IR-Annealing Technology for Glass Products

The advantages of IR annealing of glass and glass products, as compared with convective annealing, are demonstrated. Results of testing of IR annealing of glass products are described.     

Fine Annealing of Optical Glass

Since the most important characteristic of optical glass is the uniformity of its refractive index, which is itself a function of fictive temperature, any fine annealing treatment must be such as to bring about substantial uniformity in fictive temperature. Methods of accomplishing this are reviewed. In terms of total required time in the annealing process, the most efficient method consists of soaking the glass for a short time at a temperature near the annealing point and cooling at a constant rate to a temperature below the annealing range and at an increased rate to room temperature. Formulas are given for specifying the parameters in the annealing schedule in terms of the final condition of the glass as to stress and index. The several outstanding advantages of this method of annealing are discussed.     

Mathematical Models for Statistical Analysis and Control of Sheet Glass Annealing

A method and application results are described for using mathematical models in statistical analysis and control of the annealing regime of a glass band transported inside a tunnel furnace. The results of a computational experiment estimating the efficiency of the algorithms of the annealing regime control are discussed. The possibility for reducing waste and improving the quality of polished glass annealing is demonstrated.     

Optimum Schedule for Annealing Flat Glass

This paper formulates and solves the problem of optimum annealing of glass in which one seeks to minimize either residual stress or annealing time. An approximate analysis shows that residual stress is a weighted integral of cooling rates and that an optimum schedule is obtained when the cooling rate is inversely proportional to the square root of the weighting function. Several multibreak annealing schedules are investigated. It is found that a practical and nearly optimum schedule in this class is a two-break schedule that cools glass most slowly in a 65°CC interval and most rapidly outside this interval. It yields an optimum stress significantly lower than that of a constant-rate annealing schedule. Furthermore, the optimum is not very sensitive to minor changes in the schedule.     

Modelling Annealing Lehrs for Flat Glass

Computer simulation of heat transfer in annealing lehrs for flat glass is combined with a method developed earlier for the calculation of stresses in glass. With this combined model one can predict stresses produced by annealing schedules that are readily realized in practice. Implications for the design, operation, and energy economy of lehrs are discussed.     

High-precision molding simulation prediction of glass lens profile for a new lanthanide optical glass

Precision glass lens molding (PGLM) is a recently developed method for fabricating glass optical components with high precision in large volumes. Lanthanum optical glasses are extensively used as optical materials owing to their superior optical properties, such as high refractive index, low dispersion, and high transparency. However, the transformation temperature of currently available high refractive index glass is generally above 650 °C and poses a challenge in manufacturing ultra-hard molds, durable coatings, and high-temperature molding equipment using PGLM. In this study, a preparation method for obtaining high refractive index, low -melting -point lanthanide optical glass (B-ZLaT198) used in PGLM was developed to reduce the transformation temperature. The developed method also characterizes the glass refractive indices and thermal-mechanical properties. To achieve the high-precision prediction of a molding shape in a simulation, a viscoelastic constitutive model of glass was established based on a micro-deformation uniaxial compression creep test. Moreover, by solving the Tool-Narayanasway-Moynihan model parameters based on the specific heat capacity fitting of optical glass at different heating and cooling rates, the input parameters of the structural relaxation model (SRM) for simulation prediction of aspheric glass lens profile deviation in the annealing stage were obtained. Finally, the profile deviation of the aspheric lens was predicted using a finite element model simulation. The results showed that the simulation’s predicted profile of an aspheric lens using the SRM model was in good agreement with that of experimental molding profile. In addition, using the SRM provided a higher prediction accuracy than that of the thermal expansion model in the annealing stage. Adopting the SRM was necessary for the annealing simulations of molding pressing and also verified the accuracy of the proposed viscoelastic characterization method for calculating the thermomechanical parameters of optical glasses.     

浮法玻璃的应力与退火

玻璃的退火是浮法平板玻璃生产过程的一个重要环节。文章阐述了玻璃热应力产生和消除方法,指出在线应力检测是控制退火质量的较好途径。     

超薄浮法玻璃显微硬度测量对退火工艺的指导研究

采用带图像分析自动转塔显微硬度计HXD-2000 TMC/LCD进行超薄浮法玻璃显微硬度测量,利用测量结果指导超薄浮法玻璃退火工艺参数调整。退火工艺调整前超薄玻璃的显微硬度分布不均匀,显微硬度平均值的最小值和最大值分别是517.6 kg/mm2、561.4 kg/mm2;退火工艺调整后超薄玻璃的显微硬度分布均匀,显微硬度平均值的最小值和最大值分别是为543.4 kg/mm2、548.7 kg/mm2。结果表明:通过测量超薄浮法玻璃显微硬度,调整玻璃退火工艺,对超薄玻璃生产调整退火参数起指导作用。     

玻璃制品电热退火窑计算机辅助设计

根据Ｌ．Ｈ．Ａｄａｍｓ和Ｅ．Ｄ．Ｗｉｌｌｉａｍｓｏｎ的退火原理和退火规则，建立了玻璃制品电热退火窑的热平衡数学模型，并由计算机计算，计算结果基本上符合实际，应用此软件，可以进行玻璃制品电热退火窑的计算机辅助设计。     

浅论特种玻璃退火窑的传动

特种玻璃退火窑的传动有其特殊性,高温区的辊子材质采用陶瓷辊,其传动方式有三种,对特种玻璃退火窑传动的一些体会与大家探讨。     

浮法在线Low-E玻璃退火窑的设计及控制

结合在线低辐射镀膜的特性,论述了在线Low-E镀膜生产线退火窑设计和操控应注意的几个问题.     

RELATION BETWEEN INELASTIC DEFORMABILITY AND THERMAL EXPANSION OF GLASS IN ITS ANNEALING RANGE*

In accordance with experience concerning the behavior of glass at temperatures within its annealing range, an equation is proposed which relates the various extraordinary heat effects to the inelastic deformability and to the degree of superheating or undercooling. By using this equation in connection with the thermal-expansion curves of a glass within its annealing range, certain constants that are related to the coefficient of viscosity and its changes with temperature and the degree of superheating or undercooling have been determined with reasonable results. Such results make it possible to estimate the inelastic deformability of a glass in its various conditions at all annealing temperatures and are therefore valuable in connection with problems that are encountered in the process of annealing glass. The apparent success achieved in applying the proposed equation to experimental data suggests that the concepts underlying this equation are fundamental and must be considered in any theory concerning the constitution of glass or that of any other extremely viscous liquid.     

VARIATIONS CAUSED IN THE HEATING CURVES OF GLASS BY HEAT TREATMENT1

The variations produced in the heating curves of a glass by previously subjecting it to different heat treatments are often fully indicative of the nature of these previous treatments, and they also bear a relation to changes caused in numerous other characteristics of glass by this same means. The differences in the heating curves arise from differences in the thermal properties of the glass and especially from changes in the magnitude and character of the exothermic and endothermic effects. The physico-chemical processes causing the endothermic are the reverse of those producing the exothermic, i.e., the two effects are related as in the case of the similar and well-known phenomena observed at an inversion point such as is found in many crystals. They are, however, not confined to the usual relatively narrow temperature ranges and are also much more subject to undercooling and superheating. Apparently this resistance to the physico-chemical processes increases rapidly as the temperature is lowered making it possible by rapid cooling to suppress the exothermic processes to a great extent and thereby prepare the way for relatively large exothermic effects on subsequent heating. Since the preparatory exothermic activity is insufficient, the endothermic effects in the heating curves of chilled glasses are never pronounced but may become quite large in these curves if in the annealing, the exothermic processes have the opportunity to continue their activity into the range of relatively low annealing temperatures. During annealing the exothermic activity progresses more and more slowly toward a limit which may be advanced by reducing the annealing temperature. The physicochemical condition which the glass would have if the limit for any given annealing temperature were reached is termed the equilibrium condition of the glass for that temperature and such an equilibrium is presumably kinetic in character. The continuous series made up of all these equilibrium conditions corresponding to the various temperatures in the annealing range is called the equilibrium sequence. It is shown that about any portion of such a sequence, a glass may be made to follow any number of apparently closed cycles and that in traversing these cycles it passes through a series of intermediate conditions which in general do not coincide with the equilibrium sequence except where this is practically insured by very thorough annealing at constant temperatures. At ordinary atmospheric temperatures, the usual type of glass is always in such an intermediate series since in ordinary practice it is impossible to extend the realizable equilibrium sequence tci temperatures much below the lower limit of the practical annealing range. In this range, however, very low rates of cooling or heating will cause a glass to follow its equilibrium sequence with relative closeness after coincidence has once been practically established. In view of the present insufficient knowledge concerning the constitution of glass, the particular processes involved in these changes of physico-chemical condition are presumably too complex and varied for analysis. Apparently, however, the activity of the exothermic type gives rise to a series of molecular readjustments which often limit the ability of the glass to reach other conditions having possibly greater stability especially at relatively low temperatures. In some cases these readjustments may insure a greater permanency to the vitreous state as long as the glass is not heated above the temperatures producing them. A relatively clear conception of these readjustments and of the general behavior of glass in the annealing range may be gained from a consideration of the changing conditions in any physico-chemical system, e.g., a solution, where the equilibrium condition depends upon the temperature but normally does not change simultaneously with it. From the standpoint of investigating certain properties and characteristics, systems like glass yield advantages since their reaction rates are low and give opportunity for many observations during any change of importance and also since the thermal effects caused by superheating and undercooling are readily detectable. The relation which the changes in physico-chemical condition bear to certain problems in practical annealing is also considered, and from the discussion it is evident that annealing procedures may often be manipulated so that the resultant changes in certain propertics (notably the refractivity) will cause a glass to meet standards of requirement which it would normally fail to reach if annealed according to a fixed schedule prescribed for its general type. Although the tolerances of present-day standards are so lenient that adjustments of this character are seldom required or employed, it is believed that the time is rapidly approaching when an extended use will be made of them especially in those cases where a highly-standardized production of optical instruments of great precision is attempted. More important from the optical instrument standpoint, however, is the need of always annealing a glass in such a way that the physicochemical condition is fully uniform throughout the whole piece or blank from which an optical part is produced. In many cases gradients no greater than a small fraction of a degree will, if they exist during annealing, produce nonuniformities which cause greater disturbances than strains of considerable magnitude.     

Automatic control of operating conditions in the annealing lehr of a thermally polished glass line

A computerzed system was developed and integrated into a thermally polished glass line to control the temperature parameters in its annealing lehr. This served to optimize the annealing of Metelitsa glass, to cut down to 2 h the time required for the lehr to attain steady-state operation, and to raise the glass yield to 0.75. Suitable prompts were devised for operators in charge of the annealing operation, and the optimal format was found for the presentation of information about the on-going process. Translated from Steklo i Keramika, No. 7, pp. 3–5, July, 1997.     

DTA evidence for physical orientation (crystallinity) in PVC

A difference has been observed in the DTA and DSC curves for the glass transition of both PVC homopolymer and acetate copolymer, depending on the rate of quenching or annealing below the glass transition temperature. The difference has the appearance of an endothermal peak added to the glass transition curve and is attributed to an alignment of stereoregular chain segments of adjacent polymer molecules. The lengths of chain segments are assumed to be so short that no x-ray evidence of crystallinity was obtained. The orientation process involved has an activation energy of 47.8 kcal./mole in the homopolymer and 43.6 kcal./mole in the copolymer. The measured rate of the process agrees with the principle of time–temperature superposition, the rates becoming equal for homopolymer and copolymer at equal temperatures below their glass transition temperatures.     

DESIGN OF A FURNACE FOR ANNEALING OPTICAL GLASS1

Design of a natural-gas furnace for annealing optical glass.—Most of the furnaces built for annealing regular glassware are unsuitable for optical glass due to irregularity and inequality of temperatures. Working drawings are given for a successful optical glass annealing furnace operated by natural gas. The design is novel in the placing of the flues and burners in such a manner as to supply the heat and remove it in a symmetrical manner, thus obtaining uniformity of temperature.     

用Monte Carlo法对浮法玻璃退火窑间接冷却区内热过程进行数值模拟

基于MonteCarlo法及数值模拟算法,建立了浮法玻璃退火窑间接冷却区（辐射换热冷却区）通用的退火模型,该模型可以对浮法玻璃带在间接冷却区内的退火冷却过程进行模拟仿真。对仿真数据进行现场测试,结果表明：玻璃带与风管的计算值与测量值的最大误差分别为2．12％和-4．64％,整体误差控制在5％以内。     

厚板一次清边及退火缺陷的判断和改善

简单分析了厚板生产时经过退火调整实现一次清边的过程,并结合退火理论对退火不良时出现的玻璃缺陷的判断方法和改善措施进行了分析阐述。     

中国浮法玻璃退火窑的发展现状、改进和提高

介绍了浮法玻璃退火窑结构特点和发展状况,论述了国内浮法玻璃退火窑最新的技术进展,并对改进和提高退火窑技术的可行措施进行了分析和探讨。     

Stress and Volume Relaxation in Annealing Flat Glass

Laboratory simulation of the industrial process of annealing sheet glass has yielded data on the genesis of stresses in initially stress-free glass. The experimental results differed from expectations based on classical annealing theory in that stresses began to develop in the annealing range even when the glass was being cooled at a constant rate, i.e. even in the absence of any changes of temperature gradients within the glass. Typically, these stresses account for 40% of the total residual stress in glass annealed according to a linear schedule. The remaining 60% are the well-known thermoelastic stresses that arise later in the annealing process from the decay of temperature gradients in the glass. The stresses observed to arise in glass as it is being cooled at a constant rate are attributed to volume relaxation effects which, in parts of the annealing range, generate stresses rapidly enough that they are not dissipated by stress relaxation. A mathematical model of annealing is proposed that takes account of both stress and structural relaxation. The model fits the experimentally observed evolution of stresses during linear cooling. It also suggests that (with the activation energies of stress and structural relaxation about the same) the actual rate, at any given temperature, of structural relaxation is about 4 times lower than that of stress relaxation.