Improvements in the Bobbins and Cores of Solenoids for Enclosed Electric Arc Lamps.
Year: 1897

page_text: Improvements in the Bobbins and Cores of Solenoids for Enclosed
Electric Arc Lamps.
We, WILLIAM JAMES DAVY, and GEORGE THOMAS-DAVIES, Engineers, both of
Horsell Road Works, Highbury, in the County of London, do hereby declare the
nature of this invention to be as follows:-
-
The object of this invention is to provide a bobbin and core that will work
successfully and continuously with alternating and rectified currents. Hitherto
bobbins have failed to stand any lengthened tests on such currents, their
failure being due to the high temperature caused by the eddy and secondary
currents which are induced by the alternating induction through the coil when the
bobbins are formed of metal. It is necessary to make the bobbins fairly air tight,
and in this respect the ordinary construction of alternating bobbins is unsatis-
factory and a failure for enclosed are lamps. It is necessary to have a bobbin
which shall resist the effect of the fairly high temperatures which obtain, due to
the conduction of heat from the arc, which shall be stiff longitudinally and which
shall limit the circulation of secondary currents when the solenoid with which
it is wound is traversed by an alternating or rectified current. The insulation of
the wire forming the solenoids must be such that the high temperature shall not
in time destroy its properties. The above conditions we attain as follows:-
Two sheets, one preferably of thin German silver, the other of thin asbestos
paper or cloth of a width equal to the length of the proposed bobbin and of a
length sufficient to permit of one or more convolutions when wound in spiral
form upon a mandrel of a diameter equal to the inside bore of the proposed bobbin.
The convolutions of the metal and abestos are cemented together to form a rigid
tube by means of shellac varnish or cement.
In carrying out this invention a sheet of asbestos is first covered with shellac
then a sheet of German silver slightly shorter than the asbestos is laid upon it
and the two wound around a mandrel of the bore of the bobbin thus forming a
tube. This tube is then wound with wire and the whole dried. The internal
portion of the tube is bare German silver with a tongue of asbestos projecting
past its joint thus preventing the German silver from forming continuous metal
for a secondary circuit. Brass stiffening rings are provided on the outside ends
of the tube, the outer surface of which is asbestos, which can be shellaced and
painted.
The core of the solenoid in the lamp to which this arrangement and construc-
tion is applicable may be annular in cross section and laminated. Our method
of forming these cores is to take a number of strips of laminated soft iron, two
wires are then threaded through holes in the ends and the assemblage of strips
thus threaded are curved around a tube and the ends of the wires secured by being
twisted together. It is an advantage to sandwich in between these strips,

page_text: asbestos washers which are threaded on the wire to silence the noise due to vibra-
tion. The tube is then withdrawn leaving a circular laminated core.
Dated this 14th day of September 1897.
WHEATLEY & MACKENZIE,
40, Chancery Lane, London, W.C., Agents.
Improvements in the Bobbins and Cores of Solenoids for Enclosed
,Electric Arc Lamps.
We, WILLIAM JAMES DAVY, and GEORGE THOMAS-DAVIES, Engineers, both of
Horsell Road Works, Highbury, in the County of London, 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:-
The object of this invention is to provide a bobbin and core that will work
successfully and continuously with alternating and rectified currents. Hitherto
bobbins have failed to stand any lengthened tests on such currents, their
failure being due to the high temperature caused by the arc eddy and secondary
currents which are induced by the alternating induction through the coil when the
bobbins are formed of metal. It is necessary to make the bobbins fairly air tight,
and in this respect the ordinary construction of alternating bobbins is unsatis-
factory and a failure for enclosed arc lamps. It is necessary to have a bobbin
which shall resist the effect of the fairly high temperatures which obtain, due to
the conduction of heat from the arc, which shall be stiff longitudinally and which
shall limit the circulation of secondary currents when the solenoid with which
it is wound is traversed by an alternating or rectified current. The insulation of
the wire forming the solenoids must be such that the high temperature shall not
in time destroy its properties. The above conditions we attain as follows:-
Two sheets, one preferably of thin German silver, the other of thin asbestos
paper or cloth of a width equal to the length of the proposed bobbin and of a
length sufficient to permit of one or more convolutions when wound in spiral
form upon a mandrel of a diameter equal to the inside bore of the proposed bobbin.
The convolutions of the metal and asbestos are cemented together to form a rigid
tube by means of shellac varnish or cement.
a
In carrying out this invention a sheet of asbestos is first covered with shellac
then a sheet of German silver slightly shorter than the asbestos is laid upon it
and the two wound around a mandrel of the bore of the bobbin thus forming
tube. This tube is then wound with wire and the whole dried. The internal
portion of the tube is bare German silver with a tongue of asbestos projecting
past its joint thus preventing the German silver from forming continuous metal
for a secondary circuit. Brass stiffening rings are provided on the outside ends
of the tube, the outer surface of which is asbestos, which can be shellaced and
painted.
The core of the solenoid in the lamp to which this arrangement and construc-
tion is applicable may be annular in cross section and laminated. Our method
of forming these cores is to take a number of strips of laminated soft iron, two
wires are then threaded through holes in the ends and the assemblage of strips
thus threaded are curved around a tube and the ends of the wires secured by being
twisted together. It is an advantage to sandwich in between these strips,
asbestos washers which are threaded on the wire to silence the noise due to vibra-
tion. The tube is then withdrawn leaving a circular laminated core.
In the accompanying sheet of illustrative drawings Fig. 1 is a cross section

page_text: through a partly constructed bobbin and core and Fig. 2 is an elevation of the
same and Fig. 3 is an elevation of a complete bobbin and core.
The laminated core is built up of longitudinal iron strips a threaded together
on the wires b and curved around the tube f. The bobbin consists of the asbestos
sheet c and the German silver sheet d. The bobbin is held up by the brass split
rings e rivetted through the sheets d & c.
Having now particularly described and ascertained the nature of our said inven-
tion, and in what manner the same is to be performed we declare that what we
claim is:-
-
1. The improved core substantially as described.
2. The improved bobbin substantially as described.
3. The combined bobbin and core substantially as described.
WHEATLEY & MACKENZIE,
40, Chancery Lane, London, W.C., Agents.