With the vigorous implementation of policies and regulations related to building energy conservation around the world, the gradual popularization of building energy conservation knowledge, and the increasing demand for insulating glass with high energy-saving configurations, the market brought about by the large-scale production of Low-E coated glass The relative increase in increments makes it possible to continuously increase the effective demand for high-performance insulating glass. As a result, Low-E coated insulating glass has become more and more widely used. However, the application of Low-E glass brings two problems that we have not encountered before:
Insulating glass filled with inert gas helps to improve the sealing life and reduce heat convection while inflating. The necessary initial inflation concentration and air tightness of the insulating glass are the basic guarantees to solve these two problems.
1. The Basic Knowledge of Inflating Argon Gas
Generally speaking, the inert gas used in the inflatable insulating glass is argon, which is colorless, odorless and non-toxic. Its molecular weight is 38% heavier than air and the thermal conductivity is smaller than air.
Because 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 achieve 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 insulating glass inflation cannot be separated from the discussion of the basic concepts of laminar and turbulent flow.
Laminar flow and turbulent flow are the result of the combined action of inertial force and viscous force when 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.
Figure 1 The basic concepts of laminar flow and turbulent 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 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 physical quantities show different changes in time and space.
At present, the low inflation quality of insulated glass in developed country is caused to a large extent 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 insulated glass. Once the laminar flow and turbulent flow of the inflated insulated glass finally give the inert gas concentration the same standard, people cannot distinguish it with the naked eye. The concentration trend of the inert gas in the insulated glass after diffusion. If the high-voltage discharge method is used to detect the initial concentration of such gas-filled insulated glass online, the concentration obtained will be higher than the actual concentration after diffusion.
There are two results:
The above-mentioned expression about the laminar flow and turbulent flow of fluid is to reveal the possibility and characteristics of turbulent flow during the transition of the fluid motion state during the inflation process of insulating glass.
Figure 2 The automatic insulating glass production line with inflation processing
2. The Influence of Turbulence on the Inflation Process Anconcentration Measurement
When turbulent flow occurs in the air-filled insulated glass, part of the air in the insulated glass cavity cannot always be replaced by the filled argon gas. Therefore, the initial concentration of the air-filled insulated glass with turbulent flow 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 insulated glass has turbulent flow, the concentration detected by the hollow glass vent sensor is generally higher than the turbulent air in the center of the hollow glass cavity, and the complete diffusion of the inert gas of the insulated glass requires 6~8 hour.
"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 insulating glass. Otherwise, under the condition of turbulent flow in the air-filled insulated glass, the inspector will give a wrong judgment. For the air-filled insulated glass with turbulent flow, the position of the insulating 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 flow of gas filled insulating glass, that is, the air position, and the concentration given is the concentration of inert gas.
Therefore, it is necessary to get the correct concentration figure after the inflated insulating 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.
However, this testing method is a post-test of product quality. After the inflated insulating glass is placed for 6-8 hours, the second sealant is basically cured. If the concentration of the inflated insulating glass does not meet the requirements, the rework of the inflated insulating glass is time-consuming and laborious.
Figure 3 The insulating glass filled with argon gas detection 1
There are two other possibilities:
Furthermore, under these conditions, the correct way for us to ensure the concentration of the air-filled insulating glass is to control the production process of the air-filled insulating glass instead of the quality control of the product.
3. The Production Control of Gas-filled Insulating Glass Producing
The production process control concept of inflatable insulating glass is the analysis, diagnosis and real-time monitoring of the operation technology and the production process adopted to ensure that the inflatable insulating glass production process is in a controlled state and the production process that affects the quality of the inflated 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:
First, the sensor compares the gas collected from the exhaust hole with the gas concentration set to determine whether it meets the requirements;
Second, the sensor dynamically compares the gas collected by the vent with the set gas concentration and gives real-time curves of 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 inflatable insulating glass is that it belongs to the non-qualified product inspection after the fact. The production control of the European insulating glass standard actually 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 inflatable insulating glass stipulates that at least 3 pieces of inflatable insulating glass are less than 100 pieces per shift. 1 piece shall be sampled. It takes about 6-8 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 performed 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 or not. 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 inflated insulating 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 so as 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 understanding the basic principle of insulating glass inflation and the necessity of the production process of inflatable insulating glass, we need to consider the main inflation technology and specific methods. In a nutshell, 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. Generally speaking, 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 sheet is assembled. It has the advantages of high automation, short inflation time and stable concentration. Details can be seen in insulating glass air-floating production line; manual inflation is carried out offline after the hollow glass is made of tablets, before or after the second sealant coating. In terms of stock: ordinary manual inflating equipment is characterized by slower inflation speed, higher gas consumption, and low concentration. It is true that both inflation methods require production process control. Some world-renowned glass manufacturers are upgrading online inflation to adopt real-time monitoring methods. In China, only the fully automatic insulating glass air-floating production line has real-time monitoring of the inflation process and The function of the inflatable effect.
Video 1 The Argon Gas Filling Processing on Insulating Glass Production Line
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.
The choice of insulating glass filling equipment mainly needs to consider three aspects: initial filling concentration, filling 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 insulating glass production line is the stability of the air-filled quality of the equipment. The key to increasing the inert gas concentration of the inflated hollow 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 carry out inflation and forced air extraction simultaneously. Although the inflation speed is increased and the inflation time is shortened, forced air extraction can easily cause turbulence in the gas flow in the cavity. When the sensor detects the inert gas and judges that it has reached the setting 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, the inflation speed is greatly improved, and the turbulence that may be generated during the inflation process is avoided. Ensure the required aeration concentration.
In order to increase the inert gas concentration of the gas-filled insulating glass, 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 gas-filled insulating glass is an after-the-fact test that is an auxiliary means to ensure the initial concentration of the gas. Turbulent flow is an important reason for the low inflation quality of insulating glass. 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 intelligent rapid inflation equipment is cost-effective, has a small investment, and is durable. For those enterprises that need to improve the inflation level but cannot find a good inflation method, the air-floating insulating glass production line produced by LIJIANG Glass is a kind of a better choice.