Nodular Iron Testing with Resonant Inspection

May 17, 2022, 08:53 AM by System
May 17, 2022

THE MODAL SHOP, INC.’s Resonant Acoustic Method Nondestructive Test (NDT-RAM™) systems are ideal for nodularity testing for manufacturers or users of ductile iron cast parts. The technology has proven effective as an in-line solution for many ductile iron parts manufacturers. Unlike subjective methods such as visual inspection, NDT-RAM offers objective, criteria-driven results. The inspection system software compares each part's resonant signature against reference criteria limits and accepts or rejects the part accordingly.

NDT-RAM systems are ideal for 100% inspection requirements of manufacturers or users of ductile iron castings; manufacturers who have significant inspection costs (either material or labor), produce or use safety-critical parts, have substantial scrap costs due to false rejects or who are simply wanting to improve their part quality can benefit from NDT-RAM technology. With no part preparation required, this technique can objectively identify resonant frequency shifts caused by internal and external flaws such as low nodularity. NDT-RAM also provides screening for cracks, voids, chips, holes, porosity, material density, out-of-tolerance dimensions, variations in hardness, residual stress, bonding failures, heat-treating processes and missed manufacturing processes.

Cast iron is a metal alloy characterized by relatively high carbon content. During the metal’s solidification, this carbon content can form graphite, with tiny, irregular flakes that disrupt the crystalline structure, sometimes causing cracks and unwanted brittleness. In ductile iron, the graphite forms spherical, rounded nodules helping to inhibit the formation of cracks and providing enhanced ductility and machinability. Low nodularity in a ductile iron part can cause catastrophic failure in the field. NDT-RAM systems detect low nodularity by easily distinguishing the sound signature the part emits when impacted because the relationship between nodularity and resonant frequency is practically linear. NDT-RAM compares the part’s sound signature (up to 50 kHz, while the human ear is only good to 20 kHz) to a series of criteria bands set up with known good samples and objectively determines if the part is within the “good” parameters. The system can be set up as an end-of-line quality inspection station or upstream in the production as a process monitor to avoid expensive secondary operations on bad parts.

A free parts evaluation is offered for feasibility testing of your parts and system rentals are available allowing you to try the system in your factory before buying. For free parts testing, specification sheets, application data, competitive product upgrades, pricing or to schedule a rental or demonstration, please contact THE MODAL SHOP, INC., 3149 E. Kemper Road Cincinnati, OH 45241-1516, internet:, (800) 860-4867, fax (513) 458-2172 or e-mail:

LanSharc and NDT-RAM are trademarks of The Modal Shop, Inc.