The hollow glass is filled with inert gas, which not only helps to improve the energy-saving effect of the hollow glass but also helps to protect the film layer of the offline Low-E glass. Therefore, it is very important to discuss how to improve the initial concentration and airtightness of the gas hollow glass. This article's purpose is to discuss the production control of inflatable insulating glass and product quality inspection, with a focus on production process control, and a brief discussion on the current manual inflation methods.
Initial concentration, laminar flow, turbulent flow, production process control, quality inspection, inert gas diffusion of inflatable insulating glass
With the vigorous implementation of policies, guidelines, and regulations related to building energy conservation in various countries around the world, and the gradual popularization of building energy conservation knowledge, people's demand for insulating glass with high energy-saving configuration is also increasing, and the large-scale production of low-emissivity coated glass has brought market growth. The relative increase in the amount has made it possible to continuously increase the effective demand for high-performance insulating glass. As a result, more and more widespread applications of low-emissivity coated insulating glass have emerged, which is in the ascendant. However, the application of Low-E glass has brought about two problems that we have not encountered before. After the radiation problem, it becomes very urgent to reduce the heat convection in the hollow glass cavity.
Inert gas filling of hollow glass helps to improve the seal life and reduce heat convection at the same time, and the necessary initial filling concentration and airtightness of the filled 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 gas-filled insulating glass, such as the production process control of gas-filled hollow glass and product quality testing. Manufacturers of glass inflatable equipment choose the correct inflatable equipment.
Basic knowledge of inflatable
Generally speaking, the inert gas used in gas-filled insulating glass is argon, which is colorless, odorless, and non-toxic. Its molecular weight is 38% heavier than air, and its thermal conductivity is smaller than air.
Since the density of argon is higher than that of air, when the hollow glass is inflated, the argon filling (inlet) pores are at the lower end, and the air outlet (exhaust) pores 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. Whether the inflation quality is high or not is related to whether the gas produces laminar flow or turbulence. Therefore, discussing the quality of insulating glass inflation cannot be separated from the discussion of the basic concepts of laminar flow and turbulent flow.
The result of the combined action of inertial force and viscous force when the viscous fluid moves. The main difference between viscous fluid motion and ideal fluid motion is that in addition to inertial force, there is also a viscous force on the micelles. According to the characteristics of these two forces, they have different effects on the motion behavior of fluid micelles. By 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, in the flow of viscous fluid, the flow behavior is determined by the results of these two forces. The result of the combined action of inertial force and viscous force when the viscous fluid moves. 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, the gas movement produces turbulence.
Figure 1 The difference between laminar flow and turbulent flow 1
Intuitively, as the simplest image of fluid motion, laminar flow can be seen as fluid layers that are adjacent to each other and have "deterministic material meaning", or there are no "fluid line elements" that cross each other. An extension of sliding motion. Simply put, laminar flow is the stratified flow of fluid. At this time, there is no essential difference between the Newtonian viscous stress of the fluid in motion and the mechanical mechanism that resists each other's sliding motion between solids. The basic characteristics of turbulence are vorticity, irregularity, randomness, diffusivity, and dissipativeness. It is a kind of vortex structure of different sizes and different frequencies so that its physical quantity changes in time and space. Out of irregular randomness.
Figure 2 Schematic diagram of turbulent flow when insulating glass is inflated
Figure 3 Schematic diagram of turbulence curve during the inflation process of insulating glass
At present, the inflation quality of hollow glass is not high, which is caused to a large extent by the turbulence generated during the inflation process (see Figure 2 and Figure 3). It is assumed that the sensor of the inflatable device only recognizes the concentration of inert gas collected at the vent hole of the hollow glass, and the final inert gas concentration is given by the laminar flow and turbulent flow of the inflated hollow glass also meets the standard requirements, and people can't distinguish with the naked eye. Which piece of insulating glass has the concentration trend of the inert gas after diffusion. If the high-voltage discharge method is used to detect the initial concentration of such gas-filled insulating glass online, the obtained concentration will be higher than the actual concentration after diffusion.
There are two results: (1) If the manufacturer judges that the product with turbulence is qualified for delivery 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) The gas-filled insulating glass with the obvious change of concentration will confuse the manufacturer because the product has no defects in the sealing, and the product tested is only the initial concentration.
The above expressions of laminar flow and turbulent flow of fluids are intended to reveal the possibility and characteristics of turbulent flow during the transition of the fluid motion state of the hollow glass during inflation. Further elaboration on this is beyond the scope of this article, and this article The key point is to discuss the influence of turbulence on the concentration during the inflation process and how to avoid the generation of turbulence.
Figure 4 3-point measurement of high voltage discharge
Influence of turbulence on inflation process and concentration measurement
When turbulent flow occurs in the gas-filled hollow glass, part of the air in the hollow glass cavity cannot be replaced by the filled argon gas. Therefore, the initial concentration of the gas-filled hollow glass with the turbulent flow can hardly meet the requirements specified in the standard. In addition, the turbulence generated during the inflation process makes the air still exist in the center of the hollow glass cavity. When the hollow glass has turbulent flow, the concentration detected by the hollow glass vent sensor should generally be higher than the inert gas of the hollow glass to completely diffuse the turbulent air in the center of the cavity, and the inert gas of the hollow glass It takes 6-8 hours for the complete diffusion. If this method is used 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 inflated hollow glass, the inspector will give a wrong judgment. If there is a turbulent air-filled hollow glass, 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 (see Figure 2). According to the three measurement points recommended by the manufacturer, it just avoids the turbulent air position of the air-filled insulating glass, and the concentration given is the concentration of the inert gas (see Figure 4); therefore, it is necessary to place 6 in the air-filled insulating glass. After -8 hours, get the correct concentration figure. According to the survey, some manufacturers self-test the initial concentration of gas-filled insulating glass above 90%, but the actual concentration measured by a third party is significantly lower than 90%, and some are even less than 70%. It is difficult for us to find any sealing defects through the appearance inspection of these gas-filled glass seals with large differences in concentration. 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 solidifies. If the concentration of the inflated insulating glass does not meet the requirements, the rework of the inflated insulating glass is a time-consuming and laborious task. 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) It is impossible to use ordinary inflation methods, namely natural inflation and inflation and forced extraction. To avoid turbulence, even if the randomly inspected glass meets the concentration requirements, unless we have real-time monitoring numbers for each piece of glass during the inflation process, we cannot accurately guarantee that the entire batch of inflated glass is qualified.
It can be seen that unless the inflatable equipment we use can effectively avoid the occurrence of turbulence or always maintain a stable laminar flow in the inflating 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, not the quality control of the product.
Inflatable hollow rose production control
The concept of production process control of inflatable insulating glass is to ensure that the production process of inflatable insulating glass is in a controlled state, and the analysis, diagnosis, and real-time monitoring of the operation technology and production process adopted in the production process that affects the quality of the inflatable concentration. Its role 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 formulate and implement control plans to ensure the quality of the process. Argon is a colorless and odorless gas, and its filling concentration is not easy to measure. The current test methods can be roughly divided into two types: (1) The sensor compares the gas collected from the exhaust air with the set gas concentration to determine whether it meets the requirements; (2) The sensor collects the gas from the exhaust air. The gas is dynamically compared with the set gas concentration and real-time curves such as concentration, air pressure, and flow rate are given. It is judged not only from the concentration but also from the shape of the curve, the actual concentration of the gas. Compared with the two, because the second method is not only a comparison of two sets but a description of the entire inflation process, it is the most advanced production control method for real-time monitoring of the inflation process.
The quality control of the concentration of gas-filled insulating glass is characterized by the fact that it is a substandard product inspection. The production control of the European insulating glass standard EN1279-6 refers to the measurement of the concentration of the inflatable hollow glass composite. It should be understood as the quality control or inspection of the product, rather than the real production process control. The sampling test of the initial concentration of the inflatable insulating glass stipulates that 1 piece/1000 pieces/class, at least 3 pieces, when the inflated hollow glass is less than 100 pieces per shift, 1 piece shall be randomly checked. The argon in the gas-filled insulating glass takes about 6-8 hours to completely diffuse. Therefore, the detection of the initial concentration of 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 6-8 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, to effectively avoid the turbulence that may occur during the inflation process of the hollow glass, and to improve and ensure the stability of the inflation quality.
Smart inflation technology
After clarifying the basic principle of the inflation of insulating glass and the necessity of the production process of inflatable insulating glass, we need to consider the main inflation technology and specific methods next. In a nutshell, the choice of inflatable equipment can be considered from the technical characteristics of the equipment. From the perspective of the degree of integration with the hollow glass production line, the inflation technology is divided into online inflation and offline inflation; from the perspective of the degree of production automation, the inflation technology is divided into automatic inflation and manual inflation. Generally speaking, online inflation, as the name suggests, means that the inflation process is done on the hollow glass production line. The inflation process is completed after the frame of insulating glass and before the assembly (such as the Lisec production line, the Bystronic production line and Jinan LIJIANG Glass production line). It has a high degree of automation. , It is completed before the assembly (such as the Lisec production line, the Bystronic production line and Jinan LIJIANG Glass production line). It has the advantages of high automation, short inflation time, and stable concentration. The disadvantages are a large waste of inert gas; manual inflation is performed in the second after the insulating glass is combined. The sealant is applied offline before or after coating. Generally speaking, ordinary manual inflating equipment is characterized by slower inflation speed, higher gas consumption, and low concentration. Both inflating methods indeed require production process control. Some European glass manufacturers use real-time monitoring for online inflation upgrades, but the focus of this article is to discuss manual inflation methods.
The display video of Jinan LIJIANG Glass insulating glass inflation process 1
Generally speaking, there are three main ways to inflate manual inflation equipment: natural inflation, inflation and exhaust at the same time, and program control inflation and exhaust at the same time (see Table 1). The flow rate of natural inflation is generally about 5 liters/minute, the flow rate of inflation and exhaust at the same time is between 12-18 liters/minute, and the flow rate of program-controlled charging and exhausting 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 first describe them separately and then discuss them together.
Needless to say, the first consideration when choosing a gas-filled insulating glass is the stability of the gas-filled quality of the equipment. The key to increasing the concentration of inflated hollow glass lies in whether the inflatable equipment can avoid the appearance of turbulence during the inflating process and monitor the inflating 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 is not guaranteed, and the gas consumption is large, which is not suitable for the production of a large amount of hollow glass inflation. The second method is to synchronize the inflation and forced air extraction. Although the inflation speed is increased and the inflation time is shortened, the forced air extraction easily causes the turbulence of the gas flow in the cavity to appear. When the sensor detects the inert gas and judges that it has reached When the concentration value is set, it may not be the true concentration of gas-filled glass. The third method is program control inflation and pumping. The 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. Flow, thus ensuring the required aeration concentration (see Figure 5 above).
Figure 5 The laminar flow curve display of the hollow glass inflating process
To increase the concentration of 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 insulating glass should be as short as possible on the ground; if the long side has to be placed on the ground, in general, it should be considered to extend the inflation time appropriately.
Insulating glass cannot be placed horizontally and inflated. Some companies inflate the hollow glass flat when making small samples, and it is difficult to achieve the required concentration.
The production process control 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 a post-test, which is an auxiliary means to ensure the initial concentration of inflation.
At present, 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 inert gas consumption. advantage. In addition, the smart fast inflatable equipment is cost-effective, has the characteristics of small investment, and durability. It is a good choice for those enterprises that urgently need to improve the inflation level but cannot find a good inflation method.