ACCELERATED AGING TESTS
When we buy something we always hope that it will last over time, that even after years it will remain aesthetically the same and that it will not suffer structural damage.
The primary causes of outdoor aging are sunlight (especially UV), high temperature and rain, dew and high humidity. These atmospheric agents can cause innumerable damages, such as color change, loss of gloss, structural weakening, cracking, chalking and oxidation.
With the accelerated aging tests it is possible to recreate in a few days or weeks precisely such damages that usually occur over the course of months or years in outdoor environments.
It is an aging simulation with which a special instrument subjects the selected materials to alternating cycles of radiation with special UV lamps and humidity, as well as controlled high temperatures.
Xenotest chambers are the fundamental tools, both for performing tests for research and development and for quality control, on materials that are exposed
to direct sunlight, sunlight behind glass or indoor lighting. Therefore, they provide the most realistic reproduction of the full spectrum of sunlight, which includes ultraviolet, visible and infrared radiation.
Each tool allows you to set different parameters.
- Radiation: the transfer of energy between two bodies by means of electromagnetic waves.
- Reading point: The wavelength to which reference is made to choose the correct irradiation.
- Chamber temperature and humidity: These parameters influence the degradation of materials when they are subjected to physical stress while trying to maintain equilibrium with the surrounding environment and are set via a sensor.
- Black Panel Temperature: Provides an estimate of the temperature of the samples inside the test chamber.
- Filter type: There are three general categories of filters based on component type and/or placement in the vehicle. Within each category there can be many different types of filters. Each filter consists of a special flat glass specifically designed to have a particular transmission. Some filters can be:
UV AGING CHAMBERS
UV aging chambers reproduce the damage caused by sunlight, rain and dew by subjecting samples to alternating cycles of UV radiation and humidity at controlled elevated temperatures.
The instrument simulates the effects of sunlight through the use of special UV fluorescent lamps, which provide the most realistic simulation of the short wavelength portion of sunlight.
There are two types of lamps:
- UVA-340 Lamps: provide an excellent simulation of the critical short wavelengths of sunlight in the region from 365 nm up to the solar cut-off of 295 nm.
- UVB-313 Lamps: Maximize acceleration by using shorter, more aggressive wavelengths than those typically arriving at the Earth’s surface. UVB-313 lamps are more used for R&D and Quality Control or for testing materials that must have high durability, because they may produce unrealistic and too severe results for some materials.
UV allows for two approaches to humidity simulation. For many applications humidity via condensation is the best way to simulate the attack of humidity on the outside.
The UV simulates this condition using a condensation mechanism. During the condensing cycle, the water tank at the bottom of the test chamber is heated and steam is produced. The hot steam maintains the chamber at 100% relative humidity, at a high temperature.
In some real outdoor environments, a rapid change in temperature can occur as materials heated by a hot sunny day are cooled by a sudden rain. The result is thermal shock and causes problems for many products.
The UV water spray is very useful for reproducing the thermal shock and/or mechanical erosion caused by rain.
After the aging tests, any chromatic variations can be immediately appreciated. The variations that are required by most of the specifications are instrumental, i.e.:
- Brilliance/Gloss: performed using a glossmeter which allows you to give a general indication of the brightness of the aesthetic finish of the component and its variation based on the aging performed.
- Colour: performed using a spectrophotometer with which the colorimetric coordinates of the CIE L*a*b* space of a mass-pigmented or newly painted component and after aging are identified. Generally the difference of the color expressed as ΔE is requested, but sometimes it can be interesting to evaluate the difference in the single coordinates or ΔL, which indicates the light/dark change, Δb which allows to evaluate the yellowing and Δa which measures the variation in the color space from green to red.
- Adhesion: CROSS-CUT incision to be performed on the samples after aging, using a single-blade cutter and grid mask, followed by tearing with TESA tape. It is performed on painted components to verify the goodness of the adhesion of the paint to the substrate.
new – after aging new adhesion test – adhesion after accelerated aging
In our laboratories we can perform the tests indicated and many others,
visit our site on LABORATORY TESTS !
A special thank you goes to my colleague Dr. Lucia Pirone, part of the Plastlab Team as a laboratory technician, who raises awareness on this issue so as to provide us with new content for these #laboratory pills!