Ultrasonic Inspection is very slow and has a “blind” spot between the probe and 3mm into the surface. Ultrasonics can miss cracks. However, it will provide information deep into the gear cast.
An argument can be made on the relevance of finding casting imperfections:
- Ultrasonic inspection would detect porosity and inclusions in the cast but it is harder to detect surface cracks unless they propagate to the surface from the inclusion. It’s important to understand that porosity and inclusions found in the cast that have not propagated to the surface cannot be repaired.
- ASTM E2905 detects 100% of all gear teeth surface indications larger than .40mm.
- The reason why casting imperfections are not as important is because there is no way to repair them.
- It’s only when the casting imperfection creates a crack that propagates to the surface that it becomes a problem. These are on cast gears only.
- Any casting imperfections should be identified by the manufacturer’s Quality Control Program before the gear leaves the plant.