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Technical Discussions
NDTman
NDTman
00:45 Mar-16-2008
Demagnetization of Long Hollow Shaft in MPI

Dear Friends,

I have tried demagnetizing a long hollow shaft (approximately 0.500 inch thick, 9 feet long and having a O/D of 8 inches) on a MPI Bench Unit but find it difficult to achieve less than 3 gauss on all areas of the shaft as per the ASTM E1444-05 requirement.

This shaft has been previously magnetized longitudinally for inspection using 4ooo Amps FWDC.

I have used the machine's Coil which was set to 4500 Amps on AC Demag Mode to demagnetize the shaft but it is not effective.

Is it the right thing to do if I insert a flexible cable (2 inch O/D) through the internal diameter of the shaft and pass AC and DC current through the flexible cable to demagnetize the shaft? If I could use this method, what current should I use for AC and DC to demag?

Please advise the appropriate method and current to use for this demagnetization to be effective. Thank you in advance.


 
 Reply 
 
Michel
NDT Inspector,
consultant, Canada, Joined Sep 2006, 868

Michel

NDT Inspector,
consultant,
Canada,
Joined Sep 2006
868
05:18 Mar-16-2008
Re: Demagnetization of Long Hollow Shaft in MPI
----------- Start Original Message -----------
: Dear Friends,
: I have tried demagnetizing a long hollow shaft (approximately 0.500 inch thick, 9 feet long and having a O/D of 8 inches) on a MPI Bench Unit but find it difficult to achieve less than 3 gauss on all areas of the shaft as per the ASTM E1444-05 requirement.
: This shaft has been previously magnetized longitudinally for inspection using 4ooo Amps FWDC.
: I have used the machine's Coil which was set to 4500 Amps on AC Demag Mode to demagnetize the shaft but it is not effective.
: Is it the right thing to do if I insert a flexible cable (2 inch O/D) through the internal diameter of the shaft and pass AC and DC current through the flexible cable to demagnetize the shaft? If I could use this method, what current should I use for AC and DC to demag?
: Please advise the appropriate method and current to use for this demagnetization to be effective. Thank you in advance.
------------ End Original Message ------------

HI NDTman,

As far as demagnetisation, you're on the right track. You just have to change a few parameters.

If I understand your setup, you are trying to demag by leaving the part in the bench and using the coil in the demag mode (collapsing hysterisis loop) to demagnetise your part. When you do this, remember that the coil effective area of demagnetisation will be the same as its effective area of magnetisation you used for the inspection of that part. Proof of this is your difficulty in getting below 3 gauss. Using DC current, won't do it. You don't have the reversing effect of AC and the collapsing hysterisis loop.

The best way according to the info you have provided (you will need 2 or 3 man for this job) is to set a coil beside your machine using your flexible cable. Remember you amperage should be equal or greater than what you have previously used. Than you apply current to the coil and you and your buddy walk the part through the flexible coil. For demagnetisation to be effective, you will shut the power off only when you are at least 3 feet away from the coil. This should do the trick.

Cheerios,



 
 Reply 
 
Ed T
Ed T
05:36 Mar-16-2008
Re: Demagnetization of Long Hollow Shaft in MPI
Try the coil like Michel said. Now this may sound funny and some people may think I am crazy, but I going to tell you how we used to demagnetize axles made from hardened steel.

Wrap at least a 3 turn coil around the shaft. Make sure it is oriented East and West.
If your machine has a 30 point stepdown abilty use it.

Use the maximum AC current you can decreasing the amperage as you go on and beat each end of the shaft with rubber mallets. That wil do it. Trust me.

----------- Start Original Message -----------

: : Dear Friends,
: : I have tried demagnetizing a long hollow shaft (approximately 0.500 inch thick, 9 feet long and having a O/D of 8 inches) on a MPI Bench Unit but find it difficult to achieve less than 3 gauss on all areas of the shaft as per the ASTM E1444-05 requirement.
: : This shaft has been previously magnetized longitudinally for inspection using 4ooo Amps FWDC.
: : I have used the machine's Coil which was set to 4500 Amps on AC Demag Mode to demagnetize the shaft but it is not effective.
: : Is it the right thing to do if I insert a flexible cable (2 inch O/D) through the internal diameter of the shaft and pass AC and DC current through the flexible cable to demagnetize the shaft? If I could use this method, what current should I use for AC and DC to demag?
: : Please advise the appropriate method and current to use for this demagnetization to be effective. Thank you in advance.
: HI NDTman,
: As far as demagnetisation, you're on the right track. You just have to change a few parameters.
: If I understand your setup, you are trying to demag by leaving the part in the bench and using the coil in the demag mode (collapsing hysterisis loop) to demagnetise your part. When you do this, remember that the coil effective area of demagnetisation will be the same as its effective area of magnetisation you used for the inspection of that part. Proof of this is your difficulty in getting below 3 gauss. Using DC current, won't do it. You don't have the reversing effect of AC and the collapsing hysterisis loop.
: The best way according to the info you have provided (you will need 2 or 3 man for this job) is to set a coil beside your machine using your flexible cable. Remember you amperage should be equal or greater than what you have previously used. Than you apply current to the coil and you and your buddy walk the part through the flexible coil. For demagnetisation to be effective, you will shut the power off only when you are at least 3 feet away from the coil. This should do the trick.
: Cheerios,
------------ End Original Message ------------




 
 Reply 
 
Michel
Michel
02:27 Mar-16-2008
Re: Demagnetization of Long Hollow Shaft in MPI
Hi Ed,

Good point, I've forgot about the east - west alignment. I haven't done bench work in quite some time. Nice to know that others will keep you on your toes. About the rubber mallet, well I've learn something new today. So it was a good day.

Cheerios,

----------- Start Original Message -----------
: Try the coil like Michel said. Now this may sound funny and some people may think I am crazy, but I going to tell you how we used to demagnetize axles made from hardened steel.
: Wrap at least a 3 turn coil around the shaft. Make sure it is oriented East and West.
: If your machine has a 30 point stepdown abilty use it.
: Use the maximum AC current you can decreasing the amperage as you go on and beat each end of the shaft with rubber mallets. That wil do it. Trust me.
: : : Dear Friends,
: : : I have tried demagnetizing a long hollow shaft (approximately 0.500 inch thick, 9 feet long and having a O/D of 8 inches) on a MPI Bench Unit but find it difficult to achieve less than 3 gauss on all areas of the shaft as per the ASTM E1444-05 requirement.
: : : This shaft has been previously magnetized longitudinally for inspection using 4ooo Amps FWDC.
: : : I have used the machine's Coil which was set to 4500 Amps on AC Demag Mode to demagnetize the shaft but it is not effective.
: : : Is it the right thing to do if I insert a flexible cable (2 inch O/D) through the internal diameter of the shaft and pass AC and DC current through the flexible cable to demagnetize the shaft? If I could use this method, what current should I use for AC and DC to demag?
: : : Please advise the appropriate method and current to use for this demagnetization to be effective. Thank you in advance.
: : HI NDTman,
: : As far as demagnetisation, you're on the right track. You just have to change a few parameters.
: : If I understand your setup, you are trying to demag by leaving the part in the bench and using the coil in the demag mode (collapsing hysterisis loop) to demagnetise your part. When you do this, remember that the coil effective area of demagnetisation will be the same as its effective area of magnetisation you used for the inspection of that part. Proof of this is your difficulty in getting below 3 gauss. Using DC current, won't do it. You don't have the reversing effect of AC and the collapsing hysterisis loop.
: : The best way according to the info you have provided (you will need 2 or 3 man for this job) is to set a coil beside your machine using your flexible cable. Remember you amperage should be equal or greater than what you have previously used. Than you apply current to the coil and you and your buddy walk the part through the flexible coil. For demagnetisation to be effective, you will shut the power off only when you are at least 3 feet away from the coil. This should do the trick.
: : Cheerios,
------------ End Original Message ------------




 
 Reply 
 
NDTman
NDTman
06:58 Mar-17-2008
Re: Demagnetization of Long Hollow Shaft in MPI
Dear Friends,
Thanks for your advice. Is it a correct method to insert the 2 inch diameter flexible cable through the I/D of the part and passing AC and DC current in the demag mode through the cable? I could get less than 3 gauss when I use this method to demag but is this the proper way to do it?
You see...the part is quite heavy to be carried by 2 or 3 persons to pass through the coil (as Michel had advised) so I don't think that would do because we have quite a number of shafts to demag at a time.
: Hi Ed,
: Good point, I've forgot about the east - west alignment. I haven't done bench work in quite some time. Nice to know that others will keep you on your toes. About the rubber mallet, well I've learn something new today. So it was a good day.
: Cheerios,
: : Try the coil like Michel said. Now this may sound funny and some people may think I am crazy, but I going to tell you how we used to demagnetize axles made from hardened steel.
: : Wrap at least a 3 turn coil around the shaft. Make sure it is oriented East and West.
: : If your machine has a 30 point stepdown abilty use it.
: : Use the maximum AC current you can decreasing the amperage as you go on and beat each end of the shaft with rubber mallets. That wil do it. Trust me.
: : : : Dear Friends,
: : : : I have tried demagnetizing a long hollow shaft (approximately 0.500 inch thick, 9 feet long and having a O/D of 8 inches) on a MPI Bench Unit but find it difficult to achieve less than 3 gauss on all areas of the shaft as per the ASTM E1444-05 requirement.
: : : : This shaft has been previously magnetized longitudinally for inspection using 4ooo Amps FWDC.
: : : : I have used the machine's Coil which was set to 4500 Amps on AC Demag Mode to demagnetize the shaft but it is not effective.
: : : : Is it the right thing to do if I insert a flexible cable (2 inch O/D) through the internal diameter of the shaft and pass AC and DC current through the flexible cable to demagnetize the shaft? If I could use this method, what current should I use for AC and DC to demag?
: : : : Please advise the appropriate method and current to use for this demagnetization to be effective. Thank you in advance.
: : : HI NDTman,
: : : As far as demagnetisation, you're on the right track. You just have to change a few parameters.
: : : If I understand your setup, you are trying to demag by leaving the part in the bench and using the coil in the demag mode (collapsing hysterisis loop) to demagnetise your part. When you do this, remember that the coil effective area of demagnetisation will be the same as its effective area of magnetisation you used for the inspection of that part. Proof of this is your difficulty in getting below 3 gauss. Using DC current, won't do it. You don't have the reversing effect of AC and the collapsing hysterisis loop.
: : : The best way according to the info you have provided (you will need 2 or 3 man for this job) is to set a coil beside your machine using your flexible cable. Remember you amperage should be equal or greater than what you have previously used. Than you apply current to the coil and you and your buddy walk the part through the flexible coil. For demagnetisation to be effective, you will shut the power off only when you are at least 3 feet away from the coil. This should do the trick.
: : : Cheerios,
------------ End Original Message ------------




 
 Reply 
 
DJ Kallhof
DJ Kallhof
03:39 Mar-17-2008
Re: Demagnetization of Long Hollow Shaft in MPI
Good Day,
I have had to deal with the magnetization and demag of long tubular shafts in the aircraft industry for quite some time now. Some can be more difficult then others. I do, however have a few pointers.
1. Slowly walk a gauss meter the length of the shaft, being careful not to max it out. Look for a uniform field. An improperly magnetized shaft can have many seperate leakage fields causing the meter to fluctuate positive to negative many times over, from one end to the other. A uniform field makes for an easier subject to demag. If the field fluctuates, center the coil and give it a couple of shots, just enough to overcome the unwanted field.
2. If able, slide the stands used to suspend the shaft as close to the ends as possible. The effective field of the coil may extend the length of it's diameter, but the closer the better. Also, if the shaft is magnetized centered in the coil, pulling it against the side of the coil will increase your chances. If your stand has rollers, spinning it may help as well.
3. Lastly, Start with your coil centered on the shafts length. Press your demag button and wait for the 30 point step down. Move it about a foot down and repeat. Work your way to one end of the shaft only. Center the coil again and repeat the sequence going the other way. Take your gauss meter and run it the length of the shaft again. Start the next series where your gauss meter registered + or - 1 gauss.
This should get you legal.
----------- Start Original Message -----------
: Dear Friends,
: Thanks for your advice. Is it a correct method to insert the 2 inch diameter flexible cable through the I/D of the part and passing AC and DC current in the demag mode through the cable? I could get less than 3 gauss when I use this method to demag but is this the proper way to do it?
: You see...the part is quite heavy to be carried by 2 or 3 persons to pass through the coil (as Michel had advised) so I don't think that would do because we have quite a number of shafts to demag at a time.
: : Hi Ed,
: : Good point, I've forgot about the east - west alignment. I haven't done bench work in quite some time. Nice to know that others will keep you on your toes. About the rubber mallet, well I've learn something new today. So it was a good day.
: : Cheerios,
: : : Try the coil like Michel said. Now this may sound funny and some people may think I am crazy, but I going to tell you how we used to demagnetize axles made from hardened steel.
: : : Wrap at least a 3 turn coil around the shaft. Make sure it is oriented East and West.
: : : If your machine has a 30 point stepdown abilty use it.
: : : Use the maximum AC current you can decreasing the amperage as you go on and beat each end of the shaft with rubber mallets. That wil do it. Trust me.
: : : : : Dear Friends,
: : : : : I have tried demagnetizing a long hollow shaft (approximately 0.500 inch thick, 9 feet long and having a O/D of 8 inches) on a MPI Bench Unit but find it difficult to achieve less than3 gauss on all areas of the shaft as per the ASTM E1444-05 requirement.
: : : : : This shaft has been previously magnetized longitudinally for inspection using 4ooo Amps FWDC.
: : : : : I have used the machine's Coil which was set to 4500 Amps on AC Demag Mode to demagnetize the shaft but it is not effective.
: : : : : Is it the right thing to do if I insert a flexible cable (2 inch O/D) through the internal diameter of the shaft and pass AC and DC current through the flexible cable to demagnetize the shaft? If I could use this method, what current should I use for AC and DC to demag?
: : : : : Please advise the appropriate method and current to use for this demagnetization to be effective. Thank you in advance.
: : : : HI NDTman,
: : : : As far as demagnetisation, you're on the right track. You just have to change a few parameters.
: : : : If I understand your setup, you are trying to demag by leaving the part in the bench and using the coil in the demag mode (collapsing hysterisisloop) to demagnetise your part. When you do this, remember that the coil effective area of demagnetisation will be the same as its effective area of magnetisation you used for the inspection of that part. Proof of this is your difficulty in getting below 3 gauss. Using DC current, won't do it. You don't have the reversing effect of AC and the collapsing hysterisis loop.
: : : : The best way according to the info you have provided (you will need 2 or 3 man for this job) is to set a coil beside your machine using your flexible cable. Remember you amperage should be equal or greater than what you have previously used. Than you apply current to the coil and you and your buddy walk the part through the flexible coil. For demagnetisation to be effective, you will shut the power off only when you are at least 3 feet away from the coil. This should do the trick.
: : : : Cheerios,
------------ End Original Message ------------




 
 Reply 
 
j Boodoosingh
j Boodoosingh
07:03 Jun-23-2008
Re: Demagnetization of Long Hollow Shaft in MPI
So guys, i need to demagnetise a solid 2inches diameter, 3 feet, 316 stainless steel shaft. Any ideas.


 
 Reply 
 
mandar vinze
Engineering, manufacturer
magnafield controls, India, Joined May 2006, 3

mandar vinze

Engineering, manufacturer
magnafield controls,
India,
Joined May 2006
3
07:23 Jun-24-2008
Re: Demagnetization of Long Hollow Shaft in MPI
----------- Start Original Message -----------
: So guys, i need to demagnetise a solid 2inches diameter, 3 feet, 316 stainless steel shaft. Any ideas.
------------ End Original Message ------------

send us details of cause of magnetization and we can supply suitable demag


 
 Reply 
 

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