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Building materials purchase guide: Insulating glass raw material selection and process control

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Building materials purchase guide: Insulating glass raw material selection and process control

Date of release:2019-03-12 Author: Click:

Aluminum windows and doors plant home to tell you: hollow glass contemporary architecture as an important material used in China has been very popular. At present, there are more than 1,000 insulating glass production enterprises in China, and there are also hundreds of raw material production enterprises. 
  With the intensification of competition, some enterprises choose low-quality or unqualified raw materials to reduce costs, and the process control is not strict or even meets the most basic production conditions, resulting in unqualified insulating glass flowing into the market, seriously affecting the healthy development of the insulating glass industry. . 
  This paper briefly analyzes the selection of raw materials and the control of production process that affect the quality of insulating glass, and clarifies its influence on the quality of insulating glass. 
  Unqualified insulating glass can cause problems such as air layer dew point and glass bursting. 
  point in theair layer The dewpoint is the temperature at which the humidity of the air sealed in the air layer reaches saturation. Below this temperature, the water vapor in the air layer condenses into liquid or solid water.The increase in dew point of the hollow glass is caused by the outside water entering the air layer and not being absorbed by the desiccant, which will seriously affect the use and energy saving effect. 
  Poor quality of raw materials, such as high penetration rate of sealant water, low adsorption capacity of desiccant and poor control of production process, such as poor glass cleaning, uneven coating of butyl rubber, poor sealing of corners and insufficient thickness of glue. The humidity in the production environment can cause an increase in the dew point of the hollow glass. 
  The glass bursting
  causes the hollow glass to burst and has both production reasons, as well as material selection and installation reasons. The greater the temperature difference between the temperature at which the insulating glass is produced and the environment in which it is used, the more pronounced the deflection of the glass. When the stress generated by this deformation exceeds the maximum stress that the glass can withstand, the bursting of the insulating glass occurs. 
  Insulating glass is produced by using endothermic glass and coated glass. Under the irradiation of sunlight, there is a large temperature difference at different points of the glass, which generates thermal stress and may also cause damage to the glass.
  The insulating glass sealant is hard and the elasticity is not good, which will restrict the deformation of the glass due to the change of the ambient temperature, so that the stress of the edge of the insulating glass increases, and the volatile component of the insulating glass sealant is more, which will cause the sealant to shrink too much. In particular, it will increase the possibility of the first winter explosion. This article only discusses the material and process. 
  Reasonable selection of raw materials 
  Original glass film The original film for 
  manufacturing hollow glass can be ordinary float glass, coated glass, heat absorbing glass, tempered glass and laminated glass. It should meet the corresponding national standards when selecting. In particular, the coated glass and the heat absorbing glass may be broken due to a large temperature difference between the center and the side of the glass after the glass absorbs heat. 
  Today, the importance of seal life to insulating glass has been recognized. The sealing and structural stability of the insulating glass system is achieved by means of an insulating glass sealant. The traditional tank aluminum hollow glass system should adopt a two-way seal form, with the first sealant to prevent the ingress of moisture, and the second sealant to maintain the stability of the structure. If the insulating glass system uses only a single-pass seal, the insulating glass sealant not only serves as a sealing but also functions as a structure, but so far, there is no sealant that can simultaneously have excellent sealing and structural properties. . In general, in the double-pass sealing system, the glue for the first seal has high water vapor transmission resistance, but the structure is poor; and the second sealant has high structural performance and poor resistance to water vapor transmission. 
  The first sealant of insulating glass. The first sealant generally uses the familiar butyl rubber. Its function is to control and ensure the minimum penetration of water and solvent into the sealed space of the insulating glass. Another function of the sealant is when the insulating glass is inflated. Effectively blocks the bleed out of the inert gas. Therefore, butyl rubber is required to have the following characteristics: 1 It must have good adhesion, and a perfect seal between the two sheets of glass and the spacer by ensuring perfect bonding of the glass and the spacer. 2 should have a high degree of water vapor permeability. 3 should have a certain bond strength to prevent the glass displacement before the second seal to reduce the occurrence of hollow glass stack. In order to improve the service life of the insulating glass, the butyl rubber should have the above-mentioned performance, and should also have good weather resistance, aging resistance and durability.
  Although butyl rubber has strong waterproof gas permeability and aging resistance, but the structure is poor, so the structural strength of the insulating glass is mainly achieved by the second sealant. 
  Insulating glass second sealant. The second sealant effectively bonds the various components constituting the insulating glass into a single body to form an insulating glass member. The second sealant should have the following characteristics. 
  1 should have strong bonding properties. By maintaining a certain strength, it avoids excessive displacement due to the dynamic load or static load of the insulating glass, so that the first sealant can have the function of blocking moisture. Therefore, the second sealant must have good mechanical properties and good adhesion to glass and other components, tensile and shear strength to withstand all dynamic and static loads. 
  2 should have good elasticity. It is very important that the second sealant should be able to restore its initial mechanical properties after it has been deformed by dynamic loading. Because during the use, due to the influence of temperature changes, the gas in the hollow glass always shrinks or expands continuously, which will directly cause premature failure of the insulating glass or bursting of the glass. 
  The expansion and contraction of the air layer poses new problems for the performance of the sealant. Should the edge sealant be softer to accommodate changes in gas volume in the compartment? If such a water vapor permeation (MVT) area may increase, affecting the service life of the insulating glass; if the water vapor permeation area is kept substantially constant, should the sealant be harder? However, such a result restricts the deformation of the glass, which increases the stress at the edge of the insulating glass, which may cause the glass to burst. The insulating glass sealant should not only effectively resist the expansion of the water vapor permeation area of the insulating glass, but also make the edge stress of the insulating glass lower than the stress causing the glass to break. 
  3 should have strong weather resistance and aging resistance. The second glue should have strong ability to adapt to climate change to ensure its function and long life. These climate changes include temperature, water, ultraviolet light and other factors, and sealants should not lose their effectiveness prematurely due to changes in these climatic factors.
  Polysulfide rubber, polyurethane rubber and silicone rubber are often used as the second sealant for insulating glass. They all have good weather resistance, aging resistance and durability, and have good adhesion to glass and other components. Ability. Among them, polysulfide rubber has the longest use history and the largest amount of use, accounting for 76% of the global market share of insulating glass rubber. Polysulfide sealants are highly resistant to many types of oils and solvents. At the same time, it is also very good in anti-aging, anti-ozone, anti-oxidation, anti-sunlight and anti-climate cycle. However, if exposed to air at 60 ° C, the bonding ability of polysulfide rubber and glass will be weakened, and some polysulfide rubber containing more plasticizer will decompose. Silicone glue is characterized by good chemical and physical compatibility with the contact material; excellent fluid properties, easy extrusion and coating; high mechanical strength, able to withstand various kinds of insulating glass Dynamic and static loads. Based on these characteristics, silicone rubber has been widely used in curtain wall insulating glass. Polysulfide rubber and silicone rubber are familiar to us. Polyurethane sealant is a sealing material that has been rapidly developed in recent years, and its market share in the hollow glass sealant market is increasing. 
  Polyurethane adhesive has the characteristics of low viscosity, fast curing, and no solvent. 
  1 low viscosity, and good flow and fall resistance. Low viscosity means easier application of the sealant and better wetting of the glass and spacer strips. There is no need to level or remove the sealant after coating, which is especially useful for automated production lines. 
  2 curing fast, the curing state of the polyurethane sealant after 3 hours can achieve the hardness of handling the insulating glass, in contrast, the polysulfide rubber takes 5 hours. 
  3 Does not contain a solvent, does not cause glass stress caused by colloid shrinkage, and reduces the possibility of cracking of the insulating glass in the first winter. Solvent-Containing Sealant If the solvent evaporates from the edge sealant, the sealant remains in full contact with the glass, but the stress caused by the shrinkage of the colloid becomes the stress applied to the edge of the glass. Because the insulating glass deflects inward in the winter, the spacer acts as a stress fulcrum, which increases the likelihood of rupture in the first winter after installation of the glass. 
  The purpose of using desiccant for insulating glass is to adsorb the moisture and volatile organic solvent sealed in the spacer layer during the production of the insulating glass; the second is to continuously adsorb the moisture entering the spacer through the sealant during the use of the insulating glass. The drying of the gas in the insulating glass is maintained. Correct selection of a suitable desiccant can improve the overall performance of the insulating glass, reduce the flexural deformation of the insulating glass, and reduce the occurrence of cracking of the insulating glass. 
  The main raw materials for the manufacture of hollow glass desiccants are silica gel, molecular sieves, mixtures of silica gel and molecular sieves, and new binders containing desiccants (for U-shaped spacers). The choice of desiccant should be determined according to its adsorption performance, mainly considering its adsorption capacity for water, air, and solvent. The drying agent commonly used in domestic insulating glass is molecular sieve, and the molecular sieve has the types of 3A, 4A, 13X and the like according to the pore size. 3A molecular sieve only absorbs water vapor; 4A molecular sieve absorbs water vapor, air, etc.; 13X can absorb water vapor, air, SF6, organic solvent and the like. The performance comparison of various types of desiccant is shown in Table 1. 
  Table 1 Comparison of desiccant adsorption capacity In addition to the choice of desiccant, in addition to the adsorption capacity of water, it is also necessary to consider whether there is solvent in the hollow glass spacer frame for adsorption, and drying. The adsorption of air to the agent is also a factor that must be considered. Since the desiccant has low-temperature gas adsorption and high-temperature gas desorption capacity, the adsorption and desorption of the gas by the hollow glass desiccant directly affects the deflection of the glass. 
  During the use of the insulating glass, the gas between the interlayers may shrink or expand due to the influence of temperature changes, causing the glass to flex inward or outward. If there is no organic solvent to be adsorbed inside the hollow glass, a large pore size (adsorbed gas) molecular sieve is selected. When the ambient temperature is low, the air inside the hollow glass is adsorbed, which makes the inward deflection of the hollow glass more obvious. At high temperatures, under the desorption of molecular sieves, gas is released, which exacerbates the outward deflection of the glass. 
  Finally, the choice of desiccant should also consider whether the insulating glass is inflated. The inflatable hollow glass cannot use a large-aperture molecular sieve capable of adsorbing inert gas or solvent. Otherwise, the concentration of the inflated body will be lowered and the aeration effect will be affected. 
  Therefore, the choice of insulating glass desiccant should also consider which sealing system is used in production and what other materials are used in the insulating glass.
  Hot melt butyl rubber, polyurethane rubber, silicone rubber and butyl rubber will not release organic solvents into the spacer even under very bad weather conditions. In this case, 3A molecular sieve is the best choice. Some polysulfide single-pass sealing systems and two-pass sealing systems of polysulfide and butyl rubber may release organic solvents into the air layer, so it is recommended to use a mixture of 3A and 13X molecular sieves. Table 2 lists several cases in which the desiccant and the sealant are properly matched. 
  Table 2, Selection spacer of desiccant The function of the 
  hollow glass spacer is to separate the two sheets of glass of the insulating glass to form a spacer layer, so that the hollow glass forms a uniform cavity. A desiccant is stored inside the spacer for drying and adsorbing moisture and chemical volatiles in the spacer. In addition, the spacer strips and gussets also have the function of supporting and improving the sealing of the product, forming a solid waterproof gas barrier, thereby improving the integrity and durability of the hollow glass unit. The factors to consider when selecting the spacer are the strength and appearance quality of the spacer; whether it is compatible with the sealant; whether there is a warm edge requirement. There are many types of spacer strips, such as traditional metal spacer strips, non-metal resin spacer strips, hybrid spacer strips, etc. Now newly developed U-shaped metal strips with warm edge concept, super spacer strips, and the most used aluminum spacer strips. . 
  Insulating glass production process control 
  Glass cleaning 
  glass is best to use mechanical cleaning, especially large glass, can be added with appropriate amount of cleaning agent when cleaning, the last should be washed with deionized active water to ensure that the glass surface is clean and free of dirt, so that the seal The glue is firmly bonded. 
  Control points: Use deionized water to keep the cleaning water clean. 
  Metal spacers 
  Detach or chemical treatment should be used when using metal spacers. If the insulating glass made of the smudged spacer strip is installed on the window, after a long period of sunlight, the oil trace is gradually volatilized and adsorbed on the inner surface of the insulating glass to form an oil film, which affects the visual effect of the insulating glass. In addition, the sealant and the spacer strip are not firmly bonded, resulting in seal failure. 
  Control points: Before use, the aluminum spacers should be anodized or decontaminated. 
  Production environment humidity control
  The humidity of the production environment mainly affects the effective adsorption capacity and residual adsorption capacity of the desiccant. The residual adsorption capacity refers to the absorption of the moisture of the spacer layer by the desiccant after the insulating glass is sealed, so that the initial dew point reaches the requirement, and in addition, the desiccant has the adsorption capacity, and the adsorption capacity of this part is called the residual adsorption capacity. Quantitatively, it is equal to the effective adsorption capacity minus the adsorption capacity of the desiccant to adsorb moisture trapped in the air in the spacer layer. 
  The effect of the residual adsorption capacity is to continuously adsorb moisture diffusing from the periphery into the spacer layer. The amount of residual adsorption determines the amount of moisture adsorbed into the spacer by the diffusion of the insulating glass during use, which determines the speed at which the water accumulates in the spacer layer, thereby determining the effective use time of the insulating glass. The length of time. When the humidity of the insulating glass production environment is large, the moisture first sealed in the spacer layer is large, and the adsorption capacity of the desiccant is large, and the residual adsorption capacity is reduced. Therefore, the influence of humidity on the effective use time of the insulating glass is crucial. To extend the effective use of insulating glass, it is necessary to control the humidity of the production environment to a lower level. Generally, the ambient humidity of the workshop is not higher than 75%. 
  Control points: Add the necessary dehumidification equipment or try to avoid rainy weather production. 
  Ambient temperature during production When 
  producing insulating glass, the pressure sealed in the spacer is the pressure at the production ambient temperature. In the course of use, the temperature difference between the use temperature and the production environment is often large. The thermal expansion and contraction of air changes the pressure of the air. In summer, the ambient temperature is generally higher than the temperature of the production environment. The air in the spacer layer expands to produce positive pressure, especially the insulating glass made of heat absorbing glass. The heat absorption effect of the glass is very strong, the air temperature in the spacer layer is higher, and the positive pressure generated is larger. When the pressure due to the expansion of the spacer air is higher than the breaking pressure of the glass, the glass will burst. Also in winter, the production temperature is higher than the ambient temperature at the time of use, the air in the spacer layer shrinks, and a negative pressure is generated. When the glass area is large and the spacer frame is small, the central portions of the two sheets of glass may be attached together. Spots similar to rainbows seriously affect the use of the effect. When combined with wind and snow loads, it is possible to rupture the glass. In addition, China's vast territory, such as the difference between the pressure of supply and demand, can also cause the glass to deform, the temperature is generally controlled in the range of 23 ± 2 ° C.
  Control points: Install the air conditioner in the operation workshop and install a breathing tube or capillary on the insulating glass if necessary. 
  The seal of the first sealant (butyl rubber) 
  butyl rubber determines the service life of the insulating glass to a large extent, requiring uniform and uninterrupted width, the width is 3 to 5 mm, and the thickness is controlled at 0.3. In the range of ~0.5 mm, especially in the corners, it is easy to break the glue. 
  Control points: Clean the glue mouth in time to make the butyl glue evenly heated, and the temperature is about 125 °C. 
  The thickness of the 
  second sealant and the bonding of the second sealant are the key parts of the insulating glass, so there are special provisions in the national standard: when using the double-pass seal, the thickness of the adhesive layer is 5-7 mm, When the single layer sealant is used, the thickness of the adhesive layer is 8 to 12 mm. Since the amount of diffusion of the gas is inversely proportional to the thickness of the adhesive layer, the thicker the adhesive layer, the longer the life. 
  In the sealing and bonding, the extrusion should not be avoided, so that there are fine pores on the gel. The two-component sealant should be mixed evenly. Do not mix too much at the time of manual operation to avoid pre-cure effect on the bond strength. When the coating is used as the original film, the film removal process should be increased. 
  Control points: Make a reasonable thickness of the rubber layer and ensure that the thickness is uniform. When mixing, adjust the ratio of the two components according to the temperature change. 
  Shortening the production process time of the insulating glass 
  Shortening the process time means minimizing the contact time of the desiccant with the air during the production of the insulating glass to reduce the loss of the adsorption capacity, so that the desiccant has a higher residual adsorption capacity. Generally, it is not more than two hours from the molecular sieve filling to the final sealing. At the same time, the activity of the molecular sieve (ie adsorption capacity) should be checked before filling. The simplest method is to do a temperature rising experiment: after mixing the same weight of water (room temperature) and molecular sieve, if the water temperature rises above 30 °C, the molecular sieve does not fail. Otherwise, the molecular sieve has been partially or partially ineffective and should be used after drying. 
  Control points: Reasonably arrange the production time of each process, reduce the waiting time after filling the molecular sieve, and carry out the temperature rising experiment before each filling.
  Because the structural composition and production process of the insulating glass are relatively simple, many people pay insufficient attention to the control of their materials and processes, so that the service life of the insulating glass cannot meet the design requirements. Only by rationally selecting raw materials, strictly controlling the quality of the production process, and improving quality awareness can improve the overall level of China's insulating glass industry.

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