IMPROVEMENTS IN THE MANUFACTURE OF ANNEALED, HARDENED, AND TOUGHENED GLASS ARTICLES, AND IN THE MEANS EMPLOYED THEREFOR
Year: 1879

page_text: In the Matter of Letters Patent granted to Frederick Siemens, of Dresden,
in the German Empire, for the Invention of "IMPROVEMENTS IN THE
MANUFACTURE OF ANNEALED, HARDENED, AND TOUGHENED GLASS
ARTICLES, AND IN THE MEANS EMPLOYED THEREFOR," bearing date the
15th December 1879, No. 5135.
DISCLAIMER AND MEMORANDUM OF ALTERATION as proposed to
be entered by the said Frederick Siemens pursuant to the Statutes in that
case made and provided.
WHEREAS Her Majesty Queen Victoria, by Her Letters Patent under the
Great Seal of the United Kingdom of Great Britain and Ireland, bearing date at
Westminster the 15th December 1879, in the forty third year of Her reign,
did give and grant unto me, the said Frederick Siemens, my executors, adminis-
trators, and assigns the sole privilege for the term of fourteen years thence next
ensuing, of making, using, exercising, and vending within the United Kingdom
of Great Britain and Ireland, the Channel Islands, and Isle of Man, the said
Invention of " IMPROVEMENTS IN THE MANUFACTURE OF ANNEALED, HARDENED,
AND TOUGHENED GLASS ARTICLES, AND IN THE MEANS EMPLOYED THEREFOR:"
And whereas in pursuance of a proviso in the said Letters Patent contained, I,
the said Frederick Siemens, did within six calendar months next after the date of
the said Letters Patent cause a Specification or instrument in writing under my
hand and seal purporting to describe and ascertain the nature of the said Invention,
and in what manner the same was to be performed to be duly filed in the Great
Seal Patent Office:
And whereas since filing the said Specification I have ascertained that the
second and third claiming clauses therein may be objected to on the ground that
they claim matters which at the date of the said Letters Patent were not altogether
novel, and I have no desire to retain any claim in respect of these matters.

page_text: I therefore disclaim and alter the said Specification in manner following, that
is to say:
Referring to the Queen's Printors copy of the said Specification, at page 9, I omit
the second and third claims comprised in lines 14 to 22 inclusive; at page 9, line
23, for "Fourth "I substitute " Second;" before "referred" I insert "hereinbefore;"
and after the word "referred" I insert the word " to ;" and I omit " in the preceding
claim."
And the said Specification when so disclaimed, altered, and amended, will read
as follows:-
(Iere follows usual Preamble to Final Specification.)
This Invention has more particularly for its object to enable glass articles of
irregular shape to be annealed, hardened, and toughened in the course of manufacture
by special applications of processes and apparatus such as were described in the
Specifications to Letters Patent, No. 1637 of 1875, No. 1657 of 1877, and No. 1118
of 1879.
In carrying out such processes for cooling, hardening, and toughening glass
articles, it has been found that much more perfect results can be obtained by
applying them to a glass plate or slab of uniform thickness than to glass articles of
any other form by effecting the uniform cooling of such a plate after it has been
uniformly heated only from the two parallel surfaces thereof. If the heating or
cooling be applied also to the edges or circumferential surfaces, these and the parts
nearest them will be sooner heated or cooled than the central parts, as the former
present more surface to the heating or cooling influence than the latter. From
this it is obvious that the simple immersion of a glass body in a cooling element of
whatever nature necessarily effects an unequal cooling of the body, because the
various parts thereof offer surfaces of varying proportions to the cooling element.
Hence it will be seen that a uniform cooling of glass bodies can only be effected
when they assume the form of a plate of uniform thickness, and the uniform
cooling is effected only from the two parallel sides, and in a degree corresponding
to the power of conduction of the glass, that is, not exceeding such power. Such a
plate may be considered as consisting of several parts fitted together, such parts
having any desired form, but so that they fit together in order that the continuous
conduction of heat is at no point interrupted; such a plate would also comply
with the above stated conditions, and consequently render a uniform cooling
possible.
In practice it is however not possible to fit glass bodies, in particular those of
irregular shape, so perfectly together that no hollows spaces intervene between
them, and yet it is necessary to approach the above described "ideal plate" as
nearly as possible. I effect this by filling in such hollow spaces as are formed with
a material which at least approximately has the same properties as glass with
respect to the influence of heat; I therefore thus produce artifically a plate, and
assuming uniform heating to have been effected, I effect the cooling exclusively on
the two parallel sides. If the cooling is effected too rapidly so that its intensity
exceeds the heat conducting power of the glass body, excessive hardening will take
place, that is, a state of tension will be produced, resulting in spontaneous ruptures,
such state of tension and consequent rupture is however more generally caused by
unequal cooling, such as has been above referred to. The rapidity with which the
cooling of a glass body may be effected in order to attain the greatest possible
durability depends essentially upon its volume or mass and upon its form. Of
the latter I am rendered almost independent by means of my peculiar mode of
cooling, and I have therefore practically only to consider the volume or mass.
Here the same precautions have to be taken as with my method of hardening, that
is, thick glass bodies must be cooled more slowly than thinner ones.
In my
me thod of press hardening I complied with this requirement by introducing
between the glass and the cooling pressing surface partially isolating layers; in my
present process I employ similar means, as will be presently shown,

page_text: Theoretically means would be thus afforded for effecting in irregular shaped glass
bodies a uniform heating or cooling in all parts. A uniformly heated glass body
renders possible a more rapid uniform cooling; by this a hardening is always
effected which results in increased durability.
The body which I have found most suitable for carrying out the above described
process is sand, by preferenco with an admixture of burnt and pulverised clay;
but I do not limit myself to this material. I will now proceed to describe the
method and means I have employed in applying such process to the manufacture
of glass articles, such as plates, railway sleepers, millstones, and the like, premising
that all articles operated upon should be in the first instance formed by casting in
moulds and not by the blowing operation.
The consecutive manipulations that are employed are as follows:-
1. Preparation of the moulds for the glass body to be manufactured.
2. The introduction of the glass into such mould.
3. Uniform heating and production of the "ideal plate."
4. Cooling the same.
1. The preparation of the moulds for the glass body may either take place once
for several operations, or a special mould may be made for each glass body to be
produced. In the first case I employ iron as the material for the mould; in the
latter case I employ moulding sand mixed with clay. The application of iron
moulds is of course very limited with regard to the configuration of the glass body
to be produced, or else very complicated apparatus is required in consequence of
the necessary divisions of the mould, which would be very expensive and would
render the manipulation very difficult in every respect. In addition the iron
moulds have other disadvantages in their rapid absorption of heat which only
affects the glass body superficially; this can certainly be very much reduced by
heating the mould, but even then the absorption of heat from the surface may in
some circumstances have such a detrimental effect that the use of iron moulds has
to be abandoned; this particularly occurs with thick or heavy glass bodies.
Another disadvantage results from the fact that in this case the cast glass articles
have to be placed in the heating oven without a mould. This of course assumes
the glass body to be to a certain extent rigid, and consequently to have been
cooled in order to enable its transport to the heating oven to be effected without
complicated appliances; it is equally difficult to maintain its correct shape in the
heating oven without special appliances, in particular when the weight is great.
The use of iron casting moulds is therefore inostly limited to the manufacture of
glass articles of the most simple form in large quantities, such, for instance, as
flooring slabs. Under certain circumstances I also use combined moulds, that is,
partly of 11on and partly of sand. This occurs when the articles to be cast are
undercut, in which cases sand cores are used for their production in the iron
moulds, thereby obviating a complicated dividing of the mould. The sand mould
has a much more general application, as it is not subject to any limitation relatively
to the configuration of the articles to be cast. The preparation is quite analogous
to that of the mould for iron castings, namely, by moulding in iron boxes from a
pattern of the article to be produced. In preparing the iron inould boxes for this
purpose care must be taken that they correspond as nearly as possible to the
form of the article to be manufactured, that is, that the thickness of the sand mould
shall be at all points as uniform as possible in order to facilitate as much as possible
the subsequent uniform heating. Furthermore the mould boxes should be as light,
and therefore as thin as possible. After preparing the moist sand moulds they are
blackened with graphite and baked in a drying chamber. The blackening with
graphite has for its object partly to prevent the adhesion of the glass to the sand
mould, and partly to effect a more perfect running in the glass than would be
possible without it. The same means are used as in casting in iron; channels are
formed for the ready escape of the gases evolved in casting, so as to prevent air
Lubbles ben g formed. Coal powder, chopped straw, etc., are mixed with the
compound of clay and sand, which substances in burning away during the drying
of
A

page_text: of the mould leave porosities through which the gases can escape. The process is
therefore similar to that of mass moulding. If holes occur in the glass body to be
produced cores are used, which may also be of sand, but in some cases I prefer iron
coles. These are prepared by coating correspondingly formed pieces of iron with
clay puddle and then dusting them over with moulding sand, and after drying they
are painted with graphite. Experience has here shewn that the article to be
produced cannot possibly be kept entire if the core, whether of sand or iron,
remains in the article during the cooling process; this results inevitably in the
breaking up of the article. This is caused by the imperfect nature of the core
material, that is, in its incapacity of expanding and contracting uniformly with the
glass. It is therefore indispensable to remove the cores. This is done after the
uniform heating has been effected, and renders necessary a special operation before
the cooling, which I shall refer to later on.
2. The introduction of the glass into the mould is effected either by tapping
from a glass melting tank of suitable construction by pouring from a pot or ladle,
or by taking the glass up with a metal rod, from which it is allowed to run into the
mould. In the latter case the casting is effected by from 3 to 5 operators,
according to the size of the article to be produced. If the casting is effected from
a glass melting tank, this is of course done continuously, and the moulds then lave
to be brought to the tapping hole, whereas with the other two modes of casting
the glass is brought to the mould. In the first case a suitable heating arrange-
ment should be provided at the tapping hole, either by duect fire heat or otherwise,
in order to prevent the accumulation of cooled solidified glass preventing the
flow into the moulds. A gas jet may be conveniently used for this purpose. In
casting the following precautions have to be taken :-The mould must always be
warm, particularly if iron moulds are used. With sand moulds the preliminary
warining has the further object of rendering the graphite absolutely dry, as this is
very hygroscopic, and always causes bubbles when moist. The casting is therefore
effected while the moulds are still warm as they come from the drying chamber.
3. Uniform Heating or Preparation of the "Ideal Plate."-Two cases may here
occur. If the cast article is of simple form without holes, one and the same oven
is employed for the heating and for preparing the ideal plate. If the above
described operation of removing cores after heating has to be performed, the part of
the oven in which the cooling of the uniformly heated plate is effected consists of a
special construction separable from the oven. The construction of the heating oven
is of very simple nature; the heating may be effected either by direct fire heat, or
preferably by gaseous fuel. It is to be particularly observed that the bed of the
heating oven should receive sufficient heat by means of flues. In the heating oven
is contained the sand which is to be employed in the preparation of the "ideal plate,"
and which is brought to the same temperature as the glass articles. The heating
process must be regulated chiefly by experience; if there are many bodies of one
and the saine simple shape and well distributed mass the time required for perfect
heating is soon ascertained; but with glass bodies of complicated form and not
regularly distributed mass it is different. In this case the appliances hereinbefore
mentioned must be used in order to compensate as much as possible for the
imperfections of the filling material. This is effected by removing certain parts of
the mould, and under certain circumstances also the mould box. It is absolutely
necessary to remove the cores unless these be made of a yielding or collapsible
nature to be presently described. If they have to be removed the mould with the
glass casting in it brought to the working door of the oven and the sand cores are
removed by digging out, while the iron cores are simply drawn out by means of
tongs. The subsequent running of the hot sand into the core holes does not hurt,
because it can readily give way during the cooling. If desired the holes may be
covered with pieces of thin heated sheet metal so as to prevent the entrance of sand.
In many cases it will be desirable and of practical advantage to avoid the necessity
for removing the cores, for which purpose these may be of such a construction that they
are capable of yielding to the pressure of the glass during its contraction on cooling,
is

page_text: and which are termed "collapsible" or "spring cores." For sand and loam cores
this is effected by the insertion of metal plates of a thickness corresponding to the
size of the core, and so arranged as to divide the core into two or more separate
parts. These plates may either be inserted while the core is being made up, or
they may be introduced after the separate parts thereof have been formed and
baked. If these plates are withdrawn after the glass article has been cast, but
before it is introduced into the before mentioned heating oven, sufficient space will
be formed in the core to allow this to yield to the requisite extent on the cooling
of the glass. The liquid glass will not run through the narrow apertures left
by the withdrawal of the plates, because it very rapidly cools against the surface
of the core to a sufficient extent to prevent this. If the cores be made of iron which
is used for simple forms, such as cylindrical cores, they are made of sheet metal
of suitable strength bent into the requisite shape, but with the edges overlapping
instead of butting against each other. The core thus constitutes a spring, which
yields perfectly to the shrinking pressure of the glass without the hole or recess
formed by the core becoming deformed in any way; such spring cores of thin
metal will of course cool down with the glass, and are only removed when this
is quite cold. The glass articles having been heated to the requisite extent and
the cores if necessary removed, as above described, the "ideal plate" is then
formed. The arrangement which I employ for this purpose and for cooling the
plate is the truck described in my previous Patent above referred to, constructed
to suit the process of cooling here to be observed, that is, with sides protected by
double metal plates with a single top and single bottom. This truck is first
heated in an oven or stove of the construction described in the Specification to the
said Patent, and then brought to the heating oven, the bottom covered with a
corresponding layer of heated sand, on which are bedded the cast and prepared
glass bodies, and upon this is placed another layer of the heated sand, after which
the cover is closed and the truck placed aside to cool; the cooling is therefore only
effected through the single cover and bottom. In bedding the glass articles, it is to
be particularly observed that no part of the iron mould box touches the sides of
the truck; this would at once cause a defective conduction of heat. There must
be sufficient sand at the sides. In most cases I prefer to introduce the truck
directly into the heating oven; in this case a recess is formed in the working floor
of the oven, which is at the same height as the bottom of the truck above the floor
of the works, while its base is on the same level with such floor so as to carry the
continuation of the tramway thereon.
Instead of the truck an iron box or case of similar construction with closing cover
can be introduced into the heating oven. In this box the formation of the "ideal
plate" is effected; the box is then closed, and is then removed from the heating oven
by any suitable means for the purpose of cooling. In cooling it is to be particularly
observed that this shall take place uniformly from the two parallel surfaces. The box
must therefore, for example, not touch the ground with the bottom surface, that is,
it must not stand, but should be suspended. The most simple case is that in which
the heating the preparation and cooling of the ideal plate can all be effected in one
and the same oven, as is possible with flooring slabs. These are cast in iron moulds,
are then introduced into an oven, which is essentially the same as the truck-cooling
oven described in the before mentioned Specification; the plates are there placed
on a planed table until they are uniformly heated. The bottom of the truck is
then covered with a corresponding layer of sand, on which the heated plates are
laid. The truck being filled, heated sand is placed over the contents; the entire
plate thus formed is left some time in the oven, and after closing the cover the
truck is removed for cooling, which takes place in the desired manner from the top
and bottom. A pair of ovens are always used for this purpose, as described in the
above named Specification. The apparent defect that the bottom of the truck is
cooled by the current of air passing to the combustion chamber of the oven, and
that thus uniform heating of the "ideal plate" cannot be effected, is met by making
the bottom of the truck also double, and by placing upon the lower or outer bottom

page_text: a sufficient layer of sand to form an isolating layer during the heating on removal
of the truck from the oven, the lower bottom with its layer of sand is removed,
whereby the uniform cooling only from the top and the bottom surfaces is rendered
possible.
The accompanying Drawing shews by way of example the before described mode
of carrying out my Invention, wherein the heating and formation of the "ideal
plate" are effected in one and the same oven, part of which is formed by the truck
in which the cooling is afterwards effected, this arrangement being more particularly
applicable for the production of flooring plates, tiles, roof lights, and generally for
articles of small and comparatively uniform height. For effecting a continuous
working a pair of such ovens are required, of which the one is being heated while
the other is in operation.
Fig. 1 of the Drawing shews a vertical longitudinal section of one oven on line
X, X, Fig. 3; Fig 2 shews a cross section of a pair of ovens on line Y, Y, Fig. 3;
and Fig. 3 shows a sectional plan on line Z, Z, Fig 1. The ovens are heated by
gaseous fuel, the combustible gas being introduced through the main flue G and
passages g, and issuing through the ports f into the oven, the requisite air supply
for combustion being also caused to enter through these ports fiom passages into
which it flows from beneath the bottom of the truck, as indicated by the arrows.
The products of combustion pass off through the chimnies c. a is the working
door, opposite to which is the levelling table r, consisting of a planed cast iron
plate of suitable thickness to prevent warping. On to this table the glass slabs are
placed directly from the casting moulds, and upon it they become uniformly heated
to the requisite degree, and at the same time assume the perfectly level shape
required. The truck T which forms the floor of the oven in a similar manner to
that described in the Specification to my before mentioned previous Patent is
constructed of sheet iron, the bottom and front end w being single, and the latter
being arranged to turn down, as shewn at Fig. 1, while the back and sides are
made double with intervening air spaces. In the roof of the oven above the
middle of the truck is fixed the sand magazine S, from which the annd, heated to
the same temperature as the oven, is caused to descend into the truck on opening
the valve u by means of an external lever. The sides of the truck are provided
with flanges dipping into sand troughs v for forming an air-tight joint, with the
sides of the oven, as shewn, and the outer end of the truck has a sand trough v³,
into which dips a removeable plate b for the same purpose. The cover of the truck
consists simply of a flanged plate which is either fitted on after the truck has been
removed from the oven, or it may be slid on through the narrow aperture in front
after removal of the plate b before the truck is wheeled out. The trucks of both
the ovens having in the first instance bad a layer of sand placed in them, which is
carefully levelled, they are run into the oven, and the hermetic sand joint is formed
as described; also the sand is introduced into the magazine S, and the whole is
heated up to the required degree.
The glass articles having been cast are introduced as hot as practicable into the
one oven on to the table r, which is large enough to receive several such articles,
in order that they may be there heated to an uniform degree. The articles are
then placed on the sand bed of the truck and more of the articles are placed on the
table to be heated, which articles are afterwards transferred in like manner to
the truck. When the truck is filled with glass articles, the valve u is opened and
sand is allowed to flow down over the glass articles in such quantity as when
levelled down with a rake to form a sufficiently thick layer over them. The cover &
is then placed on the truck, the front end w having been first turned up, and the
truck is removed and placed aside to cool. A similar truck with its prepared sand
bed is then introduced into the oven, and fresh sand is, if necessary, filled into the
magazine and the whole is heated up, while the before described operation of
heating the glass articles and filling them into the truck is being carried out in the 5
adjoining oven, which has been heated during the filling operation carried on in the
other one.

page_text: The hinged side w being for convenience sake made single instead of double, as
are the other sides, the greater conduction of heat at that side may be counteracted
by placing an increased quantity of sand between it and the glass articles nearest
to it. Also as before described, the cooling action of the current of air passing into
the oven below the truck may be counteracted by introducing below-the bottom of
the truck a second bottom having a layer of sand, which second bottom is removed
when the truck has received its charge.
Having thus described the nature of my said Invention, and in what manner
the same is to be performed, I claim,―
First. The manufacture of hardened, toughened, or annealed glass articles by
first heating them uniformly and after imbedding them in heated sand or other
substance having approximately the same heat conducting power as glass, in such a
manner as to produce a body presenting two parallel heat conducting surfaces,
subjecting the same to a uniforin cooling action applied only to such parallel
surfaces, substantially as herein described.
Second. Constructing trucks, such as are hereinbefore referred to, with a double
bottom, the lower one of which is provided with a non conducting layer of sand
or other material, and is removeable for the purpose of cooling after the heating of
the glass articles has been effected, substantially as and for the purposes described.
In witness whereof, I, the said Frederick Siemens, have hereunto set my
hand and seal, this Ninth day of June, in the year of our Lord One
thousand eight hundred and eighty.
FREDERICK SIEMENS. (L.S.)
In witness whereof. I. the said Frederick Siemens, have hereunto set my
I hereby grant my fiat, giving leave to the above named Frederick Siemens,
to file in the Office of the Commissioners of Patents for Inventions, with the
Specification to which the same relates, the above written Disclaimer and
Memorandum of Alteration.

page_text: "
LETTERS PATENT to Frederick Siemens, of Dresden, in the German Empire,
for the Invention of "IMPROVEMENTS IN THE MANUFACTURE OF ANNEALED,
HARDENED, AND TOUGHENED GLASS ARTICLES, AND IN THE MEANS EMPLOYED
THEREFOR.
"
Sealed the 20th February 1880, and dated the 15th December 1879.
PROVISIONAL SPECIFICATION left by the said Frederick Siemens at the
Office of the Commissioners of Patents on the 15th December 1879.
FREDERICK SIEMENS, of Dresden, in the German Empire. "IMPROVEMENTS IN
THE MANUFACTURE OF ANNEALED, HARDENED, AND TOUGHENED GLASS ARTICLES,
AND IN THE MEANS EMPLOYED THEREFOR.”
This Invention has more particularly for its object to enable glass articles of
irregular shape to be annealed, hardened, and toughened in the course of manu-
facture by special applications of processes and apparatus such as were described
in the Specifications to Letters Patent No. 1637, of 1875, No. 1657, of 1877, and
No. 1118, of 1879.
In carrying out such processes for cooling, hardening, and toughening glass
articles, it has been found that much more perfect results can be obtained by
applying them to a glass plate or slab of uniform thickness than to glass articles
of any other form by effecting the cooling of such a plate after it has been uniformly
heated only from the two parallel surfaces thereof. If the heating or cooling be
applied also to the edges or circumferential surfaces, these and the parts nearest
them will be sooner heated or cooled than the central parts, as the former present
more surface to the heating or cooling influence than the latter. Unequal tensions
or strains are thus produced in the glass body which fiequently result in its
spontaneous rupture; this result will also be produced if the cooling takes place
more rapidly than is consistent with the conducting power of the glass. It is

page_text: therefore necessary in order to effect the proper treatment of glass articles of
irregular shape to place them as nearly as possible under the same conditions as
a glass slab or plate of uniform thickness cooled at a suitably regulated rate only
at its parallel faces. For this purpose I arrange such articles along with a material
of approximately the same conductivity as glass, such as sand, or mixtures thereof
with clay, preferably burnt, so as to present the form of a slab or plate of uniform
thickness, all the interstices or irregularities being filled up so that the rate of
conduction throughout may be as nearly as possible uniform. I thus produce an
artificial plate or slab of the character required, and having uniformly heated it
I effect its cooling exclusively at its two parallel sides. The rate of cooling depends
mostly on the thickness, that is to say, the thicker the plate the more slowly should
it be cooled. If in any case the cooling is allowed to proceed too rapidly, a state of
tension will be produced occasioning spontaneous rupture, whereas when the cooling
is duly moderated the glass is so hardened and toughened as to possess great
strength and durability. In manufacturing the articles to be treated I have
recourse to casting in much the same mauner as in casting iron. The moulds for
this purpose may be of iron, but generally it is preferable to use moulding sand
mixed with the materials usually employed to give porosity, the moulds being
dressed as usual on the surface, and thoroughly dried by baking. For undercut
patterns and boles or vacuities cores are used as in iron moulding The moulding
box should correspond nearly to the shape of the article to be cast, so that there
may be round it a nearly uniform thickness of sand in order to facilitate the
subsequent uniform heating and cooling. For casting articles of a simple and
uniform shape, such as slabs for flooring, iron moulds may be employed with some
advantage, as they serve for repeated castings, but in general the sand mould is to
be preferred. The moulds may be filled from the tapping hole of a tank, or from
a pot or ladle, or by running the molten glass from metal rods by which it has
been taken up. In all cases, but particularly when iron moulds are used, the
moulds should be heated before filling. The articles cast are heated in a furnace
either by direct fire heat, or preferably by a gas flame, and it is convenient at the
same time to heat the sand or other material that is to be employed along with
them to make up the artificial slab for cooling. Before or during the heating of
the castings all cores are removed, as if these were left in during the subsequent
cooling they would give rise to unequal strains and consequent fractures. The
castings when uniformly heated along with the filling-up material are made up
into the artificial slab or plate form to be cooled, and in order that these parts of
the process may be conveniently carried on, I employ for the purpose annealing
trucks constructed and worked as described in the Specification to Patent No. 1118,
of 1879. Such a truck, made with double plated sides and single plated bottom
and cover, is brought to the heating oven, and having its bottom covered with a
layer of heated sand, the glass articles are bedded in the sand layer; they are then
covered by heated sand, care being taken that all interstices are filled, and the
cover being put on, the truck is removed to be cooled. In many cases it is con-
venient to heat and cool the glass castings without removing them from their
moulding boxes, and in such cases care is to taken that the box should nowhere
touch the sides of the cooling truck, otherwise there would be inequality of
conduction, and consequent irregularity in the cooling. For convenience of moving
the articles into the truck, the beating oven is made with a recess into which the
truck is wheeled, its bottom being on a level with the oven floor. Instead of a
truck an iron box may be employed, but it is less convenient for moving, and as it
has to be cooled uniformly on its lower as well as its upper surface it must be
suspended or supported so as to expose its lower surface. The box or truck body
charged with the glass articles and filling-up material constitutes virtually the slab
or plate of uniforin thickness, protected around its circumference by the double
plating, and exposed for cooling only on its parallel upper and lower surfaces.
When the glass castings are of a simple and uniform character, such as slabs for

page_text: flooring, the process may be somewhat simplified; these slabs, which are usually
cast in iron moulds, are placed in the heating oven, and when uniformly heated are
placed on a sand layer on the bottom of the truck; they are then covered with a
layer of sand, and the truck with its contents having been left for some time
exposed to the heat of the oven, the cover is put on and the truck is removed to
cool. In order to provide against irregularity of heating when the truck forms
part of the oven, as described in the abovenamed Specification, it is made with a
removeable second or lower bottom supporting an insulating layer of sand while
the truck is being heated, so that any currents of air passing in contact with its
under surface will not affect the the uniform heating; this bottom and its sand layer
is removed when the truck is withdrawn to cool.
.

page_text: DIECIFICATION pursuance of the conditions of the Letters Fatent meu oy
the said Frederick Siemens in the Great Seal Patent Office on the 14th June
1880.
FREDERICK SIEMENS, of Dresden, in the German Empire. "IMPROVEMENTS IN
THE MANUFACTURE OF ANNEALED, HARDENED, AND TOUGHENED GLASS ARTICLES,
AND IN THE MEANS EMPLOYED THEREFOR."
This Invention has more particularly for its object to enable glass articles of
irregular shape to be annealed, hardened, and toughened in the course of manufacture
by special applications of processes and apparatus, such as were described in the
Specifications to Letters Patent, No. 1637 of 1875, No. 1657 of 1877, and No. 1118
of 1879.
In carrying out such processes for cooling, hardening, and toughening glass
articles, it has been found that much more perfect results can be obtained by
applying them to a glass plate or slab of uniform thickness than to glass articles of
any other form by effecting the uniform cooling of such a plate after it has been
uniformly heated only from the two parallel surfaces thereof. If the heating or
cooling be applied also to the edges or circumferential surfaces, these and the parts
nearest them will be sooner heated or cooled than the central parts, as the former
present moro surface to the heating or cooling influence than the latter. From this
it is obvious that the simple immersion of a glass body in a cooling element of
whatever nature necessarily effects an unequal cooling of the body, because the
various parts thereof offer surfaces of varying proportions to the cooling element.
Hence it will be seen that a uniform cooling of glass bodies can only be effected
when they assume the form of a plate of uniform thickness, and the uniform cooling
is effected only from the two parallel sides, and in a degree corresponding to the
power of conduction of the glass that is not exceeding such power. Such a plate
may be considered as consisting of several parts fitted together, such parts having
any desired form, but so that they fit together in order that the continuous
conduction of heat is at no point interrupted; such a plate would also comply
with the above stated conditions, and consequently render a uniform cooling
possible. In practice it is however not possible to fit glass bodies, in particular
those of irregular shape, so perfectly together that no hollow spaces intervene
between them, and yet it is necessary to approach the above described "ideal plate" an
nearly as possible. I effect this by filling in such hollow spaces as are formed with a
material which at least approximately has the same properties as glass with respect
to the influence of heat. I therefore thus produce artificially a plate, and assuming
uniform heating to have been effected, I effect the cooling exclusively on the two
parallel sides. If the cooling is effected too rapidly, so that its intensity exceeds
the heat conducting power of the glass body, excessive hardening will take place, that
is, a state of tension will be produced, resulting in spontaneous ruptures; such state
of tension and consequent rupture is however more generally caused by unequal
cooling, such as has been above referred to. The rapidity with which the cooling of a
glass body may be effected, in order to attain the greatest possible durability,
depends essentially upon its volume or mass and upon its form. Of the latter I
am rendered almost independent by means of my peculiar mode of cooling, and I
have therefore practically only to consider the volume or mass. Here the same
precautions have to be taken as with my method of hardening, that is, thick glass
bodies must be cooled more slowly than thinner ones. In my method of press
hardening I complied with this requirement by introducing between the glass and
the cooling pressing surface partially isolating layers, in my present process I
employ similar means, as will be presently shewn.
Theoretically means would be thus afforded for effecting in irregular shaped glass
bodies a uniform heating or cooling in all parts. A uniformly heated glass body

page_text: The body which I have found most suitable for carrying out the above described
process is sand, by preference with an admixture of burnt and pulverised clay, but
I do not limit myself to this material. I will now proceed to describe the method
and means I have employed in applying such process to the manufacture of glass
articles, such as plates, railway sleepers, millstones, and the like, premising that all
articles operated upon should be in the first instance formed by casting in moulds
and not by the blowing operation.
The consecutive manipulations that are employed are as follows:-
1.) Preparation of the moulds for the glass body to be inanufactured.
2.) The introduction of the glass into such mould.
3.) Uniform heating and production of the "ideal plate."
4.) Cooling the same.
1.) The preparation of the moulds for the glass body may either take place once
for several operations or a special mould may be made for each glass body to be
produced. In the first case I employ iron as the material for the mould; in the
latter case I employ moulding sand mixed with clay. The application of iron moulds
is of course very limited with regard to the configuration of the glass body to be
produced, or else very complicated apparatus is required in consequence of the
necessary divisions of the mould, which would be very expensive, and would
render the manipulation very difficult in every respect. In addition, the iron
moulds have other disadvantages in their rapid absorption of heat, which only
affects the glass body superficially; this can certainly be very much reduced
by heating the mould, but even then the absorption of heat from the surface
may in some circumstances have such a detrimental effect that the use of
iron moulds has to be abandoned; this particularly occurs with thick or heavy
glass bodies. Another disadvantage results from the fact that in this case the
cast glass articles have to be placed in the heating oven without a mould. This
of course assumes the glass body to be to a certain extent rigid, and consequently
to have been cooled in order to enable its transport to the heating oven to be
effected without complicated appliances; it is equally difficult to maintain its
correct shape in the heating oven without special appliances, in particular when the
weight is great. The use of iron casting moulds is therefore mostly limited to the
manufacture of glass articles of the most simple form in large quantities, such, for
instance, as flooring slabs. Under certain circumstances I also use combined moulds,
that is, partly of iron and partly of sand This occurs when the articles to be cust
are undercut, in which cases sand cores are used for their production in the iron
moulds, thereby obviating a complicated dividing of the mould. The sand mould
has a much more general application as it is not subject to any limitation relatively
to the configuration of the articles to be cast. The preparation is quite analogous
to that of the mould for iron castings, namely, by moulding in iron boxes from a
pattern of the article to be produced. In preparing the iron mould-boxes for this
purpose care must be taken that they correspond as nearly as possible to the form
of the article to be manufactured, that is, that the thickness of the sand mould
shall be at all points as uniform as possible in order to facilitate as much as possible
the subsequent uniform heating. Furthermore the mould boxes should be as light
and therefore as thin as possible After preparing the moist sand moulds they are
blackened with graphite and baked in a drying chamber. The blackening with
graphite has for its object partly to prevent the adhesion of the glass to the sand
mould, and partly to effect a more perfect running in of the glass than would be
possible without it. The same means are used as in casting in iron; channels are
formed for the ready escape of the gases evolved in casting so as to prevent air
bubbles being formed. Coal powder, chopped straw, etc., are mixed with the
compound of clay and sand, which substances in burning away during the drying
of the mould leave porosities through which the gases can escape. The process is
therefore similar to that of mass moulding. If holes occur in the glass body to be

page_text: produced cores are used, which may also be of sand, but in some cases I prefer iron
cores. These are prepared by coating correspondingly formed pieces of iron with
clay puddle and then dusting them over with moulding sand, and after drying they
are painted with graphite. Experience has here shewn that the article to be
produced cannot possibly be kept antire if the core, whether of sand or iron, remains
in the article during the cooling process; this results inevitably in the breaking up
of the article. This is caused by the imperfect nature of the core material, that is,
in its incapacity of expanding and contracting uniformly with the glass. It is
therefore indispensable to remove the cores. This is done after the uniforin heating
has been effected, and renders necessary a special operation before the cooling,
which I shall refer to later on.
2.) The introduction of the glass into the mould is effected either by tapping
from a glass melting tank of suitable construction, by pouring from a pot or ladle,
or by taking the glass up with a metal rod, from which it is allowed to run into
the mould. In the latter case the casting is effected by from 3 to 5 operators,
according to the size of the article to be produced. If the casting is effected from
a glass melting tank this is of course done continuously, and the moulds then have
to be brought to the tapping hole, whereas with the other two modes of casting the
glass is brought to the mould. In the first case a suitable heating arrangement
should be provided at the tapping hole, either by direct fire heat or otherwise, in
order to prevent the accumulation of cooled solidified glass preventing the flow into
the moulds. A gas jet may be conveniently used for this purpose. In casting, the
following precautions have to be taken :-The mould must always be warm,
particularly if iron moulds are used. With sand moulds the preliminary warming
has the further object of rendering the graphite absolutely dry, as this is very
hygroscopic, and always causes bubbles when moist. The casting is therefore
effected while the moulds are still warm as they come from the drying chamber.
3.) Uniform Heating or Preparation of the "Ideal Plate "-Two cases may here
occur. If the cast article is of simple form without holes ono and the same oven is
employed for the heating and for preparing the ideal plate. If the above
described operation of removing cores after heating has to be performed, the part of
the oven in which the cooling of the uniformly heated plate is effected consists of
a special construction separable from the oven. The construction of the heating
oven is of very simple nature; the heating may be effected either by direct fire
heat or preferably by gaseous fuel. It is to be particularly observed that the bed
of the heating oven should receive sufficient heat by means of flues. In the heating
oven is contained the sand which is to be employed in the preparation of the "ideal
plate," and which is brought to the same temperature as the glass articles. The
heating process must be regulated chiefly by experience; if there are mamy bodies
of one and the same simple shape and well distributed mass the time required for
perfect heating is soon ascertained, but with glass bodies of complicated form and
not regularly distributed mass it is different. In this case the appliances herein-
before mentioned must be used in order to compensate as much as possible for
the imperfections of the filling material. This is effected by removing certain
parts of the mould and under certain circumstances also the mould box. It is
absolutely necessary to remove the cores unless these be made of a yielding or
collapsible nature, to be presently described. If they have to be removed the
mould with the glass casting in it is brought to the working door of the oven and
the sand cores are removed by digging out, while the iron cores are simply drawn
out by means of tongs. The subsequent running of the hot sand into the core holes
does not hurt because it can readily give way during the cooling. If desired, the
holes may be covered with pieces of thin heated sheet metal so as to prevent the
entrance of sand. In many cases it will be desirable and of practical advantage to
avoid the necessity for removing the cores, for which purpose these may be of such a
construction that they are capable of yielding to the pressure of the glass during its
contraction on cooling, and which are termed "collapsible" or "spring cores'
" For
sand and loam cores this is effected by the insertion of metal plates of a thickness

page_text: corresponding to the size of the core, and so arranged as to divide the core into two
or more separate parts. These plates may either be inserted while the core is being
made up, or they may be introduced after the separate parts thereof have been
formed and baked. If these plates are withdrawn after the glass article has been
cast, but before it is introduced into the before mentioned heating oven, sufficient
space will be formed in the core to allow this to yield to the requisite extent on the
cooling of the glass. The liquid glass will not run through the narrow apertures
left by the withdrawal of the plates, because it very rapidly cools against the
surface of the core to a sufficient extent to prevent this. If the cores be made of
iron, which is used for simple forms such as cylindrical cores, they are made of sheet
metal of suitable strength bent into the requisite shape, but with the edges
overlapping instead of butting against each other. The core thus constitutes a spring
which yields perfectly to the shrinking pressure of the glass without the hole or
recess formed by the core becoming deformed in any way, such spring cores of thin
metal will of course cool down with the glass, and are only removed when this is
quite cold. The glass articles having been heated to the requisite extent, and the
cores, if necessary, removed as above described, the "ideal plate" is then formed.
The arrangement which I employ for this purpose and for cooling the plate is the
truck described in my previous Patent above referred to, constructed to suit the
process of cooling here to be observed, that is, with sides protected by double metal
plates with a single top and single bottom. This truck is first heated in an oven
or stove of the construction described in the Specification to the said Patent, and
then brought to the heating oven, the bottom covered with a corresponding layer
of heated sand, on which are bedded the cast and prepared glass bodies, and upon
this is placed another layer of the heated sand, after which the cover is closed and
the truck placed aside to cool; the cooling is therefore only effected through the
single cover and bottom. In bedding the glass articles it is to be particularly
observed that no part of the iron mould box touches the sides of the truck; this
would at once cause a defective conduction of heat, there must be sufficient sand at
the sides. In most cases I prefer to introduce the truck directly into the heating
oven; in this case a recess is formed in the working floor of the oven, which is at the
same height as the bottom of the truck above the floor of the works, while
its base is on the same level with such floor so as to carry the continuation of the
tramway thereon
Instead of the truck an iron box or case of similar construction with closing
cover can be introduced into the heating oven. In this box the formation of the
"ideal plate" is effected, the box is then closed and is then removed from the heating
oven by any suitable means for the purpose of cooling. In cooling it is to be
particularly observed that this shall take place uniformly from the two parallel
surfaces. The box must therefore, for example, not touch the ground with the
bottom surface, that is, it must not stand but should be suspended. The most
simple case is that in which the heating, the preparation, and cooling of the ideal
plate can all be effected in one and the same oven, as is possible with flooring slabs.
These are cast in iron moulds, are then introduced into an oven, which is essentially
the same as the truck-cooling oven described in the beforementioned Specification;
the plates are there placed on a planed table until they are uniformly heated.
The bottom of the truck is then covered with a corresponding layer of sand, on
which the heated plates are laid. The truck being filled heated sand is placed over
the contents; the entire plate thus formed is left some time in the oven, and after
closing the cover the truck is removed for cooling, which takes place in the desired
manner from the top and the bottom. A pair of ovens are always used for this
purpose, as described in the above named Specification. The apparent defect that
the bottom of the truck is cooled by the current of air passing to the combustion
chamber of the oven, and that thus uniform heating of the "ideal plate" cannot be
effected, is met by making the bottom of the truck also double, and by placing
upon the lower or outer bottom a sufficient layer of sand to form an isolating layer
during the heating. On removal of the truck from the oven the lower bottom with

page_text: its layer of sand is removed, whereby the uniform cooling only from the top and
the bottom surfaces is rendered possible.
The accompanying Drawing shews, by way of example, the before described
mode of carrying out my Invention wherein the heating and formation of the
"ideal plate" are effected in one and the same oven, part of which is formed by the 5
truck in which the cooling is afterwards effected; this arrangement being more
particularly applicable for the production of flooring plates, tiles, roof lights, and
generally for articles of small and comparatively uniform height. For effecting a
continuous working a pair of such ovens are required, of which the one is being
heated while the other is in operation.
Fig. 1 of the Drawing shews a vertical longitudinal section of one oven on line
X, X, Fig. 3; Fig. 2 shews a cross section of a pair of ovens on line Y, Y, Fig 3;
and Fig. 3 shews a sectional plan on line Z, Z, Fig. 1. The ovens are heated by
gaseous fuel, the combustible gas being introduced through the main flue Gand
passages g, and issuing through the ports f into the oven, the requisite air supply 1
for combustion being also caused to enter through these ports from passages 1, into
which it flows from beneath the bottom of the truck, as indicated by the arrows.
The products of combustion pass off through the chimnies e. a is the working
door, opposite to which is the levelling table r, consisting of a planed cast iron plate
of suitable thickness to prevent warping. On to this table the glass slabs are i
placed directly from the casting moulds, and upon it they become uniformly
heated to the requisite degree, and at the same time assume the perfectly level
shape required. The truck T, which forms the floor of the oven in a similar manner
to that described in the Specification to my before mentioned previous Patent, is
constructed of sheet iron, the bottom and front end w being single, and the latter
being arranged to turn down, as shewn at Fig. 1, while the back and sides are made
double with intervening air spaces. In the roof of the oven, above the middle of
the truck, is fixed the sand magazine S, from which the sand, heated to the same
temperature as the oven, is caused to descend into the truck on opening the valve u
by means of an external lever. The sides of the truck are provided with flanges
dipping into sand troughs v for forming an air tight joint with the sides of the
oven as shewn; and the outer end of tho truck has a sand trough v¹, into which
dips a removeable plate 6 for the same purpose. The cover of the track consists
simply of a flanged plate, which is either fitted on after the truck has been removed
from the oven, or it may be slid on through the narrow aperture in front after
removal of the plate b before the truck is wheeled out. The trucks of both the
ovens having in the first instance had a layer of sand placed in them, which is
carefully levelled, they are run into the oven, and the hermetic sand joint is
formed as described; also the sand is introduced into the magazine S, and the
whole is heated up to the required degree.
The glass articles having been cast are introduced as hot as practicable into the
one oven on to the table r, which is large enough to receive several such articles
in order that they may be there heated to an uniform degree. The articles are
then placed on the sand bed of the truck, and more of the articles are placed on
the table r to be heated, which articles are afterwards transferred in like manner
to the truck. When the truck is filled with glass articles the valve u is opened
and sand is allowed to flow down over the glass articles in such quantity as, when
levelled down with a rake, to form a sufficiently thick layer over them. The cover
is then placed on the truck, the front end w having been first turned up, and the
truck is removed and placed aside to cool. A similar truck with its prepared sand
bed is then introduced into the oven, and fresh sand is, if necessary, filled into the
magazine, and the whole is heated up, while the before described operation of
heating the glass articles and filling them into the truck is being carried out in the
adjoining oven, which has been heated during the filling operation carried on in
the other one.
The hinged side w being for convenience sake made single instead of double, as
are the other sides, the greater conduction of heat at that side may be counteracted

page_text: by placing an increased quantity of sand between it and the glass articles nearest
to it. Also, as before described, the cooling action of the current of air passing
into the oven below the truck may be counteracted by introducing below the
bottom of the truck a second bottom having a layer of sand, which second bottom
is removed when the truck has received its charge.
Having thus described the nature of my said Invention, and in what manner the
same is to be performed, I claim,―
First. The manufacture of hardened, toughened, or annealed glass articles by first
heating them uniformly and after imbedding them in heated sand, or other
substance having approximately the same heat-conducting power as glass in such
a manner as to produce a body presenting two parallel heat conducting surfaces,
subjecting the same to a uniform cooling action applied only to such parallel
surfaces, substantially as heroin described
Second. The method of converting irregularly shaped glass bodies into a body
having two parallel heat conducting surfaces by the aid of sand or other
substances or compounds having approximately the same heat-conducting powers
as glass, substantially as and for the purposes herein described
Third. In the toughening, hardening, or annealing of glass articles, the use in
combination with the heating oven of a truck or box, on the bottom of which is
placed a layer of heated sand or other suitable substance on which the glass articles
are bedded, while another layer of heated sand or other suitable substance is placed
over the glass articles, substantially as and for the purposes herein described.
Fourth. Constructing trucks such as are referred to in the preceding claim with
a double bottom, the lower one of which is provided with a non-conducting layer
of sand or other material, and is removeable for the purpose of cooling after the
heating of the glass articles has been effected, substantially as and for the purposes
described.
In witness whereof, I, the said Frederick Siemens, have hereunto set my hand
and seal, this Ninth day of June, in the year of our Lord One thousand