Because of PE powder coating, the preheating temperature of the steel pipe is as high as 300℃. And for EP powder coating, the preheating temperature of the steel pipe is 200℃. The curing temperature of EP and PE powders is 200℃. Of course, the preheating temperature of the steel pipe varies slightly according to the different tempering of the powder.
PE powder undergoes physical changes during curing and can be repeatedly heated, melted, and cured. EP powder undergoes chemical changes during curing, which are irreversible after curing and cannot be repaired.
In the PE powder coated steel pipe, due to the high temperature, only the inside and outside can be coated at the same time. Therefore, the production line is equipped with an internal coating mechanism and an internal and external coating mechanism in the preheating furnace and the surface drying furnace, an internal coating buckle powder system, an internal coating push-pull rod spraying system, and a fluidized bed dip coating PE powder. Various internal coating methods can be targeted at various customer requirements, and the coating method can be flexibly selected.
The steel pipe is coated externally between the flat surface drying furnace and the bridge curing furnace of the production line. A connecting device is set between the flat surface drying furnace and the bridge-type curing furnace, which is a lifting and translation device, so that the steel pipe is connected from the flat surface drying furnace to the steel pipe external coating.
In terms of coating method, the small-diameter pipe DN15-DN300 adopts steel pipe rotation, with clamping rotating seats at both ends, and the electrostatic powder spraying gun reciprocates along the longitudinal translation of the steel pipe to perform powder spraying operations and complete the steel pipe external coating process.
The large-diameter steel pipe DN15-DN500 adopts a steel pipe that does not rotate. The external coating powder spraying box carries an electrostatic powder spraying gun, which reciprocates and moves along the longitudinal direction of the steel pipe to complete the powder spraying operation.
The small-diameter steel pipe DN15-DN100 pipe mouth is slightly manually sprayed with powder, and the appearance quality of the pipe mouth after curing can meet the requirements.
If the large-diameter steel pipe DN100-DN500 adopts a clamping seat to clamp the steel pipe rotation, the plastic-coated steel pipe mouth will inevitably form a powder rotating device, and the quality of the plastic-coated steel pipe mouth after curing is not beautiful. Therefore, it is advisable to adopt a spraying method in which the steel pipe does not rotate and the spray gun swings longitudinally. Since the steel pipe is directly suspended on the bridge-type curing furnace, the mouth of the plastic-coated steel pipe does not have a clamping seat. After external spraying, it directly enters the curing furnace, and the appearance quality of the pipe mouth is beautiful after curing. 20 years ago, because the problem of spray gun swinging could not be solved, the problem of uniform powder coating on the steel pipe could not be solved, so this method of direct spraying without rotating the steel pipe was cancelled. In the past 10 years, most domestic steel pipe external coating methods have that the steel pipe adopted a clamping seat to rotate, and the electrostatic powder spray gun moves longitudinally along the steel pipe for spraying. This method is still difficult to deal with the quality problem of the mouth of the plastic-coated steel pipe. Due to the existence of the spray gun swinging mechanism, the uniformity of the coating on the steel pipe is improved. The relative position of the steel pipe and the spray gun has rotation and longitudinal movement, so that the steel pipe can be sprayed with powder evenly.
Post time: Jul-11-2025