How to use the down-the-hole hammer and drill bit reasonably
(I) The speed of the down-the-hole hammer during drilling
The speed of the down-the-hole hammer, during the drilling process, the main function of the rotation of the down-the-hole hammer is to make the drill bit alloy rotate to a certain angle for the next impact on the rock. There are many descriptions of the speed of the down-the-hole hammer in some domestic materials. But according to our experience, when impacting hard rock, it is more reasonable for the drill bit side teeth (the outermost alloy teeth of the drill bit) to rotate 1/3~1/2 for each impact of the down-the-hole hammer. We have also proved through a large number of experiments that the speed of the down-the-hole hammer affects the rock drilling speed. Too fast or too slow will affect the drilling efficiency.
The drilling speed of the down-the-hole hammer can be determined by the following formula: n=fd/(πD) n-------down-the-hole hammer speed (r/min) f--------down-the-hole hammer impact frequency (times/min) d--------drill bit side tooth alloy diameter (mm) π-----pi (3.14) D--------drill hole diameter (mm) The speed of the down-the-hole hammer is not only related to the hammer frequency, drill hole diameter, drill bit side tooth alloy diameter, but also has a great relationship with the rock properties. In drilling operations, the life and cost of the drill bit are of great concern to every user. So how to improve the service life of the drill bit is yet to be explored. Reasonable speed selection can not only increase the drilling speed, but also increase the service life of the drill tool and reduce the cost of use. Since the drilling speed is related to many factors, whether it is pressure, rock hardness, down-the-hole hammer frequency, or the shape and size of the drill bit alloy teeth, we still need to make corrections according to the actual situation when drilling and drilling. For water well construction, the general speed of 10~30 r/min is more reasonable.
(II) Axial pressure during drilling
The main purpose of the axial pressure (drilling pressure) of the down-the-hole hammer during drilling is to overcome the reaction force during impact and make the drill bit alloy in close contact with the rock at the bottom of the hole. It is related to the type of down-the-hole hammer, the hardness of the rock, and the pressure provided to the down-the-hole hammer by the air compressor. Each down-the-hole hammer has its own axial pressure range. As the diameter of the hole increases, the axial pressure increases; as the pressure increases, the axial pressure increases; as the hardness of the rock increases, the axial pressure increases. However, we generally recommend that 6Kg~14.6Kg of axial pressure be applied per millimeter of the hole diameter. For example, when using an SPM360 down-the-hole hammer with an SPM360-152 drill bit to drill a hole with a diameter of 152mm at a pressure lower than 1.7Mpa, the axial pressure required is 6Kg X152=912Kg. However, when the rock hardness is harder, we need to appropriately increase the axial pressure, which can be determined by observing the on-site use of the drilling tool. But when we carry out deep hole construction, we must consider the weight of the drilling tool, so that the actual axial pressure we get should be: Actual axial pressure = theoretical axial pressure - drill rod deadweight - DTH hammer deadweight - drill bit deadweight Tests show that reasonable axial pressure can improve drilling efficiency. Blindly increasing axial pressure will not only fail to improve impact efficiency, but also aggravate drill bit wear. Therefore, the following factors must be considered in the reasonable selection of axial pressure: 1. The type of DTH hammer and the diameter of the hole 2. The physical and mechanical properties of the rock, mainly the hardness of the rock 3. The pressure and gas volume provided by the air compressor to the DTH hammer.
(III) Torque during drilling
The torque required for the DTH hammer to drill is mainly provided by the drilling rig, which is mainly to enable the DTH hammer to achieve the rotation required during construction. Generally, the rotation torque required for each millimeter of drilling diameter is 1.06N·M, which is more reasonable, but considering other factors in the hole, we recommend that the torque is about 2.7N·M per millimeter (mm) of drilling diameter. At the same time, as the drilling depth increases, the torque also needs to increase; as the rock hardness becomes harder, the torque also needs to be increased, so when we drill holes: 1. Drilling diameter 2. Drilling depth 3. Rock formation conditions Through the above analysis, the "three elements" of down-the-hole hammer and drill bit drilling are obtained, namely speed, shaft pressure, and torque. Reasonable selection of the three elements of drilling during the drilling process can effectively improve drilling efficiency and reduce use costs.
