Cleaning Process Specification Questions

The cleaning process is the “recipe” for cleaning.  Like any culinary recipe, it should clearly define the ingredients, times, temperatures and the method of application to be used for cleaning.  Most cleaning consists of at least the three basic steps of washing, rinsing and drying.

Wash –

The purpose of washing is to remove contaminants from the parts being cleaned and contain them in such a way that they are not re-deposited on the parts.  Soluble contaminants generally go into solution with the washing chemistry while non-soluble contaminants are suspended in the cleaning solution to be swept away and removed by filtration or some other means.  The washing process needs to be adequate to achieve the cleanliness required by the cleanliness specification.

Wash Parameters

  • Chemistry and concentration
  • Temperature
  • Method of application (immersion, spray, ultrasonics, other).  This should include other pertinent details such as spray pressure or volume, ultrasonic frequency, critical part positioning, agitation, rotation, etc.
  • Time

Rinse –

The purpose of rinsing is to remove any residues remaining on the parts from cleaning.  These may include residual cleaning chemistry and, in some cases, some remnant of the solubilized or suspended contaminant remaining on the parts from the cleaning process.

Rinse Parameters

  • Water quality.  Tap, RO water or DI water, for example.
  • Temperature
  • Method of application (immersion, spay, ultrasonics, other).  As in the case of cleaning, this should include other pertinent details such as spray pressure or volume, ultrasonic frequency, critical part positioning, agitation, rotation, etc.
  • Time

Dry –

Although not always required, drying is a critical part of many cleaning processes.  In some cases, parts need to be absolutely dry while in others the removal of standing water is all that is required.  This should be part of the cleaning specification.

Dry Parameters

  • Air quality.  Room air, filtered air, HEPA filtered air, other gasses, etc.
  • Temperature
  • Method of application (circulated air, radient, blow-off, vacuum, etc.)
  • Time

The cleaning process is usually determined by small scale testing in-house or by a facility operated by a chemical or equipment supplier.  If testing is performed by an outside entity, it is natural that those suppliers will submit reports that are biased toward the chemicals or equipment they supply.  Proper analysis of these reports is critical but often difficult especially when the end user doesn’t have an experienced cleaning specialist on staff.

Here are a few questions to ask a chemical or equipment supplier regarding process recommendations –

  • What is unique about the recommended chemical that makes it better suited than any other for this process?  Were other options considered and tested?  What were the results?
  • If spray, immersion, ultrasonics or any other specific means of application is recommended, why was this method chosen?  Can the chemistry be used with another method as well or must it be used only in the recommended way?
  • Are there safety issues with using the selected chemistry?  What is the life of the chemistry?  What limits its life?  Can it be replenished?  What is required for disposal?
  • Was the chemistry chosen for any properties other than cleaning?  Rust or oxidation prevention, for example.  Are there other considerations that should be taken into account?
  • What is the cost?

Although not complete, the above list may be useful to those trying to define a cleaning process.

 –  FJF  –


3 comments on “Cleaning Process Specification Questions

  • Hello John,
    Thank you very much for your reply.

    Here are the updates regarding the problem.
    ” The problem is solved now, just by not applying the Ultrasonic effect to tank 3″. But, I don’t understand the reason behind this.

    The parts are tested and confirmed in the Laboratory that, it is bacterial contamination.

    According to machine instructions, tank 3 is meant for cleaning and it should be used with cleaning agent like tank 1. But in our production process, we are just using tank 3 as rinsing tank (without cleaner). So, we are running the machine with only one cleaning tank and remaining for rinsing.
    Here, the actual problem comes into the picture. I will explain it three cases.

    Case 1: (No bacterial contamination, good cleaning)

    If I run the machine without tank 3, like tank 1 for cleaning, tank 2, 4, 5 for rinsing. tank 5 is with filters (1 micron). Here we didn’t get any problem and the cleaning performance is good.

    Case 2: (No bacterial contamination, good cleaning)

    If I run the machine including tank 3, like tank 1 for cleaning and tank 2,3,4,5 for rinsing. Important point is, here I used tank 3 without ultrasonic effect but with filtration.

    Case 3: (Bacterial contamination problem (white stains on parts), bad coating).

    Here, the process is same like case 2. But, I just added Ultrasonic effect to tank 3. As, I know that ultrasonic rinsing is better than normal rinsing. Also, important point to mention is, the parts which we are cleaning here are the speaker grills made of stainless steel. We know that speaker grills are made with many tiny holes on the surface. As many articles and reports mentioned, ultrasonic rinsing is mainly good to clean blind holes on the parts. But, here in my experience, it is totally reverse. I am getting good cleaning performance without ultrasonic effect in rinsing tank.
    I just don’t understand the reason for this.

    Please let me know, am I doing any mistake in Ultrasonic rinsing? or I understood it in a wrong way?


  • John Fuchs says:

    Sandy –
    Sorry for the delay in response. It would be helpful for me to know the following – – What do you mean by bacterial contamination. What leads you to believe that it is bacterial? Second, are you sure there is no residual chemistry in tank 3 that may be causing the problem. If you examine parts that have been through the process to tank 3 and then removed without further processing do you see the problem existing already? It is hard to imagine a contaminant that would “appear” as a result of a previous process like this. Please let me know.

  • Hello John,

    I am a Research student working to solve surface preparation problems of stainless steel parts before coating. We have an Ultrasonic cleaning line with huge tanks of 900 liters each. The cleaning process goes like
    tank 1: with Ultrasonic and filters for cleaning
    tank 2: for rinsing
    tank 3: with ultrasonic and filters for cleaning
    tank 4: rinsing
    tank 5: rinsing with filters
    tank 6: Immersion not four sided skimming. (Just dipping in a tank full of pure DI water )
    Note: We are using DI water in all tanks.
    Since we don’t need cleaning solution in tank 3 we are using it as a rinsing tank. But it is supposed to be with cleaner.
    By using this process we are getting serious bacterial contamination on parts after drying which is affecting the coating very badly.
    We are using 65°C temp in all the tanks to stop bacterial formation.
    But if I use the program which goes through tank 1,2,4,5 the parts are very good and no problems since 3 months.
    Recently I again tried to use all the tanks but the same problem again repeated. ie., white bacterial spots after cleaning and also after PVD coating.
    First I thought the problem is with last rinsing tank which has no continuous water flow or very little if I should say.
    But even if I don’t use tank 6 the same problem is repeating. Finally I found that the problem is with tank 3 which has ultrasonic effect with filters.
    If I don’t use this tank 3 the cleaning process is good without any bacterial problems. I really don’t understand the problem.
    According to many reports ultrasonic rinsing is very good than without it. But in my case it is simply opposite.
    The parts which we are cleaning is stainless steel loud speakers for automotive applications. As we know the surface of the parts are totally covered with small holes.
    I read in one article that ultrasonic effect in rinsing will make the contamination to stick hardly to the parts and make the situation worse. Is it true? Please help me with your analysis.

    Thanking you

    Thank you

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