Eddy Current Array Raises the Bar for RCS Steel Bar Inspection

Improve surface inspection of round corner square steel bars by replacing labour-intensive magnetic particle testing.

Figure 1: Round corner square billets need to be inspected, with a close up of typical indications that need to be detected.

Round corner square billets are large engineering steel bars mainly used in forging steel parts. Smaller bars can be sent through a straightener then passed through fixed inline inspection equipment. Larger size bars can be harder to straighten and thus may not be sent to inline equipment without risking that a bad bend rams the bar though the high-tech inspection machine. They thus need to be inspected manually.

Being made of a magnetic material, these bars can be inspected using Magnetic Particle Inspection (MPI), but a typical magnetic yoke will only cover a small area. To inspect the four sides and four corners of a 9.14-meter (30-foot) bar requires many repetitive activations of the magnetic yoke, and a batch of bars would appear as a nearly endless task. Over the years, workers can develop strain-related injuries and need constant rotation.

The surface of these bars needed a new inspection solution.

A custom eddy current array probe with 90-degree coverage designed to scan along the axis of the bars in a smooth continuous motion.

Figure 2: Customization of the eddy current array solution used in the Spyne probes.

Figure 3: Ceramic pads protect the coils from wear.

Figure 4: Reference sample with EDM notches compared to a screen capture of the same area. Notch D and G are 0.254 millimeters (0.010 inches) deep, which is shallower than the detection target. The system is tuned to ignore these shallow notches since they would be false positives, below the target depth.

To improve the situation, Eddyfi Technologies relies on years of experience in the deployment of Eddy Current Array (ECA) solutions in rough environments.

This custom probe repackages the successful inspection solution of the Spyne™ probe into a system specialized for round corner squares.

The probe uses an array of 96 coils with a diameter of 4.5 millimeters (0.77 inches) which provides full coverage of one face and one rounded corner per scan pass. Using long single-driver topology, it is sensitive to defects in any orientation. The probe can also be used with an encoder to record the exact position of the detected indications.

Considering the rough surface of the inspected material, the coils are protected by highly durable ceramics shoes. A special spring-loaded design and accurate machining allows the coils to keep close to the varying shape of the billet’s rounded corner.

Using C-scan imaging combined with high-accuracy impedance signals for confirmation, this ECA configuration can detect defects 6 millimeters (0.25 inches) long defects as shallow as 0.5 millimeters (0.020 inches) deep.

According to the client, “The Eddyfi team did an excellent job on this custom probe. It is in full production being used non-stop for 8 hours a day, 5 days a week with no issues. It is extremely accurate and built rugged enough to tolerate the daily abuse of a rough steel surface. Thanks to the fine folks at Eddyfi. By the way, we are using the Spyne on our round bars with the same excellent results!”