1.Poor ultrasonic penetration
The complex interface of coarse grain and uneven structure enhances the scattering of ultrasonic wave, and the energy attenuation is large, so that the detectable thickness is smaller than that of forgings.
2.There are many interference clutter
When the sound wave scatters on the interface of non-uniform, non dense structure and coarse grain, the scattering signal intensity is large and is received by the probe; The rough casting surface will form clutter when it reflects the sound wave; These will be displayed as messy forest echo (also known as grass echo) on the oscillograph screen, which may drown the defect echo and hinder the identification of the defect echo.
3.Poor surface coupling conditions
The surface of steel castings is rough, which is not conducive to acoustic coupling. The surface hardness is large and grinding is difficult.
4.It is difficult to quantify defects
Due to the large attenuation of sound wave and complex defect shape of steel castings, the quantitative evaluation of defects based on artificial defects has large error, and it is more difficult to quantify defects by calculation method.
The above is the difficulty of casting inspection, which limits the casting inspection to a certain extent. On the other hand, due to the low quality requirements of castings, the size and quantity of single defects are allowed to be large, and the regularity of casting defects is strong, so the casting inspection still has a certain value.