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Posted: 6/20/2010 6:18:21 PM EDT
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There has to be some limit on the size of the cracks that can be detected, no?
Also, who (man or machine) checks the test results? |
| Any cracks detected by magna-fluxing obviously were not visible, or they wouldn't need the process at all. As I understand it, the magnetic flux follows faults in the metal that you ordinarily would not see. It has been used for many years in the auto industry for high-stress items like connecting rods, etc. |
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Quoted:
It's a rather crude form of NDI that only detects flaws near the surface. +1 im new to ARs. but i come from the world of racing and have built my share of high end engines/cars. best in testing methods for metals are used by Indy car and NASCAR. really the true mother ship is the aerospace crowed. i.e. NASA, lockheed martin, ext. keep in mind there is something called good enough, they have to keep stuff affordable. but if we ever need to run an AR on the moon, who knows.... here is something to read. |
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Quoted: thanks for the link ... interesting reading. If those very small peening marks can lead to failure of that high performance gear shaft, then I am not left with a warm and fuzzy feeling about the small cracks on the MIM gas key of my LMT bolt. A gear shaft is a high stress area. A gas key is not. If the cracks were going to cause a problem, surely by now we would hear about it... They've been out for quite awhile now.... |
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Quoted:
There has to be some limit on the size of the cracks that can be detected, no? Also, who (man or machine) checks the test results? MIL-B-1159E specifies AMS-2640 MPI testing. Here's a quick description from a testing site I know: This is a nondestructive method of inspection to determine the existence and extent of surface and near surface cracks in ferromagnetic materials. Finely divided magnetic particles, applied to a part during magnetization, are attracted to any magnetic-leakage fields created by discontinuities. The magnetic particles are attracted to the discontinuous areas and outline these areas so surface and near surface cracks can be identified. Though compared to an input shaft, an AR gas key doesn't undergo the same stresses. However, if your gas key fails - your rifle fails. I don't know what the MIL spec is for gas keys on M4's or M16's, but something tells me having cracks and being injection molded isn't one of them. |
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an axle was the first thing that came to mind for a comparison.
im sure a bolt cracks in the area with least mass. but im wondering which force is more at fault, reciprocating or rotational? i have never held a broken bolt. but i would guess it would be hard to tell. axles have enough meat to eyeball it. maybe someone with more notches on there bed post will chime in. edited to add, MIM stuff is wack IMO. that mess is injection molded into form like plastics. there could be bubbles, dirt, or who knows what in the injection process. not milled from a solid stock, forging, or round. i dont know what they are using for gas keys. im only a week or so deep into ARs. so much to learn and i have so little time these days. |
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