large stone fishing bit ) and suitable for soft rock (5 ≤ Ra ≤ 20MPa) mode: flat-headed spiral drill bit + hard rock sand bucket. There are also rotary drilling rigs with reverse circulation method and Rotary Drilling Rig
with large-diameter pneumatic down-the-hole hammer method, but these two methods can not reflect the advantages of rotary drilling rig, not much to explain here.
5, how to fish large blocks: the use of Drill Pipe
with a drill bit to directly remove the large stones falling off the hole is the most effective way to obtain large rocks in the rotary digging method. The operator should perceive that the large rock has fallen off from the rock mass. After the large rock falls off the rock mass, it is judged whether the crushed slag or the whole is salvaged according to the characteristics of the rock. There is currently no shortage of large rock tools from the hole in the market. However, it is necessary to solve the problem of drilling large rocks in deep holes, and large rocks cannot be drilled and cannot continue.