Rock-in test of SR200R rotary drilling rig and discussion on some problems
From August 9, 2007 to September 7, 2007, Beijing Sany Heavy Machinery Co., Ltd. used the newly developed SR200R rotary drilling rig to carry out a rock-entry test. The test site was "Yongfuqiang Quarry" in Zhoukoudian, Beijing. The rock-entry geology is fully weathered to unweathered granite. On September 7th, the test personnel drilled for dozens of visiting customers and experts from the Pile Workers Association. The weakly weathered granite 118mm was drilled in 4 minutes with a φ1250 rock-socketed drill bit, and the weakly weathered granite was drilled in 2 minutes with a φ1000 single-head single screw drill bit. 196mm. On-site experts and customers are quite satisfied with the effect of rock entry. The relevant experiment records are shown in Table 1 "Field Test Records".
Geographical environment of the rock test site
Geographical environment of the rock test site
Test conclusion: It has been confirmed that the SR200R rotary drilling rig can realize drilling in granite with Ra≤210MPa. It has been proved that the use of operating techniques can produce impact on hard rock, thereby improving the rock-entry capacity and efficiency of the drilling rig. It has been proved that by alternately using drill bits of different structures, two or more types of drill bits can form a free surface with each other, which improves the efficiency of rock drilling. It has been confirmed that the vertical accuracy of the drilling is 1/100.
Through the drilling test of limestone and granite with the SR200R rotary drilling rig, I have experienced and realized the following six problems:
1. The basic conditions for the main engine of the rock drilling rotary drilling rig:
The law of energy dissipation in rocks and the dynamic fracture criterion clearly point out: "When the loaded energy is less than a certain threshold, the loaded energy does not participate in crack propagation at all, and all is useless dissipated energy; when the loaded energy reaches the dynamic fracture criterion, the rock Dynamic destruction, energy dissipation without power consumption is about 15%.” With this theory as a starting point, the rock-entry rotary drilling rig must have a large pressurizing capacity and a large power head power (large torque and high speed). First of all, the rock can realize the penetration of the rock joints and the formation of cracks under the action of large pressure, and the cohesion disappears so that it can be separated from the rock mass only by overcoming the frictional force; the small rock mass can be squeezed to freedom under the pressure. When the crack propagates to the free surface, the small rock mass is sheared and separated from the rock mass; it is also possible to realize that the complete rock with RQD greater than 75 can form cuttings under the action of rolling. Only when the intact rock is turned into fragments and debris can drilling can be achieved. Secondly, the hydraulic power head with high torque and high speed is a necessary condition for realizing impact operation. On the cutting track of the bit picks, the picks hit the protruding rock mass, and the power head is decelerated. When the picks pass the protruding rock mass, the speed will accelerate and rush towards the new protruding rock mass. The body is constantly impacted. The greater the speed difference between high speed and low speed, the greater the impact of protruding rock mass. Only the hydraulic power head with high torque and high speed can increase the speed difference between high speed and low speed. For rotary drilling rigs (power Smaller rock-breaking machinery) In terms of rock entry, the impact can effectively create some large loads to cross the "threshold value" of brittle fracture or plastic yield of the rock, and the rotary drilling rig must achieve the impact process in order to enter the rock. From the perspective of rock entry conditions, the equipment's own anti-vibration ability must be improved. Vibration sources in rock entry operations are the interaction between the drill bit and the rock, the bending deformation of the drill pipe, the eccentricity of the drill bit, and the uneven distribution of the quality of the drill tool. The weight-on-bit continuously circulates in the pressurization, decompression, and floating modes. This cycle is controlled by the operator, and its frequency is about 0.10 to 0.3 Hz, which is also one of the vibration sources of rock drilling. Secondly, during the rock-entry operation, one or several drill teeth continuously hit the raised rock to form an irregular "brake" phenomenon. The higher the drill speed, the more uneven the rock, the higher the frequency of "brake". This vibration sometimes The frequency is very high, and the regularity of vibration excitation, superposition and exhaustion is also very poor. From the above vibration sources, the damage to the equipment caused by forced vibration cannot be offset by active vibration, and the equipment's own anti-vibration ability must be improved.
Judging from the "threshold value" of brittle fracture or plastic yield of rock fracture, it is required that sufficient force must be applied to the rock. This requires that the rock-entry rotary drilling rig must have sufficient weight to achieve the large pressurization capacity of the drilling rig.
In short, large pressure, high power of the power head and sufficient weight of the drilling rig are the basic requirements for the rotary drilling rig itself when entering the rock.
2. The penetration of rotary digging into rock is realized by impact:
From the perspective of the way in which the force is applied to the rock during rock drilling, various drilling rigs strive to achieve an impact on the rock, because the impact causes the force output by the equipment to far exceed the static output. For example, the down-the-hole hammer directly impacts the rock through the impactor; in reverse circulation drilling, the cone hob and wedge hob are used to realize the impact on the rock during the rotation process through the different gyration radius of each point on the hob.
The rock drilling operation of the rotary drilling rig realizes the impact on the rock by controlling the weight on bit. The weight-on-bit continuously cyclically floats, pressurizes, and depressurizes three beats in the mode shown in Figure 2. During pressurization, the rotation resistance of the drill bit increases and decelerates. When decompression, the rotation resistance of the drill bit decreases and accelerates. From the momentum and impulse conversion equation (), it can be seen that the greater the speed change and the shorter the change time, the greater the impact on the rock. Through the impact, the problem of insufficient force of the drilling rig on the rock is effectively solved, and it is difficult to exceed the low load value of the broken rock. The impact on the rock is also conducive to the formation of free surfaces. During the continuous rotation of the drill, the cutter head intermittently impacts the rock, resulting in continuous formation of unevenness in the direction of the cutter movement, and new bumps are formed after the old bumps are destroyed. These irregularities are the free surface for drilling. Both large free surfaces and small free surfaces are beneficial to the deformation of the rock after being loaded (especially under impact load) and peeled from the whole rock mass to form cuttings, thereby increasing the drilling efficiency. The large pressurizing capacity of the drilling rig and the large power head power are the equipment conditions to achieve rock entry, and the conversion of the equipment capacity into effective rock breaking capacity must be reasonably coordinated by the pulse pressurizing operation mode. From Figure 2 "Reasonable Pressure Mode for Rock Drilling", the rock drilling pressure mode of rotary drilling rig is a combination of dynamic and static loads, and static load can increase the peak force of impact dynamic load. The static load can also press the drill teeth on the rock at the bottom of the hole, so that the dynamic load is directly transferred to the rock, reducing power transmission loss and power loss from elastic collision. The dynamic load is conducive to make the load acting on the rock exceed a threshold value.
The cutting trajectory formed by the rock-socketed tube drill in the rock-entry pressure mode
3. The effective transfer of the rock penetration capacity and pressure mode of the rotary drilling rig and the basic requirements that the drill pipe should meet:
When the rotary drilling rig is drilled into the rock, the torque and pressure of the equipment and the pressure mode of the equipment are transmitted on the rock through the drill pipe. The drill pipe plays a vital role in the transmission of the ability of the main engine and the way of action on the rock. . In order to realize the impact on the rock, the operator must control the pressurizing device to pressurize, depressurize, and float the drill rod in a cycle to make the rock subject to impact. If this impulsive pressure is absorbed by the elastic deformation of the structure in the transmission process, the rock will not get an effective impact. In this test, it is a single-section drill pipe, which is conducive to the transmission of controllable WOB. Figure 2 shows a reasonable rock pressure mode. The pressure may be attenuated by the transmission of multi-layer rods during the large and small cycles, and the multi-layer drill pipe is transmitted The pressure mode problem needs to be considered. The smaller the number of drill pipe layers, the more conducive to the formation of the impact of the drilling rig on the rock. When the multi-layer drill pipe is not fully extended, the greater the rigidity of the drill pipe buffer spring, the more conducive to the transmission of pulsed WOB. Excessive weight-on-bit at the peak point of pulsed weight-on-bit may cause local instability and deformation of the drill pipe or fatigue fracture due to repeated radial alternating loads in a certain part of the instability. Therefore, the drill pipe body should be thickened to enhance the radial deformation resistance; the material elasticity should be increased to enhance the fatigue resistance under alternating loads.
4. The drill bit must be paid attention to during rock drilling operations:
Among the mechanical properties of rocks, the compressive resistance is strong, and the tensile, shearing, and bending resistance is much worse. However, due to the limitation of the working space, it is difficult for underground drilling tools to directly stretch, shear, and bend the rock directly. . This requires a drill bit to convert the pressure and torque provided by the equipment into stretching, shearing, and bending of the rock. To make the drill bit effectively drill into the rock formation, the problems should be solved from the following five aspects. 1. Drill bit structure and tooth arrangement: The drill bit structure and tooth arrangement determine what free surface, the size of the free surface, and how many free surfaces can be drilled. It can be seen from Figure 4, Figure 5, and Figure 6 that the early drilling of the bit provides a free surface for the later drilling.
Figure 4. Free surface formed by taper spiral drill bit drilling
Figure 5. Free surface formed by taper auger drilling
Figure 6. Free surface formed by alternate operation of cone spiral and barrel drill
The drill bit drilled earlier creates a broken free surface for the next drill bit. After the rock mass is stressed, the unconstrained free surface provides space for the movement of small rock blocks. From Figure 4, it can be seen that the pressure on the cutter has been converted into shear force, tensile force or bending moment. The rock mass is under the action of these forces. Stripped from the large rock mass. The alternate operation of two or more drill bits can provide free surfaces to each other (as shown in Figure 6), which greatly improves the drilling efficiency, thereby improving the rock breaking capacity and reducing the excessive power demand for the main engine. For rock entry, different rock formation properties must be equipped with drill bits in a targeted manner. The structure of the drill bit, the shape of the tool on the drill bit (pick, bucket tooth, etc.) and arrangement (density, spatial angle) should be based on the strength of the rock mass. , The degree of joint development, the inclination angle of the joint, the void ratio, the structure spacing, the cohesion of the shear strength of the rock mass, and the friction angle are set in a targeted manner. Universal operation drill bits do not exist.
2. Movement of cuttings: cuttings can hinder the drilling of the drill bit in the hole, the resistance of cuttings is small, and the equipment capacity is used for effective work. Use spiral drill bits, rock-socketed tube drills, slag buckets and other drill bits to cooperate with drilling, and generally use the principle of screw conveying to transport and guide the movement and discharge of slag chips. Drilling with a drill with smooth flow of slag and chips is less labor-saving.
Figure 7. The structure of slag cuttings formed on the rock-socketed tube drill
Figure 8. Single-head single-screw spiral
Figure 10. Slag cuttings enter the drill barrel from the gap of the spiral guide bar
3. Tooth failure mode: Tooth is a tool that directly acts on the rock. There are roughly four main failure modes in use: First, the frictional heat is too large, and the contact surface between the tooth and the rock layer is softened (or even melted) layer by layer and is squeezed by the rock. Pressure and friction flow; secondly, poor wear resistance; thirdly, there are few drill teeth working at the same time on one drill bit and overload operation; fourthly, the impact load is too large and the teeth are broken. Others include the cemented carbide is too soft, the cemented carbide and the carcass are unqualified. Picks that fail due to overheating and softening belong to the poor thermal strength of the carcass material; large furrows appear on the carcass, indicating that the hardness of the carcass is much lower than the hardness of the abrasive; the cemented carbide has visible furrows, which is too soft for the cemented carbide; The reason for the loss of cemented carbide is poor brazing quality; a small number of tooth overload operations are caused by irregular tooth arrangement of the drill bit. At present, the major cause of tooth failure is the poor quality of the teeth. Firstly, the picks produced by professional manufacturers have a low market share. Non-professional manufacturers basically do not know what performance teeth can meet the requirements of use; secondly, the user buys the teeth cheaply. , Regardless of cost performance.
Figure eleven, failed picks
4. Cooperative use of several drill bits: The purpose of the cooperative use of several drill bits is to interactively provide a free surface that is conducive to rock crushing. After the rock is broken, the broken rock is taken out. This involves two issues. The structure interaction of the drill bit provides the possibility of a free surface that is conducive to rock fragmentation; second, the control of the drilling depth of each drill tool. Commonly used drill bit matching modes for rock drilling with rotary drill bits are those suitable for hard rock (15≤Ra≤200MPa): cone spiral drill bit + rock-socketed barrel drill + hard rock sand bucket + other tools (such as large rock fishing bit) And suitable for soft rock (5≤Ra≤20MPa) mode: flat spiral drill bit + hard rock sand bucket. There are also rotary drilling rigs with reverse circulation construction method and rotary drilling rigs with large-diameter pneumatic DTH hammer construction methods, etc., but neither of these two construction methods can reflect the advantages of rotary drilling rigs, so I will not explain more here.
5. How to get large rocks: Using a drill pipe with a drill bit to directly get the large rocks that fall off the hole is an effective way to get large rocks in the rotary excavation method. The operator should feel that the large rock has fallen off the rock mass. After the large rock has fallen off the rock mass, it is necessary to judge whether it is slag removal after crushing or the whole salvage according to the characteristics of the rock. At present, there is a lack of tools for salvaging large blocks of rocks from the hole in the market. However, the problem of fishing large rocks in deep holes must be resolved. If the large rocks cannot be removed, drilling cannot continue.
5. We must strive to reduce equipment damage and accidents caused by vibration:
The causes of equipment vibration are explained in the "Basic conditions for the main engine of the rotary drilling rig to enter the rock". The vibration hazards are as follows: ① The equipment structure is accelerated by the stress cycle under the action of vibration, and the structure has premature fatigue failure. ②Because of the uncertainty of the vibration direction, the structure of the drilling rig is complicated to load, and excessive triaxial forces are formed inside the structure, and the equipment is easily damaged. ③Due to the excitation, superposition and failure of vibration, many structures change from static load to dynamic load, and most of them are impact load, which puts forward high requirements on the equipment. ④Accelerate the development and growth of structural defects, such as welding microcracks and the transition layer in the hardened zone of the heat-affected zone, the internal defects of the material, and the heat treatment micro-defects will absorb energy from the vibration to develop and grow.
In order to reduce equipment damage and accidents caused by vibration, the design and growth of a rotary drilling rig suitable for rock drilling should be based on the following points: ①Calculate structural reliability from the perspective of dynamic load and fatigue. ② Strictly select materials, select appropriate processing techniques and strictly implement them. ③Reduce the application of structures that are prone to failure in vibration (such as screw connections).
Sixth, some suggestions for the use of rock drilling rotary drilling rig construction:
1. The effective service life of the tool is an important factor affecting drilling efficiency and economy, and qualified picks (or bucket teeth) must be selected.
2. Choose one kind of drill rod and several kinds of drill bits that are compatible with the project.
3. Different operating methods should be adopted when drilling into geology with different lithology.
4. Control the depth of each drilling, master the method and timing of slag removal, and the cooling of the tool.
5. The drilling efficiency of the rock formation is 1/20 to 1/5 of that of the soil layer, and the equipment and tools are much more worn than the soil layer. It is necessary to choose a project with a reasonable project cost.