Top hammer drilling uses a percussive force at the top combined with a rotational energy that transmits through a rod to a drill bit that crushes rock. It is a drilling method that is preliminary used in mining, construction and operations under ground. Fatigue strength plays an important role in the drill rods life span. A top hammer drill rod has a through hole in the center called a flush hole used to flush up the drilling cuttings. The flush hole is a weak spot in the rod. In this preliminary study the purpose was to investigate if, and how, the surface in the flush hole affects the fatigue strength in rock drill rods. Four test methods; Refined inner surface, lathed core, without lubricant and sealed hollow bar. With three samples of each method that affected the surface of the flush hole, were used in the manufacturing of the rods and compared to references. Different tests were applied to measure the quality of the flush hole and of the rods. The material used were fatigue tested under a pulsating pull-pull condition with flushing water. Finally, the fracture surfaces were studied. The fatigue test showed that refined inner surface had supreme fatigue strength, the other methods exhibit approximately 10% more cycles than the references. In conclusion the inner surface affects the fatigue strength. The parameter with the most distinct correlation to the fatigue test was surface roughness. Other parameters that seems to affect were oxidation, hardness and scratches. To obtain statistical certainty more samples are needed.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:uu-488634 |
| Date | January 2022 |
| Creators | Hållström, Erik |
| Publisher | Uppsala universitet, Tillämpad materialvetenskap |
| Source Sets | DiVA Archive at Upsalla University |
| Language | Swedish |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | UPTEC F, 1401-5757 ; 22060 |
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