This invention relates generally to the formation of holes in metal workpieces by means of a metal disintegrator which operates on a thermo-fracture principle.
Metal disintegrators for forming holes in workpieces are sold by Electro Arc Manufacturing Company of Ann Arbor, Mich. The model 2-S disintegrator sold by that company includes an elongated hollow electrode (called a disintrode) adapted to be vibrated and adapted to be connected to one terminal of a voltage source. The workpiece is connected to the other terminal of the voltage source and, when the vibrating electrode approaches the workpiece, an electrical arc jumps across the gap between the electrode and the workpiece and heats the workpiece. At the same time, liquid coolant is ejected out of the electrode and quenches the workpiece. The combined action of the heating and cooling fractures the material of the workpiece and causes the material to disintegrate so as to form a hole in the workpiece. Some of the material removed from the hole forms a core which moves into the hollow electrode.
In certain instances, it is necessary to be able to form a hole without creating particles or chips of any significant size. One such case involves the formation of holes in pipes for carrying cooling water in a nuclear power generating station. Typical specifications require that the insides of the pipes be free of particles of a size greater than twenty-five microns. There presently is no effective way of forming holes in installed pipes while keeping the insides of the pipes free of large particles as the holes are formed. Accordingly, it has been necessary heretofore to disconnect the pipes, form the holes, clean chips and particles from the insides of the pipes, and then re-connect the pipes. This involves an expensive and time-consuming process.