Process for spraying polyurethane on inner wall of nodular cast iron pipe

The invention relates to a process for spraying polyurethane on the inner wall of a nodular cast iron pipe, in particular to the process for spraying the polyurethane on the inner wall of the DN100-DN300 nodular cast iron pipe. The steps of the process are as follows: 1. processing the inner surface: (1) removing rust and oxide skins; (2) shot-blasting, further removing the rust on the surface of the nodular cast iron pipe, and eliminating stress; (3) removing floating dust; 2. heating and drying; 3. preparing for the spraying: (1) storing coatings; (2) stirring the coatings; (3)_heating and heat-preserving the coatings; (4)_spraying for trial; 4. spraying the polyurethane: polyurethane components A and B are heated, filtered and heat-preserved according to the volume ratio of 1:1, are conveyed into a special mixer under high pressure for high-speed collision mixing or spiral mixing, and are then sprayed onto the surface of the nodular cast iron pipe by a spray gun or a spray cup at high speed in an atomized manner; 5. cleaning the mixer and the spray gun or the spray cup. The thickness of a film formed in one step can be up to 3mm and the adhesive power of the coatings is high, so that the invention can meet the demand for spraying the polyurethane on the inner wall of the small-caliber nodular cast iron pipe.