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Can the same surface treatment line be used for different substrates

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Q. My question is if we can process titanium, cres, iron and titanium on the same surface treatment line, with same common baths, like de-greasing or rinsing?

Thank you

Cornel Marius
- Baia Mare- Romania
April 5, 2022

A. Hi Cornel. There are a few processes that may work for multiple metals; for example, it may be possible to do de-greasing of stainless steel, plain steel, and cast iron in the same degreaser, but as a general rule the answer is no: aluminum cannot withstand the strong hot alkalies used for steel and it cannot be electrocleaned. Brass and copper can be electrocleaned but need milder solutions than steel. Hydrochloric acid is the most common acid dip for steel but shouldn't be used for stainless. Aluminum requires zincating before plating, stainless requires Wood's nickel strike before plating, titanium usually requires rigorous and specialized pretreatment.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey
April 2022

May 12, 2022

A. Hi Cornel,
To add to what Ted said:

Individual processes on a line that don't etch or remove material are often, if not usually, fine. And some baths you wouldn't expect to be shareable actually are, under certain conditions.

Vapor degreasing simply dissolves and purges organic (hydrocarbon) contaminants, while leaving the inorganic substrate alone. The caveat being that if there's water contamination in the degreaser, you can end up with problems, but that's a whole 'nother issue...

Mild detergents? Sure. Check the manufacturer spec sheet, and look for materials that the soap is considered non-etching, and use your experience to narrow down the tank conditions even more if you need to. Example: I have a clean room ultrasonic soap tank. The soap is rated for a wide range of substrates, and the manufacturer gives pH limits. I've found staining on Al at the high end of the range, but the ferrous alloys are fine, so we just tightened shop limits.

Another example is a proprietary phosphoric-bifluoride "satin mask" acid etch, that works great on Al and Ti, and is a really effective cleaner for some types of stainless. It sludges out by design.

Electropolish- this is a fun one. The formulation I use (phosphoric-glycolic proprietary), you can run brass and stainless in it after loading it with aluminum, but flip that around, and it's a disaster! However, knowing that means getting more life out of it prior to sending off as waste. Also, it's another self-sludging tank.

Last one I've got is that you can use a sulfuric hardcoat tank to blue-anodize titanium, if it's kept up to a tighter set of contaminant levels.

There are plenty of baths that can be shared, but more that can't, or that need extra testing (solution and product) if you want to share them.

Best advice I can give you is run test specimens, and send them out for whatever testing you need to pass to make sure you can share tanks, as proof of process.

Rachel Mackintosh
- Greenfield, Vermont

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