US2897417A - Fixture for magnetizing toroidal permanent magnets - Google Patents

Description

F. x. MHGDONOUGH ETAL 2,897,417

FIXTURE FOR MAGNETIZING TOROIDAL PERMANENT MAGNETS Filed Oct. 17, 1957 2 Sheets-Sheet 1 H41 j" 3 FIG. 1

INVENTOR. PEAK/5' A. MKDO/VOUGI/ LESL/E M VAN? ATTOENE)? July 28, 1959 F. x. M DONOUGH El AL 2,897,417

FIXTURE FOR MAGNETIZING TOROIDAL PERMANENT MAGNETS Filed Oct. 17, 1957 2 Sheets-Sheet 2 oha z" A TOE/V5) United States Patent FIXTURE FOR MAGNETIZING TOROIDAL PERMANENT MAGNETS Francis X. MacDonough, Stoneham, and Leslie M. Vant, Reading, Mass., assign'ors to Bomac Laboratories Inc., Beverly, Mass., a corporation of Massachusetts Application October 17, 1957, Serial No. 690,767

2 Claims. (Cl. 317-203) The present invention relates to electron discharge devices of the type having toroidal or bowl-shaped permanent magnets and more particularly to a novel method of and fixture for magnetizing such magnets,

Electron discharge devices in which permanent magnets are employed to produce the transverse magnetic field necessary for the flow of electrons include magnetron and backward wave oscillators. A development of recent origin discloses a toroidal magnet completely enveloping the tube for maximum efiiciency and elimination of the side and outside leakage flux components. A detailed description will be found in U.S. Patent No. 2,787,728, issued April 2, 1957, to P. W. Crapuchettes.

The primary object of the present invention is the provision of a novel method of and fixture for magnetizing toroidal permanent magnets.

Another object is the provision of a magnetizing method and fixture for toroidal magnets which achieves magnetic saturation efiieiently and requires a less costly operation.

The common method of magnetizing magnets heretofore employed involve the use of either a single internal loop or multi-turn external coils together with an elaborate impulse circuit under the so-called brute force method.

The main disadvantage in the use of the single loop resides in the fact that the magnetizing must be performed prior to assembly of the magnets to the tube body. Problems of retaining the field while assembling the magnets, preventing attraction of metallic particles in the area of the mating surfaces or possible tube damage will arise with this method. Further, space limitations between the magnets and the tube body generally preclude the use of this method.

The alternative method employing multi-turn coils of a low current capacity wire on the outside of the magnet does not achieve satisfactory saturation or stability when employed for toroid shaped magnets,

In accordance with the teachings of the present invention there is provided a novel method and fixture for magnetizing the paired toroidal magnets mounted on a completed tube body assembly. Broadly, the invention provides a fixture having a configuration which completely surrounds the magnet. The fixture may be cast from a highly conductive material such as copper and is designed to handle [high peak currents in the order of 200,000 amperes. A gap is provided along the radius of the cast member to interrupt the conductive path and essentially form an external single loop of relatively large mass. A connector may be cast in the fixture to mate with a similarly fabricated member. The mating fixtures are then connected to an impulse type magnetizer capable of generating extremely high current pulses of short duration. With the fixture and method disclosed herein saturation and stability will be realized in magnetizing toroidal magnets.

The aforementioned features, objects and advantages will be apparent after consideration of the following detailed description of a selected embodiment and reference to the accompanying drawings, in which:

Fig. l is a view partly in section of the embodiment of the invention in the operative position with an electron discharge device having toroidal magnets shown in perspective;

Fig. 2 is a perspective view of the embodiment shown with an oppositely disposed similar embodiment, to illustrate the method of the invention; and

Fig. 3 is a view of the magnetic return path keeper assembly employed with the embodiment of the invention.

Referring now to Figs. 1 and 2 the illustrative device 1 employing toroidal magnets is a magnetron of conventional construction. Only external structure has been shown since this is material to a description of the invention. The tube envelope is completely surrounded by the toroidal magnets 2 and 3 and has two axial extensions enclosing the ends of the envelope. Extension 4 encloses the cathode support assembly with terminals 5, 6 and 7. Extension 8 houses the tuning assembly with the actuator assembly omitted for simplicity. Threaded rod 9 forms the connecting means for the actuator.

According to the teachings of the invention, the magnetizing fixture 10 comprises a substantially frusto-conical shaped member 11 having a tapered axial passageway 12 for accommodation of the tube extensions previously described. Member 11 is fabricated in the form of a casting of a highly conductive metal such as for example copper. An enlarged connector tab 13 having an aperture may also be cast as an integral part of member 11 along the periphery of the widest dimension.

The inside of member 11 is hollowed to define a receiving chamber 15 conforming to the overall shape of the toroidal magnet 2 or 3. Hence the overall fixture resembles a bowl or skull cap. Notches 16 and 17 are also provided to allow for other external magnetron structure not shown, such as the output coupler which is positioned within notch 16. An air gap formed by a saw cut 18 along the radius of member 11 as well as another saw cut 19 along the joining edge of the tab 13 converts the fixture into effectively a single open-ended loop. A conductor cable 20 may be secured to the member 11 as shown at 21 with a copper block 23 at the outer end for connection to the magnetizing circuit. A 600 ampere welding cable may for example be selected.

The method of the invention will now be described employing a pair of similar bowl fixture members 10 in oppositely disposed relationship. The tube 1 with assembled magnets 2 and 3 may, therefore, be completely enveloped by the fixture members and is retained in this position by means of a steel bolt and nut arrangement 24. To assure good contact between the mating surfaces of tabs 13 and to act as a separator of the mating surfaces of members 10 a strip of copper wire mesh 14 may be utilized. Steel pole pieces 25 and 26 are then inserted in passageways 12 and encircle tube extensions 4 and 8 respectively to concentrate the flux developed by fixture members 10 into the lowest reluctance path along the axis of symmetry of the tube. Conductors 20 may then be fastened to appropriate leads from an impulse magnetizer having a very low impedance. As an example, a Model 8100 Raytheon Manufacturing Co. condenser discharging type impulse magnetizer provides for current pulses up to 200,000 amperes peak with a DC charging voltage adjustable to 3000 volts. With this equipment and the magnetizing fixture of the invention saturation may be achieved in a matter of milliseconds.

In the design of the embodiment of the invention consideration was directed to the concentration of magnetic flux along the axis of symmetry of the device where the tube electrode structure requiring an intense magnetic 3 t field is located. Hence in the bowl-shaped fixture the cross sectional area adjacent the passageway 12 as indicated by the line AA was increased to approximanl tw e he ants. e ti na a a f the Wa l t ut: we defining cham 15 a ndica d b th l n .+B b low t l e c a Fi 1 Wit t i n rati greater conductivity exists around the reducing necli por- @9 @1 6 n e the P rt n ar n a ama cu rent will How in the neck region. Efife'ctively more, ampere turns are produced in this region which leads to an' inreat d ma n iz n force According to k o et z n P o edure m tal i e r m b P o e t Su p y the ma n tic ater thereby a r n a u a io wi h a minim m o fii h r e o bow current n am le o one y t j pl y d hown, in 3 comp s n s l shorting has 27 a d Z i i m y b s cu ed to nse pole Pieces 2.5%?? with hr d d ro 2 a d 3 te d n therebs w Re a n nut 3 swr d 9 th n o d 2 9 and 3,0 retain the overall fixture assembly.

It may also be advisable to insulate the mating surfaces of members 10 in the region adjacent the connecttabs 13. Hence the rim 32 on the side of the loop secured to conductors 20 may be coated with any satis factory insulating material, for example, paint or tape. This will prevent accidental by-passing or shunting of current between the conductor cables 20. It is necessary that all the current must flow through each bowl in the tend d P t With the method and fixture disclosed herein the toroidal magnet may be demagnetized simply by the reversal of the current flow or reversal of the tube within the bowl fixture,

What is claimed is:

1. A fixture for use in the impulse method of magnetizing paired toroidal magnets oppositely disposed on a magnetron tube having tubular extensions, said fixture comprising a pair of similar frusto-conical shaped metallic members adapted to completely envelop the magnetron magnets when said members are in mating relah n th ar e en s, in cqn q e ch o said metallic members having wall structure commencing at the, L e end de n g q o tti t d m ns tntd 1Q t0. the afiaurati i of c ma et, a co nectortab. laterally disposed at a point along the peripheral edge adjacent' the large end, said member being bisected throughout its length by means of a slot commencing adjacent to said tab to thereby define an open ended loop of large mass and current conducting means secured to said member along the outer surface thereof for connection to an impulse magnetizing apparatus.

K fiigtureaccording to claim' 1 wherein the ratio of the cross sectional area of the wall structure at the conical end to the cross sectional area of the wall structure of the hollow portion surrounding the magnet is approximately 2:1 P

References Cited in the file of this patent UNITED, .STATES PAT NTS OTHER REFERENCES is m u a cti e for e a en Magne s:

Electronics, August l95 5, pages 12 112 3.

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