Flat Glass Manufacturing Research Articles

Influence of spout lip set-height on flow behavior during the glass float process

One of the most widely employed procedures for flat glass manufacture is float process proposed by Pilkington. Nowadays, there is great demand for thinner float glass of high optical quality. The most important stage of float process is the glass forming in tin bath. In this study, the ANSYS Fluent 14.0 software is adopted to develop a multiphase numerical model and simulate the flow phenomena of molten glass when it is spouted over a lip onto the tin bath under protective atmosphere. The influence of spout lip set-height on flow behavior of molten glass and tin at tin bath entrance is investigated. The results of 2D simulation indicate that the velocity at the vertex of spout lip, the depth where glass dips into tin bath as well as wetback flow increase with the set-height. From results of 3D simulation, the expansion of glass ribbon and velocity gradient along lateral direction of tin bath occurs as molten glass floats on molten tin. The velocity components of Vy and Vx of wetback flow are significant at the edge while are extremely low near symmetry plane. The larger velocity components of Vy and Vx of wetback flow are achieved with increase of spout lip set-height, which would facilitate more glass containing impurities to flow towards the edge of glass ribbon and improve the glass forming quality. The simulation results are supposed to guide the optimization design of spout lip.

Dynamic programming and mixed integer programming based algorithms for the online glass cutting problem with defects and production targets

In flat glass manufacturing, glass products of various dimensions are cut from a glass ribbon that runs continuously on a conveyor belt. Placement of glass products on the glass ribbon is restricted by the defects of varying severity located on the ribbon as well as the quality grades of the products to be cut. In addition to cutting products, a common practice is to remove defective parts of the glass ribbon as scrap glass. As the glass ribbon moves continuously, cutting decisions need to be made within seconds, which makes this online problem very challenging. A simplifying assumption is to limit scrap cuts to those made immediately behind a defect (a cut-behind-fault or CBF). We propose an online algorithm for the glass cutting problem that solves a series of static cutting problems over a rolling horizon. We solve the static problem using two methods: a dynamic programming algorithm (DP) that utilises the CBF assumption and a mixed integer programming (MIP) formulation with no CBF restriction. While both methods improve the process yield substantially, the results indicate that MIP significantly outperforms DP, which suggests that the computational benefit of the CBF assumption comes at a cost of inferior solution quality.

Brief history of the flat glass patent – Sixty years of the float process

This paper deals with one of the single most important innovations made in Great Britain since World War II. It is certainly one of the greatest process inventions of the twentieth century. The float process is one of the most widely used methods for flat glass manufacturing as it ensures security, high quality and productivity. From a historical point this innovation was the beginning of a revolutionary change in the mass production of flat glass for the building and automotive sectors. More specifically this innovation eliminates the traditional operations of rolling, grinding and polishing the glass surface while creating a high quality and inexpensive flat glass product. The first patent was applied for on December 10th, 1953 by Pilkington and Bickerstaff. This paper presents a brief discussion from the 1960s in a historical perspective about this amazing discovery and the main patents related to it. More than 23,900 patents using the term “flat glass” have been filed around the world, according to the European Patent Office databases. These numbers just continue to grow as do total sales worldwide. Looking for titles using flat glass, we found 2,409 patents filed. Curiously, for the same period 1,131 patents were published with float glass in the title and just 3,995 with the term in the title or abstract. So, statistically, there are more published patents using the term ‘flat’ than ‘float’ glass process.

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In-process cutting losses are often found in flat glass manufacturing of the case study company. Since the standard for cutter wheel usage has not been set, the over-worn cutter wheels are often used. The objective of this research is to set the standard of cutter wheel usage in order to reduce cutting losses from using over-worn cutter wheels. The factors related to cutting quality are studied such as cutting distance, pressure, and cutting wheel diameters. The regression model is applied to show the relationship of the three factors in order to estimate the appropriate use of cutting wheel before it is worn off for the case of 2-millimeters glass thickness under 890 meters per hour of speed. The study found that the appropriate pressures for cutting wheel diameter ranges of 4.0-4.3 millimeters, 4.4-4.7 millimeters, and 4.8-5.0 millimeters are 0.50 kgf/cm, 0.52 kgf/cm, and 0.55 kgf/cm respectively. The simulation model was used to compare the result from regression model and actual data. The result showed that cutting loss can be reduced to 48% and the distant cut by the cutter wheel is increased by 40% when following the suggested standard usage developed by the regression model which can enhance the efficiency of cutter wheel and prevent cutting losses before it occurs.

A study of the behavior of volatiles in the float process

The float process is one of the most widely employed methods for flat glass manufacturing. Tin speck on the top surface of the glass sheet is one of the specific defects for the float process, caused by droplets derived from volatiles from the molten tin surface. That is, the volatilized materials from the tin surface are advected and diffused in the gas flow and finally drop onto the glass ribbon. The gas flow is complex and difficult to understand, because it is driven not only by advection but also buoyancy convection. We have studied the behavior of volatiles by carrying out the computational simulation of the gas flow and the mass transfer for the first time. Remarkably the mechanism and the characteristic of the behavior of volatiles have been revealed. The technique can be used to optimize the operation and to design float baths in order to minimize tin speck.

New Approaches to Titania and Silica CVD

The companion article by Mark Allendorf highlights the importance of on-line CVD coating for flat glass manufacture. Two smaller, but fast growing, markets are those of precision optics and telecommunications. Both these markets are driven by the rapidly developing requirement for high throughputs. Current deposition methods rely on PVD techniques that are augmented with cumbersome tooling to move the complex geometries and thereby achieve time-averaged deposition over whole surface areas. Such techniques limit throughput and usually give a non-uniform deposit on parts of the coated sample, necessitating special alignment within an optic system and thereby incurring significant costs.

Thin Films on Float Glass: The Extraordinary Possibilities

Beginning in the late 1950s, and up to present time, the continuous float process has become, worldwide, the preferred method of flat glass manufacture. For almost all architectural and vehicular uses, the glass ribbon is made within a narrow range of soda−lime−silica composition. For centuries up to the 20th, flat glass had been made commercially by batch processes. Thereafter, prefloat continuous processes were introduced either to draw fire-polished sheets upward in ambient air or to draw glass horizontally through rollers, followed by grinding and polishing of both rough surfaces. Respectively, these were sheet and polished plate glass. However, despite the significant glassmaking changes, the flat glass article itself remained an essentially undifferentiated window to the untrained user. There were, of course, improvements in bulk quality and distortion over time, as well as cost gains and new body tints. Beginning with the late 1960s, new thin film technologies were applied to change the surface pro...

A tree-search method for solving a cutting stock assignment problem

Many production environments such as carpet or flat glass manufacturing have linked operations that perform completely different activities. In this paper, we consider a two-stage manufacturing process involving a cutting operation, followed by an assignment operation. Raw material is cut to meet product demand with minimum trim loss, and assignments are made to minimize resource requirements. This cutting stock assignment problem is formulated as a large-scale, mixed-integer nonlinear programming problem. We propose a solution methodology based on decomposition and tree search heuristic strategies. We report on extensive computational experiments on a wide range of problems, and apply statistical techniques to determine significant factors. For all small-size problems tested, our method found the exact optimal solution. For practical-size problems, our method was about two orders of magnitude faster and produced solutions that were one-third better than tabu search.

Electromagnetic Processing of Materials. Applications of The Magnetic Field to Flat Glass Manufacture.

Electromagnetic Processing of Materials. Applications of The Magnetic Field to Flat Glass Manufacture.