While an industrial parts washer can go a long way, it’s only part of a comprehensive clean parts process…
Today, parts production is laid out to take best possible advantage of available floor space for economic reasons. Various process steps such as parts machining (e.g. turning, grinding and milling), cleaning, transport, storage and assembly are thus executed in close proximity to each other. Resulting contamination — for example, grinding dust, chips, particulates stirred up by people or factory trucks — can thus be easily carried over from one process step to the next. Contamination of this sort can only be avoided or reduced if factors such as clean production sequences and a clean manufacturing environment are taken into consideration when the production facility is laid out. A further important aspect is increasing employee awareness for cleanliness at the workplace.
An Effective Cleaning Concept
The great influence of parts cleanliness on subsequent product quality makes parts cleaning a value creation step within the manufacturing sequence. An effective cleaning strategy is essential in order to manage this step economically. Some of the most important considerations include which machining processes need to be followed up by a cleaning step, and which results need to be attained. Strict requirements for parts cleanliness can be fulfilled with up-to-date cleaning systems, for example with a cabinet parts washer — assuming the cleaning process has been well matched to the work pieces to be cleaned and existing contamination, as well as the required results, with regard to process technology, cleaning agent, temperature and duration.
Looking at the cleaning system as a “problem solver” at the end of the production process which provides the required cleanliness at a single stroke is certainly unrealistic—and uneconomical. Furthermore, expectations such as these would necessitate highly complex cleaning systems, resulting in high investment and operating costs. The following applies in general: the less contamination is carried over from manufacturing, the faster and more economically the desired results can be achieved.
Cleaning and transport containers also influence parts cleanliness. Due to corrosion, a damaged coating layer or the carryover of contaminated cleaning agents, cleaning racks and bulk goods containers can themselves be transformed into sources of contamination. It’s wrong to assume that containers which are only used to transport cleaned parts always remain clean. Transport containers must also be subjected to regular cleaning, in order to prevent recontamination of cleaned parts through contact with the container.
Temporary Corrosion Protection—Part of the Overall Process
During production—for example, after degreasing, as well as during and after machining processes—very clean surfaces are exposed to the air, which are highly susceptible to corrosion. Aqueous machining media are also frequently used which, as a rule, promote corrosion. Effective drying and/or cleaning is thus advisable, without delay, after processing with aqueous or corrosive media. Chips and metallic rubbings must also be removed as quickly as possible, because this type of contamination may lead to corrosion, even underneath protective coatings. Storage times between the individual machining steps should also be kept as short as possible. However, due to the fact that this cannot always be assured, temporary preservation is an imperative part of the manufacturing process for many workpieces.
Preservation during the Cleaning Process
Workpieces are protected from corrosion during the cleaning process by means of additives contained in the used cleaning agent. In order to provide parts with protection during subsequent storage and transport as well, temporary preservation is required. It makes good sense to apply the preservative while the parts are in the cleaning system. Oily, aqueous and wax-like substances are available to this end. Processes such as phosphate coating can also be carried out within the cleaning system.
Corrosion protection oils, emulsions and greases are used for corrosion protection purposes. Corrosion protection oils are mineral oil raffinates with various viscosities. The viscosity determines the thickness of the oil film, and thus the degree of protection. Corrosion protection emulsions consist of aqueous emulsions containing mineral oils and waxes, to which biocides and corrosion inhibitors have been added. These additives prevent the aqueous phases from causing corrosion before they evaporate. As opposed to corrosion protection oils, corrosion protection greases can be applied in greater thicknesses— they consist of Vaseline to which inhibitors have been added in order to increase the degree of protection. Fatty acid and amine adducts are normally used for temporary, aqueous corrosion protection. These substances are added to the final rinsing bath in the cleaning system, and may also be added to aqueous machining media such as coolant water. They create a dense film on the surface of the treated material which only seldom disrupts subsequent processes and thus, as a rule, need not be removed. Volatility and the hydrophobic effect can be adjusted by selecting the appropriate substance.
Hydrophobing agents create a water-repellent coating which facilitates drying, and which is washed away only slowly by condensate. However, these film layers can only be removed with alkalines. Corrosion protection waxes are complex, fluid systems made of waxes or wax-like substances, mineral spirits and corrosion inhibiting additives. They form workable, hard layers which are resistant to touch.
Criteria for the Selection of Temporary Corrosion Protection
Depending upon the selected corrosion protection medium and how thickly it’s applied, temporary preservation usually protects the workpiece for a duration of a few hours to two years. Which processes the parts will be subjected to after preservation is a critical factor in selecting the right medium. Being able to easily remove the corrosion protection medium prior to further process steps is an additional criterion, because it may impair surface finishing results.
If the part will be sent immediately to the next process or to assembly, a thin, perhaps even volatile protective layer is usually adequate. In this case, it must be kept in mind that even a fingerprint could be enough to trigger the corrosion process. If a lengthy period of storage or transport is required, longer term protection must be applied. Solutions of this sort include, for example, the so-called VCI materials (volatile corrosion inhibitors). They consist of powders and liquids, as well as impregnated films and paper. Due to the fact that the corrosion inhibitors contained in these materials are volatilized into the ambient air, the parts—if they’re not packaged in VCI film—must be stored and transported in containers which are airtight to the greatest possible extent.
Adapted from Process Cleaning Magazine.