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Analysis and avoidance of the reasons for the rupture of building insulated glass.

In recent years, with the rapid economic and social development of some developing countries and the promotion of urbanization and building energy conservation policies, the building-insulated glass manufacturing industry has also made great progress. As a glass structure with good performance, insulated glass refers to a product in which two or more pieces of glass are evenly spaced with effective support and bonded and sealed at the periphery so that a dry gas space is formed between the glass layers. It has good performance and functions such as heat insulation, heat preservation, sound insulation, anti-condensation, energy saving, safety, environmental protection, and new decoration, and is widely used in the construction industry.

With the increasing market demand for insulated glass and its wide application in the construction field, the quality of insulated glass in various countries in the world is uneven, and there is a serious phenomenon of inferior quality in the market, and the quality of insulated glass products will be on the agenda, especially the problem of broken insulated glass, which is directly related to the safety of people's living and living environment, has emerged. This article will analyze the reasons for the rupture of insulated glass and build evasion measures in the whole process of building from project initiation to use.

1. Geographical environment

Factors such as shade, orientation, climate temperature difference, air pressure, and other factors in the geographical environment of the building may cause uneven distribution of the temperature difference of the insulated glass so that the temperature difference of the glass exceeds the limit and breaks.

1.1 The Property Location of Glass Curtain Wall Building

The outdoor objects of the building or the building structure itself leave shadows on the insulated glass, resulting in different heat absorption in different parts of the insulated glass and there is a temperature difference. The more irregular the shadow shape, the easier the glass is to break. For example, for glass installed in an environment where sunlight is not uniform, half of it is exposed to direct sunlight, and the other half is shaded by awnings, columns, porches, etc., while the rear of the other half is a transparent room; the glass installed on the ground at one end or the vertical side against the wall is easy to cause uneven distribution of temperature difference so that the temperature difference of the glass exceeds the limit and breaks.

The orientation of building insulated glass is very important. For example, the insulated glass installed facing east and south in cold and temperate regions with a large temperature difference between morning and evening is easy to break. The thermal stress of the glass facing south, north, or other directions is different, especially for the glass with larger heat absorption, the glass used in the east, southeast, south, and southwest is much more heat-absorbing than other surfaces; The thermal stress cracking of the glass should be considered as an important factor in the design. It is recommended to strengthen the glass and process it into tempered, semi-toughened (coated) insulated glass or choose white glass or coated insulated glass with high light transmittance.

1.2 Environmental changes

Changes in ambient temperature and air pressure will cause changes in the structure of the insulated glass part and the overall system. Once this change exceeds the limit that the insulated glass can bear, it will cause the insulated glass to break.

The single piece of glass that constitutes the insulated glass is broken due to thermal stress caused by thermal expansion and contraction due to changes in ambient temperature. Glass will expand and contract under the influence of temperature changes. The linear expansion coefficient of glass is 1*10-5, and a piece of glass with a side length of 1500 mm. In the high-temperature season of summer in the southern hemisphere, when the temperature rises by 80 °C under the sunlight, it will When the extension is 1.2 mm, the thermal stress in the glass body increases and the width and thickness of the structural adhesive are too large, which affects the free expansion and contraction of the insulated glass and aggravates the glass breakage. Whether the glass is strengthened or not is determined according to the above situation, and the color, size, and type of the selected glass should be implemented in strict accordance with the relevant specifications.

The structure of the insulated glass system breaks the glass due to the thermal expansion and contraction of the gas in the spacer layer caused by the difference in ambient temperature. When working with insulated glass, the pressure sealed in the spacer layer is the pressure at the working environment temperature. In the summer of the northern hemisphere, the operating environment temperature of insulated glass is generally higher than the operating environment temperature, and the air in the spacer layer expands and generates positive pressure, especially the insulated glass made of heat-absorbing glass or coated glass, the heat-absorbing effect of glass The higher the air temperature in the spacer layer, the greater the positive pressure generated. Glass breaks when the pressure due to the expansion of the spacer air is higher than the glass's breaking pressure. Also in winter, when the operating environment temperature is higher than the operating environment temperature, the air in the spacer layer shrinks, and negative pressure is generated. When the glass area is large and the spacer layer is small, the center of the two pieces of glass may be stuck together. Deformation beyond the limit will break.

Figure 1 Thermal expansion and contraction of insulated glass

Figure 1 Thermal expansion and contraction of insulated glass

The air pressure between the working place and the place where the insulated glass is used is quite different, and the insulated glass can also be deformed and broken. The difference in air pressure between different regions is also different. When the deformation caused by this air pressure exceeds the limit of the glass, it will break. To solve the deformation problem caused by the air pressure difference of the insulated glass, it is necessary to install the pressure regulating device (such as a breathing tube, capillary or pressure regulating valve, etc.) during the operation of the insulated glass, or to correct the insulated glass at the construction site.

2. The Architectural Design

At present, with the pursuit of architectural space effect and function of buildings by architects and the advocacy of national energy-saving policies, the selection of insulated glass should comprehensively consider the performance, function, and appearance of glass. When choosing to use heat-absorbing glass and coated glass as the original sheet to make insulated glass, the thermal expansion coefficient of coated glass is much larger than that of ordinary glass, and the thermal stress is more obvious. When designing, not only the selection of insulated glass but also the use environment must be considered. After a comprehensive evaluation, it is determined, such as building location, orientation, ambient temperature, and other factors, as well as the color of the glass, light transmittance, shading effect, etc. It is recommended to use reinforced heat-absorbing glass or coated glass with higher light transmittance to make insulated glass, and calculate the thermal stress of the glass following the relevant industry standard "Technical Regulations for Architectural Glass Application".

The choice of glass thickness and size is critical, and wind loads and thermal stresses must be considered. The structural deformation caused by the interlayer changes of the main structure of the building under the action of wind loads can also make the glass ruptured civil structure change under the action of various loads, it must force the insulated glass and keep synchronous displacement. , if there is not enough clearance between the edge of the insulated glass and the frame to accommodate this displacement, the glass will be crushed. The larger the surface of the glass plate, the greater the deformation after thermal expansion, and the larger the restraint reaction force formed, correspondingly causing greater thermal stress and increasing the probability of thermal cracking; the larger the plate surface size, the easier it is to be subjected to other loads the greater the superposition effect of the probability of thermal stress cracking. If the glass area is large and the thickness is small, the glass is resistant to bending and thermal stress and is easily broken. The selection of thickness of the insulated glass and the size of the panel surface must be calculated according to the requirements of wind load and thermal stress. Reasonable design is a crucial factor to reduce the impact in this regard. The use of glass is different in height and region, and it should be adjusted according to the actual situation, and the calculation shall prevail.

3. Glass manufacturers

3.1 The material quality of original glass film 

The material quality of the original glass sheet itself is an important factor affecting the rupture of the medium glass. The original sheet has visible defects such as uneven thickness, poor flatness, scars on the surface, and bubbles and slag inclusions in the glass. The energy-saving glass used in today's buildings is generally body-colored and coated (including Low-E glass) insulated glass. High thermal stress, high thermal stress can easily break the glass. In the production process of coated glass, if the equipment is not advanced and the coating process is not strict, it is easy to produce defects such as uneven film thickness and incomplete annealing during the coating process. . Therefore, the quality of the original glass must be strictly controlled. For the coated glass, not only the selection of high-quality fresh glass originals, but also whether the equipment is advanced, whether the automatic production software is excellent, and whether the technology is skilled.

Figure  2 The production of original insulating glass sheets

Figure  2 The production of original insulating glass sheets

3.2 The quality standards for glass deep processing

The tiny cracks in the glass when it is cut can cause the glass to break. Glass is a brittle material, and its edge tensile strength is closely related to edge defects. Any edge defect will reduce the edge tensile strength by a dozen times. Due to the different architectural design requirements, the cutting and processing of the glass are also different. The glass is cut with a special tool. When the glass is cut, due to the poor cutting quality, there are boundary irregularities on the edge of the glass. When the glass is flat, the edges are chipped and the corners are chipped, or there are cracks. When the glass is heated and expanded, due to the internal stress, it is very easy to break at the defective point on the edge. Therefore, the edge of the cut glass must be straight and smooth, and defects such as chipped edges, tooth edges, and chipped corners are allowed. Using machine chamfering, machine grinding, or fine grinding) the quality of glass edging is also an important factor affecting the rupture of insulated glass. Improving the processing quality of the edge is to improve the resistance of insulated glass to thermal breakage.One of the key factors is the cracking ability. The edge is the weakest part of the glass, and there are many micro-cracks and defects (such as chipping, chipping, uneven clamping, etc.) glass edge defects will lead to stress concentration and seriously reduce the allowable tensile stress. When encountering excessive thermal stress, The impact of external force greatly reduces the tensile strength of the glass, and the rupture generally starts from the edge of the glass, which is easy to cause rupture from here. In the edging operation, it is best to edge the glass edge, and strictly check the quality of glass edging.

Figure 3 The cutting processing of original insulating glass sheets

Figure 3 The cutting processing of original insulating glass sheets

The self-explosion of tempered glass caused by the presence of nickel sulfide inside (the phenomenon that tempered glass breaks automatically without direct external action) is an important factor for the rupture of insulated glass. The typical feature of the self-explosion of glass is a butterfly spot. The glass fragments are distributed radially. Two glass blocks in the radiation center resemble butterfly wings, commonly known as "butterfly spots". The raw materials of glass usually contain trace amounts of sulfur and silver. During the melting process, the silver alloy fragments will also increase the content of the bun in the glass. When the glass is heated, these substances chemically react to form tiny sulfide bun crystals. Silver sulfide crystals exist in two forms: a phase stable at high temperature and phase B stable at room temperature. The high temperature in the glass tempering process converts all silver sulfide crystals into a phase. But because the cooling process of tempered glass is very rapid, the silver sulfide crystals do not have enough time to transform into the P phase. This leaves an unstable a-phase crystal in the glass, which is like a compressed spring ready to re-transform into the p-phase without warning. The silver sulfide crystal expands by 4% when it is converted from the a-phase to the p-phase. If the a-phase crystal is located in the center of the glass with the greatest tension, the pressure body created by the expansion causes the entire glass to break. An effective way to reduce the self-explosion of tempered glass is to perform homogenization treatment (HST) on tempered glass. Homogenization treatment is to reheat the tempered glass to about 290 degrees and keep it warm for 2 hours so that the magnesium sulfide completes the crystal phase transformation before the glass leaves the factory so that the glass that may self-explode in the future will be broken in advance in the factory. According to international practice, the self-explosion rate of tempered glass after homogenization treatment can be reduced to less than 0.15%. Controlling according to this practice is an effective method to ensure a low self-explosion rate of tempered glass.

Each processing procedure of insulated glass is the formation stage of insulated glass, and the quality control of this stage will directly affect the effectiveness of insulated glass sealing.

The quality of the sealing method and the choice of desiccant have a profound impact on whether the insulated glass is broken. The sealant for making insulated glass requires good elasticity under high and low-temperature conditions so that it can expand and contract synchronously with the glass so that the glass does not generate large stress. The sealant is hard and has poor elasticity, which will restrict the deformation of the glass due to changes in ambient temperature, and increase the stress on the edge of the insulated glass, resulting in rupture. And some low-quality sealants have more volatile components, and the colloid shrinks too much when the glue is cured, which will especially increase the possibility of cracking in the first winter. In addition, the insulated glass sealant is required to have less organic volatiles (less than 1.5%) to prevent the sealant from shrinking too much and causing cracks; improper selection of desiccant will cause negative pressure in the spacer layer after the insulated glass is sealed. , causing the glass to flex and deform, coupled with changes in ambient temperature and air pressure, when the stress generated by this deformation exceeds the maximum stress that the glass can withstand, the rupture of the insulated glass also occurs. Therefore, the auxiliary materials for making insulated glass should ensure the use of high-quality products.

The Influence of insulated glass lamination process on rupture. When the insulated glass is produced by the horizontal method (at present, the horizontal method is used for manual or semi-manual production or when the plate surface is too large to be operated on the automatic line), because the supported area of the lower part of the glass is small and the support is mostly in the center, and the upper glass is All the weight of the insulated glass is added to the lower piece of glass, so that the lower piece of glass bends upwards, and the upper piece of glass bends downwards due to its weight, resulting in the thinning of the spacer layer of the insulated glass. In the prestressed, larger area of the insulated glass, this phenomenon is more prominent. Due to the existence of prestress on the glass, its ability to resist external forces is reduced, and it is prone to rupture when external factors change greatly. The defects in the above operations must be supplemented in time. When using the automatic insulated glass outer sheet inflatable production line, after the sheet is glued and glued, inert gas must be filled into the hollow glass cavity in time to reconcile this deformation, to avoid Broken insulated glass due to deformation during operation.

3.3 The packaging and transportation of finished insulated glass

The transportation of insulated glass is usually packaged in an iron frame or wooden box. insulated glass is different from other glass. When it is under pressure, it is a single piece of force. The uneven force between the glasses can easily lead to the rupture of the insulated glass. In addition, there is a defect in the glass edge treatment during production. During transportation, the glass edge produces tiny cracks due to collisions, which are not easy to be found before installation (due to the surrounding glue). After installation, the crack growth is affected by external forces, and the glass is broken. When packaging insulated glass, pay attention to the use of soft backing paper or pads to separate the glass from each other and keep the force between the glasses evenly, to ensure that the iron frame or wooden box is firm and not easily deformed, to avoid the extrusion between the insulated glass, the insulated glass product must be Upright placement for transport.

Figure 4 The actual installation of insulated glass

4. The construction and installation of insulated glass

The construction and installation of the insulated glass on the wall or after the upper frame is tightened or loosened, whether there is a support at the bottom of the glass, what hardness material is used to seal the glass and the surrounding frame or sealed with glass glue, etc., all of which have a close impact on the breakage of the glass. . During installation, the frame is not flat or the quality of the elastic sealing strip is not good, and the glass may be bent and deformed to generate prestress. Due to the existence of the glass prestress, its wind resistance strength is reduced, and even rupture occurs. Avoid prestressing the insulated glass during installation. The frame for installing the glass should be flat, and the surrounding sealing material in contact with the glass should have good elasticity so that the glass does not deform in any way.

The thermal insulation of the frame on which the glass is installed is also a factor that affects the rupture of insulated glass. When installing insulated glass, use an elastic material with a low thermal conductivity as a liner as much as possible. Glass is a poor conductor of heat. Insulate the glass from the aluminum frame with good thermal conductivity and the cold wall, to reduce the uneven temperature difference of the glass. Formation. To avoid the above problems, the installation must be carried out following the relevant industry standards "Technical Specifications for Application of Architectural Glass" following the design drawings and specifications. When installing the glass, try to thermally insulate the glass from the aluminum frame, and balance the lower part with two rubber blocks to ensure that they have enough expansion space to maintain absolute separation, elastic contact, and thermal insulation.

5. The building materials glass owners use

In the use of building materials glass owners, insulated glass is not only affected by the impact of hard objects or sharp objects, causing glass breakage, but also affected by the re-radiation of the indoor sunshade device after the owner is using it. Such as indoor dark curtains, blinds window and indoor glass surface paste or hanging device pattern, or advertising channel shading device, indoor shading device increases glass temperature non-uniformity, but also increases the probability of thermal stress rupture, the above devices should be avoided as much as possible. Indoor heat radiation sources directly acting on insulated glass can also cause obvious temperature changes in different parts of the glass and cause rupture. Thermal stress increases the breakage probability of insulated glass. To prevent the thermal stress cracking of insulating glass under the above conditions, improve the wind pressure strength and thermal stress strength of the glass, and reduce the probability of thermal stress cracking, it is recommended to strengthen the glass.

For more information about Jinan LIJIANG Glass insulating glass processing equipment and insulating glass processing accessories, please click here to learn more. 

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