July 2008

Document updated in August, 2008

Some requirements ask for a monthly or weekly check of the density of the dry developer in the duststorm cabinet.

This requirement makes us uncomfortable.

Dry powders are "fluffy" powders, i.e. very light powders that a very smooth air movement will send away. These powders are complex mixes of different white absorbing, or less absorbing, minerals with a tiny amount of organic additives.

When taking powders out of the case (cans, cartons, bags, etc) in which they are delivered, it is a good idea first to stir them, carefully just to prevent too much of it be inhaled, but enough to get an homogeneous mix of the different particles, which have a large size range (from 10 nanometers up to 10 micrometers, that is a 1 000 factor!) and different densities. Doing so, within seconds, one may see the VOLUME increases by 2 to 4, or more! That means the same quantity, say one kilogram, will have a volume 2 to 4 times larger! Further, if one puts powder in a 1-liter beaker, as stated in the requirement, very quickly one sees the "powder top level" going down. That means what seemed as 1 liter 10 seconds before is now, say, 0.9 liter. If one waits for 30 seconds more, the volume may go down to 0.8 liter!! All this with the same MASS of powder!

When is there a real liter of powder??

Hence, it is in fact impossible to measure the powder REAL density, and it is impossible to check the inuse powder density against a brand-new powder density!!

That's why this test gives a figure only for the apparent density or apparent specific gravity.

Furthermore, in dust-storm cabinets, it is better to have a VERY SMALL amount of powder, enough say for one shift. At the end of the shift, almost no powder is left in the cabinet, and in any way, far less than the liter required for the test! So, the test cannot then be performed!

Less paper, less useless work ...

But the dry powder quality shall be daily checked for any lump and fluorescence.

To be in line with Nadcap AS 7114/1 para. 5.6 requirement, better to follow the ASTM E 1417-05, par 7.8.2.7 specification which makes it mandatory to apply dry developer powder the same way as for inspection on a 10 cm-dia metallic plate. Then the plate is seen under UV-A radiation. If 10 or more fluorescent speckles are seen, then the developer is out of tolerance and shall be discarded.

As suggested by one of our readers, there is a very simple method not to have to check the developer; it is good enough to replace it every day. Due to the small quantity, it does not raise problem. Suck up the old developer, check under UV-A the absence of fluorescence, check the appearance of the new developer and put the just needed quantity into the cabinet.

This process is very well accepted by auditors.

Pierre CHEMIN and Patrick DUBOSC, welcome any comment, any idea. If you have some examples you would like to see discussed here, please give us all the useful indications. If you require confidentially, we would modify locations, names and some parameters to prevent any traceability.
Nevertheless, we are convinced that our site may be a kind of surge-valve: the topic is NOT to target this company, or that auditor; but it is always to make users think, to make them ask themselves, or others, the right questions.

We may also give advice, once again on a confidential basis if needed: please, feel free to ask questions, to document our data basis: about Material Safety Data Sheets (MSDS), about environment, a chemical name you don't understand, a Penetrant process you have heard about, etc.
We have plenty of examples, some being out of all the specifications/standards, which led to the discontinuities detection, when the "current, normal, processes" prevented discontinuity finding.