Selection of Flaw Detection Method for CNC Roll Grinding Machine
In daily production process, the CNC roll grinding machine will be equipped with eddy current flaw detection function, but it can only detect the open cracks and soft spots on the roll surface, and cannot detect the closed cracks on the roll surface and the internal cracks of the roll. Most factories can only rely on manual sampling inspections for these internal defects, and cannot conduct full-cycle monitoring. In the case of more high-speed steel rolls being put into use, the accident rate will increase. Optimizing the on-board flaw detection method of roll grinding machine will effectively solve this problem.
The American Association for Nondestructive Testing (ASNT) has announced 10 official nondestructive testing methods, of which five are commonly used in CNC roll grinder flaw detection: eddy current flaw detection, ultrasonic flaw detection, liquid penetrant flaw detection, magnetic particle flaw detection, and visual flaw detection ( Three of them are suitable for airborne flaw detection for roll grinding machines: eddy current flaw detection, ultrasonic flaw detection and surface wave flaw detection).
Eddy current test has the following advantages:
(1) It can detect various metal rolls;
(2) Surface opening cracks, soft spots and inclusions can be detected;
(3) Low quality requirements on the surface of the roll, free from interference from water and oil;
(4) Flaw detection can be performed while grinding to improve grinding efficiency. However, eddy current testing also has limitations:
(5) It can only detect cracks on the surface of the roll, but cannot detect deep cracks inside the roll;
(6) Only the relative severity of the crack can be displayed, but not the specific depth of the crack;
(7) If there is magnetism on the surface of the roll, it will interfere with the results of flaw detection.
Ultrasonic flaw detection has the following advantages:
(1) It can detect the internal defects of the roll, such as: inclusions, pores, bonded layers, and pressure cracks;
(2) It can clearly show the specific depth of internal cracks and the expansion area of cracks;
Ultrasonic flaw detection also has limitations:
(3) Cracks on the surface of the roll cannot be detected, and the depth of 0~2mm on the surface of the roll is a blind area for ultrasonic testing;
(4) Soft spot defects on the roll surface cannot be detected. For the work roll, the soft spots and inclusion defects on the surface are also very important, and the soft spots and inclusions can be detected by eddy current testing.
Surface wave flaw detection has the following advantages:
(1) Small defects that can be detected are 2.0mm×0.3mm×0.1mm;
(2) Sensitive to both circumferential cracks and axial cracks;
(3) Near-surface cracks can be detected. For example, some cracks do not form openings on the surface of the roll, and the eddy current cannot be detected, but the surface wave can be detected. The detection depth range is 0-5mm, and the probe frequency is 2MHz.
Surface wave testing also has limitations:
(4) Cannot detect soft spot defects on the surface of the roll;
(5) The specific depth of the defect cannot be displayed;
(6) It is suitable for detecting rolls made of high-chromium steel, high-chromium iron, high-speed steel, and forged steel. It is not suitable for detecting ordinary infinitely chilled rolls, but can detect improved infinitely chilled rolls.