Analysis and Countermeasures of the Causes of the Edge Lines of Float Glass

0 Introduction In the past ten years, the domestic glass industry has developed extremely rapidly. The oversaturation of the market has resulted in increasingly fierce competition among enterprises. For glass original glass manufacturers, the control of quality and cost is the primary goal of maximizing their profits. This article analyzes the reasons for the problem that the edge line of the glass plate affects the total yield that has occurred with the commissioning of the domestic large-scale float production line in recent years, and proposes an improvement plan from the perspective of production, as well as from the perspective of design and construction. Recommendations accordingly. 1 Example of the influence of the side line on the total yield of glass production In one of the two 900t/d float production lines in China, there are formed glass plate edge lines on the left and right sides. If the width of the original glass plate is enlarged, the product quality is guaranteed not to be affected; if there is no edge line, the original plate width can be reduced by 50~150mm, so that the total yield can be improved without increasing the control level and investment 2 Causes of side lines There are two types of edge lines: one is that the liquid glass near the wall of the flow channel flows out of the lip brick and is partially folded, and flows back to the deformation line formed by the wet back brick, which is the so-called J-Line (J-Line); The second is the (upper) contour line of the molten glass (Vacano) after passing through the flow gate. The edge line is formed as shown in Figure 1. According to the theoretical forming conditions of float glass, the edge line is within the range of edge cutting. However, due to the design of domestic kilns and tin baths, the runners and launders are installed before the kiln, basically no expansion joints are reserved. At the same time, the thermal expansion control of the kiln and tin bath is lacking during the baking process. The runner is squeezed by the working part to move too much downstream, and the bottom shell of the tin bath moves a little upstream, resulting in two of the three key dimensions of the lip area of ??the tin bath. The distance between the eight-shaped bricks) deviates from the design requirements, the recirculation distance of the wet back zone becomes longer, and the distance between the projection point of the lip brick and the eight-shaped bricks increases, which causes the J-shaped line or contour line to move to the inner side of the glass plate. Because the glass ribbon at its location has a large optical distortion and is far away from the edge of the glass and cannot be cut during edge cutting, the width of the original plate must be enlarged to ensure product quality, which ultimately affects the total product yield. 3 Plans and measures to reduce the influence of the side line in the production process The formation of the edge line of the glass ribbon is caused by the longer recirculation distance in the wet back zone and the larger the distance between the projection point of the lip brick and the eight-character brick. In the actual production process, two aspects can be considered to reduce the impact of the edge line on the total. The impact of yield. (1) Reduce the recirculation distance in the wet back zone. Due to the design and the backward expansion of the glass melting furnace work department, it is difficult to change the lip brick if it is found to be too deep one day after production. Therefore, it is difficult to operate and control, and the effect is small, so it is not recommended. (2) Reduce the distance between the projection point of the lip brick and the eight-character brick. By adding a fixed edge brick with a height and width of 70~90mm on the inner side of the original eight-character brick, the distance between the projection point of the lip brick and the eight-character brick is reduced, so that the edge line goes to the edge of the board and falls outside the net board width. Reduce edge loss. 1 Added fixed edge bricks. Add sillimanite or sintered mullite for edge fixing bricks, and symmetrical processing on the other side. Length A is 600~800mm, height and width B and C are 70~90mm, and D is set according to the depth of tin liquid at the front end of the tin bath. The angle X is determined according to the opening of the eight-character brick. 3 Installation and use. Before installation, put the fixing rod on the rear end of the fixed side brick with the bolt hole position directly above, fix the fixed side brick with bolts and auxiliary washers, then open the edge seal at the front entrance of the tin tank, clean the upstream part of the eight-shaped brick, and fix the fixed side brick. Advance along the edge of the eight-character brick and slowly press it into the tin liquid. The upstream side of the fixed side brick is close to the side brick of the runner, and the level and extension length of the fixed side brick are adjusted. The extension length needs to be adjusted according to the actual situation. 4 Effect evaluation. After installing the new fixed edge bricks, the edge line is moved to a position 110~140mm away from the edge of the glass strip, which basically falls outside the net plate width, reducing edge loss and increasing the theoretical total yield when producing conventional glass Increased from 1.33% to 2.75%. 4 Suggestions for design and construction (1) Generally, in the design of the tin bath, the height of the lower edge of the launder from the tin liquid level is 50~70mm, and the length of the launder into the trough (distance from the backing brick) is 60~130mm. In a large-tonnage kiln The above parameters take the maximum value. Since the runner and launder are installed before the kiln in the domestic tin bath design, no expansion joints are reserved. Considering the expansion of the lip bricks pushed into the tin bath, the maximum length of the launder can be shortened to 10mm. , That is, the length of the runner into the groove (distance from the backing brick) in the design is 60~100mm. (2) In the domestic tin bath design, the roller connection method still exists between the front end (1bay) of the tank bottom steel plate and the tank bottom secondary beam. Compared with the bolted connection method, the former is more likely to occur during the baking process. The tin bath expands forward, so during the construction process, the two connection methods of 1bay should take fixed measures to ensure that the tin bath does not expand forward during the baking process, but steadily expands towards the transition roller table and the annealing kiln. (3) During the installation of the runner lip bricks, carefully construct in accordance with the design drawings to ensure the construction quality and measure the distance between the projection point of the lip bricks and the backing bricks. Before the temperature of the kiln and the tin bath is heated up, one is to mark the position of the projection point of the lip brick, and then to measure and compare the changes in the cold value after the baking; the second is to thoroughly inspect all the steel structures of the tin bath to ensure that the tin The trough body can smoothly expand backward through the roller. At the same time, in the process of heating up, timely inspections should be done and the expansion situation should be grasped through the ruler. (4) After the production line has been put into production for a few years, if the runners and lip bricks are eroded and must be replaced, the runners can be modified, that is, the spare runner bricks, etc. can be shortened or the runner bricks can be re-sized and redesigned by professionals. Custom-made bricks (when processing spare bricks, consider that the side bricks of the runner have a certain angle and size changes. The size error between the front and rear brick interfaces will easily form the steps of the runner side bricks. Pay special attention to the processing accuracy and ensure that the runner installation conforms to Process requirements), that is, shorten the length of the launder, which is determined according to the actual length of the launder in comparison with the design requirements.