NAD Use with Type 1 and Type 2 Penetrants
We recently had a question concerning the type of developer to use with fluorescent penetrant. In this particular case, the person with the question
was using both visible and fluorescent penetrants. He was using Met-L-Chek D-70 developer with the visible penetrant and a different brand of developer with the fluorescent penetrant. There are a couple of things that can be said about this situation. The first is that Met-LChek developer is qualified for, and listed on the QPL for use with both visible and fluorescent penetrants. The second thing is that according to AMS-2644 any manufacturer’s brand of developer (if qualified) is permitted to be used with any other manufacturer’s penetrant. The last thing is that Met-L-Chek D-70 is the AMS 2644 standard. It simply complicates things to have two different brands of developer in use when one will satisfy both situations.
New Aerosol Package
Met-L-Chek Company will begin shipping aerosol products in a new “bullet” aerosol package in February 2012. The new package features a seamless high pressure container which reduces leakage with increased can safety. Another feature will be the new shrink wrap label
rather than the commonly used paper labels. Same high quality product in a new package. Still supplied 12 cans per case rather than 9 (like
some suppliers), which makes the Met-L-Chek® products the best value on the market.
Electrostatic Penetrant Spray, Film Thickness & De-wetting
Electrostatic spraying of penetrant is a popular and economic way to apply penetrant to parts in many applications, where it replaces immersion
of the parts. In general, less penetrant is used because the coating on the parts is thinner. So, how much thinner is it? Well, this is another of those questions that has no readily available formula to make the calculation, and which has dimensions that are difficult to assess. It is a case where the operator has a lot to do with the process, in that one operator might spray parts with more penetrant than another operator. It is also a case where the geometry of the parts plays a roll in that some parts might have interstices or cavities that trap penetrant when the part is immersed, but do not do so when sprayed electrostatically. The part does not have to be dripping penetrant to find flaws but the surface must be covered. In general, it is acknowledged that the spray method uses less penetrant than the immersion method. But for specific applications, simply making comparative tests with the operators and parts being tested will yield the answers sought. And, with regard to the thickness of penetrant on a part, the subject of de-wetting comes up from time to time. This is when a part that is coated with penetrant has the penetrant coating retract, as though the part has not been wetted by the penetrant. This phenomenon is noted on some alloys, and the concern is whether the penetrant has coated well enough that it has entered any flaws. If this condition is encountered, one can check by exposing the part to UV-A and looking to see if the de-wetted area fluoresces. If it
does, it is confirmation that the penetrant has coated the surface sufficiently.
A Bit More About UV-A Intensity
Betty Cheng, of Spectronics has pointed out that there is an existing warning in ASTM E-2297-04 Sec 6.5.2 which discusses high intensity UV-A lamps and UV fading. This section points out that fading is a possibility under excessive intensity and warns that caution is necessary. It does not recommend any upper limit to the intensity of the light source, such as is under discussion in Committee E-07 at present.