| abstract |
1,058,409. Making internally finned tubes. CALUMET & HECLA Inc. Feb. 18, 1965 [April 23, 1964], No. 7135/65. Heading B3A. In a method of producing an internally finned tube unit, a first metal tube is extruded to provide internal fins, drawn to reduce its external diameter and telescoped within a second metal tube. The telescoped tubes are then drawn to bring them in tight contact with one another. The first tube may be age hardened after extrusion and preferably has a higher yield strength than the outer tube. The tubes may be of aluminium alloy and copper respectively, but the outer tube may also be of brass, coppernickel alloy or the like. |