The working feature of air DTH hammer is that it is powered by compressed air (including compressed air containing foam), and the energy of compressed air generated by compressor passes through DTH hammer, an energy conversion device. High-frequency energy impact is generated on the rock to be broken. When this energy impact reaches the critical crushing work of rock, volume crushing occurs. Through the rotary drive of drilling rig and drill pipe, the continuous crushing ability of rock is formed. At the same time, after work, the gas cools the drill bit and discharges powder at a certain wind speed to achieve the purpose of drilling.
From the point of view of rock breaking, DTH hammer drill mainly impacts rock breaking, while rotation changes the position of impact rock breaking and plays an auxiliary role in rock breaking. Therefore, drilling efficiency depends largely on the performance and quality of the impactor. Its important features are high drilling efficiency in hard rock, long bit life, low rotation speed, small torque and light axial pressure.
2. Working principle of air DTH hammer
As shown in Figure 2-5, there is a piston in the cylinder. When compressed air enters the upper cavity of the cylinder from the air inlet, the pressure of compressed air acts on the upper end of the piston, pushing the piston to move downwards and impacting the tail of the drill bit when it reaches the end point. During the downward movement of the piston, the gas in the lower chamber of the cylinder is discharged from the exhaust port. On the contrary, when compressed air enters the lower chamber from the exhaust port, the piston moves upward, and the gas in the upper chamber is exhausted from the air inlet. If the direction of air intake and exhaust is constantly changed, the reciprocating motion of the piston in the cylinder can be realized, thus repeatedly impacting the tail of the drill bit and realizing the continuous operation of impacting the drill bit. The aperture range of NU-MA pneumatic DTH hammer is 89 ~ 89~ 1092mm, the impact frequency is 1750 ~ 925 times /min and the working pressure is 2.4 ~ 1.4 MPa. The hole diameter of domestic Jiaxing pneumatic DTH hammer is 85 ~ 450 mm, the impact frequency is 1200 ~ 840 times /min and the working pressure is 0.63 ~ 1.6 MPa.
Figure 2-5 Schematic diagram of working principle of air DTH hammer
3. Type of collider
1) According to the gas distribution mode and characteristics of the impactor, it can be divided into valve type and valveless type. The valve plate of the valve impactor controls the gas distribution. According to the exhaust mode, it can be divided into two types: side exhaust and middle exhaust. The earliest use is side exhaust, because the gas in the cylinder is discharged from both sides of the drill bit, so it is called side exhaust impactor. Central exhaust means that the gas in the cylinder is exhausted through the central hole of the drill bit, which has more complicated structure than the side surface and high machining accuracy. This kind of impactor can discharge rock powder in time without repeated crushing, which reduces the wear of drill bit and improves drilling efficiency. This structure is improved on the basis of side exhaust, and now it is basically this type of structure.
The valveless impactor has no valve, and the gas distribution system for controlling the reciprocating motion of the piston is arranged on the cylinder wall, and the piston automatically exhausts when it moves. Because this kind of impactor does not use valve plate to distribute gas, it can use the expansion work of compressed air to push the piston to move, thus reducing power consumption. It is characterized by few parts, simple structure and convenient processing. Compared with valve impactor, the pressure consumption can be saved by about 30%. Valveless impactor can be divided into side exhaust and middle exhaust according to the exhaust mode. At present, valveless impactors with central exhaust are mostly used.
2) According to the rated working pressure of impactor, it can be divided into low wind pressure impactor and medium-high pressure impactor. Generally, the rated working pressure of low wind pressure impactor is 0.5 ~ 0.8 MPa, that of medium wind pressure impactor is 0.9 ~ 1.4 MPa, and that of high wind pressure impactor is higher than 1.5MPa.
3) According to the drilling diameter of the impactor, it can be divided into small-caliber impactor and large-caliber impactor. Small diameter within 200 mm, large diameter greater than 200 mm..
4) According to the form of DTH hammer center through hole, it can be divided into ordinary type, hollow type and eccentric type, with different application ranges.
5) In order to expand the application field, it also includes single-head large-caliber pneumatic DTH hammer and multi-head large-caliber clustered pneumatic DTH hammer.
4.DTH hammer bit
DTH hammer is a tool to transfer impact energy and directly crush rocks. It forms an integral mechanism with the impactor. The structure and manufacturing quality of drill bit directly affect the use effect of DTH hammer. Therefore, according to the different physical and mechanical properties of rocks, it is an important technical condition to reasonably select different types and structures of drill bits to improve drilling efficiency and prolong the service life of drill bits.
DTH hammer drills basically use the following types of drill bits: ① concentric alloy ball-toothed drill bit, ② eccentric alloy ball-toothed drill bit, ③ blade-shaped alloy drill bit, and ④ reverse circulation alloy ball-toothed drill bit.
5.DTH hammer drilling technical parameters
Although the operation technology of DTH hammer drill is relatively simple, it must be operated scientifically and skillfully to achieve ideal drilling effect. Drilling efficiency depends not only on the performance of air compressor, impactor and drill bit, but also on reasonable operation and correct selection of drilling technical parameters.
(1) wind pressure and air volume
When drilling with DTH hammer, the drilling speed is closely related to the pressure of compressed air used. When selecting an air compressor, while fully referring to the wind pressure value specified by DTH hammer, we should also consider the extra pressure brought by pipeline consumption, overcome the back pressure of water column, start DTH hammer, and maintain the pressure drop of air or air foam circulation. Generally speaking, higher air pressure will improve the working efficiency of DTH hammer, and air pressure also determines the drilling depth of DTH hammer. The deeper the drilling depth, the greater the required air pressure, which is why DTH hammer drill is equipped with supercharger.
Regarding the air volume required for DTH hammer drilling, one is the air volume required for rock breaking drilling, and the other is that this air volume value can also meet the demand of cuttings discharge. Due to the fast drilling speed of DTH hammer and large debris particles, large air volume is needed to clean the bottom hole. For ordinary DTH hammer positive circulation drilling, the cuttings are discharged from the bottom of the hole through the gap between the drill pipe and the hole wall, and the airflow speed should reach 20m/s as much as possible, generally not less than 15m/s, otherwise there will be more cuttings in the hole, which will seriously affect the drilling efficiency.
(2) WOB
The basic working process of air DTH hammer is to break rocks under the action of static pressure (WOB), impact force and rotating force. The main function of WOB is to make the bit teeth closely contact with the rock, overcome the rebound force of the impactor and drilling tool, and thus effectively transfer the impact work from the impactor. WOB is too small to overcome the back pressure and rebound force when the impactor works, which directly affects the effective transmission of impact work. Excessive WOB will increase the rotational resistance and make the bit wear prematurely. For a DTH hammer with a diameter of 2 16mm, the optimum pressure is about1.5t. Generally speaking, according to the diameter of DTH hammer, the pressure can be increased by 0.5 ~ 0.8 kn for every increase of 1cm, which can be adjusted appropriately according to the formation conditions.
(3) Speed
The rotating speed of DTH hammer plays a decisive role in drilling smoothly and prolonging the life of bit. When DTH hammer drills holes, the only purpose of rotation is that after each impact, the spherical teeth on the hammer can fall on the new rock surface, and the spherical teeth on the outer edge of the bit are particularly sensitive to rotation. If the rotation speed is too slow, the ball teeth on the drill bit will hit the previously impacted pit, which will cause the drill bit to be unstable, hinder the rotation and reduce the drilling efficiency; If the rotating speed is too fast, the ROP will not increase, and the ball teeth of the drill bit will wear prematurely due to strong friction. Therefore, the proper hammer speed will prolong the life of the drill bit, but the choice of reasonable speed is mainly related to the impact work produced by the impactor, the impact frequency, the form of the drill bit and the physical and mechanical properties of the drilled rock.
The general requirements of optimum bit speed are to obtain effective drilling speed, smooth operation and economical bit life. Campbell of American Water Wells Association (NWWA) thinks that DTH hammer has an optimal rotation angle, namely 1 1, and the relationship between the optimal rotation angle and rotational speed and impact frequency is as follows:
Modern coalfield geological exploration technology
Where: a is the best rotation angle (degree); N is the rotational speed, r/min; F is the impact frequency, times/minute.
(4) Operation technology of 4)DTH hammer
1) In the opening stage, care must be taken not to make the hammer deviate from the orifice to prevent the orifice filling from collapsing.
2) When starting drilling, reduce the air pressure so that the air can only drive the DTH hammer to run, and then increase the pressure to improve the efficiency after the work is stable.
3) Foaming agent should be added during positive circulation drilling, which is helpful to clean up the cuttings in drilling, stabilize the hole wall and control the water gushing in the hole.
4)DTH hammer must work under the required air pressure. Too high air pressure will obviously shorten the service life of the parts, while too low air pressure will reduce the drilling efficiency and shorten the service life of the hammer.
5) In order to remove the rock slag in the hole in time and reduce the wear of drilling tools, DTH hammer should be frequently lifted from the bottom of the hole to fully discharge the rock slag in the hole.
6) If the hole actually collapses, keep the DTH hammer working and move up and down in the hole immediately. If necessary, the rotating speed can be increased until the DTH hammer can move freely up and down to discharge the rock slag out of the hole.
7) When connecting the drill pipe, pay special attention to the cleanliness of the drill pipe, so as to avoid sand, rust and other dirt in the pipe from entering the DTH hammer, causing parts damage or drilling stoppage accidents. Therefore, it is necessary to ensure the cleanliness and smoothness of the gas path and apply thread oil to the thread of the drill pipe.
8) After a drill pipe is finished, the rock slag in the hole should be purged first to reduce the gas volume, and then slowly put it into the bottom of the hole, and then slowly stop the gas after a while, and then add the drill pipe to prevent the rock slag from flowing back into the DTH hammer.
9) When replacing the drill bit, ensure that the diameter of the replacement drill bit is smaller than that of the replacement drill bit to prevent the drill bit from tripping in.
10) It is forbidden to reverse the drilling tool to prevent it from falling into the hole.
5. Characteristics and application scope of air DTH hammer drilling
1) This technology has the advantages of high drilling efficiency, long bit life, low required rotation speed, low torque and low axial pressure, and has the functions of deviation prevention and correction. At the same time, the loss of equipment and drilling tools is also very small, which has been recognized by people.
2) DTH hammer drilling is one of the most effective methods to improve the drilling efficiency of hard rock at present. Production practice shows that its drilling efficiency is about 10 times higher than that of rotary drilling rig, especially in arid and water-deficient areas and exposed areas of surface rocks, which can effectively drill and achieve the purpose of improving production efficiency and reducing construction cost.
3) The ability of air DTH hammer drilling technology to carry rock powder mainly depends on the upward speed of air. When the gap in the drilled outer space is too large, it is difficult for rock powder to return. Air DTH hammer drill is suitable for drilling construction with drilling diameter below 400 mm. ..
4) Air DTH hammer drilling is suitable for drilling hard strata, and impact drilling in Quaternary topsoil, especially soft soil, is easy to cause hole wall collapse. When drilling into the broken stratum, air leakage and cuttings are difficult to return, and air DTH hammer drilling construction cannot be carried out.
5) Air DTH hammer drilling belongs to negative pressure underbalanced drilling, and formation water is easy to invade the borehole. If the water output is greater than 65438+1100m3/h, the drilling efficiency will be reduced, or even the construction will be impossible. In this case, it is necessary to add foam to the air, if necessary, increase the air volume through an external air compressor, and increase the wind pressure through a booster, so that the drilling cost will rise.