Coating of the inner surface of tubes

A spray coating tool for continuously and gradually coating the inner surface of a tube by means of spraying a desired paint from a nozzle, while being shifted inside along the axial direction of said tube, comprising:

• a nozzle cap consisting of a hollow cylindrical portion, a hollow conical portion extended therefrom, and a gas blowing opening formed at a zenith of said hollow conical portion;
• a nozzle insert installed in said nozzle cap, consisting of a hexagonal prism portion inscribed in said hollow cylindrical portion of said nozzle cap, and provided with three spiral grooves on the external surface thereof, a conical portion extended from said hexagonal prism portion, being faced with a small gap to the inner surface of said hollow conical portion of said nozzle cap, and a paint supply passage extending through along the axis of said nozzle insert;
• an outer cylindrical casing, to which said nozzle cap is connected;
• an inner cylindrical casing disposed in said outer cylindrical casing, to which said nozzle insert is connected;
• a first center guide, for connecting said nozzle cap to one end of said outer cylindrical casing, being of hexagonal shape in cross section with a dimension suitable to be inscribed to the inner surface of said tube to be coated;
• a second center guide fastened to the other end of said outer cylindrical casing, being of hexagonal shape in cross section, with a dimension suitable to be inscribed to the inner surface of said tube to be coated;
• and
• a double hose connected via said second center guide to said outer cylindrical casing, whose inner tube being a paint supply passage and outer tube an atomizing gas passage, whereby atomizing gas supplied between said nozzle cap and said nozzle insert, being imparted a straight going force by six straightly elongated grooves formed between the inner surface of said nozzle cap and each of six sides of said hexagonal prism portion and a spirally going force by the three spiral grooves, will be blown through said gas blowing opening so as to spirally spray in atomization the paint supplied from the inner tube of said double hose through to said inner cylindrical casing and the paint supply passage along the axis of said nozzle insert.