POSSIBILITY OF IDENTIFYING DEFECTS IN MASSIVE CAST STRUCTURES BY NON-DESTRUCTIVE TESTING METHODS

Abstract

In the context of improving methods and means of non-destructive testing (NDT), along with increasing in formativeness, complex technical problems arise. For example, when examining structural elements with a service life of more than 20 – 30 years, modern NC tools detect defects that have not been rejected by the manufacturer. Assessment of the impact of such defects on the operability of the structure requires a comprehensive study using NC and strain gauge. The purpose of the work is to evaluate the parameters of defects in a cast part of a hydraulic stamping press with a service life of more than 60 years in order to make a decision on the possibility of its further operation. The defect was investigated using magnetic powder, eddy current and ultrasonic control methods. By means of strain gauges, mechanical stresses are measured directly during operation. The indicator pattern of the magnetic particle inspection defect has signs uncharacteristic for fatigue defects: branching, intermittent and broken (not smooth) character. To quantify the degree of smoothness of the indicator pattern, it is proposed to use a fractal dimension, which for the defect under study was 1.07. The estimated depth of the defect detected by the eddy current method was from 4 to 6 mm, by ultrasound – from 8 to 18 mm. The presence of an echo signal by a direct converter indicates the volumetric nature of the defect. After mechanical removal of the surface layer with a thickness of 2 mm in some areas, the width of the defect increased to 2 mm, and the depth to – 20 mm. On the inner side surface of the defect, a dense, dark scale characteristic of high temperatures is visually determined.The defect is classified as a casting shell with a depth of 20 mm. No traces of fatigue failure were found. Compressive mechanical stresses with an amplitude of no more than 41 MPa amounted to less than 20 % of the fatigue endurance limit of 35L steel. During the year, the average number of working cycles is 20 thousand, repeated examination of the press defect is recommended in 5 – 10 years (100 – 200 thousand cycles).