| 摘要 |
1293394 Percussive drills GENERAL DYNAMICS CORP 5 Nov 1969 [14 Nov 1968] 54316/69 Heading B4C [Also in Division E1] A vibratory percussive drill has a hammer 18 (Fig. 1) which is reciprocated, e.g. pneumatically, to apply impulses to an anvil connected to a drill bit 48. The anvil includes a relatively resilient member in the form of a shaft 44 of titanium alloy, and a drill steel 34 extending from the shaft 44 to the bit 48, and the stiffness of the spring and the mass of the hammer are chosen to maximize the energy transferred into the material being drilled. The system is arranged so that Q=ecS#Cs>0À7 and preferably >1À5, where e, c and S are respectively the density, sonic velocity and cross-sectional area of the drill steel, #=2# x impact frequency, and Cs is the compliance (the inverse of the stiffness) of the spring. In another embodiment (Fig. 3), the spring is mounted on the tip of the hammer 60 and comprises concentric tubes 62a, 62b joined together.
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