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Anti-corrosion coating weather resistance artificial aging test

2022-12-23

Artificial aging test of anti-corrosion coating is one of the important parts of weather resistance test. The weather resistance test refers to anti-corrosion coatings (including various materials, especially various polymer-based synthetic materials, represented here by anti-corrosion coatings) against sunlight, humidity, rain, dew, wind, frost, etc. The ability to maintain the original performance under the destructive effect of climatic conditions.

In order to simulate various climatic factors in nature to create a so-called artificial climate in the laboratory and achieve the goal of accelerated testing, artificial weather aging test machines are generally used for testing.

According to the light source used, the artificial weathering tester can be divided into ultraviolet carbon arc type, sunlight carbon arc type, ult typeraviolet fluorescent lamp, the xenon arc lamp type and the metal halide lamp type. This article focuses on xenon lamp type artificial weather aging test equipment and ultraviolet fluorescent lamp type artificial weather aging test equipment.

1. Xenon lamp type artificial weather aging test equipment

The xenon lamp type artificial weather aging test chamber should be made of corrosion-resistant materials, and the internal devices include : the radiation source of the filter system, temperature and humidity adjustment system, sample frame, black standard thermometer, irradiance meter, etc. It can not only more effectively simulate various outdoor climate characteristics, such as: simulation of the sun's spectral distribution, adjustment to different standard filter combinations, constant black standard temperature, cabinet temperature, humidity, rainfall, darkness, condensation, etc. dew, straling of one sun/two suns, etc. In addition, the degree of automation has also been greatly improved. It can store a variety of international, European, American, Japanese and other industries rial products (paints, auto parts, plastics, textiles, etc.) artificial weather resistance testing standards, and can also set up a variety of user testing programs. The accuracy of the instrument performance standard and the repeatability of the test data are also continuously improved. The xenon lamp type artificial weathering test equipment can more accurately simulate the spectrum of sunlight, so despite the high operating cost, most users still need to use the test results of the xenon lamp type artificial weathering tester to predict the weather resistance of future products. Especially for judging the weather resistance of the material color, it should be done with a xenon lamp type artmoderate weather aging tester.

1. The structure of xenon lamp type aging machine

The Xenon arc lamp is a very powerful light source, from 1000 watts to 5000 watts. A large amount of infrared emission will cause the temperature of the sample to rise very quickly. The lamp itself is also very hot. Therefore, by the cooling method of the lamp tube, the xenon lamp aging machine can be divided into water-cooled type and air-cooled type. To take full advantage of the lamp tube's radiation sources, the sample is generally placed in a circle around the lamp tube. And made in a rotatable structure. Called the rotating drum. The structure in which the sample is placed on a plane and the lamp tubes are arranged on the upper part of the test box is called an aircraft arrangement type. The water-cooled xenon lamp aging machine can make the lamp tubes operate at high power and achieve higher efficiency.function, but the water cooling system requires isolation of water, electricity and optical path, and the structure is complex. Deionized water requirements for cooling are also high, resulting in a high price for the water-cooled xenon lamp aging machine. On the contrary, the xenon lamp type air-cooled aging machine has a simple structure, but the luminous efficiency is high and low, and the price is relatively low. At present, the new international standard has no requirements for the structure of the aging machine.

2. Filtering the radiation spectrum of xenon lamps

Since the spectrum of xenon lamps has a large number of pulse peaks, it must be filtered to obtain a spectrum close to sunlight. See Table 2 for common filter combinations and application area for xenon lamp aging machines:

Table 2 Common filter combinations and application area

For example As As weeGiven in Table 2, a variety of simulation tests for indoor and outdoor conditions can be obtained through the combination of different filters. Different combinations will produce different spectra and radiation intensities, which can cause significant differences in test results. The aging of the optical filter can significantly reduce the ultraviolet emission of the xenon arc lamp, and the internal and external optical filters must be replaced regularly in strict accordance with the regulations of the instrument. In addition, scale and other residues on the filter can also affect the permeability of the filter, so the filter should be cleaned regularly.

3. Irradiation intensity and control points

Irradiance refers to the ratio of light energy radiated onto a surface. A weather resistance test chamber must control the intensity of the light radiationto achieve the goal of speeding up experiments and reproducing test results. Changes in light irradiance affect the rate at which materials deteriorate, while changes in the wavelength of light (such as the energy distribution of the spectrum) affect both the rate and type of material deterioration. By controlling the irradiation intensity of the light, it is possible to keep the test conditions in line with the actual situation.

Xenon lamp aging machines generally have a radiation intensity feedback control system. When controlled at 0.68 W/m2/nm, the irradiance intensity of the test machine is approximately equal to the intensity of direct sunlight at midday in summer. Increasing the irradiation intensity can sometimes accelerate the aging rate, but the effect on some materials is not necessarily obvious, and increasing the agingringing speed sometimes does not correspond to the actual situation. It is necessary to refer to the natural climate exposure comparison test to get the correct result.

4. Temperature and humidity control

The radiation of light energy on the test panel increases the temperature of the test panel. Different colors have different temperature rises due to different absorbed energy. The darker the color, the higher the temperature, the higher the black and the lower the white. Usually, the aging tester uses the standard black body temperature to unify the surface temperature of the irradiated object, also called the black panel temperature. The board temperature sensor is a heat conductive plate with temperature sensing active elements inside. The surface is covered with flat black paint that can absorb 93% of all incident radiant light within a wavelength of 2500 nm and has a ghas good resistance to aging. The back and the test plate are placed on the same surface of the heat conduction plate. The instrument adjusts the temperature of the black panel temperature sensor by controlling the external cold air blowing over the surface of the sample to stabilize it at approximately 60°C. Due to the thermal conductivity and heat-absorbing effect of the back bottom plate, other samples will also be present at

Lab

close to this temperature status. Under special application conditions, the temperature of the insulating black body (there are heat insulating materials around and at the bottom of the sensor) and the temperature of the white board are used as temperature control targets of the test sample. The gas temperature of the box is used as an indirect temperature environmental instrument, and the control system is also set if it is belowsuitable control object.

In general, an increase in temperature of 10 degrees Celsius will double the rate of chemical reactions. But the photochemical reaction is not a usual simple one-step reaction. The initial photochemical reaction is not affected by heat, while the second step reaction is affected by heat. Increasing the temperature can generally accelerate the aging rate, but the effect on some materials is not necessarily obvious. Therefore, raising the temperature to accelerate the aging rate sometimes does not correspond to the actual situation. Therefore, it is necessary to increase the aging rate and reduce the error. The blackboard temperature usually cannot be higher than the actual higher temperature used.

Humidity has a major influence on the aging of the coating, but the high temperature xenon lamp radiation makes humidity controlhard to reach. In general, there is a device to adjust the evaporation of water vapor to adjust humidity in the box. Relative humidity is maintained at approximately 50%+/-5%.

5. Cycle

Some people may think that continuous light can accelerate the aging rate and shorten the aging time. But in fact, many materials require a certain interval before chemical reactions can occur. The instrument has a cycle program to control the test to follow a cycle, such as a few hours of light and a few hours of no light. The program is also designed with water spray or immersion steps. Such aging is both close to the real situation and faster.

2. Ultraviolet fluorescent lamp type artificial weathering test equipment

The ultraviolet fluorescent lamp type artificial weathering test equipment is also made of corrosion-resistantmaterials and the internal device contains a radiation source composed of UV light tubes, temperature control system, heating water storage tank for simulating moisture, sample rack, black standard thermometer, irradiance meter, etc.

Although ultraviolet light (UV) only accounts for 6% of the sunlight, it is the main light factor that reduces the durability of outdoor products. Thisbecause the photochemical influence of sunlight increases as the wavelength decreases. Therefore, when simulating the destructive effect of sunlight on the physical properties of materials, it is not necessary to reproduce the entire sunlight spectrum. In most cases, only short-wavelength UV light is needed.

1. The wavelength range of UV energy

The ultraviolet weathering machine uses fluorescent UV lamps. The reason is that they are more stable than other lamps and have better reproducibility of test results. ItA better method should be to use fluorescent UV lamps to simulate the impact of sunlight on the physical properties of materials, such as brightness reduction, cracking and peeling. There are different types of UV lamps available. These UV lamps mainly produce ultraviolet light, not visible or infrared light. The main difference between the lamps is that the total UV energy produced by each of them is concentrated at different spectral wavelength ranges. Different lamps will produce different test results. The actual exposure application environment may dictate the type of UV lamp to use.

UVA-340 is excellent The critical short-wavelength range of the simulated sunlight spectrum, the name UVA-340 indicates the wavelength characteristic of the emission peak (expressed in nm), that is, the wavelength of the emission peak is 340nm. The wavelength range is theA band, i.e. the spectrum from 295 to 360 nm. UVA-340 only produces a spectrum of UV wavelengths found in sunlight.

UVB-313, increasingly used for accelerated testing. UVB-313 can quickly provide experimental results. The short-wavelength UV rays they use are more intense than the UV light waves commonly found on the surface of the Earth today. While these UV lamps, which are much shorter than the natural wavelength, can greatly speed up the test, it can also lead to inconsistent and realistic degradation damage to some materials. The UVB-313 exposure program is extremely useful in QC and R&D applications and when testing sustainable materials.

2. Radiation intensity control

Like the xenon arc lamp device, the ultraviolet fluorescent lamp type artificial weathering test equipment generally has a radiance intensity feedback control system.speed, to achieve accelerated experiment and reproduce test results. Variations in light irradiation can affect the rate at which material quality deteriorates. Typically, a UVA-340 lamp with a peak wavelength of 340 nm is used. Adjust the irradiance intensity to 0.68 w/m2/nm, which corresponds to the intensity of direct sunlight at noon in summer. It delivers results quickly without compromising on its relevance. To speed up data acquisition, the light intensity can be made 75% higher than the intensity of sunlight at noon in summer.

3. Simulate the influence of dew

The time that outdoor materials come into contact with moisture can be up to 12 hours per day. The results of the study indicated that the main cause of this outdoor humidity was dew, not rain. The simulation of dew is realized by the principle of condensation. There is a water storage tank at the bottom of the test boxst, which is heated to generate water vapor during the condensation cycle. The hot steam maintains the relative humidity in the test chamber at 100% and maintains a relatively high temperature. The design ensures that the test samples actually form the side walls of the chamber, exposing the back of the samples to ambient air. Due to the cooling effect of the ambient air, the surface temperature of the test piece drops to a few degrees below the steam temperature. This temperature difference causes liquid water to condense on the surface of the sample throughout the condensation cycle. The professional channel of this condensation is very stable pure distilled water. This pure water increases the reproducibility of the test while avoiding the problem of water spots: as exposure to outdoor humidity can last up to 12 hours per day, the humidity cycle typically takes several hours. The standThe recommended condensing cycle generally takes at least 4 hours.

4. Simulate the impact of rainwater

For some applications, adding water mist can better simulate the environmental conditions of the final use. Roofing, automotive materials and anti-corrosion coatings used on metal buildings or structures are often subject to sudden changes in temperature. For example, in the hot summer, when the surface temperature of the heat accumulation is very high, suddenly due to heavy rainfall and disappears. Due to the frequent erosion by rainwater, the coating layer of the steel construction, including paint and dye, will corrode accordingly. Recent research has shown that this rain wash can wash away the chalk layer of the anti-degradation coating on the material surface, exposing the coating itself directly to the damaging effects of UV and moisture. This process can be repeated many timesrepeated, resulting in increased degradation of the material. It cannot be reproduced by condensation alone. The addition of water spray to reproduce these environmental conditions may increase the relevance of some paint weathering tests.

5. Temperature control

First-order photochemical reactions are not sensitive to temperature changes. However, the rate of the subsequent secondary reaction is closely related to the temperature change. In general, as the temperature increases, the rate of reaction increases. Therefore, temperature control during the UV exposure experiment is very important. In addition, it is necessary to control the test temperature used in the accelerated test to be equal to the higher temperature encountered by the material in practice.application. Similarly, the ultraviolet aging tester also uses the standard blackbody temperature to measure the surfacepaint temperature of the irradiated object. Since the instrument has only the ultraviolet part of the spectrum, the temperature of the test plate is generally determined by the temperature of the box. The temperature setting of the UV trap can vary from 50C to 80C depending on the light level and ambient temperature of the room.

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