US2275904A - Magnet structure - Google Patents

Description

March 10, 1942. G. H. HOWE MAGNET STRUCTURE Filed nec. 19, 1959 claims.

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Patented Mar. 10, 1942 UNITED STATES lPATENT OFFICE eral York `Electric Company, a corporation of New Application December 19, 1939, Serial No. 310,014

4 Claims.

This invention relates to magnets and more particularly to permanent magnets of the lifting or holding type and has for its object the `provision of improved magnets of this character which are capable of producing maximum attractive force between the magnet poles and a relatively movable armature or keeper element.

In accordance with my invention in its preferred form I provide a plurality of permanent magnet elements, each magnet being preferably composed of a magnetic material having a high coercive force, and each having pole pieces of comparatively high permeability, high saturation, magnetic material. One of the pole faces oi the first magnet is arranged in such a manner that it overlaps thepole faces of the two poles of the second magnet and the other pole face of the first magnet is in contact with the pole face of like polarity of the second magnet. With this arrangement, three working air gaps are formed so that the combined iiux from both of the magnets passes through a common working air gap. In this way, a lifting or holding magnet is obtained having a great attractive power.

The novel features which are characteristic of my invention are pointed out in the appended My invention, however, will be understood more readily from reference to the following specification when considered -in connection with the accompanying drawing in which Figs. 1 and 2 illustrate respectively vertical section and exploded perspective views of one of the permanent magnet elements employed in illustrating the principles of my invention. Fig, 3 is a plan view illustrating the approximate relative pole face areas in contact between the two magnets when they are arranged in accordance with my invention. Fig. 4 is an elevational view of the holding magnet elements arranged in accordance with my invention.

Referring to Figs. 1 land .2 of the drawing I have illustrated a'permanent magnet element ill of cylindrical construction and having polar portions N and S formed on opposite sides of a transverse groove lvl in one end of the cylindri- The magnet thus has a substantially U-shape cross section. I may provide a pair of pole pieces I2 and i3 for engagingthe polar portions N and S, respectively of the permanent magnet element III. In forming these pole pieces I have found it convenient to employ an annular disk and secure it to the polar portions N and S in any convenient manner, such as bya soldering process of the character'dis- 55 closed and claimed in my United States Patent 2,169,098,1assigned to the same assignee as the present invention. A slot such as I4 may then be formed in the disk by means of a milling cutter or the like in order to separate the pole pieces I2 and I3.

In constructing the permanent magnet element i0 I prefer to employ magnetic materials which are characterized by a high coercive force in order that the magnet may be made highly resistant to various demagnetizing influences. I do not intend, however, that my invention shall be limited to the employment of a particular magnetic material, but I have found that highly satisfactory results may be obtained by the employment of permanent magnet alloys containing iron, nickel, and aluminum as the basic or essential ingredients. These magnets may be prepared in accordance with the teachings of United States Patents Nos. 1,947,274 and 1,968,569, to Wm. E. Ruder, and2,027,994 to 2,028,000, inclusive, to Tokushichi Mishima, or, if desired, the magnet may be formed by a sintering process, as disclosed in my copending application Serial No. 196,691, iiled March 18, 1938, U. S, Patent No. 2,192,743, entitled, Sintered permanent magnet, and assigned to the same assignee as the present invention. Magnets composed of such alloys not only have a high coercive force but they also exhibit a fairly high residual induction so that by their use a maximum amount of magnetic energy is made available with a minimum volume of magnetic material, and a permanent magnet of long life is obtained.

' The magnets I0 are illustrated for use in connection with pole pieces of different magnetic material from that of the magnets and I prefer to employ pole pieces which are composed of a high permeability, high saturation, magnetic material such as, for example, annealed cold rolled iron or an alloy of 35 to 50 per cent cobaltiron. In the design of magnets for lifting or holding purposes it is desired to obtain maximum attractive force between the magnet poles and a relatively movable armature lor keeper element. Magnets of this character are provided with small working air gaps and since the attractive force between two surfaces in contact or separated by a. small air gap is proportional to the product of the square of the flux density times the area of the air gap, it is obviously advantageous to maintain a high flux density at the'working air gap. By employing high permeability, high saturation, magnetic material for the p ole pieces, I thereby obtain a high flux density at the working air gap and at the same time the permanent magnet is operated at its most emcient flux density. In other words, the flux may be concentrated in the working air gap without affecting the ux density in the magnet. Whereas, if the pole pieces were c onstructed of the same material as the permanent magnet element, the concentration of flux would result in a loss of magnetomotive force in the magnet poles. Thus, if the same high density is to be maintained at the working surface considerably more magnetomotive force would be required.

Referring to Figs. 3 and 4, I have illustrated a pair of identical permanent magnet elements I of the type illustrated in Figs. 1 and 2 and having high permeability, high saturation, pole pieces I2 and I3 positioned with their polar faces in abutting or opposed relation to form contact surfaces i5, I8 and II, respectively. The pole pieces are of substantial thickness and have relatively large face or contact areas. It will be observed that the contact surfaces I5 and I6 are formed between the pole face of the pole piece I2 of the upper magnet and the pole faces of both pole pieces of the lower magnet while the contact surface I1 is formed between the pole face area of the pole piece I3 of the upper magnet and the pole face area of the pole piece I3 of like polarity of the lower magnet. The relative contact areas are clearly shown in Fig. 3 by the cross-hatched portions. Thus, the flux from the lower magnet, as indicated by the dotted line I8, passes between the pole piece contact surfaces at I6 and between the pole piece contact surfaces at I6. Likewise, the flux produced by the upper magnet, as indicated by the dotted line IS, passes between the pole piece contact surfaces at I6 and between the pole piece contact surfaces at I1. It will thus be seen that the sum of the fluxes of the two magnets is forced through the common air gap formed between the pole piece contact surfaces at I6.

To obtain a better understanding of the principles of my invention, assume'that the two magnets are positioned with their pole faces in abutting relation and so arranged that each pole of one magnet makes contact respectively with a pole of unlike polarity of the other magnet. A series closed circuit magnetic path including the two magnets and two working air gaps is thereby formed. The total flux in each magnet is thus the same and this same flux. neglecting leakage, crosses the two working air gaps. By arranging the parts in accordance with my invention, three working air gaps are provided two of which carry the flux of one magnet and one of which carries the combined flux of both magnets. Since the area ci each working gap in this arrangement is greatly reduced, other factors remaining the same, the flux density in each gap will be correspondingly increased. The flux density in the gap I8 ls quite high as compared to the series arrangement just described, since the area of the working gap is now much smaller and this gap now carries the sum of the fluxes produced by the two magnets. The result is a greatly increased attractive force.

The flux lines I9 in the upper magnet iind a, path of lower reluctance through the gap I8 than through the path including the gap I5. 'I'he same holds true for the flux emanating from the other magnet as regards the gap I1. Consequently, no appreciable repulsion force exists between the magnets even though they are arranged with their poles of like polarity in abutting relation.

The permanent magnets of Fig. 4 are shown mounted between an upper member 20 and a lower member 2|. 'Ihe upper member 2U, to which the upper magnet is secured, may serve as a support, for example, while the lower member 2i which is secured to the lower magnet may be any member to which a force is applied tending to separate the permanent magnet elements, such for example as a weight or spring.

In arranging the permanent magnet elements it is, of course, desirable that the contact surfaces at I5, I8 and I1 be properly prepared with regard to smoothness, surface contact, and the like in order to obtain the maximum pull under a given set of conditions. Also, referring to Fig. 3, the areas of the pole faces at their contact portions i5, IS and Il should be proportioned to obtain a uniform iiux density at each contact, and in the embodiment disclosed, the contact area at I8 is made approximately twice that of either I5 or I1 since the combined flux of both of the magnets passes through the contact surface at I6, whereas each of the other contact areas is required to carry the flux from only one magnet.

I have thus provided an improved permanent magnet for producing a large magnetic attractive force. Magnetic devices vof this character may be found particularly useful in those cases where it is desired to produce a force having a steep gradient, as in certain circuit breaker and switch operations. Also, it may be found useful in numerous other applications where a tenacious attration is required between two surfaces.

In accordance with the provisions of the patent statutes, I have described the principle ol' operation of my inventionin connection with the use of permanently magnetized elements which I now consider to represent the best embodiment thereof but I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means, such for example as electromagnetic devices.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a first permanent magnet structure of substantially U-shape cross section having a magnet body oi relatively high coercive force material and pole pieces composed of relatively low coercive force material having a permeability substantially greater than that of the magnet body, said pole pieces forming pole faces of opposite polarity, and a second permanent magnet structure of substantially U-shape cross section having a magnet body of relatively high coercive force material and pole pieces composed of relatively low coercive force material having a permeability substantially greater than that of the magnet body, said pole pieces forming pole faces of opposite polarity, said magnet structures being arranged with their pole faces in opposed relation in such a manner that a pole face of one polarity of said first permanent magnet is in con tact with both of the pole faces of said second permanent magnet and the pole face of opposite 'polarity of said first permanent magnet is in contact with the pole face of like polarity of said second permanent magnet, the aforesaid pole pieces being of substantial thickness.

2. In combination, a first permanent magnet element in the form of a cylinder having a transverse groove in one end thereof, said element being formed from a high coercive force material and having polar portions of substantial thickness, said portions being formed from a relatively low coercive force material having a per.. meability substantially greater than that of the magnet element, the pole faces of said magnet being arranged on opposite sides of said groove, and a second permanent magnet element in the form of a cylinder having a transverse groove in one end thereof, said second magnet element being formed from a high coercive force material and having polar portions formed from a relatively low coercive` force material having a permeability substantially greater than that of the second magnet element, said polar portions having substantial thickness, the pole faces of said second magnet being arranged on opposite sides of said groove, said second magnet being arranged with its pole faces in opposed relation to the pole faces of said first permanent magnet in such a manner that a pole face of one of said magnets is in contact with both of the pole faces of the other of said magnets and the other pole face of said one magnet is in contact with the pole face of like polarity of said other magnet.

3. In a magnetic device of the lifting or holding type, firstv and second magnet structures, each of which comprises a permanent magnet of high coercive force material and pole pieces of substantial thickness formed from a relatively low coercive force material having a permeability substantially greater than that of the magnet body and having pole faces of opposite polarity, said magnets being arranged with the pole faces of one magnet in abutting relation with the pole faces of the other magnet to form three working contact areas, the first and second of said contact areas being formed respectively by positioning one .of the pole faces of said lirst magnet to have a portion thereof in contact with the pole face of like polarity of said second magnet and another portion thereof in contact with the pole face of unlike polarity of said second magnet, and the third contact area being formed by positioning the other pole face of said first magnet in contact with the pole face of like polarity of said second magnet, said first and third contact areas being substantially equal in magnitude and the sum of said areas being substantially equal to said second contact area.

4. In a holding magnet, a first permanent magnet comprising a magnet body of high coercive force material and pole pieces composed of relatively low coercive force material having a permeability substantially greater than that of lthe magnet body and-a second permanent magnet comprising a magnet body of high coercive force material and pole pieces composedl of relatively low coercive force material having a permeability substantially greater than that of the magnet body, the. said pole pieces being of substantial thickness and also having relatively large face areas, a pole piece of one polarity of said first magnet being arranged in contact with and

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