Measures to improve the service life of tooth wheel drill bits
To improve the service life of the drill bit of the tooth wheel drilling rig, the storage, transport and use of the drill bit are in accordance with the routine operation, but also should take the following measures to improve the service life of the drill bit.
(i) Reasonable selection of tooth shape of the tooth wheel drill bit
Correctly selecting the tooth shape of the tooth wheel drill bit can not only prolong the service life of the drill bit, but also improve the perforation speed and reduce the cost of perforation. The selection of the tooth shape of the drill bit is mainly based on the physical and mechanical properties of the ore rock, i.e. the compressive strength, hardness and drillability of the rock. In addition, the diameter size and water content of the drilled holes should be considered, as well as the technical performance of the tooth wheel drilling rig.
1. When drilling in hard rock strata, we usually use ball-tooth drills, which are suitable for drilling in extremely hard and wear-resistant mineral rock because the teeth of ball-tooth drills are shorter in protrusion but denser in thickness, which can withstand greater axial pressure.
2. When drilling in softer rocks, we usually use wedge shaped drill bits with longer protruding teeth and sparser teeth, which are suitable for drilling in soft and plastic rocks.
If the two are not properly selected, and the spherical bit is used for piercing in soft rock, the starting life is longer but the drilling speed of the rig is very low. Taking into account the drilling cost of the rig, the total cost of drilling is higher. On the other hand, if the wedge tooth drill bit is used to perforate in extremely hard and abrasion-resistant mineral rock, the alloy teeth will wear out or break very quickly. Therefore, reasonable selection of drill bit tooth shape can improve the service life of the drill bit.
(ii) Reasonable selection of the best perforating work system
The perforating speed of the drill bit is related to the physical and mechanical properties of the rock being perforated, the axial pressure exerted on the drill bit, the slewing speed of the drilling tool, the torque of the drill bit, the shape of the teeth of the tooth wheel and the number of teeth participating in the crushing of the rock at the same time, as well as the amount of compressed air used for blowing out the blast hole, and many other factors. According to the rock crushing mechanism of tooth wheel drilling rig perforation, one of the most important parameters that determine the perforation working system is the shaft pressure, slewing speed and air volume of slag discharge.
1. The influence of shaft pressure on the life of drill bit.
In order to effectively break the rock, the drill bit must be applied enough axial pressure so that the stress caused by the teeth of the tooth wheel is enough to overcome the compressive strength of the rock, but the axial pressure applied to the drill bit has a certain reasonable value, that is, it can't be too large, nor too small. When the axial pressure value exceeds the optimum value to a certain extent, the axial pressure is increased again, the perforation speed does not increase, and the axial pressure is too large will also cause the fracture of the carbide teeth or make the bearing of the drill bit damaged.
2. Influence of rotary speed on the drill bit
Within a certain range, the perforating speed of the tooth wheel drilling rig increases with the increase of the rotary speed of the drilling tool, but the rotary speed is too large, which not only makes it difficult to discharge the slag at the bottom of the hole and produces the secondary crushing of the rock, but also produces a strong vibration, which affects the service life of the drill bit. The rotational speed of the drill bit must ensure that the teeth of the tooth wheel have enough contact time with the rock to achieve effective volumetric crushing of the rock. In hard rock, with the increase of rotational speed, the impact load increases, which makes the teeth of the tooth wheel and the bearings wear significantly more, so the use of high rotational speed is limited. But when the rock is softer, usually adopts the high speed, low axial pressure working condition.
3. The influence of air volume of discharging ballast on the life of drill bit
The size of discharging air volume directly affects the service life of the drill bit. Increase the wind volume, can effectively wash the hole bottom rock ballast, improve the tooth wheel teeth broken rock conditions. At the same time, it can reduce the wear and tear of the claw back of the tooth claw, and can better cool the bearing of the tooth wheel, prolonging the life of the tooth wheel. In addition, it can also reduce the hole bottom residual ballast and increase the effective hole depth. However, it should be pointed out that whether the bottom of the hole and the rock ballast can be discharged smoothly mainly depends on the speed of discharging the ballast back to the wind, and the speed of discharging the ballast back to the wind is affected by the wind volume and the annular space between the drilling rod and the hole wall. Therefore, when considering the effect of discharging ballast, we can't simply pursue the capacity of air compressor. Do not only can get the best discharging effect, but also reduce unnecessary wind consumption as far as possible.
4. Improve the drilling rig driver's operation technology level
When drilling, due to the change of lithology, the rotary speed and shaft pressure should also be changed accordingly, so that the rotary speed and shaft pressure match, and do not cause the drill bit bias grinding. In addition the following operating precautions should be observed:
① When drilling, the hole should be kept clean and free of metal fallout;
② When opening the hole, should keep the drilling machine stable, opening the hole is not easy to open the speed too fast, to avoid playing oblique holes, affecting the service life of the drill bit;
③ When starting drilling or using a new drill bit, lower axial pressure should be applied first for running-in drilling for a period of time, and then increase to normal axial pressure;
④ Before the drill bit enters into the gun hole, open the air valve to supply the ballast discharge pressure wind for the drill pipe and drill bit, and in the whole perforating process until the drill bit is put out of the hole, it should always be guaranteed to supply enough wind volume to discharge the ballast;
⑤ When there is water hole or adopting wind and water mixing to remove dust, it is easy to make the life of drill bit decrease, at this time, it should choose the drill bit with appropriate nozzle and improve the wind pressure at the drill bit to protect the bearing of drill bit;
(6) After drilling the shell hole and raising the drill bit, the drill bit should be inspected, and the temperature of the three tines should be roughly similar, and the tine with the greatest heat and high temperature may have its bearing's pressurised air cooling duct blocked by rock ballast or dirt, which should be inspected and dealt with;
(vii) Do not use bent drill pipe for drilling, as the bent drill pipe is easy to make the drill bit bear unbalanced load, causing local partial grinding of the drill bit and damaging the drill bit;
(8) Prevent misoperation so that the drill bit does not fall into the hole. The sudden impact load will damage or scrap the drill bit;
⑨ When stopping the drill for some reason, the tooth wheel should be rotated by hand and blown with pressurised air to ensure that the tooth wheel rotates flexibly and freely when it is re-used;
⑩The drilling rig can not continue to operate when the rod clamping phenomenon occurs during the operation, and deal with it in time.
The use of a rod stabiliser placed on the upper part of the drill bit can keep the drill bit well centred, preventing the gun hole from being skewed and reducing vibration and the required twisting refusal. The reduction of vibration while drilling and the smooth running of the bit will reduce the wear of the teeth and prolong the service life of the tooth wheel as well as the whole bit. With alloy columns, this strengthens the wear resistance, so that the wear plate does not wear out too fast, which affects the stability of the drill bit, and greatly improves the service life of the drill bit.
Conclusion
Over the years, through the above aspects of work practice, improve the service life of mining tooth wheel drill bit, while making the cost of perforation has been significantly reduced. From the original average metres of about 800 metres, to 1800 metres in 2010. It has certain reference value and promotion role for reducing perforation cost in open pit mines.