Ultrasonic inspection can also be found lost wax casting, internal defects such as porosity, crack, inclusion, shrinkage, etc.Wall thickness of steel, using this method can detect the biggest (1000 mm) of a method.The working frequency of ultrasonic inspection with often above 1 MHZ.Ultrasonic spread from one medium to another medium in the interface will produce reflection, especially when the ultrasound by metal to air almost 99% to reflect from the interface.Ultrasonic inspection is the application of this feature to find the internal defects of casting.When the probe to move slowly on the castings, such as the lost wax casting casting defects, the reflection on the oscillograph screen appears only detect T wave and reflection on the bottom of form B wave;If something defective castings, also appeared on defect reflection of F wave, the defects, the greater the F wave height is, the greater the which can determine the location and severity of defects in the castings.