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Detection of Internal Defects in Bearings – Part 4

written by: kkaarthic • edited by: Lamar Stonecypher • updated: 12/25/2008

This article describes about the Eddy Current inspection tests carried out on bearings to know about their internal defects. These tests if required can also be carried out by the end user to know the condition of the bearing before use.

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    All bearings undergo a lot of rigorous machining and processes that shape them to carry the heavy axial and radial loads. There is every possibility that a defect or flaw can occur in the bearing in any stage of its manufacturing process. Making each component of the thousands of the bearings manufactured to undergo rigorous inspection tests will practically be impossible. Yet a sampling lot from the thousands of bearings are made to undergo tests that verify the credibility of the bearings for its internal defects.

    Though various methods of detecting the internal flaws are present, each one of them tends to concentrate on detecting only one or two types of defects. There is a method by which a majority of these defects can be determined. It is known as the Eddy Current Testing of bearings.

    Methodology of Testing

    1. The bearing or the bearing component to be tested is held in a test fixture. The test fixture is capable of passing current to the component to be tested.

    2. Once the current is induced in the bearing work piece, it generates circular eddy current in the bearing component.

    3. The eddy current generates a test field which is just the opposite to that of the test core.

    4. This eddy field is detected as a impedance change in the test core coil.

    5. The discontinuities in the bearing components tend to show up as changes in the eddy current path length or as field fluctuations caused by the eddy current.

    This method is quite advantageous than the other methods in the following aspects.

    • It detects surface and sub-surface deformities and discontinuities.
    • It is even capable to detecting minor dimensional variations in the bearing components.
    • The best part of the above method is that it is capable of detecting variations in coating and hardness thickness in the bearing component.
    • It is also capable of detecting changes in permeability of the bearing.

    Drawbacks

    The drawback in this method is that it requires special testing arrangement to carry out the test and specialized instrumentation to do the same.

    We will discuss on the other types of non destructive testing methods of bearings in the forthcoming articles.

Detection of Internal Flaws in Bearings

This series deals with the methodologies used for detecting the internal flaws in the bearings other than the dimensional inaccuracies present in the bearing.
  1. Detection of Internal defects in Bearings – Part 1
  2. Detection of Internal defects in Bearings – Part 2
  3. Detection of Internal Flaws in Bearings – Part 3
  4. Detection of Internal Defects in Bearings – Part 4
  5. Detection of Internal Defects in Bearings – Part 5

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