Mil-C-5541E
Mil-C-5541E
(OP)
Class 1A has no color stated
Class 3 has none
so if there is no color specified,is clear assumed??
Class 3 has none
so if there is no color specified,is clear assumed??
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RE: Mil-C-5541E
Color is not specified in MIL-C-5541E nor its material qualification spec. MIL-C-81706. It is most commonly yellow-to-gold for Class 1A, depending upon the Al alloy. The color arises from the chromate formed by a chromic acid solution, which is the long-established, most efficient means of meeting the salt spray requirements. [as-yet, nothing meets the EU's directive re carcinogens that is nearly as cost-effective.] The only non-gold Class 1A I am aware of is a specialty product used to touch-up black anodize.
Class 3 coatings are commomly produced in the same process solution by using a shorter time, and hence are a lighter color (pale yellow). 'Clear' is a customer-specified option. It is produced either in a solution formulated to give a clear coating, or by using hot water to leach out the color (bad for corrosion resistance).
A customer specification of 'chemfilm' defaults to Class 1A and hence, gold. If you want 'Clear,' it must be explicitly specified, i.e., as Class 3, Clear. Note: production workers frequently rely upon color for process control, obviously problematic for clear.
ASTM B449 discusses colors of chromate coatings on aluminum.
RE: Mil-C-5541E
While you may wish assume that a "customer" specification of "chemfilm" defaults to a "Class IA" coating (and be right the vast majority of time), a review MIL-C-5541E will show that there is no "Default", or "Unless Otherwise Specified", "Class" where MIL-L-5541 is invoked -- Class must be explicitly specified.
RE: Mil-C-5541E
The spec. uses language like "should specify the Class 1A or 3," not must, and remember that all of Section 6 is helpful guidance, not mandatory information.
MIL-C-5541E, Section 6.3 [final sentence at bottom of p. 8]
"If the coating class is not specified, Class 1A is recommended."
Ken V.
RE: Mil-C-5541E
However:
Common-Sense Rule #1: When in doubt, ask. Why risk assuming?
The non-common-sense part: (my emphasis)
"1.2.1 Classification: The chemical conversion coatings shall be of the following classes, as specified (see 6.2)"
"6.2 Ordering data: Acquisition documents should specify the following:"
"b. Class of coating (see 1.2.1)"
and some more of Section 6.3:
"6.3 Interchangeability." ... "Detail drawing of parts of requiring treatment in accordance with this specification should specify either Class 1A or 3 and any paint finishing systems required to meet the performance desired."
and, finally, followed by the statement you referenced:
"If the coating class is not specified, Class 1A is recommended."
IMO, this language falls well short of establishing a default, or unless otherwise specified, Class. Personally, I'll take an "as specified" and two "shoulds" over a "recommended" any day. And the "recommended" that you want to follow is in the same Section 6, "non-mandatory", information that you seem to be asking me to "ignore"...
RE: Mil-C-5541E
Re Common-Sense Rule #1: When in doubt, ask. Why risk assuming?
Of course, standard procedure is to ask. It is only an issue when some little machine shop has a know-nothing driver drop off a rush job at the end of day for next 6 AM p/u, and we can’t contact anyone. Purchase order says simply 'C/F.'
Re: "If the coating class is not specified, Class 1A is recommended."
This is sufficient to establish a default, legally speaking.
Thanks for your link to earlier thread. Seems like the same questions keep popping up.
By the way, I have been following Sanchem for years. Excellent articles in Metal Finishing and also in Products Finishing http://www.pfonline.com/articles/090203.html .
However, their environmentally-friendly, chrome-free conversion coating seems energy- and time-unfriendly. Prior to their proprietary process solution, need to produce a hydrated alumina basecoat by boiling the cleaned aluminum in DI water. Maybe they have something new, but I haven’t seen any of their major CC products that are electrically conductive per MIL-C-5541 Class 3; final product is a permanganate-alumina; maybe you were referring to their pretreatment Sanchem 1000 deoxidizer/desmutter?
RE: Mil-C-5541E
http://www.finishing.com/193/42.html