Need to Know: Metalcasters Take a New Approach

April 14, 2005
to Ultrasonic Testing

Ultrasonic testing (UT) is widely used by metalcasters to detect sub-surface defects, measure thickness, and determine certain material properties.

UT by the conventional method involves generating ultrasound with a piezoelectric crystal that converts electrical energy into mechanical energy. Then, that mechanical energy is transmitted into the test subject by means of a liquid couplant. Because the sound is transmitted into the part through a liquid from an outside transducer, this technique has limited usefulness when the test subject is hot, oily, or dirty — or when it has a rough or oxidized surface. Also, conventional UT can’t easily be applied to on-line testing.

The temate Casting Inspection system, as developed by Innerspec Technologies Inc. takes a different approach to UT. It uses electromagnetic acoustic transducer (EMAT) technology, which generates the sound in the part being inspected as opposed to in a transducer. With this approach, no liquid couplant or immersion tank is required.

Innerspec has developed temate CI into a comprehensive solution for ultrasonic inspection of metal castings. It is capable of integrating several inspections and measurements into one integrated system, and it can be used to inspect castings of iron, aluminum, alloy, and other metals.

It’s already been adopted by one of the U.S. foundry industry’s leading producers, which is taking advantage of the sensor’s design flexibility by using the device to inspect a large area of an aluminum casting.

Because it doesn’t use a couplant, the temate CI system generates more reliable readings (no couplant errors) and makes this technology easier to automate and integrate into production. It can work with regular and irregular geometries, with rough, dirty, and even rusted surfaces, and with hot materials. It can be used to inspect 100% of a production run of castings. And, it can be used for in-line or off-line inspection, manually or in an automated, high-speed setup.

For flaw detection, the system can incorporate one or more sensors working in parallel or in array, and use a combination of reflection and attenuation techniques specifically designed for the part and the type of defects. Innerspec Technologies’ proprietary flexible sensor technology permits transducer overlapping to achieve complete coverage and maximum sensitivity in one inspection pass. This distinctive capability simplifies fixturing and automation, and can significantly increase inspection speeds.

For thickness inspection, the system measures the speed needed for a pulse of ultrasound to travel from one transducer to another (pitch-catch) — or return to the same transducer (pulse-echo) — and correlate it with the known velocity of sound in the material.

Changes in ultrasonic wave propagation speed, along with energy losses from interactions with microstructures, can also be used to gain information about the properties of materials. A typical application involves measuring the degree of nodularity in cast iron determined by the shape and uniformity of the graphite nodules or flakes.

An EMAT consists of a magnet and a coil that is placed near the surface of the metal to be inspected. Using Lorentz forces and magnetostriction (together or separately), the EMAT and the metal of the test subject interact and generate an acoustic wave within the material, thus making the object to be inspected its own transducer.

Software integrates all components into a system with an easy-to-use Windows interface. Results are displayed in real-time and stored in a database for record-keeping and analysis. The system can generate standard and custom inspection reports.

Innerspec builds and supplies complete turnkey solutions for full automation or use by low-skilled operators.