As a lot of , Mil-Std-750 TM 1071 was just lately modified and the hermeticity specification was tightened by two orders of magnitude. This had a big impression on Mil-Prf-19500 element suppliers and compelled them to judge and buy new leak take a look at gear. This was as a result of most standard helium mass spectrometry (HMS) leak detectors lack the precision and sensitivity to measure leak charges to the brand new spec. Of course you possibly can obtain the specified sensitivity when you’re prepared to “helium bomb” the elements for some ridiculous period of time like 100 hours or so. A two order magnitude discount within the Lair spec restrict from 1E-06 cc/sec to 1E-08 cc/sec requires equal HMS readings to be within the low 1E-10 or excessive 1E-11 cc/sec Helium, for typical bomb time and strain situations.
Mil-Std-883 TM 1014 is at the moment underneath revision. At a latest authorities coordination assembly there are proposed modifications to the specification that will require element suppliers to as soon as once more consider and buy new leak take a look at gear. The TM 1014 is the defacto leak take a look at, hermeticity commonplace and is used and referenced by many extra firms within the protection, aerospace, telecom and medical machine neighborhood. A spec change to this vital take a look at methodology could have profound implications for a lot of firms inside and past the army/aerospace business.
There are basically three take a look at procedures and related gear that may meet the proposed new standards. They are: Optical Leak Test (OLT), Cumulative Helium Leak Detection (CHLD) and Radioisotope Kr-85. The take a look at situations for every of those take a look at strategies are completely totally different. The Radioisotope methodology forces a radioactive tracer fuel Kr-85 combination right into a bundle after which counts the variety of radioactive molecules that stay inside at ambient temperature and strain situations. CHLD extends the sensitivity of standard HMS. Like HMS, CHLD forces a tracer fuel into the bundle after which measures a leak fee, or instantly identifies a gross leak by detecting a sign burst. In both case the escaping helium is measured whereas the half is underneath vacuum. OLT alternatively, exactly measures the lid or bundle deflection whereas the half is underneath strain, and there’s no injection of a tracer fuel. OLT thus eliminates the priority of residual tracer fuel on the floor, which tends to confound the outcomes for each helium and Kr-85 testing. OLT additionally performs a gross and effective leak take a look at in the identical cross and is “fail safe” for gross leakers.
If the brand new model of TM 1014 causes you to must buy new gear then my recommendation can be to judge all three strategies and choose the one which most closely fits the leak fee requirement to your specific bundle kind, bundle quantity, anticipated throughput ect. Be particularly cautious that any new gear is ready to detect and fail for any potential “gross leakers”. Gross leaks are a serious trigger for concern as a result of they will simply result in early area failures. Moisture induced failure mechanisms have been nicely chronicled within the literature over time and an element with a “gross leak” is vulnerable to a lot of these failures. In my opinion there is not an enormous distinction in an element leaking at 2E-09 Lair vs. 9E-10 Lair, however there certainly is an issue in “gross leak” escapes that evade detection and get constructed up into our army programs.
Remember to transform all the things again to “air equivalent” leak charges for information utilized in comparability research and the brand new specification ranges. This will be tough and remember for the explanations acknowledged above exact “correlation” amongst the three strategies might not be achievable. However, based mostly on my expertise all three strategies are able to assembly the brand new specs and are scientifically sound. They additionally agree cheap nicely with one another when seen as “go/no-go” attributes information. In my thoughts that’s what the leak take a look at is all about. It’s a one time verify on the seal course of accomplished on the manufacturing unit flooring underneath idealized situations. To use the leak take a look at information to make reliability predictions or undertaking anticipated lifetimes within the area is fraught with issues. The first of which is relating the measured leak fee to an precise theoretical mannequin to foretell moisture ingress right into a sealed enclosure, then issue within the moisture susceptibility of the parts inside. Not for the lighthearted.
Each one in every of these main strategies has benefits and downsides so purchaser beware!
Comments