A coated test panel is exposed to a cyclic wet (salt fog), drying and humidity test schedule and the effects of exposure are evaluated by criteria agreed in advance between the purchaser and the supplier. The salt fog test solution shall be prepared by dissolving sodium chloride in water to give a concentration of (50±10) g/l. The PH of the solution shall be in the range of 6.0 to 7.0.
The spray cabinet shall be made from or lined with materials which are resistant to corrosion by the sprayed solution, and shall have a roof which prevents condensed moisture dripping onto the test specimens. The cabinet shall have a capacity of not less than 0.4m³ in order to ensure even distribution of the spray.
Cabinets with a volume greater than 2m³ are difficult to operate unless careful consideration is given to their design and construction. The number and the position of the atomizers and baffles required to produce an even spray distribution within the limits specified shall be in accordance with Appendices A B C D and E.
The heating, insulation and means of temperature control shall be such as required to produce a uniform temperature within the cabinet at all positions where test specimen are exposed. The temperature inside the cabinet shall be controlled to within the limits of ±2℃.
If the cabinet has been used for a spray test, or for any other purpose, using a solution differing from that specified for the current test cycle, it shall be thoroughly cleaned before use. The blowers shall be capable of maintaining the cabinet and its contents at the specified temperatures and achieving the required heating rates. The temperature shall be controlled by a thermostat element placed within the cabinet at least 100mm from the walls of the cabinet.
The apparatus for spraying the salt solution shall comprise a supply of clean compressed air at a controlled pressure, a reservoir to contain the solution to be sprayed, and one or more atomizers made of metal resistant to the solution. The compressed-air supply to each atomizers shall be passed through a filter to remove all traces of oil or solid matter, shall be at a suitable pressure depending upon the types of atomizer nozzle and shall be adjusted so that the rate of collection of spray in the cabinet and the concentration of the collected spray are kept within the specified limits as shown Appendices A B C D and E.
The reservoir containing the solution to be sprayed shall be a tank made of material resistant to the solution and shall be provided with means of maintaining a constant flow to the atomizers. The atomizers shall be made of insert material, for example, glass or plastic.
Drying air for the drying cabinet shall be 20% to 30% relative humidity for cycles A and D and of 30% to 70% relative humidity for cycles B,C and E. The air shall be passed through a filter to remove all traces of oil or solid matter and shall have a flow rate sufficient to ensure that, at the start of a dry phase, no drops of moisture are visible on the panels after the drying time specified for cycles A and D and after 45min for cycles B,C and E. The panels shall not be dried by heater inside the cabinet walls.
At least two collecting devices of a chemical insert materials shall be used. The collecting devices shall be placed in the zone of the cabinet where the test panels are placed, one close to the spray atomizers and one remote from the spray atomizers. They shall be placed so that only spray and not liquid falling from test panels or parts of the cabinet is collected. The number of collecting devices shall be at least twice the number of atomizers.
Racks shall be constructed from insert non-metallic material such as glass, plastic or suitably coated wood. Exceptionally, test panels may be suspended. In this case, the material used shall be synthetic fibre, cotton thread or other insert insulting material; on no account shall metallic material be used. All racks shall be placed at the same level in the cabinet so that the solution cannot drip from panels or racks at one level onto other panels placed below.
The control equipment shall provide wet (salt fog)/dry/humidity cycles for the times and temperatures specified in Appendices A B C D and E. Unless otherwise specified or agreed by the purchaser and/or supplier the selection of the sample shall be in accordance with AS 2483. Representative samples shall be taken from the full width of the coated metal to be tested, of sufficient size to carry out the required tests.
The number and types of test specimens and their shape and dimensions, shall be selected in accordance with the specification covering the product items under test. Unless otherwise agreed, flat specimens shall be 150mm×75mm.
If test specimens are cut from a larger coated item, the cutting shall be carried out in such a way that the coating is not damaged in the area adjacent to the cut. Unless otherwise specified, cut edges shall be adequately protected with a suitable medium that is stable under the conditions of the test, such as paint, wax or adhesive tape.
Test specimens shall be thoroughly cleaned before testing. The cleaning method employed shall depend on the nature of the surface and the contaminants, and shall not include the use of any abrasives or solvents that could attack the coating.
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