US1875004A - Permanent magnet - Google Patents

Description

Aug. 30,1932; p. L. HORSBURGH ET'AL 1,375,004

PERMANENT MAGNET I Filed Jim 51. 1930 2 Sheets-She et 1 Patented M13530, 1 932 V p I Q 4 UNITED STATES PATENT OFFICE enonen nonnnn an nonsnunon mummy swrr'r rnvrcx, or snnrrmnn, mmnnm, assrenons or one-mm 'ro swmr rnvrcx am) sons rmrrnnor sunr- IIELD, ENGLAND, A; BRITISH COIPANY, AND ONE-H.ALF 1'0 DABWINSV LIMITED, 01 SHEFFIELD, ENGLAND, A. BRITISH GUI! V PERMANENT MAGNET Application filed January 81,1!30, No. 424,957, and in Great Britain August 22, 192 9.

This invention relates to permanent magclaims as soft iron for brevity) the flux nets and more particularly to permanent density in the gap can be greatly mcreased, magnet units intended 'for use with sound and a permanent magnet unit obtained of a reproducing or transmitting apparatus of the strength comparablev with that of electrokind in which a diaphragm 1s connected to magnet units as now commonly employed, a a coil situated in a magnetic field or gap. especially if the poles are shaped so that their Various attempts have been made to procross sectional area decreases in the direction duce a satisfactory permanent magnet unit of'the gap and it is a feature of our inventlon of the above kind, but these have not been tothus make the said poles. p

m altogether successful. In cases where the In the case where the-block is cast in one magnet unit has been built up of separate with a numberlof loop-like limbs (two, four parts it possesses certain defects, particularly or six, for example) integral with the crown, in that it has not realized adequate magnetic they may radiate from the base and crown strength owing to the presence of mechaniof a common or central pole-piece torming u cal joints, or to the necessityfor assembling part of what has been termed above the body a the parts after the magnets have been magportion, which is preferably circular incross netized,or to the units being so costly as to section, the adjacent ends of the loop-like be commercially prohibitive exce t in spelimbs being separated fromthe crown by the cial cases; moreover, there'is a liability of aforesaid trepanning or similaroperation so m certain of the parts to move and thus disturb that they are curved in conformity there the continuity of the gap. r with to form a numbenof segmental (zaps be- According to this invention most of these. tween the crown and the adjacent en ofthe defects are overcome by making the permalimbs. It is preferable howevelg-that the nent magnet or ma etunit of magnet steel lock be so castand the'trepanning or simir 95 cast in the form 0? p more loop like limbs extending outwardly cent ends oi the limbs remain united together a.

a or radiall from the base and crown ofthe by a web ofimetal forming an integral part'of body portlon of which they form an integral the casting so that the central pole-piece is part and. forming a gap around the crown surroundedby metal constituting the outer V 30 by a trepanningzor similar operation to acwall of a continuous circular ga with the/' 5 commodate the coil or moving part ofasound result that the ma etic flux is su tantially reproducing or-tra'nsmitting ap aratus, the equalized around t e wholeof the gap; The block thus formed with the sea gap being web of metal moreover prevents the loo subjected toa hardening operation and sublike limbs from becoming'distorted e'speci gs sequently magnetized. In a magnet' unit ly duringhardening or operations subsequent 33 thus made, and having the gap ormed as to the casting,which might occur, andtodif- 7 above"'s'tated there are no mechanical joints ferent extents, if no web of metal were pres and thus the .full-magneto motive force of ent. Instead of forming the circular gap by the magnet steel is available right up to the "trepanning as aforesaid it may be formed by h ,40 ap, unhindered by-any reluctances intro- -.'casting the unit with a space between the in uced by mechanical 'joints. In this case crownflandthe adjacent "ends of the limbs however as. the unit is. composed of magnet for softiron pole pieces suitably. 'shapedito teel alone, the magnetic'flux'density obtain-;- -form the gap. s able at the gap is b the permeability. Inthe where the unit has only a le 6 of the magnet steehfbuti the unit is made; oopkeimb, 88 i may hate, y so that the poles at the opposite sides of the where lightness is adesideiatum, e

gap are. rovided withmaterial of higher tron -of t e metal, around the crownni a perme,ab 'the magnet steel (for ex which the extends outwardly- (whether ample soft iron or cobalt iron and herein: castof magnetsteel or of-magnet steel and a block having one or lar operation be so performed that the-adjaf to after referred to in the specification and Soft iron) maybe separatedthemfiomiby "it!!! 40 Figure Figure 7, but with the soft iron pole a in the aforesaid trepanningor similaroperation to form a circular p surrounding the crown, the outer wall said gap being continuous; or the circular gap may be formed bycasting the unitwith the crown and'the ada'centends of the limbs separate and pro-' vi them with soft iron pole pieces suit-' abiy shaped to form the gap. t is desirable that in all cases the ag e- I! ate cross-sectional area of the indiv1 ual bs or the ores-sectional area of the single unit should be equal to the cross-sectional area of the common pole piece.

The magnet steel used is preferably a high percentage cobalt steel (9% to 35% cobalt). We do not however confine ourselves to the use of this steel as other magnet steels suitable for the manufacture of permanentmagnets may be employed.

In orderthat the said invention may be clearly understood and readily carried into effect, the same will now be more fully described with reference to the accompanying drawings in which 7 Figures 1 and 2 are respectively a Ian and a vertical section on theline 22 of e ure 1 showin one form of the metal bloc cast wholly 0 ma et steel and prior to being formed with e gap," and i 3 and 4 aresimilar views showing e block after it has been formed with the gap.

Figures 5 and 6 are vertical sections showing a metal block cast in two metals viz. l8 magnet steel and soft iron, before and after trelpanningpf thega respectively.

lgure 1s a plan owing the metal block asdcast for use with soft iron pole pieces an 8 is a section on the line8-8 of shown separate from the block and section.

F' 9 and 10 are similar views showa ing e block after it has been fitted with the le pieces. a

Figures 11 and 12 are respectively a plan and a'vertical section on the linens-12 of Figure 11 showing the ga ped cast metal a. block havin ga single loope limb.

Figures 13 and 14 are respectively a and a side elevation of a tool suitable for use in formingthe gap. in the castmetal Y blocks by a trepanning operation, and

I8 Figure'15 is an enlar ged plan view of a portion of the tool shown in Figure 13.

In F' p 1 to 4, A, Aare the loop-like limbs o the cast metal block which extend radially from the base A and crown A of the .0 body portion or pole-piece A with which they form an integralor mechanically jointless artfiip'rior to the formation of the gap B ,1 ande2) which is subsequently efi by a trepanning or e8 ,operationjas aforesaid, the said soft iron through a suitable eedin'g aper is filled. In the plane of contact of the two parts immediately surrounding the gap are and 6 is cast in two metals, one magnet steel,

and the other soft iron orother material of higher permeability than the ma et steel. In castlng such a metal block t e a ropriate quantity-of one metal is poure mto the mould and is followed by the second metal so that the two metals'unite or co1nv bine at their junction during the casting? operation as indicated by the cross hatching in 1 Figures 5. and 6. The metal block may be cast in an inverted condition in a moulding box by first pourin the molten ture into a central opening in the mould until it reaches the requisite hei ht which is about one third of the height 0 the main portion" of the block. After allowing a time interval to elapse suflicient for the soft iron already cast to become in a more or less semi-plastic condition the molten magnet steel 1s ouredinto the mould through the said fee ing aperture until the entire mould metals indicated by the cross hatching in Figures 5 and 6 mergin takes place between them. After the meta s have solidified the moulding box is opened and the. casting removed. The loop-like limbs A, A, the base A and the central pole piece A, which constitute the bulk or main rtion of the block, are of magnet steel whi e the crown A and the adjacent portions of the'limbs and web areof soft iron. The gap B is trepanned in the block in the same manner as in the case of the block illustrated. in Fi ures 1 to 4 after the casting operation so t at the of soft iron as' shown in Fi relO. 'It is important that the said gap should be in all cases accurately formed and as its width x will not generally exceed two millimeters, it is made after the operation and before hardenin by a trepanning or similar operation in w ich a tool like that illustrated by Figures 13to 15 is employed with advantage. This tool comprises a number of cutters 0 so carried or mounted'on a sup rt or head E as to lie on or near thecircum erence of a circle the diameter of which corresponds with that of the circular p B to be made. The cute ters e are .sligh y less in width than that of the gap to be made and are curved to con-. form to the curvature of the gap and the cutting edges eof' consecutive cuttersare on y opposite sides (see Figure 13 so that while one cutteracts on the inner of thegap under formation the next cutter acts on the outer face thereof and so on. The cutter sup port or head E is of cylindrical form carrying at one end the cutters and having at the other end a tapered portion E for securing it inosition in a lathe or other machine tool; he depth of the cutters is such that there is at all times a clearance between the top of cross section in the lower part of Figure 8,

. i. e. with the crown and the adjacent ends of the limbs separated with a central circular opening a and a central pole piece or body portion A of reduced length. The inner edge of the opening a and the annular face of the hollow central pole piece or body portion A are machined and the opening in the pole piece or body portion reamered out. The

' central pole piece A is provided with a soft iron extension piece or body portion a) and a soft iron ring a is fitted to the inside of the opening a. A concentric stub a on the extension piecea enters the hole in the central pole piece or body portion, the stub 11 being turned so that it is a slack fit in the aforesaid hole and its end being counter-sunk. The ring a also isturned so that it is a press fit in the opening a. In order to complete the magnet unit the ring is pressed in and the extension piece is loosely placed in position inthe opening and a spacing tube of dimensions corresponding to those of the gap is placed between them so 'as' to maintain them concentric. The unit is then turned upside down and placed on a rigid surface. and a tool insertedthrough the hole in the'central pole piece or body portion and given a blow in order to expand the stub on the extension piece against the wall of the hole tomaintain it in position. The spacing tube is then withdrawn leaving the ring and extension piece secured in position. It is to be observed that the rin a lies in the same lane as'the ad acent on s of the loop-like lim s'A and the associated webs a and that therefore themagnetic lines pass from the block of magnetic steel to the soft iron without appreciaof the ring and o the extension piece is suchv that the cross-sectional area through which the magnetic lines pass diminishes in a directiontowards the gap, and, as the material is one of a permeability which will allow of it, the flux density increases accordingly. This effect would not be obtained to the same extent by tapering the pole pieces of a magnet composed wholly of magnet steel on account of its relativel low permeability as aforesaid. In order to o tain the best results magnetically it is desirable that the pro ortion of magnet steel to soft iron should as high as practicable and for the magnet les'to be as near as possible to the gap: I l; weight steel comprising a of soft iron in the arrangement illustrated in Figures 7 v to 10 is about 10% of that of the magnet steel. Similar considerations to the arrangement of Figure 6.

apply It is advisable not to reduce the proportional}! of soft iron to below the aforesaid figure as it might then be necessary to reduce the cross sectional'area so rapidly as to be likely to lead to a leakage of magnetic lines. The soft iron pole piece or pieces should be so associated with the end or ends of the loop-like limbs or with the central pole piece or body portion that they form virtually an extension thereof, that is to say,'the form-in eifect a contlnuation and are not, .or example, secured thereto L80.

in an overlapping manner. In the case of the arrangement illustrated in Figures 7 to 10 for example thesoft iron ring a is for this purpose inserted in the circular opening a 1n such a manner that-it does not unduly pro trude either above or below the adjacent ends of the loop-like limbs.

The magnetizing, which is carried out after the gap has been formed and the block hardened, may be effected in any suitable manner.

In the example shown by Figures 11 and 12 the gapped cast metal block consists of a single loop-like limb A one end of which extends from the base A of the cylindrical body portion or pole-piece h and the other end of which is of ring-like formation sur rounding the crown of thepole piece or body portion A and constituting a continuous outer wall a of the circular gap B. A unit of this form may be made from a metal block cast of two metals, or from onekhaving separate pole pieces of soft iron associated therewith, as in the case of a metal block of the form having a number of loop-like limbs.

It is to be understood thatthe term mag' not block referred to in the appended claims is intended to include not only a permanent magnet but also a block for use in the manufacture of a permanent magnet. r

at we claim and desire to secure by Let ters Patent of the United States is roel. A magnet block of permanent magnet steel and having a body portion and inc ing a loop-like limb extending. outwardly or radially from the base of the body portion of which it forms an integral or mechanically jointless part and inwardl towards the crown gap around the of the body portion, an a crown of said body portion;

. 2. A magnet fb ock. of permanentmagnet 12.- steel and having a body ,portiop a'j-p'lurality' 1 of loop-likeglimbs extending bdtwardly or 1*: radially from the'base of the bodyportionf Of which they form an integral or inechani- '5 cally jointless part and inwardly towards the the crown of said body portion.

crown of the body portion and a gap around '3. A magnet block of permanent mhgnet,

dy portionandlinclud mg;- a loop-like limb extending outwardly or tab - radiallyfrom the base and crown of the body portion .of which it forms an integral or mechanical'ly jointless art and a continuous gap it around the crown o the body portion.

4. A magnet block of permanent magnet steel comprising a body portion, a plurality of loop-like limbs extending outwardly or radially from the base and crown of the body a loop block in that part consisting-of so plurality of loop-like limbs extending. outwardly or radially from the base of the body portion of which they form an integral part 1y or radially from the base and upwardly.

'. and inwardly towards the crown of the'body portion where they, are joined by integral webs.

7 A block for magnet steel comprising a body portion hav- .inga lower base part and an upper crown part and a loop-like limbextendin'g outwardtowards' the crown of the body portion of which it forms an integral or mechanically jointless part," the metal of the end of i the .limb adjacent to the crown forming an extension surrounding the latter.

'8. A magnet block-of permanent magnet steel comprising a body portion having a 40: andincluding aloo -like limb extending outwardly or radially tion of which they form an'integra 'of'thelimbs.

lower base part and an upper crown part cm the. base of the body portion of which it forms an integral part and-inwardl towards the crown and se 1 rated pole pieces .of soft iron interposed tween the crown and. the end-of the limb.

*9. A magnet block of permanent steel comprising abody portion having a lower base apart and anupper crown part and a plurality of loop-like limbs extending outward- 1y or radially p and inwardlytowards the crown of the body portion and separated pole pieces of soft iron 1nterposed between the crown and the ends 10. The manufacture of a permanent mag net; or magnet unit which consists in casting a block of magnet steel integral with a number of loop-like limbs extending outwardly or radially from the base of a body portion and inwardly towards the crown thereof,

for'min said block with a" gap around the crown t 'ere'ofoli a machining operation, subthus formed with said gap jectin'g the b a magnet of permanent froin'the base of the'body .por-

to a hardening operation, inserting soft iron po e pieces'in said gapand subsequently magnetizing the bloc 11. A magnet ing mainly of permanent magnet steel and portion having a lower base part and an upper crown part and including a loop-like limb extending outwardly or radially from the base of the'body portion ofwhich it forms an integral ormechanically jointless part and inwardly towards the crown ofthe web and a gap in said'blockin that part consisting of soft iron.

12. A magnet block of permanent magnet steel, comprising a vbodysportion having a lower base part and an upper crown part and including a loop-like limb extending outwardly or radially from the base of the body portion of whichit forms an integral part and inwardly towards the crown and a pole piece of soft iron interposed between the crown and the end of the limb.

13. A'magnet block of permanent magnet block of'cast metal consistbody portion where it is joined by an integral steel comprising a body portionhaving a low- 1 er base part and an upper crown part and including a loop-like limb'extending outwardly or radially from the base of the body portion of hich it forms an integral part and inwardly towards the crown and separated pole pieces consisting of a ring and of an extension piece interposed between the crown and the end of the limb.

14. A magnet block of permanent magnet steel comprising a body portion having a lower base part and an up r crown wardly or radia y from the base of the body portion of which it forms an inte al part and inwardly towards the crown an a single shaped member of soft iron inter osed between the end'of the limb and t e crown and having an air ga therein.

- 15. A magnet bloc of permanent magnet steel comprisin a body portion and'including aloopl olike 'mb extending outwardly or radially of which it forms 'an integral part and inwardly towards. the crown and/a pole piece ofsoft iron interposed between the crownand the end of the limb the proportion'by weight art and including a 100 -like hmb extendmg 'outm thebase of the body portion of magnet steel to that of iron being about ten to one.

7 at block of permanent mag net,- steel comprising a body portion and includ in a loop-like limb extendingoutwardly orra ially from the'base of the body portion.

of which it forms an integral 'or mechanically j ointless, art and inwardly towards the crownof, the y I pole piece interpose between the endof the limb and the CI0Wl1.tl1B soft iron portion being arranged relatively-to the magnet steel so that the magnetic lines pass from the magrtion and a soft iron 10' partly .of soft iron' and comprising a body Y net steel to the soft iron without any abrupt change of direction.

17 A magnet block of permanent ma et I steel comprising a body-portion and inc udfi' ing' a loop-like limb' extending outwardly or radially from the base of the body por tion of whlch it forms an integral or mechanically jointless art and inwardly towards the crown of the y rtion and a soft iron 10 le piece interposef between the end of the b and the crown so that it forms extensions thereof. a '18. The manufacture of a permanent magnet or magnet unit which consists in casting a blockof magnet steel with a loop-like limb extendin outwardly or radially from the base of t e body portion of which it forms an integral or mechanicall jointless part, and castin the crown of t e bod portion 7 j and the on of the 160 -like limb 0 soft iron so thatthe-two met unite at their -]'unc-' tion during the castingoo eration.

' GEORGE ALD LEE HORSBURGIL I BERRY SWIFT/LEVEL.

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