A study on high frequency hammering system and its impact loads — Second report

摘要

Following the former report [1] presented at Oceans 2010 Seattle, the author continued the research on realistic hammering system to crash very hard rock efficiently such as chert or basalt or andesite whose compression strength is around 200∼250MPa. Gems have larger compression strength but most rocks are less than or equal to these value. Thus, this capability is enough to drill into the hard rock area. The high frequency mechanism is to use thrust roller bearing with swelled raceway whose number of swells is the same as that of the rollers. This mechanism can make the high frequency vibration easily because the frequency is given by multiplication of shaft rotation and the number of rollers. Also this mechanism can make the size of vibrator so small as that of the size of the thrust bearing. Another feature of this mechanism is that the vibrator can be located at the hitting end of the rod, which means the reduction of the impact load is negligible even if it is applied to the deep drilling with long drill pipe. The former paper discussed the mechanism to produce this crashing load on the flat hammer head, but flat head requires very large thrust force to crash the rock. So, hammering by uneven loading is introduced which has protuberances to concentrate the hammering impact on narrow area. Also the required power consumption is calculated in order to make the system realistic one. As this thrust bearing has swelled surface, stress concentration shall happen on thrust bearing, and this stress concentration and the life time of the bearing is discussed. The matter to be solved is to compensate the high frequency volume change due to the axial vibration. A new compensation method is proposed here. As this mechanism can be very small, four types of application are shown. The first is the 21st century''s Mohole where very deep drilling is requested with hard rocks. Coring system can easily be introduced. The second is deep sea mine prospecting by surface ship-- suspending this system like a piston coring method, which shall realize coring at very short time. The third is peeling-off machine which can be applied for getting cobalt crust on the sea floor. The fourth is to use this vibrator as a low frequency underwater sound source. This study is still by numerical simulation, but various considerations are involved. In this paper, they are discussed.