US 3255512 A
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June 14, 1966 R. D. LOCHNER ETAL 3,
MOLDING A FERROMAGNETIC CASING UPON AN ELECTRICAL COMPONENT Filed Aug. 17, 1962 INVENTORS @ryMo m D Lou/-09 BY CHJPLfS 14. Eva/e, III
United States Patent MOLDING A FERROMAGNETIC CASING UPON AN ELECTRICAL COMPONENT Raymond D. Lochner and Charles A. Fowler Ill, Annapolis, Md., assignors to Trident Engineering Associates, Inc., Annapolis, Md., a corporation of Maryland Filed Aug. 17, 1962, Ser. No. 217,655 5 Claims. (Cl. 29-15556) This invention relates generally to high-permeability term-plastic materials, and more particularly to a novel magnetically-soft material which may be cast or molded in combination with electrical components to-form electromagnetic devices, as well as to methods and apparatus for fabricating such devices.
The operation of virtually all electromagnetic devices requires the use of ferromagnetic materials. Such materials fall into two classes, the first of which consists of magnetically soft substances of high permeability, and the second of magnetically hard substances, i.e., those which may be permanently magnetized. The present invention deals with only magnetically soft material.
The ease with which a magnetic substance can be magnetized is given by the B/H ratio, called permeability. The value B is a measure of the amount or intensity of magnetization, and H represents the magnetic force necessary to produce the magnetic induction B. In many applications, such as motors, generators, transformers and relays, it is desirable to have magnetic material of high permeability but with low iron losses.
When the material is exposed to a rapidly varying magnetic field, as is the case in most magnetic devices, the material is not only subject to hysteresis losses, but also to eddy current losses, resulting from the flow of electric currents within the material induced by the changing flux. Eddycurrent losses increase with higher frequencies and with greater material conductivity. The summation of hysteresis and eddy current losses is often called the core or iron loss of the material.
Various expedients' are used to cut down power losses in electromagnetic devices and machinery. Thus the ad dition of silicon to iron produces an alloy of increased resistivity, and has the effect not only of decreasing iron losses but also improving the permeability of the material. However, such alloys are relatively difficult to machine and handle, and do not readily lend themselves to use in the making of miniature and subminiature electromagnetic parts, such as motors of extremely small size. It is also known to laminate ferromagnetic materials in order to reduce iron losses, but this also is a distinct disadvantage in many practical applications, particularly in the making of smallscale devices.
Accordingly, it is the principal object of the invention to provide a ferro-plastic, magnetically soft material characterized by high permeability and extremely lowiron losses, which material is moldable in conjunction with electrical components to form completed electromagnetic devices.
More particularly, it is an object of this invention to provide a material constituted by a saturate mixture of carbonyliron powder in a plastic insulating medium, the material being moldable about electric components to operate, when cured, as a ferromagnetic element in an electromagnetic device.
Patented June 14, 1966 Another object of the invention is to provide a term plastic material of high permeability and high electrical resistance, the material being useable directly in its solid form in transformers, motors, and in all other devices requiring non-conductive magnetic properties, as well as good thermal conductivity.
A significant feature of the invention as applied, for example, to motor armatures and stators, is that it makes it possible to cast the coils, commutators and shaft in a single operation, thus reducing the cost of winding laminated and insulated armatures. An important advantage of the invention is that the magnetic material combines the qualities of high permeability and good electrical insulation with high thermal conductivity, thereby avoiding the need to insulate the electrical components from the material and yet permitting effective heat dissipation.
Briefly stated, these objects are accomplished in a process for fabricating electromagnetic devices in a single casting operation, wherein carbonyl iron particles are mixed in a plastic solution, preferably an epoxy resin, to provide a mixture which is moldable about an electrical component such that when the mixture is cured, it forms a solid insulating core or casing of high permeability.
For a better understanding of the invention as well as other objects and further features thereof, reference is made to the following detailed description, to be read in conjunction with the accompanying drawing, wherein:
FIG. 1 is a perspective viewvof one form of electromagnetic device made in accordance with the invention; and
FIG. 2 is a section taken through the mold for fabricating said device.
Referring now to FIG. 1, we shall assume, illustrating a process in accordance with the invention, that it is desired to produce an electromagnetic device in the form of a tubular coil 10 set within a cup-shaped casing 11 of magnetically soft material, a permanent magnet 12 being inserted into the coil and being anchored in the base 11a of the casing. Connecting leads 13 from the coil pass through the base of the casing 11.
In accordance with the invention, the coil 10 is first prewound on a mandrel and then coated with a suitable nonconductive material serving to hold the windings together and to maintainthe desired coil shape.
As shown in FIG. 2, the coil is placed within a mold 14, preferably formed of Teflon, whose internal diameter is equal to the outside diameter of the casing 11, and whose height is equal to the height of the casing. The coil 10 is placed centrally in an upright position within the mold, the top surface of the coil lying below the opening of the mold to an extent equal to'the desired thick ness of the base 11a of the casing.
Inserted in the axial opening of the coil is a permanent magnet rod 12 whose length is somewhat longer than that of the coil. The free space within the mold is now filled with a saturate mixture of carbonyl iron particles in a plastic solution, preferably an epoxy resin, the mixture when cured forming the casing 11.
Carbonyl iron powder is commercially prepared by decomposing iron carbonyl (Fe[CO] in the vapor phase, and it consists of extremely small particles which are almost perfect spheres. The particle size distribution can be controlled in practice by temperature, pressure and other operation conditions, and may vary from about 3 to 20 microns. Spheroid particle sizes up to 60 microns by way of may be conveniently used. Among the powders uiable are those manufactured by General Aniline & Film (ompany (Dyestulf and Chemical Division) as 6AF Cart onyl lron Powder #E/B 375-2PQ01. A
These powders are mixed with a thermosetting resin such as epoxy or phenolic resins which are commercially available. Many of these resins cure at room temperature, and in producing articles in accordance with the present process, the carbonyl iron powder preferably thoroughly mixed in a chemists mortar. In practice, a standard epoxy may be used, such as Ciba 502 resin with Ciba 951 hardener.
Because of the spherical shape of the carbonyl iron particles, very high packing ratios can be obtained without difficulty. The greatest theoretical concentration for carbonyl iron spheres is 76.4% carbonyl iron by volume. ln practice, upwards of 70% carbonyl iron by volume has been produced, thus approaching the maximum possible to produce a product having good insulation properties, high thermal conductivity, high permeability, as well as excellent mechanical characteristics.
After the carbonyl iron and epoxy resin are thoroughly mixed to form a saturate solution, the resultant product is comparatively dry. Just prior to use, the proper proportions of hardener are added, resulting in a high-viscosity mixture which may be poured or injected into the mold to fill all available space not occupied by the coil and magnetic rod.
The mixture is then allowed to cure, the cure time, which may for example be perature and the proportions of hardener used. The resultant material has a hard, greyish-black consistency with a Brinnell or Rockwell characteristic similar to epoxy resin, but slightly more brittle and readily machinable.
The hardened material consists of spheres of carbonyl iron in an insulating matrix of epoxy. Since the individual spheres are of magnetically soft material which are microscopically separated from each other, in effect'a laminated structure is produced having low eddy current and iron losses. Thus the material magnetically serves the same function as laminated magnetic material without, however, the need for insulation. Moreover, it is possible to mold the magnetic material about the prewound electrical components rather than to wind wire about the material.
It has been found that the mixture of resin and carbonyl iron will hold up for a considerable period if it is protected from air and moisture by means of a suitable package. Then when a quantity of the mixture is to be used, hardener is added as needed just before injecting or feeding the mixture into the mold.
Essentially the method disclosed above to fabricate cup-shaped electromagnets, may be used in the making of motors. In this instance, as before, the motor coils are pre-wound on mandrels and coated to hold the windings together and to maintain the desired shape. The coils are then soldered to commutators and made ready for insertion into the Teflon mold. This is done by placing the coils on a shaft with the commutators in their proper position, the whole assembly being inserted into the mold.
Next, the saturated carbonyl iron-resin mixture is forced into the mold to fill every space not occupied by the windings, shaft and commutators. End pieces are placed on the mold to exactly center the shaft therein. After curing, the component is pressed from the mold and installed in the motor mount and operated.
When it is desired, as is the case in some magnetic devices, to orient the magnetic characteristics of the carbonyl iron, this can be done by subjecting the mixture in the mold while still ungelled, to a strong direct-current electromagnetic field. As with most magnetic materials, carbonyl iron crystals are most easily magnetized along one particular crystallographic direction or axis, and the magnetic field acts to orient the particles while they are and resin are 24 hours, depending upon temstill free to move in the plastic solution so that as many' of them as possible have their directions of easy magnetization aligned in the direction of the field. In a sense, the resultant material may be said to be grain-oriented, and it has been found that such grain-orientation significantly augments the permeability of the material.
The invention is not limited to epoxy, and similar results may be obtained with polymers such as polyesters, urethane rubber, and with phenolics. Polymers or monomers may be used with injection molding techniques for shaping the material.
Thus the material may be used in substitution for laminated iron in electrical rotors and stators, as well as for cores in transformers. The material is not only relatively low in cost, but because of its moldable properties it may be readily shaped as desired and thereby reduce fabrication cost considerably. The material is non-conductive, and maybe added to the ends of iron cores to reduce the noise of metal to metal contacts.-
The material of the invention lends itself to the production of electromagnetic components in a single casting operation. Conventionally in a motor, for example, the coils, must be wound about the stator elements, and cannot ordinarily be pro-wound. With the present invention, in the case of motor armatures, the coils, commutators and shafts may be cast in a single operation, thus reducing the costs of winding coils on laminated and insulated armatures. In this way all coils may be mass wound with precise measurement, at significantly lower cost than that obtained with existing methods. The stators may be similarly cast with the pre-wound field windings in place. The ferro-magnetic material is moldable at room temperature, and the casting process has no deleterious effect on the coils.
Miniature transformers of predetermined size and quality can bemass produced with the aid of qualiay control in mixing the material. Since this core material is non-conductive, there is no need to insulate the windings from the core, and miniaturization with a high degree of forecasted quality is feasible.
While there has been shown what is considered to be a preferred embodiment of the invention, it is to be understood that many changes and modifications may be made therein without departing from the essential spirit of the invention as defined in the appended claims.
What is claimed is:
1. The process for fabricating electromagnetic devices constituted by an electrical component in combination with a shaped element having high permeability, comprising the steps of supporting said component within a mold to form a space having the contours of said element, filling said space with a saturated mixture of carbonyl derived iron spheroidal particles in a resin solution, and subjecting the solution in the ungclled state to an electromagnetic field to orient the carbonyl particles, whereby when the solution is thereafter cured it produces a solid element in which said component is embedded.
2. The process as set forth in claim 1, wherein said resin is epoxy.
3. The process as set forth in claim 1, wherein said resin is phenolic.
4. The method as set forth in claim 1, wherein a hardener is added to said mixture.
5. The method as set forth in claim 1, wherein the concentration of said carbonyl iron particles is in the order of 70% by volume.
References Cited by the Examiner UNITED STATES PATENTS 2,814,744 11/1957 Demetriou 310-43 2,820,914 1/1958 Rudoff 3l043 3,024,392 3/1962 Baerman 29-15559 X (Other references on following page) UNITED STATES PATENTS OTHER REFERENCES 3,063,433 12/1962 wmblewski at 33 95 XR The Iron and Steel Institute: Symposium on Powder 3,070,041 1/1963 Schornstheimer 29-45559 x Metallurgy. 1947. pages by h 3,077,026 2/1963 Blackburn 9 155 53 Treatise on Powder Metallurgy, vol. 11, pages 293-295, 3,093,888 6/1963 Huguley 29-45553 5 12, 1951' 3,110,675 11/1963 Brailowsky 29-15559 X WHITMORE A. WILTZ, Primary Examiner. FQREIGN PATENTS MILTON O. HIRSHFIELD, Examiner. 625,640 8/ 1961 Canada. R. W; CHURCH, Assistant Examiner.