What is technical cleanliness?

Technical cleanliness describes the contamination allowed on a part at delivery. It covers particles, such as chips, grinding dust, blasting media and loose burrs, and film residues such as coolant, oil, grease, cleaning agent and fingerprints. The requirement is usually stated as a maximum number of particles per size class, a largest permitted particle or a residue mass, and for vacuum applications also as a limit on organic residues that outgas under vacuum. A note such as clean and grease-free, without a method and a limit, is not a measurable requirement.

What does the standard say about technical cleanliness?

For particles on automotive components, ISO 16232 and the VDA 19.1 guideline describe how contamination is rinsed off the part, collected on a filter and analysed by counting, sizing or weighing. For hydraulic components ISO 18413 is often cited. These documents mainly fix the method; the limit comes from the drawing or the customer specification. A cleanliness value only means something once the extraction method, the analysed surface area, the size classes and the acceptance rule are stated. Vacuum and semiconductor customers often work to their own specification, which prescribes agents, cleaning steps, packaging and checks.

How does technical cleanliness work in practice?

A cleanliness requirement touches the whole route, not just the last step. Burrs that come loose later become particles themselves, so deburring and cleaning belong together. Cleaning is done, for example, in an aqueous ultrasonic line with rinsing and drying, or with a solvent, in house or subcontracted. During manufacture the specification may rule out certain coolants, silicones or marker pens and require gloves. Clean packaging follows, sometimes in a cleanroom, and possibly a cleanliness analysis per batch in a laboratory. What this adds depends on the requirement, the geometry with its bores and blind holes, the batch size and what you can do yourself; on simple milled parts it can be a large share of the price.

What is technical cleanliness often confused with?

Technical cleanliness is not deburring: a burr-free part can still hold chips in its bores and threads. Nor is it surface roughness: roughness describes the texture of the surface, cleanliness what lies on it, although a rough or porous surface holds dirt more readily. And it is not a cleanroom class: a class under ISO 14644-1 describes particles in the air of a room, not what lies on the part.