How To Choose The Model Of Crawler DTH (Two)?

Jan. 07, 2020

Down-the-hole drilling rigs are increasingly used in grouting operations, and most grouting reinforcements are performed in the open air. This article mainly discusses how to choose the model of crawler DTH drill rig.

2. Selection of technical parameters of rig

According to the requirements of grouting hole diameter, depth, and drilling angle, drill bits and drill rods of the same diameter and length need to be equipped to meet the technical requirements of drilling. At the same time, the drill arm and guide rail of the rig should have a variety of adjustable Angle to meet construction needs.

A crawler mounted DTH drill rig can be equipped with drills of various diameter specifications, and can be flexibly selected according to the requirements of the construction aperture. The drilling depth is adjusted by using a small number of drill rods. The length of the drill rod is generally 2-9m, etc. The drill rod is connected by male and female threads. The outer diameter of the drill pipe affects the drilling efficiency. According to the theory of fluid dynamics, only when the air velocity in the annular channel formed by the drill pipe and the hole wall is greater than the suspension speed of the rock slag, the slag can be smoothly discharged out of the hole. The air velocity inside is mainly determined by the cross-sectional area and length of the channel. The smaller the cross-sectional area of the channel, the higher the flow rate; the longer the channel, the lower the flow rate. Therefore, the larger the diameter of the drill pipe, the higher the air velocity and the better the slag removal effect. Of course, it can be too small to pass through the slag, and the ring width of the general circular section is 10-25 mm. This item can be used as a basis for investigating whether the rig's drill pipe and drill bit match and the approximate estimation of work efficiency.

How To Choose The Model Of Crawler DTH (Two)?cid=9

Crawler DTH Drill Rig

(3) Rotating speed, torque and thrust pressure of drilling rig

The size and matching of parameters such as the rotating speed, rotating torque and thrust pressure of the drilling rig directly affect the drilling speed and drilling cost. Choosing the proper rotation speed has a great effect on reducing machine vibration, increasing the life of the drill bit and accelerating the drilling speed. The rotation speed is determined according to the drilling diameter, drill structure, impactor frequency, and rock properties. The recommended rotation speed is: when the drill diameter D is 100 mm, the rotation speed n should be 30 ~ 40 r / min; when D = 150 mm, n is 15 ~ 30 r / min; when D = 200 mm, n should be 10 ~ 20 r / min; when D = 250 mm, n should be 8 ~ 15 r / min.

Slewing torque is mainly used to overcome the frictional resistance between the drill and the bottom of the hole, the shear resistance, and the frictional resistance between the drill and the wall of the hole during normal drilling. The resistance moment of the drilling tool is proportional to the drilling diameter and hole depth. The torque required for normal drilling is small and large, and the drilling resistance torque for bore diameters below 150 mm is generally about 1000 N.m. Generally, the torque of the drilling rig itself is much larger than this value. The larger the torque, the easier it is to unload the drill pipe, the stronger the ability to prevent stuck drilling, and the deeper the depth of the hole that can be drilled. When drilling in fractured zones with relatively developed joints and large-bore deep-hole drilling operations, a drill with a relatively large torque must be selected.

The low thrust pressure only affects the drill life, and more importantly, it directly affects the drilling speed. If the thrust pressure is too large, the drilling tool will rotate continuously and generate a slewing impact. At the same time, the bottom of the hole will be excessively broken, which will waste energy and affect the drilling speed. It will also accelerate the wear of the drill bit. The rebound of the drill is intensified, and the small drill bit can be close to the bottom of the hole, so that the small impact energy can effectively affect the rock at the bottom of the hole, which affects the drilling efficiency and accelerates the damage of the rig and the drilling tool.

Recommended thrust axial pressure under the diameter of  drill: When the drill diameter D = 100 mm, the optimal axial thrust F is 4 000 ~ 6000 N; when D = 150 mm, F should be 6 000 ~ 10 000 N; When D = 200 mm, F should be 10 000 to 14000 N; when D = 250 mm, F should be 14 000 to 18 000 N.

Understand the impact of the above parameters on the drilling of the DTH drilling rig and the best matching method. When selecting a small rig of the same model, you can compare and verify its related technical parameters to determine whether it meets the principle of optimal matching.

(4) Working pressure and gas consumption

DTH drill rig is the compressed air provided by the air compressor and sent to the impactor through the oil mist device, which provides power to the impactor, making the piston in the impactor reciprocate, and the impact drill to complete the drilling. Blow out the drilling slag from the hole to empty the hole for grouting in the next step. The working pressure of the rig is the air pressure of the rig during normal drilling, and the unit is M Pa. The air consumption is the amount of compressed air required to complete the hole cleaning.

Simply said that the higher the working pressure, the faster the impact drilling speed, but the higher the working pressure, the faster the hole formation speed of the appropriate impactor is selected, and the empirical values of wind pressure and hole formation speed of the hole: The wind pressure is 0.990.98, 1.05, 1.05 ~ 1. 121. 12 ~ 1. 19 M Pa, and the pore forming speeds are 11.16, 13.4, 14, 15.3 m / h.

According to the actual working efficiency requirements of the project, choose a drilling rig with a suitable working pressure. The small energy pressure is too low, which results in the low efficiency of the rig. The small energy pressure is too high, which excessively meets the required working efficiency. The choice of working pressure of the drilling rig also affects the pressure matching of the air compressor. A high pore-forming speed means that a high-power air compressor is required to match it. Selecting a high pore-forming speed by itself will cause waste of funds.

3. Investment recovery of equipment

When purchasing the tracked down-the-hole drilling rig, economic factors such as equipment investment, income, depreciation, and maintenance must also be considered. The following methods can be used for evaluation.