SSP/CCT Corrosion Testing Chamber Q-FOG-SSP/CCT
Cyclic corrosion testing provides the best possible laboratory simulation of natural atmospheric corrosion. Research indicates that test results are similar to the outdoors in structure, morphology, and relative corrosion rates.
The Q-Fog CCT and SSP advantages include the elimination of manually moving test specimens from one chamber to another and the laborious spraying of test specimens while reducing variability in results from excessive specimen handling.
Before cyclic corrosion testing, conventional salt spray (a continuous salt spray at 35°C) was the standard way to simulate corrosion in a lab. Because traditional salt spray methods failed to mimic the outdoors's natural wet/dry cycles, test results frequently correlated poorly to outdoors.
In a Q-FOG cyclic corrosion tester, specimens are exposed to different environments in a repetitive cycle that mimics the outdoors. Simple cycles like Prohesion may involve cycling between salt fog and dry conditions. More sophisticated automotive methods may call for multi-step cycles incorporating humidity or condensation, salt spray, and dry-off.
It can cycle through a series of the most significant corrosion environments within one Q-FOG chamber. Even highly complex test cycles can easily be programmed with the Q-FOG controller.
The Q-FOG SSP corrosion tester can perform numerous accelerated corrosion tests, including continuous salt spray (ASTM B117 and ISO 9227) and Prohesion (ASTM G85 Annex 5). The Prohesion test uses fast cycling, rapid temperature changes, a low humidity dry-off cycle and a different corrosive solution to provide a more realistic test. Many researchers have found this test valuable for industrial maintenance coatings. Continuous salt spray exposures are widely specified for testing components and coatings for corrosion resistance. Applications include plated and painted finishes, aerospace and military components, and electrical/electronic systems. Most of these tests are performed to particular specifications, such as ASTM B117 (Salt Spray) and BS 3900 F4.
These tests are widely used for comparative corrosion testing. They are typically run at an elevated temperature and do not incorporate a dry-off cycle. They require heated, humidified air for the spray.
The Q-FOG model CCT has all the advantages of the model SSP but adds the flexibility of including 100% humidity. Automotive corrosion test methods typically call for exposing specimens to a repetitive cycle of salt spray, high humidity, low humidity dry-off, and ambient conditions. These test methods were initially developed as labour-intensive manual procedures. The multi-functional Q-FOG CCT corrosion tester is designed to perform these cyclic tests automatically in a single chamber. Additionally, the CCT model can run Copper-Accelerated Acetic-Acid Salt Spray (CASS) tests such as ASTM B368 or ISO 9227 CASS.
The Q-FOG cyclic corrosion chamber has superior fog dispersion compared to conventional systems, which cannot vary volume and distance independently. A variable speed peristaltic pump controls the amount of corrosive solution delivered to the spray atomiser, while the air pressure regulator controls the distance of the "throw".
Space utilisation is maximised, and maintenance is minimised with the Q-FOG tester's internal solution reservoir. The 120L reservoir has enough capacity to run most tests for seven days or more. The reservoir has an integral salt filter and a built-in alarm to alert the operator when the solution is low.
Q-FOG testers can change temperatures exceptionally fast because of their unique internal chamber heater and high volume cooling/dry-off blower. An additional air heater allows very low humidity dry-off exposures. Conventional chambers with water jackets cannot cycle rapidly because of the thermal mass of the water, nor can they produce low humidity.
The Q-FOG test chamber is designed with easy specimen mounting and simple programming to cycle between four conditions: Fog, Dry-Off, 100% Humidity (Model CCT only), and Dwell. A built-in microprocessor controls test conditions, time, and temperature. A remarkably simple user interface featuring dual, full-colour touch screens allows for easy user programming and operation.
Temperature Range+20°C to +70°C
Humidity Range95 to 100%
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- What is Cyclic Corrosion testing?
- Cyclic corrosion testing is intended to be a more realistic way to perform salt spray tests than traditional, steady-state exposures. Because actual atmospheric exposures usually include both wet and dry conditions, it makes sense to pattern accelerated laboratory tests after these natural cyclic conditions. Research indicates that, with cyclic corrosion tests, the relative corrosion rates, structure and morphology are more similar to those seen outdoors. Consequently, cyclic tests usually give a better correlation to outdoors than conventional salt spray tests. They effectively evaluate various corrosion mechanisms, including general, galvanic, and crevice corrosion.
Cyclic corrosion testing is intended to produce failures representative of the type found in corrosive outdoor environments. CCT tests expose specimens to different environments in a repetitive cycle. Simple exposures like Prohesion may include cycling between salt fog and dry conditions. More sophisticated automotive methods call for multi-step cycles incorporating immersion, humidity, condensation, salt fog, and dry-off. Initially, these automotive test procedures were designed to be performed by hand. Laboratory personnel manually moved samples from salt spray chambers to humidity chambers to drying racks, etc. More recently, microprocessor-controlled chambers have been used to automate these exposures and reduce variability.
- Can the Q-Fog tester control relative humidity?
- The Q-FOG model CRH can ramp to and maintain a defined RH value and temperature through the use of an air preconditioner, an air control module, and special atomizing humidification nozzles. Deionized (DI) water is required for proper operation. The Q-FOG model CCT has the capability of 95-100% humidity control.
- What specimen mounting options are available with the Q-Fog?
- Standard test panel racks are available to accommodate flat specimens, such as Q-PANEL standard substrates. Odd-shaped parts (e.g. large, three-dimensional specimens) can be mounted on special 20 mm hanging rods. A rack-level or diffusion-level grate kit may be used for extremely large or heavy three-dimensional objects (such as metal wheel rims, engine parts, etc.).
- What if my test requires quicker heat up times?
- Rapid Ramp Heater capability enables the performance of some corrosion tests that have very fast transition times.
- What is Dew Point?
The dew point is the temperature at which dew (condensation) forms and is a measure of atmospheric moisture. It is the temperature to which air must be cooled at constant pressure and water content to reach saturation. Dew points are expressed as a temperature. Higher dew points correlate to higher moisture content, also known as absolute humidity.
The dew point represents the lowest temperature to which air with specific temperature and relative humidity (RH) can be cooled. At the dew point, air has a relative humidity of 100%, and additional cooling produces condensation rather than lowering the air temperature.
- Why is Relative Humidity important in laboratory corrosion testing?
Corrosion is caused when a metal is in contact with water and an electrolyte, such as a salt. In this corrosive environment, metals react to form metal oxides. Except for noble metals such as gold, silver, and platinum, all metals exist as oxides in the environment. Corrosion is effectively nature’s way of returning refined metals back into their natural state.
Although this concept is simple, the practice of simulating outdoor corrosion in the laboratory is very difficult. Multiple oxides can form as a result of complex multi-step reactions that are dependent on specific environmental conditions. Environmental cycling of temperature and moisture is the main reason that outdoor corrosion mechanisms are so complex. In weathering, we often talk about dew (condensation) and rain as they relate to moisture. In corrosion, there is another term related to moisture, called deliquescence. This is the phenomenon where any salt will form a liquid solution when the environment exceeds a relative humidity threshold. This threshold is known as the deliquescence relative humidity (DRH) and varies for different salts.
Deliquescence of salts can affect strongly the time of wetness of materials, which plays a major role in the corrosion experienced by specimens. To address this, temperature and humidity transitions specified in modern corrosion test cycles are usually controlled to ensure that the time above the DRH during a transition is consistent, regardless of which tester is used to run the cycle. Without controlled transitions, repeatability and reproducibility drop considerably.