Eddy Current Non-Destructive Testing (NDT) can be used to test a variety of different metal types.
Non-Ferrous Metal Sorting
This is conductivity testing, and for dedicated applications, a conductivity meter may be a better choice. From the impedance plane diagram, one can observe that the indication from a conductivity change is essentially the same as from a crack, and both meter and impedance plane type crack detectors can be successfully used to sort similar metals using a suitable absolute probe. It should be remembered that:
- Widely different metals may be a similar conductivity
- Allowable values for similar alloys may overlap
- An alloy of one material can, in vastly different states of heat treatment, have the same electrical conductivity
However, once these caveats are understood then conductivity measurement can be used as part of a quality control system. Suitable test frequencies used are in the range of 10 kHz to 2 MHz, although account should be taken of the material thickness to ensure the depth of penetration is less than one-third of the material thickness.
Ferrous Metal Sorting
Ferrous material may be sorted using eddy current impedance plane equipment. Unfortunately, it is not possible to produce quantitative values due to the reading obtained being related to electrical conductivity, magnetic permeability, and the depth of the change in material properties. Frequencies to use are 100 Hz to 10 kHz. The use of two or more frequencies gives additional information about the depth of the material properties such as in induction hardening.
If you have a Material Sorting application that you think Eddy Current NDT from ETher NDE could help you with, please do not hesitate to get in touch via email@example.com.