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

1. The preface

To ensure good indoor lighting and visual transparency, glass materials are widely used in buildings and are an irreplaceable product. Of the flat glass produced, 80% is used in buildings, and 80% of the glass used in buildings is used in glass curtain walls. To ensure 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 the most widely used energy-saving glass at present, and is also known as "today's glass"'

To meet the energy-saving requirements of buildings, 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 indoor permeability requirements, the pursuit of insulating glass with a super large panel size has become the choice of designers and owners. Therefore, insulating glass with an area of more than 5m2 has been more and more used in curtain walls. However, as the size of the insulating glass increases, it is not uncommon for the insulating glass to produce a patch (the inner and outer glass are sucked and contacted together, and the contact part is generally at the center of the plate). to have a greater impact. At present, my relevant standards and regulations do not explicitly require that hollow glass is not allowed to produce sag deformation and patch phenomenon. People generally pay attention to the material performance, preparation process, airtight durability, and self-explosion in the preparation process of insulating glass, but the preparation of a good insulating glass product should not be pasted during the application process.

2. The hazard and cause analysis of insulating glass patch

The well-prepared insulating glass should not be attached during use, but as the length and width of the insulating glass increase, if some improper preparation processes are adopted, it may cause sticking in the subsequent service process. film phenomenon. Once the inner and outer sheets of the insulating glass are attached, the biggest harm is that the glass or the film layer will be damaged due to contact at the attachment part, and the energy-saving effect of the insulating glass will be reduced. Visible spots are formed due to the damage to the contact parts, which seriously affects the appearance of the glass. The following is an analysis of a curtain wall project detection case in a city in the northern hemisphere to illustrate the phenomenon of the inner and outer sheets of insulating glass and the harmful manifestations it brings. The project adopts low-emissivity coated single-cavity insulating glass. The length and width of the insulating glass are 2600mmx2500mm. And other white or milky white spots, and as time goes by, some spots will grow up, none of these glass spots appeared before installation. Through on-site investigation, on-site photography, and observation and analysis of glass spots, the distribution characteristics of spots are summarized as follows:

All the spots are densely distributed in groups of 30cm in length and width

In the central area of the hollow glass plate below, most of the spots are distributed singly, and few are connected. The photo of the spots is shown in Figure 1.

^{Figure 1 Enlarged photo of the glass spot in the center of the insulating glass plate}

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

^{Figure 2 Newton's rings near a speck of insulating glass}

(3) In the spot where the spot occurs, there is a position on the glass with a film surface (film layer damage), and there is also a position on the glass surface without a film surface (glass damage).

(4) By measuring the thickness of the cavity of the hollow layer near the spots, the values are small, most of which are below 5mm, and some are even close to 0, indicating that the inner and outer sheets are close to each other or even in contact. The on-site measurement is shown in Figure 3.

^{(a) At the center of the board (b) At the edge of the board}

^{Figure 3 On-site measurement value of insulating glass thickness}

The definition of Newton's ring in "Insulating Glass" (informative appendix) is as follows: due to reasons such as manufacturing or environmental conditions when two pieces of insulating glass are in contact or close to contact at the center, there will be two series of rings due to light interference. Colored concentric rings, this optical effect is called Newton's rings. Its center is at or near the point of contact of the two pieces of glass. These rings are circular or oval. According to the on-site measurement results, the sag of the hollow glass makes the contact between the inner and outer glass patches is the culprit that leads to the formation of visible spots. The reason for the contact between the inner and outer sheets of the insulating glass is the depression deformation caused by the hollow glass production and the ambient temperature during use. It is formed by the superimposed action of the concave deformation of the hollow glass. Since the surface of tempered glass is not flat, one or more points of contact will be formed first near the contact part. At the same time, under the action of external temperature change, wind load, or vibration load, the point contact part of the glass will form stress concentration, Mutual fatigue, extrusion, and friction will cause contact damage or film layer damage and stripping of the glass at this part, and the surface will become rough, forming diffuse reflection of light and causing spots visible to the naked eye. In addition, the film layer at the contact part can also cause the "contact separation" phenomenon of the film layer due to electrostatic action, resulting in the formation of spots.

3. The insulating glass patch control measures

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

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

The permissible value of the thickness thinning of the hollow layer caused by the concave deformation of the hollow layer of insulating glass is not stipulated in the current standard. The initial concave deformation of the hollow layer of insulating glass caused by manufacturing reasons mainly considers the following processing technology issues:

(1) The horizontal sealing process is used to replace the normal vertical sealing process. Due to the self-weight of the glass, the glass is sunken and deformed, resulting in the contact or proximity of the centers of the inner and outer glass plates. After sealing, the gas inside and outside the glass cavity does not circulate. , resulting in the deformed glass not being able to restore flatness after the glass is placed vertically, resulting in permanent concave deformation of horizontal sealing method. To solve the problem of the central depression of large-sized insulating glass, the inflatable method can be used, that is, when making the spacer frame, use an inflatable corner, and when coating the outer butyl sealant, leave the corner vertically seal the insulating glass. After getting up, fill a certain amount of argon-gas  from the inflatable corner to eliminate the depression in the middle of the glass, then tighten the supporting plug of the inflatable corner, and then manually or automatically coating the sealant.

(2) For double-hollow insulating glass filled with air, improper inflation control can easily lead to the deformation of the glass's hollow cavity. If the offline gas filling is used, the quantity of gas inflated into the two hollow cavities is inconsistent, or one side is leaked, or the inflation pressure is inconsistent, which will easily lead to the deformation of the double hollow cavity of the glass and cause the glass defect of this project. In addition, when filling the gas, the glass should be placed vertically, (maybe you would ask how to let the glass placed vertically, you will demand an automaitc insulating glass production line with argon-gas flling function)and the vertical angle should be controlled. If the vertical angle of the glass is too large, the hollow cavity on the pressure side will be deformed due to excessive force on one side.

(3) Using original sheets of toughened glass with large bow-shaped bending for assembling will increase the uncertainty of the thickness value of the hollow layer of insulating glass, which will easily lead to an increase in the probability that the initial thickness value of the hollow layer in the center of the plate is too small after merging, 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 effect of ambient temperature on the hollow deformation of insulating glass

Ambient temperature is an important factor leading to insulating glass mounting. When the ambient temperature when the insulating glass is used is lower than the corresponding ambient temperature when the insulating glass is produced, due to the air-cooled compression pressure drop in the airtight cavity, there is an air pressure difference on both sides of the insulating glass panel, and the insulating glass is concaved under the action of the pressure difference. The concave deformation of insulating glass caused by the poor environment is the largest at the center of the plate, which can be calculated theoretically. Under the condition of not considering the external load, for the gas sealed in the hollow layer, according to the ideal gas state equilibrium equation is:

In the formula: 

P₀ is the local atmospheric pressure; V₀ is divided into the initial volume of the hollow layer of the insulating glass; V₀ is the temperature during the production of the insulating glass; T is the ambient temperature during service; is the volume change, and its value can be obtained by integration as:

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

dagger

Assuming that the insulating glass panel is simply supported on four sides, the maximum deflection and stress calculation formula at the center of the panel after being subjected to the action of △ the body is:

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

Substituting formula (4) into formula (5), the maximum deformation of insulating glass due to ambient temperature difference can be obtained. To quantitatively analyze the influence of ambient temperature on the concave 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 use environment temperature is -30°C, then according to the above calculation method, the calculation is different The maximum deformation of the insulating glass plate under the side length dimension (equal length and width) is shown in Figure 4.

^{Figure 4 The maximum deformation of 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 increases continuously, but it does not show a linear relationship. When the size of the glass increases to more than 1.0m, the glass deformation increases The speed slows down rapidly and tends to a limit value, which is about 3.5mm. That is to say, the concave deformation value of the hollow layer (the maximum thickness reduction value) caused by the temperature difference is about 7mm (the sum of the maximum deformation values of the inner and outer glass pieces). Since the thickness of the hollow layer of most of the glass is 12mm, and some are 9mm, the inner and outer sheets of the insulating glass will not be in contact with each other under the separate action of temperature difference.

The concave-convex deformation of the insulating glass caused by the ambient temperature difference is inevitable. To prevent the inner and outer sheets of the insulating glass from sticking in the later service process, the initial maximum concave deformation at the center of the sheet during preparation should be controlled, that is when When the initial maximum sag deformation at the center of the panel is less than the design thickness of the insulating glass cavity (generally 12mm) minus the maximum sag deformation at the center of the panel caused by the ambient temperature difference (preferable value is 7mm), it is generally possible to avoid the internal and external damage 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 caused by the production.

4. The summary

(1) The patching of the inner and outer sheets of the insulating glass can cause contact damage and visible spots at the contact parts, which will affect the appearance of the glass and reduce the energy-saving effect of the glass.

(2) The patching of the inner and outer sheets of the insulating glass is caused by the superposition of the initial maximum concave deformation of the hollow layer at the center of the plate due to manufacturing factors of the insulating glass, and the change in the thickness of the hollow layer of the insulating glass at the center of the plate caused by the decrease in ambient temperature.

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

(4) Insulating glass manufacturers should try their best to control the initial sag deformation value of the hollow layer at the center of the insulating glass plate during production. It can avoid the phenomenon of patching in the subsequent use process.

^{For more information about LIJIANG Glass insulated glass production line and insulated glass producing machine, please click here to learn more.}