Improvements in Cores for Electrical Apparatus and the Method of Forming the same.
Year: 1889

page_text: Date of Application, 9th July, 1889
Complete Specification Left, 29th Mar., 1890-Accepted, 17th May, 1890
PROVISIONAL SPECIFICATION.
Improvements in Cores for Electrical Apparatus and the Method of
Forming the same.
A communication from abroad by THE WESTINGHOUSE ELECTRIC COMPANY, of
Pittsburgh, Pennsylvania, United States of America (Case 36).
I, WILLIAM PHILLIPS THOMPSON, F.C.S., M.I.M.E., of the Agency for Foreign
Patent Solicitors 6, Lord Street, Liverpool & 6, Bink Street, Manchester, both in
the County of Lancaster and 323 High Holborn in the County of Middlesex, Civil
Engineer, do hereby declare the nature of this invention to be as follows:-
The invention relates to certain improvements in the manufacture of cores for
electrical apparatus, such for instance as the cores of electric inductoriums or converters,
the cores of armatures for electric generators and motors, and other similar apparatus.
It has been found in practice that cores for electrical apparatus which are subjected
to a rapid change of magnetic condition, are inore efficient and less liable to become
heated when built of electrically insulated laminae of soft iron, than when made solid.
This is due to the fact that in solid cores the electric currents generated therein
circulate within the same. Such currents, while of comparatively low electromotive
force, are of considerable quantity, and are liable to heat the core and render the
apparatus less efficient. The use of laminated cores, has, therefore, become quite
universal. In some instances the adjacent laminae have been held apart by thin
In other instances thin
washers leaving narrow air-spaces between the laminae.
sheets of paper, fibre or other non-conducting material are placed between the
laminae of soft iron. It is usually desirable that the mass of iron in proximity to
the coils of wire applied to the core should be as great as possible. The presence
of the insulation between the laminae lessens somewhat the amount of iron which
is contained in core of a given size, and, therefore, tends to detract from the
efficiency of the core. For this reason it is desirable that the insulation between the
laminae should be as thin as possible. The use of washers or thin plates of insulating
material is therefore objectionable because it requires a considerable separation of the
successive plates.
S
Another plan is to obtain the insulation by pasting very thin sheets of paper or
other insulating material to one surface of the sheets of soft iron, from which the
laminae are afterwards stamped. In this way very thin insulation may be obtained
and the proportion of iron in the core correspondingly increased. But even with this
form of insulation the non-conducting material is found to occupy about one-sixth as
much space as the iron. Another difficulty sometimes encountered in this
construction is that the operation of stamping the plates forms a burr along the cut
edges, and when the plates are placed together, the burrs are liable to pierce
through the sheets of paper and thus destroy to a greater or less extent the
insulation between the different plates. The tendency of Foucault or eddy currents
to circulate is usually greater near the conducting wires than in the body of the
core and, therefore, the presence of the burrs forming electrical connections at the
edges is the more objectionable.
The object of the present invention is to overcome these difficulties, and to reduce
to a minimum the spices, occupied by the insulation, and at the same time to
provide a method of manufacturing the core which will secure the required insulation
between the laminae, and shall also cheapen and improve the construction of the core.
The invention consists in first stamping from sheets of suitable magnetizable
Inaterial, such as soft iron, plates of the required size and form from which to build
up the core; then subjecting the plates to an annealing process which is carried to

page_text: such an extent that a thin film of oxide is formed over their entire surfaces, and
over, also, the burrs or rough edges produced by the stamping process; and
afterwards building up the core by placing such plates side by side.
The annealing process is carried on in the following manner :-
The plates are arranged in smail piles in a suitable annealing box. The box is then
placed in an oven and gradually heated. This step in practice usually occupies from
six to twelve hours. When the proper temperature has been reached, it is kept
approximately constant for a sufficient time to produce the required effects. This
may be varied in different instances, but it is usual to continue to so heat the
plates for about twelve hours. They are then allowed to cool gradually, the heat
being gradually lessened. This may occupy a somewhat greater length of time,
say from twelve to twenty-four hours. The gradual cooling secures thoroughly
annealed soft plates.
After this treatment the plates are found to be coated with a dark film or very
thin scale. This scale consists chiefly of magnetic oxide. It is such a poor conductor
of electricity as in effect to amount to an insulator, and at the same time, it is
more or less magnetic, so that it serves, when the plates are placed together, not
only to insulate them from each other, but also as a magnetizable material for the
core, thus combining two desirable qualities. At the same time the insulation is
extremely thin and therefore allows the plates themselves to be brought into very
close proximity. The thickness of the scale or film is found to be about two
thousandths of an inch upon each surface, so that the core consists almost entirely
of magnetizable material, and the plates themselves are separated the smallest possible
distance.
The oxide is very firmly attached to the surface of the plates, and can only be
removed by attrition, so that the plates may be handled without special care and
without endangering the insulation.
It is desirable that the plates should be as soft as possible. As already stated, the
annealing process has the effect of removing whatever temper may have been given
to, or remains in the plates, thus softening them and satisfying this requirement. The
metal cannot, in practice, he so perfectly annealed while in the form of large sheets
from which the plates are stamped, as it is impossible to heat and cool them
evenly; neither can it be thoroughly annealed before it is rolled into sheets because
the subsequent operation of rolling tends to harden it.
Armatures for electric generators and motors may be thus built up of laminae which
are annealed, but when the surface of an armature, thus built up, is turned down in
order to obtain a smooth and true exterior, the edges of the plates are turned over or
upset, so that the metal of contiguous plates is brought into contact, thus completing
an electrical connection through the surface of the core, the portion where the tendency
to establish eddy currents is very great, and thus partially defeating the object of the
insulation. This difficulty may be overcome by first building up an armature of plates
of the proper size and shape, then turning it down to remove irregularities and obtain
the required dimensions, then taking the armature apart, separating the laminae from
each other, then applying the insulation as by annealing them and finally reassembling
them as before. In this manner the burrs formed upon the edges of the plates by the
process of turning the armature down, are either reduced or covered with an insulating
oxide of the metal, and when the plates are reassembled they are separated from each
other by the oxide which affords the required insulation.
The invention is applicable to cores of other apparatus than the armatures of
generators and motors, and in fact is applicable to any apparatus requiring insulated
laminae which is turned off to any given shape or size after the laminae have been
first assembled.
Another portion of the invention consists in building up the core of an armature
of plates through which holes or openings are formed for allowing the circulation of
the air through the interior, certain of the plates having openings of different
diameter, size or shape from those of the other laminae. The plates having different
sizes may either alternate with each other in position, or groups of one pattern may

page_text: alternate with groups of another pattern, so that the radiating surface within the
armature is greatly increased.
In the accompanying drawings,
Figure 1 is a side view of a plate employed in building certain forms of
converters:
Figure 2 is a plan of a converter having a core of the character described.
Figure 3 is a section of an armature, and
Figures 4, 5 and 6-are armature core plates.
Referring to Figures 1 and 2:-A, represents the core of the converter of the
construction which it is preferred to employ, and C1, C2, the primary and secondary
coils, respectively. The converter may, however, be constructed with a single coil, a
portion of the length being designed to be connected in one cireuit and a portion in
another, or a single coil may be connected entirely in one circuit. The core is.
composed of thin sheets or plates of magnetizable material, such for instance as
soft iron. In preparing these plates, rectangular plates are stamped with two
holes ee, and these holes are preferably of a rectangular shape, and of such size as
to receive the coils of wire. Each hole e¹ e2 is cut open at f¹, f². These cuts f¹ f
may converge as shown in the figure.
After the plates have been properly stamped their surfaces are oxidized preferably
by being placed in suitable vessels and gradually heated to a very high temperature.
They are kept at such a temperature a proper length of time and then allowed to cool
slowly. This step in the process has the double effect of thoroughly annealing and
softening the metal and coating the surfaces with a thin film of magnetic oxide.
film also, covers the edges and reduces the burrs produced by the stamping, covering
them with an insulating material. In this manner the entire surface of each plate is .
sufficiently insulated to prevent any considerable circulation of Foucault or eddy
currents in the core.
This
The plates are then placed one against another, their central tongues being inserted
within the coils, alternate plates being preferably inserted from opposite sides. The
manner of building up the core and the shape of the plates may, however, be
materially varied without departing from the spirit of the invention.
Figures 3 and 4 illustrate the construction of cores of armatures for electric
machines. The plates A¹ are stamped as before, the shape and form being suited to
the particular form of armature desired. They are then annealed and thereby softened
and coated by a film of insulating oxide and afterwards placed together side by side
to form the complete armature core shown.
Referring to the Figures 3, 4, 5, and 6, A¹ represents an armature shaft," and
B1, B2, end plates for the armature core. The armature, may with advantage, be
constructed with reinforcing plates, 61, 62 applied to the plates B', B. In forming,
the armature core, sheets or plates c¹, c², of magnetizable material such as for instance
soft iron, are placed over the shaft and piled upon the plate B¹. When a sufficient
number has been applied to the shaft they are pressed firmly together by suitable
mechanical means, and the end-plate B2 and a reinforcing plate bare held in place
in any convenient manner, as, for instance by a nut D turning upon a screw-thread
upon the armature shaft.
In practice it is difficult to cut the plates originally of such exact shape as to cause
them to conform when laid together on account of the tendency to buckle, so that
when first laid together they are of approximately the proper shape and size but
usually have slight variations in size or circumference and therefore it is desirable
that the outer surfaces of the armature be turned down so that it shall be true and fit
exactly and revolve evenly within the field-magnet to which it is to be applied:
Therefore, it is placed in a suitable lathe and turned in a manner well understood.
By this operation, however, a burr or overlapping edge is liable to be formed upon
the surfaces of the plates, so that the contiguous plates are to a greater or less extent
connected in one continuous electrical circuit. After the armature has been turned
off in this manner, therefore, it is taken to pieces, the plates being separated from
each other. They are then coated by insulating material. This is preferably

page_text: accomplished by placing them in a suitable annealing furnace and bringing to a
proper temperature to reduce the surface of the plate to a non-conducting oxide or a
more or less perfectly insulating oxide of the metal. After this process which may
be accomplished in any convenient well-known manner, the plates are re-assembled
and the armature is again built up and the plates bound together as before. The
armature-core will now be composed of laminae separated from each other hy the
required insulation without the intervention of separate sheets or plates of insulating
material. The plates are formed with openings which are placed opposite each other
so that the resultant holes will extend throughout the length of the armature. For
the purpose of increasing the radiating surface formed within such openings, certain
plates are made to project a greater distance into the openings than the others. Το
accomplish this, certain of the plates are formed with larger openings, or openings of
different shapes from the others; thus in Figure 4, there is shown a plate having
eight radial openings, e¹, of a certain size and shape, and in Figure 5 another plate is
shown, which is to be used in the same armature having in this instance the same
number of openings, but larger. These plates inay be placed alternately, or a group
of any required number of one pattern may be placed together and then a group of
another pattern.
This latter arrangement is usually preferred for the reason that it
allows a wider space to intervene between the surfaces which project within the
longitudinal openings of the armature.
These surfaces together afford a large radiating surface, with which the air, which
circulates through the armature when it is revolving, is allowed to come in contact,
thus causing the armature to remain much cooler than would otherwise be the case.
In Figure 6 two plates are shown as placed against each other and it will be noticed
that the inner ends of the radial openings correspond approximately in size and shape,
while the greatest difference of size and shape is obtained at the outer edges of the
openings; that is to say, the portions which move at the greatest rapidity when the
armature is revolving. It is evident that other patterns of openings than those herein
shown may be employed if desired; but those here described will be sufficient to
disclose the invention.
Dated this 8th day of July 1889
COMPLETE SPECIFICATION.
Improvements in Cores for Electrical Apparatus and the Method of
Forming the same.
A communication from abroad by THE WESTINGHOUSE ELECTRIC COMPANY, of
Pittsburgh, Pennsylvania, United States of America.
I, WILLIAM PHILLIPS THOMPSON F.C.S. M.I.M.E. of the Agency for Foreign
Patent Solicitors of 6, Lord Street, Liverpool, & 6, Bank Street Manchester both
in the County of Lancaster & 323 High Holborn in the County of Middlesex,
Civil Engineer, 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 invention relates to certain improvements in the manufacture of cores for
electrical apparatus, such as for instance the cores of electric inductoriums or
converters, the cores of armatures for electric generators and motors, and other similar
apparatus.
It has been found in practice that cores for electrical apparatus, which are subjected
to a rapid change of magnetic condition, are more efficient and less liable to become
heated when built of electrically insulated laminae of soft iron, than when made solid.
This is due to the fact that, in solid cores, the electric currents generated therein
circulate within the same. Such currents, while of comparatively low electromotive
force, are of considerable quantity, and are liable to heat the core and render the

page_text: apparatus less efficient. The use of laminated cores has, therefore, become quite
universal. In some instances, the adjacent laminae have been held apart by thin
washers leaving narrow air-spaces between the laminae. In other instances, thin
sheets of paper, fibre or other non-conducting material are placed between the laminae
of soft iron. It is usually desirable that the mass of iron in proximity to the coils
of wire applied the core should be as great as possible. The presence of the insulation
between the laminae lessens somewhat the amount of iron which is contained in a
core of a given size, and, therefore, tends to detract from the efficiency of the core.
For this reason, it is desirable that the insulation between the laminae should be as
thin as possible. The use of washers or thin plates of insulating material is,
therefore, objectionable, because it requires a considerable separation of the successive
plates.
Another plan is to obtain the insulation by pasting very thin sheets of paper or
other insulating material to one surface of the sheets of soft iron, from which the
laminae are afterwards stamped. In this way very thin insulation may be obtained
and the proportion of iron in the core correspondingly increased. But even with this
form of insulation, the non-conducting material is found to occupy about one-sixth
as much space as 'the iron. Another difficulty sometimes encountered in this
construction is that the operation of stamping the plates forms a burr along the cut
edges, and when the plates are placed together, the burrs are liable to pierce through the
sheets of paper and thus destroy to a greater or less extent the insulation between the
different plates. The tendency of Foucault or eddy currents to circulate is usually
greater near the conducting wires than in the body of the core, and, therefore,
the presence of the burrs forming electrical connections at the edges is the more
objectionable.
The object of the present invention is to overcome these difficulties, and to reduce
to a minimum the spaces occupied by the insulation, and at the same time to provide a
method of manufacturing the core which will secure the required insulation between
the laminae, and shall also cheapen and improve the construction of the core.
The invention consists in first stamping from sheets of suitable magnetisable
inaterial, such as soft iron, plates of the required size and form, from which to
build up the core,
then subjecting the plates to an annealing process which is carried"
to such an extent that a thin film of oxide is formed over their entire surfaces, and
over, also, the burrs.or rough edges produced by the stamping process, and afterwards
building up the core by placing such plates side by side.
The annealing process is carried on in the following manner :-
The plates are arranged in small piles in a suitable annealing box. The box is
then placed in an oven and gradually heated. This step in practice usually occupies
from six to twelve hours. When the proper temperature has been reached, it is kept
approximately constant for a sufficient time to produce the required effects. This
may be varied in different instances, but it is usual to continue to so heat the plates
for about twelve hours. They are then allowed to cool gradually, the heat being
gradually lessened. This may occupy a somewhat greater length of time, say from
twelve to twenty-four hours. The gradual cooling secures thoroughly annealed soft
plates.
After this treatment, the plates are found to be coated with a dark film or very
thin scale. This scale consists chiefly of magnetic oxide. It is such a poor conductor
of electricity as in effect to amount to an insulator, and, at the same time, it is more or
less magnetic, so that it serves, when the plates are placed together, not only to
insulate them from each other, but also as a magnetisable material for the core,
thus combining two desirable qualities. At the same time, the insulation is extremely
thin and therefore allows the plates themselves to be brought into very close
proximity. The thickness of the scale or film is found to be about two thousandths
of an inch upon each surface, so that the core consists almost entirely of
magnetisable material, and the plates themselves are separated the smallest possible
distance.
The oxide is very firmly attached to the surface of the plates, and can only be removed
:

page_text: by attrition, so that the plates may be handled without special care and without
endangering the insulation.
It is desirable that the plates should be as soft as possible. As already stated, the
annealing process has the effect of removing whatever temper may have been given to.
or remain in the plates, thus softening them and satisfying this requirement. The metal
cannot, in practice, be so perfectly annealed while in the form of large sheets from
which the plates are stamped, as it is impossible to heat and cool them evenly;
neither can it be thoroughly annealed before it is rolled into sheets because the
subsequent operation of rolling tends to harden it.
Arinatures for electric generators and motors may be thus built up of laminae
which are annealed, but when the surface of an areiature, thus built up, is turned
down in order to obtain a smooth and true exterior, the edges of the plates are
turned over or upset, so that the metal of contiguous plates is brought into contact,
thus completing an electrical connection through the surface of the core, the portion
where the tendency to establish eddy currents is very great, and thus partially
defeating, the object of the insulation. This difficulty may be overcome by first
building up an armature of plates of the proper size and shape; then turning it down to
remove irregularities and obtain the required dimensions, then. taking the armature
apart, separating the laminae from each other, then applying the insulation as by
annealing them, finally reassembling them as before. In this manner the burrs,
formed upon the edges of the plates by the process of turning the aricature down, are
either reduced or covered with an insulating oxide of the metal, and when the plates
are reassembled they are separated from each other by the oxide which affords the.
required insulation.
.1
The invention is applicable to cores of other apparatus than the armatures of
generators and motors, and in fact is applicable to any apparatus requiring insulated
laminae which is turned off to any given shape or size after the laminae have been
first assembled.
Another portion of the invention consists in building up the core of an armature of
plates through which holes or openings are formed for allowing the circulation of the
air through the interior, certain of the plates having openings of different diameter,
size or shape from those of the other laminae. The plates having different sizes may
either alternate with each other in position; or groups of one pattern may alternate
with groups of another pattern, so that the radiating surface within the armature is
greatly increased.
In the drawings accompanying the provisional specification:
Figure 1 is a side view of a plate employed in building certain forms of
converters.
Figure 2 is a plan of a converter having a core of the character described.
Figure 3 is, a section of an arinature, and
Figures 4, 5 and 6 are armature core plates.
Referring to Figures 1 and 2:-
A represents the core of the converter of the construction which it is preferred to
einploy, and C1, C2, the primary and secondary coils, respectively. The converter
may, however, he constructed with a single coil, a portion of the length being designed
to be connected in one circuit and a portion in another, or a single coil may be con-
nected entirely in one circuit. The core is composed of thin sheets or plates a¹ of
magnetisable material, such for instance as soft iron. In preparing these plates,
rectangular plates are stamped with two holes el e² and these holes are preferably of a
Each hole et e
rectangular shape, and of such size as to receive the coils of wire.
is cut open at f¹ƒ2. These cuts flf may converge as shown in the Figure.
After the plates have been properly stamped their surfaces are oxidised, preferably
in the manner already described.
The plates are then placed one against another, their central tongues being inserted
within the coils, alternate plates being preferably inserted from opposite sides. The
manner of building up the core and the shape of the plates may, however, be
materially varied without departing from the spirit of the invention.

page_text: Figures 3 and 4 illustrate the construction of cores of armatures for electric
machines. The plates A¹ are stamped as before, the shape and form being suited to
the particular form of armature desired. They are then annealed and thereby
softened and coated by a film of insulating oxide and afterward placed together side
by side to form the complete armature core shown.
Referring to the Figures 3, 4, 5, and 6, A¹ represents an armature shait, and
B1 B2 end plates for the armature core. The armature may, with advantage, he con-
structed with reinforcing plates 12 applied to the plates B1 B2. In forming the
armature core, sheets or plates cl c² of magnetisable material, such as for instance
soft iron, are placed over the shaft and piled upon the plate B¹. When a sufficient
number has been applied to the shaft they are pressed firmly together by suitable
mechanical means, and the end-plate B2 and a reinforcing plate bare held in place
in any convenient manner, as for instance, by a nut D turning upon a screw-thread
upon the armature shaft.
In, practice it is difficult to cut the plates originally of such exact shape as to
cause them to conform when laid together on account of the tendency to buckle,
so that when first laid together they are of approximately the proper shape and
size but usually have slight variations in size or circumference, and therefore it is
desirable that the outer surfaces of the armature be turned down so that it shall be
true and fit exactly and revolve evenly within the field magnet to which it is to
be applied. Therefore, it is placed in a suitable lathe and turned in a manner
well understood. It is then taken to pieces, the plates being separated from each
other. They are then preferably annealed and coated by insulating material,
preferably magnetic oxide, in the manner already described. After this process, the
plates are reassembled, and the armature is again built up and the plates bound
together as before. The armature-core will now be composed of laminae separated
from each other by the required insulation without the intervention of separate
sheets or plates of insulating material. The plates are formed with openings which
are placed opposite each other so that the resultant holes will extend throughout
the length of the arunature. For the purpose of increasing the radiating surface
formed within such openings, certain plates are made to project a greater distance
into the openings, than the others. To accomplish this, certain of the plates are
formed with larger openings or openings of different shapes from the others; thus,
in Figure 4, there is shown a plate having eight radial openings el, of a certain
size and shape, and in Figure 5 another plate is shown, which is to be used in the
same armature, having in this instance the same number of openings, but larger.
These plates may be placed alternately, or a group of any required number of one
pattern may he placed together and then a group of another pattern. This latter
arrangement is usually preferred for the reason that it allows a wider space to
intervene between the surfaces which project within the longitudinal openings of the
armature.
These surfaces together afford a large radiating surface, with which the air,
which circulates through the armature when it is revolving, is allowed to come in
contact, thus causing the armature to remain much cooler than would otherwise be
the case.
In Figure 6, two plates are shown as placed against each other, and it will be
noticed that the inner ends of the radial openings correspond approximately in size
and shape, while the greatest difference of size and shape is obtained at the outer
edges of the opening, that is to say, the portions which move at the greatest rapidity
when the armature is revolving. It is evident that other patterns of openings than
those herein shown may be employed if desired; but those here described will be
sufficient to disclose the invention.
Having now particularly described and ascertained the nature of the said invention,
and in what manner the same is to be performed, as communicated to me by my foreign
correspondents, I declare that what I claim is :-

page_text: as for instance plates of converters, armatures or field magnets of dynamos which
consists in first stamping out the plates of magnetisable material such as soft iron,
shaping them or otherwise, and afterwards annealing and coating them with an
insulating oxide and building up the core from such annealed plates, substantially as
described.
2. The construction of laminated cores for electrical machinery by first stamping
out the plates, assembling them together, preferably shaping them in position,
separating them and afterwards annealing and coating them with an insulating oxide
and building up.
3. A core for electrical apparatus consisting of thin plates of magnetisable material
placed side by side and intervening layers of laminae of electrically insulating
magnetic oxide formed upon and covering the entire surfaces and edges of the plates,
substantially as described.
4. An armature for electric machines composed of laminae of magnetisable material
having openings from end to end or otherwise, the openings through certain of said
laminae being of different shape or size from those of other of the laminae, the
different forms being placed alternately or in groups.
Dated this 28th day of March 1890.
WM. P. THOMPSON & Co.,
Agents for the Applicant.