NAVISTAR CEMS AT-1 2001 Edition, October 1, 2001
Ultrasonic Steel Cleanliness Test
This method covers a procedure for rating steel cleanliness by means of an automatic computerized ultrasonic system. The test is performed on a volumetric rather than a surface examination basis and thus inherently has a much greater capability of providing reliable inclusion content information. The system provides for detecting and counting various size inclusions. It consists of an ultrasonic test instrument, a search unit, a means of recording signals, reference test blocks and an immersion tank with suitable scanning facilities. Pulsed sound waves penetrate the steel sample through a fluid coupling and upon encountering a discontinuity such as a nonmetallic inclusion, are reflected with an energy level dependent upon the defect area and contour. The reflected ultrasound is sorted into 16 evenly spaced categories or inclusion size levels and counted. The computer calculates a cleanliness index which is based upon the percentage of counts in each category multiplied by an empirical weighting factor for each category.