Extrusion die for manufacturing tube with small hollow portions, mandrel used for said extrusion die, and multi-hollowed tube manu-factured by using said extrusion die

A mandrel to be combined with a female die for regulating an outer periphery of a tube with a plurality of small hollow portions arranged in a width direction of the tube to form an extrusion die for manufacturing the tube,

• wherein said mandrel includes a body portion and a comb-shaped portion protruded from said body portion, said comb-shaped portion including a plurality of columnar portions disposed in a width direction of said comb-shaped portion at certain intervals,
• wherein an outer periphery of a tip end portion of each of said plurality of columnar portions constitutes a bearing portion for defining an inner periphery of each of the plurality of small hollow portions of the tube,
• wherein each of said plurality of columnar portions has outside surfaces opposed in a thickness direction of said comb-shaped portion, and at least one of said outside surfaces has an inwardly dented portion behind said bearing portion, said inwardly dented portion constituting an extrusion material filling space, and
• wherein said at least one of said outside surfaces extending from a basal end portion of each of said plurality of columnar portions to said inwardly dented portion is formed into an inclined or curved surface for leading extrusion material to said inwardly dented portion, and said at least one of said outside surfaces extending from said dented portion to said bearing portion is formed into an inwardly curved surface.

A method for manufacturing a heat exchanging tube by extruding extrusion material through an extrusion die, wherein said extrusion die comprises:

• a female die for defining an outer periphery of the tube;
• and
• a mandrel combined with said female die,
• wherein said mandrel includes a body portion and a comb-shaped portion protruded from said body portion, said comb-shaped portion including a plurality of columnar portions disposed in a width direction of said comb-shaped portion at certain intervals,
• wherein an outer periphery of a tip end portion of each of said plurality of columnar portions constitutes a bearing portion for defining an inner periphery of each of the plurality of small hollow portions of the tube,
• wherein each of said plurality of columnar portions has outside surfaces opposed in a thickness direction of said comb-shaped portion, and at least one of said outside surfaces has an inwardly dented portion behind said bearing portion, said inwardly dented portion constituting an extrusion material filling space, and
• wherein said at least one of said outside surfaces extending from a basal end portion of each of said plurality of columnar portions to said inwardly dented portion is formed into an inclined or curved surface for leading extrusion material to said inwardly dented portion, and said at least one of said outside surfaces extending from said dented portion to said bearing portion is formed into an inwardly curved surface.