Challenging Cleaning Applications

The technology of parts cleaning is a very sophisticated science today.  Most cleaning challenges can be met with the proper combination of equipment, chemistry and technique.  In my 45 year involvement with parts cleaning, I have seen many twists and turns along the way.  Applications that were considered “impossible” 10 or 20 years ago are now routinely successful.  In spite of all the advances, however, there are a few cleaning challenges that still haven’t been conquered.  For the applications engineer, it is a very difficult thing to say, “I’m sorry, but I don’t have a solution.”  It’s a bit like a Doctor telling a patient that he/she has a disease or condition that can not be cured.  It’s something you never like to do.  However, like the Doctors, those in the parts cleaning “practice” still keep trying!

Because it’s sometimes more valuable to know what you can’t do than what you can, I would like to spend a little blog time on cleaning applications that are still without a practical or universal solution.  The upcoming comments can be taken in two ways – –   For some, they may be seen as an aid in preventing promises that can’t be kept.  For others, they will provide a list of challenges which, if they can be solved, promise significant noteriety and potential monetary reward since most are associated with real and identified needs with ready customers awaiting solutions.

I would like to start off our discussion of cleaning challenges with one that is very specific and has been bugging me, personally, for a long time – – Removing varnish and carbon deposits from pistons in engine remanufacturing operations.  Carbon, in itself, is not really a cleaning challenge.  In its pure form as a powder or a compressed solid it’s pretty much just another particle removal requirement that can easily be solved using a mild alkaline chemistry containing wetting agents and with a little mechanical assist.  However, when the same carbon has been deposited along with “varnish” products of combustion in the cylinder of an internal combustion engine the story changes drastically.  That stuff is on there to stay!  Although there are chemistries that may attack and dissolve the varnish holding the carbon in place, most of them are very strong caustics like sodium hydroxide.  Unfortunately, many pistons with carbon and varnish buildup are made of Aluminum or one of its alloys.  Caustic chemistries attack aluminum and, therefore, can not be used!  A caustic chemistry with sufficient strength to remove carbon and varnish deposits will also dissolve an aluminum piston.  In a limited number of cases, the challenge has been nearly met using a mild caustic in combination with ultrasonics with extended exposure times (hours to days).  In most instances, this is not a practical solution because of the old “time is money” addage.  Replacing the piston or the entire engine is a more cost effective solution.

Of course, there are also pistons made of alloys that are not attacked by caustics.  These are usually found in larger engines where the potential payback for cleaning may be substantially greater than it is for an automobile engine, for example.  So, under the right conditions removing varnish and carbon deposits from pistons may be practical but in the vast majority of cases it remains unsolved with today’s cleaning technologies.

Upcoming blogs will discuss more cleaning applications that are more dream than reality.


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4 Responses to Challenging Cleaning Applications

  1. John Fuchs says:

    Equipment for oxygen use is commonly cleaned using NOC (Naval Oxygen Cleaner). This relatively non-volitile and safe material was developed to be used in a flushing process. It can also be used in conjunction with ultrasonics and is very effective. Cleaning equipment for oxygen is nothing to be made light of. Amazingly small amounts of contaminant can cause HUGE problems in a pure oxygen environment. If you would like more information on NOC, just send me an email at and I’ll give you the references.

  2. peterfirefly says:

    Well, I was just thinking out loud. It’s clear that it would be more expensive than ultrasonics in a water tank or the vapour degreaser.
    I figured the oxidizer would be the cheapest next level, provided it doesn’t corrode the aluminium.

    Btw: You have taught me a lot through this blog over the last few days so I really should say a heartfelt thank you! :)

    I found it because I was wondering how to remove oil, fingerprints, etc. — basically anything flammable — from inside a pipe + valve system that was going to be used for liquid oxygen in a rocket. Not that I’m actually building rockets but I have enjoyed following John Carmack’s Armadillo Aerospace and Paul Breed’s Unreasonable Rocket for a few years and they /do/ build rockets and blog about it.

    Making sure that the pipes were really, really clean before they sent LOX through seemed to be a slow and cumbersome manual process involving several different solvents and at least one overnight bath so I figured that there had to be a smarter way.

    Googling ‘degreasing’ or some variant of that uncovered this treasure trove of information on a subject that I hadn’t even known existed.

    Thank you again!

  3. John Fuchs says:

    Go for it! Remember, cleaning pistons won’t support a huge expenditure in equipment or labor. FJF

  4. peterfirefly says:

    I was wondering if you could use an oxidizer to clean the piston?
    The aluminium should already have a protective oxide layer — or if it doesn’t, one is going to form quickly anyway — so it shouldn’t care. Would H2O2 or natriumpersulfate work, perhaps? Or maybe something halogen-based?

    Another option might be laser ablation. It works for thin carbonaceous deposits for the guys who play with optical windows into combustion engines (for instrumentation) and those who play with laser “spark” plugs. It doesn’t seem to work for mineralized deposits, though :(

    A third option may be a plasma of reactive ions — it seems to work rather well in the chip industry. Dunno if LCD and solar cell production also use that method or if they get by with something cheaper/simpler.

    A fourth option may be lasers with a frequency finetuned to the binding energies of a few selected molecular bonds combined with a way to prevent the bonds from reforming, if necessary. Either whisk them away with a gas/liquid stream or give them something else to react with. It sounds like science fiction but the technique works well enough that it can be used for uranium isotope separation! Plus, lasers and their control circuitry keep getting cheaper, smaller, easier, and more versatile.

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