Method for manufacturing a tube fitting

A method for manufacturing a coated tube fitting that is capable of coupling a tube made from metal and provided with an annular portion upon an end portion thereof, to a mating member by being installed upon an external periphery of the tube and by being fastened to the mating member in a state wherein the coated tube fitting contacts the annular portion, the annular portion projecting in a radially outward direction from the tube, the method comprising:

• a preparation step of preparing a tube fitting;
• and
• a coating step of forming a resin coating layer upon a coated region provided upon a surface of the tube fitting;
• wherein:
• the coating step comprises a dipping step of dipping the tube fitting into a coating material that includes as components a polyethylene based substance, a lubricant, and solid particles and having viscosity within a range of 4.24 to 5.27 mPa·s at 25° C. measured using a rotational viscosimeter conforming to the ISO 2555:1990 standard with a rotational speed of a spindle of the rotational viscosimeter set to 60 rpm, and adhering the coating material to the coated region, and a drying step of, after the dipping step, drying the coating material which is adhered to the coated region of the tube fitting;
• and
• in the dipping step, with mass per unit area w (g/m2) of the resin coating layer being defined as being a value obtained by dividing a mass difference between a state of the tube fitting with the resin coating layer and a state of the tube fitting without the resin coating layer by a surface area of the coated region, the mass per unit area w is controlled within a range 0.79<w<10.07 by dipping the tube fitting while regulating a temperature of the coating material within a range of 30° C. to 40° C.