Patent ID: 8191251

Claim:
A method of forming a rustproof film on a PC strand, the method comprising: conveying the PC strand at a line speed of 5 to 10 m/min through a process line; untwisting the PC strand to separate surrounding wires from a core wire in the PC strand; applying a synthetic resin powder coating material on each outer peripheral surface of the core wire and the surrounding wires in the untwisted state; heating to adhere the coating uniformly on each of the peripheral surfaces; cooling to form a resin film, after said cooling operation, twisting the surrounding wires around the core wire, wherein the heating operation includes pre-heating performed before said applying the synthetic resin powder coating material operation and post-heating performed after said applying the synthetic resin powder coating material operation, wherein the heating temperature in the post-heating is set in a range of 120-220° C., wherein the heating temperature in the pre-heating is set 30 to 130° C. higher than the heating temperature in the post-heating operation, wherein the synthetic resin powder coating material has an average grain size of 40 to 50 μm to provide a set thickness for the resin film, and wherein the thickness of the resin film is 200±80 μm.