Salt Spray Failure Question (ASTM B 633 and B 117)

[JLang]

Hello fellow covers,

Wondering if I can get some help/insight from some of our more experienced members here. We are having an issue with the zinc electroplating of 2" screw. Our supplier has given us a certification showing that the parts passed 200 hr salt spray after processing. However, over the course of the past two months we have tested nearly 20 pcs (at both our customers location and a third party A2LA lab) at different intervals and the majority of them have failed. Our supplier is not accepting our rejection based on the ideas that (1) handling the parts can negatively affect the SST (even though we wore gloves throught the whole process) (2) ASTM B 633 says that a salt spray test must be completed within 72 hours of the chromate curing.

I am mostly concerned with the second item. It would appear that is indeed what the spec says, but something about that does not seem right to me. By the time you consider shipping parts from a plater back to the manufacturer, to us (a distributor), and then to the customer you are already well over 72 hours, meaning a customer can never be gauranteed valid results in their testing laboratory. This does not seem right to me at all. Has anybody had a similar experience before or could give a little more insight into this?

I can see this issue from both the customer's and the manufacturer's point of view, but would love somebody else's opinion.

I would greatly appreciate your help as this is starting to get quite frustrating!

 

[Stijloor]

A Quick Bump!

Can someone help?

Thank you very much!!

 

[silver ring]

Your supplier is wrong. I have never heard such a requirment (72 hrs). Go and check your supplier process. How are they plating the parts. It seems there is a variation in their plating process. The reason for this variation should be found.

If you cannot solve the problem change your supplier. To me it seems there is a serious problem about their facility or about their quality understanding.

 

[p1stonbroke]

The Standard does indeed state:

"10.3 Corrosion Resistance—When specified in the contract or purchase order, determine the corrosion resistance in accordance with Practice B 117. Subject the selected samples to the salt spray test; the length of time to be applicable for the type of supplementary coating shall be in accordance with the requirements of 7.4. To secure uniformity of results, age Types II, III, V, and VI supplementary coatings at room temperature for 24 h before subjection to the salt spray. The salt spray test shall commence within 72 h of the completion of the aging period."

my question though is where does this 200 hours come from?
the table (table 2) relating to the tcorrosion resistance requirements is as follows:

I As-plated without supplementary treatments
II With colored chromate coatings 96 (hours)
III With colorless chromate conversion coatings 12 (hours)
IV With phosphate conversion coatings (hours)
V With colorless passivate 72 (hours)
VI With colored passivate 120 (hours)

so there is nothing stating 200 hours here..... ?

Bear in mind that the test is conducted on a flat plate, iff you are testing the screws themselves, then youa re onto a loser to begin with, as parts with complex angles, hollows and recessed elements do not get the same level of treatment as a flat plate because of bubbles, solution beign trapped and where appropriate current distribution.

If you can satisfy yourself that the sample passes the appropriate test, and that the production runs are manufactured using the same process, then the parts should be acceptable. If you want to duplicate the testing, then you need to duplicate the test requirements, including the type of sample used, and within the timescales defined.

 

[charanjit singh]

I agree with Silver Ring. There seems to be something wrong at the supplier's end. We have experience of salt-spray testing of zinc-plated parts as per ASTM B117 but have never come across a problem of the type mentioned by you. Please verify thorughly the process control conditions at your plater's works.

 

[JLang]

my question though is where does this 200 hours come from?
the table (table 2) relating to the tcorrosion resistance requirements is as follows:

I As-plated without supplementary treatments
II With colored chromate coatings 96 (hours)
III With colorless chromate conversion coatings 12 (hours)
IV With phosphate conversion coatings (hours)
V With colorless passivate 72 (hours)
VI With colored passivate 120 (hours)

so there is nothing stating 200 hours here..... ?

Thank you everyone for your feedback. The trouble we have is that they supplier has a specification they can point to, and we just have the feeling that this is bad business practice.

As for the 200 hour requirement, that comes from our customer. They requested a plating that can with stand 200 hours with no red rust. The supplier is saying this B 633 standard is a "general practice" type standard for electro plating and can be applied to all plating specifications.

 

[Jim Wynne]

Hello fellow covers,

Wondering if I can get some help/insight from some of our more experienced members here. We are having an issue with the zinc electroplating of 2" screw. Our supplier has given us a certification showing that the parts passed 200 hr salt spray after processing. However, over the course of the past two months we have tested nearly 20 pcs (at both our customers location and a third party A2LA lab) at different intervals and the majority of them have failed. Our supplier is not accepting our rejection based on the ideas that (1) handling the parts can negatively affect the SST (even though we wore gloves throught the whole process) (2) ASTM B 633 says that a salt spray test must be completed within 72 hours of the chromate curing.

I am mostly concerned with the second item. It would appear that is indeed what the spec says, but something about that does not seem right to me. By the time you consider shipping parts from a plater back to the manufacturer, to us (a distributor), and then to the customer you are already well over 72 hours, meaning a customer can never be gauranteed valid results in their testing laboratory. This does not seem right to me at all. Has anybody had a similar experience before or could give a little more insight into this?

I can see this issue from both the customer's and the manufacturer's point of view, but would love somebody else's opinion.

I would greatly appreciate your help as this is starting to get quite frustrating!

I think the 72-hour thing is more or less arbitrary and serves to ensure that the parts don't lay around in uncontrolled ambient conditions for too long.

If your supplier is doing the salt spray testing in-house, you can ask for it to be done (at your expense, of course) at an independent lab, and make acceptance contingent on the results of that testing.

There is no way to consistently correlate salt spray test results with corrosion resistance in end use, simply because the number of variables in end use is too great. You need to differentiate between white (oxidation of the zinc) and red (oxidation of the base metal) corrosion; white corrosion signals failure of the chromate and red signals failure of the chromate and the zinc coating. If what you're seeing in your independent testing is red rust, the 72-hour thing is pretty irrelevant.

 

[JLang]

Jim,

We have done just that. We have sent samples to an independent certified lab twice and had parts fail both the white rust (25 hours) and red rust (200 hours) requirement. Supplier is still not accepting results. Wants us to go back and verify the angle of the parts, the pH levels, etc. Our opinion is that it is an A2LA accredited lab, that should be enough in and of itself, correct?

 

[Jim Wynne]

Jim,

We have done just that. We have sent samples to an independent certified lab twice and had parts fail both the white rust (25 hours) and red rust (200 hours) requirement. Supplier is still not accepting results. Wants us to go back and verify the angle of the parts, the pH levels, etc. Our opinion is that it is an A2LA accredited lab, that should be enough in and of itself, correct?

What I am saying is that the use of an independent lab should be a requirement for all future processing by the supplier. Take his own lab out of the equation permanently. You should be assuming at this point that your supplier's methods are at least very questionable.

Have you done any analysis of the plating thickness? Rather than using indirect methods such as XRF, you might want to have some parts microsectioned and have the plating thickness measured directly. If the parts are failing, it's either because the thickness isn't what it should be or the coatings (zinc and chromate) are too porous.

 

[JLang]

Thanks for clarifying Jim. I misunderstood the first time. I like that idea moving forward. We do not have plating thickness results from a seperate lab yet, that would probably be a good route to go. Thanks again for your advice.