The analysis of the hazards and prevention and control of the inner and outer sheets of insulating glass.

1. The Preface

To ensure good indoor lighting and visual permeability, glass materials are widely used in buildings and are an irreplaceable product. Among the flat glass produced in developed country, 80% is used in buildings, and the glass used in buildings, 80% is applied to the glass curtain wall. my country is the country with the largest glass curtain wall production and usage in the world. The existing glass curtain wall stock exceeds 1 billion m², and the annual new output exceeds 100 million m², which is more than 50% of the global total. To ensure the good thermal insulation performance of the building, the glass used on the curtain wall must be energy-saving glass. As an excellent energy-saving glass variety, insulating glass is currently the most widely used energy-saving glass, also known as "Niantian glass". 

To meet the requirements of building energy conservation, in recent years, most of the newly built glass curtain walls in my country have used insulating glass. With the continuous improvement of people's aesthetic standards and requirements for indoor permeability, the pursuit of ultra-large panel size insulating glass has become the choice of designers and owners. Therefore, insulating glass with an area of more than 5 m has been increasingly used in the curtain wall. However, with the increase in the size of the insulating glass, it is not uncommon for the insulating glass to produce a patch (the inner and outer two pieces of glass are sucked and contacted together, and the contact part is generally at the center of the plate), and it is not uncommon for the appearance of the insulating glass and the energy-saving effect, which have a greater impact. At present, many developed country's relevant standards and regulations do not require that hollow glass is not allowed to produce concave deformation and patch phenomenon. People are generally concerned about the material properties, preparation process, airtight durability, and self-explosion during the preparation of insulating glass. However, for well-prepared insulating glass products, there should be no patch phenomenon during the application process.

2. The harm and cause analysis of insulating glass patch

The well-prepared insulating glass should not have a patch phenomenon during use, but with the increase of the length and width of insulating glass, if some improper preparation processes are adopted, it may lead to the subsequent service process film phenomenon.

Once the patch phenomenon occurs in the inner and outer sheets of the insulating glass, the biggest harm is that the contact damage to the glass or film layer will occur at the patch site, and the energy-saving effect of the insulating glass will be reduced. affect the appearance of glass. The following is an analysis of a case of a curtain wall project in a city in the northern country, to illustrate the phenomenon of internal and external sheets of insulating glass and their harmful performance. The project uses low-emissivity coated single-chamber insulating glass. The length and width of the insulating glass are 2600 mm * 2500 mm. The curtain wall glass was all installed in the summer of 2016. However, since the winter of 2017, it has been found that many pieces of insulating glass appear grouped. A variable number of white or milky white spots and some spots will grow over time, and these glass spots did not appear before installation. Through on-site investigation, on-site photography and observation and analysis of glass spots are carried out, and the distribution characteristics of spots are summarized as follows:

(1) All the spots are densely distributed in the central area of the hollow glass plate with a length and width of less than 30 cm. Most of the spots are distributed individually and are rarely connected as a whole. The photo of the spots is shown in Figure 1. 

^{Figure 1 The center of the hollow glass plate Partial glass spot magnified photo}

(2) The spots are all distributed on the inner surface of the glass corresponding to the cavity of the hollow layer, and near the spots, circular or elliptical Newton rings can be seen (see Figure 2)

^{Figure 2 Newton's rings near the spot of insulating glass}

(3) The spots where spots are generated include glass with film surface (film layer damage) and glass surface without film surface (glass damage)

(4) By measuring the thickness of the hollow layer cavity near the corresponding spots, the values are all small, most of them are below 5 mm, and some are even close to 0, indicating that the inner and outer sheets are close to or even in contact with each other, and the on-site measurement is shown in Figure 3.0.86

^{Figure 3 (a) at the center of the plate of insulating glass}

^{Figure 4 (b) at the edge of the plate of insulating glass}

Field measurement value of insulating glass thickness "The international standards of insulating glass processing " E.2 (informative appendix) defines Newton's ring as follows: due to manufacturing or environmental conditions, when two pieces of insulating glass are in contact or close to contact at the center, there will be a series of colored concentric rings due to light interference, this optical effect is called Newton's rings. Its center is at the point of contact or proximity of the two pieces of glass. These rings are circular or oval. According to the on-site measurement results, it can be seen that the contact between the inner and outer glass patches caused by the hollow glass depression is the culprit for the formation of visible spots, and the contact between the inner and outer sheets of the insulating glass is caused by the production of the insulating glass.The concave deformation is formed by the superposition of the concave deformation of the insulating glass caused by the decrease of the ambient temperature during use. 

Since the surface of tempered glass is not flat, under the action of one or more loads near the contact part, stress concentration, mutual fatigue extrusion, and friction will form at the point of the contact part of the glass, resulting in contact damage or film on the glass at this part. Layer damage and delamination, and the surface become rough, forming light diffuse reflection, resulting in visible spots. In addition, the film layer at the contact part can also cause the phenomenon of "contact separation" of the film layer due to electrostatic action, resulting in the formation of spots.

3. The insulating glass patch control measures

To control the inner and outer sheets of insulating glass, one is to control the initial concave deformation caused by the manufacture of insulating glass, and try to make the thickness of the cavity layer in the center of the plate after the insulating glass is as close to the thickness of the side cavity layer as possible. Control the dent deformation caused by temperature differences during service.

3.1 The causes and control of the initial concave deformation of the hollow layer of insulating glass

The permissible value of the thickness reduction of the hollow layer caused by the concave deformation of the hollow layer of the insulating glass is not stipulated in the current national standard. For the initial concave deformation of the hollow layer of insulating glass caused by manufacturing reasons, the following processing problems are mainly considered:

(1) The horizontal (horizontal) sealing process by manual insulating glass sealing equipment is used to replace the normal vertical process. Due to the self-weight of the glass, the glass is dented and deformed, resulting in the contact or proximity of the inner and outer glass plates. After sealing, the gas inside and outside the glass cavity If the glass is not circulated, the deformed glass cannot be restored to flatness after the glass is placed upright, resulting in permanent depression and deformation. To solve the problem of depression in the middle of large-sized insulating glass, the horizontal sealing method can use the inflatable method, that is, when making the spacer frame, use an inflatable gusset. After getting up, fill a certain amount of argon gas or dry air from the inflatable gusset to eliminate the depression in the middle of the glass, then plug the supporting plug of the inflatable gusset, and then manually fill the sealant.

(2) For the double hollow chlorine-filled insulating glass, improper control of inflation can easily lead to the deformation of the glass hollow cavity. If there is used the off-line argon gas filling by automatic insulating glass production line, the quantity of gas charged in the two hollow cavities is inconsistent, one of the two hollow cavities is leaked or the inflation pressure is inconsistent, which will easily lead to the deformation of the glass double hollow cavity and cause the glass defects of the project. In addition, the glass should be placed upright when filled with argon, and the angle of erection should be controlled. If the glass is placed at an excessively large angle, the hollow cavity on the compressed side will be deformed due to excessive force on one side.

(3) Using the original tempered glass sheet with large bow bending for lamination will increase the uncertainty of the thickness value of the hollow layer of the insulating glass, which will easily lead to an increase in the probability that the initial thickness of the hollow layer in the center of the plate is too small after lamination. , and the larger the glass plate, the greater the probability that the initial thickness of the hollow layer in the center of the plate is too small.

3.2 The influence of ambient temperature on the depression deformation of insulating glass

Ambient temperature is an important factor leading to insulating glass patches. When the ambient temperature when the insulating glass is used is lower than the corresponding ambient temperature when the insulating glass is produced, there is a pressure difference on both sides of the insulating glass panel due to the drop in the air-cold compression pressure of the airtight cavity, and the insulating glass is concave under the action of the pressure difference. The concave deformation of insulating glass caused by a poor environment is the largest at the center of the plate, which can be calculated theoretically. Without considering the external load, for the gas enclosed in the hollow layer, according to the ideal gas

The body state balance equation is:

In this formula:

P₀ is the local atmospheric pressure; 

V₀ is the initial volume of the hollow layer of the insulating glass; 

T₀ is the temperature during the production of the insulating glass; 

T is the service time

The ambient temperature; 

_△P is the pressure change of the hollow layer after the temperature difference, 

_△V is the volume change, and its value can be obtained by integration as ,

Substituting Equation (2) into Equation (1), the pressure change of the gas in the hollow layer of the insulating glass due to the temperature change can be obtained. The calculation formula is:

then get:

Assuming that the insulating glass panel is simply supported on four sides, after being acted by AP, the maximum deflection and stress at the center of the panel are calculated as:

Among them, the back is related to the ratio of the long and short sides of the board, and the values are shown in Table 1.

Table 1 "The take value of K Values"

The maximum deformation of the insulating glass due to the ambient temperature difference can be obtained by substituting the △ body obtained by the formula (4) into the formula (5). To quantitatively analyze the influence of the ambient temperature on the depression deformation at the center of the insulating glass plate, assuming that the specification of the insulating glass is 6mm+12mm+6mm, the production environment temperature is 20°C, and the operating environment temperature is -30°C, according to the above calculation method, calculate the different sides. The maximum deformation of the insulating glass plate under the long dimension (the length and width are equal) is shown in Figure 4.

^{Figure 5 The maximum deformation of the insulating glass of different sizes caused by temperature difference}

It can be seen from Figure 4 that with the increase of the side length of the insulating glass, the maximum deformation caused by the temperature difference continues to increase, but it is not linear. When the glass size increases to more than 1.0 m, the glass deformation increases. The rate slows down rapidly and tends to a limit value, which is around 3.5 mm. That is to say, the concave deformation value of the hollow layer (the maximum value of thickness reduction) caused by the temperature difference is about 7 mm (the sum of the maximum deformation values of the inner and outer two pieces of glass). Since the thickness of the hollow layer of most of the glass in my country is 12 mm, and some are 9 mm, therefore, under the action of the temperature difference alone, the inner and outer sheets of the insulating glass will not be in contact with each other.

The concave and convex deformation of the insulating glass caused by the environmental temperature difference is inevitable. To prevent the inner and outer sheets of the insulating glass from being patched during the later service process, the initial maximum concave deformation at the center of the plate should be controlled during preparation, that is, when When the initial maximum concave deformation at the center of the plate is less than the design thickness of the hollow glass cavity (usually 12 mm) minus the maximum concave deformation at the center of the plate caused by the ambient temperature difference (mm), it is generally possible to avoid the inside and outside of the insulating glass. patch phenomenon. Therefore, insulating glass manufacturers should try their best to control the initial concave deformation value of the hollow layer at the center of the insulating glass plate during production.

4. The summary

(1) Insulating glass inner and outer sheet patches can cause contact damage and form visible spots on the contact part, which affects the appearance of the glass and reduces the energy-saving effect of the glass.

(2) The inner and outer sheet patch of insulating glass is caused by the initial maximum concave deformation of the hollow layer at the center of the plate formed by the manufacturing factory of the insulating glass, and the superposition of the thickness change of the hollow layer of the insulating glass at the center of the plate caused by the decrease of the ambient temperature.

(3) The maximum concave deformation value of the hollow layer at the center of the insulating glass plate caused by the temperature difference increases with the increase of the size of the insulating glass, but the limit value is about 7 mm.

(4) Insulating glass manufacturers should try their best to control the initial concave deformation value of the hollow layer at the center of the insulating glass plate during production. For the insulating glass with a design thickness of 12 mm, when the initial concave deformation value at the center of the plate is less than 5 mm, the general patch phenomenon can be avoided during subsequent use.

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