A Conversation with Troy Libby, MAC® Application Engineer
Troy Libby is a Senior Application Engineer in a design group at Magnetic Analysis Corporation. He has over 25 years experience in eddy current technology including designing inspection instruments, test coils and probes. Working closely with customers to meet their specifications, he has designed custom coils and probes to work with a range of critical applications.
What are some advantages of using eddy current testing for wire products, and is it cost-effective?
Eddy current testing offers fast, reliable, and non-contact detection of surface and near-surface defects in wire products—making it ideal for continuous production environments. One of its key advantages is real-time flaw detection early in the process, which helps prevent the use of defective material and reduces costly downstream rework or scrap. This early identification of issues contributes to a strong return on investment, making eddy current systems a highly cost-effective quality control solution for wire producers.
What has been the most challenging application in wire to design a test system for in your career at MAC®?
The most challenging application was testing ovate wire at production speeds of 3,000 feet per minute. (914.4mpm) The unique egg-shaped cross-section of ovate wire made it difficult to test, as the system needed to account for distance compensation during inspection. This challenge required a solution that wasn’t dependent on lift-off—the distance between the probe and the material—ensuring accurate flaw detection regardless of variations in this distance.To solve this, a high-speed rotary system operating at 18,000 RPM with distance compensation probes was designed. This system was capable of equalizing flaw signals 360° around the wire. After successfully installing the system at the customer's plant, it proved highly effective in testing their material, ensuring reliable and consistent results.
When should a rotary be used instead of an encircling coil for wire testing?
Rotary eddy current testers are the preferred solution when detecting long, continuous surface flaws that might be missed by traditional encircling coils. The rotary’s probe technology excels at identifying longitudinal defects with high precision, making it ideal for applications where surface integrity is critical.
Rotary testers are easily integrated into continuous wire operations, such as wire drawing, parts forming, or straight and cut lines. Selection of rotary speed is based on production parameters—specifically, how quickly the wire is being drawn and the minimum flaw length you need to detect. For example, a 1,000 RPM rotary is suitable for slower operations, while a high-speed 18,000 RPM unit is available for faster production lines and finer defect resolution. Additionally, rotaries equipped with ceramic bushings offer enhanced durability and extended wear life, especially important in high-throughput environments.
It’s also worth noting that some industry test standards require a combination of both rotary and encircling coil technologies. This dual approach supports comprehensive detection—capturing long, longitudinal flaws with the rotary, and short, transverse defects with the encircling coil. By selecting the right configuration for your specific application, you ensure reliable, high-quality results that meet the most demanding testing requirements.
What is a test standard used for?
A test standard is a piece or spool of wire containing a known, intentional defect—used to calibrate and verify the performance of non-destructive testing equipment. These defects, which simulate the types of flaws that may unintentionally occur during production, are typically created using EDM notches (electrical discharge machining) or chemical etching for consistency and accuracy.
MAC® works directly with customers by performing calibration and Factory Acceptance Tests using their supplied test standards. This process ensures that the equipment is precisely configured to detect the specific types of defects relevant to their material and application—providing confidence that the system will perform reliably in production. In some cases, customers may also use actual defects found in their production material as a reference standard to assist with equipment setup and validation.
What happens when you receive samples to test without a standard?
When samples are submitted without a standard, it’s typically because the customer doesn’t have a tester and the end user has raised concerns about the material. Often, limited information is provided—such as the material type or its intended application—which can extend testing time.
If flaw-like signals are detected during testing, a detailed report is prepared and sent to the customer. Depending on the industry, one of two things usually follows: either a representative is sent to witness a retest, or the marked material is returned to their facility for further evaluation.
This process allows for a transparent relationship with our customers and helps them take the appropriate next steps based on the test results.
How difficult is it to set up an off-line inspection for small diameter wire?
Setup is typically very straightforward. Most wire producers already have reel-to-reel lines with idlers in place. In most cases, the customer simply provides a small mounting plate to position the test coil between the idlers. The only additional requirements are the testing electronics and on-site training—both of which are easily integrated into existing operations.
What is the fastest speed at which you’ve tested wire?
The testing speed depends on the wire material and size, with typical speeds ranging from 100 to 3,200 feet per minute (30.48 - 975.36m) MAC® has successfully provided systems capable of testing wire at speeds up to 5,000 feet per minute. At these high speeds, idlers are strategically placed before and after the test coil to eliminate wire vibrations that would otherwise effect the test. Additionally, MAC® systems are equipped with encoders that monitor line speed in real time, allowing automatic optimization for both low and high-speed testing.
What can attendees expect to see from MAC® at the upcoming exhibition?
MAC will be showcasing (Booth #553) our advanced Minimac® II electronics, a fully digital system featuring a modern embedded design. Attendees will see a live demonstration of eddy current testing, where a precision wire standard— containing a .002” EDM notch—will be articulated along a linear rail to generate real-time flaw signals. This setup highlights the exceptional sensitivity and accuracy of the Minimac® II in detecting surface defects. Additionally, the system will feature our proprietary wire grading software. This software seamlessly integrates with your testing process, enabling users to efficiently grade spools of wire as they are tested—streamlining quality control and documentation.
Also on display will be our economical 25MM Rotomac® rotary. Ideal for low-speed wire testing or integration on a draw block, this unit offers plug-and-play convenience with a standard 110-volt outlet and operates at 1,000 RPM. It's a reliable solution for operations seeking high performance at a lower cost. The test coil features a ceramic bobbin, compatible with ceramic bushings, making it suitable for applications requiring minimal material contact and extended durability. Built-in air ports provide positive air pressure to keep oxide dust from accumulating within the coil. This is critical, as excessive dust buildup can cause surface scratches on the wire—something this design helps proactively prevent. With these systems, MAC continues to deliver efficient, reliable, and cost-effective NDT solutions tailored for the wire industry.
