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Re: Magnetic particle examination – crankshafts
Although common to the automotive engine rebuilding industry, the commercial engine (truck & marine diesel) rebuilding community has for many years employed a different technique to check for cracks in crankshafts and other rotating components. The most widely used process is fluorescent dye penetrant testing. The reasons for this are as follows:
1). Dye penetrant does not require that a magnetic field be introduced into the part. Do you want your crankshaft acting like a magnetic drain plug?
2). We are talking “in service cracks” and as such, are ALWAYS open to the surface. Some proponents of “Magnaflux” will tell you that dye penetrant will not locate sub-surface discontinuities. My answer to that line is that a sub-surface flaw is not likely to cause a failure. I’m sure the good Dr. Porsche & Co. subjected the cranks to non-destructive testing at many stages of the manufacturing process. Gross sub-surface flaws would have been weeded out during that process. Porsche may have employed magnetic particle examination on the final product, but also, would have subjected the crank to a proper degaussing. I suspect that most machine shops do not have the proper equipment, nor do they have the expertise to properly degauss a crank. “Pass it through the coil and call it a done deal”. Going back to surface and sub-surface; as cracks are surface breaking they will respond nicely to dye penetrant. Pay particular attention to the radius on either side of the journal, and the oil passages. I prefer the fluorescent type, but a non-fluorescent type will work just fine. One word of caution; dye penetrant will not tolerate dirt, grease or other contaminates. The part needs to be clean. Magnaflux Corp. makes a handy kit that is available from most commercial supply houses.
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