1. The main reason for the rise in dew point
The dew point of the insulating glass refers to the temperature at which the humidity of the air sealed in the air layer reaches a state of saturation. Below this temperature, the water vapor in the air layer condenses into liquid or solid water. The correspondence between the dew point and the relative humidity of the air and the water content in the air.
Obviously, the higher the water content, the higher the dew point temperature of the air. When the inner surface temperature 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 dew point of the national standard GB11944-89 „Insulated Glass“ is a 40 ° C). The rise in dew point of the hollow glass is caused by the outside water entering the air layer and not being absorbed by the desiccant. The following three reasons can cause the dew point of the
insulated glass factory to rise:
(1) The mechanical impurities present in the sealant or the capillary pores which are discontinuously squeezed during the rubber coating process, and the water in the air flows or diffuses through the gas under the action of the pressure difference or the concentration gradient inside and outside the air layer. Entry into the air layer increases the moisture content of the hollow glass air layer.
(2) The water vapor diffuses into the air layer through the polymer (the sealant is generally a high molecular polymer). Any polymer is not absolutely gas impermeable, as is the case with the sealant polysulfide rubber, silicone rubber, butyl rubber, etc., which are commonly used for insulating glass. The presence of these polymer materials, their two distortions in the difference in the degree of susceptibility (pressure difference or concentration difference) constitutes the driving force for the isothermal diffusion of the polymer. In a higher degree of fugacity, the aggregated g/J molecule moves into the ring polymer due to adsorbed gas molecules (air and water) and passes through the polymer chain from the other side of the polymer – the lower fugacity The side is released. For the sealant of insulating glass, the main diffuser is the moisture in the air.
The diffusion of water follows the following relationship:
Where: J-diffusion speed. Refers to the amount of diffusion of a certain amount of polymer per unit area per unit area. P-gas permeability coefficient. It is a physical property of materials. The thickness of the L-polymer. The partial pressure difference of the gas on both sides of the P-polymer.
It can be seen from the above formula that the factors affecting the diffusion of water vapor are mainly the gas permeability coefficient (air tightness) of the polymer: the thickness of the rubber layer and the partial pressure difference of water vapor inside and outside the air layer. Water vapor diffusion is the main cause of 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 it is sealed to the air layer. It is a function of the performance of the molecular sieve, the humidity of the air, the amount of loading, and the time it takes to place in the air. The desiccant sealed in the hollow glass air layer mainly has two functions – it is to absorb the water sealed in the air during production – so that the insulating glass has a qualified initial dew point: the second is continuous adsorption from the environment. The desiccant is required to have a strong adsorption capacity by diffusing the moisture in the layer to the air in the layer of the air and keeping the insulating glass consistent with the dew point required for use. If the adsorption capacity of the desiccant is poor, the water that diffuses into the air layer cannot be effectively adsorbed, which causes the water to accumulate in the air, the water pressure rises, and the dew point of the insulating glass rises.
2, the reason for the glass burst
There are many reasons for the bursting of the insulating glass. There are production aspects, as well as installation aspects. The main reasons for glass bursting can be summarized as follows:
(1) Production ambient temperature When the insulating glass is produced, the pressure sealed in the air layer is the pressure at the production environment temperature. During use, it is often the case that the temperature of use and the temperature of the production environment differ greatly. The thermal expansion and contraction of air changes 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 produces a positive pressure, especially with heat absorbing glass and coating. Insulating glass made of glass has a very strong heat absorption effect. The higher the temperature rise in the air layer, the greater the positive pressure produced. When the pressure due to the expansion of the air layer air is higher than the breaking pressure of the glass, the glass may be broken. Most of the glass bursts are caused by this cause. Also in the winter, the ambient temperature is low, and the air in the air layer shrinks to generate a negative pressure. Under the combined action of wind and snow loads, the glass will also burst.
(2) Choosing improper glass. The use of unreinforced heat-absorbing glass on the sunny side of the building, and the use of heat-absorbing glass in the sun-facing surface, it is easy to absorb solar energy and heat up.
(3) The glass is deformed during production. When producing hollow glass by the horizontal method (currently, almost all of the manual production is horizontal), because the area under which the lower glass is supported is small and the support points are mostly at the center, and the weight of the upper glass is all added to the lower glass. The sheet glass is bent upward, resulting in a thinning of the air layer thickness of the insulating glass. When the glass is installed and used, there is naturally a negative pressure in the air layer, and the phenomenon that the glass has a large pre-stressed insulating glass is more prominent. The presence of pre-stress on the glass reduces its resistance to wind pressure and its ability to withstand external forces. It is prone to cracking when external factors change.
(4) Prestressing occurs on the glass when the glass is installed. When the glass is installed, the frame is not flat or the quality of the elastic sealing strip is poor, so that the glass is bent and deformed, so that the pre-stress of the glass and the presence of the pre-stress of the glass reduce the wind pressure resistance of the glass and even burst.
(5) There is a small crack in the edge of the glass. In the production, the quality of the glass edging is not good or the edge of the glass during transportation is not easily found due to collision due to small cracks due to collision (due to the peripheral coating).