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topic 61107

Motor housing with sharp edges from the manufacturing process


May 13, 2020

Q. I have an issue related to a customer using Ri=2 ISO 4628 for an automotive component with sharp edges, that they feel failed salt spray testing of 720 hours. But they use this standard from their assembly drawing used for fasteners installation. What would be a comparable standard for testing parts with sharp edges. I think this specification would not work for parts with sharp edges for testing for salt spray. Your thoughts.

George Allen
- St Peters missouri


May 2020

A. Hi George. I don't know whether the edges should be deburred or rounded; and ISO 4628 is a big standard with at least 10 parts, and I neither have the whole standard nor pretend to be a expert on the subject. However, while you seem to be quoting the evaluation criteria of ISO 4628-3 [affil. link to spec at Techstreet] regarding permissable degree of rusting, what remains missing from the discussion so far is the standard for conducting the salt spray test prior to this inspection & evaluation of the degree of rusting.

When you consult the standard for conducting the salt spray test, I think you may find that it calls for testing, not shaped and finished parts, but flat panels inclined at 15°; and that even then, the edges of the test panels are supposed to be masked.

People do play fast & loose with salt spray test specifications, and they test finished parts for one reason or another, but it generally is not valid, and a very 'iffy' area, to claim that a finished part 'failed' salt spray testing if the salt spray exposure was half-assed and not in accord with the requirements of a standard :-)

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Aloha -- an idea worth spreading


May 14, 2020

Q. Thanks Ted for the valuable information; so quick question, when utilizing ISO 4628-3 for salt spray testing, flat panels are used for the testing, not shaped or finish parts, correct? My customer insist that the ISO specification could be used on a finish part with sharp edges, not to exceed .5% in a rust area, and still achieve the same result. Is that true?

George Allen
- St. Peters Missouri


May 2020

A. Hi again. I don't have a copy of ISO 4628-3, so I can't quote it, but I don't think it's a spec for 'salt spray testing' at all; I think it's inspection guidance for evaluation of degree of rust.

It seems to me that you had "party A" subject the parts to some sort of spray of salt solution; then you had "party B" evaluate the degree of rust on the parts in accord with ISO 4628-3 and tell you that the degree of rusting is excessive. I'm saying that party B is probably correct that the degree of rusting is excessive ... but that someone has to determine what salt spray test was specified: ASTM B117 [affil. link to spec at Techstreet] or ISO 9227 [affil. link to spec at Techstreet] or whatever, and whether the salt spray test was conducted in accord with it ... and that I suspect, because people are talking about rusting at 'sharp edges', perhaps it wasn't conducted in actual accord with any specification at all.

I and probably other readers have no interest in being drawn into a contract dispute about how to adjust/rewrite/interpret ISO 4628-3 to make up for the fact that the parts were subjected to an unknown but probably invalid salt spray test ... I'm just pointing out what strikes me as probably the loose end/open question that may require fixing.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Aloha -- an idea worth spreading


May 15, 2020

Q. Ted, I understand your point, this is the acceptance criteria that the parts are held to, No base metal corrosion, no signs of blistering or decomposition phenomena, slight changes in color and gloss permitted, cracking peeling or softening to a point where the paint can be scratch off down to the base metal with a finger nail shall not be permitted. Areas which are damaged by the manufacturing process and areas with sharp edges, the degree of rusting is Ri=2 (medium according to ISO 4628. I am not trying to drag you into any conflict, I just want to be able to support my organization to stand firm with the testing criteria I think is incorrect. They want us to send finished parts for salt spray testing, when we should be sending flat panels instead. The salt spray test would be under ISO 9227. I just need to understand what type of test samples should be tested, finish or flat panels. Thank you in advance for your help.

George Allen [returning]
- St. Peters Missouri


May 2020

A. Hi again George. Okay, it is good progress to clearly understand that the salt spray test is to be conducted according to ISO 9227. The next step is to make sure that you have a copy of ISO 9227 on hand, have read it, and are familiar with it -- and are not relying on an opinion from someone who doesn't have a copy of it and is talking about the general vagaries involved in salt spray testing :-)
I don't think I'm misleading you, but you will need to quote exactly what the current version of ISO 9227 says, not my or your guesses about what it may say :-)

Good luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Aloha -- an idea worth spreading

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