IMPROVEMENTS IN ANNEALING AND TEMPERING GLASS, AND IN APPARATUS EMPLOYED THEREFOR
Year: 1879

page_text: LETTERS PATENT to Alexander Melville Clark, of 53, Chancery Lane, in the
"
County of Middlesex, Patent Agent, for the Invention of "IMPROVEMENTS IN
ANNEALING AND TEMPERING GLASS, AND IN APPARATUS EMPLOYED THEREFOR'
A communication from abroad by Joseph Martial Auguste, Deherrypon, of
Paris, France.
PROVISIONAL SPECIFICATION left by the said Alexander Melville Clark at
the Office of the Commissioners of Patents on the 17th September 1879.
ALEXANDER MELVILLE CLARK, of 53, Chancery Lane, in the County of Middlesex,
Patent Agent. "IMPROVEMENTS IN ANNEALING AND TEMPERING GLASS, AND IN
APPARATUS EMPLOYED THEREFOR." [A communication from abroad by Joseph
Martial Auguste Deherrypon, of Paris, France.]
The coefficient of elasticity of glass is extremely variable, according as its
molecular condition has been more or less affected by tempering, which as in the
case of steel is effected not only by dipping the glass article in a liquid more or less
heated, but also by cooling it more or less suddenly, in a fluid such as air.
"
The Indians and Kabyles temper the blades of their yataghans after heating them
Rupert's
by whirling them rapidly in the air instead of plunging them. in water.
drops" may also be produced by whirling a drop of glass in the air. A Rupert's
drop may be taken as an extreme example of tempering, highly heated glass in a
relatively very cold liquid. It is well known that in falling into cold water the
surface or skin of the glass. drop becomes suddenly contracted; it acquires great
hardness, and at same time excessive: fragility. By merely, breaking off the tail end,.
the entire drop.explodes and becomes, reduced to powder. The same phenomenon is
observed in articles of glass which are cooled spontaneously in the air. When a
spoilt bottle is thrown on one side by the workman, before completion, it becomes
tempered by exposure to the circum ambient air, and acquires, the characteristic.
T

page_text: properties of the "Rupert's drops," for if a small fragment of glass or other
substance equally light be dropped into it, it will be sufficient to brake it, and even
cause it to explode. In either case the result of the tempering in increasing the
hardness of the glass has been to considerably affect its molecular arrangement.
M de Luynes who has succeeded in analysing the peculiar phenomenon of the
Rupert's drop has demonstrated by microscopical examination that the structure of
the glass drop resembled a succession of independent blades or laminae doubled
upon themselves like a series of spring plates, the point of attachment being at the
tail end of the drop, and that by breaking this end the ephemeral equilibrium of
the molecules is destroyed, and the glass becomes reduced to powder. This excessive
fragility is not however irremediable, since if a Rupert's drop be reheated, and
afterwards gradually cooled (ie., annealed) it looses all its explosive properties, and
is not more liable to break than ordinary well manufactured glass. It is then
annealed glass (i.c., lowered in temper), its coefficient of elasticity which was nil
ranking with that of glass annealed in the ordinary way.
25.
All glass articles, whether blown or moulded are necessarily air-tempered during the
time that (when in the hands of the workman before being conveyed to the annealing
arch) they lose their plastic consistency, and become hardened in the cold air. It
is at this time that the molecular arrangement takes place under more or less
unstable conditions, according to the intensity and duration of this air-tempering.
Owing to the constant opening and closing of the annealing arch, and its unequal
heating, glass does not become properly annealed, but the injurious effects of the
air-tempering are merely arrested more or less completely, and to this necessarily
irregular action are attributable the variations in the toughness and elasticity of
glass. The tempering of glass articles in very hot liquids as practiced by M. de la
Bastie, evidently increases their hardness and resistance to blows, but it also
deprives them of a portion of their elasticity and molecular cohesion. When such
an article is accidentally broken or its "skin" injured, it flies into a thousand
fragments like the "Rupert's drop," and from the same causes, it being in fact only
a variety of "Rupert's drop," and differing only from it in the infinitely lesser
difference between the temperature of the article, and that of the liquid in which it
is tempered. It also differs from it in the qualities which it acquires by a gradual
and progressive cooling in the liquid in which it is plunged. If then the tempering
of glass increases its hardness, it also considerably dimishes its elasticity, and this
quality can only be restored to it as we have seen in the case of the "Rupert's
drop" by reheating the glass to a temperature approaching that at which it softens
(that is to say, to the point where it spontaneously becomes air-tempered, for
example), and then allowing it to cool very gradually in a suitably heated medium.
Elasticity is a quality essential to the uses of glass, thus it is its elasticity and not
its hardness which enables champagne and aerated water bottles to withstand the
prolonged pressures to which they are necessarily subjected, and also enables it to
withstand repeated and sudden changes of temperature. A champagne bottle
if made of an insufficiently elastic glass can only be once used, as its entire
strength of resistance will be exhausted, and cannot sustain a second time the
prolonged pressure of the gasses of fermentation. This has been proved by the fact
of a bottle tested to 20 atmospheres, and having resisted this enormous pressure
ultimately breaking under a pressure of 5 to 6 atmospheres only. To give another
example, a pane of glass supporting a momentary pressure of, say 25 kilogrammes,
will, after the lapse of some hours break beneath the continued but lesser pressure
of 17 kilogrammes. These facts, and many others, relating to the resistance of glass
to sudden changes of temperature, prove, that in the majority of cases elasticity is
more necessary to glass than hardness. The latter quality is obtained by tempering,
while elasticity is obtained as above mentioned by gradually reheating the glass
to a temperature (dull red), at which it was more or less injuriously air-tempered,
and then allowing it to gradually cool in a suitable medium. The following are
the means employed to obtain this result.

page_text: The apparatus of this Invention for annealing glass is composed of a circular or
rectangular oven in which crystal or other glass objects of all kinds are piled so as
to economise space as much as possible, without however running the risk of
rendering them misshapen by too great a weight when their temperature ap-
proaches that at which they soften. For this purpose the oven is furnished with
a kind of seggars or stands of fireclay.
The oven is heated by one or preferably by two furnaces placed symmetrically
opposite one another, their capacity varying with that of the oven and the tem-
perature to be attained. The furnaces are fed with coke or other smokeless fuel
through a hopper capable of being hermetically closed (as is also the ash pit), the
blast necessary for combustion being introduced beneath the grate at a pressure
which may be as high as 15 centimetres of mercury on the gauge. A chamber similar
to those of the Siemens regenerative furnaces separates the oven from each of the
furnaces. These chambers are filled with bricks built up in quincunx order with
zigzag interstices between them so as to prolong the traverse of the furnace gases
in order to acoumulate and regulate the heat before their introduction into the
oven. After filtering through these passages and accumulating the heat the gases
are introduced into the oven, the heat being increased when it is desired to heat it
gradually or decreased for cooling it. The chambers in this case instead of being
regenerators, are heat accumulators and regulators. The oven, chambers and furnaces
are hermetically enclosed in a sheet or cast iron casing. At the lower part of the
oven on its lateral faces, openings are made provided with conical plugs (or cocks)
for the escape of the gases whilst maintaing a sufficent pressure and avoiding any
return draught or their too rapid escape. The oven is also provided with a manhole
for charging and discharging it.
Suppose the oven to be filled and the fires lighted; at starting, the blast is turned
on beneath the grate bars at a very low pressure and in only the necessary quantity
to light the coke and gradually heat the furnace. The heat of the furnace is next
imparted to the bricks of the accumulator, which gradually becomes more and
more heated by the contact of the gases which at first only reach the oven in
a cool condition, but become hotter as the accumulator becomes more highly heated.
In about an hour's time the pressure of the blast is slightly increased and is thence-
forth gradually raised, according to the indications afforded of the temperatre of
the gases at the outlet orifices. The bricks in the accumulator becoming still more
heated, the last rows viz:-those next the oven acquire a low red temperature, and
the gases in contact with the same show at their escape a temperature of about
400° C. The pressure in the oven is from 5 to 6 centimetres, which is sufficient to
envelop the interior and exterior of such articles as sinall necked bottles, in the
same manner as if immersed in a liquid. The volume ond pressure of air introduced
beneath the grate is still gradually increased, and the temperature of the gases in
the oven soon reaches 525°, that is to say a dull red heat; this temperature is
maintained for an instant and the furnaces then stoked once more for the last time
after having sensibly reduced the pressure. It is however always necessary that
this pressure be sufficient to maintain, a perfect and constant plenum in the oven,
this result being readily obtainable by reducing at will the size of the escape
orifices. The oven resembles in short the pressure regulator in the blowing engines
of blast furnaces. Under the action of the diminished blast the remainder of the
fuel becomes consumed and very soon after the blast only becomes heated from the
sides of the furnace itself, and takes up the necessary complement of heat by
filtering through the network of bricks in the accumulator which themselves become
proportionately but slowly cooled. The cooling of the oven and the glass it contains
is also slow and progressive, and it is without any sudden changes and by insensible
transitions of temperature that the articles contained in the oven after having
acquired at first a dull red heat gradually fall to that of the air we breathe. They
are than annealed. The method hereinbefore described will be readily distinguished
from all those which under the denomination of annealing have hitherto been

page_text: proposed or practised, the distinguishing features of novelty and economy consisting
more particularly in,-
1st. The employment of the heat regulator and accumulator described for ob-
taining a gradual heating and cooling of the glass.
2nd. The employment of gases under pressure in the interior of the apparatus, so
as to keep the interior and exterior of narrow necked bottles at a uniform temperature
the same as if they were immersed in liquids. I reverse the right of applying this
process and apparatus for the purpose of giving the high temper to glass as well as
for annealing. Effectively the said apparatus and process which are here employed
in annealing can evidently be equally well employed in giving the high temper to
glass.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Alexander Melville Clark in the Great Seal Patent Office on the 16th
March 1880.
ALEXANDER MELVILLE CLARK, of 53, Chancery Lane, in the County of Middlesex,
Patent Agent. "IMPROVEMENTS IN ANNEALING AND TEMPERING GLASS, AND IN
APPARATUS EMPLOYED THEREFOR." A communication from abroad by Joseph
Martial Auguste Deherrypon, of Paris, France.
The co-efficient of elasticity of glass is extremely variable, according as its molecular
condition has been more or less affected by tempering, which, as in the case of steel,
is effected not only by dipping the glass article in a liquid more or less heated, but
also by cooling it more or less suddenly in a fluid such as air.
The Indians and Kabyles temper the blades of their yataghans after heating them
by whirling them rapidly in the air instead of plunging them in water. "Rupert's
drops" may also be produced by whirling a drop of glass in the air. A Rupert's
drop may be taken as an extreme example of tempering highly heated glass in a
relatively very cold liquid. It is well known that in falling into cold water the
surface or skin of the glass drop becomes suddenly contracted; it acquires great
hardness and at the same time excessive fragility. By merely breaking off the tail
end the entire drop explodes and becomes reduced to powder. The same phenomenon
is observed in articles of glass which are cooled spontaneously in the air. When a
spoiled bottle is thrown on one side by the workman before completion it becomes
tempered by exposure to the circumambient air, and acquires the characteristic
properties of the Rupert's drops, for if a small fragment of glass or other substance
equally light be dropped into it it will be sufficient to break it and even cause it to
explode. In either case the result of the tempering, in increasing the hardness of
the glass, has been to considerably affect its molecular arrangement.
M: de Luynes, who has succeeded in analysing the peculiar phenomenon of the
Rupert's drop, has demonstrated by microscopical examination that the structure of
the glass drop resembled a succession of independent blades or laminæ doubled upon
themselves like a series of spring plates, the point of attachment being at the tail
end of the drop, and that by breaking this end the ephemeral equilibrium of the
molecules is destroyed, and the glass becomes reduced to powder. This excessive
fragility is not however irremediable, since if a Rupert's drop be reheated and after-
wards gradually cooled, i.e., annealed, it loses all its explosive properties and is not
more liable to break than ordinary well manufactured glass. It is then annealed
glass, i.e., lowered in temper, its co-efficient of elasticity, which was nil, ranking
with that of glass annealed in the ordinary way.
All glass articles, whether blown or moulded, are necessarily air tempered during
the time that (when in the hands of the workman before being conveyed to the
annealing arch) they lose their plastic consistency and become hardened in the cold
air. It is at this time that the molecular arrangement takes place under more or less
unstable conditions, according to the intensity and duration of this air tempering.
Owing to the constant opening and closing of the annealing arch, and its unequal
heating, glass does not become properly annealed, but the injurious effects of the
air tempering are merely arrested more or less completely, and to this necessarily
irregular action are attributable the variation in the toughness and elasticity of glass.
The tempering of glass articles in very hot liquids, as practised by M. de la Bastie,
evidently increases their hardness and resistance to blows, but it also deprives them
of a portion of their elasticity and molecular cohesion. When such an article is
accidentally broken or its "skin" injured it flies into a thousand fragments like
the Rupert's drop, and from the same causes, it being in fact only a variety of
Rupert's drop, and differing only from it in the infinitely lesser difference between the
temperature of the article and that of the liquid in which it is tempered. It also
differs from it in the qualities which it acquires by a gradual and progressive cooling

page_text: in the liquid in which it is plunged. If then the tempering of glass increases its
hardness, it also considerably diminishes its elasticity, and this quality can only be
restored to it, as we have seen in the case of the Rupert's drop, by reheating the
glass to a temperature approaching that at which it softens, that is to say, to the
point where it spontaneously becomes air tempered for example, and then allowing
it to cool very gradually in a suitable heated medium.
Elasticity is a quality essential to the uses of glass. Thus it is its elasticity, and
not its hardness, which enables champagne and aerated-water bottles to withstand
the prolonged pressures to which they are necessarily subjected, and also enables
them to withstand repeated and sudden changes of temperature. A champagne
bottle, if made of an insufficiently elastic glass, can only be once used, as its entire
strength of resistance will be exhausted, and cannot sustain a second time the pro-
longed pressure of the gases of fermentation; this has been proved by the fact of a
bottle tested to 20 atmospheres, and having resisted this enormous pressure, ultimately
breaking under a pressure of gas of from 5 to 6 atmospheres only. To give another
example, a pane of glass supporting a momentary pressure of, say 25 kilogrammes,
will after the lapse of some hours break beneath the continued but less pressure of
17 kilogrammes. These facts and many others relating to the resistance of glass to
sudden changes of temperature prove that in the majority of cases elasticity is more
necessary to glass than hardness. The latter quality is obtained by tempering,
while elasticity is obtained, as above mentioned, by gradually reheating the glass to
a temperature (dull red) at which it was more or less injuriously air-tempered, and
then allowing it to gradually cool in a suitable medium. The following are the means
employed to obtain this result:-
--
The apparatus of this Invention for annealing glass, one example of which is
illustrated in the accompanying Drawings, is composed of a circular or rectangular
oven in which crystal or other glass objects of all kinds are piled so as to economise
space as much as possible, without however running the risk of rendering them mis-
shapen by too great a superincumbent weight when their temperature approaches
that at which they soften. For this purpose the oven is furnished with a kind of
seggars or stands of fire-clay. Figure 1 is a central longitudinal section of an oven
of rectangular form, and Figure 2 a horizontal section of same taken on line x-x,
Figure 1.
The oven a is heated by a furnace 6 whose capacity varies with that of the oven
and the temperature to be attained. The furnace is fed with coke or other smoke-
less fuel through a hopper c capable of being hermetically closed by a cover d.
The ash pit e is also closed by an air tight door, the blast necessary for combustion
and for the formation of the gases being introduced beneath the grate through a
tuyere fat a pressure which may be as high as 15 centimetres of mercury on the
gauge. A chamber g. similar to those of the Siemens' regenerative furnaces separates
the oven from each of the furnaces. These chambers are filled with bricks built up
in quincunx order, with zigzag interstices between them so as to prolong the
traverse of the furnace gases, in order to accumulate and regulate the heat of the
gases before their introduction into the oven. After filtering through these passages
and accumulating the heat the gases are introduced into the oven, the heat of the
gases being thereby progressively increased when it is desired to heat the oven
gradually or, progressively decreased for cooling it. The chamber is therefore not
a regenerator but a heat accumulator and regulator. The oven chamber and furnace
are hermetically enclosed in a sheet or cast iron casing. At the lower part of the
oven on its lateral faces openings are made, provided with conical plugs (or cocks) 6
for the escape of the gases whilst maintaining a sufficient pressure and avoiding any
return of the gases or their too rapid escape. The oven is also provided with a
manhole for charging and discharging it. Several furnaces and accumulators
arranged as above mentioned may also be combined with a single oven; for
example, the rectangular oven shown in the Drawing may have two furnaces and 5
two accumulators symmetrically arranged, or the oven may be made of polygonal
or circular form, to be combined with a number of furnaces and accumulators.

page_text: Suppose the oven to be filled, and the fires lighted, at starting the blast is turned
on beneath the grate bars at a very low pressure and in only the necessary quantity
to light the coke and gradually heat the furnace. The heat of the furnace is next
imparted to the bricks of the accumulator, which gradually become more and more
heated by the contact of the gases which at first only reach the oven in a cool
condition, but become hotter as the accumulator becomes more highly heated. In
about an hour's time the pressure of the blast is slightly increased, and is thence-
forth gradually raised, according to the indications afforded of the temperature of
the gases at the outlet orifices. The bricks in the accumulator being still more
heated the last rows, viz., those next the oven, acquire a dull red temperature, and
the gases in contact with the same show at their escape a temperature of about
400° C. The pressure in the oven is from 5 to 6 centimetres, which is sufficient to
envelope internally and externally as if bathed in a liquid such articles as small
necked bottles. The volume and pressure of air introduced beneath the grate is
still gradually increased, and the temperature of the gases in the oven soon reaches
525° C. This temperature is maintained for an instant, and the furnaces then
stoked once more for the last time, after having sensibly reduced the pressure. It
is however always necessary that this pressure be sufficient to maintain a perfect
and constant plenum in the oven, this result being readily obtainable by reducing
at will the size of the escape orifices. The oven resembles in short the pressure
regulator in the blowing engines of blast furnaces. Under the action of the
diminished blast the remainder of the fuel becomes consumed, and very soon after
the blast only becomes heated from the sides of the furnace itself, and takes up the
necessary complement of heat by filtering through the network of bricks in the
accumulator, which themselves become proportionately but slowly cooled. The
cooling of the oven and the glass it contains is also slow and progressive, and it is
without any sudden changes and by insensible transitions of temperature that the
articles contained in the oven, after having acquired at first a dull red heat, gradually
fall to that of the air we breathe, and are thus annealed.
The method hereinbefore described will be readily distinguished from all those
which under the denomination of annealing have hitherto been proposed or practised,
the distinguishing features of novelty and economy consisting more particularly in,
1st, the employment of the accumulator and regulator of heat described for obtaining
a gradual heating and cooling of the glass; 2nd, the employment of gases under
pressure in the interior of the apparatus, so as to keep the interior and exterior of
narrow necked bottles at a uniform temperature, as if they were immersed in and
filled with a liquid. The apparatus hereinbefore described may also be employed
for the purpose of giving the high temper to glass, as well as for annealing, the
novelty consisting chiefly in the employment for this purpose of gases under
pressure.
It has been before shown that glass can be as perfectly tempered by contact of a
fluid as with that of a liquid, and I will now proceed to describe the means to be
employed for tempering articles of glass of all kinds and forms by suddenly lowering
to a suitable extent the temperature of the gaseous medium in which they have
been raised to a nascent red heat in the apparatus before described. Suppose the
articles of glass stacked in the said apparatus to have attained a dull red heat, or
nearly approaching the temperature at which they soften, at this moment the blast
beneath the grate is shut off, and expansion naturally takes place in the oven until
the gauges cease to indicate any pressure. At the same instant air under pressure
and at a temperature of, say, 200° C., is suddenly admitted from a suitable reservoir
through nozzles placed at different points of the oven; the pressure in the oven
thereby is considerably increased, and the expanded gases at 500° C. are driven
back, and together with the gases at 200° are forced out gradually in the inverse
direction to that in which they were introduced, that is to say, they are driven off
by this superior pressure first through the accumulator, then through the furnace,
and out through an opening provided in the ash pit. Fresh quantities of com-
pressed air at 200° C. (more or less) are continually introduced to maintain the

page_text: oven at the same temperature and pressure, which air has free access both to the
interior and exterior of the small necked bottles to be tempered. The cooling of
the glass may then be rapidly but gradually effected.
Having described the nature of the said Invention, and the manner of performing
the same, I declare that what I claim as the Invention to be protected by the
herein before in part recited Letters Patent is,―
1st. The process of annealing articles of glass, consisting in placing them in a
suitable oven, and surrounding them with a gaseous medium at a sufficient pressure
to envelop the articles both internally and externally, the said gaseous medium
being first brought to a temperature approaching that at which the glass softens,
and then slowly and gradually cooled, together with the articles bathed therein, as
specified.
2nd. The process of tempering glass articles, consisting in placing them in a
suitable oven, and surrounding them by a gaseous medium at a sufficient pressure
to envelop them internally and externally, the gaseous medium being first brought
to a temperature approaching that at which the glass softens, and then suddenly
cooled to a suitable degree, as specified.
3rd. In an oven for tempering or for annealing glass the combination of one or
more furnaces having closed ash pits with a charging hopper likewise hermetically
closed and tuyere beneath the ash pit, as and for the purpose herein before shown
and described.
4th. In an oven for tempering or annealing glass the combination of one or more
furnaces constructed as specified in the preceding claim, with one or more brick
chambers forming accumulators and regulators of heat, with openings in the sides
of the oven provided with plugs or cocks, as shown and described for the purpose
specified.
In witness whereof, I, the said Alexander Melville Clark, have hereunto set
my hand and seal, this Sixteenth day of March, in the year of our Lord One
thousand eight hundred and eighty.
A. M. CLARK. (LS.).