Issue 42

J.-f. He et alii, Frattura ed Integrità Strutturale, 42 (2017) 263-271; DOI: 10.3221/IGF-ESIS.42.28 270 the longer service life of the hydraulic hammer will be. In order to improve the service life of hydraulic hammer with horizontal oriented sliders, the moving velocity of the anvil should be less than 4m/s, thus the abrasion rate of oriented sliders in horizontal directional or vertical well drilling is acceptable. According to the filed application results of the hydraulic hammer with horizontal oriented sliders, the abrasion of the anvil inside the hydraulic hammer will be dramatically aggravated while the moving velocity of the anvil exceeds 3m/s [19]. Thereby the simulation results have shown extraordinary agreements with the actual cases of hydraulic hammer in directional well drilling. It can be suggested that the moving velocity of the anvil with horizontal oriented sliders should be significantly controlled in horizontal directional well drilling, which contributes to the improvement of service life of hydraulic hammer with horizontal oriented sliders. Effects of Friction Coefficient on the Abrasion Property of Horizontal Oriented Sliders The effect of friction coefficient of the anvil on abrasion rate of horizontal oriented slider has been numerically analyzed by FEA method. As shown in Fig. 8, it can be concluded that abrasion rate of oriented sliders is approximately exponentially increases with the friction coefficient of oriented sliders. While the friction coefficient between oriented sliders and external cylinder exceeds 0.2, the maximum abrasion rate of oriented slider will be up to 16.5%, which seriously reduce the service life of hydraulic hammers in horizontal directional well drilling. While the friction coefficient of horizontal oriented sliders is less than 0.05, the minimum abrasion rate of oriented sliders is much more considerable. Therefore the design of hydraulic hammers with oriented sliders is qualified due to the friction coefficient of PTFE with carbon fiber is 0.02. Figure 8 : Variation of friction coefficient on the abrasion property of hydraulic hammer with horizontal oriented sliders. The service life of hydraulic hammers is severely influenced by friction coefficient of oriented sliders in horizontal directional well drilling. Once the horizontal oriented sliders are abraded, the horizontal alignment among piston, the anvil and oriented sliders will be damaged, which will lead to the failure of hydraulic hammer with oriented sliders in horizontal direction well drilling. Thereby the friction coefficient of horizontal oriented sliders must be controlled in order to reduce the abrasion rate of hydraulic hammer with horizontal oriented sliders. Conclusions have been drawn that the friction coefficient of oriented sliders should be less than 0.2 in order to improve the service life of the hydraulic hammer with oriented sliders in horizontal directional well drilling. C ONCLUSIONS 1) Hydraulic hammer with horizontal oriented sliders have been designed, and corresponding numerical models have been developed to investigate the effects of anvil mass, friction coefficient and moving velocity of the anvil on abrasion rate of oriented sliders.