Abstract: A method and apparatus for coating a long tube of small diameter by means of inserting a supplying hose of double structure, with a spray nozzle ahead and two separately extending inner and outer hoses for supplying paint and compressed air respectively therethrough, into the long tube from one end opening thereof toward the other end opening thereof, and retracting the spray nozzle, when it has reached the destination, while spraying the paint at a predetermined speed. The inner hose for the paint is made of flexible material as an elastic hose for being compressive in the diametrical direction under the pressure from the compressed air in the outer hose and again restorable to the original shape when the pressure is released.

Abstract: A spray coating tool used for coating the inner surface of a tube. The tool sprays a desired paint through a nozzle while the tool is being shifted inside the tube to be coated along the axis of the same tube. In the nozzle a nozzle insert having a prism portion, on the external surface of which at least one spiral groove is formed, is inscribed to the inner surface of a hollow cylindrical space of a nozzle cap of the above-mentioned nozzle. A plurality of straightly elongated grooves, formed between the inner surface of the nozzle cap and the sides of the prism portion of the nozzle insert, and the spiral groove function to impart atomizing gas a straightly going force and a spirally going force, so as to spirally spray the paint supplied through a paint supply passage extending along the axis of the nozzle insert.