Grinding Burn Detection
Grinding thermal damages, also known as grinding burns, will shorten the fatigue life of critical, dynamically loaded components and can lead to severe failures. Grinding burns occur when the energy from grinding produces too much heat. Grinding burn decreases hardness and causes tensile residual stress.
The grinding process has many parameters that affect grinding quality. Grinding burns may occur if any of following parameters are not optimal:
- Force
- Cutting speed
- Cutting fluid
- Wheel wear
- Wheel dressing
Why grinding burn detection is important
The surface of a freshly ground component may appear to be fine, but unseen damages below the surface, when undetected, can lead to serious problems for the end user.
Grinding burns will:
- shorten the fatigue life
- cause severe failures in dynamically loaded, critical components
- change stress and microstructure
Undetected grinding burn may cause:
- Internal quality failure on production line
- extra costs: rework, scrap
- External quality failure
- warranty cases
- brand value loss
Grinding burn detection methods
Grinding burn can be detected non-destructively with following methods:
- Barkhausen noise analysis (BNA) which detects hardness changes and residual stress caused by grinding burns
- X-ray diffraction method (XRD) which measures residual stresses caused by grinding burns
- Nital etching (NE) where over heated area will appear darker when part is etched
See following table for method comparison:
| Feature | BNA | XRD | NE |
|---|---|---|---|
| Objective | ✔ | ✔ | – |
| Reliable | ✔ | ✔ | – |
| Fast | ✔ | – | ✔ |
| Evaluation through coatings | ✔ | – | – |
| Can easily examine large areas | ✔ | – | ✔ |
| Influenced by both stress and microstructure | ✔ | ✔ | – |
| Can be automated | ✔ | ✔ | – |
| Environmentally friendly | ✔ | ✔ | – |
Barkhausen noise analysis
Barkhausen noise analysis is a non-destructive method involving the measurement of a noise-like signal induced in a ferromagnetic material by an applied magnetic field. There are two main material characteristics that directly affect the intensity of the Barkhausen noise signal: hardness and stress. The Barkhausen noise method reacts to even the smallest burns as burned areas increase the signal.
With the Barkhausen noise method, it is possible to measure through coatings which makes it an indispensable method for detecting grinding burns on critical components, like landing gears.
X-ray diffraction
Grinding burn causes residual stress. The Non-destructive X-ray diffraction method allows measuring the absolute residual stress value.
X-rays have high energy and short wavelength when compared to visible light making them ideal for probing the interplanar distances in crystalline materials.
Nital Etching
Nital etch inspection to detect signs of grinding burn involves a chemical mixture of nitric acid and ethanol which will corrode the gear sample and reveal microstructure variations in steel. The overheated area will appear darker than the surrounding area after the test.
Stresstech provides turnkey solutions for grinding burn detection
With Stresstech products, grinding burn detection can be performed effortlessly in production lines, laboratories, and even in the field.
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