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

1. Preface

In order to ensure good indoor lighting and visual permeability, glass materials are widely used in buildings and are an irreplaceable product. Of the flat glass produced in most developed and developing countries in the world, 80% is used in buildings, and 80% of the glass used in buildings is used in glass curtain walls. China is the country with the largest glass curtain wall production and usage in the world. The existing glass curtain wall stock exceeds 1 billion ㎡, and the annual new output exceeds 100 million ㎡, which is more than 50% of the global total. In order 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". In order to meet the requirements of building energy efficiency, in recent years, most of the newly built glass curtain walls in most developed countries and some developing countries 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 5m has been increasingly used in curtain wall. However, with the increase of 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. have a greater impact. At present, the relevant international standards and regulations do not explicitly require that hollow glass is not allowed to produce concave deformation and patch phenomenon. People generally pay attention to 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. Harm and cause analysis of insulating glass patch

With the increase of the length and width of the insulating glass, if the insulating glass manufacturer and processor adopts some improper preparation processes, it may lead to the patch phenomenon in the subsequent service process. Once the patch phenomenon occurs in the inner and outer sheets of the insulating glass, the biggest harm is that the contact damage of 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 Jinan LIJIANG Glass analyzes a case of a curtain wall project in a city in a high latitude region of the northern hemisphere to illustrate the phenomenon of internal and external sheet patching of insulating glass and its harmful performance. A curtain wall project in a city adopts low-emissivity coated single-chamber insulating glass. The length and width of the insulating glass are 2600mm*2500mm. The curtain wall glass was all installed in the summer of 2016, but since the winter of 2017, many pieces of insulating glass have been found one after another. There are white or milky white spots of varying numbers in groups, and some spots will grow up 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 a 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 Enlarged photo of glass spots in the center of the hollow glass plate}

(2) The spots are distributed on the corresponding inner surface of the glass in the cavity of the hollow layer. Near the spots, circular or elliptical Newton's rings can be seen (could have seen the Figure 2).

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

(3) There are glass positions with film surface (film layer damage) and glass surface positions without film surface (glass damage) where spots are generated.

(4) By measuring the thickness of the hollow layer cavity at the corresponding positions near the spots, the values are all small, most of which are below 5 mm, and some even under the action of load, stress concentration, mutual fatigue extrusion and Friction will cause contact damage or film damage and peeling of the glass in this part, and the surface will become rough, resulting in diffuse reflection of light, causing visible spots to the naked eye. In addition, the film layer at the contact position can also cause the phenomenon of "contact separation" of the film layer due to electrostatic action, resulting in the formation of spots.

3. 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 difference during service.

3.1 The reasons for the initial concave deformation of the hollow layer of insulating glass and the allowable value of the thinning of the thickness of the hollow layer caused by the concave deformation of the hollow layer of the insulating glass are not clearly stipulated by relevant international standards at present. The initial concave deformation of the hollow layer of the insulating glass caused by the manufacturing of the insulating glass mainly considers the following processing problems:

(1) The horizontal sealing process of insulating glass production is used to replace the normal vertical process. Due to the self-weight of the glass, the glass is dented and deformed, causing the inner and outer two glass plates to contact or approach the center. After sealing, due to 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 concave deformation. The horizontal sealing method needs to solve the problem of air pressure difference on both sides of the insulating glass panel, and the hollow glass is concave under the action of the pressure difference. The concave deformation of insulating glass caused by 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 state equilibrium equation:

In the formula:

P₀ is the local atmospheric pressure;

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

T₀ is the temperature during the production of insulating glass;

T is the ambient temperature during service;

△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 integrating:

pointDD,Substitute the formula (2) into the formula 

(1) to get the gas in the hollow layer of the insulating glass

The pressure change due to temperature change is calculated as:64a965X=-D, D(3n(a2+63)2D,then get:XPo+Vo-./(XP+Va)P?-4X ATP.V.AP=2X 

As suming 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:

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 rate increases. It slows down rapidly and tends to a limit value, which is about 3.5 mm. That is to say, the concave deformation value (the maximum value of thickness reduction) of the hollow layer 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-convex deformation of the insulating glass caused by the environmental temperature difference is unavoidable, so that the inner and outer sheets of the insulating glass will not be patched in the later service process, the initial maximum concave deformation at the center of the plate should be controlled during preparation, that is, when the plate When the initial maximum concave deformation at the center 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 (7 mm), the inner and outer sheets of the insulating glass can generally be avoided. 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 production.

4. Summary

(1) The inner and outer sheets of insulating glass can cause contact damage and form 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 inner and outer sheet patch of insulating glass is caused by the superposition of the initial maximum concave deformation of the hollow layer at the center of the plate caused by the manufacturing factors of the insulating glass, and 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. Generally, the patch phenomenon can be avoided in the subsequent use process.

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