Over-burden drill hammer - with annular drill crown retained by threaded ring and receiving impact blows on shoulder

摘要

The parent patent described a down-the-hole hammer for drilling holes through unconsolidated overburden in which a collar on an inner drill bit transfers the impact blows also through a shoulder to the annular outer drill crown. In the addn. the latter has a limited axial movement in splines of the outer drill tube string. A ring with a circular segment cross-section which can be inserted through the spline grooves retains the outer drill crown. This design reduces the wear of the hammer components of the parent patent and raises its efficiency still further.