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Environmental Test Chambers for ISO 16701

Environmental Test Chambers for ISO 16701 Corrosion of Metals and Alloys
Atmospheric corrosion of metallic materials, with or without corrosion protection, is influenced by many environmental factors, the importance of which might vary with the type of metallic material and with the type of environment. It is therefore not possible to design a laboratory corrosion test in such a way that the full complexity of real in-service conditions are taken into account.
Acceleration (forced conditions) as such can also have a negative impact on the correlation to field performance. Nevertheless, tests with humidity cycling and only intermittent exposure to salt solution will generally provide a better correlation to field performance than tests using continuous salt spray.
This International Standard was developed in the automotive context, where the major contributor to corrosion is the use of winter time de-icing road salt in cool/cold temperate areas around the world, here as sodium chloride compounds acting in cyclic humidity conditions.
The test procedure is moderately forced by humidity and salt and intended to be applicable for quality assurance of the metals and corrosion protections typically encountered in motor vehicles. The method can have relevance also in other areas of application, provided representing similar climatic conditions with an influence of sodium chloride compounds.
This International Standard specifies the test method, the reagents, and the procedure to be used in an accelerated atmospheric corrosion test constituting a 6 h exposure to a slightly acidified solution of 1 % NaCl twice weekly, followed by a condition of controlled humidity cycling between 95 % RH and 50 % RH at a constant temperature of 35°C.
This International Standard does not specify the dimensions of the tests specimens, the exposure period to be used for a particular product, or the interpretation of the results. Such details are provided in the appropriate product specifications.
The accelerated laboratory corrosion test applies to:
— metals and their alloys,
— metallic coatings (anodic or cathodic),
— chemical conversion coatings, and
— organic coatings on metallic materials.
As alt solution, prepared by dissolving a sufficient mass of sodium chloride in distilled or deionized water to a concentration of 10g1-1±1g1-1. The distilled or deionized water used shall have a conductivity not higher than 2 mS m-1 at 25 °C±2°C.
The climate chamber shall be designed so that the following test conditions can be obtained, controlled and monitored during the test.
An instantaneous maximum deviation from set relative humidity value of ±4 % in the range from 50 % to 95 % at 35 ℃, which corresponds to a temperature accuracy requirement of ±0,8C at that temperature.For the mean value in relative humidity during a period of constant climatic conditions 7 h to 8 h an accuracy of ±2 % shall apply, corresponding to temperature accuracy requirement of in this case ±0,4°C.
To meet the temperature and humidity accuracy requirements, the climate chamber should be equipped with means for efficient circulation of air to provide for small temperature and humidity variations in the chamber. Sufficient insulation of the chamber walls and lids are required in order to avoid excessive condensation on these surfaces.
The spraying device for salt solution installed in the climate chamber shall be capable of producing a finely distributed uniform vertical downward flow of mist or small droplets falling on the test obiects at a linear flow rate of 15 mm h-1 ±5 mm h-1,If a graduated glass cylinder with a collecting area of 80 cm2 is used to check whether this flow rate is within the specified range, the collection rate of salt solution shall be 120 ml h-1 ± 40 ml h-1.
The climate chamber shall be equipped with a system for forced airflow drying, as after spraying/wet stand-by all test objects should be dried from excessive macro wetness and climate control shall be made possible to regain within a reasonable time.
Forced drying is preferably arranged by supercooling and reheating an internal circulating flow.Alternatively, drying can be arranged by letting a forced flow of pre-heated ambient air ventilate the chamber. For a climate chamber of the volume 1 m3 to 2 m3 an airflow rate of 50 1s-1 to 100 Is-1 is recommended. The forced airflow shall not be pre-heated to such temperature levels that the maximum chamber temperature of 35 °C is exceeded.
The test objects shall be placed in the chamber on stands with their test surface facing upwards. The angle at which the surface of the test specimens is exposed in the chamber is important. For flat test objects the angle at which the test surface is inclined shall preferably be 20° ± 5° to the vertical. In the case of irregular surfaces, e.g. entire components, this angle shall be adhered to as closely as possible.
The stands with the test objects shall be placed on the same level of the climate chamber. The stands shall be made of inert non-metallic material, such as glass, plastic or suitably coated wood. If it is necessary to suspend the test object, the material used shall on no account be metallic but shall be synthetic fibre, cotton thread, or other inert insulating material.
Execute an exposure test in the climate chamber according to the following scheme of 12 h cycles.In the 1st cycle, the 8th cycle, the 15th cycle, and subsequently every seventh cycle, a cycle A with salt spraying as specified in 6.2.3 is used. In the other cycles, a cycle B as specified in 6.2.2 is used.
Cycle B is composed of the following steps:
Step 1: Exposure at 35 C and 95 % RH for 4h.
Step 2: Exposure at 35 C to a linear reduction of relative humidity with time from 95 % RH to 50% RH over a total period of2h.
Step 3: Exposure at 35 C and at 50 % RH for 4h.
Step 4: Exposure at 35 C to a linear increase of relative humidity with time from 50 % RH to 95 % RH over a total period of 2 h.
Cycle B is composed of the following steps:
Step 1: Exposure at 35 C and 95 % RH for 4h.
Step 2: Exposure at 35 C to a linear reduction of relative humidity with time from 95 % RH to 50% RH over a total period of2h.
Step 3: Exposure at 35 C and at 50 % RH for 4h.
Step 4: Exposure at 35 C to a linear increase of relative humidity with time from 50 % RH to 95 % RH over a total period of 2 h.
Step 5a: Remove the test objects from the climate chamber and immerse them for 15 min in the specified salt solution at a temperature of 35C. After emersion, manually spray the test objects with salt solution to restore droplets on the surface.
Step6a: After manual over-spraying, let excessive fluid run off then return the test objects to the test chamber at 35 °C with the relative humidity set point at 95 % to 99 % for 1 h 45 min.
Steps 5 a) and 6 a) are then repeated in sequence two more times to give a total period of wetness of 6 h.
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