Cleaning process 2

[adamant]

Hello!

Can anybody give me some advice on cleaning?
In case of some extremely oily, greasy or otherwise soiled engine parts with rough surfaces, my coatings keep peeling of after deposition.
I have tried cleaning with benzine, an industrial washing machine, ultrasonic baths and different commercial purifiers.

Do I need some special etching process?
What kind of process do you recommend? What parameters? Which cleaning agents might be best?
What about shot peeling?

Thanks for any help!

 

[aspearin1]

Have you had success with clean parts, or are all parts coming in dirty? If you're not having success with detergents and ultrasonic washers (which are usually pretty good) to remove dirt and grease. Or even benzene, then the problem may not be the dirt, but rather a existing coating that needs to be stripped off, or perhaps an surface oxide that needs to come off. You may be looking at an acid strip or etch. What's your material? What's your coating?

ChemE, M.E. EIT
"The only constant in life is change." -Bruce Lee

 

[adamant]

Thank you for the reply.

With clean steel parts we don't have problems.
With ground 16MnCrS5 (e.g.) surfaces we do.
I suppose embedded oil from the grinding process is the problem. Oxide layers should be removed by our plasma etching.
We do PVD coating.

 

[tomwalz]

Try Easy Off oven cleaner asnd see if that helps. Solvents dissolve or dilute and always leave a very faint residue. Caustic sodas saponify which means they break down the oils and greases into soap which is easily removed by water. (Remember pioneers making soap with wood ash ((lye)) and fat?)

Also look up water break testing.

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessor.com

 

[adamant]

Thank you.
We wash the parts in deionised water before we dry them and put them in the vacuum chamber, wherer they are plasma etched. On most steel parts, the coating adheres well.

It seems really to be a problem with surface embedded residues from mechanical processing. This grinding medium seems to be partially enclosed, then freed in the vacuum chamber, not in our cleaning processes.

 

[tomwalz]

Is it oil and grease or embedded particles?

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessor.com

 

[adamant]

Oil and grease, I suppose.

 

[tomwalz]

If it is oil and grease then try a chemical attack to break them down. Deionized water won't do you any good as a cleaner unless you can get it under the embedded oil and grease and float the oil and grease out of the pits which is extremely difficult to impossible to do.

If your problems are in a vacuum furnace then it is almost certainly trapped liquid as a solid won’t expand much in a vacuum if it expands at all.

Try a strong caustic cleaning to saponify the trapped liquids.


Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessor.com

 

[kenvlach]

Hi adamant,
Have you solved the problem yet? It is a type I have seen many times – cutting oil or polishing compound embedded in the material, trapped by burnishing over of the metal. Mostly happens with metals that are softer and tough to machine, like 316L SS & some Al alloys, especially if dull tooling or sharp abrasives used with too much pressure. Also happens if a rough surface is burnished without precleaning.

Sometimes, the heat of a hot caustic solution will expand the trapped oil enough that it forces its way out. (and for aluminum, the caustic etches away the surface to free embedded material).

The next step up in cleaning your alloy would be electrocleaning in a hot caustic solution (Oakite 90, 150-160[sup]o[/sup]F) which generates gas (H[sub]2[/sub] or O[sub]2[/sub], depending on polarity) at the surface of the metal. The gas gets under and blows stuff off the surface. Reverse the polarity a few times. Alloys highly susceptible to hydrogen embrittlement should be mostly treated anodically.

Next. If you still have embedded material, remove a thin surface layer of metal. Anodic clean in 25 vol% sulfuric acid*. This is the opposite of electroplating; i.e., dissolution of a thin layer of the metal. You will note an oil sheen forming on the solution surface as oil is liberated. Go back to a caustic cleaner since mineral acids aren't much good for organics.

*If available, use electropolishing solution. Same principle, nicer product.

 

[adamant]

Thank you very much!
Currently we are cleaning with our washing machine and an ultrasonic caustic bath, though this process is far from perfect.
For the most soiled machine parts, our project partner does the cleaning, so we have only to remove the surface oil for conservation.

 

[1ton]

Hello

Can someone advice a painting spec. for an exhaust stack ? Area of concern would be at the top end where the exhaust comes out.
Thank
1ton

 

[kenvlach]

1ton,
You will get more responses if you start a new thread. Perhaps call it "Exhaust stack paint." Tell whether the stack is steel or whatever, and what fuel or other combustable is being burned, and what temperatures might be expected.

I do have 2 suggestions:
1) Look for a high temperature (1200[sup]o[/sup]F) aluminum paint that meets (US) Federal spec. TT-P-28G. "This specification covers an aluminum, heat-resistant paint that will withstand solvents, normal weather exposure, and temperatures to 1200[sup]o[/sup]F."

2) Browse some on-line catalogs. E.g., McMaster-Carr at

http://www.mcmaster.com/

Catalog page 1945+
"High-Temperature Paint and Primer— Put an end to corrosion forming on carbon steel and stainless steel that is exposed to high temperatures. These high-quality, heat-resistant coatings are solvent based; can be used both indoors and outdoors. Great for smokestacks, incinerators, heaters, heat exchangers, and insulated vessels."

Catalog page 1947:
"High-Temperature Stainless Steel Coatings— The best choice for boilers, stacks, piping, and similar indoor applications, these solvent-based coatings withstand temperatures as high as 1200° F."