Improvements in the Manufacture of Carbons for Electric Arc-lamps.
Year: 1892

page_text: Date of Application, 23rd June, 1892-Accepted, 17th Dec., 1892
COMPLETE SPECIFICATION.
Improvements in the Manufacture of Carbons for Electric
Arc-lamps.
I, CARL BRAUN, of the firm of Mabla and Braun, of Nuremberg, in the Empire
of Germany, Arc-light Carbon Manufacturers, 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 :-
My invention relates to the manufacture of carbons for electric arc-lamps.
The processes heretofore found available, and giving good results in the manu-
facture of carbons having a core are all characterized by the fact that the material
of the core is inserted in a semi-liquid or powdered state into the previously manu-
factured hollow carbon.
The process used in America for producing carbons is alone an exception to the
above as the carbons there are formed between two half parts of a mould or com-
presser in which the material is made ready for burning by pressing the two halves
together. In carrying out that process a core of carbon which has been previously
pressed may be placed approximately in the middle of a mass of carbon to be com-
pressed round it in the manner referred to above, in order to obtain the core as a
wick. The carbons manufactured by such a process, however, are in spite of the
very good material used in their manufacture of such bad quality that every
attempt to introduce them into Europe has failed, notwithstanding their very
moderate cost. No attempt has therefore ever been made in Europe to imitate the
American process.
The process which forms the subject of the present invention is quite different
from all herein before referred to, since it consists in the fact that a solid core-wick
is grasped and carried along automatically with an ensheathing carbon which is
being continuously formed.
In this process the core-wick, previously made separately, is guided into the
inside of a mandrel contained in a press, in such a manner that it only projects a
little beyond this mandrel into the mass of carbon, and the carbon mass, spreading
round the mandrel under the action of the plunger of the press advances towards
the outlet of the press and takes at the same tine a form corresponding with the
conical shape of the point of the mandrel, forming a hollow body of constantly
diminishing size until having reached a point immediately in front of the point of
the mandrel, it closely surrounds the core-wick which projects from the latter, and
draws it with itself into the mouth-piece of the press in which the formation of the
outer surface of the ensheathing carbon (that is to say, of the completed carbon)
is finally effected.
In this process it is only necessary, as has been said, to lead the core-wick once
for all into the mandrel, the carbon mass as it spreads round it effects the farther
movement of the core-wick, as the result of the pressure to which it is subjected,
which is exerted by a hydraulic press, the piston of which will usually form the
plunger of the mass-press. If the core-wick consists of single rods these will
usually be simply placed in the mandrel by hand. The core-wick may, however,
during its separate preparation, be coiled upon a drum of very considerable
diameter, upon which it may then be dried, and be thereafter unwound from
the drum and led through the mandrel into the mass which is to be pressed
round it.
The continued unwinding of the core-wick then takes place automatically 'bý
means of the ensheathing mass in the press above referred to.
In order to avoid the use of a drum of very large dimensions for winding un and

page_text: unwinding the core-wick, the drying may be effected in the unwound, straight
condition of the wick by drawing it in this condition through a drying oven.
The carbon with its wick may be cut into suitable lengths as it passes continuously.
out of the press, but it may also be again used as a core-wick for a thicker carbon,
being then a carbon with double concentric core-wick.
Such an arrangement of several concentric surrounded core-wicks is of great
value as regards the production of light, since experience proves that carbons with:
core-wicks give a lighting effect so much the better the more gradual the reduction:
of the hardness and density of the same from within toward the outer circumference..
And such a gradual reduction can only be obtained to the extent desirable, in the
thicker carbons, by repeated surrounding, drying, and re-surrounding the core with
a suitable carbon-mass.
To enable my continuous process of sheathing a solid core-wick with carbon (the
former being automatically carried along by the latter) to be fully understood I
will describe the apparatus in which the process is to be effected with reference to
the accompanying drawing which represents a longitudinal section of a portion of
the mass-press containing a mandrel and a mouth-piece.
A is the portion of the press which can be screwed by the screw-threaded
connection on the other portion which contains the plunger.
N is a fixed mouth-piece. In a straight line behind the hollow of this mouth-
piece is placed the mandrel M K which can be so adjusted with reference to the
mouth-piece N that between the external conoidal portion of the head K of the
mandrel, and the inner surface of the mouth-piece N and of the bore of the body A
of the attachment, which here communicates with the mouth-piece, there is a
gradual reduction in the size of the cross section of the mass under pressure,
until the point occupied by the wick-rod S, so that this rod S is tightly and firmly
surrounded and pressed by the mass O from the press, but so that the mass can
only move forward and toward the mouth-piece N in firm and safe union with the
rod ensheathed by the same.
The gradual reduction of the cross section of the pressed mass is therefore of
special importance, because if the convergence of the cross-section be either too
slow or too rapid the wick-rod will remain in its original position, since in the former
case the mass will not adhere to it sufficiently to carry it along with itself, and in
the latter case the mass may even drive the rod backwards by exerting too great
pressure upon it. Even when the wick-rod is carried along indeed, but is pressed
more severely than necessary, the result is unsatisfactory since the carbon-rods then
tend to crack or break later on.
In order that the mandrel may easily be arranged at the most suitable distance
from the mouth-piece, the former is screwed into the attachment A by means of a
long thread, and in order that it may be used for core-wicks of various degrees of
thickness its conoidal head K may be easily exchanged for another, and the bore
of the head is considerably narrower than that of the hinder part of the
mandrel M.
The cleaning of the attachment A may be readily effected after removal of the
cleaning-screw T.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manuer the same is to be performed, I declare that what I
claim is :-
1. A process for the manufacture of carbon-rods with core-wicks, characterized
by the introduction of a separately made and hardened core-wick into the bore of
a mandrel (MK) which core is coated under pressure by the carbon mass provided
for the formation of the sheath, so that as the mass passes toward the point of the
mandrel it grasps and draws with it the core-wick as it projects from the point of
the mandrel, embracing it with gentle pressure as it passes through the formative
.pozzle of the press and issues from it, substantially as herein before described.
2. A process of the nature described in Claim I applied to the manufacture of

page_text: carbon-rods with core-wicks, in which a hardened carbon with a core-wick is used
as the wick to be surrounded, in order to prepare thicker carbons, the density of
which varies at different distances from the middle line, substantially as herein-
before described.
3. For the purpose of making the carbons with core-wicks, according to the
process specified in Claims 1 and 2, the employment of a mandrel which is situated
coaxially with the nozzle of the press, and can be adjusted with reference to the
latter, through the co-axial bore of which mandrel the core-wick is conducted into
the carbon-mass, and is closely surrounded by the latter and carried on by it.
through the nozzle of the press, substantially as hereinbefore described and
illustrated in the accompanying drawing.
4. In a process such as is claimed in Claims 1 and 2, conducting the core-wick
continuously into the mass by which it is to be ensheathed, substantially as
hereinbefore described.
G. F. REDFERN Co.,
4, South Street, Finsbury, London, Agents for the Applicant.