Tubing with inner baffle fins and method of producing it

Claim 2

Method of forming tubing, which comprises providing a round metal tube blank having an axis, an annular peripheral wall about said axis, and inner metal fins on said wall extending helically thereon in one direction and being spaced from said axis; partially compressing the blank from two opposite sides for interpress of opposed fins at their crossings; and expanding the partially compressed blank to separate the fins from their interpress.

Claim 3

Method of forming tubing, which comprises providing a round metal tube blank having an axis, an annular peripheral wall about said axis, and inner fins on and integral with said wall and extending helically thereon at the same helix angle and parallel to each other, with said fins being of equal height and spaced from said axis; partially flattening the blank from two opposite sides into oblong cross-section with two opposite flat wall sections at a spacing at which the fins on one flat wall section are at their crossings with the fins on the other flat wall section interpressed with the latter fins; and expanding the partially flattened blank to separate the interpRessed fins.

Claim 4

Method of forming tubing, which comprises providing a round metal tube blank having an axis, an annular peripheral wall about said axis, and inner fins on and integral with said wall and extending helically thereon at the same helix angle and parallel to each other, with said fins being of equal height and spaced from said axis; partially flattening the blank from two opposite sides into oblong cross-section with two opposite flat wall sections at a spacing at which the fins on one flat wall section are at their crossings with the fins on the other flat wall section interpressed with the latter fins; and expanding the partially flattened blank to separate the interpRessed fins.

Claim 5

Method of forming tubing as in claim 2, in which the partially flattened blank is expanded by internal fluid pressure.

Claim 6

Method of forming tubing as in claim 2, in which the blank is partially flattened to have the opposite flat wall sections extend parallel to each other.

Claim 7

Method of forming tubing as in claim 2, in which the blank is partially flattened for interpress of the fins on the opposite flat wall sections at their crossings over the entire height of the fins.

Claim 8

Method of forming tubing as in claim 2, in which the blank is partially flattened for interpress of the fins on the opposite flat wall sections at their crossings over less than the height of the fins.

Claim 9

Method of forming tubing as in claim 2, in which the helix angle of the fins in the blank is other than 45*, so that the fins on the opposite flat wall sections cross each other at an angle other than 90*.

Claim 10

Method of forming tubing as in claim 2, in which the blank is partially flattened progressively between rotary companion rolls.

Claim 11

Method of forming tubing as in claim 2, in which the partially flattened blank is by internal fluid pressure expanded with its peripheral wall into near annular cross-sectional shape.

Claim 12

Method of forming tubing as in claim 9, in which the expanded blank is drawn through a round shaping die for formation of its peripheral wall into annular cross-sectional shape.

Claim 13

Method of forming tubing as in claim 2, in which the expanded blank is drawn through a die opening of other than circular cross-section.

Claim 14

Method of forming tubing as in claim 2, in which the expanded blank is passed between rotary companion rolls for formation of its peripheral wall into a cross-sectional shape other than round.