METHOD FOR FORMING RUSTPROOF FILM ON PC STRAND

Provided is a method for the highly efficient formation of a uniform, high-quality film with which increased line speed, improved productivity, and cost reduction can be envisaged. A method for forming a rustproof film on PC stranded (1) conveying the PC strand through a process line, including untwisting step of untwisting the PC strand to separate surrounding wires (1b) from a core wire (1a) in the PC strand; a coating step of applying a synthetic resin powder coating material on each outer peripheral surface of the core wire and the surrounding wires in the untwisted state; a heating step of heating to adhere the coating uniformly on the core wire and the surrounding wires; a cooling step of cooling the coating uniformly adhered on the core wire and the surrounding wires through the coating step and the heating step; a twisting step of twisting the surrounding wires with a resin film (26) to restore the original state with the core wire provided with the resin film, wherein: the heating step includes pre-heating and post-heating performed before and after the coating step of applying the synthetic resin powder coating material, the heating temperature in the post-heating is set in the range of 150-250 C, the heating temperature in the post-heating is set in the range of 120-220 C, and the heating temperature in the pre-heating is set 30 to 130 C higher than the heating temperature in the post-heating, the synthetic resin powder coating material has an average grain size of 40 to 50 µm to provide a thickness set for the resin film, the series of process lines has a line speed of 5 to 10 m/min, wherein: resin film in thickness of 200±80 µm is formed respectively on the core wire and the surrounding wires

Provided is a method for the highly efficient formation of a uniform, high-quality film with which increased line speed, improved productivity, and cost reduction can be envisaged. A method for forming a rustproof film on PC stranded (1) conveying the PC strand through a process line, including untwisting step of untwisting the PC strand to separate surrounding wires (1b) from a core wire (1a) in the PC strand; a coating step of applying a synthetic resin powder coating material on each outer peripheral surface of the core wire and the surrounding wires in the untwisted state; a heating step of heating to adhere the coating uniformly on the core wire and the surrounding wires; a cooling step of cooling the coating uniformly adhered on the core wire and the surrounding wires through the coating step and the heating step; a twisting step of twisting the surrounding wires with a resin film (26) to restore the original state with the core wire provided with the resin film, wherein: the heating step includes pre-heating and post-heating performed before and after the coating step of applying the synthetic resin powder coating material, the heating temperature in the post-heating is set in the range of 150-250 C, the heating temperature in the post-heating is set in the range of 120-220 C, and the heating temperature in the pre-heating is set 30 to 130 C higher than the heating temperature in the post-heating, the synthetic resin powder coating material has an average grain size of 40 to 50 µm to provide a thickness set for the resin film, the series of process lines has a line speed of 5 to 10 m/min, wherein: resin film in thickness of 200±80 µm is formed respectively on the core wire and the surrounding wires