Design and Development of a Conical Boring Device to Enlarge a Pilot Hole through Rock.

摘要

This report summarizes an-effort completed during the second year of a multi-year program to design and develop a conical self-advancing and self-rotating boring machine. The conical borer will use a proven and energy effective mechanical fragmentation system - roller cutters - and will operate as a reaming device to enlarge an existing 8 3/4 inch pilot hole to a final 39 inch bore. The general research approach has been to continue the development efforts begun under Contract H021044 during which a prototype single stage conical borer was fabricated and proof tested. In the current program detailed testing and refinement of the cutting structure of the prototype borer was completed. As a result of this research a marked reduction in the values of the thrust loads which were obtained during the first year proof tests was achieved. Thrust loads of approximately 10 percent of that required for conventional tri-cone bit were observed. The specific energy required (inch-pounds per cubic inch of rock removed) was only 13 percent higher than that of a comparable tri-cone bit. This is considered very good in view of the extensive development history of tri-cone cutters. The detailed design of the borer (Phase II) was completed. Design layouts are presented in this report.