The problem: Grind temper on a crankshaft fillet radius
A manufacturer experienced a quality leak due to grind temper on a crankshaft fillet radius which led to premature failure in service. Nital etch was initially used to sort the suspect parts but the results did not correlate with fatigue life data. Barkhausen noise was then investigated as an alternative to nital etch.
The testing method: Non-destructive Barkhausen noise method
Barkhausen noise was used via hand testing at strategic locations on the circumference of the shaft at the fillet radius.
Barkhausen noise proved to be a superior method over Nital etch for predicting failures. Note that all of the parts with etch rating of 5 or greater failed Nital etch inspection and were scrapped. Barkhausen noise inspection reduced the occurrence of “false rejects” and correlated closely to the fatigue life results. This ultimately saved the customer a significant amount of money in unnecessary scrap and allowed them to perform inspections on 100% of the parts in lieu of a statistical survey with nital etch.
Instrument used for this application:
Barkhausen noise signal analyzer Rollscan 350 is designed for surface quality control and testing of near-surface defects such as grinding burns, heat treatment defects, as well as changes in stress and microstructure in a wide variety of ferritic steel and other ferromagnetic materials.