| 摘要 |
<p>The core-cutting bit for .e.g rock-drills has an annular cutting head mounted on a tubular metal support. The support-tube is of sheet steel which has been rolled into the desired cylindrical form, and has a wall thickness of at least twice the thickness of the constituent sheet-steel. Both the bore and the external surfaces of the support-tube fall within an annular cross-section with all surfaces, except at a localised longitudinal joint zone, cylindrical. A single piece of metal sheet (1) is pref. spiral-rolled. An offset part (2) of the tube wall between the longitudinal edges (3, 4) of the sheet provides the annular cross-sectional profile. The support-tubes may be of mild steel sheet.</p> |
