At present, the mainstream product of photovoltaic glass is low-iron tempered patterned glass (also known as tempered suede glass) with a thickness of 3.2mm or 4mm. In the wavelength range of the solar cell’s spectral response (380~1100nm), the light transmittance can reach Above 91%, it has a high reflectivity for infrared light with a wavelength greater than 1200nm. It is made by using a special embossing roller to press a special pyramid pattern on the surface of the ultra-white glass, as shown in Figure 1.
At present, there are mainly the following two production processes for photovoltaic glass.
(1) The production process of Gridfa glass was invented in 1961 by the Belgian Gravibel Manufacturing Company. The grid method organically combines the grooveless and flat drawing processes, and adopts the non-grooved forming pool and the flat drawing method to achieve the purpose of drawing flat glass from the free liquid surface, and the thickness of 0.8~12mm can be drawn smoothly. The biggest feature of the glass is that it can produce thin glass below 3mm stably for a long time, and has good flatness, small thickness difference, and excellent product quality.
(2) The float glass production process is completed in a tin bath with protective gas (N2 and H2). The molten glass flows continuously from the kiln and floats on the surface of the relatively dense tin liquid. Under the action of gravity and surface tension, the glass liquid spreads and flattens on the tin liquid surface to form upper and lower surfaces, which are smooth and hardened. , After cooling, it is led to the transition roller table. The roller of the roller table rotates to pull the glass ribbon out of the tin bath into the annealing dense, after annealing and cutting, a flat glass product is obtained.
Tempered glass is divided into physical tempered glass (tempered tempered glass) and chemical tempered glass.
(1) Physically tempered glass is obtained by cutting ordinary annealed glass to the required size, then heating it to about 700°C close to its softening point, and then performing rapid and uniform cooling (usually 5-6mm glass is heated at 700°C. Under heating for about 240s, cooling for about 150s. 8~10mm glass is heated at 700℃ for about 500s and cooling for about 300s. In short, the heating and cooling time is different according to the thickness of the glass). After the tempering treatment, uniform compressive stress is formed on the surface of the glass, while tensile stress is formed inside. The bending and impact strength of the glass is improved, and its strength is about 4 times that of ordinary annealed glass. For the tempered glass that has been tempered, it cannot be processed or damaged, otherwise it will be “battered”.
The disadvantages of physically tempered glass include the following aspects:
①The glass after physical tempering can not be cut or processed, and the glass can only be processed to the required shape before tempering, and then tempered.
② Although the strength of physical tempered glass is stronger than that of ordinary glass, tempered glass may explode when the temperature difference changes greatly, while ordinary glass will not explode. The automatic explosion of tempered glass without direct mechanical external force is called the spontaneous explosion of tempered glass.
③The physical tempered glass still has optical distortion. As the glass undergoes a rapid cold wind pressure of about 720°C during the tempering process, there will be wind spots on the glass surface, and there will be unevenness on the surface of the glass. The severity is determined by the quality of the equipment, so the glass after physical tempering Can’t make mirror.
(2) Chemically tempered glass is based on ion diffusion mechanism and external factors to change the surface structure of the glass to form a certain thickness of stress layer, thereby greatly improving the strength of the glass surface.
The specific method is to put ordinary float glass in potassium nitrate molten salt liquid. At a temperature of 450°C to 500°C, the Na+ ions in the glass undergo thermal vibration due to heating, while the Na+ with a smaller radius in the original glass surface The ions are exchanged with K+ ions with a larger radius in the potassium nitrate molten salt medium. The space occupied by Na+ ions with a smaller ion radius is occupied by K+ ions with a larger ion radius. The resulting compressive stress can be significantly enhanced.
The characteristics of chemically toughened glass include the following aspects:
①The strength of chemically toughened glass is several times higher than that of ordinary glass. The bending strength is 3-5 times that of ordinary glass, and the impact strength is 5-10 times that of ordinary glass. The strength is improved and the safety is also improved.
②The load-bearing capacity is increased, and the fragile nature is improved. Even if the toughened glass is damaged, there are fragments with no sharp angles, which greatly reduces the damage to the human body.
③Because of the special production process of chemical tempering, its yield is higher than that of physical tempering, and there is no self-explosion and no stress spots.
④Chemical toughened glass has good thermal stability, can withstand temperature changes of 200 ℃, and has obvious effects on preventing thermal cracking.
⑤ Its high light transmittance and flatness are guaranteed to be consistent with the original glass and can be cut. It is suitable for glass of various thicknesses, special-shaped glass that is not restricted by geometric shapes, and surface strength enhancement of various craft glass.