Bearings as we all know are precise machine elements which are manufactured with utmost care. Whenever we purchase or buy a bearing we tend to look only at the external aspects of the bearing like finish, dimensions, etc. Any internal flaws present in the bearing go unnoticed to the buyer and is only visible to him after the bearing fails abruptly without any cause.
In order to detect the internal flaws two methodologies can be followed
1. Destructive testing – This is not possible because the bearing is purchased for an intended use and destructing it, in no way answers the ultimate usage of a perfect bearing.
2. Non Destructive testing – This is a best and well known method for testing of the bearings as the bearings are tested without any damage to them. Moreover a bearing passing through these tests can be utilized as a flaw free bearing.
Non destructive testing has the advantage of detecting the internal flaws and imperfections in the various bearing components that with other means of testing can go undetected. Some of the methods that are used for the non-destructive testing of bearings are
· Liquid Penetrant Inspection
· Magnetic Particle Inspection
· Etch Inspection
· Eddy Current Inspection
· Barkhausen Inspection
All the above methodologies can be used for detecting the internal defects in bearings. We will look in detail on these inspection methods.
Liquid Penetrant Inspection
This methodology is quite familiar to all testing engineers worldwide. The methodology makes use of three liquids
· Cleaner – A Liquid that cleans the surface of the dirt and oil particles to make it dry. This is normally a chemical like the paint thinner.
· Penetrant – This liquid is applied after cleaning the surface with the cleaner. The liquid is less viscous and hence easily seeps into the cracks present in the surface. The liquid is allowed to cool down on the surface for a short period of time.
· Developer - This is a powder based liquid, which is applied over the area where the penetrant is applied. The developer acts as a blotter pulling up the penetrant from the cracks indicating the cracks present in the surface.
This methodology is quite cheap and effective to a certain effect in detecting the surface cracks in the bearings. The internal defects present in the bearing cannot be found out using this method.
The remaining non-destructive testing methodologies for detecting the internal flaws of the bearings will be described in the forthcoming articles.