The effectiveness, low cost of equipment, and high degree of flexibility associated with spray cleaning has made this method popular for many years. Specialised methods of spray cleaning include steam cleaning, in which the cleaning solution is injected into a stream of high-pressure steam, and flow cleaning, in which the cleaning solution is flooded onto the part at high volume but at relatively low pressure.
Spray cleaning is accomplished by pumping the cleaning solution from a reservoir through a pipe system (“header” and “risers”) and finally out of spray nozzles onto the part to be cleaned. The pressure at which the solution is applied to the part can vary from as low as 14 kPa (2 psi) to as much as 13’800 kPa (2’000 psi). In general, higher spray pressure produces greater mechanical forces for removing soils from a metal surface. Mechanical effects are especially important for the removal of insoluble particles such as dust, metal fines, and carbon smut.
Spray washing machines are usually engineered to a particular installation. Part, size, volume, time necessary to clean and rinse, and subsequent operations are factors that influence individual machine design. Many machines provide more than one washing stage, as well as for rinsing and forced air drying. They can be batch cabinet style or in-line conveyor.
Spray cleaners are prepared with low foaming surfactants that minimize foam formation, even at high spray pressure. Over the last few years, low-foaming surfactants designed for spray cleaning have achieved cleaning performance comparable to that of surfactants used for immersion cleaning.
Considerable progress has been made in recent years to lower the operating temperature of alkaline cleaners. A considerable cost savings results from this decrease in energy demand.
In emulsion cleaning, manual spray/flush over large parts in a vented tank at low pressure (only enough to deliver the emulsion to the work, approximately 35 kPa, or 5 psi). With the operator at the point of contact, there is still potential exposure, depending on the particular emulsion and the temperature.
Because flammable or combustible liquids become explosive when sprayed, they should only be used in applications with proper safety precautions, such as fire suppression systems or inert gas blanketing.
High pressure cleaning usually starts from 500 psi, low pressure cleaning equipment operates at pressures below 14 to 20 bar (200 to 300 psi).
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