A study on high frequency hammering system and its impact loads

Deep sea floor mineral deposits are promising resources and studies of various methods of recovering them are underway. Crushing the deposits is the typical method. This method may be good for hydro-thermal deposits recovery. However, thin deposits like Cobalt-rich manganese crust which is sticking on hard rock will be very difficult to recover by this crushing method because abundant of rocks without deposits will be recovered also. Thus, inventions of other unique methods such as peeling off method must be requested. Conventional drilling is done by rotating a drill bit. But there are some stratums where rotary drilling destroys the hole itself. This typical stratum is alternate layers of hard and soft stratums, such as chalk and chert. In order to penetrate this type of stratum, rotary drilling will not be good and the other method should be pursued. Considering these peeling-off method and non-rotary drilling method, the author proposes a new concept of high frequency hammering system. The similar system is now used for piling to secure the stability of the land. Its frequency is 50 to 60Hz at the maximum, and it is an inertia type hammering with a limited impact load. As the result, this system is good for soil, but not good for hard rock. Moreover, this system requires heavy weight and large volume. Thus, the hammering mechanics has to be located at the top of the piles, and shallow penetration can only be expected. The author pursues to develop a new system with the higher frequency hammering of 100 to 300Hz or more at fixed amplitude of displacement. This system can be expected to give much larger impact load than the inertia type hammering to cut out hard rocks, and also is expected to become very small in size and weight. This system will be applicable for peeling off the thin sticking deposits and also will become a small downhole drilling system. This paper will show the mechanism of hammering, and also will show the impact loads in order to think wheth- r this system can crush various types of hard rocks.