Environmental Test Chamber Selection Guide

The Environmental Test Chamber Selection Guide is detailed:

Below we will share the environmental test chamber selection guide for you to choose, so how to choose the environmental test chamber? Now the details are as follows:

Chemical raw materials: coatings, plastics and other organic materials exposed to natural climatic conditions and light radiation will cause light loss, fading, yellowing, peeling, cracking, loss of tensile strength and the whole layer falling off after a period of time. Even indoor light or sunlight through window panes can cause damage to substances such as pigments or dyes. Therefore, for coatings for outdoor use, such as architectural exterior coatings and automotive coatings, weather resistance and lightfastness are the most important test items.

While everyone agrees that the weatherability and lightfastness of coatings are important, there are disagreements about what is the best way to test them. There are many ways to evaluate the weather resistance and light fastness of coatings at home and abroad. The commonly used methods include natural climate aging test, xenon arc lamp irradiation, or carbon arc lamp irradiation, ultraviolet lamp irradiation and other artificial accelerated climate aging test methods. This article will explore how to choose the right testing method.

1 Natural climate aging test

The natural climate aging test method is widely used at home and abroad. The main reason for this is that the results of the natural climate aging experiment are more realistic, the cost is lower and the operation is simple and convenient. Although we can perform natural climate aging tests anywhere, the internationally recognized test site is Florida in the United States because of its abundant sunshine.

However, the disadvantage of natural climate aging testing is that the test takes a long time, and the tester may not have so many years to wait for the test results of a product. In addition, even in Florida, the climate cannot be exactly the same from year to year, so the reproducibility of the test results is not ideal.

2 Xenon arc radiation test

The xenon arc radiation test is considered to be the test that best mimics the full solar spectrum because it produces ultraviolet, visible, and infrared light. Because of this, it is considered to be the most widely adopted method at home and abroad.

However, this approach also has its limitations, namely the stability of the xenon arc light source and the resulting complexity of the test system. Xenon arc light sources must be filtered to reduce undesirable radiation. A variety of filter glass types are available to achieve different irradiance distributions. The choice of glass depends on the type of material being tested and its end use. Altering the filter glass can change the type of short-wavelength UV light transmitted, thus changing the rate and type of damage to the material. There are 3 types of filtration that are commonly used, daylight, window glass and extended UV light.

Typical xenon arc radiation is equipped with an irradiance control system. The irradiance control system is important in the Xenon arc radiation test, because the spectral stability of the xenon arc light source is worse than that of the fluorescent ultraviolet light. Someone abroad has investigated the difference between the spectrum of a new xenon arc lamp and an old xenon arc lamp that has been used for 1000h. The results show that the spectral energy distribution varies significantly not only in the long wavelength range of the light source with the extension of the lamp use time, but also in the short wavelength range. The reason for this change is the aging of the xenon arc lamp, which is its own intrinsic property.

There are also a number of remedies available for this change. For example, increase the frequency of lamp replacement to mitigate the effects of light aging. Alternatively, the irradiance can be controlled with a sensor. Despite the changes in spectral energy distribution caused by lamp aging, xenon arc lamps are still a reliable and realistic light source for weathering and sunlight resistance tests.

Most xenon arc radiation tests use water spray or automatic temperature control system (surface water spray proposed by the national standard GB/T1865-1997) when simulating wetting conditions. The limitation of the water spray method is that when relatively cool water is sprayed on a relatively hot board, the board cools down, which slows down the process of material destruction.

In xenon arc radiation testing, the use of high-purity water is required to prevent the formation of deposits on the surface of the test plate. As a result, the operating costs are higher.

3. Ultraviolet lamp irradiation test

The UV lamp irradiation aging test uses a fluorescent UV lamp to simulate the damaging effect of sunlight on durable materials. This is different from the xenon arc lamps mentioned earlier, which are electrically similar to ordinary cold fluorescent lamps for lighting, but produce more UV light than visible or infrared light.

For different exposure applications, there are different types of lamps with different spectrums to choose from. The UVA-340 lamp simulates sunlight well in the predominantly short-wavelength ultraviolet spectral range. The spectral energy distribution (SPD) of the UVA-340 lamp is close to that of the 360 nm split from the solar spectrum. UV-B lamps are also commonly used to accelerate the artificial climate aging test lamp. It destroys materials faster than UV-A lamps, but its shorter wavelength energy output than 360nm can cause deviations from actual test results for many materials.

Irradiance (light intensity) control is necessary to obtain accurate and reproducible results. Most UV aging test sets are equipped with an irradiance control system. These precise irradiance control systems allow the user to select the irradiance meter when performing the test. With the feedback control system, irradiance can be continuously and automatically monitored and precisely controlled. The control system automatically compensates for illuminance deficiencies due to aging of the lamp or other reasons by adjusting the power of the lamp.

Fluorescent UV lamps simplify irradiance control due to their inherent spectral stability. All light sources weaken over time. But fluorescent lamps, unlike other types of lamps, do not change their spectral energy distribution over time. This feature is also a major advantage because it improves the reproducibility of test results.

Tests have shown that there is no significant difference in the output power of a 2h lamp and a 5600h lamp in an aging test system equipped with irradiance control, and the irradiance control device can maintain a constant light intensity. In addition, there is no change in the distribution of their spectral energy, which is very different from xenon arc lamps.

One of the main advantages of using the purple lamp weathering test is that it simulates the damaging effects of a more realistic outdoor humid environment on the material. When the material is placed outdoors, it is estimated that it is subjected to moisture frequently for at least 12 hours a day. Because this dampness is mostly in the form of condensation, a special condensation principle is used to mimic outdoor humidity in the accelerated artificial climate weathering test. 

During such a condensation cycle, the water tank at the bottom of the test chamber is heated to generate steam. The hot steam keeps the chamber environment at 100% relative humidity at high temperatures. The test chamber is designed so that the test plate actually forms the side wall of the test chamber. In this way, the back of the plate is exposed to room air at room temperature. The cooling effect of the room air reduces the temperature of the surface of the test plate by several degrees compared to the temperature of the steam. These temperature differences allow the water to continuously drop to the surface under test during the condensation cycle. The resulting condensate is a stable, pure distilled water. This water improves the reproducibility of experimental results, eliminates water sediment contamination and simplifies test equipment installation and operation.

Because the material is generally exposed to moisture outdoors for a long time, a typical circulating condensing system requires a minimum test time of 4 hours. The condensation process is carried out under heated conditions (50°C), which greatly accelerates the rate of damage to the material by moisture. Condensation cycles carried out over long, heated conditions are more effective at reproducing the destruction of materials by humid environments than other methods such as water spray, impregnation, and other high-humidity environments.

4 Knot Terminology

Although the national standard stipulates and the current prevailing test method in China is xenon arc radiation, xenon arc radiation and ultraviolet photoaging test are widely used test methods abroad. These two methods are based on completely different principles. The xenon lamp illumination test chamber mimics the entire solar spectrum, including ultraviolet, visible and infrared light, and is designed to simulate sunlight. The ultraviolet light aging test does not attempt to imitate the sun's rays, but only imitates the destructive effect of the sun's rays. It is based on the principle that durable materials that have been exposed outdoors for a long time are most damaged by the aging caused by short-wave ultraviolet light.

In addition, even if the aging test is carried out in a natural climate, there is also a way to accelerate the test sample, which is to install the test sample in a model frame that can rotate with the sun rising and falling, so that the sample remains in a state of direct sunlight most of the time to obtain the accelerated test results. Before the 80s of the 20th century, carbon arc lamps or direct ultraviolet lamps were used. Parallel tests can also shorten the inspection period, but there is no easy answer to which test method is best. The choice of method depends on factors such as the material to be tested, the end application of the material, the mode of damage to the material concerned, and financial resources.