PURPOSE: To facilitate the formation of a lining layer and enable rigid bonding by spraying polyurethane resin to the inner surface of an iron tank to form a polyurethan resin lining layer.

CONSTITUTION: Cold setting polyurethane resin is sprayed onto the inner surface of an iron tank 2, forming the outer layer of a barrel tank 1, by a nozzle gun so as to provide a polyurethane resin lining layer 3. This lining layer 3 is naturally hardened to manufacture the desired barrel tank 1. The thickness of the lining layer 3 can be set freely by the spraying time quantity, but 10-15mm is appropriate in the case of the barrel tank 1. The hardness of the hardened lining layer 3 ideal for barrel polishing is 80°-90° (JIS-A specification). Or a 475 thermosetting polyurethane resin containing an inorganic polishing material is sprayed onto the inner surface of the iron tank 2 to form the lining layer 3.