• Topic #58588 "Salt spray test: Can't get adequate solution flow"

A. Replace the muslin cloth on the end of the aspirator pick up tube. Adjust the float valve for the liquid level to a little higher level. I had a similar problem once and found that I had a tiny flap of plastic in the aspirator that acted like a flapper or reverse flow valve. You could not see it in the "retracted position" but it really shut off the flow when it was under pressure. Found it by blind dumb luck.

A. Steve -

If the collection rates are even, but low, James is probably correct in his reply that the flow of solution is obstructed. Depending upon the manufacturer of the chamber, there should be a salt solution filter between the solution reservoir and nozzle. It may need replaced or simply cleaned. Check all the fittings to be certain you are not losing air pressure or solution flow. If you raise the bubble tower air pressure, make sure you raise the temperature too. (Refer to ASTM B117 for the actual operating conditions.)

Good luck.

A. Nila,

Inconsistent condensate collection can be caused several different ways depending on the type and model of your salt spray cabinet. Some cabinets allow for slight directional adjustments to provide consistent coverage. Another factor could be that the nozzle could be slightly clogged or a particle caught in the orifice which would result in a misdirected fog. A final possibility could be the nozzle air pressure. Too high a pressure and the fog will spread wider, too low and the fog will settle closer to the nozzle. It may be silly, but you also need to make sure your collection vessels are not placed directly under panels or holding devices which may drip and cause errant readings.

Best of Luck,

First I would say that this problem is not unusual. Are you working to ASTM B117? One thing you might try is replacing your filter.

Contact the cabinet manufacturer for suggestions on how to adjust for more even collection rates. Have the following information available: cab temperature, air pressure, humidifying tower temperature, collection rate in each collector. If possible, send them a digital photo. Also, be sure the cabinet is level and properly vented.

A. Hi Gregory,

One thing that needs to be clarified is that ASTM B117 is a specification for everything connected with the salt spray cabinet, like design, amount of collections, pH of salt solution, etc. It does not address failure criteria.

If the test is being performed in a way that is outside the specifications of ASTM B117, then the results should called into question. One of those specs is the position of the test specimens.

A. Greg - B117 definitely states that the specimens should be at 15-30 degree angle, unless otherwise agreed upon. It sounds more like the evaluation criteria is in question. There are a number of ASTM standards for evaluation, ASTM D1654, ASTM D610 and ASTM D714. You should establish the "significant surface" and evaluate that area only.

SAE USCAR1-3 requires that the orientation of the primary axis of the fastener to be 25 ± 3 degrees from vertical. I recommend that you obtain this standard, as it describes the proper procedure for testing fasteners, and it is suitable for shaft components as well.

Painted panels should be tested at a 15 - 30 degree angle. For other parts, the significant surface should be a 15 - 30 degree angle whenever possible. Position the test specimen to minimize solution collection in crevices.

A. Hi Russell -

I'm not surprised that you get better results!

But I don't believe that laying the parts horizontally is what was intended.

I believe that the main plane of the part is to be oriented in the 15 to 30 degrees from vertical angle.

It would be hard to argue that the main plane of your part is 15 to 30 degrees from vertical if you are laying them flat.

A. Thanks, Russell. I don't particularly have a response, but you have certainly offered an interesting observation. I would certainly agree that the purpose of a salt spray test should be to test the coating rather than to demonstrate the weaknesses of the test :-)

Is there a possibility that the cover is so poorly insulated that the chamber is cooler in the top one inch than just two inches lower?

A. I think that the failure on the lower portions might be caused by the fact that the lower portion of the part has material being dissolved and dragged down on top of it.

For example we see this same thing sometimes when we test aluminum sheet metal.

Is it possible for you to design your coating so that even the longer parts are able to pass salt spray on their lower portions?

If you lay your parts flat, I don't see how you could be meeting the 15 to 30 degree angle requirement.

That's my two cents anyhow.

thanks

A. From the standpoint that you no longer have a significant surface you have twice as much area to look at.
Since it is vertical, it does not have the condensation running down the inclined face, so it would NOT be as stringent as what the spec calls for.

A. Good day Michelle.
The nature of the salt spray test is to subject the specimen to salt fog as a condensate. The lesser incline will produce a situation where "beads" of condensate will run off the specimen at a faster rate than a specimen at say 30 degrees, where the bead has a chance to "sit".
Chromic acid anodize test panels are by far the most difficult to pass at an incline of only 6 degrees and @ 336 hrs., as the anodize thickness is far thinner than other anodize processes. An example is Cadmium test panels @ 15-30 degrees where the thickness is usually two times greater or IVD panels (aluminum on steel) @ 15-30 degrees for 672 hrs.
Hope this helps.