10 min read

1. The overview

With the mandatory implementation of building energy-saving regulations in some developed countries, it has become an inevitable trend to use insulating glass as a raw material for glass construction in buildings. Insulating glass is distinguished according to its performance and grade and is generally divided into low-grade double-white insulating glass, mid-range solar control coated insulating glass and high-grade Low-E coated insulating glass. Double-white insulating glass is mostly used in ordinary civil buildings; solar control film and low-emissivity film insulating glass are mostly used in high-end civil buildings, hotels, shopping malls, office buildings, and other buildings that require high decorative and energy-saving effects. The glass commonly used in buildings used to be about 1m2 each. With the continuous improvement of people's aesthetic standards, a glass of 3, 4m2, or even larger per piece is widely used. The single glass area is too large, the visual effect is very good, and its impact resistance performance is reduced, there is a safety hazard, and it has brought certain difficulties to the production and installation of the glass. Insulating glass is distinguished according to the sealant coating process, and there are two types of vertical sealing method and horizontal sealing method. The vertical sealing method is that the insulating glass is coated with the outer sealant by the automatic sealing machine under the nearly vertical condition. At this time, the self-weight of the glass forms a vertical component, which is transmitted to the bottom, and the force of the horizontal component of the center of the glass is very strong. Small without severe mid-sag. This kind of vertical sealing machine is only equipped with high-grade insulating glass production lines, and the price is relatively high. The horizontal sealing method is to place the insulating glass horizontally on the Manual Rotated Sealant Spreading Table when applying the last sealant. There are thousands of insulating glass production lines in my country, and many production lines adopt the horizontal sealing method.

A few years ago, an Indian glass manufacturer customer served by LIJIANG Glass used a horizontal sealing machine to produce large-scale (more than 3m2) coated hollow glass products. There were two batches of products. The customer reported that there was a round shape in the middle. Rainbow, there are still several de-molding phenomena, the demoulding point is as big as a rice grain, and the defective glass accounts for 1/3~1/2 of the total. The film layer of the coated insulating glass is inside, and the film release should be produced during the production process. Both coated glass and insulating glass are produced by our own company. During the production process, there are full-time inspectors in each process. Such a large defect and such a large quantity can't miss an inspection, and the glass installation personnel reflected in the construction This kind of defect was not found at the time, but it was only discovered when the glass was cleaned after all the installation, and it felt that the glass installed first had a large defect, and the glass installed later had a small defect. LIJIANG Glass immediately sent after-sales technicians to the site to check, and the feedback was true. It was suspected that the size of the glass was too large, and the middle contact was caused by two pieces of glass rubbing against each other during transportation. Because the glass does have depressions, it is possible to contact and rub against each other, but friction generally produces strip-shaped defects. How can there be round defects like rice grains?

2. The symptoms of deficiency

This batch of glass is 6/9/6 coated insulating glass, which is an insulating glass composed of 6mm coated glass, 9mm aluminum spacer, and 6mm white glass. More than one hundred of them are about 1700 mm*2100 mm in size. The glass has been installed. There are more than 40 pieces of glass with a circular rainbow in the middle and nearly 20 pieces with an indistinct circular rainbow. Press the middle of the glass lightly with your finger, and the circular rainbow will be obvious. In the middle of the hollow glass with a clear rainbow, which is the area where the rainbow appears, the coated glass has one or two drop-shaped release points ranging from 0.5mm to 1.5mm. The color of the white glass substrate, there is fog on the edge of the release point, the color changes gradually, and there are white spots of the same shape on the white glass at the corresponding position.

3. The analysis of symptoms

Coated insulating glass is coated with a layer of stainless steel on the white glass and then coated with a layer of titanium nitride. Coated insulating glass products have been produced by glass deep-processing enterprises with automatic insulating glass production equipment for many years. The product quality is very stable, and its physical and chemical indicators such as grinding resistance, acid resistance, and alkali resistance also meet the requirements of industry standards. Therefore, it is impossible It is the defiling phenomenon in the insulating glass is caused by the quality defect of the coated glass. Some coated insulating glass manufacturers previously believed that the friction during transportation would cause the internal release of the insulating glass. There is no reason for this, because there are no traces of friction on the glass surface on site, and the shape of the release film is not like that caused by friction...

We are confused by the shape of the release film, and wonder about the white spot with the same shape as the release film on the white glass opposite the release point, what is that? How did it come about? We removed a piece of insulating glass and cut it open. We found that the white spots on the white glass could be touched by hand, with obvious bulges, and the adhesion was so firm that it could not be scratched off with fingernails. After careful research and analysis, we conclude that the white spot on the white glass is the coating material. The main reason for the release of the insulating glass is static electricity, and the secondary reason is the depression in the middle of the glass. The form of the release is a rainbow.

3.1 Causes of static electricity

The matter is composed of molecules, molecules are composed of atoms, and atoms are composed of negatively charged electrons and positively charged protons. Under normal conditions, the number of protons in an atom is the same as the number of electrons, and the positive and negative balance is positive and negative, so it shows no charge to the outside. The electrons around the nucleus will break away from the orbit by an external force, leaving the original nucleus and invading other atoms. The atom is positively charged due to the reduction of the number of electrons, which is called a cation; the atom that receives electrons is charged due to the increase in the number of electrons Negative charges are called anions. The cause of unbalanced electron distribution is that electrons are de-orbited by an external force, which contains various energies (such as kinetic energy, potential energy, thermal energy, chemical energy, etc.). In daily life, any two objects of different materials are separated after contact, and static electricity can be generated. When two different objects come into contact with each other, one object loses some charge, such as electrons being transferred to another object to make it positively charged, and the other object that gets some remaining electrons becomes negatively charged. If the charge is difficult to neutralize during the separation process, the charge will accumulate and the object will be charged with static electricity. Therefore, when an object is in contact with other objects and then separated, it will be charged with static electricity. Usually, when a plastic film is peeled off from an object, it is a typical "contact separation" electrification, and the static electricity generated by undressing in the daily tongue is also "contact separation" electrification. Solids, liquids, and even gases are charged with static electricity due to contact separation. This is because the gas is also composed of molecules and atoms, and when the air flows, the molecules and atoms will also undergo "contact separation" to generate electricity. We all know about friction electrification but rarely hear about contact electrification. In essence, triboelectrification is a process of contact and separation, resulting in an imbalance of positive and negative charges. Friction is a process of continuous contact and separation, so triboelectrification is essentially contacted separation electrification.

The measures to prevent static electricity are generally to reduce the flow rate and flow rate, improve the process links with strong electrification, and use equipment and materials with less electrification. The simplest and most reliable way is to ground the device with a wire, which can lead the charge to the ground and avoid static electricity accumulation. Appropriately increasing the humidity of the working environment, allowing the charge to be released at any time, can also effectively eliminate static electricity. This is the reason why it is not easy to do a good electrostatic test in humid weather. For static electricity, a concealed accident-prone cause, it is necessary to maximize its strengths and avoid its weaknesses, and also make it serve human beings. For example, electrostatic printing, electrostatic spraying, electrostatic flocking, electrostatic dust removal technology, etc., have been widely used in industrial production and life.

3.2 The reason for the glass rainbow

This circular rainbow in the middle of the insulating glass is Newton's circle. Newton's circles are interference patterns that appear when two sheets of glass come into contact and are easier to see than Brewster's circles. The two sheets of glass are separated by a thin layer of air, and very small changes in the air layer may result in linear, circular, or somewhat irregular interference patterns like contour lines on a map. In the insulating glass processing industry, Newton's circles may become clear if the air layer shrinks so that the two sheets of glass meet in the middle. After the light passes through the first piece of glass, the Part of it reaches the second glass, part of it is reflected by the second interface back to the first interface, reflected from the first interface, and passes through the first glass to the third interface. Then it is reflected by the third interface, passes through the first piece of glass, and is reflected by the first interface back to the second interface. At the same time, another part of the light passes through the first glass, is reflected by the second interface back to the first glass, is reflected by the first interface, reaches the third interface, and then is reflected to the second interface to combine with other parts of the light. , resulting in interference fringes, forming some light and dark concentric rings. For example, if the convex surface of a convex lens with a large radius of curvature is in contact with a flat glass, the contact point can be seen as a dark spot surrounded by some bright and dark-colored rings when exposed to sunlight or white light; When illuminated by colored light, it appears as some monochromatic circles with alternating light and dark. These circles are at different distances and gradually narrow as the distance from the center point increases. They are interference fringes formed by the interference of light rays reflected on the spherical surface and the plane.

3.3 Reasons for the release of the insulating glass

The insulating glass is produced by the horizontal sealing method. When the outer sealant is applied, the middle part is lifted by the base of the sealing table, and there is a vacuum suction cup under the base, which firmly grasps the glass and prevents force when applying the sealant. slide. There is a length-adjustable support arm on each side of the base, and the length of the support arm can be adjusted according to the size of the glass on the sealing table so that it can be supported on the four sides of the glass to prevent the glass from being lifted in the middle and falling around... The length of the support arm is limited. When the size of the insulating glass is too large, it cannot support the edge of the glass, which will cause the middle of the lower part of the insulating glass to bulge up, forming an inverted pot bottom shape. Since only four sides of the upper piece of glass are supported by aluminum strips, under the action of gravity, the middle is sunken down to form the bottom of a pot. For the 6/9/6 insulating glass whose length and width are both greater than 2m, the middle parts of the upper and lower sheets of glass are even completely in contact with each other. The sealant coating around the insulating glass is completed. After the glass is erected, the middle cavity is isolated from the outside atmosphere, forming a negative pressure, causing the central part of the insulating glass to remain in a concave shape. When the depression is serious to a certain extent, a circular rainbow appears.
During the production process of insulating glass, it must go through the glass washing and drying machine. There is an "air knife" at the end of the automatic glass washing and drying machine. While "scraping" the water on the glass surface, the "air knife" also generates static electricity on the glass surface. At the end of the glass washing machine "air knife" of LIJIANG Glass automatic insulating glass production line, a conductive device was originally installed to ground the dried glass surface to eliminate static electricity. Due to untimely maintenance, the device often pollutes the glass surface and affects production. The maintenance personnel do not realize its importance and are too lazy to maintain it regularly, so they dismantle it. The insulating glass is subjected to wind force during transportation and after installation, and the gap between the two pieces of glass will be small for hours. The tiny raised points on the glass surface will generate static electricity accumulation, and after a long enough distance, electrostatic adsorption will occur. , transfer the molecules and atoms of the film material to the white glass bit by bit.

4. The solutions

4.1 Measures to eliminate insulating glass depression

4.1.1 How to distinguish the severity of depression

Most of the insulating glass produced by the horizontal sealing method will have a depression in the middle, but the degree of depression is not enough. For small-sized and narrow-shaped insulating glass, when the outer sealant is applied horizontally, depending on the rigidity of the glass itself, the depression in the middle part is very small, and the larger the size, the larger the depression in the middle part.

Table 1 Statistical table of hollow glass depressions of different thicknesses and sizes/mm

We made statistics on the depression of insulating glass with different thicknesses produced by the horizontal sealing method, and the data are shown in Table 1. Considering that the size of glass in the production process is generally not an integer, and there are few square glasses, we take the glass whose aspect ratio does not exceed L5 and whose short side length is within ±50mm of the nominal length as the sampling object.

4.1.2 How to solve the sag problem

Horizontal sealing method 

To solve the problem of the central depression of large-sized insulating glass, you can use the inflatable method, that is, when making the spacer frame, use an inflatable corner, and when coating the outer sealant, leave the corner vertically seal the insulating glass. After getting up, fill a certain amount of nitrogen or dry air from the inflatable gusset to eliminate the depression in the middle of the glass, then tighten the supporting plug of the inflatable gusset, and then manually add the sealant. According to the statistical data in Table 1, considering the fluctuation in actual production and the convenience for operators to remember, we require that when using a certain thickness of glass to produce insulating glass, when the dimensions of both sides are larger than the dimensions in Table 2, production should be carried out according to the anti-sag regulations: 

① When making the frame, use inflatable corners and supporting aluminum strips; 

②When sealing the glue, do not seal the corners first; 

③When the glass is placed upright, fill in a certain amount of nitrogen to make the glass surface nearly flat, then plug and inflate The gusseted corners are matched with plugs, and the second sealant is filled manually. 

At the same time, regularly inspect the telescopic arm of the horizontal rotary sealing table to reduce the movement between the telescopic tubes, so that it can keep the edge and middle of the glass on a horizontal plane as much as possible, and avoid the bottom of the insulating glass from forming an inverted pot bottom.

Table 2 Anti-sag dimension of glass

4.2 Measures to eliminate static electricity

After realizing that the internal release of the coated insulating glass is caused by static electricity, and the static electricity is caused by the "air knife" of the automatic glass washing and drying machine, LIJIANG Glass repaired the glass grounding hanging device at the end of the "air knife" again, and regularly inspected it Grounding conditions, and remind glass deep processing manufacturers to do regular cleaning of conductive devices in time to ensure that the glass is not polluted.

5. The summary

By solving the problem of internal stripping of coated insulating glass, we have a deeper understanding of static electricity, and a further understanding of insulating glass, specially coated insulating glass, the phenomenon of stripping of coated insulating glass and rainbows, and accumulated glass Experience in deep processing production process.

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