introduction
As a glass product with special safety function, laminated glass is widely used in various occasions. With people's understanding and understanding of the characteristics of laminated glass, its market demand is increasing, and its varieties and functions are more diversified, which is a very promising market. One of the promising safety glass products. Market demand has driven new Low-E glass interlayers, energy-saving film interlayers, color film interlayers, SGP film interlayers, ultra-thick interlayers, wire interlayers and various laminated glass products with different thicknesses, varieties and process combinations that meet various functions With the development and promotion of the use of laminated glass, the interlayer process is becoming more and more complex. Objectively, the production technology and equipment of laminated glass are required to be continuously updated and improved to meet the production process requirements of various new products.
The pre-pressing machine is one of the key equipments for interlayer production. The traditional and common pre-pressing methods for glass heating are mainly divided into two types: infrared heating and convection heating. The two heating technologies can also be used in combination. The traditional heating method of pre-pressing machines has continuously increased the heating limitations of various new products. Objectively, the equipment is required to be innovatively improved to meet the pre-pressing and heating needs of various products, avoid local overheating or insufficient heating, and ensure pre- The laminated pre-pressing technology of forced convection heating method came into being, which provided more favorable technical support for the variety of laminated glass. Some manufacturers have developed a pre-pressing machine that uses a fan blowing cycle to form forced convection heating in the furnace, which effectively solves the problems faced in the production of uniform heating of various products, improves the heating performance of the equipment, improves the production efficiency of laminated glass, and improves product quality. , the energy saving is better.
1 The role of the pre-press
The pre-pressing machine removes a large amount of air from the glass and the PVB film in the middle layer by heating and rolling to realize the edge sealing of the glass to ensure the quality of the finished product after high pressure. The pre-pressing machine used for the production of laminated glass generally includes four parts: preheating section, primary pre-pressing roll, heating section and secondary pressing roll. After the second rolling, the glass is almost uniform and translucent, and the best state is transparent at a distance of about 30mm from the edge. Pre-pressing has a great impact on the quality of laminated glass products, and the glass is in good exhaust and edge sealing condition, which can avoid defects such as bubbles and degumming after high pressure of the glass, and ensure product yield and quality.
2 Limitations of conventional pre-presses
2.1 Analysis of glass heating demand
In actual production, during the heating and rolling process of the pre-pressing machine after the glass is combined, the heating conditions will vary due to the heating conditions in the furnace and the shape, size and structure of the glass. Adjust the temperature, speed, etc., and some also adjust the placement method to cope with and solve the heating changes and needs of different glasses and ensure the rolling effect. If there is a glass with an angle and a long sharp corner, the sharp corner will be heated more and overheated during the pre-pressing heating process; the interval between the glass entering the pre-pressing machine is long, causing the temperature of the interval in the furnace to be too high, and the latter one will be overheated. The glass is heated more in the direction of the furnace, and the edges are overheated, and the edge sealing is too early; even if the glass with good specifications has a short interval between them and continues to enter the pre-pressing section, the glass may continue to absorb heat, and some parts may not be heated enough and edge sealing Not good; the heat accumulates in the hard-to-reach parts of the glass, causing local heating and overheating. Under normal circumstances, the edge of the laminated glass will be heated higher than the middle position of the plate, causing the edge of the glass to be sealed in advance. The reason is that the edge temperature is higher than the middle position, and the edge absorbs heat faster.
Some glass structures are more complex, beyond the conventional or more difficult to process, which will also affect the uniform heating of the glass in the furnace. For example, Low-E laminated glass, due to the heat reflection characteristics of the Low-E glass film layer, the heating temperature of one side of the film layer is significantly lower than that of the non-Low-E side, which makes uniform heating more difficult than conventional glass, which is not conducive to the realization of heat sealing. Edge; more than 3 layers of laminated glass, thick plate glass and large plate glass, due to the influence of the number of layers, thickness and plate surface of the glass, the glass heating cannot be fully realized.
The above situations are all problems faced in the pre-pressing process. The main reason is that the temperature uniformity in the pre-pressing furnace is poor, and the local temperature is too high or too low, which will cause glass exhaust and poor edge sealing, and the glass will be degummed after high temperature and high pressure. , The problem of air bubbles affects the product yield and quality. It is necessary to adjust one or more of the temperature, speed parameters and glass placement methods in time for different situations to ensure proper heating and rolling effects. Improve the temperature uniformity in the furnace, avoid local high or low temperature, can better achieve uniform heating of all parts of the glass, cooperate with human process operation intervention, improve the edge sealing effect of glass pre-pressing, improve product yield and make full use of energy .
2.2 Limitations of conventional pre-presses
According to different situations, targeted measures can be taken to solve the poor pre-pressing: if the glass is placed at a certain angle into the pre-pressing machine, the edge is partially progressively rolled and sealed to ensure that the edge and tail can achieve better exhaust edge sealing; Reduce the temperature or speed to achieve sufficient and uniform heating, ensure the uniformity of heating, avoid overheating and seal the edges in advance; when the furnace temperature drops, extend the glass entry time to ensure that the temperature meets the requirements and other measures. Taking these steps may also have limitations and new innovations. The problem. Common pre-pressing machines that rely on infrared and convection heating will have uneven temperature in production due to various reasons, which is unfavorable for pre-pressing heating, especially for some glass with complex structure, large plate surface and strong heat reflection. , the temperature unevenness will be more obvious, which will have a greater impact on the glass exhaust edge sealing. Although the operator has taken various technical measures to improve the preloading effect based on experience, it is still difficult to solve the heating uniformity from the equipment itself. sexual issues. The forced convection heating method can achieve uniform temperature as a whole by injecting airflow into the furnace and forming heat through the airflow to continuously circulate in the furnace. In view of the uneven heating, this defect can be solved from the wooden body of the equipment, which is a good way to avoid Local overheating and insufficient local heating.
3 Features and advantages of forced convection heating pre-press
3.1 Heating characteristics of forced convection pre-press
The forced convection heating of the pre-press is mainly by injecting air flow into the furnace through the fan to form a circulation. Under the action of the air flow, the part with high heat flows to the part with low heat, so as to keep the temperature in the furnace as uniform as possible. This heating method was first used in tempering furnaces in the deep processing industry, which greatly improved the heating efficiency of tempered glass, effectively reduced energy consumption, and significantly improved product quality, especially for Low-E glass heating. , After more than 10 years of development, the tempering furnace with forced convection heating has become the mainstream production equipment for tempering furnaces. The heating principles of the forced convection pre-press and the forced convection tempering furnace are similar, but the specific implementation methods are different. Some sandwich equipment manufacturers have actively researched and absorbed the heating technology of forced convection tempering furnaces, and applied this heating principle to the pre-pressing machine to pre-press and heat the glass, realizing a transformation of the heating technology of the pre-pressing machine and a great improvement. The problem of temperature inhomogeneity in pre-pressing production of laminated glass is solved. The advantages of forced convection pre-compressor are mainly reflected in the aspects of divination.
3.2 Temperature uniformity
Uneven heating is the most important problem in the pre-pressing production of laminated glass. The traditional pre-pressing machine is limited by the heating method and the influence of different glass sizes, glass heating changes, furnace feeding speed control and other factors. In the process of machine heating, it is easy to cause poor temperature uniformity in the furnace, resulting in insufficient heating or overheating of the glass locally, which affects the effect of exhaust edge sealing and causes the glass to fail after high pressure, which is relatively common in pre-pressing production. question. On the other hand, in the pre-presser with forced convection heating, the heat in the furnace is stirred by the air flow sent by the fan, so that the heat flows from a high position to a low position, and the heat distribution in the furnace is continuously improved, so that the temperature in the furnace tends to be Uniformity to avoid local heating overheating. The fan forced convection pre-compressor that the author has contacted adopts a high temperature resistant circulating fan, which cooperates with the in-furnace diversion device to form an internal circulation of thermal energy in the furnace to maintain the uniformity of the temperature in the furnace and improve the problem of uneven heating. Relieve the problem of local overheating or insufficient heating, achieve a satisfactory pre-pressing effect, and solve the heating problems of different types of laminated glass.
The advantages of forced convection uniform heating are described below with examples for two typical laminated glass production.
The heating advantage of thick plate glass: when thick plate glass enters the roller press, the interior of the glass is heated slowly due to the thicker glass, while the outer surface is heated faster than the middle part, especially the edge is heated faster, which is easy to cause the middle part. It has not been heated and exhausted, but the edge has been sealed, and the air cannot be removed and a large amount of air remains, resulting in degumming and air bubbles after high pressure of the glass, which is a fatal problem for laminated glass. In conventional pre-pressing production, the solution to this problem is to use "warm water to boil a frog" to reduce the temperature and speed, so as to achieve the uniform heating of the glass as much as possible, the production efficiency is low and the problem cannot be fundamentally solved. When the forced convection roller press is used to produce thick plates, the air flow generated by the fan moves in the furnace where the heat is high and flows to the low position, and the heat continuously forms a uniform distribution in the furnace, which is beneficial to increase the heat absorption in the middle part of the plate, while reducing the heat. Overheating at the edge position can effectively avoid premature edge sealing, improve exhaust conditions, and form an ideal edge sealing effect.
Low-E glass heating advantages: Low-E glass has strong reflectivity to heat due to its own film characteristics, so that the heat transferred to the film surface is reflected, and the heat absorption efficiency towards the side of the film surface is significantly reduced, and the heat in the furnace is reduced. A surplus is formed on the side facing the film surface. For non-convective pre-pressing machines, there is no better way to improve it. The accumulation of excess heat not only heats the edge of the glass quickly, but also aggravates the heat accumulation at the edge, causing the edge Overheating and sealing the edges in advance, the energy consumption is also large. Some manufacturers glue the Low-E glass film layer and the interlayer to make laminated glass, the interlayer is in contact with the Low-E film surface, and the heat reflection of the film layer directly heats the interlayer film again, and the heating situation is improved, but this brings three The first problem is that after bonding with the interlayer film, the heat supply/heat transfer coefficient is much larger than the heat transfer coefficient of Low-E, which means that the Low-E film layer is short-circuited and loses its contribution to the U value of the heat transfer coefficient. The second is that Low-E is that the mechanical characteristics (tensile force and shear force, etc.) of the multi-silver film layer are poor, which reduces the firmness of the laminated glass. The third is that the immersion of water vapor is more likely to oxidize the Low-E film layer, and further reduce the mechanical and light properties of the laminated glass.
When Low-E glass is used for interlayer production, the film can only be exposed to the outside without losing its functional properties, and it needs to be combined with other glass to make it hollow. Forced convection is the most targeted for the problem of reflected heat of Low-E glass, and plays a positive role in dredging. Through forced convection, the heat is evenly distributed in the upper and lower parts, which effectively solves the heat reflection problem faced by Low-E laminated glass in rolling. , improve the heating efficiency and improve the problem of exhaust edge sealing. Maintaining temperature uniformity in the pre-pressing furnace is of great significance to the pre-pressing production of laminated glass, which is conducive to glass heating, exhaust and edge sealing, and ensures the pre-pressing effect, especially for the continuously added special products.
3.3 Energy saving
Under normal circumstances, some parts of the glass are not heated enough during the production process. The only way to do this is to increase the heating temperature or reduce the operating speed, or use both. The drawbacks of this solution are also obvious, which may lead to overheating at the edge. phenomenon, consumes energy and affects production efficiency, and is also not conducive to product quality control. The heat forms circulating convection in the furnace, the temperature uniformity is better and the heat is fully utilized, which not only improves the heating efficiency, but also speeds up the production progress and the production efficiency is higher. Compared with pre-pressing furnaces with other heating methods, the forced convection furnace has a lower heating temperature setting, but the production speed is not slow. The temperature setting of the traditional pre-pressing machine is generally around 120-280 °C, while the forced convection roller press that the author contacts The maximum temperature setting of the glass is only about 150 ℃. Some enterprise personnel have done a comparative test on the temperature setting of the forced convection pre-pressing furnace and the infrared radiation pre-pressing furnace to produce Low-E glass. The same glass structure and size, infrared radiation pre-pressing The furnace temperature was set to zone 1: 180°C in the upper part and 160°C in the lower part; zone 2: 230°C in the upper part and 200°C in the lower part, and the speed was 0.8-0.9m/min. The temperature of the forced convection pre-pressing furnace is set to zone 1 and 2: the upper part is 90°C, the lower part is 90°C, and the speed is 0.6-0.8m/min. The difference is that the forced convection method in this test is lower than the infrared radiation method in terms of heating efficiency, while the forced convection pre-pressure heating furnace I contacted is no different or even faster than the traditional pre-pressure heating furnace. The improvement of heating efficiency is Significantly, the production efficiency improvement space is also large, and the energy saving effect is better.
3.4 Improve product quality
The biggest feature of the forced convection roller press is to improve the temperature uniformity in the furnace, which is conducive to the uniform heating of the glass, and the problem of overheating at the edge of the glass is also effectively controlled, which solves the most important problem faced by the traditional roller press. The effect of glass pre-pressing and exhaust edge sealing has been significantly improved, and the exhaust edge sealing effect of various new products and complex products has also been effectively improved, which further improves the yield of sandwich production and better control of product quality.
4 Conclusion
Forced convection roller press has obvious advantages in the production of laminated glass, and it also has good effects in improving production efficiency, saving energy, improving product quality, etc., improving the quality of enterprise products, and continuously meeting customer needs and satisfaction. Increase the economic benefits of the enterprise. However, there are many processes involved in the production of laminated glass, from slicing to edging, tempering, color glaze and even external processing. Better improve product yield and quality, enhance the market competitiveness of enterprises, achieve energy conservation and efficiency, and create more economic and social benefits for enterprises.
- Transferred from Xinglass.com
