Cause analysis and countermeasures for the failure of insulating glass
Insulating glass has been widely used as a high- and mid-range material in construction and other fields. In addition to the large-scale use in construction, the consumption in other industries such as railway transportation and refrigeration industries is also gradually increasing.
Insulating glass has been widely used as a high- and mid-range material in construction and other fields. In addition to the large-scale use in construction, the consumption in other industries such as railway transportation and refrigeration industries is also gradually increasing. As a deep-processed product of glass, insulating glass is more expensive and is often used in key parts, such as high-rise buildings, train air-conditioning windows, refrigerator observation windows, etc. After installation and use, it is very difficult to replace it once there are quality problems and damages, and the replacement cost is very high. Therefore, higher requirements are put forward for the long-term effective use of insulating glass. Although there is no clear regulation on the effective use time of insulating glass, the manufacturer should take various measures to ensure that the effective use time of insulating glass is long enough to meet the needs of various uses.
Insulating glass is a glass product in which two or more pieces of glass are separated by a spacer frame with a desiccant in the middle, and the periphery is sealed. It is a composite product, and its performance and functions are different from ordinary glass. There are problems with service life and expiration date. The main reasons that affect the effective use time of insulating glass are the increase in the dew point of the air layer, the loss of the integrity of the glass, and the attenuation of the function. The original intention is many aspects such as the performance of the manufacturing material, the manufacturing process and control, and the installation method. This article analyzes various factors that affect the effective use time of insulating glass and proposes measures to extend the effective use time of the insulating glass.
1. The main reason for the failure of insulating glass
There are two direct reasons for the failure of insulating glass: One is the rise of dew point in the air layer. When the ambient temperature is reduced to make the temperature of the glass surface lower than the dew point of the gas in the air layer, the water vapor in the air layer will produce condensation or frost on the inner surface of the glass (the condensation on the inner surface of the glass is higher than 0°C). Frosting at 0℃). Due to condensation or frost on the inner surface of the glass, it will seriously affect the perspective of the insulating glass and reduce the insulation effect of the insulating glass (the term "insulation" is provided by the industry encyclopedia). At the same time, long-term condensation will occur. Make the inner surface of the glass mildew or alkali evolution' to produce white spots. The second is the explosion of insulating glass. Hollow glass explodes due to improper installation, environmental temperature changes, sunlight and wind pressure during installation and use. After the glass breaks (even if there are very small cracks), it will lose its tightness. Condensation and frost appear in the air and lose their function.
We have investigated the failure of insulating glass after two years of use. The failure rate is 3-5%. The ratio of various failure causes is shown in Table 1. It can be seen from Table 1 that's the largest proportion of failure caused is the rise in dew point (condensation in the hollow layer)' followed by glass burst. These two reasons constituted 89% of the total failures.
2. Analysis of the causes of failure of insulating glass
2.1 The main reason for the increase in dew point:
The dew point of hollow glass refers to the temperature when the humidity of the air sealed in the air layer reaches a saturated state. When the temperature is lower than this temperature, the water vapor in the air layer will condense into liquid or solid water. See Table 2 for the correspondence between dew point, relative humidity of the air, and moisture content in the air.
The higher the water content, the higher the dew point temperature of the air. When the temperature of the inner surface of the glass is lower than the dew point of the air in the air layer, the water in the air will condense or frost on the inner surface of the glass (the international standard "Insulating Glass" stipulates that the dew point is -40°C). The increase in the dew point of the hollow glass is caused by the fact that water from the outside enters the air layer but cannot be absorbed by the desiccant. The following three reasons can cause the dew point of insulating glass to rise:
(1) Mechanical impurities in the sealant or capillary holes that are discontinuously extruded during the gluing process during production. Under the action of the pressure difference or concentration gradient between the inside and outside of the air layer, the water in the air circulates or diffuses through the gas. Entering into the air layer increases the moisture content in the hollow glass air layer.
(2) Water vapor diffuses through polymers (the term "polymer" is provided by Google) (sealants are generally high molecular polymers) into the air layer. No polymer is impermeable, such as polysulfide rubber, silicone rubber (the term "silicone rubber" is provided by Google), butyl rubber, etc., which are usually used as sealants for insulating glass. For these polymer materials (the term "polymer material" is provided by Google), the existence of the fugacity difference (pressure difference or concentration difference) of the two guillotines constitutes the driving force for the isothermal diffusion of polymers. In the higher fugacity, the polymerized g/J molecules enter the ring polymer due to the adsorption of gas molecules (air and water), move, and pass through the polymer chain from the other side of the polymer-lower fugacity Release on one side. For insulating glass sealant, the main diffuser is the moisture in the air.
The diffusion of water follows the following relationship:
J=P/L P (1)
In the formula:
J-diffusion rate.
Refers to the amount of diffusion of gas through a certain thickness of polymer per unit time and unit area. P-gas permeability coefficient. It is a physical property of the material garden.
L-Polymer thickness
P-The gas partial pressure difference on both sides of the polymer
It can be seen from the above formula that the main factors affecting the diffusion of water vapor are the gas permeability coefficient (air tightness) of the polymer: the thickness of the glue layer and the water vapor partial pressure difference between the inside and outside of the air layer.
Water vapor diffusion is the main reason for the failure of insulating glass.
(3) The effective adsorption capacity of the desiccant is low. The effective adsorption capacity of the hollow glass desiccant refers to the adsorption capacity of the desiccant after being sealed in the air layer. It is a function of molecular sieve performance, air humidity, filling amount, and time in the air. The desiccant sealed in the air layer of the hollow glass has two main functions: it is to absorb the water sealed in the air during production so that the hollow glass has a qualified initial dew point: the second is the continuous adsorption from the environment The water that diffuses into the air layer through the glue layer keeps the insulating glass always having a dew point that meets the requirements of use. Therefore, the desiccant must have a strong adsorption capacity. If the adsorption capacity of the desiccant is poor and cannot effectively absorb the water that diffuses into the air layer, it will cause the water to accumulate in the air, the water pressure will increase, and the dew point of the insulating glass will increase.
The dew point of insulating glass 1
2.2 Reasons for glass burst:
There are many reasons for the hollow glass to burst. There are production aspects and installation aspects. The main causes of glass burst can be summarized as the following:
(1) Production environment temperature
When producing insulating glass, the pressure sealed in the air layer is the pressure at the production environment temperature. During use, there is often a large difference between the use temperature and the production environment temperature. The thermal expansion and contraction of air will change the pressure of the air layer. In summer, the ambient temperature is generally higher than the production environment temperature. The air in the hollow glass air layer expands, and the air layer generates positive pressure, especially with heat-absorbing glass and The insulating glass made of coated glass has a strong heat absorption effect. The higher the temperature rise in the air layer, the greater the positive pressure generated. When the pressure caused by the expansion of the air layer is higher than the breaking pressure of the glass, the glass will break. Most of the glass bursts are caused by this reason. Also in winter, when the ambient temperature is low, the air in the air layer shrinks and produces negative pressure. Under the combined action of wind and snow loads, the glass will also burst.
(2) Improper selection of glass
Using unreinforced heat-absorbing glass on the sun-facing side of the building, the curved heat-absorbing glass can easily absorb solar energy and heat up when used on the sun-facing side, causing a thermal explosion.
(3) Glass is deformed during production
When the horizontal method is used to produce insulating glass (at present, almost all manual production is the horizontal method) because the lower glass is less supported by the area and the supporting points are mostly in the center, the weight of the upper glass is all added to the lower glass. The piece of glass bends upwards (the term "bend" is provided by the industry encyclopedia), which results in the thinning of the air layer of the insulating glass. When the glass is installed and used, there is naturally a negative pressure in the air layer, and the phenomenon of hollow glass with a large prestressed area on the glass is more prominent. Due to the existence of prestress on the glass, it reduces its wind pressure resistance and external force resistance. It is prone to breakage when external factors change.
(4) When installing glass, prestress is generated on the glass
When the glass is installed, the frame is not flat or the quality of the elastic sealing strip is not good, which causes the glass to bend and deform, which causes the glass to be prestressed.
(5) There is a small crack in the edge of the glass
The quality of glass edging is not good in production or small cracks are generated on the edge of the glass due to collision during transportation, and it is not easy to be found before installation (due to the surrounding glue). After installation, the cracks grow, and the glass breaks.
The main causes of insulating glass burst 1
3. Measures to extend the use time of insulating glass
To extend the effective use time of insulating glass, it must be controlled from various aspects such as production process conditions, raw material selection, transportation, and installation, etc.
3.1 Strictly control the humidity of the production environment
The humidity of the production environment mainly affects the effective adsorption capacity and remaining adsorption capacity of the desiccant. The remaining adsorption capacity means that after the insulating glass is sealed, the desiccant absorbs the moisture in the air to make the initial dew point meet the requirements, and the desiccant also has a certain adsorption capacity. This part of the adsorption capacity is called the residual adsorption capacity. Quantitatively speaking, It is equal to the effective adsorption capacity minus the adsorption capacity of the desiccant to absorb water in the air sealed in the air layer.
The function of the remaining adsorption capacity is to continuously absorb the water that diffuses into the air layer from the periphery. The size of the remaining adsorption capacity determines the adsorption capacity of the insulating glass desiccant for the insulating glass during the use of the insulating glass, and the size of the adsorption capacity of the water that diffuses into the air layer through the edge, and also determines the speed of the accumulation of water in the air, thus determining It depends on the length of effective use time of the insulating glass.
The production environment of insulating glass processing
When the humidity of the insulating glass production environment is high, the moisture first sealed in the air is large, and the adsorption capacity of the consuming desiccant is large, and the remaining adsorption capacity is small. When the environmental humidity increases from 40% to 80%, the moisture content in the air doubles: Secondly, the environmental humidity has a great influence on the adsorption rate of the desiccant. The greater the humidity, the faster the absorption rate of the desiccant, and the general production process The desiccant should be exposed to the air for some time. During this period, the adsorption capacity of the desiccant is proportional to the environmental humidity. The remaining adsorption capacity of the desiccant decreases with the increase of humidity, so the humidity is effective for insulating glass. The impact of usage time is of utmost importance. To extend the effective use time of insulating glass, it is necessary to control the humidity of the production environment to a lower level.
3.2 Reduce the diffusion of water through the polymer
(1) Choose a sealant with a low permeability coefficient
Choosing an insulating glass sealant with a low gas permeability coefficient is one of the effective measures to reduce the gas diffusion rate. Commonly used sealants in the production of insulating glass are T-based rubber, polysulfide rubber, and silicone rubber. Their gas permeability coefficients are butyl rubber ← 15g/m DCM, polysulfide rubber 7-8g/m DCM, and silicone rubber 1015g/m DCM. It can be seen that the gas permeability coefficient of butyl rubber is the smallest. With butyl rubber, its useful life is better than single-pass sealed insulating glass. The sealant of single-pass insulating glass should be polysulfide glue instead of silicone rubber.
(2) Reasonably determine the thickness of the adhesive layer
It can be seen from formula (1) that the amount of gas diffused through the polymer is inversely proportional to the thickness of the glue layer. The thicker the glue layer, the less the amount of diffusion. Therefore, the national standard stipulates: When using double sealant, the thickness of the glue layer is 5-7mm `When using a single-layer sealant, the thickness of the adhesive layer is 8-12mm` to ensure that the thickness of the adhesive layer is also an important part of reducing the diffusion of water vapor. The thickness and uniformity of the adhesive layer must be ensured during production.
(3) Reduce the difference in humidity between the inside and outside of the insulating glass glue layer.
The diffusion of gas in formula (1) is proportional to the partial pressure difference of water vapor inside and outside the insulating glass. Reducing the difference in humidity between the inside and outside of the glue layer can reduce the diffusion of water vapor through the glue layer. As an insulating glass, the lower the humidity (partial pressure of water vapor) of the air layer, the better. To reduce P, the only way to reduce the humidity (or partial pressure of water vapor) of the external environment is to achieve. To achieve this goal, the installation frame can be opened with drainage holes so that the accumulated water flowing into the frame along the glass surface can be quickly discharged, to keep the glass periphery dry and reduce the amount of water vapor diffusion of the hollow glass.
3.3 Shorten the production process time
The shortening of the production process time here means to minimize the time that the desiccant is in contact with the atmosphere during the production of hollow glass to reduce the loss of adsorption capacity so that the desiccant has a higher residual adsorption capacity, that is, the desiccant is sealed in the hollow glass Try to minimize the loss of adsorption capacity before the middle.
3.4 Reasonably control the air gap of the partition frame
The desiccant is generally poured into the partition frame under the condition of sealing. The water in the adsorbing atmosphere is carried out through the air guiding slot (hole). The larger the air guiding slot (hole), the higher the water absorption rate of the desiccant during the production process. The faster the effective adsorption capacity is, the greater the loss. Therefore, the air conduction gap of the insulating glass partition frame is as small as possible. As long as the insulating glass can be guaranteed to have an initial dew point that meets the requirements of the standard, it is more appropriate.
3.5 Choose a desiccant with an appropriate adsorption rate
For the production of insulating glass, sometimes the infusion of desiccant is not carried out in a completely sealed environment. During the infusion process, the desiccant is exposed to the air and will quickly absorb water from the air. If the adsorption rate of the desiccant is low, the adsorption amount of the desiccant at the same time will be small, and the effective adsorption capacity lost will also be small.
The insulating glass desiccant 1
3.6 Reasonable packaging and transportation
Insulating glass packaging boxes and packaging racks, the supporting parts of the glass are best placed around the glass so that the pressure is transmitted through the spacer frame to reduce the damage of the glass` Provided) consistent with the forward direction of transportation.
3.7 When installing, try to make sure that there is no pre-stress on the glass.
The frame of the installation should be flat. Ensure that the surrounding material in contact with the glass is a good elastic material so that the glass does not produce any deformation.
3.8 Reasonable choice of hollow glass structure
When hollow glass is used on the roof, especially the hollow glass made of heat-absorbing glass because it bears its weight and snow load, it is close to the vertical load in summer and the wind pressure load is large, so the glass is easy to break. The single piece of insulating glass in this part should preferably be tempered.
4. Conclusion
Through the selection, processing and manufacturing, packaging, transportation and installation, and other links to control "can prevent premature failure of insulating glass" to extend its use time and reduce maintenance costs. This will not only bring economic benefits but also get better social benefits and corporate reputation.
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