With the vigorous implementation of policies and regulations on building energy efficiency in various countries and the gradual popularization of building energy efficiency knowledge, people’s demand for insulating glass with high energy-saving configurations is also increasing. The market increase brought about by the large-scale production of low-emissivity coated glass The relative increase makes it possible to continuously increase the effective demand for high-performance insulating glass. As a result, more and more applications of low-emissivity coated insulating glass are in the ascendant. However, the application of Low-E glass brings two problems that we have not encountered before:
(1) The requirements for sealing life of insulating glass made with offline low-emissivity coating have become more prominent;
(2) After using low-emissivity glass to solve the heat radiation problem, it becomes very urgent to reduce the heat convection in the hollow glass cavity.
Filling a hollow glass with inert gas helps to improve the sealing life and reduce heat convection at the same time. The initial filling concentration and airtightness necessary for filling hollow glass are the basic guarantees to solve these two problems. This article focuses on the related issues involved in increasing the initial concentration of inflatable insulating glass, such as the production process control and product quality testing of inflated insulating glass. It is designed to help those who have inflated the insulating glass but the concentration is less than 90% and those who are considering inflating the insulating glass. The manufacturer of the equipment chooses the correct inflatable equipment.
1. Basic knowledge of inflatable
Generally speaking, the inert gas used in inflatable insulating glass is argon. It has the characteristics of colorless, odorless, and non-toxic, and its molecular weight is 38% heavier than air. The thermal conductivity is smaller than air.
Since the density of argon is higher than that of air, the argon filling (inlet) holes are at the lower end when the hollow glass is filled, and the air outlet (exhaust) holes are at the upper end to replace the air in the hollow glass to reach the required argon concentration.
The inflation process of hollow glass is essentially a process in which the flowing gas transfers from one state of motion to another state. Whether the inflation quality is high or not and whether the gas generates laminar flow or turbulent flow. Therefore, discussing the quality of hollow glass inflation cannot be separated from the discussion of the basic concepts of laminar and turbulent flow.
Laminar flow and turbulent flows are the results of the combined inertia force and viscous force when the viscous fluid moves. The main difference between viscous fluid motion and ideal fluid motion is that the force of the microcluster is viscous in addition to the inertial force. According to the characteristics of these two forces, they have different influences on the behavior of the fluid mass movement. According to the definition, the role of viscous force is to prevent the relative movement of fluid clusters, and the role of inertial force is just the opposite of the role of viscous force. Therefore, the behavior of the flow in viscous fluid flow is determined by the results of these two forces. Under the condition that the effect of viscous force is much greater than that of inertial force, the gas movement produces laminar flow. On the contrary, when the effect of inertial force is much greater than the effect of viscous force, gas movement produces turbulence.
The laminar flow and the turbulence flow 1
Intuitively seen as fluid motion-the simplest image laminar flow can be seen as a fluid layer that is adjacent to each other and has a "determined material meaning", or there is no "fluid line element" that crosses each other to slip. An extension of the movement. Simply put, laminar flow is the stratified flow of fluid. At this time, there is no essential difference in the mechanical mechanism of the fluid under Newtonian viscous stress and the solids resisting each other's sliding motion. The basic characteristics of turbulence are vortex, irregular, random, diffusive, and dissipative. It is composed of vortex structures with different sizes and different frequencies so that the physical quantities show different changes in time and space.
At present, the low inflation quality of hollow glass is largely caused by the turbulence generated during the inflation process. It is assumed that the sensor of the inflatable device only recognizes the concentration of the inert gas collected at the vent hole of the hollow glass. Once the laminar flow and turbulent flow of the inflated hollow glass finally give the inert gas concentration the same standard. It requires people to use the naked eye to distinguish it. The concentration trend of the inert gas in the hollow glass after diffusion. If the high-voltage discharge method is used to detect the initial concentration of such gas-filled insulating glass online, the concentration obtained will be higher than the actual concentration after diffusion.
There are two results:
1) If the manufacturer judges the product with the turbulent flow as qualified to be delivered to the customer or sent to the laboratory for testing, the actual concentration after diffusion will be lower than the concentration at the beginning of the test.
2) This kind of gas-filled insulating glass with obvious changes in concentration will confuse the manufacturer because the product has no flaws in its sealing, and the product tested is only the initial concentration.
The above expressions about the laminar flow and turbulent flow of the fluid are intended to reveal the possibility and characteristics of turbulent flow during the transition of the fluid motion state during the hollow glass inflation process.
2. The influence of turbulence on the inflation process and concentration measurement
Part of the air in the hollow glass cavity cannot be replaced by the filled argon when the gas-filled hollow glass generates turbulent flow. Therefore, the initial concentration of the turbulent gas-filled hollow glass can hardly meet the requirements of the standard. In addition, the turbulence generated during the inflation process causes the air to still exist in the center of the hollow glass cavity. When the hollow glass has turbulent flow, the concentration detected by the air vent sensor is generally higher than the turbulent air in the center of the hollow glass cavity. The complete diffusion of the inert gas of the hollow glass requires 6~8 hours.
If you use this method for online detection, the measured concentration is significantly higher than the actual concentration after diffusion. Therefore, we cannot use this detection method as an online detection method for inflated hollow glass. Otherwise, under the condition of turbulent flow in the air-filled hollow glass, the inspector will give a wrong judgment. For the air-filled hollow glass with turbulent flow, the position of the hollow glass detected by the high-voltage discharge method should be as close as possible to the position of the spacer. According to the three measurement points recommended by the manufacturer, it just avoids the turbulent gas of the inflated hollow glass, that is, the air position and the concentration given is the concentration of the inert gas.
Therefore, it is necessary to get the correct concentration figure after the inflated hollow glass is placed for 6 to 8 hours. According to the survey, the initial concentration of inflatable insulating glass self-tested by some manufacturers is above 90%, but the actual concentration measured by a third party is significantly lower than 90%, and some are even less than 70%. Through the appearance inspection of these gas-filled glass seals with large differences in concentration, it is difficult for us to find any sealing defects. Therefore, we infer that one of the reasons for this phenomenon is caused by turbulence.
The production of secondary sealing of insulating glass 1
However, this detection method is a post-test of product quality. After the inflated hollow glass is placed for 6-8 hours, the second sealant is cured. If the concentration of the inflated hollow glass does not meet the requirements, the rework of the inflated hollow glass is time-consuming and laborious.
In addition, there are two possibilities:
(1) If the inflation method is not improved, we still cannot guarantee that the inflation concentration of the reworked product meets the requirements;
(2) The use of ordinary inflation methods, namely natural inflation and inflation and forced air extraction, cannot avoid turbulence in rabbits.
Even if the randomly checked glass meets the concentration requirements, we cannot unless we have real-time monitoring numbers for each piece of glass during the inflation process. It is guaranteed that the entire batch of gas-filled glass is qualified. It can be seen that unless the inflation equipment we use can effectively avoid the occurrence of turbulence, or always maintain a stable laminar flow during the inflation process, we cannot rule out the authenticity of the concentration detected online. Furthermore, under these conditions, the correct way for us to ensure the concentration of the air-filled insulating glass can only be to control the production process of the air-filled insulating glass rather than the quality control of the product.
3. Production control of inflatable insulating glass
The production process control concept of gas-filled insulating glass is to ensure that the production process of gas-filled hollow glass is in a controlled state and analyze, diagnose, and monitor the production process in the production process that affects the quality of the gas concentration. Its function is to systematically arrange the quality control of the production process, to focus on the factors that directly or indirectly affect the quality of the process, and to develop and implement a control plan to ensure the quality of the process. Argon is a colorless and odorless gas, and its gas concentration is not easy to measure.
The previous test methods can be roughly divided into two types:
1) The sensor compares the gas collected from the exhaust hole with the set gas concentration to determine whether it meets the requirements;
2) The sensor dynamically compares the gas collected by the vent with the set gas concentration and provides real-time curves such as concentration, air pressure, and flow rate not only from the concentration but also from the shape of the curve to determine the actual concentration of the gas.
The comparison of the two values is a description of the entire inflation process. It is the most advanced production control method for real-time monitoring of the inflation process.
The characteristic of the quality control of the concentration of gas-filled insulating glass is that it is a post-mortem product test. The production control of the European insulating glass standard EN1279~6 means that the measurement of the concentration of the inflatable insulating glass composite should be understood as the quality control or inspection of the product rather than the real production process control. The sampling test for the initial concentration of gas-filled insulating glass stipulates that `1 piece/1000 pieces/class` at least 3 pieces. When there are less than 100 pieces of gas-filled hollow glass per shift, one piece shall be spot-checked. It takes about 6 to 8 hours for the argon in the gas-filled insulating glass to completely diffuse. Therefore, the detection of the initial concentration of the argon in the insulating glass can only be carried out after the gas is completely diffused. Therefore, whether it is the online detection of the concentration of the gas-filled insulating glass or the detection after 6 to 8 hours after the inert gas has completely diffused, it can only be a judgment of whether the product is qualified. If the result of this sampling test is overall unqualified, the discovery of the problem is too late.
In summary, the main reason for the low initial concentration of the inflated hollow glass is the turbulence that occurs during the inflation process. The significance of the production control of the inflatable hollow glass is to monitor the entire inflation process in real-time to effectively avoid the turbulence that may occur during the inflation process of the hollow glass and ensure the stability of the inflation quality.
4. Smart inflation technology
After knowing the basic principle of inflating hollow glass and the necessity of the production process of inflatable hollow glass, we need to consider the main inflation technology and specific methods. In summary, the selection of inflatable equipment can be considered from the technical characteristics of the equipment. From the perspective of the degree of integration with the insulating glass production line, the inflation technology is divided into online inflation and offline inflation; in terms of the degree of production automation, the inflation technology is divided into automatic inflation and manual inflation. In a word, online inflation, as the name implies, means that the inflation process is completed on the hollow glass production line after the hollow glass is framed and before the assembly (such as the Lisec production line, the Bystronic production line and the Jinan LIJIANG Glass production line). It has a high degree of automation, a short inflation time, and the advantage of stable concentration. The disadvantage is that the waste of inert gas is large; manual inflation is performed offline after the hollow glass buccal tablet is applied before or after the second sealant is applied. In terms of stock, the characteristics of ordinary manual inflating equipment are slower inflation speed, higher gas consumption, and low concentration. Both methods of inflation indeed require production process control in Europe-some glass manufacturers are upgrading online inflation to adopt real-time monitoring methods.
Generally speaking, there are three main ways to inflate manual inflation equipment: natural inflation, inflation and exhaust at the same time, and program-controlled inflation and exhaust at the same time. The flow rate of natural inflation-the flow rate is about 5 liters/minute. The flow rate of inflation and exhaust at the same time is between 12 and 18 liters/minute. The flow rate of the program-controlled inflation and exhaust process can be as high as 90 liters/minute.
There are three main issues to consider when choosing insulating glass inflation equipment: initial inflation concentration, inflation time, and gas consumption. In this regard, we will first describe them separately and then discuss them together.
Needless to say, the first consideration when choosing an air-filled hollow glass clover is the stability of the air-filled quality of the equipment. The key to increasing the inert gas concentration of the inflated insulating glass is whether the inflating equipment can avoid turbulence during the inflation process to monitor the inflation process in real-time. The characteristic of the natural inflation method is that the equipment investment is small, but the inflation speed is too slow, the inflation concentration does not guarantee the large gas consumption, and it is not suitable for the production of a large amount of hollow glass inflation. The second method is to synchronize inflation and forced air extraction. Although the inflation speed has been increased to shorten the inflation time, forced air extraction can easily cause turbulence in the gas flow in the cavity. When the sensor detects inert gas and judges that it has reached the set value The concentration value may not be the true concentration of gas-filled glass. The third method is program-controlled inflation and pumping. Its essence is to intelligently control the inflation process. Through real-time monitoring of the air pressure and flow rate during the inflation process, greatly improves the inflation speed and avoids the turbulence that may be generated during the inflation process. Ensure the required aeration concentration.
To increase the inert gas concentration of the gas-filled insulating glass, some other details need to be paid attention to. Here is only a list of issues related to the vertical placement of insulating glass when it is inflated. The vertical placement of the inflated hollow glass should be as short as possible on the ground; if the long side has to be placed on the ground, in general, the inflation time should be appropriately extended.
Insulating glass cannot be placed horizontally and inflated. It is difficult for some companies to inflate the hollow glass to achieve the required concentration when making small samples.
The control of the production process of gas-filled insulating glass is an important guarantee for increasing the gas-filled concentration. In contrast, the quality control of inflated insulating glass is post-testing, which is an auxiliary means to ensure the initial concentration of inflation.
Turbulent flow is an important reason for the low inflation quality of hollow glass in the most country. The use of intelligent control rapid inflation method can not only ensure the laminar flow of the inflation process to reach the initial concentration specified by the standard, but also has the advantages of fast inflation speed and low inert gas consumption. In addition, the smart quick inflation equipment is cost-effective, which has the characteristics of small investment and durability. It is a better choice for those enterprises that urgently need to improve the inflation level but cannot find a good inflation method.