How is the inner and outer coating of ductile iron pipe constructed?

The construction methods of the inner and outer coating of ductile iron pipes are different, and the following is a specific introduction:

Inner coating application

Cement mortar inner coating construction

Preparation: First of all, the inner wall of the ductile iron pipe should be cleaned to remove oil, rust, dust and other impurities. Mechanical sandblasting or chemical cleaning can be used to achieve the specified cleanliness and roughness of the inner wall. Then, according to the specifications and construction requirements of the pipeline, prepare the cement mortar spraying equipment, such as spray gun, air compressor, mortar mixer, etc., and debug the equipment to normal operation. At the same time, prepare cement, sand, additives and other materials according to the design mix ratio to ensure that the material quality meets the requirements.

Spraying construction: The mixed cement mortar is evenly sprayed on the inner wall of the pipeline through the spray gun. When spraying, it is necessary to control the pressure, Angle and moving speed of the spray gun to ensure uniform coating thickness. Generally speaking, the pressure of the spray gun is controlled between 0.3-0.5MPa, and the moving speed is about 1-2 meters per minute. For pipelines with large pipe diameters, automatic spraying equipment can be used to improve construction efficiency and coating quality.

Curing treatment: After spraying, the inner coating of cement mortar should be cured in time. The curing method is usually to maintain a certain humidity in the pipeline, which can be used to inject water or cover wet sacks in the pipeline, and the curing time is generally 7-14 days to ensure that the cement mortar is fully hydrated to meet the design strength and performance requirements.

Epoxy resin inner coating construction

Surface treatment: The inner wall of the pipeline is also strictly cleaned and derusted first, requiring high cleanliness and roughness to ensure good adhesion between the epoxy resin coating and the pipe wall. Generally, sandblasting is used to make the surface of the pipe wall show a uniform pockmarked surface, and the roughness reaches Ra 50-100μm or so.

Coating construction: There are many coating methods of epoxy resin coating, common brush coating, roll coating and spray. Spraying method is commonly used for coating construction in ductile iron tubes. Pour the epoxy paint into the spray equipment and spray the paint evenly on the inner wall of the pipe through the spray gun. When spraying, pay attention to the ambient temperature and humidity, the general temperature is controlled between 5-35 ° C, and the humidity does not exceed 80%. At the same time, according to the characteristics of the coating and coating thickness requirements, control the pressure and spraying times of the spray gun, usually need to spray 2-3 times, each spraying interval according to the drying time of the coating, generally 2-4 hours.

Curing treatment: After coating is complete, the epoxy coating is cured under specified temperature and humidity conditions. Curing time varies according to the type of paint and environmental conditions, generally 24-72 hours. During the curing process, the pipeline should be avoided from external pollution and damage to ensure that the performance of the coating reaches the best state.

Coating application

Asphalt paint external coating construction

Surface pretreatment: First of the outer wall of the ductile iron pipe for rust and oil removal treatment, can use shot blasting or chemical rust removal method, so that the outer wall surface cleanliness of Sa2.5 or more, that is, completely remove the metal surface of oil, rust, oxide and other impurities, so that the surface shows a uniform metal luster.

Painting construction: the asphalt paint is heated to the specified temperature, generally 150-180 ° C, so that it has good fluidity and coating performance. Then, the asphalt paint is evenly coated on the outer wall of the pipeline by spraying or dipping. When spraying, it is necessary to control the pressure and distance of the spray gun to ensure uniform coating thickness, and the general coating thickness is 0.2-0.5mm. When dipping, make sure that the pipe is soaked in the asphalt paint for enough time to ensure the integrity and thickness of the coating.

Cooling and drying: After painting is completed, let the pipe cool naturally or use air cooling to cool it quickly, so that the asphalt paint solidifies quickly. In the drying process, to prevent the coating by rain, dust and other pollution, the general drying time is 24-48 hours.

Polyethylene outer coating construction

Surface treatment: Rust removal, oil removal and coarsening treatment are carried out on the outer wall of the ductile iron pipe to improve the adhesion between the polyethylene coating and the pipe wall. Sandblasting is usually used to make the surface roughness of the tube wall reach Ra 30-50 μm.

Coating process: The common construction methods of polyethylene outer coating are extrusion winding method and spraying method. The extrusion winding method is to heat polyethylene particles to a molten state, extrude them into bands by an extruder, and then wind them on the outer wall of the pipe to form a coating. The spraying method is to spray polyethylene powder on the outer wall of the preheated pipe through a special spray gun, and the powder is melted at high temperature and attached to the pipe wall to form a coating. No matter which method is used, it is necessary to control the construction temperature, speed and coating thickness. The general construction temperature is between 200-250 ° C, and the coating thickness is determined according to the engineering requirements, usually 1-3mm.

Quality testing: After the construction is completed, the quality of the polyethylene outer coating should be tested, mainly to check the thickness, adhesion, pinhole and other indicators of the coating. The coating thickness was measured by magnetic thickness gauge, the adhesion was measured by grid method, and the pinhole was detected by high voltage EDM tester. If the problem is found, timely repair or rework treatment to ensure the quality and protective performance of the outer coating.