Heat transfer tube having grooved inner surface and production method therefor

A method for producing a heat transfer tube having a grooved inner surface, comprising:

• a rolling step of running a metallic board material between at least one pair of fin forming rollers so as to roll onto a surface of said board material a pair of projecting strip portions parallel to both side edges of said board material and respectively separated from said side edges, and a plurality of fins which are arranged in an area between said projecting strip portions so that said fins are arranged at an angle which intersects with the axis of said heat transfer tube;
• a tube forming step of passing the board material onto which said projecting strip portions and said fins have been formed through a plurality of forming rollers so as to form said board material into a tube with said projecting strip portions and said fins positioned on the inside surface;
• and
• a welding step of heating both side edges of said board material which has been formed into a tube shape and adjoining said side edges.

A heat transfer tube having a grooved inner surface, comprising:

• a metallic tube having an inner circumferential surface;
• a plurality of fins formed on said inner circumferential surface of said metallic tube so as to protrude from said inner circumferential surface;
• and
• a weld portion formed on the inner circumferential surface of said metallic tube, extending in an axial direction of said metallic tube;
• wherein
• the thickness of said metallic tube in groove portions formed between said fins is formed such as to increase in approaching said weld portion in an area surrounding said weld portion wherein the central angle is within 30.degree..about.90.degree. on both sides from the center of said weld portion.

A method for producing a heat transfer tube having a grooved inner surface, comprising:

• a rolling step of running a metallic board material between al least one pair of fin forming rollers so as to roll onto a surface of said board material a plurality of fins which protrude from said surface, such that the thickness of said board material in groove portions between said fins increases in approaching side edges of said board material within areas around said side edges extending to 10.about.30% of the width of said board material;
• a tube forming step of passing the board material onto which said fins have been formed through a plurality of forming rollers to form said board material into a tube shape with said fins positioned on the inside;
• and
• a welding step of heating both side edges of said board material which has been formed into a tube shape and adjoining said side edges.

A heat transfer tube having a grooved inner surface, comprising:

• a metallic tube having an inner circumferential surface;
• a plurality of fins formed on said inner circumferential surface of said metallic tube so as to protrude from said inner circumferential surface;
• and
• a weld portion formed on the inner circumferential surface of said metallic tube, extending in an axial direction of said metallic tube;
• wherein
• the bottom widths of groove portions formed between said fins are formed such as to gradually increase in approaching said weld portion in an area surrounding said weld portion wherein the central angle is within 30.degree..about.90.degree. on both sides from the center of said weld portion.

A method for producing a heat transfer tube having a grooved inner surface, comprising:

• a rolling step of running a metallic board material between al least one pair of fin forming rollers so as to roll onto a surface of said board material a plurality of fins which protrude from said surface, such that the bottom widths said groove portions between said fins increases in approaching side edges of said board material within areas around said side edges extending to 10.about.30% of the width of said board material;
• a tube forming step of passing the board material onto which said fins have been formed through a plurality of forming rollers to form said board material into a tube shape with said fins positioned on the inside;
• and
• a welding step of heating both side edges of said board material which has been formed into a tube shape and adjoining said side edges.