Washing here means usage of water, detergent / soap, some form of scrubbing action for washing and often heat is also employed to get better washing / cleaning. Likewise, industrial cleaning is an extension of these kinds of washing with some elements of sophistication and advanced techniques to achieve consistency of desired cleaning.
The selection of aqueous cleaning chemical is dependent on the ability of the chemical to dissolve and clean the soil and the selection of type of cleaning equipment is dependent on the substrate of the material and the amount of soil to be removed. Presently, aqueous cleaning chemicals are available for cleaning both ferrous and non-ferrous metals to a high degree of cleaning efficiency and consistently. Selection of number of stages (single stage or multistage) of cleaning equipment also depends on various factors like type and amount of soil, type of equipment, substrate, heat, agitation, etc.
Aqueous cleaning agents are somewhat complex in nature because it comprises a variety of materials, surfactants, coupling agents, building agents, sequestering agents and others. Soils that can be cleaned with aqueous cleaning agents are lube oil, water-soluble oil, silicone grease, petroleum grease, dust, fingerprints, loose burr, etc. Aqueous cleaning is often broadly defined as a cleaning process that combines the chemical solvency of a water based cleaning solution with some type of mechanical / thermal energy. It has replaced and is increasingly opted for over solvents on considerations of environmental regulations and safety and cost.
The aqueous cleaning process is more complex than the solvent process it is replacing. For example, many vapour degreasers get the wash/rinse/ dry cycle in one step. However, in an aqueous based process, it may require three or more separate process steps, wash>rinse>dry, and at times two or more washing cycles and two or more rinsing cycles, besides thorough drying, to achieve the desired precision cleaning. Washing exposes the parts to a cleaning agent to remove the soils, rinsing removes the cleaning agents from the parts and finally drying removes the water from the parts. However, aqueous cleaning enhances cleaning efficiency, lower operating costs, greater repeatability, better process control and minimal environmental impact.
Mechanical energy for aqueous cleaning is provided by three forms: scrubbing action in an immersion washing equipment by circulation of tank solution by mechanical pump and at times with dunking arrangement; spraying pressure with a spray system or jet spray; and cavitations process with an ultrasonic equipment. An easy and economical process, Immersion cleaning, means submerging of parts into the cleaning solution. Turbulation of the solution during the wash cycle dramatically increases cleaning efficiency and it is well suited for large parts with light soil with hidden surfaces that cannot be impinged upon effectively by spraying.
Spray cleaning is a very effective method and is generally used for parts having high soil or contaminations so that they can be exposed to spray jet washing. As the contaminants are easily exposed, they can be quickly removed by spraying pressure of the Spray Cleaning equipment. Spray cleaners can drastically reduce the cleaning time because of the jet spray. Ultrasonic cleaning equipment is best suited and effective for cleaning small and intricate components with profiles, bores and crevices, as cavitations will reach all areas for cleaning action. Immersion and spray cleaning are also combined with ultrasonic cleaning equipment for greater and precision cleaning and throughput with short cleaning cycle.
Aqueous cleaning delivers better result with agitation (greater the agitation, greater will be cleaning and shorter will be the time required for cleaning), allowing enough time for cleaning action to take place, right concentration of chemical and temperature, reduces viscosity of soil and makes it more fluid and the cleaning chemical becomes more aggressive in the presence of higher temperature. They are often called as TACT (time, agitation, chemical, temperature). Besides, good water quality is required. Often people use demineralised, deionised water, free of minerals and salts, to get precision cleaning and leave no residue after cleaning, followed by rinse/dry. If precision cleaning is desired, the word WATCH (stands for water, agitation, time, chemical and temperature) assumes importance and becomes watchword of quality. Of course, each one is variable and depends upon the degree or efficiency of cleaning desired.
Aqueous cleaning system generally comprises a 3-stage, viz., wash, rinse and dry. Rinsing is desired in most cases, but can be done away when residue or stain mark is of no consequence, depending upon next operation of part, like painting, machining, etc. Optimum results and life of aqueous cleaning solution depend upon various parameters such as contaminants, oil skimming, filtration, maintaining concentration by topping up, maintenance of the equipment including temperature maintenance, etc. The life of the solution can be extended greatly by removing oil, grease, etc., by oil skimming and heavy particulate material by filtering (oil skimmer and filtering system will make the soil removal automatics and they are a quick fix). A cleaning bath is not to be treated, as a waste pit, but as a place where soils are discarded for removal from the bath. It will extend the life of the solution, besides preventing recontamination or re-deposition of the soil.
There may be higher foaming action or stopped by proper usage of defoamer (anti-foaming liquid). With aqueous solution there will with aqueous cleaning chemicals due to contaminants, spraying pressure, water quality and that can be easily suppressed be concern for corrosion, rust etc., which can be effectively tackled by drying thoroughly after washing/rinsing with the rust inhibitors present in the ingredients of chemical and if need be by using appropriate VCI (vapour corrosion inhibitors) for added or extended protection. In order to select the right cleaning chemical, equipment and its configurations, it is often desired that a trial take place with the buyers team at equipment makers works. Before that, there should be a discussion involving process people at buyers end for veering round the selection of type of equipment. In order to ensure consistent results, cleaning test is to be routinely performed to assure cleaning quality and also some validation process is occasionally performed.
Presently, a variety of aqueous cleaning chemicals are available to clean toughest soil with high efficiency and consistency and in fact aqueous cleaning will not only meet present days toughest requirement and but also stands for the future as well as it ensures precision cleaning all-round safety and savings. No wonder it is a preferred technology for achieving precision cleaning and to do away with toxics and solvents and associated environmental degradations and safety concerns.