Industrial component cleaning.
How parts are cleaned.

Particulate cleanliness describes the number, size, mass or type of solid residues on a component. Film-related cleanliness refers to thin, often invisible layers of oils, greases, additives, salts or organic residues. Both may require different test methods and cleaning mechanisms. A specification should therefore clearly state which contamination is critical to function and how it is assessed.

Technical cleanliness is a function-related quality criterion: a component may only retain such a quantity and size of relevant contaminants that the intended function is reliably fulfilled. This requirement is usually described in terms of measurable limit values and a defined test method. It is not an absolute concept of cleanliness and must always be derived from the component’s function, the manufacturing process and the associated risk.

‘High Purity’ refers to particularly high, application-specific purity requirements, for example in semiconductor technology, optics, medical technology or vacuum technology. In addition to particles, molecular, ionic or organic residues, as well as outgassing and cleanroom suitability, can be decisive factors. Technical cleanliness often focuses on particle limits critical to function; High Purity usually takes into account a broader spectrum of contamination and a controlled process and environmental chain.

Aqueous media are particularly suitable for polar contaminants such as salts, emulsions, abrasion particles or polishing pastes, and can be adapted to the material and the task at hand using acidic, neutral or alkaline cleaning agents. Oils and greases can also be emulsified or dispersed using suitable chemicals. The overall process usually requires rinsing, media maintenance and a drying stage tailored to the component and cycle time.

Solvents are primarily used to remove non-polar contaminants such as machining oils, greases and waxes. Hydrocarbons and modified alcohols offer varying degrees of solvent power depending on the task; modified alcohols can also dissolve substances with limited polarity. Material compatibility, residual oils, safety and environmental requirements, as well as the use of closed-system technology, must all be taken into account when making a selection.

An important guiding principle is ‘like dissolves like’: polar contaminants often indicate aqueous media, whilst non-polar oils and fats often indicate solvents. In practice, other factors also play a role, such as the material, geometry, cleanliness target, drying, media treatment, carry-over from previous processes, regulatory and safety considerations, and total cost of ownership. In the case of mixed contamination, a combined or multi-stage approach may be appropriate.

Rinsing removes dissolved or loosened contaminants and residual cleaning chemicals from the component surface. The number and quality of the rinse stages, water quality, cascade flow, part movement and media treatment all influence the absence of residues and the formation of stains. Where high purity requirements apply, treated water and a defined final rinse stage may be necessary.

Common solutions include hot-air, recirculating air, vacuum and, where appropriate, combined drying methods. The choice depends on the material, mass, geometry, cavities, residual moisture requirements and cycle time. Vacuum drying aids the removal of moisture from complex internal contours; however, it requires a suitable component temperature and process design. It is crucial that no stains, corrosion or media residues form and that the parts reach the subsequent process in a dry state.

Filtration removes particulate contaminants from the media circuit. Depending on the type of contamination, the process may be supplemented by oil separation, fine filtration, water treatment or distillation. Effective media maintenance stabilises cleaning performance, reduces re-contamination and extends the service life of the bath. It must be designed taking into account the level of contamination, the required particle size, throughput and chemical composition, and monitored through defined checks.

In aqueous systems, the consumption rates of cleaning components can vary. To ensure consistent results, the concentration and level of contamination should be monitored using suitable analytical methods and topped up as required based on consumption. In addition, temperature, pH, conductivity and other application-specific parameters are relevant. It is advisable to establish defined test intervals, limit values, responsibilities and traceable documentation.

The starting points are the component material and geometry, the type and amount of contamination, the required cleanliness level, throughput, cycle time, the subsequent process and the available space. From these, the cleaning medium, mechanical action, temperature, process time, and rinsing and drying steps are determined. Cleaning trials using original parts and real-world contamination provide a robust basis for system design and acceptance testing.

In spray cleaning, the cleaning medium strikes the surface via nozzles at a defined velocity and angle. This method is particularly suitable for easily accessible external surfaces and components with low to medium geometric complexity. Cleaning effectiveness and reproducibility depend largely on the spray pattern, pressure, distance, component movement, chemicals and the nature of the contamination. Concealed internal contours or deep blind holes may require additional processes.

Immersion cleaning wets the entire component and is therefore suitable for complex geometries, undercuts and blind holes. The chemical action of the bath is often enhanced by rotation, swivelling, flooding or ultrasonic agitation. It is important to ensure that cavities are properly vented, that parts are correctly oriented, and that the cleaning solution drains off or is completely removed.

In pressure flushing, cleaning fluid is directed via nozzles below the bath level. Strong flows and changing pressure conditions create turbulence at edges and a suction effect in recesses. This aids the removal of particles from complex internal geometries. Injection flushing is frequently used as a mechanical supplement and combined with filtration, part agitation or further process steps.

Ultrasound causes cavitation in the cleaning bath: microscopically small bubbles form and implode, creating localised currents and pressure pulses that dislodge contaminants from the surface. The frequency, power, condition of the bath, temperature, arrangement of the parts and the material all influence the result. Ultrasonics is particularly suitable for fine particles and complex geometries, but must be validated on a case-by-case basis for sensitive surfaces.

Precisely directed high-pressure water jets can simultaneously clean components and remove defined machining burrs. The process is particularly suitable for intersecting bores, internal edges and functionally critical areas. Pressure, nozzle, distance, angle of incidence, path guidance and component clamping are tailored to the material and the burr. Suitability can be verified through deburring trials and an assessment of any potential impact on the surface.

A combination is advisable when different types of contamination or geometries cannot be reliably controlled using a single cleaning mechanism. Examples include spraying combined with pressure flushing for external and internal areas, or ultrasonic cleaning combined with multi-stage rinsing for high cleanliness requirements. The decisive factor is the entire process, including media maintenance and drying; additional process steps are only justified if they make a measurable contribution to the target cleanliness and process stability.