as per ASTM for circular shot NI=K/(L/D).
but i am not very clear at the time of calculating L/D for many parts Viz Crankshaft/Camshafts/spindles and other difficult geometry components.
your valuable responce are awaited.
15:49 Mar-09-2009 Michel Couture NDT Inspector, consultant, Canada, Joined Sep 2006 818
Re: Circular shot current calculationIn Reply to Ehsan at 06:11 Mar-09-2009 (Opening).
Andreas brought a valid point. But one thing I would like to mention to all who do MT is the formulas given in ASTM E709 and E1444 are in my opinion only guidleine or starting point if you will. On factor we never really consider in our calculation is: "permeability".
For this reason, when I taught MT, I used to tell my students the calculations are only a starting point. I would always magnetised my parts using a lower amperage than what my calculation showed me. Always, verify with my pie gauge or QQI to ensure you are getting the proper magnetisation. You will be surprise at how low the amperage is compare to calculations. Other things to consider when doing MT is particle mobility and background.
One other thing, whenever you do MT, try to picture the part as being a straight piece of round stock. You were talking about a crackshaft, well how long would it be if it was straight?
Remember, always verify your magntisation with a QQI or pie gauge.
19:17 Mar-09-2009 Andreas NDT Inspector, Specially in the oilfield Tuboscope Vetco(Deutschland)Gmbh, Germany, Joined Oct 1999 126
Re: Circular shot current calculationIn Reply to Michel Couture at 15:49 Mar-09-2009 .
The E 709 eveen state that is only a guideline and you should verify the field by a "gausmeter" , correct would be a Tesla meter to use correct SI units.
I like the so called "Burmah-Castrol strip" , it shows you the magnitude and direction of the field.
If you see the three indication on the strip ,the field is 2.4 kA/m or greater (2 - 6 kA/m is required by EN specs).If not placed perpendicular (90° ) to the applied magnetic ,then no indication will be shown.