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Technical Discussions
Navish M
Navish M
07:54 Jan-12-2009
Lifting Capacity of Yokes

Hello All,

What is the reason behind the lifting capacity of yokes 40lbs on permanent magnet and 10lbs on AC yokes?

Thanks

    
 
 Reply 
 
Nigel Armstrong
Engineering, - Specialist services
United Kingdom, Joined Oct 2000, 1096

Nigel Armstrong

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1096
12:27 Jan-12-2009
Re: Lifting Capacity of Yokes
In Reply to Navish M at 07:54 Jan-12-2009 (Opening).

Navish

The requirement of 40lb lift is for DC as well as permanent yokes. DC produces a constant-direction, constant-strength field whereas AC produces a 50 Hz reversing direction and fluctuating-strength field. Have you ever tried lifting MORE than 10lb with an AC yoke, very difficult. Even the 10lb lift needs a well-maintained, flat-footed and deftly handled AC yoke to persistently achieve the lift.

    
 
 Reply 
 
Sibusiso MZILA
Engineering, Pipeline integrity
Transnet SOC Limited, South Africa, Joined May 2004, 13

Sibusiso MZILA

Engineering, Pipeline integrity
Transnet SOC Limited,
South Africa,
Joined May 2004
13
10:06 Jan-13-2009
Re: Lifting Capacity of Yokes
In Reply to Navish M at 07:54 Jan-12-2009 (Opening).

The major reason for this difference is based on the expected or required depth of penetration; AC has a maximum of 2mm penetration for surface testing whilst DC is expected to penetrate up to 8mm for surface and sub-surface testing.

    
 
 Reply 
 
Nilesh
Nilesh
13:48 Jan-13-2009
Re: Lifting Capacity of Yokes
In Reply to Navish M at 07:54 Jan-12-2009 (Opening).

Navish Mujawar,
Lifting capacity of yokes are 40 lbs for DC as well as permanent yoke.
Permanent yoke shall have 40 lbs since we are not using any current with it. So fully charged Permanent yoke lift 40 lbs. Due course of time its lifting capacity will drop down in that case you have to send it for re charging. These are used for normally sub surface discontinuities. But for AC as Mr. Nigel explained in one second AC changing its polarity for fifty times. So there is no chance for creating hard magnetic field. and it can lift 10 lbs. Its again gives us better results for surface discontinuities. AC producing magnetic field with sine wave current.
better mobility for particles and lighter penetration in material.

    
 
 Reply 
 

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