1) For small and medium-sized castings (especially investment precision castings), they have small volume, light weight and less processing capacity. They can be magnetized in at least two roughly vertical directions on the fixed magnetic particle flaw detector. It is better to use DC or pulsating DC current and test it by wet continuous method. Direct energization method, threading method, magnetization method and coil method can be used.
2) For larger and heavier castings, magnetization shall be carried out locally or in zones in at least two roughly vertical directions. It is better to use the portable or mobile magnetic particle flaw detector with DC or half wave rectification, and use the contact method or yoke method, dry method continuous method or wet method continuous method to detect the local or zoning of castings. The detection shall generally be carried out in two mutually perpendicular directions.
3) In order to prevent the casting in contact with the electrode from burning out, it is recommended to take the following measures: do not turn on the current when the contact is not in full contact with the casting surface, and remove the contact only when the current has been disconnected. And use sufficiently clean and suitable contacts. For the machined smooth surface, the yoke method should be used.
4) Due to the influence of casting stress, some cracks (cold cracks) of steel castings will delay cracking, so they should not be tested immediately after casting, but should be tested again after 1 ~ 2 days.
5) If the casting defect exceeds the acceptance standard and is rejected, and excavation (shovel) and repair welding are allowed, pay attention to controlling the generation of delayed cracks in the repair welding area.
6) The inspection shall be carried out with the naked eye, and a magnifying glass of no more than 3 times can be used only in the inspection of quality grades 001 and 01.