What is Component Cleaning?
During most component manufacturing processes, contaminants in the form of lubricants, polishing soaps, cutting fluids etc. are introduced to facilitate the activity being undertaken. On completion of the activity, these contaminants need to be removed from the item, either to allow the next stage of the process to be carried out, or to ensure that they are in an acceptable condition to be supplied to the end user.
The complexity of the cleaning process will depend not only on the nature and amount of the contaminant but also the standard of cleanliness required. Thus, a process to remove unwanted stains to ensure a cosmetically clean surface may be fundamentally different to one removing contaminants that affect the operation or functionality of a product.
How Clean Is ‘Clean’?
This is a simple question but the answer can be more complex. Establishing what is an acceptable standard of cleanliness needs to take into account factors such as the application and the required functionality of the part.
In a maintenance cleaning environment, or where it is necessary to clean a part between manufacturing stages, ‘clean’ may simply mean removal of the specific contaminant to such an extent as to facilitate further working of the part. By contrast, a surgical implant, or a printed circuit board that forms part of a missile guidance system must be cleaned to a much higher standard.
Thus, determining what is ‘clean’ will involve some form of assessment and comparison with an established pass/fail criterion. Assessment methods can be of two, basic types:
- Qualitative methods e.g. visual inspection, which may include wiping to look for a visible residue.
- Quantitative methods e.g. measuring contamination using established surface analysis techniques.
What Are Cleaning Specifications?
In some manufacturing sectors, cleaning specifications have been established that have taken account of the various factors taken into account when determining the cleanliness of a surface (See How Clean is ‘Clean’?). These specifications provide detailed information on the type of cleaning process to be used, including the approved chemicals, process conditions and cleaning times to ensure an acceptable standard of cleanliness is obtained.
Such specifications are common in many sectors of industry, including aerospace and medical equipment.
What Is Semi-Aqueous Cleaning?
The semi-aqueous cleaning process incorporates an organic medium to clean components and then water as the rinse medium. It, theoretically, utilises the specific cleaning benefits of both solvent and aqueous cleaning to effectively remove both organic and inorganic contaminants. The organic wash solution becomes progressively contaminated with use and so must be periodically replaced with fresh solution. The rinse water is also continuously purified to remove the organic component.
The cleaning process normally utilises liquid immersion cleaning with either spray under immersion or ultrasonic agitation.
Which Is Better – Solvent, Aqueous or Semi-Aqueous Cleaning?
As has already been established, cleaning involves the removal of a contaminant from the surface of a component. In determining the most suitable process for a particular application, it is important to consider a number of factors:
- The nature of the component e.g. the materials of construction, its geometry, whether it is susceptible to corrosion etc.
- The nature of the contaminant e.g. whether it is organic or inorganic, polar or non-polar, liquid or solid, soluble or insoluble.
- The impact of previous working on the contaminant e.g. whether its nature has changed due to temperature or pressure, whether it is fresh or has aged or hardened.
There is no definitive answer to which process is best, since they all can achieve similar standards of cleanliness across the vast majority of applications. All three processes offer advantages and disadvantages:
Solvents are generally considered to be hazardous chemicals but cleaning processes are generally quick, simple and effective. Aqueous and semi-aqueous cleaning chemicals are considered to have advantages from a health and safety perspective but cleaning processes are generally more complex and slower.
All three technologies impact on the environment. Aqueous impacts in terms of energy and water consumption and effluent disposal, whilst the environmental impact of solvents relate to their initial manufacture, release to atmosphere during use, and disposal of waste.
By the correct selection of process and equipment, it is possible to utilise the advantages of both technologies whilst effectively managing the potential disadvantages.
What Is Ultrasonic Cleaning?
Ultrasonic cleaning utilises high-frequency sound waves to create mechanical agitation within the cleaning medium to produce a versatile, high-performance cleaning process effective on a wide range of contaminants and substrates.
Ultrasonic waves are mechanical pressure waves generated when high frequency, high voltage, current is applied to ultrasonic transducers. Ultrasonic waves interact with the irradiated liquid to create tiny bubbles of vapour, which grow to a maximum size and then implode, releasing energy. The energy released from an implosion close to the surface of the component fragments or disintegrates the contaminant and the generated pressure wave carries the fragments away from the surface.
The energy released by the implosions can penetrate deep into crevices, blind holes and other, generally inaccessible areas to produce a consistent, uniform cleaning effect on even the most complex component geometries.