The root cause of exposed defects after tooth milling is that the internal defects after rough machining are not treated in time, and the root cause of these defects is that according to the existing domestic and foreign steel casting nondestructive testing standards, ultrasonic flaw detection does not detect defects exceeding the allowable standard. It is these small equivalent or small area defects that do not exceed the standard that are exposed after the final milling. If the defects that do not exceed the standard can be cleaned in time in the process of ultrasonic testing, it will undoubtedly bring great convenience to the removal and repair of defects after tooth milling.
The existing domestic and foreign standards do not treat such small equivalent or small area defects as hazardous defects. In order to reflect the defects that do not exceed the standard in the ultrasonic flaw detection report, it is necessary to formulate a standard implemented within the enterprise. The enterprise standard is independently controlled by the enterprise, and the ultrasonic flaw detection of the tooth surface of cast steel large gear can be carried out according to the internal standard of the enterprise. Through the enterprise flaw detection standard, the quality of cast steel gears can be controlled, and the small equivalent or small area defects can be repaired before milling, so that the tooth surface defects will not be exposed after milling.
Because the material of steel castings is not as uniform as that of forgings, the sensitivity of ultrasonic flaw detection of steel castings is generally used φ 6 equivalent, the allowable defect area is mostly different according to different standards and grades. Many times of flaw detection practice has proved that at the tooth surface, the defect with a tooth height depth from the tooth surface is φ 6. Based on the equivalent, defects with an area of more than 80mm2 may be exposed to the tooth surface.