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Symbolic illustration of a cleanliness inspection: a reflected-light microscope above an aluminum cast housing, beside it a screen with a particle image and a mesh basket holding washed-out residues; in the foreground lies a filled-in form sheet

“Clean” is not a condition you can see. It is a value you measure.

Technical Cleanliness and Residual Contamination

Nearly every inquiry carries the same word — residual contamination, technical cleanliness, cleanliness requirement — and almost never does it say what exactly it means. This page clarifies which result has to be verified, how it is measured and what we commit to before a system leaves the factory.
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1 · The challenge

Two misunderstandings that make projects harder time and again

In conversations it sounds specific: “The residual contamination values are not right.” · “The cleanliness requirement is not being met.”

Residual burr and residual contamination are two different results

  • Residual burr

    Is the burr gone?

  • Residual contamination

    Is the part clean?

In deburring in particular the two get confused — yet they are two questions, not one. A component can be free of burrs and still be contaminated, and the other way around. Both results have to be verified separately: anyone who checks only one does not know the condition of the part.

Cleanliness is not visible

Whether a part reaches the required cleanliness cannot be seen by looking at it. It is decided by measurable quantities — particle count, particle size, residual contamination amount — tested by defined methods. For quality assurance that means: it is not the visual impression that counts, but the verification. And this verification has to be reproducible, not succeed once.

2 · Engineering considerations

It is not the parts cleaning system that decides how clean a part has to be

It is what happens to the part afterwards. Adhesive bonding, coating, painting: the downstream process sets the requirement.

It is exactly at this point that an inquiry often reveals its real reason — cleaning is not the goal, the step after it is, and that step does not work without a clean surface. That is why the cleanliness requirement stands at the beginning of every system design with us, not at the end: as one of the parameters from which the method, the water quality and the process chain are derived in the first place.

Water quality is part of cleanliness, not an accessory

Which water quality is needed follows from the residual contamination requirement, the material and the downstream process — city water, softened water or deionized water (DI water). If parts are bonded or coated after cleaning, that changes the requirement fundamentally. Where necessary, we design the complete water treatment as well — up to osmosis and evaporator.

When the requirement is unrealistic

Unrealistically low residual contamination requirements are the most common reason why a task cannot be solved as stated. We say so before the quotation, not after the acceptance. This is not a refusal out of convenience, but the precondition for a requirement, once committed to, actually standing reproducibly in the end. A cleanliness that cannot be held permanently is not an achievable goal — even if it could be shown in a single cleaning trial.

3 · How the result is verified

Five test methods — and one of them does not test the part

  • Visual inspection

    Burr visibly present or not.

  • Camera-based inspection

    The same, automated, reproducible, in cycle.

  • Residual burr inspection

    The deburring result itself.

  • Residual contamination analysis

    Cleanliness, where required to VDA 19 / ISO 16232.

  • Process monitoring

    The running process, not the individual part. It keeps the process within its window — the precondition for not having to test every part. The verification shifts from the individual part to the process.

What VDA 19 and ISO 16232 govern

These standards define how technical cleanliness is measured, so that a value is comparable and repeatable.

From the component to a verifiable value

  1. 01ExtractionThe particles are released from the component and collected.
  2. 02Gravimetric analysisThe residual contamination mass is determined.
  3. 03Optical analysisThe number and size of the particles are recorded microscopically.
  4. 04Particle size classesThe result is expressed in classes and thereby made comparable.

That is how “clean” becomes a verifiable value — and a cleanliness requirement becomes a commitment that can be checked.

The verification is not carried out by whoever built the system

Anyone who builds a system and then measures for themselves whether it reaches the committed values is assessing their own work. That is why ITR does not carry out residual contamination analyses itself. The analysis lies with an independent, accredited test laboratory that is not bound by instructions from ITR — measurement follows your specifications, or VDA 19 / ISO 16232 where these are required.

For you that means: the number on which release depends does not come from us. If the system does not reach the agreed values, we do not release it — and that decision rests on a result for which a third party is responsible.

4 · The result

Only when the values are right does the system leave the factory

The entire verification leads up to a commitment that stands at the beginning and not in the fine print.

If the agreed residual contamination values are not reached, the system is not released.

Testing takes place twice — at the internal factory acceptance test with original components and again at the site acceptance test at the customer’s site. Only the second acceptance proves under your real conditions what the first committed to.

The measure is repeatability: the system has to reach the required cleanliness permanently in the intended operation, not in one good individual case. That is exactly what the system design is aimed at from the outset.

Where this topic belongs

The common denominator of both core processes

Technical cleanliness concerns cleaning and deburring alike — and every industry with defined requirements.
Industrial Parts CleaningHigh-Precision Water Jet Deburring
Automotive industryAerospaceElectronics industryFoundry and die casting
Technical terms in the Glossary

Questions and answers

Frequently asked questions from quality managers and buyers

All the answers are above on this page — here they appear once more as a question.

What does technical cleanliness mean?

“Clean” is not a condition you can see. It is a value you measure. Technical cleanliness describes the defined condition of a component with regard to remaining particles — by particle count, particle size and residual contamination amount, tested by specified methods. For quality assurance that means: it is not the visual impression that counts, but the verification.

What is residual contamination?

Contaminants that remain on or in a component after the cleaning process. Residual contamination is not the same as residual burr — these are two different results, and this page treats them separately.

What is the difference between residual burr and residual contamination?

They are two different results, and in deburring they are regularly confused. Residual burr answers: is the burr gone? Residual contamination answers: is the part clean? A component can be free of burrs and still be contaminated — and the other way around. Both results have to be verified separately. Anyone who checks only one does not know the condition of the part.

What determines how clean a component has to be?

Not the parts cleaning system, but the downstream process. Adhesive bonding, coating and painting set the requirement. At this point an inquiry often reveals its real reason: cleaning is not the goal, the step after it is, and that step does not work without a clean surface. That is why the cleanliness requirement stands at the beginning of every system design with us, not at the end.

To which standards is technical cleanliness tested?

To VDA 19 and ISO 16232. These standards define how measurement is done, so that a value is comparable and repeatable: the particles are extracted from the component and then analyzed — gravimetrically as residual contamination mass and microscopically-optically by number and size. The result is expressed in particle size classes. That is how “clean” becomes a verifiable value.

What is VDA 19.1?

The part of VDA 19 that describes the inspection of particulate contamination of functionally relevant automotive parts — that is, the method by which residual contamination is extracted and analyzed. The current edition is the 3rd revised edition of February 2026; it superseded the 2015 edition.

What is ISO 16232?

The international standard on the cleanliness of components and systems of road vehicles. ISO 16232:2018 superseded the ten-part version of 2007 and combines it into a single document. It is closely aligned with VDA 19.1 in method, but it is a separate document with its own edition status — the two are not identical.

How is a system designed to VDA 19.1 or ISO 16232?

The standard says how measurement is done — not which value your component has to reach. That is why we design to the specific cleanliness requirement of your component, not to the standard as such. Your specification, the component and the downstream process determine the system design; the standard determines the verification.

Does ITR carry out the residual contamination analyses itself?

No — and that is deliberate. The residual contamination analysis is carried out by an independent, accredited test laboratory that is not bound by instructions from us. Anyone who builds a system and then measures for themselves whether it reaches the committed values is assessing their own work. The number on which release depends therefore comes from a third party.

What happens if the agreed residual contamination values are not reached?

Then the system is not released. Testing takes place twice: at the internal factory acceptance test (FAT) with original components and again at the site acceptance test (SAT) at the customer’s site. Only the second acceptance proves under real conditions what the first committed to. The measure is repeatability — the system has to reach the required cleanliness permanently in the intended operation, not in one good individual case.

How reproducible is industrial parts cleaning?

Reproducibility is the measure, not a side effect. The system has to reach the required cleanliness permanently in the intended operation — not just once at the acceptance, but in every shift. A residual contamination value reached once is not a verification if it is not repeatable. That is exactly what the system design is aimed at from the outset.

Which residual contamination values can be reached?

There is no blanket answer. The achievable value depends on the component, the contamination, the process and the requirement — and it arises in the system design, not in a brochure. What we can commit to, we say before the quotation; what is not achievable, likewise.

What if my cleanliness requirement is not technically achievable at all?

Unrealistically low residual contamination requirements are the most common reason why a task cannot be solved as stated — and we say so before the quotation, not after the acceptance. This is not a refusal out of convenience, but the precondition for a committed requirement standing reproducibly in the end. A cleanliness that cannot be held permanently is not an achievable goal.

Why am I not reaching my residual contamination values?

The first thing to check is whether the requirement is achievable at all: unrealistically low residual contamination requirements are the most common reason why a task cannot be solved as stated. If the requirement is achievable, the cause lies in the system design — and that begins with the component and the downstream process, not with the system.

What determines the water quality that is needed?

The residual contamination requirement, the material and the downstream process — city water, softened water or deionized water (DI water). If parts are bonded or coated after cleaning, that changes the requirement fundamentally. Water quality is therefore part of cleanliness, not an accessory. Where necessary, we design the complete water treatment as well, up to osmosis and evaporator.

Why are sealing surfaces particularly critical, and which residues interfere with the later seal?

Because here it is not enough that nothing is visible any longer. The surface has to be fit for what comes next — and that decides the requirement, not the appearance. What can interfere: oils and greases, cooling lubricants and emulsions, fine particles and chips, residues of the cleaning agent itself, mineral deposits, corrosion products and water or drying residues. Which of these are permissible depends on the downstream process: if the part is bonded, coated or painted, requirements apply that differ from those for a seal that is assembled. Then there is the geometry. Edges, recesses and poorly accessible areas decide whether the process medium reaches the surface at all — with an unfavorable component position a surface stays in the spray shadow even though pressure and program are right. And drying is part of it: a clean but wet component is not finished. For the system design it is therefore not enough to state that the sealing surface should become clean. What is needed is the specific contamination, the geometry, the downstream process and the condition that has to be verified in the end.

Applications

One task where this becomes visible

One worked-out task revolves around the verification of technical cleanliness. What tips the balance in it is on its own page.

Each case sets out the design factors, the possible system concepts and the methods in detail — here you only find what it is about.

High technical cleanliness

It is not cleanliness itself that is difficult, but its verification: a component that is clean, but not demonstrably clean, cannot be used in a manufacturing operation with a verification requirement.

Here too no single characteristic decides: which concept the task needs arises from the interplay of the design factors.

All applications

Direct contact

AddressITR GmbH powered by Zippel
Hauptstraße 31
93186 Pettendorf
Pettendorf bei Regensburg
Phone+49 (0) 9409-777 3598
Fax +49 (0) 9409-777 3607
Emailinfo@itr-anlagenbau.com

Technically responsible for this page: Kersten John — Senior Consultant Technical Cleanliness