Патент USA US2411031код для вставки
‘NOV._1_2, 1946. . A,__|_ DEYRUP - ‘ 2,411,031 _ MANUFACTURE OF OPTICAL GLASS Filed Marbh 10, 1943 INVEN TOR. ALDEN J. DEYRUP BY J A TTORNEYS. Patented Nov. 12,‘ 1946 2,411,031 gUNI'TED STATES PATENT OFFICE MANUFACTURE OF OPTICAL GLASS‘ Alden J. Deyrup, West?eld, N. ‘J., assignor to E. I. du Pont de Nemours & Company, Wilmington, ‘ . Del., a corporation of Delaware Application March 10, 1943, Serial No. 478,649 . , 2 Claims. 1 (01. 49-77) 2 , metal is also limited by the fact that many usefu glasses, such as lead glasses, cannot be safely inhomogeneity. More particularly, it relates to melted in platinum crucibles because contact of the preparation of glass of a completely homo these glasses with combustion gases in the melt geneous character, free from “seeds, cords, and 5 ing furnace may liberate reduced metals such as This invention relates to the manufacture of glass which is relatively free from solid or gaseous striae,” the resulting glass being satisfactory for lead, which then alloy with the platinum thereby use in the manufacture of optical instruments. In the commercial preparation of glass the glass batch is melted in a refractory container ruining the crucible. ' _ v Various attempts have been made to effect homogenization of glass by'stirring at low tem and the melted glass, after melting and ?ning, 10 peratures and high viscosities in order to mini mize the rate of formation of striae caused by is either drawn off and formed or, as is usual in the case of optical glass, cooled in the container solution of the refractory. However, it has been found that attempts to stir or mix glass at low and broken out in chunks. Manufactured glass temperatures (high viscosities) generally fail be is usually not completely homogeneous but con cause large quantitiesof air are entrapped during tains small gaseous bubbles termed seeds as well as inhomogeneities due to composition such as the process of stirring. I Reduction of the extent of I have now discovered a procedure whereby these inhomogeneities has attracted the extensive homogenization may be effected, either at high attention vof experts in the ?eld of glass manu facture, and considerable progress has been made in eliminating them. Seeds in commercial glass ware are generally few and small in size, and striae have been reduced to the point where they cause no substantial weakening of properly viscosities or at low viscosities, as desired, without the entrapment’ of air bubbles. Not only are air annealed glass. When glass of good optical qualities is de My improved procedure involves ?rst effecting the preliminary melting of the glass batch, with or without preliminary ?ning and stirring, fol cords and striae. bubbles not entrapped but, on the contrary, there occursduring this treatment a partial ?ning or elimination of bubbles which may originally‘ be present in the glass melt. 7 sired, however, serious difficulties are encoun lowed by passage of the glass, as a stream, or in tered in diminishing the striae to a sufficient extent. Striae in optical glass are considered continuous flow, into a homogenizer. The homo to result from variation in the composition of 30 genizer comprises an essential element, serving to the glass from point to point throughout the carry out an essential step in my process. Bas glass. These variations in composition are gen‘ ically, it consists of a means for splitting the ‘entering stream of ?uid glass into a plurality of erally attributed to the effect of solution of the streams, the resulting streams being then recom crucible or refractory wall wherein the glass batch is positioned, as well as “to volatilization of con bined in an order different from that in which they were initially split. This results in shu?iing stituents of the glass, such as alkali metal oxides, from the surface of the glass melt. In the modern or intermingling of the streams. manufacture of optical glass the batches are My invention may best be described with ref erence to the diagrams constituting the accom melted in individual crucibles and the melt stirred mechanically, the cooling taking place 40 panying drawing. Figure 1 illustrates the type of recombination desired where streams of glass rapidly under controlled conditions to arrest the having an initial order denoted A—B-—C are intermingling of striae, which may be formed at the crucible wall and surface, with the remainder shuffled and recombined to have the order B-A-C. Figure 2 represents sequential recom of the homogenized glass. It is then necessary to break the glass into chunks and to select suit 45 bination of streams of molten glass, and Figure 3 able pieces free from striae as determined by represents inverse sequential combination of a careful physical inspection. Glass of high quality ‘stream split initially into three portions. When treating the glass in accordance with the pro can be prepared by melting the batches in pots cedures illustrated in these Figures 2 and 3, re formed of inert metals such as platinum. This is objectionable, however, in that it involves the 50 combination of the streams of glass in a shu?led order does not occur, the ?nal streams, A, B, and use of equipment of considerable expense. More C, preserving their respective positions with re over, not all the striae are eliminated under such conditions, possibly because vaporization of'con spect to one another that they initially, presented at the moment of splitting or subdivision of the stituents of the glass may still occur from the top of the crucible. The utilization of pots of inert 55, main stream. 2,411,031 4 3 Figure 4 represents, diagrammatically, an ap paratus wherein such splitting and intermingling of streams may be carried out, the speci?c em cupied by the ?owing subdivided streams of mol bodiment illustrated comprising three separate cally sealed from each other as desired. As an example of homogenization in accord ance with my invention, a homogenizer similar ten glass, are marked J in Figure 4, and may be either connected to each other, or hermeti units in series of ?ve streams each, formed by subdivision of the main body of molten glass. Referring particularly to Figure 1, it is evident that the‘ stream‘ S of ?uid glasslisdividedinto.‘ to that shown in Figure 4 but having ?ve units divided streams were initially present. This rep—~ in a perforated crucible resting on top of the homogenizerz. These glass chunks were of a or dishes- F‘. with ten perforations each, and ten leaderslGifor each unit or‘dish F'was set up in a three portions. and recombined, as. atzT, in" an. order different from that in which the three sub l0 vertical tube furnace. Glass chunks were melted resents the shu?ling type of recombination. and can be eifected by suitably designing'the' homo genizer apparatus. In practice; this homogenizer badly striated and seedy glass having the follow ingapproximate composition, the product being should be so designed that no. bubble-entrapment 15 a" typical lead-?int: optical glass : Per cent will occur, either in separation, or in the recom Silica, SiO2 ____________________________ __ 46.5 bination of the ?uid streams. of. glass. The sche matic unit illustrated in Figure 1 will provide, of course, only partial mixing, as commercially e?ective embodiments of my invention, utilizing 1 principles in accordance with this diagram, will contain various units. providing either a plural ity of subdivided streams, a plurality of units, or: both a plurality of units and plurality of streams In Figure 2 the initial stream of ?owing glass U is subdivided into the three streamsA', B’, and C.’ which are then recombined in the same order Sodium oxide, NazO'____________________ __ 5.0 Potassium oxide, K20‘ ___________________ __ 1.1 Calcium oxide, CaO ____________________ __ 0.3 Lead oxide, PbO‘ ________________________ __ 47.0 Arsenic oxide, A5203 ____________________ __ 0.1 All percentages are by Weight, based on the total weight of the glass. The tube furnace was operated at 920° C., and a continuous-rod of glass was removed from the lower end of the homogenizer. Inspection of this glass showed marked improvement in the quality to form the stream V. InFigure 3; the ?owing thereof, illustrated by considerable reduction in an stream of molten glass W is subdivided into the the extent of striation and number of seeds. three streams A", B”, and C" which are then A-further test was now carried out to measure recombined, unshu?led but in the reverse order, more accurately the degree of mixing. A chunk to formthe stream X. The types of recombina of ‘cobalt blue glass weighing 10 grams was added tion of streams represented in-these Figures 2 to the glass entering the homogenizer shown in and 3 are not‘ the desired type of shuf?ing re Figure 4. The e?‘luent glass was tinted blue combination and are to be avoided in the prac through a very large volume thereof. The blue tice of my invention, since they do not result in tinted glass was cut out of the block or mass the thorough-mixing securedby theshufilingre~ and found to Weigh 9'70 grams. This indicates combination illustrated in Figurel. ‘ a surprisingly large amount of mixing, as the Figure 4 speci?cally illustrates an embodiment‘ 40 chunk'of cobalt blue glass was mixed with al of my homogenizer apparatus providing both a. most one hundred times its ‘own weight of an plurality of units and a plurality of- streams, the other glass. In contrast, a chunk of blue glass apparatus illustratedin the diagram comprising weighing 10 grams‘placed in 500 grams of clear three units each effecting asubdivision of the glass in a crucible at the same temperature re main body of glass into a series of ?ve streams 45 mained for many hours without coloring the bulk each. In this-?gure, D representsthe original of the glass through mixing or diffusion. in?owing stream. of -molten glass ?owing. into the The mixing and shu?iing' of the streams of homogenizer. E is the. rigid‘ shell or container molten glass may be accomplished solely by grav of refractory material, for example, formed of a itational ?ow. It is obvious that the homogeniz ceramic refractory, this shell-or container. being 50 ing system may be completely enclosed and her surrounded by a heated furnace (not shown). F1, metically sealed against combustion gases, no F2, F3, and F4. are perforated rigid “dishes” of mechanically moving parts being, present in said refractory material not- readily soluble inthe-mol system. Isothermal conditions may'al‘so be main ten glass. They maybe constructed of: platinum. tained, thus preventingstriae which might re or. of the usual ceramic refractories. The letter 55 sult by evaporation of constituents of the glass G isusedto denote leaders, .guide.rods,,or. wires, from‘ exposed surfaces of the molten glass;body. which serve to direct the. streams of molten glass The ease and practicability of hermetically seal exuding through theperforations asthe result ingv the "system against combustion gases. permits shu?ling of these streams- Thesemembers-rnay 60 the use of. platinum and similar inert metals, thereby reducingcontamination of the glass to be formed of platinum wire, ceramic. refractory of gravitational ?ow». in such amanner as to cause rods, or other suitable material. The letter Hr denotes the e?iuent s'treamof homogenized glass, formed by‘ the?nal commingling. of the indi-‘ vidual 1 streams. In practice; and as illustrative of complete glass~making operations, the in?owing-streamD may flow from. a. continuous melting tank»,.to which tank is fedei-ther the. raw.‘ glass-batch, or. theminimum amount. . In ordinary operations the homogenizer is maintained at'substantially uniform temperature, from in?ux of the glass toits e?lux in recom binedcondition from the apparatus. It..should'be noted that the operation of. my. improved homogenizing apparatus does not de pend on the. exact number of shu?ling- units or premelted glass chunks. Theeilluent streamof. 70 streams: per unit. of the apparatus. Generally, it-has- been observed that increasing both. the glass H may becut into gobs preliminary topress number of. shuf?ing: units and. the number of. ing toshape, or. may be drawn through formers streams per unit results in increased e?iciency of. into an annealing lehr; thus forming continuous, mixing, and therefore: a‘ superior quality. optical. rods“ or sheets. The. empty spaces vbetween suc cessive dishes F1, F2, F3, F4, etc. space notv oo 75 glass. .5 2,411,031 While I have described my invention with ref erence to certain preferred speci?c embodiments thereof, I do not wish to be limited thereto, as obvious modi?cations will occur to those skilled in the art which do not di?er from the spirit (TI or scope of the invention. 2. The method for homogenizing glass which , comprises melting a glass mass, simultaneously withdrawing contiguous portions of said mass in adjacent separate streams, interspersing said ad jacent streams and uniting them to form a sec ond glass mass in which some contiguous portions were non-contiguous portions in said ?rst-named glass mass and repeating said withdrawal of con tiguous portions of succeeding glass masses in ad I claim: 1. The method for homogenizing glass which comprises melting a glass mass, simultaneously withdrawing contiguous portions of said mass in 10 jacent separate streams, interspersing said adja adjacent separate streams, interspersing said ad cent streams and uniting them to form succeed jacent streams and uniting them to form a sec ing glass masses in which some contiguous por tions were non-contiguous portions in preceding ond glass mass in which some contiguous por tions were non-contiguous portions in said ?rst glass masses. 15 named glass mass. ALDEN J. DEYRUP.