Grinding burn detection
What are grinding burns?
Grinding thermal damages, also known as grinding burns, will shorten the fatigue life and can cause severe failures in dynamically loaded, critical components. Grinding burns will 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 effect grinding quality. Grinding burns may occur if any of following parameters are not optimal:
- 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 gone 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 burs
- 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:
|Evaluation through coatings||✔||-||-|
|Can easily examine large areas||✔||-||✔|
|Influenced by both stress and microstructure||✔||✔||-|
|Can be automated||✔||✔||-|
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 will directly affect the intensity of the Barkhausen noise signal: hardness and stress. Barkhausen noise method reacts even the smallest burns as burned areas increases the signal.
With Barkhausen noise method it is possible to measure through coatings which makes it invincible method for detecting grinding burns for example on landing gears.
Grinding burn causes residual stress. Non-destructive X-ray diffraction method allows measuring 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 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.
With Stresstech products grinding burn detection can be done effortless in production lines, laboratories and even on field.