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Failure Analysis of Boring Drill Rod
Under normal circumstances, the normal failure mode of the drilling rod of hydraulic heading drilling machine is the serious wear of R32 thread, that is, the grinding or smoothing of the thread wave crest, and the fatigue fracture due to the serious wear under the condition of more accumulated drilling footage. The way of causing R32 thread wear failure is fretting wear and impact wear,
1. Drill rod R32 thread wear of hydraulic boring machine
Under normal circumstances, the normal failure mode of the drilling rod of hydraulic heading drilling machine is the serious wear of R32 thread, that is, the grinding or smoothing of the thread wave crest, and the fatigue fracture due to the serious wear under the condition of more accumulated drilling footage. Fretting wear and impact wear are caused by R32 thread. In the rock drilling process, with the continuous rock drilling operation and the replacement of new and old drill bits, the wear degree of R32 thread is increasing, and the matching clearance between R32 thread and new and old drill bits is also increasing. The wear will gradually transition from fretting wear generated when the initial fit is good to impact wear generated when the matching clearance is large. Impact wear will lead to rapid wear of the thread, resulting in rapid wear failure of the drill rod. In addition, under the impact and torsion of the high-power hydraulic rock drill, the line contact or surface contact will be formed between the R32 thread and the old and new drill bit, resulting in local high temperature on the thread surface, reducing the hardness and wear resistance of the thread surface, and even forming corrosion pits, which will be transformed into crack sources.
2. R32 thread fracture of drill rod of hydraulic boring machine
Put the R32 thread wear failure sample into 70% hydrochloric acid and boil it for one hour, then wash it with hot water and blow dry, as shown in Figure 11(a) and (B). It can be seen from the figure that the fatigue source is the most serious at the root of R32 thread and the second buckle away from the end face of R32 thread, and there is a melting pit, which indicates that in the process of rock drilling, the stress on these two parts of the drill rod is the largest, and it is also easy to produce high temperature to form melting pit, so the drill rod of hydraulic drilling vehicle is very easy to fracture and fail at these two parts.
(2) In the process of rock drilling, the staff operates the rock drilling jumbo, and generally uses the drill rod and φ76R-32 ball tooth drill bit or reaming bit to drill the core hole of the tunneling surface. Due to the large tensile and compressive stress, torsional stress, bending stress, advancing resistance and friction force generated by φ76-R32 ball tooth drill bit and reaming bit on the thread part of the drill rod R32, it is easy to cause fracture.
(3) Fit of R32 Thread Position of Drill Rod and Drill Head of Hydraulic Excavation Drill Car
The use of drilling tools from different manufacturers in the mine has caused excess thread exposure at the R32 thread part of the hydraulic boring drill rod and the drill bit, making it difficult to ensure a good fit tolerance dimension, as shown in Figure 13. This may lead to early wear or fracture of the thread part of the R32 drill rod of the hydraulic boring machine.
2. Fracture and abnormal wear at T38 or R38 thread connection between drill rod and drill tail
During the drilling operation of the drill rod, the root of the R32 thread and the second thread of the drill rod are the parts where the stress is most concentrated and the parts that are most likely to break. The T38 and R38 thread ends of the drill rod and the drill tail are generally rarely broken, and the wear is relatively light. In case of fracture and abnormal wear, the working parameters of rock drilling jumbo and hydraulic rock drill and the change of surrounding rock geological conditions should be analyzed. Such as rock drilling rig propulsion pressure, hydraulic rock drill impact, rotating pressure, etc.
3. The drill rod shaft is broken
The fracture of the drill rod shaft rarely occurs in the rock drilling operation. Generally, it is necessary to analyze whether the drill rod shaft has defects caused by external force and the abnormal operation of the drill rod in the rock drilling operation.
4. Bending of drill rod
Drill rod in rock drilling operations appear serious bending, can not be straightened will not be used. Bending generally occurs nearR32At one end, it is often due to the complex geological conditions of the surrounding rock, resulting in partial drilling or fissure clamping, which will cause the drill rod to bend and fail.
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