|The detection of the few flaws that may occur in large production runs of metal wire or bars at production line speeds is best accomplished using the NDT techniques that are most capable of detecting the specific unacceptable conditions that are anticipated in the product.
For critical applications where the wire or bar must be free of surface, subsurface and internal defects of a variety of shapes and sizes, systems with multiple test stations at which dedicated techniques, based upon ultrasonic and eddy current methods, are often used. An example of this is shown in the accompanying picture of an automated test system for cold drawn bar. Included are an encircling differential coil eddy current tester for detecting short surface and subsurface defects such as slivers and pits; a spinning probe eddy current system to find long, surface defects such as seams; and a rotating transducer ultrasonic system for internal defects such as non metallic inclusions or stringers. Also included is an absolute coil eddy current system for detecting grade or alloy mix and a demagnetizer to minimize residual magnetism generated by the eddy current system when inspecting magnetic material.
These components are mounted on a constant center test bench with triple roll drives which are adjusted and controlled automatically through Conductor controls. This type of bench is especially useful for small diameter coil to bar installations, as small as 12 mm, where centering is critical.
By using multiple test methods, less false rejects will occur and fewer unacceptable defects will be missed than in a system using only one test method. The value of the investment is quickly returned through higher yields and fewer product claims.
Magnetic Analysis Corp (MAC)