Glass Tempering Process Research Articles

Optimization of glass spray tempering parameters based on response surface methodology and economic analysis

Glass curtain walls have gained significant popularity as building enclosure structures, owing to their exceptional performance. Consequently, it becomes imperative to reduce energy consumption during the glass tempering process to ensure sustainable development within the construction industry. In this study, an experimental design was conducted using the response surface methodology (RSM). The particle count and cooling energy consumption were selected as the response value, while the influencing factors included four process parameters, namely, the spray distance (H), mist load fraction (f), spray pressure (p), and final cooling temperature (Tz). The second order model fitting of the RSM was used to obtain the polynomial regression equation between each response and each factor. Under the optimized conditions of H = 200 mm, f = 1.03, p = 0.5 MPa, and Tz = 150 °C, the number of fractured glass particles was found to be 234, and the cooling energy consumption was 0.00048 kW·h. Further analysis indicated that under these spray conditions, the net present value was 523.90 k$, and the dynamic payback period was 1.1 years. Compared to traditional air-cooled tempering, spray tempering demonstrated superior economic performance.

Analysis of the effect of jet channel structure on the temperature uniformity of tempered glass

The air jet nozzle structure has a significant impact on the heat transfer uniformity and cooling rate of glass during the glass tempering process, and there is a lack of research on the discrepancy of different jet structures. The effects of double air knife, single air knife structures, and air hole structures on the cooling performance of glass in air-cooled tempering were investigated using numerical simulation and simplified analytical models. The calculated results are in agreement with the experimental results. The results show that the DK structure has a significant effect on improving the overall heat exchange performance of the glass, with lower surface temperatures for the same quenching time. The temperature inhomogeneities of DK, SK, and AH structures in the glass axial direction were 2.09%, 2.53%, and 3.33%, respectively, and the heat transfer uniformity of the DK structure was significantly better than the latter two. In comparison to the AH structure, the average heat transfer coefficients of the DK and SK structures increased by approximately 17.82% and 8.13%, respectively, while the heat transfer rates increased by approximately 7.05% and 4.51%. The study further improves the insufficiency of glass tempering research and provides theoretical guidance for the actual production of tempered glass.

Analysis of the influence of deflector shape on heat transfer rate in glass tempering process

To solve the problem of uneven cold air flow during the tempering process, which causes glass self-detonation, distortion, and excessive fan energy consumption. Three deflector-shaped structures are proposed to enhance the cooling efficiency of the glass. Based on the combination of fluent numerical analysis and experiment, this study gives an in-depth examination of the heat transference of glass within a quenching system. The influence of deflector shapes on the heat transfer efficiency of glass is explored. The three deflectors were compared with traditional deflectors in terms of temperature, fluid flow, total heat transfer rate, and heat transfer coefficient. The simulation results agree well with the experimental data, and the established model of the glass quenching system is reliable. The rectangular deflectors reduce the glass base temperature by 3.03 K compared to traditional deflectors. Furthermore, when the rectangular deflectors are utilized, the maximum heat transfer coefficient of the glass can be up to 96.4 W/(m2·K) and the maximum total heat transfer can be up to 2622.82 W. In comparison to the traditional deflector shape, the maximum heat transfer coefficient of the designed rectangular deflectors may be enhanced by 0.58% and the maximum total heat transfer by 0.37%. The proposed design provides a suitable solution for the optimization of the tempering process as well as for the energy savings and efficiency of tempering equipment.

Robust transparent superhydrophilic antifogging coatings on glass substrates by a facile rapid thermal process

In this study, a rapid thermal process, which can be achieved via the conventional glass tempering process, was utilized to fabricate silica-based superhydrophilic antifogging coatings with micro-nano hierarchical roughness on glass substrates. The effects of SiO2 nanoparticle and triethylborate loadings on the coatings’ properties have been systematically investigated. Moreover, the formation mechanism of such coatings has been explained. The optimal coatings demonstrate a high level of hydrophilicity with a water contact angle (WCA) of ∼ 0°. Meanwhile, such coatings exhibit good antifogging effect and robustness as well.

Numerical methodology based on fluid-structure interaction to predict the residual stress distribution in glass tempering considering non-uniform cooling

In this paper a novel numerical methodology for calculating non-uniform residual stress distributions during the glass tempering process is presented. Tempering techniques lead to non-uniform heat transfer rates causing residual stress inhomogeneities, which consequently have a direct impact on the structural behaviour of components. Nevertheless, most works in the literature do not consider the influence of local flow phenomena during thermal calculations, resulting in non-representative residual stress distributions. In this context, a novel generalised methodology based on a fluid–structure interaction one-way approach to sequentially couple the thermal and mechanical fields is presented. In this way, the unsteady and non-uniform heat transfer rate is coupled with the Narayanaswamy model to predict the non-homogeneous residual stress pattern. The obtained numerical results for the analysed impinging jet array case are in good agreement both quantitatively and qualitatively, exhibiting an average error below 10% with respect to previous experimental investigations. Finally, efforts are made to reduce the computational time. Therefore, the proposed methodology proves to be an efficient tool for understanding the underlying mechanisms and predicting the residual stress distributions during glass tempering.

Spray cooling heat transfer during glass tempering process and influencing factors on the quality of tempered glass

Compared with traditional physical tempering methods, spray cooling method has a series of advantages, such as smaller energy consumption and better tempering quality. However, this technology has not reached a mature level. Present study experimentally investigated the spray cooling for glass tempering at high water/air mass flow ratios for the first time, which verified the feasibility of the spray cooling method. Based on the Eulerian-Lagrange method, a two-phase flow model was established to simulate the spraying cooling on heated glass surface. Both wall-jet and Lagrangian wall-film models were adopted to realize the conversion of several modes of heat transfer. A good agreement between the simulated and experimental temperature and wall film distributions supported the reliability of the established model. Subsequently, the spray cooling heat transfer was numerically studied, and the effects of spray distance, mist flow rate and glass thickness on the tempering quality and heat transfer performance were discussed. The results showed that a decrease in spray distance and an increase in mist flow rate and glass thickness obviously enhanced the temperature difference and quality of the tempered glass. Within the scope of the experiment, the optimum spray distance and mist flow rate were 272.5 mm and 6.94 × 10−4 kg/s, respectively.

Structure and Screech Tone of Radially Underexpanded Jet Emitted by Facing Cylinders

An underexpanded jet has typical shock-cell structure and strongly oscillates, its behavior being known to cause many industrial problems. An underexpanded jet radially issues from intake and exhaust valves of an internal combustion engine, a pressure control valve and so on. When a supersonic jet exhausted from a circular nozzle impinges on a flat plate, the wall jet formed on the plate often becomes underexpanded and spreads out radially. Such underexpanded impinging jet is one of models of supersonic jets on laser cutting process and glass tempering process. In this study, an underexpanded jet radially discharged from a circular slit nozzle, which consists of two cylinders, was experimentally examined for different nozzle pressure ratios and for different diameters of cylinder. Jet structure was analyzed by means of a visualization e.g. Schlieren method. A noise emitted from the jet was measured and the frequency of screech tone was analyzed. The experimental results were compared with those of a two dimensional jet issuing from a rectangular nozzle. Furthermore, a comparison of visualized sound waves with the screech tone frequency reveals that the sound source measured was in the vicinity of the end of the second cell and that the length of the second or third cell was one of the most important parameters to determine the frequency of the emitted screech tone.

Performance model for tempered anti-glare LCD cover glass

A novel manufacturing process for anti-glare (AG) coating is proposed for the LCD cover glass that is purposed to significantly improve the durability of AG film, which is widely implemented in commercial products designed for outdoor use. The proposed coating method is implemented in the screen-printing process, which precedes the glass-tempering process, entails application of ZBS (ZnO-B2O3-SiO2) to the glass surface during the silk screen-printing process, and achieves the desired level of performance through the tempering process. We also implemented the experimental results to establish the primary design parameters and derive the formulae necessary to develop a performance model that can predict the haze, roughness, and transmittance of the cover glass, which are representative specification of cover glass. Experimentation was used to subsequently verify the proposed method and the performance model.

A Study on Broad Band Noise Emitted from Underexpanded Radial Jet

This study focuses on a noise emitted from a radial underexpanded jet. The underexpanded jet is well known as one of supersonic jets and it is formed when the pressure ratio across a convergent nozzle is more than the critical value. The underexpanded jet has been used in many fields, such a propulsion of rocket, laser cutting and a glass tempering process. Such jet is exhausted from a circular nozzle. The expansion wave, the compression wave and the shock wave are periodically formed in the jet, which leads to quasi-periodical shock-cell structure. On the other hand, an underexpanded jet radially issues from intake and exhaust valves of an internal combustion engine and a pressure control valve. The radial underexpanded jet does not have the quasi- periodical shock-cell structure such as the jet from the circular nozzle, its cell length decreasing along jet axis. In this study, an underexpanded jet radially discharged from a circular slit nozzle, which consists of two circular tubes, is experimentally examined for different nozzle pressure ratios. The jet structure is visualized using Schlieren method and a noise emitted from the jet is measured. Typically, the shock associated broadband noise is analyzed and a relation between the jet structure and the radiation noise frequency is discussed. As a result, it is found that the broadband noise lies on lower frequency than a screech tone and that the 1st cell length plays an important role in broadband noise radiation.

Analysis and optimization for the process of glass tempering using autoclave

A mathematical analysis of the glass tempering process was carried out using an autoclave, varying the operating parameters of the system. It was found that the process time can be reduced by up to 3.23% by changing the resistance to 15Ω, but increasing the resistance more than this value would mean compromising the quality of the final product. Thus, it is advisable to make variations of the resistance between 10Ω and15Ω, which will allow the optimization of the process time and pressures without affecting the quality of the result.

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.

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.

급속 열처리 시스템을 위한 물/공기 액적류 충돌 제트의 냉각 특성에 관한 연구

ABSTRACT In the present work, a series of numerical calculations have been conducted on the cooling of a hot surface using an air/water mist jet. In some cooling processes, such as in the glass-tempering process, direct contact between the cold water drops and the hot surface should be avoided, because this may cause surface cracks due to the sharp temperature gradients. Thus, the main focus of this study is finding the appropriate operating conditions for maximum cooling without direct contact between the drops and the surface. A series of numerical experiments have been performed, and, at the same time, those results were compared with those of the previous experiments for verification purposes. The effects of droplet impinging velocity, hot plate temperature, and liquid loading ratio for mono-dispersed drops of various sizes were studied in detail.KeyWords : Mist Flow( ), Jet Impinging( ), Hot Plate( ), Mist-jet Cooling Map액적류 충돌 제트 고온 평판 (액적충돌기준선도) # Corresponding Author : jklee99@kyungnam.ac.kr Tel: +82-55-249-2613, Fax: +82-55-249-2617

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.

超音速衝突噴流の振動モードに関する研究(噴流)

An underexpanded jet issuing from a circular nozzle is used for many industrial applications such as an assist gas for the laser cutting, a cooling jet for the glass tempering process and so on. The impinging jet on a flat plate can be considered to be a simple model of such flow field. In this paper, the oscillatory behavior of impinging jet is numerically studied by solving three dimensional Euler equations using TVD scheme. As a result, the oscillation of the impinging jet is found to be associated with the spiral motion of the free jet and so, the disturbances around the wall jet propagate in the radial and the circumferential direction simultaneously. Furthermore, an irregular oscillation caused by the behavior of the separation bubble in the jet is also discussed.

Studies of Supersonic Jets and Shock Waves Generated during Glass Tempering Process.

By using double exposure holographic interferometry, supersonic free jets emanating from nozzles which appear in the process of a glass quenching were observed. Three different nozzle shapes for producing tempered glass were tested, and an axisymmetric free jet emanating from a 4-mm-i. d. and 24-mm-long nozzle was numerically simulated by TVD finite difference scheme applied to the Navier-Stokes equations. In the stagnation pressure ranging from approximately 0.5 MPa to 0.6 MPa, good agreement was obtained between interferograms and computations. Complicated structures of free jets were well resolved and a time variation of pressure caused by shock waves in the jets which would affect the process of glass tempering was clarified.

An Experimental Observation of the Tempering of Flat Glass

Paying attention to both the thermal fractures taking place in glass tempering process and the fracture densities of tempered glass, the experiments of oil tempering of glass were performed. From these experimental data, the following results have been obtained.1) Critical thermal conditions on which the fracture takes place in tempering are depended on both the preheating temperature of glass and Biot's number. Furthermore, stress relaxation of glass surface in visco-elastic region can be determined on the basis of the conditions mentioned above.2) There exists the linear relationship between the fracture densities and the residual surface stresses determined by the procedure of extrapolation on the basis of the curve obtained by experiments.