Glass Tempering Research Articles

Fuzzy self-learning control of glass tempering and annealing temperature based on the optimised genetic big data analysis algorithm

Fuzzy self-learning control of glass tempering and annealing temperature based on the optimised genetic big data analysis algorithm

Influence of radiative heat transfer model on the computation of residual stresses in glass tempering process

AbstractDuring glass tempering, residual stresses are caused by the temperature gradient appearing between the surface and the core of the glass. It is therefore necessary to have an accurate knowledge of the heat transfer occurring during the process to obtain an accurate estimation of the residual stresses. Since glass is a semitransparent material, radiative heat transfer takes place inside the glass in addition to the conductive heat transfer. In this paper, we implemented 1‐D thermomechanical models using different methods for the computation of the radiative effects inside the glass: Rosseland approximation, P1 approximation and back ray tracing. Thermal and residual stresses results are compared to experimental results available in the literature to investigate the effects of the different methods on the heat transfer and mechanical behavior. We found that P1 approximation and back ray tracing are in good agreement with the experimental results. Finally, a numerical investigation is done by changing different parameters for which the experimental results are not available.

Heat transfer rate and uniformity of mist flow jet impingement for glass tempering

The thinning and miniaturization of components, such as liquid crystal display and solar cells, has increased the market demand for tempered ultra-thin glass. The physical tempering in glass, which is less than 2mm thick, is difficult to achieve in air jet impingement. In this study, we propose the use of mist flow jet impingement cooling technology on ultra-thin glass. The effects of the mist flow droplets diameters, nozzle inlet temperature, and mass fraction on the heat transfer rate and uniformity are numerically studied. Our performance in terms of the heat transfer rate and the uniformity is accounted for through an evaluation of the surface-averaged temperature, averaged Nusselt number, surface-averaged Nusselt number, and surface standard deviation percentage of the Nusselt number. The empirical correlation for the surface averaged Nusselt number asa function of mist flow droplet diameters is provided. The droplet diameter is the major factor affecting the heat transfer rate, while the jet inlet temperature is a minor factor. We can obtain a better heat transfer uniformity by controlling the droplet diameter of the mist flow jet impingement. Using mist flow jet impingement, we would not only greatly reduce the amount of air and save energy, but also meet the needs of sudden cooling for tempered glass with a thickness of less than 2mm.

Influence of Nozzle-to-Surface Distance Ratio and Reynolds Number Variation on Hemispherical Tempered Glass Strength and Quench Time

The quenching step in a glass tempering process is a transient heat transfer phenomenon which is governed by several parameters – Reynolds number (Re) and the nozzle diameter-to-surface distance ratio (H/D) . In this research, the effect of such parameters on the strength and quench time of hemispherical tempered glass are to be analyzed. The quenching process will use the impinging jets quench method, with an equilateral – staggered nozzle arrangements. The process is performed in an ambient air of 60 o C and with a nozzle pitch and diameter of 27 mm and 4 mm respectively. The study applies variations of Reynolds number: 2300, 10000, 20000, 30000, 40000, 50000, 60000, 70000, 80000, and 87000, and H/D: 2, 6, 9, and 12 . These variations are used to construct and solve a mathematical model, to obtain temperature distribution contours. The contours are then transformed into stress distribution graphs. From these steps, it is found that the tempered glass strength increases and the quench time decrease along with the increase of Re and the decrease of H/D. It is also found that the allowable range of operation is between Re = 8000 – 25000 for H/D =2 and Re = 8000 – 30000 for H/D = 6, 9, and 12.

Experimental investigation of the relationship between heat transfer rate and number of broken glass particles in tempering process of glass plates

Thermal glass tempering process is based on heating the glass in a furnace and suddenly cooling it down in a cooling unit. The quality of the glass obtained at the end largely depends on the heat transferred from the glass surface. In this study, the glass tempering process was conducted in a specially designed and manufactured glass tempering unit prototype, and the change in the local number of broken glass particles was examined based on the local heat transfer rate. A 6-mm-thick flat glass in 170×170mm dimensions was used in the study. Two single nozzles, 13mm in diameter and 300mm in length that were placed against each other were used for the cooling process. The distance between the nozzle and the glass plate surface was taken as 1⩽H/D⩽10, and the Reynolds number as 40,000⩽Re⩽60,000. In the sudden cooling process conducted according to different H/D ratios and Reynold numbers, the cooling times, and the local, average and stagnation-point Nusselt numbers were obtained. Then, the tempered glasses produced under these conditions were broken apart, and the number of particles was determined. The results showed that the cooling time firstly decreased and then increased with H/D ratio generally, whereas it decreased as the Reynolds number increased. It was also observed that as the average Nusselt number increased, the number of particles also increased. Besides, as the air jet moved away from the stagnation point, the Nusselt number decreased, and concordantly, the number of particles also decreased. It was found that the number of particles was substantially proportional to the heat transfer rate.

Spray mist cooling heat transfer in glass tempering process

Energy saving is a very important issue in glass plants, especially in a glass tempering process, where very high velocity air jet impingement is applied during the cooling process of glass tempering. In fact, air compressor energy may be reduced by a spray cooling due to its high heat transfer capabilities. Presently, in this paper, both pure air and water mist spray cooling are investigated in the glass tempering process. The test results indicate that thin and low-cost tempered glass can be made by mist cooling without fracture. It is possible to find the optimal water flux and duration of mist application to achieve a desirable temperature distribution in the glass for deep penetration of the cooling front but without inducing cracking during the tempering. The use of mist cooling could give about 29 % air pressure reduction for 2-mm glass plate and 50 % reduction for both 3- and 4-mm glass plates.

放射状不足膨張噴流のスクリーチ現象に関する研究

Supersonic impinging jet on at flat plate is commonly used as a simple model of flow field of industrial applications of high speed jet such as an assist gas for laser cutting, a cooling jet in glass tempering process and so on. In case of axisymmetric jet, the air flows radially along the plate after the impingement and forms an underexpanded jet under certain conditions. In this study, such radial underexpanded jet is issued from a slit nozzle, which consists of two circular tubes facing to face each other. Jets at different pressure ratios across the nozzle are experimentally visualized using Schlieren method. Screech sound radiated from the jet is measured using microphone. Position of the sound source is considered to be near the end of second cell or in the region downstream of the second cell.

Influence of Creep Model on Glass Tempering Process

In this paper, an in-depth research adopted a creep model has been conducted to focus on the stress during the process of glass tempering based on the finite element software ANSYS.During this research an simplified model of glass tempering has been established, and as a result the expected stress value of surface and mid-plane was achieved.The results show that using the creep model can also achieve the same simulation effect of glass tempering.

Identification and reduction of vibration and noise of a glass tempering system

The vibration and noise of a glass tempering machine at a factory are studied. Experiments were conducted to identify the sources of vibration and noise. It was found that main sources for vibration and noise are two air barrels, the air pipes from the fans to the glass tempering machine and the fans location. Solutions were suggested to reduce vibration and noise from these three main sources. One of the solutions that were implemented is placing rubber dampers beneath the air barrels and pipes which almost cancelled the horizontal vibrations in the building structure and reduced the vertical vibrations to a low value most likely coming from noise. There are two types of noise, namely, radiation noise from the fans through the fans room walls and transmitted noise through the pipes caused by turbulence. A glass wool noise insulating layer was installed on the wall between the fans room and factory to reduce radiation noise through this wall. Part of the air pipe system in the factory is made of a light material which produced the highest levels of noise above 110 dBA. These air pipes were wrapped by glass wool rolls and the noise level near them was reduced to below 100 dBA which comes from other machine parts. In addition, noise levels were reduced between 2 and 15 dBA at different points in the factory.

Study on the Basic Characteristics of Low Oxygen Air Combustion with Natural Gas in Glass Tempering Furnace

The basic characteristics of natural gas with low oxygen air combustion is analyzed, and low oxygen content, excess air ratio, and the change of flue gas composition are studied, the results show that using the technology of low oxygen air combustion for glass tempering furnace in production has directive significance. The composition content of carbon dioxide and water vapor increases in the combustion products. The radiation heat transfer is decreased in glass tempering furnace. The furnace temperatures are maintained in the range of 650 to 800°C.

Behavior of shock waves formed in supersonic jet impinging on flat plate

This paper focuses on the behavior of shock waves formed in an underexpanded impinging jet. The jet becomes underexpanded when the pressure ratio exceeds the critical value across the convergent nozzle discharging it. When a flat plate is placed perpendicularly to the jet, the strong shock wave called ‘plate shock' appears in the flow field near the plate. The underexpanded jet discharged from a nozzle into the atmosphere is often used for industrial applications, e.g., an assist gas of laser cutting and a cooling jet in glass tempering process. The jet impinges on the work piece and spreads out on its surface. So this study concentrates on the relation between the jet oscillation and the location of the work piece and especially discusses behavior of shock formed in jet. The impinging jet was formed under conditions of different nozzle pressure ratios and nozzle-plate spacings and was visualized using the shadowgraph and schlieren methods. The instantaneous shape of jet was measured through analyzing the pictures taken at random under each condition and the oscillation pattern was examined. In addition, under the same conditions, a numerical study was carried out using TVD scheme. As a result, it was found that the oscillation pattern of plate shock depends on its location and the nozzle pressure ratio.

Optical and Micro-Mechanical Properties of Ag-Based Low-E Glass by Magnetron Sputtering

Ag-based low-E films with a multilayer construction of top-Si3N4/SnO2/NiCrOx/Ag/ZnO/ NiCrOx/TiO2/under-SiOxNy were deposited on unheated glass by vacuum magnetron sputtering and then post-treated in the glass tempering furnace at 675±25°C for 4 min, 5 min and 6 min, respectively. The effects of tempering time on the surface morphology, optical and micro-mechanical properties have been investigated. The results show that the edge of the particles become vague with the increasing time. After tempering, the transmittance of 550 nm is higher than that of the as-deposited glass of 75.89%. Ag-based Low-E films tempered at 675±25°C for 6 min possess the biggest value of the figure of merit of 6.86×10-3 Ω-1 and exhibits the optimal optoelectronic properties. The composite nanohardness increase from 8.04 GPa to 9.23 GPa and the elastic modulus increases from 62.39 GPa to 84.58 GPa when tempered from 0 min to 6 min.

Effect of glass tempering on microstructure and functional properties of SnO2:F thin film prepared by atmosphere pressure chemical vapor deposition

The low-emission glass was prepared via depositing fluorine-doped tin oxide thin film on glass substrate by atmospheric pressure chemical vapor deposition method. The as-deposited low-emission glass was found to present a SnO2:F/SiCxOy/glass sandwich structure via focused ion beam technique and transmission microscopic measurement. After tempering process at ~650°C with varied periods, the electrical and optical properties of the SnO2:F thin film remained stable for less than 10min, but decreased dramatically when the tempering period exceeded 10min, which was mainly due to the oxygen chemisorptions and fluorine ion diffusion. It was observed that the SnO2:F thin films presented uniform polycrystalline nature of cassiterite structure throughout the tempering process. The study has therefore suggested the appropriate tempering conditions for the SnO2:F low-emission glass, and provided a critical guidance for further energy-saving glass applications.

Surface structure and electrical properties of Ag based low emissivity film by vacuum magnetron sputtering

Ag based low emissivity film was deposited on glass by vacuum magnetron sputtering and then post-treated in the glass tempering tempering furnace at 650–700°C for 4, 5 and 6 min respectively. The structural and electrical properties have been investigated as a function of post-treatment time. The results show that with increasing heated time, the structure of the film gradually crystallises and Ag2O (111) appears. The resistivity and sheet resistance have a sharp increase from as deposited to heat treated films and then decrease with increasing time. The calculated emissivity is 0·16 for the as deposited film, increases to 0·39 heated for 4 min and decreases to 0·14 heated for 6 min.

Laser sheet scattered light method for industrial measurement of thickness residual stress distribution in flat tempered glass

The paper presents the laser sheet scattered light technique, a fast optical non contact method for measuring internal stress distribution over a cross section of flat glass specimens, designed for closed loop control of glass tempering furnaces. The technique is an evolution of the scattered light method for flat glass residual stress analysis and allows a full thickness stress profile to be measured with a single shot acquisition across a glass plate without any contact. A linearly polarized laser sheet, shaped into a thin plane of parallel light beams, enters orthogonally to the side of the flat glass illuminating its full thickness. Light sheet is orthogonal to the glass surface and travels parallel to it. Stress induced birefringence through the glass affects light polarization, thus scattered light intensity detected at 90° with respect to the polarization of the incident light appears spatially modulated in intensity. A camera aligned orthogonal to the laser light polarization collects an image of fringes whose shape is digitally analyzed to measure the thickness stress state. The paper describes the development of this technique by recalling the scattered light method, then describing its automation by scanning a collimated beam across the glass thickness and finally by showing that the scan method can be substituted by the light sheet method. Light sheet method provides a full field non contact stress measurement across the glass thickness, thus allowing for a fast inspection method, suitable for industrial use. Flat glass items for industrial use have bevelled edges; this does not allow measurements close to glass surface. To solve this limit, experimental data are extrapolated by a symmetrical polynomial fitting and imposing a zero integral to the stress profile. Results on surface stress measured by the laser sheet scattered method are in agreement with those of the automated light scattered method and show a fair agreement with measurement by an epibiascope, thus proving the applicability of the method for fast and contact-less detection of residual thickness stress; the industrial application of the method is outlined, so that a tempering furnace could be controlled using feed-back data from thickness stress measurements on flat glass.

Radiative Heating of a Glass Plate

This paper aims to prove existence and uniqueness of a solution to the coupling of a nonlinear heat equation with nonlinear boundary conditions with the exact radiative transfer equation, assuming the absorption coefficient κ(λ) to be piecewise constant and null for small values of the wavelength λ as in the paper of N. Siedow, T. Grosan, D. Lochegnies, E. Romero, “Application of a New Method for Radiative Heat Tranfer to Flat Glass Tempering”, J. Am. Ceram. Soc., 88(8):2181-2187 (2005). An important observation is that for a fixed value of the wavelength λ, Planck function is a Lipschitz function with respect to the temperature. Using this fact, we deduce that the solution is at most unique. To prove existence of a solution, we define a fixed point problem related to our initial boundary value problem to which we apply Schauder theorem in a closed convex subset of the Banach separable space L 2 (0,t f ;C([0,l])). We use also Stampacchia truncation method to derive lower and upper bounds on the solution.

Fuzzy Neural Network Controller Based on Improved Genetic Algorithm for Temperature of Glass Tempering and Annealing Process

The temperature control of the glass tempering and annealing process has characteristics of time-varying parameters，nonlinear and big lag. It is difficult to meet the expected control effect with the common control method. To solve this problem，this paper puts forward a kind of fuzzy neural network controller optimized by genetic algorithm. First，it uses neural network to construct fuzzy logic system according to the structure equivalence rule，thus the optimization of fuzzy control rules and membership functions can be realized by finding the weight value of the neural network. Then，it uses the improved genetic algorithm to find the global optimum weighted factors with a high speed so to improve the performance of the controller. The simulation results show that the optimized fuzzy neural network controller can obtain an excellent control performance for the nonlinearity system with time- varying parameters and lag.

Finite element implementation of a glass tempering model in three dimensions

The present paper develops and validates a 3D model for the simulation of glass tempering. It is assembled from well-known models of temperature dependent viscoelasticity and structural relaxation and predicts both transient and steady-state stresses in complex 3D glass geometries. The theory and implementation of the model is comprehensively given and the model is carefully checked and validated. It is demonstrated that by adjusting a single parameter in the model, experimental results can be replicated accurately even for cooling rates far from normal.

Metal Corrosion and its Impact on Glass Tempering Furnace Design

A reliable well‐designed tempering furnace is considered to be the cornerstone of any modern glass‐processing facility. This paper addresses a series of engineering anomalies encountered during the commissioning of such a glass‐processing furnace. Following the installation of a furnace in a European facility, small black deposits were noticed on both the silica‐fused rollers used to transport the glass through the hearth of the furnace and on the processed glass surface itself. EDAX and scanning electron microscopy investigations indicated conclusively that the deposits were primarily constituted of sodium sulfate and trace elements consistent with stainless steel (chromium, iron, and nickel). Traditionally, high‐density glass fiber was used to insulate the roof walls and side walls of tempering furnaces; however, it was noticed in this particular case that rolled stainless steel sheeting (SS316) was used. Chemical and X‐ray diffraction analyses were used to pinpoint the origin of the deposits. It was determined that poor material selection choices taken during the design stage of the furnace in question were at fault. The combination of stainless steel and sulfur dioxide (SO2 is used as a lubricant to prevent scuffing) at elevated temperatures (>650°C) generated droplets of sodium sulfate, which condensed due to the convectional flow of the heat currents within the oven. These droplets scorched the glass surface and destroyed the fused silica rollers. As a recommendation, the usage of stainless steel and other nonrefractory metals should be avoided in the design of any future glass tempering furnaces.

Glass tempering heat transfer coefficient evaluation and air jets parameter optimization

A design of experiments (DOE) matrix of CFD simulations is used to create a mathematical model able to calculate the heat transfer coefficient for nine circular confined air jets vertically impinging on a flat plate. Typical air jets dimensions and process parameter values used in glass tempering are evaluated. The flat plate temperature is set to the constant value of 640 °C. Two different values of jet diameter (4 mm, 8 mm), of air velocity at nozzle exit (110 m/s, 140 m/s), of jet-to-jet spacing (40 mm, 60 mm), of jet-to-plate distance (40 mm, 60 mm) and of nozzle height (20 mm, 60 mm) are considered. Implemented into a Visual Basic application, the mathematical model found allow the instant evaluation of heat transfer parameters and to optimize air jets parameter configuration.