Process for coating polyurethane on inner and outer surface of nodular graphite cast iron pipe

Abstract

The technological process of painting polyurethane to inner and outer surface of nodular cast iron pipe includes the successive steps of: surface treatment comprising outer surface shot blast and inner surface polishing; surface repairing including filling the notches with putty; heating to temperature of 20-80 deg.c; spraying inner surface with high pressure air-free spraying machine, spraying bogie and spraying gun; spraying outer surface with high pressure air-free spraying machine, spraying bogie and spraying gun; coating detection comprising detecting coating thickness and electric spark detection; and product packing. The present invention has the advantages of simple construction, wide coating application temperature range, high coating mechanical strength, stable chemical performance and no environmental pollution.

Description

(1) Technical field [0001] The invention belongs to a coating process for the inner and outer surfaces of ductile iron pipes. (two), background technology [0002] At present, the inner surface of domestic ductile iron pipes is lined with cement, and the outer surface is sprayed with coal tar pitch. Coal tar pitch coating has the following disadvantages: (1) coal tar pitch is a solvent-based coating, and solvent volatilization pollutes the environment. Coal tar pitch is a carcinogen and endangers the health of workers. The country has expressly stipulated that the use of coal tar pitch paint is prohibited; (2 ) The drying time is slow, and it needs to be heated and cured in a curing furnace, which not only increases the production cost, but also affects the production efficiency; (3) The solid content of coal tar asphalt coating is low, and the spraying thickness is limited, and the thickness range is 70-100 μm; (4) Asphalt coating (5) The asphalt coating has poor chemical ...

AI Technical Summary

Problems solved by technology

Coal tar pitch coating has the following disadvantages: (1) coal tar pitch is a solvent-based coating, and the solvent volatilizes and pollutes the environment. Coal tar pitch is a carcinogen and endangers the health of workers. ) The drying time is slow, and it needs to be heated and cured in a curing furnace, which not only increases the production cost, but also affects the production efficiency; (3) The solid content of coal tar asphalt coating is low, and the spraying thickness is limited, and the thickness range is 70-100 μm; (4) Asphalt coating Poor mechanical properties of the layer, such as poor adhesion, high brittleness, and poor wear resistance; (5) Asphalt coatings have poor chemical corrosion resistance, such as poor acid and alkali resistance, and poor salt spray resistance

The cement coating has the following disadvantages: (1) The cement coating needs to be maintained and the production pace is slow; (2) The cement coating is alkaline and not acid-resistant; (3) The surface of the cement coating is rough, resulting in large water resistance. Leading to waste of energy in pipeline transportation; (4) The cement coating is brittle, easy to crack, and easy to fall off; (5) The cement coating is not wear-resistant and has a short service life, and the water delivery life is generally 20 to 30 years

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