The inner coating of large-diameter plastic-coated steel pipes for water supply and drainage

1. heating of steel pipes: hoist the steel pipes after blasting and purging onto the coating conveying roller table, and heat them with intermediate frequency induction coils. choose intermediate frequency induction heating coils of different specifications according to coating thickness, pipe diameter, and pipe wall thickness. when heating, rotate the steel pipe evenly to make the temperature of each part of the heated steel pipe uniform. the temperature difference is controlled at ±5°c.
2. when the temperature of the coated steel pipe reaches the coating temperature, start the coating trolley and open the powder outlet valve to make the powder evenly adhere to the surface of the steel pipe. before coating, calculate the powder supply amount and trolley speed according to the diameter of the steel pipe and the required coating thickness. trial coating once, coating can be carried out only after meeting the process requirements. parameters such as the powder plastic (solidification) time are by the regulations of the powder manufacturer.

grinding of large-diameter plastic-coated steel pipes for water supply and drainage:
after the steel pipe is coated, the inner and outer coatings at the end of the steel pipe should be ground. the epoxy resin powder coating on the inner surface should be removed within 30mm from the port, and the other 20mm should be ground into a gradient transition layer; the polyethylene coating on the outer surface requires remove it within 150mm from the port, and grind the end of the coating into a 30° bevel.

1. internal sandblasting of large-diameter plastic-coated steel pipes for water supply and drainage
1.1 before sandblasting, carefully remove the welding slag and splash attachments on the steel pipe, smooth the weld scars, burrs, etc., and clean the visible grease and other dirt on the surface of the metal substrate. that is to completely remove all sundries such as grease, scale, rust, etc. on the metal surface, and the area of slight discoloration caused by the remaining rust spots, scale, etc., shall not exceed 5% on any 100mm×100mm area.
1.2 for the sandblasting treatment of pipe fittings, the de-rusting grade adopts the gb/t8923-1988 standard, the outer surface is sa2 1/2 level anchor grain depth 70-90μm, and the inner surface is sa2 level anchor grain depth 40-70μm.
1.3 measure the surface of the steel pipe after sandblasting, and blow it with dry compressed air after meeting the relevant requirements. mpa), remove internal dust and residual steel grit.
1.4 the pipe fittings after blasting treatment should be heated up immediately, and placed at room temperature for no more than 24 hours to prevent the surface of the steel parts from being damp and rusted. if the surface of the steel pipe is found to be polluted or rusted before coating, it shall be reprocessed to the original rust removal level.
1.5 check the quality, cleanliness, and roughness of the surface pretreatment before coating, and enter the coating process after passing the test.
1.6 sandblasting can only be carried out when the relative humidity in the air is lower than 85%, the ambient temperature is not lower than 5°c or the surface temperature of the steel plate is not lower than 3°c above the atmospheric dew point.

2. coating of large-diameter water supply and drainage plastic-coated steel pipes
2.1 heating of steel parts: hoist the blasted and purged pipes onto the coating conveying roller table, and heat them with a heating furnace. heating to a certain temperature according to the coating thickness, pipe diameter, and pipe wall. the temperature difference is controlled at ±5°c.
2.2 coating: when the temperature of the pipe fittings reaches the coating temperature, start the coating trolley and open the powder outlet valve to make the powder evenly adhere to the surface of the pipe fittings. parameters such as the powder plastic (solidification) time are by the regulations of the powder manufacturer.
3. grinding of pipe fittings: after the pipe fittings are coated, the inner and outer coatings at the end of the steel pipe should be ground. the epoxy resin powder coating on the inner surface should be removed within 30mm from the port, and the other 20mm should be ground into a gradient transition layer; the polyethylene coating on the outer surface is required to be removed within 150mm from the port, and the end of the coating should be ground to a 30° bevel.