18:46 Feb-09-2009 aldo Engineering Italy, Joined Jan 2009 39
Hi everybody. I am studying the induced current magnetization especially the todoidal method for ring shapdes part on aeronautic components. I have a lot of questions for the forum specialist on specific ASTM par. 6.2.9 in particular on ratio between L/D. The following questions are:
1)What diameter do i take of the part? outside diameter Dout, inner diameter Din or effective diameter Deff?
2)The specific saies that ratio L/D must be less than three. Why? Whats happens if i choose a conponent wich have a ratio L/D major than three? I think that with a ratio major than three i have a overheat on component. Is correct my interpretation ?
Tanks and best regards
I have discovered important information on L/D ratio. On specific book of NDT of title:Nondestructive Evaluation - Theory, Techniques, and Applications - (Peter J. Shull) Marcel Dekker 2001, it indicates that L is: "lenght of iron core" while does not specific that type of diameter must be considered... can somebody help me for to define the diameter that is present on specific ASTM 6.2.9?
Tanks and best regards...
Hi michel Couture... Tanks your replay...
Why do the ASTM not specific the type of diameter of component? Becasue there are not information on specific textbooks or technical articles on this matter...
Looking at ASTM E1444-05, for inducing a toroidal field, typically is used for ring or disc shaped parts to find circumfrential defects. It actually uses the iron core inside your part in the coil to induce an eddy current into the part. It's good if you cannot use a central conductor or do not want to risk arcing with a head shot. As far as the formula you are looking for, use the dimensions of the iron core with your base formula 45000/(l/d) for a low fill as a beginning current and attach QQI's. I've found formulas are more than unreliable and the QQI is your best bet. I usually start almost 1000 Amps lower than my calculated and increase till the QQI's show. As far as parts with a L/D greater than 3, the core is not needed. the part should have a uniform longitudinal field with the coil shot. I do a lot of ring shaped, and if you can, use a central conductor, stay away from the toroidal, or if you must do a coil, use extension pieces of the same diameter on either side to increase your L/D. Hope it helps....
Dear Aldo ,
As far as my interpretation goes there is no formula for setting ampere turns for torroidal magnetization but should be set up using QQI shims or the hall effect gauss meter because in using the formulae it is stated that in L/D these values are considered of the part under test and not of the core further more it is clearly stated that the formulae hold true for parts having L/D more than 3 and less than 15 and it is clearly stated that torroidal magnetization is used for parts having L/D less than 3 hence the faormulae are not applicable for torroidal magnetization . This is mainly because the induced eddy currents dependent on all factors like fill factor of part to coil and also core with respect to part ID and also frequency of current used .