Coated glass is a type of industrial glass that undergoes a process of having metal oxides sprayed onto it as thin coatings, which can range from 0.01 µm to 0.8 µm in thickness. The purpose of this process is to modify the glass’s characteristics with regards to light transmission, reflection, and absorption.
In recent years, there has been a shift towards utilizing more environmentally friendly and sustainable materials, and the coated glass industry is no exception. The coated glass being produced today incorporates such elements, allowing for high performance in terms of heat resistance and visual appeal.
When it comes to the use of coated glass in the exteriors of buildings – whether commercial or non-commercial – certain standards and requirements must be met. This article outlines the specific test requirements that coated glass products must pass in order to be suitable for use in such applications.
Measurement of Performance
To determine the performance factors and spectral details of coated glass, it is necessary to use standard spectrophotometer equipment. The size of the measuring sample will depend on the type of equipment used. The transmittance of the sample must be measured at normal incidence for light and solar transmittance using wavelengths of 550 µm (representative wavelength for light and solar transmittance) and 900 µm (representative wavelength for solar transmittance), respectively.
For glass with a low emissivity coating, R-reflectance measurement should be made at 8 µm using radiation of nearly normal incidence. It is important to ensure that the measuring equipment employed is widely accepted as standard in the industry to obtain accurate and reliable results. The exact size of the measuring sample will depend on the type of equipment used and should be determined accordingly. By following these standard procedures, the performance factors and spectral details of coated glass can be accurately determined.
1. Resistance Test
The experiment involves subjecting coated glass to a water-saturated atmosphere with a constant temperature. During this process, the samples are exposed to condensation which could potentially cause surface degradation. In order to carry out the experiment, the test apparatus must have the capability to accommodate four test pieces. Additionally, the inner walls of the apparatus must be made of materials that are corrosion-resistant and will not have any adverse effects on the test pieces.
Test Procedure
The water tank for the test needs to be filled with demineralized water that has a conductivity of less than 30 µS/cm and a pH higher than 5. This is necessary for the accuracy of the test results.
The internal temperature of the cabinet must be controlled throughout the test. This will be achieved by using a reference thermocouple to maintain the temperature of the reference glass piece at 40 ± 1.5°C.
The test cabinet should be placed in a room with an ambient temperature of 23 ± 3°C. It is essential to prevent draughts, dust, moisture, and solar radiation from interfering with the test cabinet.
The reference temperature needs to be achieved within two hours of commencing heating. This is crucial to ensure the accuracy of the test results.
During the test, it is essential to monitor the formation of condensation on the glass pieces. This will help in ensuring the accuracy of the test results. The test should be continued without interruption for the required duration.
Regular checks of both the internal reference and external air temperature are necessary throughout the test. This will help in ensuring that the test results are accurate and reliable.
Standard Test Requirements
The quality requirements for the tested item stipulate that there should not be any defects longer than 3 mm. Additionally, there should be no more than one defect that falls between the length of 2 mm and 3 mm. The maximum number of defects between 1 mm and 2 mm in length allowed is five. Moreover, the coating should not exhibit any stains, scratches, or clusters of pinholes that exceed 1 mm in size.
Another important aspect of the quality assessment is the color of the tested item. When compared to the reference test piece, there should be no noticeable change in color in both reflection and transmission. This evaluation must be made within 20 seconds.
The transmittance of the tested item at two specific wavelengths, 550 nm and 900 nm, is also a crucial factor. The measured transmittance at these wavelengths should not differ by more than 0.03 from the corresponding measured value of the reference test item. Meeting all of these requirements ensures that the tested item meets the necessary quality standards.
2. Acid Resistance Test
The test requires the coated glass to be exposed to a saturated atmosphere of sulfur dioxide under constant temperature. During the test, the samples will undergo continual condensation. The surface degradation of the samples may occur due to the combination of the amount of sulfur dioxide and the presence of condensation.
Test Procedure
The test cabinet currently holds 2 liters of demineralized water that has a conductivity lower than 30 µS/cm. To begin the test, 0.2 liters of SO₂ will be added to the cabinet, and the heating system will be turned on.
The test will consist of 24-hour cycles, with each cycle having two distinct periods. The first period will be a high-temperature and condensation phase, while the second period will be an ambient temperature phase without condensation.
To begin the high-temperature and condensation phase, the temperature inside the cabinet will be raised to 40 ± 1.5°C in less than 1.5 hours. The temperature will then be maintained at this level for the next 6.5 hours, during which time the test pieces will be exposed to condensation in the SO₂ atmosphere.
Standard Test Requirements
The given statement specifies a requirement for the transmittance measurement at two different wavelengths, 550 nm and 900 nm. According to the requirement, the difference between the transmittance values obtained at these two wavelengths and the corresponding values obtained on a reference test piece should not exceed ±0.03 nm.
This requirement suggests that the accuracy and precision of the transmittance measurement at these wavelengths are important and should be closely monitored. If the difference between the measured values and the reference values exceeds the specified limit, it may indicate a problem with the measurement process, such as errors in instrument calibration or sample preparation.
Therefore, it is important to ensure that the measurement equipment used for transmittance measurements is calibrated and maintained properly to achieve accurate and reliable results. Additionally, appropriate procedures and protocols should be followed for preparing and handling the test samples to minimize any sources of error that may affect the measurement results. By adhering to these requirements, the transmittance measurement at 550 nm and 900 nm can be performed with a high level of precision and accuracy, enabling researchers to obtain reliable and meaningful data.
3. Neutral Salt Spray Test
The test involves exposing the coated glass to a constant temperature in a neutral atmosphere consisting of water and saline. The surface degradation that may occur is primarily due to the water saline spray that the glass is subjected to during the test.
Test Procedure
The test cabinet needs to undergo preparation and run for a minimum of 24 hours before the test pieces can be placed inside it.
To create a neutral salt solution, NaCl must be dissolved in demineralized water that has a conductivity of less than 30 µS/cm. The resulting concentration should be 50 ± 5 g/l at a temperature of 25 ± 2°C.
Before being used, the compressed air supplied to the spray nozzle should pass through a filter to remove all solid matter and oil. Additionally, it should be at an absolute pressure of 70 kPa to 170 kPa and passed through a saturator at a temperature of 40 ± 1.5°C.
The spray nozzle must be made of inert material and have baffles to prevent the direct impact of spray on the test pieces.
Standard Test Requirements
The requirement for a glass coating to withstand neutral salt spray should be equivalent to the condensation resistance test requirement mentioned earlier.
4. Abrasion Resistance Test
The test being referred to involves rubbing the coated surface of a piece of glass with a felt pad, in dry conditions. The purpose of this test is to determine the potential for surface degradation caused by the type of pad being used, the amount of pressure being applied, and the number of strokes administered during the rubbing process. Essentially, the goal of this test is to assess the durability and resistance of the glass’s coating.
Test Procedure
The specified metal finger for the test should have a diameter ranging from 15 mm to 20 mm. It must be driven to produce a frequency of 60 strokes per minute, with an alternating forward and backward motion of 6 strokes per minute. The stroke length should measure 120 ± 5 mm and should be parallel, ensuring that there is constant pressure over the area being tested. The shape of the area to be tested should be circular, with a diameter of 14.5 ± 0.5mm.
Standard Test Requirements
The objective is to achieve uniformity in the abraded area. Additionally, the difference between the transmittance values measured at 550 nm and 900 nm must not exceed ± 0.03 nm in comparison to the corresponding measurement obtained from the reference test piece. This criterion needs to be met to ensure consistency and accuracy in the measurement process. Therefore, it is crucial to maintain the same level of abrasion throughout the testing process to obtain reliable and accurate results.
Duration of Tests for Coated Glass
The duration of the above tests shall be as per the following table:
FAQs
How to determine the performance factors and spectral details of the coated glass?
To determine the performance factors and spectral details of coated glass, standard accepted spectrophotometer equipment will be used. The size of the measuring sample will be determined based on the type of measuring equipment used.
The transmittance of the measuring sample will be measured using normal incidence light at three different wavelengths. The first wavelength is 550 µm, which is a representative wavelength for both light and solar transmittance. The second wavelength is 900 µm, which is a representative wavelength for solar transmittance.
For glass that is said to have a low emissivity coating, a reflectance measurement will be made at 8 µm using radiation of nearly normal incidence. This will help determine the amount of radiation that is reflected by the glass.
What is the standard test requirement of the resistance test of coated glass?
The resistance test requirements for coated glass are specified as follows: Firstly, there should not be any defect larger than 3 mm, and only one defect ranging from 2 mm to 3 mm in length is acceptable. Secondly, a maximum of five defects ranging from 1 mm to 2 mm in length is allowed, and there should not be any staining, scratches, or clusters of pinholes larger than 1 mm on the coating. Thirdly, there should not be any significant color change in both reflection and transmission when compared with the reference test piece. This observation must be made within 20 seconds. Finally, the measured transmittance at 550 nm and 900 nm must not differ from the corresponding measured value on the reference test item by more than 0.03.