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How to test internal defects of investment castings?

Regarding internal defects of investment castings,commom NDT(none defects testing) methods are RT(radiographic testing) and UT(ultrasonic testing).Among which the effect of RT is better,we could get visual image which could reflect the internal defect type, shape, size and distribution.But to big and thick ihnvestment castings,UT is more effective,it could detect the location of the internal defects,the equivalent size and distribution.

1.RT(microfocus XRAY)

   Radiographic testing,normally radiation source is X ray or Y ray,thus we need ray equipments and other ancillary facilities.When investment castings are exposed in the radiation field,ray radiation intensity will be affected by the casting internal defects.The radiation intensity through investment castings will have local variation according to the size of defects and property.The ray image which have formed defects,will be image recorded by radigraphic film,or real-time detection observed by screen,or will be tested by radiation instrument.The most comon way is real-time detection observed by screen.Defect image reflected by radiographic is intuitive,Defects shape, size, number, plane position, and distribution could all be present,just defect depth could not be tested,which could be confirmed by calculating.

2.UT(ultrasonic testing)

   Ultrasonic testing is also used to test internal defects of investment castings.It is spread in the internal of investment castings by  a high frequency sound energy beam and produce reflection when meeting internal surface or defects,then we could find the defects.Ultrasonic testing used as a widely non destructive testing way,has lots of advantanges,for example,The detection sensitivity is high and  can detect tiny crack.Besides,The penetration is large and can detect heavy section castings.But the disadvantages are also exsited.It is hard to explain reflection waveform of complex sizes.And when testing we need to refer to stand testing block.