Thread inspections using thread gauges and vision systems are time and labor intensive. They are often used off-line as part of a batch sample inspection. A manufacturer of wheel bearings wanted to install a fast, clean and cost-effective test method for thread inspection – which was also 100% reliable. The customer also wanted a test that would identify the following conditions:
- Partial and damaged threads
- Oversized and undersized threads
- Broken Tap
- Missing hole
- Incorrect thread
Eddy current technology provides a fast, clean way to inspect threaded holes. In an application like this, eddy current probes are lowered into the threaded hole and the actual inspection takes place in less than a second. Multichannel instruments like the InSite HT are capable of running up to 8 probes simultaneously. Single channel instruments like the CR-11 can test one threaded hole at a time, but if combined with a robot can test multiple component holes extremely quickly.
Figure 3 shows the four coil thread inspection probe and fixture developed by Criterion NDT for this customer. The eddy current instrument was interfaced to their production material handling system. A stainless steel sleeve was placed around each eddy current coil for longevity, and a spring-loaded probe housing was developed for the test.
The eddy current thread inspection system provided a savings of approximately $100,000/year for each thread inspection production line. The inspection system paid for itself in less than one year with production savings.