The Structure&Temperature Process Design Of A Hot-pressing Furnace For Precision Glass Lens Molding

Precision glass lens has irreplaceable advantages in optical imaging. With the expansion of imaging product such as digital cameras and mobile phones, high requirements of efficiency and accuracy in glass lens production have been demanded.The traditional glass lens processing consists of multiple cutting and grinding method, which not only shows low efficiency but also performs unstable processing precision, especially in the process of machining aspheric lens. Hot pressing technology is a good solution to all these problems. Firstly, hot pressing process only needs one time molding, which simplifies the glass lens production process enormously. Secondly, the molded surface shape and accuracy is controlled by the mold surface, which means it would be easy to achieve a variety of different shape glass lens simply by produce different molds. Thirdly, it is easy to realize mass production by hot pressing technology.In this paper, conceptual design for the hot pressing furnace is raised by investigation and analysis of different kinds of materials and structures. In this area, near infrared quartz heating device is chosen to be the heating mode for its rapid thermal response and high thermal efficiency. At the same time, a strategy combines a new material named silica aerogel with great insulating ability and thermal shielding layer is proposed to be the insulation scheme. After completing the conceptual design of hot pressing furnace, quantitative simulation analysis are carried out to determine the reasonable thickness of silica aerogel which would be embedded in the out wall of furnace and the number of thermal shielding layers which need to be placed between the infrared emitter and furnace inner wall. After comparison, a heating power of3kW is chosen and the strategy combines one layer of stainless steel thermal shielding layer and a thickness of20mm silica aerogel is utilized. Many optimizations include hot pressing stick material choice and structure design based on temperature and dynamic simulation, insulating performance of plated white on infrared tube, influence of pre tightening force on mold die and mold and furnace wall oxidation effect are also carried out to accomplish the detailed design of hot pressing furnace. According to the scheme of furnace, a comprehensive temperature process contains heating, heat preservation, annealing and cooling is simulated to determine the rational heating power curve and nitrogen inlet ventilation rate.A heating module experimental platform is built up according to the simulations. Temperatures are measured by thermocouple which shows correspondence with simulation results. Comparison between experiment and simulation contributes to the optimization of both simulation model and furnace structure.