In order to check the quality of the paint film in the container (steel phase, gasoline drum, etc.), first fill the tested container with water at room temperature (15~20°C), and use 1% vaporized passivation solution for half an hour. Instead of water (relevant instrument: constant temperature Water Tank). Then, after half an hour, a metal hollow conduit is hung into the container, and a plastic rod with a heavy homemade (or made of extra heavy brass sheet) electrode is inserted into the tube. The upper end of the pipe is connected with the outer surface of the container by clips. The electrode is connected to the positive terminal of the galvanometer, and the clip is connected to the negative terminal. (Related instrument: conductivity meter)
The indication of the current meter can be used as the criterion for judging the porosity of the coating film.
When the galvanometer indicator is from 0 to 6.0x10 -6 amperes, it can be considered that the coating film is very good; when the galvanometer indicator reaches 1.8·10 -5 amperes, it can be considered that the coating film is qualified; When the indicator is from 1.86 to 6.0·10-5 amperes, it can be considered that the coating film is porous and needs to be modified. When the indicator exceeds 6.0·10 -5 amps, a new coating is required.
A schematic diagram of the test porosity apparatus is shown in Figure 168.
Porosity can also be determined as follows. Hang a metal rod with a rubber stopper at one end into the painted container so that it approaches the bottom of the container. The metal rod is connected to the positive pole of the power supply (4~6 volts), and the negative pole is connected to the metal needle attached to the outer surface of the container through a milliampmeter. Pour the applicable electrolytic solution (sodium vapor, sulfuric acid blunt, etc.) into the container to reach %. The indication of the milliampere meter can be used as a criterion for judging the porosity of the coating film.
