Abstract:
A permanent magnet radial magnetizer is provided for use in radially magnetizing a workpiece ring. This magnetizer includes a lower magic hemisphere and an upper magic hemisphere which have respective equatorial surfaces in oppositely facing relationship to form a gap that receives a workpiece ring to be radially magnetized, and which have respective permanent magnet toroidal flux-line pathways, and which enclose a spherical cavity containing an iron filler.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention generally relates to magnet design and fabrication, and in particular the invention relates to a permanent magnet radial magnetizer which has a lower magic hemisphere and an upper magic hemisphere with a gap therebetween for receiving a workpiece ring to be radially magnetized.  
         BACKGROUND OF THE INVENTION  
         [0002]    In the state of the art, radially magnetized rings are used for applications such as traveling wave tubes, klystrons, and the like. Typically, high coercivity permanent magnets of toroidal or disk-like shape are difficult to magnetize radially. The difficulty arises for toroidal magnets because the thickness of the magnet is too large thus preventing sufficient flux from flowing into the toroidal hole which can then spread radially outward. This problem is discussed in U.S. Pat. No. 4,592,889 and in a U.S. Government Technical Report DELET-TR-84-5 ERADCOM 1984.  
           [0003]    U.S. Pat. No. 4,592,889 further describes a method and apparatus for pressing and aligning radially oriented toroidal magnets. The prior art magnetizer described in U.S. Pat. No. 4,592,889 includes a magnetic flux producing means having two opposing electrical coils, two electrical insulators for embedding the coils, and a yoke member for holding a workpiece to be magnetized radially.  
           [0004]    One problem with the prior art magnetizer is that it requires a relatively high capacity power supply.  
           [0005]    As noted in the above report, an aligning field of 2-4 kilooersteds (kOe) is sufficient for alignment of the constituent magnetic powders during fabrication. However, a larger field is required to achieve complete magnetization. In the prior art magnetizer, described in U.S. Pat. No. 4,592,889, a high-current, opposing-coil impulse-magnetizer was used to provide nearly 10 kOe of field. However, a significant drawback of this prior art magnetizer is that it requires a current source of thousands of amperes (amps) capacity, as well as two opposing electrical coils of a plurality of winding which must be embedded in a relatively strong electrical insulator to hold the coil structure together. A metal case must also be used to provide additional strength and safety to the coil structures.  
         SUMMARY OF THE INVENTION  
         [0006]    Accordingly, it is an object of the present invention to provide a permanent magnet radial magnetizer that produces sufficient flux to radially magnetize a toroidal ring magnet and which does not require a high-capacity power supply.  
           [0007]    This and other objects of the invention are achieved by a compact permanent magnet structure of “magic” hemispheres with a central cavity to produce a uniform high field within the cavity for radially magnetizing toroidal ring magnets. A “magic” hemisphere is a hemispherical flux source that is also referred to as a “magic igloo.” The “magic igloo” is described more fully in U.S. Pat. No. 4,835,506, which is hereby incorporated by reference. Briefly, a permanent magnet radial magnetizer according to the principles of the invention includes a lower magic hemisphere having an axis, an upper magic hemisphere coaxially aligned with and mounted in opposition to said lower magic hemisphere, said lower magic hemisphere and said upper magic hemisphere each having an equatorial surface forming a gap therebetween for receiving a workpiece ring to be radially magnetized, said lower magic hemisphere and said upper magic hemisphere each having an inner surface which forms a spherical cavity for receiving an iron fill material, and said lower magic hemisphere and said upper magic hemisphere each having a flux line pathway comprising an axial and a radial flux component within said cavity.  
           [0008]    The use of a lower magic hemisphere and an upper magic hemisphere having respective flux pathways with coacting radial flux components avoids the problem of requiring a relatively high capacity power supply to produce a high capacity current. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The foregoing and other objects, features and advantages will be apparent from the following Detailed Description of the Invention as illustrated in the accompanying drawings, wherein:  
         [0010]    [0010]FIG. 1 is a vertical sectional view of a permanent magnet radial magnetizer according to the present invention.  
         [0011]    [0011]FIG. 2 is a vertical sectional view of a second preferred embodiment. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]    As shown in FIG. 1, a magnetizer structure or magnetizer or assembly  10  is provided. Assembly  10  is a relatively compact permanent magnet structure which does not require a high capacity power supply. Assembly  10  has a vertical axis of symmetry or axis  12 . Assembly  10  has a lower magic hemisphere  14 , which has an outer spherical surface  16  and an inner spherical surface  18  and a lower joint or equatorial surface  20 . Assembly  10  has an upper magic hemisphere  22 , which has an outer spherical surface  24  and an inner spherical surface  26  and an upper joint or equatorial surface  28 . Magic hemispheres  14 ,  22  are permanent magnets of some high energy product rigid magnetic material (e.g., SmCo 5 , Sm 2 , Co 17 , NdFeB, etc.).  
         [0013]    Said lower magic hemisphere  14  and said upper magic hemisphere  22  are coaxially aligned with each other along axis  12  and are mounted in opposition to each other so that equatorial surfaces  20 ,  28  define an annular gap  30  therebetween. Said gap  30  has a gap distance  56 . Inner surfaces  18 ,  26  form a spherical cavity  32 . Cavity  32  is partly filled with a selective fill medium such as iron fill material  34 . Iron fill material  34  is disposed within said cavity  32  in order to augment the generated magnetic flux. Assembly  10  receives an annular steel workpiece or ring  36 , which is disposed in gap  30 . Ring  36  is coaxial with magic hemispheres  14 ,  22  along axis  12 .  
         [0014]    Magic hemispheres  14 ,  22  are two permanent magnet hemispheres which are identical in magnetization orientation but which are mounted in opposition such that the resulting equatorial magnetic field faces outward. Alternatively, the magnetizations of the two permanent magnet hemispheres could be oriented in reverse so as to produce an equatorial magnetic field that faces inward. Magic hemispheres  14 ,  22  have respective lower and upper toroidal flux line pathways or lines  38 ,  40 . Flux lines  38 ,  40  each has an axial component, and a radial component. Flux lines  38 ,  40  are peripherally spaced about axis  12 . Lower flux lines  38  extend upwardly from lower magic hemisphere  14  in a direction approximately parallel to axis  12 , and then are directed radially outwardly from cavity  32  through ring  36  approximately parallel to equatorial surfaces  20 ,  28 . Upper flux lines  40  extend downwardly from upper magic hemisphere  22  in a direction approximately parallel to axis  12 , and then are directed radially outwardly from cavity  32  through ring  36  approximately parallel to equatorial surfaces  20 ,  28 . The directions of magnetization for both the top and bottom hemispheres of permanent magnet structure are shown by arrows  44  and  42 , respectively.  
         [0015]    Assembly  10  also comprises a jig  46  made of non-magnetic material. Jig  46  includes a lower jig portion  48 , which is connected to lower magic hemisphere  14  and an upper jig portion  50 , which is connected to upper magic hemisphere  22 . Jig portions  48 ,  50  have respective connectors (not shown), such as fillet welds or threaded portions, or the like, for attaching jig portions  48 ,  50  to respective magic hemispheres  14 ,  22 . Jig  46  also has an actuator (not shown) which is connected to lower and upper jig portions  48 ,  50 . The actuator (not shown) can be an electromechanical or hydraulic type actuator. The jig  46  is adjustable in order to vary the size of gap  30 . Specifically, jig  46  is used to adjust the size of gap  30  so that gap distance  56  approximately equals the thickness of workpiece ring  36 .  
         [0016]    Inner surfaces,  18 ,  26  have a common inner radius  52 . Outer surfaces  16 ,  24  also have a common outer radius  54 . In the preferred embodiment, the ratio of outer radius  54  to inner radius  52  is about three.  
         [0017]    In a second preferred embodiment, equatorial surfaces  20   a ,  28   a  each have a respective recess  60 ,  62  (FIG. 2) formed therein to accomodate a workpiece ring  36   a . Lower magic hemisphere  14   a  and upper magic hemisphere  22   a  are mounted in opposition to each other with equatorial surfaces  20   a ,  28   a  joined together in a flush relationship to each other, so that said recesses  60 ,  62  form an annular slot within assembly  10   a . Parts of second embodiment  10   a , which correspond to parts of first embodiment  10 , have the same numerals but with a subscript “a” added thereto.  
         [0018]    In operation, a ring  36  of a selective size can be placed on the lower magic hemisphere  14 . Upper magic hemisphere  22  is lowered onto the top surface of ring  36  in order to attain a maximum radial magnetization field. A relatively large repulsive force between magic hemispheres  14 ,  22  is overcome by jig  46 . Lower jig portion  48  is preferably fixed in position, and upper jig portion  50  moves axially relative thereto.  
         [0019]    A magnet with a remanence or magnetic induction of about 12 KG is used to magnetize ring  36 . Given an outer-to-inner radius ratio of about three, in combination with iron fill material  34  disposed within cavity  32  to augment the flux generated by the magnet, an outward radial field at the ring  36  is well over 1.0T. After the ring  36  is magnetized, upper magic hemisphere  22  is raised and ring  36  is removed.  
         [0020]    The magnetic field produced by assembly  10  can be varied either by a change in the outer-to-inner radius ratio or by changing the gap distance  56  of the preferred embodiment. Moreover, ring  36  could be magnetized in a radially inward direction by two permanent magnet hemispheres that are magnetized opposite to those of assembly  10  in FIG. 1.  
         [0021]    While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation and that changes may be made within the purview of the appended claims without departing from the true scope and spirit of the invention in its broader aspects.