Physical analog of shock pulse generator and high-frequency pneumatic hammer

Abstract

Many special construction operations need pneumatic percussion machines. The feasibility of increasing the penetration rate in driving of rods in soil is assessed via physical modeling. The promising nature of high-frequency pulse load generators in rock fracture at the ensured threshold value of the unit impact energy is justified. The best approach to this effect is the valve-aided air distribution implemented in pneumatic hammers of variable impact capacity. Such air distribution system uses a ring-shaped elastic valve at the compressed air exhaust from the back stroke chamber. The stable operation conditions of the ring-shaped rubber valve are determined within a wide range of impact frequency adjustment. The authors have experimentally determined the elastic valve temperature versus impact frequency, the influence of the angular orientation of the ring-shaped elastic valve cross-section on the air tightness of the back stroke chamber, as well as the values of radial and axial crumpling of the elastic valve with increasing radial gap between the piston and the device housing. The studies into pipe driving by a compound generator composed of two coaxial tandem impact facilities are analyzed. The increased impact on the pipe by the united percussive facilities at the unit blow energy higher than the threshold value ensures higher penetration rate of the pipe owing to the improved bottomhole interaction. Duty harmonization of two percussive facilities by means of frequency synchronization ensures reliable and stable operation of the compound generator. The capabilities of the machine were tested using a prototype model with smooth variation of impact frequency in a vertical channel in soil. The article describes the designs of the pneumatic hammer prototypes with smooth blow frequency variation and with mechanical synchronization of two impact bodies placed in the common housing and having the joint air distribution system.