Defects and causes of surface treatment before coating?

First check whether the chromium content of the chemical film is controlled between 30~34mg/㎡. In addition, since the defects in the chemical conversion treatment section mainly include several phenomena such as complete lack of film, partial lack of film, yellowing of film quality and ash hanging, etc., the inspection should also be carried out in a targeted manner. The sampling method for inspection: during the production process Leave a small amount of chemically coated panels not covered with organic coatings at the head and tail of the roll as samples for inspection, and send them to the chemical coating manufacturer to test the chromium content of the chemical coating on a regular basis. X-ray fluorescence, diffraction, plasma, atomic absorption or chemical Analytical method for determination of chromium content. In addition, the cause of defects can also be found according to the film quality of the surface described below.

A cause of complete lack of membrane

(1) The composition ratio of the phosphating solution is out of balance, the content of dihydrogen phosphate is low or the free acid is too high;

(2) Degreasing is not clean;

(3) The ambient temperature during the formation process is low and the time is short;

(4) Contains many impurities;

(5) There is a hardened layer on the surface of the steel strip;

Reasons for hanging dust on the surface of B steel belt

(1) There is too much precipitation in the chemical liquid material pan, and the precipitation is stirred up during construction and attached to the steel belt;

(2) Excessive oxidant in the chemical liquid;

(3) The temperature of the chemical liquid is high;

C The reason for the yellowing of the chemical conversion coating

(1) Acid ratio imbalance;

(2) The ambient temperature is low and the time is short during formation;

(3) There is excessive turbidity on the surface;

(4) Less amount of oxidant;

(5) Fe ²⁺ content is too high;

(6) Cl ^- content is high;

(7) The liquid contains arsenic impurities;

D Cause of local lack of membrane

(1) The steel belt is not clean after degreasing;

(2) Accumulation of hydrogen on the surface of the steel strip;

(3) Insufficient nitrate;

(4) The temperature is too low.