US2915682A

US2915682A - Lifting magnets

Info

Publication number: US2915682A
Application number: US634881A
Authority: US
Inventors: William L Bower
Original assignee: Neill James & Co Sheffield Ltd
Current assignee: James Neill and Co Ltd Sheffield
Priority date: 1956-01-26
Filing date: 1957-01-18
Publication date: 1959-12-01
Anticipated expiration: 1976-12-01

Description

1, 195 w. L. BOWER 2,915,682

LIFTING MAGNETS FilOd Jan. 18, 1957 3 Sheets-Sheet 2 F/G.3. g8

Inventor IAM L Bowl-1R By 9PM m, Mw 42150) Attorneys Dec. 1, 1959 Filtd Jan. 18, 1957 w. L. BOWER 2,915,682

LIFTING MAGNETS 3 Sheets-Sheet 3 F/G.8, F/G. 9.

Inventor WILLIAM LBDWER B Wm, 6x3 My mm I A ttomeyg United States Patent Neill- & Company (Sheffield) Limited, Sheflield, England Application January 18, 1957, Serial No. 634,881

Claims priority, applicationGreat' Britain January 26,1956

8 Claims. (Cl. 317-159) This. invention relates to liftin magnets. Ordinarily, these comprise electro-magnets, and call not only'for the supply of suitable direct current andconnecting cable, but also. switch-gear to effect the energising and de-energising by which the load is held and released.

The principal object of the invention is to provide a lifting magnet in which the holding power is provided by permanent magnet material. Afurther object is to provide such a magnet in wh'ich holding and releasing of the load are effected with great simplicity in the handling of themagnet.

According. to the present invention, a lifting magnet comprises a suspending member mounted with limited vertical movement, a lifting surface adapted to be brought by lowering of the suspended magnet into contact with a load'offerro'magnetic material, said surface beingrformed by at least twopole pieces separated by non-ferromagnetic" materiaL, permanent magnet material movably mounted so that its flux may be directed into and out o'f'a circuit'including the pole pieces and any ferromag: n'eticloa'd' bridging'the pole pieces, and mechanical means operated byrelative vertical movement'of the suspendingmemberwhen' the magnetis lifted from a support, to effect alternate energising and de-energising of the lifting surface by moving the permanentlmagnet material into'and'out ofthe said circuit.

Preferably,; the lifting magnet has. provision for a second circuitexcluding' thepolepieces, and the de-energisin'g'of' the lifting surface is accompanied by diversion of fluxfrom the permanent magnet material into this second circuit. When'the magnet held suspended by the suspending member'from lifting gear; such as a crane or pulley blocks, is fully lowered on to a load tobe picked up, with the permanent magnet material out of magnetic circuit with the pole pieces, the suspending member moves downwardly withrespect' to the liftingsurface. An upwardpull on the suspendingmember first causes the permanent magnet material to move into magnetic circuit with the pole pieces and the load to hold the loadbyattraction as'the' suspending member moves to the upper limit of its movement, and a continued upward pull then lifts the magnet and the attached load.

Full'loweringof the magnet and its'atta'ched load on to' a" support allows the suspending member to move down again' with respect'tothe lifting surface after which an upwardpull' on the-suspending member causes the permanent magnet material to move out ofcircuit with the-pole piecesand the load; to release the load.

Thelifting surface formed by the pole piecesaseparated by non-ferromagneticmaterial may be shaped to correspend with the shape of the ferromagnetic load to be lifted: Thus, for flat blo'cks, slabs, or sheets the surface should be fiat, and thus able to make very effective eontactwit'h thefiat surface of the material to' be lifted. However, a magnet with a flat'lifting surface will also serve for the lifting of loads with other than flat contacting'surfac'es. For" liftingarticles' in general, a cir- Patented Dec. 1, 1959 cular liftingsurface is convenient, since it need not be orientated with respect to. the lengthwise direction of elongated articles, but merely needsto be applied approximately above the centre of gravity of an article. A circular lifting surface lends itself. to a concentric arrangement of pole pieces, e.g. the endof a central core, and two annular pole pieces, with separating annuli of non-ferromagnetic material.

A housing of the whole magnet is advantageously of magnetically permeable material, which is used for diversion of the magnetic flux from the pole pieces when the permanent magnet material is moved out of circuit with the pole pieces. Thus the magnet may consist of a housing consisting essentially of magnetically permeable material anditself forming one pole piece of a lifting surface in which is embedded another pole piece, with paramagnetic material separating the pole pieces, a permanent magnet assembly movably mounted within the housing and including two other pole pieces separated by and movable with a permanent magnet, one movement of'the assembly bringing one of its pole pieces into magnetic circuit with the embedded pole piece, and the next movement bringing that-pole piece of the movable assembly out of magnetic circuit with the embedded pole piece and into magnetic circuit with the housing, the circuits inboth cases being completed-by the other pole piece of the movable assembly and the housing, the housing also carrying the suspending member and containing'the mechanical means that bring about the-movements of the assembly. i

A central core in the housing may also provide for another magnetic circuit through the embedded pole piece, or a circuitdiverted from that .pole piece.

With a circular lifting surface, the polepiecesofthe movable assembly may be of annular form. Thepermanent magnetmaterial may. then occupy a corresponding annulus, conveniently as a number ofseparate blocks, e.g. of segmental'form, for convenience in manufacture. High energy magnet material provides great lifting .power, especially if the magnet blocks are anisotropic, with their preferred direction extending from one pole piece to the other of the movable magnet assembly.

For compactness of construction, the movement of the permanent magnet material with respect to the lifting surface is preferably vertical. This requires only a relatively'small gap to be opened and closed by the vertical movement, regardlessof the large area of the gap faces that is provided because of the ample space then available in the magnet ofpermanent magnet material that is considerable in both area and volume. The gap may be formed by a serrated inner face of the lifting pole pieces, which, when the gap is closed, fits into a correspondingly serrated face in the movable part of the magnet system. The serrations increase the enact the inevitable, though veryv fine, air gap between the faces when they are fitted together, and thus reduces the reluctance'of the gap.

The suspending member. is conveniently a single lifting stem mounted centrally of the Whole magnet, and free to slide vertically by a limited amount as the magnet is lowered on to, or liftedfrom, a support. Alifting eye at the top of the stem enables the magnet to be suspended from a lifting hook.

Various forms of one-way? or ratchet mechanisms may be used to' convert the alternate upward movements of the suspending member into movements of the permanent magnet material into and out of magnetic circuit with the pole pieces of the lifting surface, and to allow the suspending member to-move downwards idly after the whole magnet has been lowered on to a support. Thus, the suspending member may have a quick-pitch sliding movernentthrough a nut that is restrained against endwise movement, the nut making pawl-and-ratchet engagement with a cam that produces the movements of the permanent magnet material into and out of circuit with the pole pieces of the lifting surface. Again, the suspending member may be formed as a rack to rotate a pinion making pawl-and-ratchet engagement with a shaft carrying one or more eccentrics to produce the movements of the permanent magnet material.

The type af ball clutch known as a silent ratchet may be used instead of a toothed ratchet.

The suspending member is raised to its uppermost position in the magnet before the whole magnet itself can be lifted, and in this interval the one-way mechanism moves the magnet assembly, say into circuit with the lifting surface pole pieces. Further effort then enables the whole magnet itself to be lifted and to carry with it any magnetic material on to which it has been lowered. When the magnet and load are again set down, and the lifting gear is lowered sufiiciently for the suspending member to move to its lowest position in the magnet, the one-way mechanismoperates idly; but the next lifting effort again moves the suspending member before the whole magnet can be lifted, and the one-way mechanism moves the magnet assembly out of circuit with the lifting surface pole pieces (and preferably into a diverting circuit) so that the load is no longer held when the whole magnet itself is lifted.

The holding and releasing of the load thus follow from the mere acts of lowering the whole magnet first on to i l a load and then on to a support where the load is to be deposited.

Two embodiments of the invention now to be described in greater detail with reference to the accompanying draw ings both have the permanent magnets arranged for vertical movement within the housing.

In the drawings:

Figure l is a vertical section through one embodiment of the invention;

and partly in section on the line 22 of Figure 1;

Figure 3 is another vertical section, taken at rightangles to Figure l; and

Figure 4 is a part sectional view taken from the same direction as Figure 3, but showing the magnet in lifting position;

Figure 5 is a vertical section through another embodiment, more compact than the embodiment shown in Figures 1 to 4, the right-hand side showing lifting posishoulders 11, 12, and is capable of being lowered and lifted to enter the recess or to register with the shoulders. A similar upper annular pole piece makes a sliding fit between deeper shoulders 16, 17 at the top of the lower part 1 of the housing and the core 2. Between the lower and upper pole pieces 14, 15 'is a permanent magnet formed by segmental blocks 18 of high energy alloy clamped between the pole pieces by bolts 19, preferably of non-ferromagnetic material, passing through the pole pieces. Two carrying lugs 20 upstanding at diametrically opposite positions on the upper pole piece 15 provide for lowering and lifting of the assembly of magnets 18 and

pole pieces

14 and 15. Peripheral notches 21 in the pole pieces (Figure 3) prevent trapping of air.

The core 2 has a central bore 22 from its upper surface, which makes a spigot-and-socket connection 23 with a guide 24 extending to the top of the cover 3, a lower flange 25 on the guide being secured by screws 26 to the I by a plug 32 in a small continuation bore 33 at the bottom of the core 2.

As indicated in Figure 3, one side of the stem 27 is formed with a long rack 34, meshing with a pinion 35 having an internal ratchet 36 mounted in horizontal bearings 37 in brackets 38 on the guide 24. The pinion 35 is an annulus rotatable about the ratchet 36, with two pins 39 rotatable in bores 40 in the pinion intersected by the ratchet 36, the pins having flats 41 the length of the ratchet to form pawls to enter two ratchet notches 42.

The engagement of the rack teeth 34 with the pinion 35 prevents rotation of the stem 27. Each end of the ratchet member 36 carries a crank pin 43 (see Figure 4), which, by rotation of the member 36 by the pawl pins 39,

; I is brought to upper and lower dead-centre positions, the Figure 2 is a plan of Figure 1, With a cover removed,

upper position being shown in Figure 4. The crank pins 43 lie in slots 44 in levers 45 pivoted at 46 to the brackets 38, and intermediately pivoted at 47 to the lugs 20 on the magnet assembly.

When the lifting eye 28 is engaged and raised (Fig- I ure 4) for the purpose of lifting the complete magnet,

the lifting stem 27 first rises in the guide 24 and core 2, and the rack 34 rotates the pawl pinion 35, the pawl flats 41 on the pins 39 engaging the ratchet notches 42 and rotating the ratchet 36 and crank pins 43 through 180:

In one such movement, the two levers 45 are raised (Figure 4), to raise the

magnet assembly

14, 15, 18, and 19 by the lugs 20; in the next, the levers 45 and the magnet assembly are lowered.

When the magnet assembly is lowered (Figures 1 and l 3), the sinking of the lower pole piece 14 into the recess In Figure 1, a housing has a generally cylindrical lower part 1, with an axial core 2 located from an upper domeshaped cover part 3. A common circular lifting surface is defined by the annular bottom edge 4 of the lower part 1, the end 5 of the core 2, and an annular pole piece 6 is embedded flush with, the annulus 4 and the core end 5, but separated from them by outer and inner

cylindrical rings

7, 8 of non-ferromagnetic material. The lifting surface thus consists of three concentric and separated pole pieces. The upper side of the pole piece 6 is separated by outer and inner flat rings 9, 10 of non-ferromagnetic material from inward and outward shoulders 11, 12 on the lower part 1 and the core 2. The upper face of the pole piece 6 has an annular recess 13 between and below the flat rings 9, 10.

The recess 13 makes a sliding fit with a lower annular pole piece 14 of a permanent magnet assembly. The pole piece 14 has a thickness equal to the depth of the 13 enables inner and outer fparallel circuits to be completed from the magnet material 18 via the pole piece 6, then through the ferromagnetic material of a load on which the whole magnet rests, and then (a) to the annulus 4 and through the lower part 1 to the upper pole piece 15, and (b) to the core end 5 and through the core 2 to the upper pole piece 15. The whole magnet is now in a condition to lift the load when it itself is lifted.

When the magnet assembly is raised (Figure 4), the withdrawal of the lower pole piece 14 from the recess 13 diverts flux from the pole piece 6, and inner and outer "parallel circuits are completed from the pole piece 14 (a) through the shoulders 11 and the lower part 1 to the upper pole piece 15 and (b) through the shoulders 12 and the core 2 to the upper pole piece 15. The whole magnet is now incapable of lifting a load, and any load previously attracted to it is released.

A spindle 48 (Figures 1 and 2), journalled in a boss 49 on the cover 3 and in a bearing 50 carried from the upper pole piece 15, is rotated as the nearer lever 45 is rocked by its crank pin 43, This rotation may be used to indicate whether the magnet" assembly is raised or lowered, and theprovision ot ahandle 51 (which maybe detachable.) provides for manual movement of the assembly. The connection of the spindle 48 to the upper pole piece 15 through the-bearing lug 50 prevents rotation of the magnet assembly with respect to the

housing parts

1, 3.

Each time the whole magnet is lowered, whether to pick up a load or to relea'se' it, the'lift'ing stem-27 is low ered (being assisted in this by the spring 30). Before the magnet can be rais'edlwith or without load), the stem 27 must first be raised andthis rotates the ratchet 36 through 180 to rock thelevers 45. If a load has been depositedwith the lowering of the whole magnet, the magnets 18 are intheir lowered position, and the rocking of the levers 45 by. afresh lifting effort on the lifting eye 28 lifts the magnets, the resistance of the weight of the rest of the assembly (assisted initially by the still-attracted load) enabling the energy exerted through the stem 27 to overcome the internal magnetic attraction and such mechanical friction as exists inthe internal mechanism.

If the magnet is-deposited on to a load to be picked up, the magnets18are'in their raised position,.and have merely to be moved mechanically to lowered position by the rocking of the levers 45 onthenextliftingetfort on the lifting eye 28, and the weight ofthe magnet provides a sufficient resistance to ensure the operation of the internal mechanism on lifting of the stem 27.

The lower face of the lower pole piece 14 and the bottom of the recess 13 could be serrated in the manner shownin Figures and 7, as described below.

In the construction shown in Figures 5 to 10, a similar lifting power to that of the previous construction is obtainable in a more compact design,,and with a smaller movement of the lifting stem.

In Figure 5, a'housing lower part 52 and core 53 form with a flush annular pole piece 54 a lifting surface 55. The upper surface of the pole piece 54 is serrated with concentric V-grooves 56' to mesh with a correspondingly serrated underface'57 of a lower'pole piece 58 of a vertically movable magnet assembly. The lower pole piece 58 is of greater radial width than the pole piece 54, with au-external lip 59 to fit round the latter, lower shoulders 60, 61 on the housing 52 anda core sleeve 62 being undercut to allow clearance for the greater width. Inner and

outer rings

63, 64 of nonferromagnetic material separate the pole piece 54 from the core 53 and the housing 52. Magnets 65 are clamped between the lower pole piece 58 and an upper pole piece 66, the latter lying between deep shoulders 67, 68 of the core sleeve 62 and the housing 52. The core sleeve 62 is secured to the core 53 by a ring 69, which provides the required full depth of the inner shoulders 67. A pin 70 through the housing 52 engages a notch 71 in'the upper pole piece 66 to prevent rotation of the magnet assembly.

A lifting stem. 72 is slidable in-a bore 73 in the core 53 and also-in a boss 74 in a cover 75, with a key 76 in the boss 74 fitting a keyway 77 in the stem to prevent rotation of the stem, while allowing it to slide from the bottom of the bore 73 until a bottom collar 78 is engaged by the ring 69. A quick pitch helical slot 79 on the stem 72 transmits a rotary movement of 90 to a nut 80 surrounding the stem above the ring 69. The nut has four ratchet teeth 31 (Figure 6) on its periphery to engage pawls 82 contained in part-cylindrical recesses 83 inside a cam ring 84 surrounding the nut. Each pawl 82 has a central notch 85 (Figure 9) to provide a face 86 (Figure 8) on which'bears the end of a spring urged thimble 87. The cam ring 84 forms an outer race for balls 88 by which it is supported from an inner race on the top of the ring 69. An upper double ball race 89 guides balls 90, 91 in corresponding races in the nut 80 and the cam ring 84. A cam groove 92 (Figure in the ring 84 receives two horizontal follower rollers 93 on lugs 94 6 on the upper pole piece'66of the magnet assembly. The cam groove 92 has pairs of upper and lower positions alternating at intervals. A 90 rotation of the'cam ring 84 on raising of. the stem 80 thus either lowers. or lifts the magnet assembly.

Lowering of themagnet' assembly completes the magrietic circuit very effectively through the intermeshing serrated faces of the lower pole piece 58 and the pole piece 54 (see Figure 5), because the increased contact area provided by the serrations reduces the reluctance of any fine air gap between the serrated surfaces. Inner and outer paralleP magnetic circuits are completed, as in Figures 1 to 5, through the ferromagnetic load and the part 52 and the core 53 respectively. Lifting of the assembly brings these grooved faces clear of each other, as in Figure 7, and the parallel circuits are completed directly through the shoulders 67, 68.

Figure 7 shows a notch 95 in the lower pole piece 58 to prevent trapping of air. The notch 71 in the-upper pole piece 66 serves the same purpose. When the magnet assembly is lifted, the upperpole piece compresses a number of springs 96 (one-shown in Figure 7), the energy of which assits the return of the magnet assembly to the position shown on the right-hand side of Figure 5.

One of the lifting lugs 94 has an extension 97 in line with a hole 93 in the cover, to provide an indication of the position of the assembly.

A bellows 99 (Figure 5) assists in keeping'foreign matter from entering the magnet.

A satisfactory factor of magnetic safety may be provided by limiting the size of the lifting eye 100 on the stem 84 (or that of the lifting eye 28 of Figure 1) so that it will only receive a lifting hook of a capacity much less than the maximum lifting power of the magnet.

What I claim is:

l. A lift ng magnet comprising a housing of magnetically permeable material and providinga lifting face adapted to make contact with a ferromagnetic load to be lifted, the lifting face being completed by inserted magnetically permeable material and non-magnetic separating material to separate the inserted material from the material of the housing, thus forming pole pieces to be bridged by the load in a magnetic circuit including those pole pieces and the load, magnetised permanent magnet material mounted within the housing so as to be movable from a position in which'that material completes the said circuit for'magnetic engagement of a load to the lifting face to a position in which the circuit is broken to release a load from the liftingface, suspending means for the entire magnet, said means having a limited amount of vertical movement relative to the housing as the magnet is lifted and lowered by use of the suspending means, and a one-way connection between the suspending means and the permanent magnet material to cause successive lifting efforts applied through the suspending means to the magnet to-effect movements of the permanent magnet material alternately to load-engaging position andv loadreleasing position v 2. A permanent magnet lifting magnet as in claim 1, wherein the movable permanent magnet material has two pole pieces movable with it, one of which remains in sliding contact with the housing in either position of that material while the other slides into and out of contact with the housing, sliding of that pole piece out of contact with the housing serving to bring it into the magnetic circuit in which the pole pieces of the lifting face are included.

3. A lifting magnet comprising a housing of magnetically permeable material and providing a lifting face adapted to make contact with a ferromagnetic load to be lifted, the lifting face being completed by inserted magnetically permeable material and non-magnetic separating material to separate the inserted material from the material of the housing, thus forming pole pieces to be bridged by the load in a magnetic circuit including those pole pieces and the load, magnetised permanent magnet material mounted within the housing so as to be movable vertically from a position in which that material completes the said circuit for magnetic engagement of a load to the lifting face to a position in which the circuit is broken to release a load from the lifting face, suspending means for the entire magnet, said means having a limited amount of vertical movement relative to the housing as the magnet is lifted and lowered by use of the suspending means, and a one-way connection between the suspending means and the permanent magnet material to cause successive lifting efforts applied through the suspending means to the magnet to effect movements of the permanent magnet material alternately to loadengaging position and load-releasing position, one pole piece of the lifting surface having a serrated form, and a correspondingly serrated face being associated with the permanent magnet material, to reduce the reluctance of the air gap between the faces when the permanent magnet material is lowered and the faces fit each other.

4. A lifting magnet comprising a suspending member mounted with limited vertical movement, a lifting surface adapted to be brought by lowering of the entire magnet when suspended into contact with a load of ferromagnetic material, said surface being formed by at least two pole pieces separated by non-ferromagnetic material, magnetised permanent magnet material movably mounted with respect to the pole pieces so that its flux may be directed into and out of a circuit including the pole pieces and any ferromagnetic load bridging the pole pieces, and a one-way mechanism consisting of a nut restrained against endwise movement, in quick-pitch connection with the suspending member, a ratchet operated by alternate rotations of the nut, and a cam operated by the ratchet to move the permanent magnet material into and out of circuit with the pole pieces at alternate upward movements of the suspending member as the magnet is lifted, thus alternately energising and de-energising the lifting surface.

5. A permanent magnet lifting magnet as in claim 4, comprising a housing, a cover enclosing the one-way mechanism, and an indicator movable through a hole in the cover and connected to the permanent manget material to show the position to which that material has been moved.

6. A lifting magnet comprising a suspending member mounted with limited vertical movement, a lifting surface adapted to be brought by lowering of the entire magnet when suspended into contact with a load of ferromagnetic material, said surface being formed by at least two pole pieces separated by non-ferromagnetic material, magnetised permanent magnet material movably mounted with respect to the pole pieces so that its flux may be directed into and out of a circuit including the pole pieces and any ferromagnetic load bridging the pole pieces, and a oneway mechanism consisting of a pinion, a rack associated with the suspending member and meshing with the pinion, a ratchet operated by alternate rotations of the pinion produced by alternate upward movements of the suspending member as the entire magnet is lifted, a shaft rotatable by the ratchet, and at least one crank on the shaft, the eccentricity of the crank serving to move the permanent magnet material into and out of circuit with the pole pieces, thus alternately energising and de-energising the lifting surface.

7. A lifting magnet comprising a suspending member in the form of a lifting stem, free to slide vertically by a limited amount, a lifting surface adapted to be brought by lowering of the entire magnet when suspended into contact with a load of ferromagnetic material, said surface being formed by at least two pole pieces separated by nonferromagnetic material, magnetised permanent magnet material movably mounted with respect to the pole pieces so that its flux may be directed into and out of a circuit including the pole pieces and any ferromagnetic load bridging the pole pieces, and ratchet mechanism forming a connection between the lifting stem and the permanent magnet material, inoperative in downward movements of the stem in the lowering of the whole magnet, but operative in upward movements of the stem in the lifting of the whole magnet to effect in alternate lifting movements respective movements into and out of circuit of the permanent magnet material and consequent alternate energising and de-energising of the lifting surface as the automatic result of lifting and lowering of the whole magnet.

8. An automatic lifting magnet comprising a magnetically permeable housing, a lifting face at the bottom of the housing comprising permeable section separated by non-magnetic material, a permanent magnet assembly mounted with freedom for vertical movement in the housing to move one end of the assembly towards and away from a permeable section of the lifting face and corresponding out of and into circuit making contact with the housing, the other end of the assembly maintaining further circuit making contact with the housing throughout the movement of the assembly, a lifting stem mounted in the housing with freedom for limited vertical movement to an extent greater than that of the permanent magnet assembly, ratchet mechanism operable positively by upward movements only of the stem in the housing, and means connecting the assembly to the ratchet mechanism to convert one upward movement of the lifting stern into an upward movement of the assembly and the next upward movement of the stem into a downward movement of the assembly, whereby a lifting effort applied to the lifting stem automatically moves the assembly into and out of circuit completing contact with the lifting face before the lifting stem is able to lift the housing and the assembly contained in it.

References Cited in the file of this patent UNITED STATES PATENTS Baermann May 10, 1938 Russell Nov. 9, 1954