Firstly, check whether the chromium content of chemical conversion film of color steel plate is controlled between 30-34mg / m. In addition, due to the defects in the treatment section, there are several phenomena such as complete lack of film, partial
film shortage, yellowing of film quality and ash hanging. Therefore, the inspection should be conducted pertinently. The sampling method: in the production process, a small amount of chemical coating plate without covering organic coating shall be
left at the coil head and tail for inspection, and the chromium content of chemical coating shall be sent to the manufacturer of chemical coating regularly, The chromium content of color steel plate can also be determined by X-ray fluorescence, diffraction,
plasma, atomic absorption or chemical analysis. In addition, the causes of defects can be found according to the film quality of the surface described below.
The reason of complete membrane defect of shape a
(1) The proportion of phosphating solution in color steel plate is out of proportion, the content of dihydrogen phosphate is low or the free acid is too high（ 2) Degreasing is not clean;
(3) The temperature of the environment is low and the time is short（ 4) There are many impurities, such as so; Many;
(5) The steel strip has a hardening layer on the surface.
B. reasons for ash hanging on the surface of steel strip B
(1) Too much precipitation in the chemical liquid tray, which is stirred up during construction, attached to the steel strip（ 2) The oxidant in the study liquid is too much;
(3) The temperature of chemical solution is high.
The reasons of yellowing of C chemical conversion film
(1) Acid ratio is out of order;
(2) The temperature of the environment is low and the time is short（ 3) There is a phenomenon in the surface;
(4) The oxidation dose is low;
(5) Fe2* content is too high;
(6) C1 "content is much;