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As an important part of architectural glass, laminated glass is used in the construction industry, transportation industry, and aviation field. It is widely used in the chemical industry and military weapons and equipment such as tanks. However, in the production process, there are various defects in laminated glass that affect the use of laminated glass. Jinan LIJIANG Glass will start with the production process of laminated glass, analyze the causes and solutions of the defects of appearance quality and performance quality of laminated glass.

1. What is laminated glass

Laminated glass is a glass product made of two or more pieces of glass, embedded and sandwiched between two layers of glass with organic material glue, and then heated and pressurized. Commonly used organic materials are glued with polyvinyl butyral film (ie PVB film), PVB film has special excellent performance, the optical index of the film is very good, the light transmittance reaches more than 90%, heat resistance, cold resistance Performance, impact resistance, elasticity, moisture resistance, and aging resistance are very good. Its refractive index is almost the same as glass. The film does not harden above -50°C and has good bonding performance at 130-140°C. At this temperature, the glass is bonded to the air pressure with high pressure, and the glass is firmly bonded to the glue layer. Laminated glass has a high-strength, elastic, and penetration-resistant middle layer, which can withstand huge impacts, and the glass is broken in time, and the fragments still stick to the film, so it has a high safety performance.

The laminated glass 1

The laminated glass 1

 2. Laminated glass production process

The laminated glass is put into the washing machine, washed and dried by the washing machine, and then transported to the laminating room where the temperature and humidity are controlled. The appearance of the glass is usually inspected here. Next, place the cut film on the glass surface. The film needs to be placed flat to ensure that there are no wrinkles, and then the second cleaned glass is placed on the film—that is, a piece of laminated glass has been closed. The filming process needs to be carried out in a very clean environment. The staff needs to wear headgear and gloves to cut off the excess film from the edge of the laminated glass. Then the glass is positioned and transferred to the rolling section. The rolling section slowly heats the glass and uses a rubber-coated roller to press out the remaining air between the glass and the film, and seal the edge of the glass. Finally, the glass is put into the autoclave. The autoclave is the last process of the laminated glass. It can make the residual air into the film and realize the uniform fluidity of the film. The autoclave process strengthens the adhesion between the film and the glass, thereby The result is a piece of glass that looks like a whole---laminated glass.

In the production process of laminated glass, the process of combining sheets, glass preheating and pre-pressing process, and glass operation in the autoclave are the more difficult processes in the production process.

The laminated glass production line 1

The laminated glass production line 1

2.1 Combining operation process

When the glass is combined, the PVB film suitable for the width of the glass should be selected first, and the film should be kept clean. Avoid directly connecting the corner film and the glass with your hands. The PVB film should be naturally flattened, and do not stretch, and align the inside and outside of the glass. The film should not have a sense of unevenness. Check whether the reserved marks overlap, and then cut off the excess film. During the cutting operation, keep the blade inclined and leave 0.5mm~2mm film at the edge of the combined film. Avoid shrinking film caused by film shrinkage. After the film and glass are combined, put on a vacuum rubber band and check the sealing strip. The tension around the glass should be even, and then the glass should be cold drawn to remove the air in the middle of the combined film, and the cooling time should not be low In 5min.

2.2 Glass preheating and prepressing process

The glass is sandwiched with PVB film, and after the air is evacuated, the combined glass is pre-heated and pre-pressed. There are three types of equipment for preheating and prepressing operations. One is the preheating and prepressing box. Because of its simple equipment, low investment, and low energy consumption, it is favored by many manufacturers. However, the disadvantage of the preheating and prepressing box is that it is low inefficiency and cannot be adapted to industrial production; transmission type vertical and horizontal preheating and prepressing machines, these two types of machinery have higher production efficiency and are suitable for large-scale production. The difference between the two is that when the glass is placed to complete the preheating and pre-pressing work, the glass is placed vertically and the other is a horizontal placement. When the vertical preheating and prepressing machine performs air evacuation operation on the glass, it has little effect on the curvature of the glass. When the horizontal preheating hot press performs air evacuation operation on the glass, because the glass is placed flat, under the influence of its gravity and the evacuation pressure, the curvature of the glass is affected. Therefore, the horizontal preheating and prepressing machine is more suitable for the production of large-size glass.

The laminated glass 2

The laminated glass 2

2.3 Operation process of glass in an autoclave

The production process in the autoclave is the last in the production of laminated glass. The pre-heated and pre-pressed glass must undergo constant temperature and high-pressure treatment before it can be used to make the PVB film and the glass laminate better bond together. Constant temperature and high-pressure treatment should be operated in an autoclave. Firstly, the semi-finished products of laminated glass that are bonded together are separated from each other and placed on a special stand for the autoclave to make it firm, and then close the door of the autoclave. The autoclave is pressurized and aerated. When the air pressure in the autoclave reaches about 0.75MPa, the autoclave is stopped. This is because the edges of the laminated glass are not firmly bonded, to make the space between the glass interlayer overflow under the action of pressure, and prevent air from entering the interlayer from the edge. When the temperature in the kettle reaches about 130°C, immediately stop heating and maintain this temperature. At this time, the laminated glass can be bonded, and the inside of the kettle is pressurized twice. Since the glass has reached the bonding temperature, the pressurization will not cause air to enter the interlayer. When the pressure reaches 1.2 MPa, stop the pressurization. And keep the pressure balance, after 1h~1.5h, reduce the temperature in the kettle to 50℃, start to exhaust, and reduce the pressure in the kettle until the air is completely discharged, open the kettle door to push out the glass. 

At this point in the production of laminated glass, there is a finishing touch, which is to inspect the glass piece by piece and trim the qualified products. Cut off the surrounding excess film; select and repair the glass containing bubbles and degumming, and re-enter the kettle to pressurize and heat. With the continuous improvement of production technology, most autoclaves have the function of automatic control. In actual operation, the processing is carried out according to the characteristics and actual conditions of laminated glass.

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