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Патент USA US2411031

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‘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.
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