IMPROVEMENTS IN THE PRODUCTION OF PLATES OR SURFACES CONTAINING INSCRIPTIONS, MARKS, OR DEVICES, AND IN THE MACHINERY OR APPARATUS EMPLOYED THEREIN
Year: 1875

page_text: PROVISIONAL SPECIFICATION left by Robert Mallet at the Office
of the Commissioners of Patents, with his Petition, on the 14th
January 1875.
I, ROBERT MALLET, of Westminster Chambers, in the City of West-
minster, Civil Engineer, do hereby declare the nature of my said
Invention for "IMPROVEMENTS IN THE PRODUCTION OF PLATES OR SURFACES
CONTAINING INSCRIPTIONS, MARKS, OR DEVICES, AND IN THE MACHINERY OR
APPARATUS EMPLOYED THEREIN," to be as follows :-
My Invention relates to an improved process for the economical
production of plates or surfaces of brass, bronze, or other metals, or
alloys of metals, or alloys combined with phosphorus, containing
inscriptions or numbers, or both, and presenting the character of such
plates when produced by the engraver on metals.
According to the ordinary method of producing plates of this
description the numbers or letters are usually sunk or incised by hand
below the surface of the plate, the cavities being afterwards filled up
with black, red, or other wax, or like resinoid material, by which the
inscription becomes apparent and legible.

page_text: Now my Invention has for its object cheapening the production of
such plates, and consequently extending the demand for them by the
substitution of mechanical means for the skilled labor of the engraver.
For this purpose I propose to cast such inscribed plates with the sunken
characters already sunk beneath the general surface of the plate, so that
the sunken parts have simply to be subsequently filled up level with the
wax or like material, and the surface of the plate polished off as in the
ordinary manner.
In carrying out my Invention I employ a peculiar process for
moulding and casting, combined with certain mechanical arrangements
for readily and perfectly forming the mould for the cavities forming the
letters or devices in or on the plates, together with certain other
apparatus for rapidly changing the models from which numerals or
marks are to be moulded.
•
The face of a sand mould from which the front of an inscribed plate,
such, for example, as that for a shop front, is to bo cast must necessarily
bo provided with the numbers or letters of the intended inscription in
relief, and this face I mould from metallic models. The model for cach
letter or numeral consists of a square or rectangular prism of steel,
bronze, or other hard metal, one end of which is of a suitable size of
surface to receive the intended letter or number, and which is by hand
or by pressure as from a die (i.e., a tool driven by pressure or by a blow,
as from a coining press) sunk into the end surface of the metal of the
prism to about the same depth as the ongraver would cut it if it were
part of an inscription plate.
A sufficient number of alphabets and numerals and of various sizes
are provided, all prisms of the same size being arranged together when
placed in a suitable frame upon a moulding table, so as to preserve their
lincs and places. Spaces between the lines are filled up with plain strips
or blocks of hard metal, and a similar arrangement is adopted for larger
spaces between the letters. All these surfaces when in place form onc
plane (for a plain flat plate) level with that of the higher parts of those
of the sunken ends of the prisms. Upon a surface or compound model
so prepared the sand mould is formed in the manner as here-aftor
described, and the face of the plate is cast from such sand mould under
pressure, the back of the plate being also moulded but plain.
The separate letter models (which are in fact prismatic types with tho

page_text: letters sunk in intaglio in place of raised in cameo, as in ordinary types)
may now be transposed to form any other inscription if the process of
moulding is not required to be repeated from the same model. From
the same depth only to which letters or numerals used to be sunk the
moulding process thus conducted admits of the edges of the sunk parts
being almost perfectly square to the plate, so as sufficiently to hold and
retain the filling wax, but if desired the edges may be rapidly undercut
by a single stroke of the hand graving tool prior to filling in with
wax.
For casting numerical plates, such, for example, as those employed
for numbering omnibusses, cabs, railway carriages, and tho like in a
determinate order, I propose to adapt the prismatic models, whether of
numbers, letters, or marks to a numbering machine, constructed upon
the principle of the machine well known as Bramah's bank note
numbering machine, and so made as to automatically change the models
of the successive numbers as desired, so that after any given number of
combinations of the separate pieces constituting the whole has been
moulded the type bearing cylinder, or one or more of the discs com-
posing it, may be turned round, and the requisite pieces thus at once
and without error changed ready for moulding the next.
Where inscription plates are of large size economy of material may be
procured by making the plate of equal thickness, or nearly so at all
parts, viz., below the sunken characters and between them. In order
to effect this the mould for the face (being made in fine plaster of Paris)
is flooded over with a cream of plaster of Paris in water, which is almost
immediately allowed to drain off, leaving only such a thickness all over
the face of the mould as is caused to adhere by absorbtivity. When dry
and hard baked and oiled this face is employed as the model for moulding
the back of the plate; the required thickness will be given to the plate
by simply modifying the proportion of water in the plaster cream, and
the time during which the flood of cream is allowed to remain on the
absorbing face of the plaster mould before drawing it off.
It is obvious that by having the prismatic moulds for the characters
in cameo in place of intaglio, that is, the characters raised above instead
of sunk beneath the general surface, inscriptions in slightly raised
characters may be produced, very suitable for tombstones and like
purposes, whilst if the spaces between such raised characters be filled up

page_text: level with wax or other suitable coloured material and all be polished
off smooth a new and very ornamental style of inscribed plate, suited to
shop plate and other uses, may be obtained.
Also in the case of sunk characters the plain face of the plate may
have devices impressed upon it by passing the plate between a pair of
engraved rollers prior to waxing and polishing it off.
Also the sunken letters or spaces between raised ones may be filled in
with vitreous enamels fused, baked, or burnt in, instead of wax; or the
sunken parts may be filled in with metal of a different colour from that
of the plate, and all polished off level.
bo
From the fineness and sharpness with which inscribed surfaces may
thus produced in substitution for engraving it is also obvious that
personal badges or numbers, such as for cabmen, conductors, or tickets
for hats and umbrellas deposited in public places, and for tables of fares
or distances, such as those painted or japanned on common tin plate and 1
used in public cabs, may be produced cheaply and of a far more durable,
legible, and ornamental description.
The framing and filling of the mould is effected in the following
manner: Around the edges of the compound type face or model for the
face of the plate is placed a square frame or moulding box secured by a
steady pins, and of a depth proportionate to the size of the plate intended
to be cast. The characters sunken in the model having been lightly
brushed over with fine plumbago or other suitable material, the surplus
being blown away, and the model plate and attached parts being mado
dry by placing the whole in an oven for a few minutes, the sunken:
surfaces and the parts immediately adjacent to them are then sifted over
with a dry powder of porcelain clay, which is obtained by subsidence
from water of natural clays, or of the prepared siliceous porcelain clay
known as slip, which is afterwards dried. Above that and to the depth
of the frame or moulding box, and somewhat above it, is filled in with
ordinary brass moulding sand moistened to a suitable degree. The plate
of a small screw or lever press, whose surface is equal to that within the
moulding box, is firmly pressed down upon the sand, so as to compress
the whole into a flat coherent plate of uniform thickness. Sufficient
moisture is after a rest of a few moments transferred from the damp
sand to the dry clay to cause the latter to adhere and form one with the
plate of sand, so that when the plate of compressed sand is withdrawn

page_text: from the model face the fire clay gives definition to the forms of the
characters now raised in the clay, the remaining part of the face con-
sisting of the ordinary moulding sand.
In order to withdraw the model from the sand contained in the
moulding box frame the apparatus may be placed on a machine
moulding table of any one of their well-known forms, such that the
model may be withdrawn with perfect steadiness, leaving the clay and
sand mould ready to be reversed, and its surface examined prior to
drying into a "dry sand mould." Similarly baked sand plates are to be
employed to mould the back of the plate, and both should meet each
other around their rims, so that when placed in position and opposite
each other they shall completely close the mould for the intended cast
plate, leaving only the gate or aperture for admission of the fluid metal,
and such air vent or vents as may be deemed necessary, both these
apertures being by preference in connection with the edges of the plate.
The baked sand plates with the characters raised upon them are then
enclosed in cast-iron flasks, with or without common moulding sand
interposed between the flask and the dried sand plates, after which the
brass, bronze, or other metal is poured in; the gate or adjutage for the
introduction of the molten metal may be formed of a clay lined
tube of length so that when filled up with the liquid metal the
pressure thereof due to that height of liquid shall be visited upon all the
interior parts of the mould, the inscribed face of the intended plate being
placed at the bottom of the mould.
When a tube is used to form the gate or adjutage it must be secured
in firm connection with the mould, or flask, or both.