Application note: Non-destructive Testing on Gear Teeth

In this application grinding burn was detected on gear flanks with automated GearScan 500 Barkhausen noise system.

The problem: Grinding burn on gear

A manufacturer of gears believed the root cause of early failure in their products was grind temper. However, the thermal defect was not being detected by Nital etch inspection.

The testing method: Non-destructive Barkhausen noise

Non-destructive Barkhausen noise (BN) was used to inspect each flank. Results were collected from a single axial pass, collected via automation (GearScan 500).

The results

Barkhausen noise results on gear
OK Gear Scans
OK Gear Aggregate (Max-Min-Avg) Data
OK Gear Aggregate (Max-Min-Avg) Data
NOK Gear Scans
NOK Gear Scans
NOK Gear Aggregate (Max-Min-Avg) Data
NOK Gear Aggregate (Max-Min-Avg) Data

The data showed the “OK” gear measured consistently across all flanks while the “NOK” (the suspected defect) gear has elevated BN signal (mp) on nearly all of the right flanks as shown below.

NOK Gear Left (green) vs. Right (red) Flank Scans
NOK Gear Left (green) vs. Right (red) Flank Scans

The increased response is an indication of grind temper that was otherwise undetectable since the burn occurred in an initial grind phase where final grinding removed the burn on the surface of the flank, rendering Nital etch ineffective.  In this case, BN is detecting the unfavorable subsurface residual stresses that still remained. This trend was shown to occur on all the suspect gears and further testing was accelerated by a quick comparison between the left and right flanks.

Instrument used for this application

GearScan 500

GearScan 500 is an automated grinding burn and heat treatment defect detection system. It is designed for quality control needs of small to medium sized gears.

GearScan 500, door closed
GearScan 500, door closed

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Article Type: Application note
application: Grinding
Part Under Inspection: Gear
Product Line: GearScan 500