Method for forming rustproof film on PC strand and PC strand

A method for forming a rustproof film on a PC strand comprising a series of steps of:

• untwisting a PC strand and loosening surrounding wires from a core wire;
• performing pre-heating while adjusting the core wire and maintaining a loosened state;
• applying a synthetic resin powder coating material on outer peripheral surfaces of the core wire and surrounding wires and forming a resin coating adhered thereto respectively;
• performing post-heating;
• cooling the wires and forming resin films individually on outer peripheral surfaces of the core wire and the surrounding wires;
• and
• twisting the surrounding wires on the core wire into an original state, wherein
• the thickness of the resin film is set to 200±80 μm,
• the pre-heating is performed within a temperature range from 60 to 150° C. so as to prevent an occurrence of a cob-webbing phenomenon as a result of melting of the synthetic resin powder coating material and the post-heating is performed within a temperature range from 150 to 250° C. in order to uniformize the thickness of the coating adhered respectively to the outer peripheral surfaces of the core wire and the surrounding wires, and the temperature of the pre-heating is set to a temperature lower than the temperature of the post-heating,
• the synthetic resin powder coating material including particles having diameters in a range from 0.1 to 250 μm is used, and the line speed in the series of steps is set to 5 to 10 m/min, and
• wherein the temperature of the pre-heating is set to be at least 20° C. lower than the temperature of the post-heating.