Key points of processing technology for oversized structural glass
[China Glass Network] 1. Preface
Architectural glass usually has only three forms of damage: bending damage, impact damage and thermal cracking, and there are no other forms of damage. Since glass is a complete elastomer, there has been no measurement of glass compressive strength, tensile strength and shear strength so far, so glass has no values ​​of compressive strength, tensile strength and shear strength. The glass strength usually used is actually the bending strength of the glass. Not to mention that glass is a typical brittle material, it should not be used as an engineering structural material. It is impossible to realize the design of glass components from the glass without compressive strength, tensile strength and shear strength. For example, glass should be used as a column at least. The calculation of the bearing capacity under the compressive stress condition of the glass column shall be calculated as the bearing capacity of the beam at least under the conditions of tensile stress and shear stress. Since the glass has no compressive strength, tensile strength and shear strength, even if the compressive stress, shear stress and tensile stress in the glass member are calculated, it is impossible to judge whether the glass member satisfies the bearing capacity requirement. Under the traditional concept, architectural glass is usually not used as an engineering structural material.
Due to the large number of microcracks on the surface of the building glass, the glass exhibits typical brittleness when broken, that is, the glass does not have any yielding performance before breaking, but shows a sudden fracture. In this sense, the architectural glass should not be used as engineering. Use of structural materials. In addition, in the process of production, transportation, storage and installation, it is inevitable that large-scale impact or scratches will be generated on the edges and surfaces of the glass. These scratches and scratches will greatly reduce the strength of the glass, so the architectural glass is typical. Brittle materials are generally used as decorative materials. When used as a building exterior material, it is mainly used as a panel material. With the continuous improvement of architectural glass production technology, after the appearance of ultra-white glass, tempered glass, composite laminated glass, especially ionic intermediate film (also known as SGP) film material, laminated glass has become a structural material, and has It has been applied in some engineering practice, that is, under certain conditions, glass can also be used as a structural material, such as glass ribs of a full glass curtain wall, glass ribs of a point glass curtain wall supported by glass ribs, and the like. These glass ribs are used as structural materials. They are required to bear wind loads when designing, and some also bear the weight load of the glass curtain wall panels. However, the use of these glass components is only established under certain conditions. In particular, in recent years, oversized structural glass has been applied in many projects, and there are successful application cases and failure lessons. This paper introduces the processing technology points of super-large-size structural glass in combination with engineering cases. The key points of design and calculation technology, technical points of construction, and technical points of installation will be elaborated in subsequent articles.
2, glass processing requirements
First of all, the superior product in ultra-white float glass should be selected, that is, the better original glass film that can be bought on the market, because the quality of the original glass film is the decisive factor of whether the glass is self-explosive after tempering. Ultra-large-size structural glass has high requirements for defects on the glass surface, and generally does not allow point defects of 1.0 mm or more. For point defects of less than 1.0 mm, one point / 10 square meters is allowed, and point defects of less than 0.5 mm are adjacent to each other. The spacing of defects must be greater than 300mm. The appearance of the surface of the glass and the defects affecting the performance of the glass are not allowed. Because the oversized tempered glass must be homogenized, in order to reduce the homogenization rate of the tempered glass, the original piece must be cleaned before cutting to avoid the use of unqualified original pieces. It is strictly forbidden to use unqualified original pieces with hard marks, thick-direction stones, and dense micro-bubbles.
The glass plate should then be precision cut and edge processed. Generally, the side length of the glass is usually allowed to be a deviation of mm, and for a large-sized glass, the side length tolerance is usually mm or even larger. For structural glass, such side lengths are allowed to be too large, because the structural glass requires precise alignment, the side length tolerance is usually mm, and the side length deviation is too large to meet the engineering requirements. The edge of the structural glass requires chamfering, and three-side fine grinding and three-side polishing should be performed because the glass plate generates a large number of cracks at the edges during the cutting process, and these cracks greatly reduce the end face strength of the glass plate through three sides. Fine grinding and polishing can remove the cracks at the edge of the glass plate to improve the strength of the glass. Structural glass usually requires drilling holes in the glass. Generally, the diameter of the diameter of the circular hole of the glass is usually mm, and for the glass of the large aperture, the diameter tolerance is larger. For structural glass, such side lengths allow for too much deviation, and the required diameter of the structural glass is usually allowed to be mm. The aperture deviation of the structural glass is not only high, but also the edge of the hole should be finely ground and polished. Because of the stress concentration on the hole of the glass plate, the deviation of the aperture size is too large and the edge edge processing is low, it is easy to cause the glass plate to be affected by the hole edge during use. The force is uneven and cracks from the edge of the hole.
Structural glass should be tempered. If it is considered that the tempered glass has a self-explosion problem and is semi-tempered, it is not suitable because the structural glass usually needs to be perforated in the glass plate, and the semi-tempered glass cannot meet the opening requirements. Even if the hole is not opened, the structural glass should be treated with tempering because the glass is a typical brittle material. After the tempering treatment, the brittleness of the glass is greatly improved, that is, the fracture toughness of the glass is improved. Although there is no method for measuring the fracture toughness of glass, and the fracture toughness is not standardized to characterize the mechanical properties of glass, the fracture toughness of glass is objective. As a structural glass, the fracture toughness is undoubtedly extremely advantageous. The semi-tempered glass has a fracture toughness much lower than that of the tempered glass, so the structural glass should be tempered. As for the self-explosion problem of tempered glass, it can be solved by the following methods: First, the original structural glass must use superior products in ultra-white float glass. The second is moderate tempering, that is, the tempered glass should allow the number of fragments to be between 30 and 90. The third is that the compressive stress on the surface of the tempered glass should be uniform, that is, the difference between the larger and smaller values ​​of the surface compressive stress should not exceed 15 MPa. The fourth is that the structural glass tempering must be homogenized. The fifth is the fine grinding and polishing of the edge of the glass plate. With these measures, the self-explosion rate of structural glass should be extremely low.
Structural glass should be laminated glass. Generally, laminated glass can be made of PVB film, but structural glass must use SGP film. Because SGP has stronger adhesion and has a certain residual strength, the laminated glass composed of SGP film has greater rigidity. Laminated glass has a stack difference, and the laminated glass generally has a large stack difference. For a large laminated glass, the larger stacking difference is up to 6 mm. As a structural glass, the stacking of laminated glass is very small, and should not exceed 1.0 mm. In particular, the stacking difference of the hole side is strictly limited, because it is necessary to ensure that a plurality of pieces of glass constituting the laminated glass work together, and at the same time, force, glass plate hole side It must be ensured that the stack is extremely small. The holes of the structural glass must be subjected to strict quality control to ensure uniform force around the hole.
3, processing equipment requirements
(1) Cutting and edging polishing equipment
At present, there is no standard to stipulate how large the glass plate is, and it is generally considered that the glass plate has an extra large size glass when the side length exceeds 8 m. Such a large plate surface requires less than 1.0 mm of side length deviation. It cannot be done by general cutting equipment. It must be processed by the machining center because the precision of the equipment in the machining center reaches the eighth decimal place.
The finishing edge of the oversized glass plate and the polishing of the edger are also required by the usual edger. In the case of oversized structural glass edging, not only the dimensional tolerances but also the edging quality must be strictly controlled. The width side dimension is controlled at ±1.0mm, the height side dimension tolerance is controlled at ±2.0mm, the diagonal line is controlled at 0.05% of the diagonal length, and the chamfer width is controlled at 2.0mm±0.5mm. The oversized structural glass must be finished with fine grinding, the end surface must be polished and bright, and the stacking of multiple pieces of glass should be controlled within 1.0mm.
(2) Tempering equipment
At present, the large processing capacity of tempering equipment is 3660mm*18000mm. The oversized tempered glass should not only control the surface stress of tempered glass, but also control the flatness and appearance visual effect of tempered glass.
The oversized tempering equipment requires the appearance quality and visual effect of the tempered glass, that is, the number of tempered glass fragments must be between 30 and 90, the surface stress of the tempered glass must be greater than 90 MPa, and the surface stress of the tempered glass is larger and smaller. The difference between the values ​​is less than 15 MPa. The temperature difference between the points in the tempering furnace shall not exceed 5 degrees, and rapid and uniform heating shall be required, and the cooling shall be rapid. The deviation of the wind pressure shall not exceed 2 MPa, and the surface stress of the tempered glass shall be formed quickly. The flatness of the oversized tempered glass is controlled within 0.005%, and the appearance visual effect of the oversized glass is required, and there is no obvious deformation and unevenness of the spot. The deformed edge of the rolling corrugation is controlled at 0.08 mm/300 mm, the middle waveform is controlled at 0.04 mm/300 mm, and the roller corrugation is required to be parallel to the bottom edge. Appearance quality: Visually observed at a distance of 1 m, no obvious pitting and local patch or patch stress spots shall be observed. The tempered glass shall not have white fog defects. The stress value of the 15 m tempered glass is 99 MPa, 90 MPa, and the stress difference is 9 MPa.
Ultra-large-size structural glass must be made of homogeneous tempered glass. The temperature during the homogenization process must reach 290 ° ± 10 °C. Under this condition, the temperature is kept for at least 2 hours (recommended for 150 minutes, because the large-sized glass area is large and the heat is not uniform. The super-large version of the glass itself is heavy, in order to ensure uniform temperature, the temperature change during the thermal insulation process is monitored and recorded at the time of heat preservation, and the temperature is reduced to 70 degrees or less. The thermocouple used for homogenization must be professionally calibrated and required to be calibrated once a year. When the oversized structural glass is homogenized, the thermocouple must be attached to the surface of the glass and posted in accordance with the position and quantity required for homogenization. After the homogenization is completed, a complete homogenization report should be provided for the homogeneous glass, otherwise the homogenization treatment is judged to be unqualified.
(3) Autoclave
The oversized structural glass must use the ionic intermediate layer as the middle layer of the laminated glass. It must be treated with high temperature and high pressure and edge sealing during processing. It has high strength bending resistance and super impact performance, and it does not break after crushing. The advantages of collapse.
The oversized structural glass must be composed of an ionic intermediate layer or a multiple ionic intermediate layer, which requires the design requirements of the structural glass. The interlayer must be spliced ​​in a clean room of 100,000 or more. The splicing room must have a temperature and humidity control device, and maintain a positive pressure, and the light is good enough. The surface of the structural glass must be cleaned and no other foreign matter remains. The surface of the glass is visually inspected before the film is spliced, and the ionic intermediate layer is visually inspected to remove foreign matter in time.
When splicing, the difference between the bottom edge and the visible edge of the structural glass is ensured. For the multi-layer glass splicing, it is necessary to ensure that the thickness direction of the laminated glass is perpendicular to the glass surface, and an intermediate layer of 1-2 mm is reserved after splicing, due to the glass plate. The surface is large, and the edge of the glass needs to be simply fixed after the film is spliced. The oversized structural glass must be processed under vacuum to ensure that the intermediate layer of the laminated glass is fully melted and bonded. The sandwich structure glass is treated with a coating edge sealant to reduce the service life of the laminated glass by absorbing the moisture in the air by the middle interlayer.
The ultra-large size autoclave has higher requirements in terms of air pressure and voltage regulation. It should be combined in a constant temperature, constant humidity, positive pressure, 100,000-class clean-mixing chamber, and for SGP sandwich splicing technology for glass with a thickness of 100 mm. On the top, the vision is flawless, and the stitching seam is invisible to the naked eye.
4. Reasons for failure cases
One of the main components of the application of the oversized glass panel is the glass rib of the point-supported glass curtain wall. Glass-ribbed-supported point-type glass curtain walls are often mistaken for full-glass curtain walls. The glass rib-supported point glass curtain wall is quite different from the full glass curtain wall. Figure 7 is a glass rib-supported point glass curtain wall, and Figure 8 is a full glass curtain wall. The panel glass and the glass rib of the full glass curtain wall are separately installed. Although the two are supported by each other, the vertical load of each is borne by itself, and the glass rib only bears the horizontal load of the panel glass. If the glass rib breaks, the surface glass will not fall. Because the surface glass is installed on the structure alone, the whole glass curtain wall generally does not have an overall collapse or fall accident. However, the glass rib-supported point-type glass curtain wall is different. The panel glass is installed on the glass rib. The glass rib not only bears its own gravity load, but also bears the gravity load of the panel glass and the horizontal load on the panel glass. If the glass rib breaks, the facial glass loses its support, the facial glass will fall, and even the entire curtain wall will collapse. Therefore, the safety requirements of the glass rib-supported point glass curtain wall are extremely high, and because of this, the glass rib rupture accident is also more. There are many reasons for the rupture of the glass ribs, such as the glass processing quality is not satisfactory, the glass rib structure is unreasonable, the design calculation is wrong, and the assembly stress is too large. This paper mainly discusses the glass rib rupture caused by the glass processing quality not meeting the requirements. The glass rib rupture caused by other reasons is left to be described in the following article.
Part of the glass rib rupture appears as self-explosion of tempered glass. The reasons are: choose ordinary flat glass, do not choose the superior product in ultra-white float glass; the degree of tempering is too high, the number of larger fragments is far more than 90; glass plate The edges are not finely ground or polished. Other reasons are that the edge of the glass plate is severely damaged; the glass plate has a large deviation in cutting size. Another reason for the rupture of the glass ribs: 1. Improper installation, use metal parts to directly contact the glass. 2. The structural glass is partially stressed or unevenly stressed, resulting in excessive local stress.
(1) Original glass quality
In recent years, the phenomenon of self-explosion of building tempered glass is relatively common. In order to reduce the self-explosion rate of tempered glass, the state has issued the JG/T455 product standard for tempered glass for building doors and windows. It is stipulated in the standard that the original glass used for the curtain wall tempered glass should be the first-class product or superior product in the ultra-white float glass, and the flat glass should be superior. For oversized structural tempered glass, superior products in ultra-white float glass should be used. However, in actual engineering, there are many projects using flat glass, which causes the self-explosion phenomenon of tempered glass to be serious. Some glasses have self-explosion before they are installed. The quality of the original tempered glass is the decisive factor of whether the tempered glass is self-explosive. To ensure the safety of the application of the oversized structural glass, and to ensure the use of the glass under normal conditions, the original tempered glass must be in the ultra-white float glass. Excellent products.
(2) homogenization treatment
The homogenized tempered glass has a very low self-explosion rate. Since the tempered glass can not be detected by homogenization treatment, in the actual project, although there is homogenization requirement for the tempered glass, the tempered glass is not homogeneously treated, and the self-explosion rate of the tempered glass is high. For oversized structural glass, homogenization must be performed.
(3) Moderate tempering
The high degree of tempering and the high self-explosion rate of tempered glass are undisputed objective facts. JG/T455 product standard for tempered glass for building doors and windows curtain wall, the allowable number of pieces of tempered glass should be between 30 and 90. For oversized structural glass, it is necessary to ensure that the number of pieces of tempered glass is between 30 and 90, which has strict requirements for the tempering furnace and the tempering process. In actual engineering, many projects with high self-explosion rate, the number of pieces of tempered glass are far above the upper limit of 90 grains.
(4) Edge processing quality
JG/T455 product standard for tempered glass for building doors and windows curtain wall, tempered glass should be polished on three sides. For oversized structural glass, it should be polished on three sides. However, in actual engineering, the quality of edge processing is far from meeting this requirement, resulting in serious glass rupture.
(5) serious damage to the edge of the glass
The tempered glass edge should not only be finished, but also properly protected in all aspects of transportation, storage and installation. The edge of the glass is severely damaged, and the breakage of the glass is difficult to avoid.
(6) Large dimensional deviation
The deviation of the size of the glass plate is large, especially the large difference of the edge of the hole is the main cause of the cracking of the glass rib in the actual project. The glass rib original glass is flat glass, the edge is rough, the edge is severely damaged, and the hole edge is large. This kind of glass can not meet the engineering requirements, and it is normal to have cracks.
5, the conclusion
The oversized structural glass is used not only for point-supported glass curtain walls supported by glass ribs, but also for glass ribs and ribless full glass curtain walls for all-glass curtain walls. The design calculation points, construction points and installation points of each will be included in subsequent articles. Detailed.
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