Method of making machine-engraved seamless tube

A method of making a perforated tubular member having a relatively thin tubular wall of metal which is perforated by an array of radial, inwardly-tapered apertures, said method comprising the steps of:

• Applying an intermediate layer of etchable material onto a core roll;
• Applying at least one metallic layer to said intermediate layer to form a metallic tube thereon;
• machine engraving funnel-shaped holes into said metallic tube, said machine engraving comprising repeated knurling steps, each said knurling step followed by an etching step to remove metal from selected locations on the knurled metal tube to form said funnel-shaped holes therein;
• etching away said intermediate layer;
• and,
• removing the thusly-machine-engraved tube from said core roll whereby accurately-dimensioned, funnel-shaped holes are formed in the tubular member without requiring separating agents, slitting, recurving, or rewelding.

A method of making a perforated tubular member having a relatively thin tubular wall of metal which is perforated by an array of radial, inwardly-tapered apertures, said method comprising the steps of:

• applying a separating layer of an electroplating separating chemical to a core roll;
• Applying at least one metallic layer over said separating layer;
• machine engraving funnel-shaped holes into said at least one metallic layer, said machine engraving comprising repeated knurling steps, each said knurling step followed by an etching step to remove metal from selected locations on the knurled metal tube to form said funnel-shaped holes therein;
• Applying sufficient force to said machine-engraved metallic tube to release said machine-engraved metallic tube from said separating layer;
• and,
• removing the thusly-machine-engraved metallic tube from said mandrel whereby accurately-dimensioned, funnel-shaped holes are formed in the metallic tubular member without requiring slitting, recurving, or rewelding.