Drill pipe is the key "hardware" of DTH Bit. It bears various stresses of drilling torque load, axial pressure, vibration, impact, extrusion, and eccentric drill pipe. The working conditions are extremely bad, so the failure of rotary drilling pipe The rate is the higher of DTH Bit. The following editor shares with you the types of DTH Bit drill pipes:
- Friction rod
The drill teeth at the bottom end of the rotary drill bit shear and crush the rock and soil to generate a torque load → the drill pipe key bar generates friction resistance → transmits the pressure output by the power head.
Because friction drill pipes rely on friction to transmit pressure, even in the maximum torque load condition, the maximum torque is divided by the drill pipe radius, and then multiplied by the friction coefficient of steel. For example, 220 mainframe uses 440mm outer diameter friction rod, The maximum pressure that can be transmitted under the maximum torque load is less than 120kN.
Due to the small axial pressure of the friction rod, its wall thickness and pipe diameter are reduced compared with the machine lock rod. Therefore, the friction rod can have one or two more sections than the machine lock rod, which increases the drilling depth ability.
- Friction bar structure: The biggest difference between the friction bar and the machine lock bar is the key bar structure, the key bar of the friction bar extends to the bottom.
Because the shaft pressure output by the friction rod is relatively low, the diameter of the core section and the wall thickness of other sections are reduced. Therefore, under the same diameter, the friction rod has one more drill rod than the machine lock rod. Other parts such as flat head, flange, upper stop sleeve, swivel, down tube, water plate, spring, spring tray, square head are basically the same.
- The principle of axial pressure transmission by the friction rod: the drill teeth at the bottom of the drill bucket cut the rock and soil to form a torque load, that is, reaction force. After the drill rod that outputs torque encounters the reaction force, it forms a positive pressure, that is, friction force. Friction resistance transmits pressure. Therefore, the friction drill pipe must rely on the load of the drill bucket to transmit the axial pressure. At the same time, the size of the drill bucket load determines the size of the pressure. For example, the pressure cannot be transmitted when it is slipping.
- Selection of friction rod: Quaternary loose/plastic geology, such as flow plastic silt, soft plastic/plastic clay, silty clay, loose/slightly dense/medium dense silt, sub-sand, fine Sand, coarse sand, gravel, pebbles, boulders, etc., fully weathered rock formations, some strongly weathered rock formations, with geological strength (ultimate bearing capacity) below 500kPa, optional friction drill pipes; in addition, deep piles, machine-locked drill pipes are not enough to drill When it is deep, friction rods can be selected, but the premise is to meet the rock and soil strength drilling, or change to abrasive drilling.
- Advantages and disadvantages of friction drill pipe:
Advantages: friction drill rods have fast drilling/drilling speed, strong drilling depth ability, no need to find lock points and unlocking, low rod probability, can improve construction efficiency and meet drilling depths;
Disadvantages: slipping, low output shaft pressure, low grounding ratio of drill teeth, hard to shear and break hard geology.
- Machine lock lever
The concave key strips on the drill rod are interlocked to form a rigid connection and transfer the pressure without relying on the load of the drill bucket. Compared with the friction drill pipe, it can transmit greater axial pressure. As long as the quality and center of gravity of the whole machine are reasonable, the theoretically set maximum pressure can be output.
- Machine lock rod structure: The key of the machine lock rod lies in the key bar structure. The drive key and the machine lock table interlock the machine lock to form a rigid connection, which transmits all the axial pressure output by the oil cylinder or the hoist to the drill bucket. In addition, due to the large output and axial pressure of the machine lock lever, its pipe diameter and wall thickness increase, which is why the machine lock lever is equipped with four sections as standard.
Other parts such as flat head, flange, stop sleeve, swivel, down tube, water plate, spring, spring tray, square head are basically the same.
- The principle of pressurization of the machine lock rod: the driving key of the power head or the driving key of the drill pipe down tube is turned forward, and under the action of the load of the drill bucket, the driving key and the machine lock point are interlocked to form a rigid connection to transmit axial pressure.
- Quickly find the lock point: The drilling rig has the function of high and low speed of the power head, and can use high-speed up/down to find the lock point when dumping slag and searching for the lock point.
When reverse unlocking, refer to the mast to mark the current power head position. When drilling down for the second time, raise the power head to the marked position in advance to achieve rapid machine lock.
When the power head machine lock reaches the bottom of the mast, it is necessary to re-lift the power head and the next machine lock point. Since the pipe body is hidden inside (except the first section), the lifting height of the power head can refer to the first section No. 1 to 2 No. Pressing table spacing.
- Unlock the machine lock lever: The stroke of the machine lock table is longer than the length of the drive key, so the drill pipe swivel is in the suspended state. Lift the power head to eliminate the suspended stroke before unlocking, and also reduce the friction between the drive key and the lock point; When the drill bucket has a drilling load, it is reversed, the core section is fixed by the resistance of the drill bit, and the drill rod and power head of other sections are reversed. Each drive key is separated from the lock point and returned to the keyway position.
- DTH Hammer unlock sequence: When the machine lock lever is fully extended, the core section is theoretically fixed when unlocking. Therefore, in addition to the core rod, the first rod of the remaining three rods has the largest mass and the largest frictional resistance. Therefore, the unlocking sequence is from the inside to the outside: the drill bucket provides resistance (the closing of the rotating bottom is related to the rock soil, the diameter of the drill bit and the drilling depth of the single bucket) → fixed core section → unlocking of the third and core sections → the second and third sections Unlock→Unlock the first section and the second section→Unlock the power head and the first section. The machine lock is the same as the unlock sequence, from the inside to the outside: the third section→the second section→the first section→power head.