| 摘要 |
<p>In order substantially to prevent burring being formed on the inner surfaces of tubing during the perforating of the tubing the walls of the tubing are provided with outwardly projecting protuberances which are cut by knife assemblies as the knife assemblies rotate about the axis of the tubing with the assemblies in an inner position, the knife assemblies which are maintained in their inner position under the influence o a reciprocable cam member being permitted by axial movement of the cam member to move to an outer position thereof in which the tubing is intermittently advanced a predetermined distance. The rotary knife assemblies are then returned to their inner position under the influence of axial movement of the cam member.</p> |
