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Detection of Internal Defects in Bearings – Part 5

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

This article describes the Barkhausen inspection tests carried out on bearings to know about their stress related 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 manufactured undergo through various stages of process to acquire the desired shape and dimensional stability. The bearing while undergoing all these processes is subjected to a great deal of stresses. These stresses can induce defects at any stage of the manufacturing process of the bearing. The defects induced due to stress are quite difficult to be analyzed using other techniques. One of the most successful methods for detecting such types of defects is the Barkhausen Method of inspection of bearings.

    Principle of Barkhausen Method

    1. This method works on the principle of magnetoelastic interaction, which is the magnetostrictive and elastic lattice strains of the material

    2. This principle in the working of this method is quite simple – A ferromagnetic piece if magnetized will tend to elongate in the direction of its magnetization and vice versa i.e. a elongated piece will get magnetized in the direction of its elongation

    3. But when the same piece is compressed, the piece tends to get magnetized 90 degrees to the direction of application of the compression load.

    4. This kind of effect in ferromagnetic materials is termed as the Barkhausen Effect.

    5. This effect can be measured by measuring the magnetic intensity in the elongated or magnetized component with the corresponding direction of magnetization.

    6. By determining the direction of magnetization the type of loading on the work piece can be easily determined.

    This principle is used for determining the defects in the bearings. This is possible because of the stress induced defects tends to induce elongations in the bearings, which in turn produce a magnetic field based on the type of loading stress pattern it has been subjected to.

    Advantages

    · The advantage of this method is that stress related failures that go unnoticed in other methodologies can be easily detected using this method

    · Apart from determining the flaws due to stresses, it is also helps in identifying the processes that tend to induce such sort of flaws in the bearing components.

    · The defects induced due to abusive grinding on the bearing components can also be determined.

    Drawbacks

    This method also has a few drawbacks. They are as follows

    · Special equipment for measuring the magnetic intensity is required as the magnetic intensity produced in certain cases will be of very low intensity.

    · Larger size bearings cannot be easily measured in this methodology.

    With this article we come to the end of the methods that are used for detecting internal defects in the bearings.

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