Study And Design Of Float Glass Annealing Lehr

Float glass and its products are widely used in architecture, traffic, transportation and economic departments. Its output and application occupy an important position in various glass products. Float glass production line mainly consists of melting furnace, tin bath, annealing lehr and cold end. Among three major thermal processes of float glass production, the quality of the annealing has direct influence on the cutting, transportation, further processing and safety of everyday use of glass. The purpose of annealing is to eliminate the residual stress and optical inhomogeneity of glass ribbon, stabilize internal structure of the glass, gurantee the mechanical strength and other properties of glass products.With the increasingly fierce competition of float glass market, products with various types and specifications, high quality and high yield have become the effective way to boost competitiveness. More and more enterprises are trying to produce ultra-thick and ultra-thin glasses. However, many problems like crack and hard cutting are found during the process of annealing. The lehr can't produce products when glass thickness changes, especially for thick glass. For example, at the first stage of producing glass with the thickness of 10mm or 12mm, it's very difficult to make lateral cutting or longitudinal cutting. Although specialists give the guidance on site, adjust the process according to the annealing curve, it proves to be useless and cause huge financial loss.All these have close relationship with the design of annealing lehr. It will cause such problems ??rack, breaking and hard cutting if irrational design, improper technological parameters and bad temperature control are adopted. Serious when can cause no finished products for several hours even many days, especially for old-tpye annealing lehr. Although the manufacturers of float glass and equipments of annealing lehr have made continuous study on the improvement of technical performance and process procedure, some problems are still found in actual production which needs analysis, improvement and innovation. Therefore, carrying out the research deeply in this field will make important practical significance.In allusion to the problems found in actual production, shortage existing in original design is indicated and upgrading proposal is put forward on the basis of overall theoretical analysis and production practice. By studying on float process of two international companies, combining control strategy for stress optimization of hot-air process with annealing state of cold-air process, a set of proper annealing process is found to guarantee the insulating and sealing of casings and optimal control of annealing temperature.Learning from deign experience and advanced technology of annealing lehr at home and abroad, a 140 t/d annealing lehr for float glass is designed by using PICAD. Annealing lehr adopts hot-air circulation, all-steel and tunnel-type structure,being made up 2 sections respectively annealing and cooling sections. The annealing section is made up of 3 sections respectively zones A, B and C, the thermal process of annealing section is radiation heat exchange. The heat exchange between glass and cooling air is achieved by heat exchanger above and below ribbon. The cooling section is made up of 2 sections respectively zones D and F, the thermal process of cooling section is forced convection heat exchange. The thermal process of zone D is hot-air forced conventio??at exchange and zone F is cold-air direct forced convention heat exchange.The lehr has the following features: To manufacture, install the lehr from the point of processing and producing, the quality of this equipment is reliable and each function of the lehr can be achieved; multiple layers insulating materials is used for the lehr with strict filling process to ensure the best insulation and sealing for casing of the lehr; according to the requirements of process to assemble the electric heating elements reasonably, reasonable design of air system for the lehr, temperature of the hot air circulation can be regulated at any time to ensure the ribbon at the important annealing area can be cooled slowly, the lehr can be controlled by automatic.As one of three major thermal equipments of float glass production line, annealing lehr should eliminate the pernament stress of the glass on one side and transport the glass to cold end on another side. If roll table is out of commission, stay time and temperature control of glass in each zone will be badly affected, causing crack or scratch. Roll table consists of a series of rollers whose quality directly affect the surface smoothness of the ribbon. The safety factors of properties of rollers should be high because of poor working conditions. However, it takes a long time to get the working condition of rollers. In mechanical engineering, FEA (finite element analysis) is widely used in study of structure, vibration and heat transmission. In this text, FEA is used in the design of roll table of annealing lehr which is effective way to improve the design, optimize structure and save test cost. The model of roll table is established by 3D Designing Software Solidworks. The working performance of rollers with different materials and structures are analyzed by Finite Element Analysis Software COSMOSWorks, which is embedded in Solidworks, to get data for the design of roll table as well as the necessary information for modification and optimization.140 t/d annealing lehr runs well after being put into production. The actual production proves that the structure is designed reasonably, temperature control curve reaches the design requirements, the glass ribbon is cooled under the control. When producing float glass with the thickness of 2.8~19 mm, daily pulling-rate reach above 140 tons adn glass is flat and smooth. The rate of finsihed products reach above 96%, realizing high quality and high yield.