Flux cored wire and manufacturing method thereof and manufacturing device thereof

A flux cored wire comprising:

• an inner tubular body formed with a first flat strip by curling up side edges of the first flat strip into a tubular body having a first seam and filled with flux inside;
• and
• an outer tubular body formed with a second flat strip by curling up side edges of the second flat strip into a tubular body having a second seam and wrapping around the inner tubular body in tight contact,
• wherein the first and second seams of the inner tubular body and the outer tubular body are located at different positions,
• wherein diameters of the inner tubular body and the outer tubular body are reduced by a drawing process,
• wherein the first and second flat strips of the inner tubular body and the outer tubular body are rolled so that longitudinal edges contact with opposite longitudinal edges to form circular cross-sections, and a thickness of a wall of the outer tubular body is greater than a thickness of a wall of the inner tubular body, and
• wherein a ratio of the flux filled inside of the inner tubular body is between 30% to 40% by weight of the entire inner tubular body including the flux, and wherein a ratio of the flux filled inside of the inner tubular body is between 12% to 15% of the total weight of the inner tubular body including the flux and the outer tubular body.