1、From Wikipedia, the free encyclopediaFloat GlassFloat glass is a sheet of glass made by floating molten glass on a bed of molten metal, typically tin, although lead and various low melting point alloys were used in the past. This method gives the sheet uniform thickness and very flat surfaces. Moder
2、n windows are made from float glass. Most float glass is soda-lime glass, but relatively minor quantities of specialty borosilicate1 and flat panel display glass are also produced using the float glass process.2 The float glass process is also known as the Pilkington process, named after the British
3、 glass manufacturer Pilkington, which pioneered the technique (invented by Sir Alastair Pilkington) in the 1950s./* http:/*/History Until the 16th century, window glass or flat glass was generally cut from large discs (or rondels) of crown glass(冕牌玻璃). Larger sheets of glass were made by blowing lar
4、ge cylinders which were cut open and flattened, then cut into panes. Most window glass in the early 19th century was made using the cylinder method(柱状法). The cylinders were 6 to 8 feet (1.8 to 2.4 m) long and 10 to 14 inches (250 to 360 mm) in diameter, limiting the width that panes of glass could b
5、e cut, and resulting in windows divided by transoms(横梁) into rectangular panels(矩形面板).The first advances in automating glass manufacturing were patented in 1848 by Henry Bessemer, an English engineer. His system produced a continuous ribbon(带) of flat glass by forming the ribbon between rollers. Thi
6、s was an expensive process, as the surfaces of the glass needed polishing. If the glass could be set on a perfectly smooth body this would reduce costs considerably. Attempts were made to form flat glass on a molten tin bath, notably in the US. Several patents were granted, but this process was unwo
7、rkable.Before the development of float glass, larger sheets of plate glass were made by casting a large puddle of glass on an iron surface, and then polishing both sides, a costly process. From the early 1920s, a continuous ribbon of plate glass was passed through a lengthy series of inline grinders
8、(联机磨床 ) and polishers, reducing glass losses and cost.Glass of lower quality, sheet glass, was made by drawing upwards from a pool of molten glass a thin sheet, held at the edges by rollers. As it cooled the rising sheet stiffened and could then be cut. The two surfaces were not as smooth or uniform
9、, and of lower quality than those of float glass. This process continued in use for many years after the development of float glass.Between 1953 and 1957, Sir Alastair Pilkington and Kenneth Bickerstaff of the UKs Pilkington Brothers developed the first successful commercial application for forming
10、a continuous ribbon of glass using a molten tin bath on which the molten glass flows unhindered under the influence of gravity.3 The success of this process lay in the careful balance of the volume of glass fed onto the bath, where it was flattened by its own weight.4 Full scale profitable sales of
11、float glass were first achieved in 1960.Manufacture Float glass uses common glass-making raw materials, typically consisting of sand, soda ash (sodium carbonate), dolomite, limestone, and salt cake (sodium sulfate) etc. Other materials may be used as colourants, refining agents(澄清剂) or to adjust the
12、 physical and chemical properties of the glass. The raw materials are 【A】mixed in a batch mixing process, then fed together with suitable cullet (waste glass), in a controlled ratio, 【B】into a furnace where it is heated to approximately 1500C. Common flat glass furnaces are 9 m wide, 45 m long, and
13、contain more than 1200 tons of glass. Once molten, the temperature of the glass is stabilised to approximately 1200C to ensure a homogeneous specific gravity.【C】The molten glass is fed into a “tin bath“, a bath of molten tin (about 34 m wide, 50 m long, 6 cm deep), from a delivery canal and is poure
14、d into the tin bath by a ceramic lip known as the spout lip（喷口）.5 The amount of glass allowed to pour onto the molten tin is controlled by a gate called a Tweel（流道控制闸门）.Tin is suitable for the float glass process because【1】 it has a high specific gravity, 【2】is cohesive, and 【3】immiscible（不相溶的） into
15、 the molten glass. Tin, however, oxidises in a natural atmosphere to form Tin dioxide (SnO2). Known in the production process as dross（结瘤）, the tin dioxide adheres to the glass. To prevent oxidation, the tin bath is provided with a positive pressure protective atmosphere consisting of a mixture of n
16、itrogen and hydrogen.The glass flows onto the tin surface forming a floating ribbon with perfectly smooth surfaces on both sides and an even thickness. As the glass flows along the tin bath, the temperature is gradually reduced from 1100C until【D】 the sheet can be lifted from the tin onto rollers （辊
17、筒）at approximately 600C. The glass ribbon is pulled off the bath by rollers at a controlled speed. Variation in the flow speed and roller speed enables glass sheets of varying thickness to be formed. Top rollers positioned above the molten tin may be used to control both the thickness and the width
18、of the glass ribbon.Once off the bath, 【E】the glass sheet passes through a lehr kiln（退火炉） for approximately 100 m, where it is further cooled gradually so that it anneals without strain and does not crack from the change in temperature. On exiting the “cold end“ of the kiln, 【F】the glass is cut by m
19、achines.Market As of 2009, the world float glass market, not including China and Russia, is dominated by the four companies: Asahi Glass（旭硝子,日本）, NSG（核供应国）/Pilkington, Saint-Gobain（神戈班）, and Guardian Industries（守护者）. Other companies include Sise Cam AS, PPG, Central Glass, Hankuk, Zeledyne, and Card
20、inal Glass Industries.6Glass batch calculationGlass batch calculation(玻璃配料计算) or glass batching is used to determine the correct mix of raw materials (batch) for a glass melt.Principle The raw materials mixture for glass melting is termed “batch“. The batch must be measured properly to achieve a giv
21、en, desired glass formulation. This batch calculation is based on the common linear regression equation:with NB and NG being the molarities 1-column matrices（摩尔分数单列矩阵） of the batch and glass components respectively, and B being the batching matrix.123 The symbol “T“ stands for the matrix transpose o
22、peration, “-1“ indicates matrix inversion, and the sign “ means the scalar product（数积）. From the molarities matrices N, percentages by weight (wt%) can easily be derived using the appropriate molar masses.Example calculation An example batch calculation may be demonstrated here. The desired glass co
23、mposition in wt% is: 67 SiO2, 12 Na2O, 10 CaO, 5 Al2O3, 1 K2O, 2 MgO, 3 B2O3, and as raw materials are used sand, trona（天然碱）, lime , albite（钠长石）, orthoclase（正长石）, dolomite（白云石）, and borax. The formulas and molar masses of the glass and batch components are listed in the following table:The batching
24、matrix B indicates the relation of the molarity in the batch (columns，列) and in the glass (rows，行) . For example, the batch component SiO2 adds 1 mol SiO2 to the glass, therefore, the intersection of the first column and row shows “1“. Trona adds 1.5 mol Na2O to the glass; albite adds 6 mol SiO2, 1
25、mol Na2O, and 1 mol Al2O3, and so on. For the example given above, the complete batching matrix is listed below. The molarity matrix NG of the glass is simply determined by dividing the desired wt% concentrations by the appropriate molar masses, e.g., for SiO2 67/60.0843 = 1.1151.The resulting molar
26、ity matrix of the batch, NB, is given here. After multiplication（乘法） with the appropriate molar masses of the batch ingredients one obtains the batch mass fraction matrix MB:or The matrix MB, normalized（归一化） to sum up to 100% as seen above, contains the final batch composition in wt%: 39.216 sand, 1
27、6.012 trona, 10.242 lime, 16.022 albite, 4.699 orthoclase, 7.276 dolomite, 6.533 borax. If this batch is melted to a glass, the desired composition given above is obtained.4 During glass melting, carbon dioxide (from trona, lime, dolomite) and water (from trona, borax) evaporate.Another simple glass
28、 batch calculation can be found at the website of the University of Washington.5Advanced batch calculation by optimization If the number of glass and batch components is not equal, if it is impossible to exactly obtain the desired glass composition using the selected batch ingredients, or if the mat
29、rix equation is not soluble for other reasons (e.g., correlation), the batch composition must be determined by optimization techniques.Calculation of glass propertiesThe calculation of glass properties allows “fine-tuning“（微调） of desired material characteristics, e.g., the refractive index.1The calc
30、ulation of glass properties (glass modeling) is used to predict glass properties of interest or glass behavior under certain conditions (e.g., during production) without experimental investigation, based on past data and experience, with the intention to save time, material, financial, and environme
31、ntal resources, or to gain scientific insight. It was first practised at the end of the 19th century by A. Winkelmann and O. Schott. The combination of several glass models together with other relevant functions can be used for optimization and six sigma procedures. In the form of statistical analys
32、is（统计分析） glass modeling can aid with accreditation （鉴定）of new data, experimental procedures, and measurement institutions (glass laboratories).History Historically, the calculation of glass properties is directly related to the founding of glass science. At the end of the 19th century the physicist
33、Ernst Abbe developed equations that allow calculating the design of optimized optical microscopes in Jena, Germany, stimulated by co-operation with the optical workshop of Carl Zeiss. Before Ernst Abbes time the building of microscopes was mainly a work of art and experienced craftsmanship, resultin
34、g in very expensive optical microscopes with variable quality. Now Ernst Abbe knew exactly how to construct an excellent microscope, but unfortunately, the required lenses （透镜）and prisms （棱镜）with specific ratios of refractive index and dispersion（色散） did not exist. Ernst Abbe was not able to find an
35、swers to his needs from glass artists and engineers; glass making was not based on science at this time.2In 1879 the young glass engineer Otto Schott sent Abbe glass samples with a special composition (lithium silicate glass) that he had prepared himself and that he hoped to show special optical pro
36、perties. Following measurements by Ernst Abbe, Schotts glass samples did not have the desired properties, and they were also not as homogeneous as desired. Nevertheless, Ernst Abbe invited Otto Schott to work on the problem further and to evaluate all possible glass components systematically. Finall
37、y, Schott succeeded in producing homogeneous glass samples, and he invented borosilicate glass with the optical properties Abbe needed.2 These inventions gave rise to the well-known companies Zeiss and Schott Glass (see also Timeline of microscope technology). Systematic glass research was born. In
38、1908, Eugene Sullivan founded glass research also in the United States (Corning, New York).3At the beginning of glass research it was most important to know the relation between the glass composition and its properties. For this purpose Otto Schott introduced the additivity principle in several publ
39、ications for calculation of glass properties.456 This principle implies that the relation between the glass composition and a specific property is linear to all glass component concentrations, assuming an ideal mixture, with Ci and bi representing specific glass component concentrations and related
40、coefficients respectively in the equation below. 【#1】The additivity principle is a simplification and only valid（有效的） within narrow composition ranges as seen in the displayed diagrams for the refractive index and the viscosity. Nevertheless, the application of the additivity principle lead the way
41、to many of Schotts inventions, including optical glasses, glasses with low thermal expansion for cooking and laboratory ware (Duran), and glasses with reduced freezing point depression for mercury thermometers. Subsequently, English7 and Gehlhoff et al.8 published similar additive glass property cal
42、culation models.【#2】 Schotts additivity principle is still widely in use today in glass research and technology.910Additivity Principle(加和原理 ): Global modelsThe mixed-alkali effect（混合碱效应）: If a glass contains more than one alkali oxide, some properties show non-additive behavior. The image shows, th
43、at the viscosity of a glass is significantly decreased.11Decreasing accuracy (精度 )of modern glass literature data for the density at 20 C in the binary system SiO2-Na2O.12Schott and many scientists and engineers afterwards applied the additivity principle to experimental data measured in their own l
44、aboratory within sufficiently narrow composition ranges (local glass models). This is most convenient because disagreements between laboratories and non-linear glass component interactions do not need to be considered. In the course of several decades of systematic glass research thousands of glass
45、compositions were studied, resulting in millions of published glass properties, collected in glass databases. This huge pool of experimental data was not investigated as a whole, until Bottinga,13, Kucuk14, Priven15, Choudhary16, Mazurin17, and Fluegel1819 published their global glass models, using
46、various approaches.【#3】 In contrast to the models by Schott the global models consider many independent data sources, making the model estimates more reliable. In addition,【#4】 global models can reveal and quantify non-additive influences of certain glass component combinations on the properties, su
47、ch as the mixed-alkali effect as seen in the diagram above, or the boron anomaly. 【#5】Global models also reflect interesting developments of glass property measurement accuracy, e.g., a decreasing accuracy of experimental data in modern scientific literature for some glass properties, shown in the d
48、iagram. They can be used for accreditation of new data, experimental procedures, and measurement institutions (glass laboratories). In the following sections (except melting enthalpy) empirical modeling techniques are presented, which seem to be a successful way for handling huge amounts of experime
49、ntal data. The resulting models are applied in contemporary engineering and research for the calculation of glass properties.Non-empirical (deductive) glass models exist.20 They are often not created to obtain reliable glass property predictions in the first place (except melting enthalpy), but to establish relations among several properties (e.g. atomic radius, atomic mass, chemical bond strength and angles, chemical valency, heat capacity) to gain scientific insight. In future, the investigat
