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22:26 Jan-08-2012
tsachi
775 views
yoke vibrat
im working in ndt and im working wit yoke and when i create a magntic field it produce vibration is it spose to be like that and if yes how much vibration it spose to give
 
 
00:16 Jan-09-2012

Joe Buckley
Engineering, Applications Technology Manager ASNT L-III,
Sonatest Ltd.,
United Kingdom,
Joined Oct 1999
332 Stand of Sonatest Ltd
Re: yoke vibrat
In Reply to tsachi on 22:26 Jan-08-2012 (Opening).

Some vibration is quite normal for an A.C yoke.
Not sure how to desribe how much. It shouldn't cause a problem.

 
 
09:58 Jan-09-2012

P V SASTRY

R & D, NDT tecniques metallurgy ,
TAKEN VRS FROM THE POSITION OF SR. DEPUTY GENERAL MANAGER BHEL CORPORATE R&D,
India,
Joined Jan 2003
117
Re: yoke vibrat
In Reply to tsachi on 22:26 Jan-08-2012 (Opening).

Dear Sir,

As mentioned by Mr. Joe Buckley, it is normal to have some vibration if the yoke is being used in AC mode. But in DC mode it should not give any vibration.

In AC mode the noise resulting from the vibration is just a hum and perceptible to the operator but barely audible to the people in the vicinity.

Again in AC mode, if either or both the poles of the yoke are not making full contact with the part, the vibration and the noise may be much the higher. Though the vibration and noise are manageable it is not a good sign as you may not be getting enough field into the part for proper testing. If the contact cannot be improved due to difficult geometry you have to use a field indicator to verify the technique.

In Ac mode if you are testing on a thin plate/part (loosely held ) the vibration and noise may be very much on the higher side but the testing itself may be Ok.

Best wishes

P V SASTRY

 
 
14:38 Jan-09-2012

Dent
Consultant, NDE Manager and Level III/3,
Consultant,
Canada,
Joined Nov 1998
187
Re: yoke vibrat
In Reply to P V SASTRY on 09:58 Jan-09-2012 .

Be careful if you use a field indicator with a yoke. You can get a 'good field' result even on wood or concrete. ASME Sect V does not allow Pie Gauges or shims with the yoke technique.



On the lighter side, some techs call the AC yoke technique the hummer method.

 
 
22:18 Jan-09-2012

Andrew Cunningham

NDT Inspector,
Canada,
Joined Jun 2008
233
Re: yoke vibrat
In Reply to tsachi on 22:26 Jan-08-2012 (Opening).

AC is an alternating current. The poles alternate from negative to positive in most parts of the world 50 times a second and some 60 Hz, and in turn the poles alternate from North to South. When then magnet is energized the magnet pulls. When the polarity is switching from the North to the South the magnetic field goes through a neutral point and does not pull. So you are feeling the magnet pulling down and neutralizing at 50 Hz.

 
 
09:41 Jan-10-2012

P V SASTRY

R & D, NDT tecniques metallurgy ,
TAKEN VRS FROM THE POSITION OF SR. DEPUTY GENERAL MANAGER BHEL CORPORATE R&D,
India,
Joined Jan 2003
117
Re: yoke vibrat
In Reply to Dent on 14:38 Jan-09-2012 .

Yes I know the pit fall and any way thanks for reminding.

In lab we have experimented with known defects ( wire cut notches and a few natural cracks in turbine blades) with different contact positions of the poles and in most positions the defects formation was there though not the same degree. Off course each time we demagnetized as the turbine blades particularly retain lot of magnetism.

Best wishes

P V SASTRY

 
 
13:15 Jan-10-2012

Nick Welland

Consultant, Quality and NDT ,
Self-employed,
Australia,
Joined Oct 1999
35
Re: yoke vibrat
In Reply to P V SASTRY on 09:41 Jan-10-2012 .

On welded fabrications, a particularly loud and repeated mains frequency vibration may also alert one that the technician may be 'dragging' the yoke.
regards
Nick

 
 
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