Description of the aqueous cleaning process

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Aqueous cleaning

The workpieces are placed in this process solution for several minutes, or placed in a spray bath. The solution is usually alkaline or neutral but may be acidic and usually working at increased temperatures (40-90°C) because of the improved cleaning effect. The main components of the aqueous cleaning system are alkalis or acids, silicates, phosphates and complexing and wetting agents. Aqueous cleaning systems work either by forming unstable emulsions (known as weak emulsion systems) or stable emulsions.

Aqueous chemical systems avoid the use of solvents. The cleaned items can remain wet if the subsequent treatment is water-based, such as electroplating. Process solutions have a shorter life, dependent on throughput and the amount of oil or grease on the workpieces. The efficiency of aqueous cleaning systems depends on the type and concentration of chemicals, the mechanical effect, the temperature and the time. The mechanical effect can be applied by spray pressure or flow rate, agitation of parts or solution, or by using ultrasonics.

Hot water is used effectively to remove oil and grease, especially from steel panels. It is widely used in the automotive industry.

Strong alkalis and silicates are not suitable for aluminium. Complexing agents (tensides) are not used in aluminium cleaners. For wetting agents, only very specific agents can be applied (for instance, on-anionic agents). Cleaning at a low temperature is possible, from 40°C upwards.

Energy usage: process tanks operate at 50-80 °C and may require fume extraction to remove water vapour and alkaline or acid fumes.

Source: BAT Surface Treatment of Metals and Plastic, Aug. 2006.


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