Process of Manufacturing Hoods or Mantles for Incandescent Gas-lights
Year: 1896

page_text: Date of Application, 16th June, 1896-Accepted, 18th July, 1896
COMPLETE SPECIFICATION.
Process of Manufacturing Hoods or Mantles for Incandescent
Gas-lights,
1, WILLIAM LAWRENCE VOELKER, of Elizabeth, in the County of Union,
State of New Jersey, U.S.A., Electrician, do hereby declare the nature of my
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 a process of manufacturing hoods or mantles for incan-
descent gas-lights. In particular, it aims to provide a process by which hoods or
mantles, that are formed of suitable incandescible materials, may be baked in a
manner to procure uniform results with respect to shrinkage and tenacity of the
hoods and the form of the same.
The process depends upon a discovery which I have made, that if a hood or
mantle, after being dried sufficiently to stand without collapsing, is plunged into
an atmosphere which is heated to a very high temperature, as say from 3500° to
4000° F., the hood will be baked without perceptible distortion of its form and
with uniform tenacity and strength in all parts of the hood. The temperature
also should be higher than that to which the mantle or hood will be subjected when
in use over a gas burner, for then the gas flame will not exert any perceptible
destructive action on, the hood or mantle.
In order to explain the difference between my invention and the method of
baking hoods heretofore employed, I will first explain the usual method by which
the hoods have been baked. This method consists in placing hoods or mantles in
large quantities at a time in a kiln or oven, before the oven has been heated to its
final degree, or placed in the oven even when cold. The oven is filled with the
hoods or mantles and their supports or holders, which holders are stuck into flat
fire-clay slabs, layer upon layer of these slabs being placed in the oven until the
same is filled. The oven doors are then closed, the firing started up and the tem-
perature allowed to rise to the desired degree. The source of heat is then shut off,
the oven allowed to cool, and the hoods or mantles removed. This process closely
follows that used by potters in baking their wares. By it, no two bakings will be
alike, nor will the hoods of any two layers of the same baking be alike either in
dimensions, height, form, or hardness, and strength of material. The variations
in dimension and height, are due to the different degrees of temperature in the
different parts of the oven. Symmetry of form of the hoods is governed by equal
distribution of the mass in all parts of the hood, but, for well known reasons, this
equal distribution of the mass is practically impossible, and under the existing
method of baking, as this distribution varies, so will the baked mantle vary from a
symmetrically perfect form, to one distorted in accordance with the inequalities of
the distribution of the material. The hoods baked on the pottery principle show
these imperfections in a marked degree, because this is a slow process of baking
and tends to aggravate and exaggerate the imperfections in the distribution of
the mass.
I, however, have discovered that if a hood or mantle is first dried sufficiently to
stand without collapsing, and is then plunged at once into a highly heated
atmosphere, say from 3500° to 4000° F., and kept there for a few minutes, the
result is an entirely superior structure; for, under these circumstances, the hood
bakes so quickly that it has not time to develop the imperfections due to the
unequal distribution of the mass, and, moreover, the considerable pressure of the

page_text: highly heated atmosphere, exerted evenly on all sides of the hood, prevents the
development of, the inequalities in the form of the hood, even, if such inequalities
should tend to be developed. Thus by my process I am able to produce hoods,
which are almost perfect in form and tenacity, and which can be duplicated every
few minutes in the day.
.The process in detail is as follows :-
Hoods, to the number of 25 or 30, having been first sufficiently dried, and of the
usual shape, are preferably suspended on the tops of the fire-clay rods. This
suspension is specially desirable, if the materials of which the hood is composed,
shrink much in the baking.
When, however, the materials of the hood do not shrink perceptibly in baking,
the hoods may be supported at their bottoms on suitable slabs, such as slabs of
nickel. These rods, if such are used, are placed upright in holes that are bored iu
a flat fire-clay slab. These slabs with their rods and hoods, are then placed in the
oven of any suitable gas-furnace (for example, such as those used for melting
platinum) that will generate and stand the intense heat necessary, the oven having
been first heated to about 3500° to 4000° F.
When the first batch of mantles is to be baked, after the oven is first heated up,
the door is opened for a short time, say half a minute. In this short time the
great pressure in the oven momentarily vents itself, before the mantles are brought
near, so that danger of shattering the mantles is obviated. But the temperature
of-the oven-is-not-perceptibly lowered by the opening of the door for so short a
time, so that, when the mantles are introduced into the oven and the door closed,
the pressure almost immediately rises again to a very high degree. After the first
batch of hoods is baked, the momentary opening of the door for taking out one
batch and introducing the next batch of mantles, is sufficient to momentarily vent
the pressure, so as to prevent injury to the hoods. The shape and size of the oven
should be such that the interior space shall be just sufficient to hold one slab of
hoods with the least possible vacant space. The heated atmosphere then comes on
the hoods with a pressure that resembles in its effects the pressure of an enveloping
mould or die. This pressure preserves the uniformity of the hoods, prevents
distortion, and together with the intense temperature of the oven and the conse-
quent rapid baking of the hood, insures a uniformity of strength and tenacity
throughout the material of the hood.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is :-
The process hereinbefore described of manufacturing hoods or mantles for
incandescent gas-lights consisting in partially drying the hood or mantle, and then
introducing it into a furnace and there exposing it at once to a temperature higher
than that to which the hood or mantle will be exposed when in use over a gas flame,
whereby the hot air of the furnace acts as a die on the hood or mantle, and the
same bakes before it can distort.
Dated this 16th day of June 1896.
S. S. BROMHEAD,
97 Newgate Street, E.C., Patent Agent.