U.S. patent number 3,848,331 [Application Number 05/396,256] was granted by the patent office on 1974-11-19 for method of producing molded stators from steel particles.
This patent grant is currently assigned to Westinghouse Electric Corporation. Invention is credited to James W. Cunningham, Norman M. Pavlik.
United States Patent |
3,848,331 |
Pavlik , et al. |
November 19, 1974 |
METHOD OF PRODUCING MOLDED STATORS FROM STEEL PARTICLES
Abstract
A method is disclosed for forming a magnetic core. The core
comprises a preformed coil about which a plurality of substantially
rectangular microlaminations of a ferromagnetic material are
disposed and the components are compressed into a unitary
structure. The method includes the steps of preforming a coil
assembling the coil in fluid-tight container together with a core
bar positioned centrally of the coil. Microlaminations are added to
the container which is thereafter pressurized to compress the
microlaminations about the coil to form a unitary structure.
Inventors: |
Pavlik; Norman M. (Pittsburgh,
PA), Cunningham; James W. (Vandergrift, PA) |
Assignee: |
Westinghouse Electric
Corporation (Pittsburgh, PA)
|
Family
ID: |
23566501 |
Appl.
No.: |
05/396,256 |
Filed: |
September 11, 1973 |
Current U.S.
Class: |
29/596; 310/43;
310/216.002; 29/608; 148/105; 419/6; 419/61; 29/606; 148/104;
310/44; 336/233; 419/65; 310/216.019 |
Current CPC
Class: |
H02K
1/12 (20130101); H02K 15/02 (20130101); Y10T
29/49009 (20150115); Y10T 29/49073 (20150115); Y10T
29/49076 (20150115) |
Current International
Class: |
H02K
1/12 (20060101); H02K 15/02 (20060101); H02K
15/06 (20060101); H02K 15/00 (20060101); H02k
015/02 () |
Field of
Search: |
;29/596,598,606,608,420
;310/216,42,44,254 ;336/233 ;264/111 ;148/104,105 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lanham; C. W.
Assistant Examiner: Hall; Carl E.
Attorney, Agent or Firm: Randig; R. T.
Claims
We claim:
1. The method of producing a molded core having at least one
conductor embedded therein employing microlaminations in which the
microlaminations are formed from a ferromagnetic material, are
substantially of an elongated rectangular cross-section, have been
annealed to decarburize, deoxidize and improve the magnetic
characteristics thereof, and in which each of the microlaminations
is provided with an electrically insulative coating on the surface
thereof, the steps comprising, preforming a conductor into a
desired configuration, assembling the preformed conductor in a
flexible container of predetermined configuration, adding
microlaminations about the conductor within the container, sealing
the container, compressing the microlaminates about the conductor
to attain a packing factor in excess of 80%, removing the pressure
and thereafter removing the molded core from the container.
2. The method of claim 1 in which the microlaminations are treated
with a binder prior to pressurization.
3. The method of claim 1, in which a core bar of predetermined
shape is disposed within the preformed conductor which is disposed
in the flexible container prior to introducing the
microlaminations.
4. The method of claim 1 in which the conductor is provided with a
conductor-to-microlaminate insulation not in excess of 3 mils in
thickness.
5. The method of claim 1 in which a yoke is applied to the molded
core, said yoke being in the form of a tape wound ring core.
6. The method of claim 1 in which a yoke is applied to the molded
core, said yoke being in the form of a plurality of punched or
stamped laminations.
7. The method of claim 1 in which the container is subjected to
vibratory energy while the microlaminations are added thereto.
8. The method of producing a molded stator employing
microlaminations in which the microlaminations are formed from low
carbon steel, are substantially rectangular in shape, have been
annealed to decarbonize and deoxidize the same and improve the
magnetic characteristics thereof and in which each of the
microlaminations is provided with a magnetically insulative coating
on the surface thereof, the steps comprising, preforming a stator
coil, preforming a stator yoke, said yoke having an outside
diameter of the desied dimension of the finished stator and an
inside diameter sufficiently great to accommodate the coil therein,
assembling the preformed yoke and the the preformed coil in a
flexible container of predetermined configuration, said coil being
positioned centrally of the yoke and both within the container,
positioning a core bar centrally within the coil, energizing the
coil, adding the microlaminates about the coil within the
container, sealing the container, pressurizing the container to
effect a packing factor in excess of about 80%, removing the
pressure and thereafter removing the molded stator from the
container.
9. The method of claim 4 in which the microlaminates are coated
with a binder prior to pressurization.
10. The method of claim 4 in which the coil is provided with a
wire-to-microlaminations electrical insulation not in excess of
about 3 mils.
11. The method of claim 4 in which the yoke is formed in the manner
of a tape wound ring core.
12. The method of claim 4 in which the yoke is formed of a
plurality of stamped or punched laminations.
13. The method of producing a molded core having at least one
conductor embedded therein employing microlaminations in which the
microlaminations are formed from a ferromagnetic material, are
substantially of an elongated rectangle cross section, have been
annealed to decarbonize, deoxidize and improve the magnetic
characteristics thereof, and in which each of the microlaminations
is provided with an electrically insulative coating on the surface
thereof, the steps comprising, preforming the conductor into a coil
configuration, assembling the preformed coil centrally within a
flexible container of predetermined configuration, positioning a
core bar in predetermined spaced relation within the coil, adding a
predetermined amount of microlaminations to the space between the
core bar and container walls and about the coil, sealing the
container, pressurizing the microlaminations and coil to attain a
packing factor in excess of 80% to form a unitary structure,
removing the pressure and thereafter removing the molded core from
the container.
14. The method of claim 9 in which the assembly is subjected to
vibratory energy during the addition of the microlaminates to the
container.
15. The method of claim 9 in which the microlaminations are treated
with a binder prior to pressurization.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
The subject matter of the present application is clearly related to
application Ser. No. 396,260 filed Sept. 11, 1973 and application
Ser. No. 396,257, filed Sept. 11, 1973, filed concurrently
herewith.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to unitary structure which comprises
a magnetic core having conductors embedded therein. Essentially the
core is formed by performing a coil and disposing the same within a
fluid tight container. Thereafter a core bar is positioned
centrally of the coil and a quantity of microlaminations is added
to the container to fill the space between the core bar, the coil
and the container. Upon filling the container with the requisite
amount of microlaminations, the container is sealed and subjected
to pressure so as to mold the entire unit into a unitary structure
which may be thereafter readily removed from the fluid tight
container.
2. Description of the Prior Art
Cores and particularly motor stator cores are generally made from
laminations. In conventional manufacturing techniques, these
laminations are punched from electrical steel sheet which are
thereafter annealed, insulated and stacked one upon the other in
order to form the core. Conductors usually in the form of coils are
then wound into the slots which have been machined within the core
structure or which are formed when the laminations are punched. The
material which is removed to produce this slot may comprise 25-40%
of the total area of each lamination and this material is lost as
scrap. Moreover the stacked core produces a slot geometry which is
limited because of the die cost. Consequently the slot fill of the
conductors is restricted since the conventional method of winding
or inserting the conductors into the slot does not permit them to
be compressed. Moreover thick liners are required to protect the
conductors from abrasion by the rough edges of the laminations
during the winding operation. Since the conductors cannot be
compressed in the current method of manufacture some of the volume
encompassed by the end turns of the windings is wasted due to the
inherent limitation of the lamination construction. It therefore
becomes apparent that it is desired to make a more efficient use of
both the space and materials involved in such magnetic cores. As a
result of the practice of the present invention both conductor and
core configurations have been improved where the stator core is
constructed by molding iron particles around the conductors and
thereby completely eliminating the presently wasted space.
Past attempts for example those described in U.S. Pat. Nos.
1,850,181; 1,669,648 and 1,982,689 to produce simple ring cores by
pressing the iron powder particles have produced very poor magnetic
properties. One factor for the poor magnetic properties is believed
to be due to the inability to achieve a sufficient density of iron.
Part of the densification aspect was slightly improved where
metallic iron in the form of flakes or wire employed in preference
to iron powder. The metallic flakes simply consisted of atomizing
molten iron into powder configuration and rolling the same to
produce a flattened elongated powder metal particle.
In order to overcome these shortcomings in the prior art practice,
the present invention teaches that small, substantially rectangular
ferromagnetic particles in the form of microlaminations which may
be formed for example from plain carbon steel sheet and processed
to yield the required magnetic properties, can be molded around a
preformed coil assembly. The resulting core formed from the
microlaminations is scrapless, has a high precision bore due to the
molding technique, utilizes more active magnetic materials since
precut slots are eliminated and in addition the molding technique
compacts the coil conductors during the molding pressurization and
thereby eliminates the need for thick slot liners. As a result both
better space factors and higher densities of both magnetic material
and conductor can be obtained with the result that such molded
cores exhibit outstanding magnetic characteristics.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view of a preformed coil employed in making a molded
motor stator with part of the insulation removed;
FIG. 2 is a view in vertical cross section of a loaded container
which is utilized in practicing the method of the present
invention;
FIG. 3 is a sectional view of the loaded container taken along the
lines III--III of FIG. 2;
FIG. 4 is a plot of the applied voltage versus the no load
ampers;
FIG. 5 is a plot of the applied voltage versus the no load watts;
and
FIG. 6 is a macrograph of a cross-section of the conductors after
pressurization and molding of the core into unitary structure.
DESCRIPTION OF THE PREFERRED EMBODIMENT
One of the basic materials which is employed in the method of the
present invention includes small substantially rectangular
parallelopipeds of magnetic material, each of which has been termed
a "microlamination." Essentially this material preferably comprises
a low carbon steel and that steel which is normally used for tin
cans is an ideal source since it is abundantly available and is
quite low in cost. Of course any other ferromagnetic material which
can be obtained in essentially this shaped particle may function
just as well. This material is preferably purchased in the
so-called black plate condition; that is the condition prior to the
application of the metal coating thereto for the tin can stock.
Essentially this material is available in a wide range of
thicknesses usually within the range between about 0.005 inch to
about 0.014 inch. While a relatively wide range of steel particle
sizes and thicknesses appears to be satisfactory it is preferred to
have the microlamination formed with the length ranging between
about 0.05 inch and about 0.06 inch, a width of between 0.01 inch
and 0.02 inch and a thickness of between 0.005 and about 0.008
inch. The laminations are usually formed from the tin can stock to
the above dimensions by cutting with a high speed rotary die cutter
in free space or the material maybe slit to the width desired and
then cut with a rotary cutter against a stationary knife edge. In
the latter case, the cutter and slitter are in line.
Other feedstock can also be employed with equally good results, for
example steel wool, scrap and billet shavings, scrap cobalt iron
can be processed into microlaminations for use in motors for
special applications, as aircraft. It will be appreciated that the
formation of the microlaminations entails a considerable amount of
stressing of the material. Accordingly where the materials are to
be used in a magnetic core the desired magnetic properties must be
developed. This aspect includes the relieving of the stresses in
the steel imparted during the formation of the microlamination plus
a deoxidation and a decarburization treatment so that the core
structure of a high density or packing factor can be obtained which
will also exhibit excellent magnetic characteristics. Thus in
developing the magnetic characteristics it is preferred to anneal
the microlaminations at a temperature within the range between
about 700.degree.C and 800.degree.C. It has been found that these
temperatures are sufficient for relieving the stresses in
microlaminates which have been induced during their processing.
In order to decarburize the microlaminations, during the initial
stage of the heat treatment at the temperature range indicated, an
atmosphere of wet hydrogen having a dew point in excess of about
+60.degree.F is utilized. The wet hydrogen atmosphere is effective
for removing the carbon content to a value of less than about 0.01%
by weight. This wet hydrogen atmosphere is maintained about the
heated microlaminations for a period of up to about 2 hours in
order to obtain the desired low carbon content therein, and
thereafter the annealing within the stated temperature range is
continued in a dry hydrogen atmosphere which is also effective for
deoxidizing the microlaminations. It has been found that forming
gas or other strongly oxidizing atmospheres that produce oxides on
the steel cannot be used since the oxide thickness adversely
affects the packing factor and thereby detracts from the overall
magnetic characteristics of the finished magnetic core. The dry
hydrogen atmosphere having a dew point of less than about
-40.degree.C is also maintained for a period of about 2 hours and
thereafter the microlaminations are cooled to room temperature
while being maintained within the protective atmosphere.
In order to develop the required core loss characteristics within
the finished core, the microlaminations must be insulated from one
another. It has been found that treatment with magnesium methylate
is a preferred medium for providing an insulating coating on the
laminations since the insulating coating is very thin and is
flexible enough to withstand the molding pressures. While other
insulating coatings may be employed, this coating provides
sufficient interlaminar resistance that after the core is molded it
will exhibit the required core loss as well as other magnetic
characteristics.
The method of the present invention is applicable to produce any
molded core having at least one conductor contained wherein and the
method is amenable to other techniques such as the so-called "free
mold" or the "fixed mold" techniques. However specific reference
will be placed in the following description to a method of molding
stators having embedded conductors therein and is applicable to the
production of a stator core for a motor it being understood that
the method is applicable to both static and dynamic electrical
apparatus where conductors are to be molded in a magnetic core.
More specifically, the method of the applicants' present invention
is directed to the utilization of a preformed coil which is used in
the manufacture of a stator for a motor. Referring now to FIG. 1
there is shown a stator coil preform 10 which comprises a plurality
of vertically extending slot conductors 12 which according to the
prior art methods of manufacturing motors would be disposed within
the slots of the stator lamination. The coil perform 10 having its
slot conductors 12 disposed as shown in FIG. 1 is formed on a
mandrel or form with the requisite number of end turns 14. The coil
preform 10 is usually formed of a electrical conductor wire such as
magnet wire to which an electrically insulative coating 16 has been
applied. The coil perform 10 may be wound on a mandrel (not shown)
and can be thereafter coated with any suitable resinous or other
insulating coating 16 of a thickness not exceeding about 3 mils
which will maintain the dimensional integrity of the coil preform
10 after it has been removed from the forming mandrel.
Referring now to FIG. 2 there is illustrated a container shown
generally at 20 which comprises a unitary structure with a base 22
and upwardly extending sidewalls 24. In practice it has been found
that such a container 20 may be formed of elastic or flexible
polyurethane resin which is cast into the desired shape. Natural
rubber, silicone rubbers and synthetic elastomers can be also
employed. Situated on the base 22 of the container 20 and within
the sidewalls 24 is a cast resin base 26 having a centrally
disposed opening therein 28 for accommodating a core bar 30 which
is centrally disposed within the container 20 and functions to
accurately position the bore of the formed molded stator so as to
accommodate the rotor of a motor. The base 26 is also provided with
an annular opening or slot 32 which is disposed for accommodating
the end turns 14 of the coil preform 10.
Reference to FIG. 3 will show in cross-section the assembled
relationship of the sidewalls 24, lot conductors 12 and core bar
30. As thus assembled, a selected quantity of the annealed and
insulated microlaminations 35 is deposited and positioned in the
space 34 between the outer container sidewalls 24 the core bar 30
and the slot windings 12. During the addition of the quantity of
microlaminations 35 in the spaces provided therefor, the entire
container and its contents are subjeted to vibratory energy so that
the "green" packing factor will be maximized in order to obtain the
highest possible packing factor in the completely molded stator
after the same has been pressurized. Where desired, in order to
obtain a preferred orientation the preformed coil may be energized
with a suitable source of electrical current in order to align the
microlaminations along the magnetic flux lines to form poles to
provide maximum magnetic cooperation with the shape and pattern in
which the coil is wound.
When a sufficient quantity of microlaminations has been added to
occupy the predetermined space, a matching top filler and seal 36
which is essentially a mirror image of the cast base 26 is disposed
in a seating arrangement on top of the microlamination 35, the coil
end turns 14 and core bar 30. As thus assembled the loaded
container is ready for pressurization to effect consolidation.
In order to compact the microlaminations 35 uniformly around the
preformed coil 14 it is preferred to apply isostatic pressure to
the assembly. Such isostatic pressurization will be effective for
densifying both the conductors 12 and the microlaminations and
since the container 20 which is preferably formed out of
polyurethane is flexible it will permit dimensional changes to
occur during the pressurization thereby enabling the attainment of
a packing factor in excess of 80%.
To effect consolidation the loaded container is placed within a
suitable isostatic pressurization chamber which is thereafter
filled with a fluid and pressurized sufficiently to cause
densification of the microlaminations and coils to occur such that
the packing factor or density thereof will be in excess of 80% of
the volume occupied by the microlaminations and the embedded
conductors. While the degree of pressurization above a certain
limit is not too cricital, it has been found that with the
application of about 50,000 psi a molded stator is produced
exhibiting a density or packing factor in excess of 80% of
theoretical.
In order to more clearly demonstrate the present invention
reference may be had to the following which describes the
construction of a two-pole dual voltage, three-quarter horsepower
induction motor. A preformed coil similar to that illustrated in
FIG. 1 was employed in which the conductors were wound on a mandrel
to provide the slot conductors 12 and the end turns 14 in the
manner illustrated in FIG. 1. After winding, and removal of the
coil preform from the mandrel the coil was treated in a fluidized
bed of dry powder of an epoxy resin of the polyglycidyl ester of a
dihydric phenol type. This fluidized bed treatment with the epoxy
resin was effective for providing a very hard out flexible
electrical insulation coating to the slot conductors as well as the
end turns.
A cast flexible polyurethane container 20 with a cast base 26 for
accurately positioning the preformed stator coil 10 was thereafter
employed in which the preformed stator coil 10 was positioned
within the cast base and a steel core bar 30 was thereafter
inserted within the interior of the coil to accurately dimension
the bore thereof. The container 20 with the cast base 26, preformed
coil 10 and core bar 30 were thereafter placed on a virbator and
previously prepared microlaminations 35 were poured into the space
34 between the core bar and the preformed coil 10, as well as
between the coil 10 and the polyurethane container 20 until a
predetermined amount of the space between the end turns of the coil
was completely filled with a mass of microlaminations compacted by
such vibration. Thereafter the top filler 36 and seal were placed
over the compacted microlaminations 35, core bar 30 and preformed
coil 10 and the entire assembly was loaded into the chamber of an
isostatic press and subjected to hydrostatic pressure of 50,000
psi. Thereafter the pressure was released and the molded stator was
then removed from the polyurethane container after removing top
filler 36. This molded stator was assembled into a three-quarter
horsepower two pole induction motor and tested with the results as
graphically illustrated in FIGS. 4 and 5.
Reference to FIG. 4, which is a plot of the applied voltage versus
the no-load amperes for both a conventionally wound motor a core
made of punched laminations as well as the motor of the present
invention, shows the improvement effected by the use of the
microlaminations in conjunction with the preformed stator coil
which are molded into a unitary stator core. For the same voltage
over the range of 120 to 240 volts, the no-load amperes are lower
for the molded stator motor of this invention.
The advantages of the present invention can be discussed quite
clearly when the same stators are employed in the same motors and
the plots of the respective applied voltage versus the no load
watts is considered. As graphically illustrated in FIG. 5,
employing a stator made in accordance with the teaching of the
present invention results in a substantial improvement over a
conventionally constructed motor. Thus at 220 volts the stator of
this invention has 120 watts at no-load versus 170 watts, a 30%
reduction. This improvement is believed to occur by reason of the
higher overall density which can be obtained employing the present
invention.
Reference is now directed to FIG. 6 which is a photomacrograph of
the cross section of the slot conductors after hydrostatic
pressing. It will be noted that by the mere application of a
hydrostatic pressure of about 50,000 psi the slot conductors have
been compressed so as to form substantially regular hexagons
throughout the cross section. By the compression of the slot
conductors, compression of the microlaminations and the elimination
of the usual slot liners, more effective amounts of metal can be
put to work in the same spare considerations. It is noted that
while the space factor of the conductor approaches 100%, no damage
was found to the wires or to the insulation. The wire to wire
insulation withstood 800 volts and the wire microlamination
insulation withstood 2600 volts. Thus there is complete integrity
to each of the individual slot conductors which is not disturbed
through the subjection of said conductors to the hydrostatic
pressing.
Another advantage of the consolidation of the microlamination
magnetic core and conductors into a solid unitary stator is that
destructive vibration which takes place between insulated windings
and liminations is greatly reduced because of the solid compaction
of the windings and the core. Thus failure of the electrical
insulator by abrasion or cut-through of the enamel on the
conductors is avoided.
In order to finish the evaluation of a similar molded core a ring
core was molded about a wire bundle under the same conditions and
thereafter the conductors were machined out and the core alone was
evaluated for magnetic performance. Density measurements indicate
that the microlaminates had been compressed to a packing factor of
about 89%. The core has a magnetic induction of 12.5 kilogausses
where binder may applied field was 50 oersteds, and 14.2 kilogauss
when the applied field was 100 oersteds. Moreover, the core
exhibited a 15 kilogauss watt loss of 5.9 watts per pound. These
are properties superior to laminated cores.
It will become apparent that while the specific example has been
illustrated employing a fluid hydrostatic pressure technique, other
methods such as a dry bag isostatic compaction technique can be
employed equally as well. Moreover, while there were no specific
binders for the microlaminates employed during pressing it will be
appreciated that where large rotational forces may be involved or
where low isostatic pressures are employed a binder may be
advantageously used. An excellent binder comprises potassium
silicate in an aqueous medium which has produced outstanding
results. It is imperative, however, that in the event that the
binder is used that the same be capable of exerting its binding
influence without entailing to excessive thicknesses, with lower
packing density of the magnetic material per se. Thus binders
generally used, for example, with iron powders such as carbowax and
organic resins were not satisfactory because of excessive
thicknesses which results in the decrease in packing density.
It will be further appreciated that if the use of the molded
microlamination body in a completed stator assembly yields too high
a reluctance it may be necessary to mold the core in the manner as
previously described and then, for reducing the reluctance, a wound
yoke can be applied as a tape of magnetic material wound on the
core which comprises the molded microlamination, the applied tape
being on the exterior portion of the stator.
In practice, a thin tape of magnetic material can be wound onto a
cylindrical bell, placed in the pressurizing container, and the
electrical conductor disposed therein, to be followed by the core
bar, and finally the microlaminations are poured in between the
tape shell and the core bar. Upon consolidation with a pressurized
fluid the entire assembly will be integrally united.
From the foregoing it will be appreciatd that substantial savings
can be effected in both the conductor as well as the cores since
for all practical purposes air gaps are eliminated and there is a
higher material density than could be obtained from employing
staked laminations as the core material and thereafter winding the
core in a manner of a conventional motor. Thus in addition to the
savings in materials as well as labor, improved performance is
obtained, resulting in the same power output from substantially
reduced inputs, or stated conversely, higher power outputs can be
obtained from the same electrical inputs.
* * * * *