For the past 50 years, xenon arc weathering has been performed mainly in two styles of instruments: flat tray and rotating rack. Each design has its advantages and disadvantages. Do you know which style is right for your test? Let’s discuss what points we should consider when trying to decide between the two.
Below you will find a simplified matrix of seven considerations that will help you determine whether to test in a flat tray or rotating rack xenon weathering instrument. The list is not exhaustive, but it covers the most common test methods.
Flat Tray Instruments
As seen in the matrix, a clear advantage of using a flat tray design is the ability to test 3D samples. In flat tray instruments, the light source is located in the ceiling of the chamber thus allowing for an unobstructed exposure area that is perfect for accommodating components and full products. The maximum size of a 3D sample that can be exposed in a flat tray device is a function of the chamber height. The closer a sample’s surface is to the light source, the higher the irradiance on that surface will be. It is critical to check the height of the test chamber in relation to your sample height prior to starting testing to ensure that you are using a device with a chamber height that is tall enough to provide a uniform exposure.
Cross Section of SUNTEST XXL+
Another advantage is the ability to work with chiller accessories. Chillers extend the chamber temperature range to the ambient and sub-ambient temperatures typically required for different types of photostability tests such as those in the pharmaceutical, medical, biological, and consumer goods industries to name a few.
The inherent disadvantages of flat tray designs are the wider irradiance and temperature uniformity tolerances as compared to rotating rack instruments. Air enters the chamber from one side and exits on the other resulting in lower chamber air temperatures on the side where air flow enters and hotter temperatures on the side where the air exits. Lower irradiance uniformity is also a disadvantage in flat tray designs with tolerances typically ranging from +/- 9-10%. Because of these issues, it is advised that sample positions in the chamber be manually rotated throughout the test to even out differences in temperature and irradiance uniformities caused by the design of the machine.
Rotating Rack Instruments
On the other hand, the number one advantage of a rotating rack design is exceptional temperature and irradiance uniformity. Specifically designed to test flat coupons of materials, rotating rack instruments expose samples to light, heat, and moisture with a +/- 2-3%* uniformity tolerance. These tight tolerances have made rotating rack instruments the design of choice for many premium brands. For example, a recent revision to a European automotive test method which historically allowed extra-large flat tray xenon devices to be used in addition to rotating rack designs now excludes flat tray devices (with the exception of testing headlight assemblies and hard coats) due to lower uniformity in flat tray devices. As the samples are mounted on an auto-rotating rack, there is no need to manually reposition the samples for improved uniformity.
Chamber view of Ci Weather-Ometer
Another rotating rack advantage is testing capacity. A Ci5000 Weather-Ometer can hold up to (111) 3” x 6” samples (+1 black panel temperature sensor), which is approximately 4x more than a large flat tray. A Ci4400 Weather-Ometer holds (77) 3” x 6” samples (3x more than a large flat tray) and the Ci3000 holds (20) samples of the same size (approximately the same amount as a large flat tray).
The obvious disadvantage of a rotating rack design is that is does not accommodate 3D specimens well due to having a spherical sample rack. Now, that is not to say that you cannot test 3D samples in a rotating rack instrument, but rather that is more difficult to properly mount the samples to the rack for even irradiance exposure than in a flat tray device.
More Information
Listen to our free
recorded Atlas Online Seminar explaining xenon flatbed and rotating rack devices in detail.