Environmental Test Chambers for VDA 233-102
The purpose of this specification is to provide an accelerated test procedure for the assessment of the corrosion behaviour of components and of the corrosion protection provided by coating systems. This specification has been created jointly by the automotive, steel and aluminum industry.
This laboratory-scale cyclic corrosion test is also suitable for assessing perforation corrosion in flanged areas or gaps and of unpainted surfaces.
This method induces corrosion processes and generates reproducible corrosion patterns which correlate well with the results obtained in natural weathering tests (DIN 55665) and driving operation. In particular, the corrosion patterns for the substrates steel, galvanised steel and aluminium closely reflect real-life phenomena. The test method is based on real corrosive climate conditions and delivers differentiated results for a large number of uses in automotive applications.
The correct execution of VDA 233-102 requires a programmable test chamber allowing continuous programming of temperature, relative humidity and salt spray.
The test should be carried out in a combination chamber allowing all programmed climates to be run, in order to ensure minimal disturbance of the climates. In exceptional cases, the test may also be conducted in several chambers.
All parts of the test equipment that come into contact with the salt spray atmosphere, condensate or test solutions shall be made of a material that is resistant to attack by the test media and does not itself affect the action of the test solutions or the salt spray/condensate.
The test chamber design shall include equipment for cooling, heating, and pressure compensation, as well as the necessary instrumentation and control equipment to set and maintain the climate data [temperature (DT=±2) °C, relative humidity (DRH=±3) %] in the closed chamber at defined temperature/humidity points. A rate of temperature change of 1,5 K/min is recommended.
The test chamber geometry shall be designed such that no drops can fall from the ceiling or side walls onto the specimens positioned below them. After spraying, the test solutions may not be returned to the reservoir. The useable space for the test is defined as that part of the chamber which is outside the actual spray jet and within a constant distribution of the spray according to Section 4.3 as demonstrated.
The test shall be performed with a solution of one wt.% sodium chloride in water.
The sodium chloride is to be dissolved in distilled or deionised water with a maximum conductivity of 20 µS/cm at (25 ± 2) °C to ensure that a concentration of (10 ± 1) g/l is achieved. The sodium chloride concentration of the sprayed and collected solution must also be (10 ± 1) g/l. The relative density of such a (10 ± 1) g/l solution is 1.005 +/- 0.0005g/cm³ at 25 °C. The quality of the deionised water, the salt and the pH-value of the collected solution are defined in DIN EN ISO 9227 (NSS-Test).
The flow-rate of test solution according to Section 4.2 to be sprayed over a defined period of time shall be chosen, such that when the solution is sprayed into the empty corrosion testing chamber over a period of at least 3 h, the mean quantity of sprayed solution collected in each of the collecting recipients placed in the chamber is (3.0 ± 1.0) ml/h. Each of these recipients shall have a horizontal collecting area of approximately 80 cm².
Suitable collecting recipients include glass or plastic funnels with a diameter of 100 mm(equivalent to the above-mentioned collecting area) which are fitted via a plug to a measuring cylinder made of glass or plastic. (For method, please refer to DIN EN ISO 9227).
To demonstrate the constant distribution of the spray, at least two of the collecting recipients shall be placed at representative positions within the useable space. The target number is at least one recipient per 4 m² of testing area.
When using the nozzle as described in Section 4.1, it has been proven appropriate to set the flow-rate of the test solution sprayed over a defined period of time, with the help exclusively of the instrumentation and control equipment, provided. The specified test pressure and the suction height are to be maintained constant.
The compressed air with a pressure of approximately 70 to 180 kPa used to generate the salt spray may not exceed the limits for total oil content and percentage of solid contaminants as specified for class 1 cleanliness according to ISO 8573-1. The temperature of the water in the compressed air humidifier is to be set dependent on the pressure of the sprayed salt solution according DIN EN ISO 9227 (NSS-test).
Test procedure The test duration is to be stipulated upon on a case by case basis. The typical test duration is six full test cycles (6 weeks). If necessary, the test duration can be changed until it is possible to draw conclusions concerning the corrosion behaviour.
Interim assessments have proven useful to determine the progression of corrosion.
A full test cycle lasts 7 days and consists of:
3 times = 24h cycle A without freezing phase, with 3 h salt spray phase (1 % NaCl solution)
3 times = 24h cycle B without freezing phase, without salt spray, including assessment of specimens (or walk-around inspection)
1 time = 24h cycle C with freezing phase, without salt spray
The specimens shall preferably be positioned in the chamber at an angle of 65° to 75° relative to the horizontal with the side to be tested uppermost. Components are to be positioned as agreed with the principal, preferably in the orientation in which they will be installed. The specimens (or components) may not contact each other or shield other specimens from the salt spray.
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