Grinding burn detection with Barkhausen noise

Barkhausen noise vs Nital ething — Non destructive Barkhausen noise analysis has a great advantage for competing methods like nital etching.

Barkhausen noise analysis meets the demand for detecting the damages in ground steels in a very reliable, cost-effective and completely non-destructive manner.

In a tempered (burned) microstructure, there are two mechanisms that increase the measured Barkhausen noise value:

A softer microstructure, which includes transformation of martensite to ferrite, results a greater Barkhausen noise value.
The tensile stresses that result from grind temper affect magnetic properties. The result is a higher Barkhausen noise value when grind temper is present.

“A grinding damage or a grinding burn” is a thermo-mechanical defect in which both thermal and mechanical loads play active roles. It is a tribology phenomenon. Even at a lower temperature, there could be dramatic residual stress changes. This is due to the mechanical load from the grinding wheel on the contact area. These changes in stresses cannot be detected non-destructively with any of the traditional methods.

Master sample procedure

Barkhausen noise analysis is an electromagnetic test method which is relative in nature. To properly leverage Barkhausen noise analysis as a process tool, the user must use reference samples or verification methods to initially set up both measurement parameters and evaluation criteria. The master sample procedure can be validated for example with X-ray diffraction measurements or nital etching. When the master sample procedure is set, Barkhausen noise analysis is an accurate method to detect microstructure changes.

Barkhausen noise vs Nital Ething vs X-ray diffraction.

Measurement procedure and results

Barkhausen noise analysis requires the use of a Barkhausen noise signal analyzer (Rollscan) and sensor. Additional data collection software can be utilized for data tracking and exporting, surface mapping, and automated measurement evaluation.

Performing Barkhausen noise measurements is a simple process:

1. Measurement area is magnetized with alternating magnetic field by the sensor

2. During magnetization the sensor measures the Barkhausen noise signal and transfers it to Rollscan

3. Real-time measured values are displayed on Rollscan and/or the ViewScan software.

Barkhausen noise analysis values presented in Rollscan 350 screen:

Barkhausen noise values on Rollscan 350 screen. — Left: No grinding burns. Right: Heavy grinding burns.

Barkhausen noise analysis values presented in ViewScan software:

Camshaft measured with Barkhausen noise analysis. — Top: No grinding burns on camshaft lobes. Middle: Light grinding burns on camshaft lobes. Bottom: Heavy burns on camshaft lobes.

Automated grinding burn detection with Barkhausen noise

The more automated the Barkhausen noise measurements are, the more accurate and faster the measurements get. Automated systems minimize operator errors and are more ergonomic. An user interface of the automated system can be simplified so that an operator sees only if the measured sample is accepted or rejected within the determined rejection limits. The more detailed information will be stored for further investigations. If the system is used to process optimization, even the smallest changes in microstructure can be visualized for the operator.

Automated systems for quality inspection are tailored for offline use. Easy to use software makes inspections intuitive and systems can adapt to various component types. Automated systems require manual sample loading.

Inline/Robot systems can be integrated into the production line to ensure immediate reaction to process changes. Production data is collected automatically and can be analyzed and used for process optimization. Inline/Robot systems can be fully automated with automated sample loading.