Improvements in or connected with the Manufacture of Concave or Hollow Objects from Plate Glass.
Year: 1892

page_text: Date of Application, 25th Oct., 1892-Accepted, 1st Apr., 1893
Improvements in or connected with the Manufacture of Concave or
Hollow Objects from Plate Glass.
I, HUGO HECKERT, Manufacturer, of Halle on the Saale, in the German Empire,
do hereby declare the nature of this invention and in what manner the same is to
be performed, to be particularly described and ascertained in and by the following
statement:-
This invention relates to the manufacture of highly concave or bulged glass
bodies for optical and other purposes, such as concave mirrors, concave glass lenses,
from flat glass plates, and is illustrated by the accompanying drawings, of which
Fig. 1 is a side view of an apparatus to be used for the manufacture of such
objects,
Fig. 2 is a plan of the same, and
Fig. 3 a section along line M-N of Fig. 2.
Figs. 4 to 7 represent consecutive stages of manufacture.
The apparatus chiefly comprises two iron rings a and c, the lower one a being
provided with a stand b, which carries the ring a in such a way, that an inner space
of suitable height is left free. The glass plate to be bulged out or moulded is
placed on the accurately smoothened upper surface of the ring a, the opening of
which corresponds, as regards its shape and size, to the bowl or concave object to
be produced (m, n, p, q, Figs. 4 and 5); and the glass plate, after having been cut
to a suitable shape, is placed on the ring a in such a manner, that the edge of
the same fits the outer circumference of the ring a. The plate is then loaded with
the ring e placed on top of it, so that the plate is held securely between the two
rings.
The apparatus built up in this way together with the glass plate mounted in the
same, is placed in an oven and heated slowly to red heat.
By this process the glass plate is weakened and caused to sink down in the
middle, under the influence of its own weight, owing to this part not being
supported, whereas that part of the same, which is held between the rings, can not
follow. In this way is formed a bowl or trough, as shown in Figs. 4 and 5, which
by continued heating and rise of temperature is caused to assume a parabolic
shape, as shown in Figs. 6 and 7. When the desired depth of bending is reached,
the whole apparatus with the suspended bowl is removed from the heating oven and
cooled slowly.
Circular bowls or troughs may also be produced in exactly the same manner, as
shown for the case of an elliptic one, and objects of various sizes may be made.
Such concave or hollow glass bodies are chiefly intended for optical purposes, for
instance, for the manufacture of concave mirrors forming segments of spheres or of
parabolas, and concave lenses.
The concave or bulged glass bodies produced by the method and means described
above, may be used for the construction of lenses in the following manner.
Two of the said glass bodies of suitable shape are so combined and arranged as
to form between them a hollow space or receptacle, which is then filled with a
transparent liquid of known refractive power.
According to the shape and arrangement of these glass bodies placed face to
face or back to back, it is possible to construct biconvex, concavo-convex, or
biconcave lenses.
For instance two convex glass bodies are placed back to back, so that their flat
rims or flanges join each other, the joint is then made tight by means of a suitable
binding substance, leaving only a small opening, for introducing the liquid into the
interior of the lens, which opening is afterwards closed.

page_text: For making concave mirrors, a simple or a compound glass body, produce
as described, is provided with a metallic coating as in the case of other glass
mirrors.
Having now particularly described and ascertained the nature of the said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is ;-
The manufacture of highly concave or bulged objects of glass for optical and
other purposes from flat sheets of glass, by fixing the edges of the latter between
rings, (while the centre is left unsupported) and then heating the plates to red heat,
substantially as described.
Dated this 25th day of October 1892.
FAIRFAX & WETTER,
433, Strand, London, Agents.