08:55 Apr-16-2004 Godfrey Hands Engineering, PRI Nadcap, United Kingdom, Joined Nov 1998 281
Re: Ball bearing inspection ----------- Start Original Message ----------- : I want to know the current availble methods for the surface defect inspection of the steel ball bearings. : The conditions are: : Material : high strength seel : Dimension : 4-20 mm in diameter : Inspection condition : online during manufacturing : Please let me know about the technologies including related documents, if available, or the website informations. : Thanks. : Zhong Soo Lim ------------ End Original Message ------------
Dear Zhong Soo Lim, I assume that you want to test either the balls / Rollers or the Rings for surface defects.
The normal method is to use Eddy Currents in a machine designed to test the components.
I used to work in the research laboratories of a multi-national bearing manufacturer as NDT engineer, and I may be able to help you find manufacturers of suitable machines.
Please provide more details of the product to be tested, e.g. Balls or Rollers or Rings? If rollers, are these taper, spherical or cylindrical. If rings, are they for taper, spherical or cylindrical rollers. What is the production speed you want to test at?
The company that I worked for had numerous machines, some testing up to 6 rollers per second for surface defects.
Dear Sir , Hope You will be fine , i am interested in NDT of rolling bodies for example as a start i am interested in a single Ball,by using surface waves(Rayleigh waves). I will be gratful for your guidance .
Thanks & Regards
Dear Waseem Anwar,
Rayleigh Wave inspection of a steel ball is certainly possible, but will be a slow process.
The difficulty lies in manipulation of the ball or of the probe to ensure 100% coverage and also to cover any orientation of defect on the ball surface.
Unlike other components, Balls do not have an obvious defect orientation, so as well as detection of defects on the surface, it will also be necessary to detect defects in any orientation.
For rollers, which have an obvious orientation, the solution becomes easier.
There is however one technique which permits detection of defects in any orientation on a ball. This is the "Delta Z" technique.
The requirement is to have a (fairly ) high frequency small diameter immersion probe with a very short focus. (e.g. 6mm diameter with 5 or 6 mm focus)
The ball is immersed in water (or other liquid), and the probe is moved towards the ball until the focus is on the ball surface. The probe then needs to move even closer to the ball surface.
When the focal length is short enough, there will be some sound being refracted by the lens of the probe, which will impinge on the ball surface in a small circle at the "Critical Angle". This will then generate "leaky" Rayleigh Waves, which will travel across the diameter of the circle, leaking out all the way, including the same point on the opposite side of the circle, where this "leaky" Rayleigh Wave will be detected by the probe.
The direct reflection signal from the ball surface will be a very large amplitude signal, but the leaky Rayleigh Wave will have a much smaller amplitude, and should appear either just before or just after the direct reflection.
Sketch it out and see.
When there is a defect present in the circle, the detected amplitude of the Rayleigh Wave which crosses the circle from one side to the other will be reduced.
For 100% inspection of the ball surface, the ball then needs to be manipulated past the probe such that 100% of the surface is inspected.