US2410794A - Electromagnet - Google Patents

Description

2 Sheets-Sheet 1 ELECTROMAGNET INVENTORS Dm/m C. WFHGHT g, ARTHUR L.WARD

D. C. WRIGHT ET AL.

Filed Nov. 24, 1942 wm 3 mm 0v Nov. 5, 1946.

{01} ATTORNEY3 NOV. 5, 1946. c -r T AL 2,410,794-

ELECTROMAGNET Filed Nov. 24, 1942 2 Sheets-Sheet 2 INVENTORS DAVID C. WmcgHT K, 'ARTHUR457. WARD afiwf M Q@z/M 7:25 ATTORNEYS;

Patented Nov. 5, 1946 UNITED STATES PATENT OFFICE ELECTROMAGN ET David C. Wright, Euclid, and Arthur L. Ward,

Shaker Heights, Ohio, assignors to The Electric Controller & Manufacturing Company, Cleveland, Ohio, a corporation of Ohio Application November 24, 194-2, Serial No. 466,732

10 Claims. 1

This invention relates to improvements in the construction of electromagnets and particularly to improvements in the construction of magnets used for lifting and transporting material.

The most widely used type of lifting magnet comprises a hollow inverted bowl-like yoke or frame of cast steel having an integral peripheral flange and an integral central boss which defines with the flange an annular channel, the flange serving as an outer pole piece and the boss serving as an inner pole piece. An annular coil unit is mounted in the annular channel co-axial with respect to the inner and outer pole pieces, and the channel opening is sealed by an annular nonmagnetic sealing plate or inner bottom plate tightly fastened to the inner and outer pole pieces and forming with the magnet frame a complete enclosure for the coil unit.

To protect the sealing plate and the coil unit of this common type of magnet from damage during operation ofthe magnet, a relatively thick annular protective plate or outer bottom plate is usually mounted beneath the sealing plate. Generally, the protective plate is formed from high manganese steel because of the high strength and the good abrasive resistant and non-magnetic properties of that alloy. It is common practice to hold the protective plate in position against the sealing plate by the clamping action of annular shoulders on inner and outer pole shoes which are fastened to the magnet frame and which engage the faces of the inner and outer pole pieces, respectively. The protective plate i clamped in place because high manganese steel is too hard to be machined or drilled and can be welded only with great difficulty. Furthermore, welded connections between the manganese steel protective plate and the magnet frame would be subjected to destructive forces due to transverse blows against the magnet and also would not be able to withstand the stresses resulting from thermal expansion and contraction consequent upon the use of the magnet for lifting hot iron or steel.

The inner pole shoe of such prior magnets is usually a thick disc having its upper surface fitted against the face of the inner pole piece with a tongue and groove or similar joint. Both pole shoes are formed of magnetic iron or steel and in addition to holding the protective plate in position also serve to carry the working flux to the load and thereby protect the pole pieces from abrasive wear. Some magnets have an axial opening extending from the top of the magnet frame through the inner pole piece and central openings.

aligned with a corresponding opening through the inner pole shoe to assist in cooling the magnet and to permit the drainage of water from a dished portion of the top surface of the magnet frame.

Heretofore, both pole shoes generally have been attached to the magnet frame by bolts extending through aligned openings in the pole shoes and. the magnet frame. The use of bolts not only requires the accurate drilling of a great number of holes through large castings, but also, due to the air gaps around the bolts, reduces the effective area of the magnetic circuit of the magnet and thereby prevents the attaimnent of maximum lifting capacity. Furthermore, loosening of the bolts due to the stretching thereof causes a further reduction in the lifting capacity because of the resultant increase in the air gap between the pole shoes and the magnet frame, and such loosening once it starts is aggravated by the repeated slamming of the pole shoes against the pole faces and bolt heads due to alternate energization and deenergization of the magnet. Alloy steel bolts withstand harder and longer usage than soft iron or steel bolts before they stretch enough to cause a large loss of lift, but, because of the inherently poor magnetic properties of suitable alloy steels, the reluctance of the magnetic circuit is increased by substitution of alloy steel bolts for iron or soft steel bolts. Another disadvantage in the use of bolts as a fastening means for the pole shoes is the difiiculty of removing them from old magnets in order to replace the pole shoes or to inspect the coil, in many cases it being necessary to cut off each bolt because of the rusting and jamming of the nuts.

This invention in one of its embodiments avoids all of the disadvantages of the bolted construction by providing welded connections between the pole shoes and the magnet frame. Changing the bolted construction to a satisfactory all-welded construction, however, has heretofore presented insupera-ble difficulties, particularly with respect to the inner pole shoe. For example, welding cannot be accomplished along the outer periphery of the inner pole shoe because the outer periphery is, in contact only with the protective plate which is not fastened to the magnet frame. Attempts have been made to weld the inner pole shoe to the bottom edge of the innerpole piece at the junction of the aligned However, if in the design of themagnet the central openings are made large enough to permit welding at this point, a magnet of given diameter must have a reduced magnetic circuit area or a magnet having a larger outside diameter than necessary must result. Furthermore, a weld near the center of the inner pole shoe and close to the working face of the magnet cannot be made strong enough to resist the destructive forces caused by the transverse blows to which the pole shoe is subject during the usual rough handling of the magnet and is subject to abrasive action.

In accordance with this invention in one of the illustrative forms shown a centrally disposed, upwardly projecting portion of the inner pole shoe of a lifting magnet fits tightly into and extends through a central axial opening in the inner pole piece and the magnet frame. The iron of the pole shoe replaces substantially all of the magnet circuit area lost due to the opening. The upwardly projecting portion of the inner pole shoe terminates near the top of the magnet frame, and the top surface thereof is securely welded to the magnet frame. A wedge fit is made between the magnet frame and the inner pole shoe substantially throughout the main flux path by tapering all or a portion of the mutually engaging surfaces of the two parts, and a drive fit is made between the telescoping portions that are not tapered. This construction and resulting cooperation of parts not only prevents the transmission to the weld of shearing and other forces caused by blows against the lower portion of the inner pole shoe, but also results in a joint of extremely low reluctance between the magnet frame and the inner pole shoe. The coil unit is secured and sealed in the annular coil space in the magnet frame by continuous welded connections between the inner and outer pole pieces and the sealing plate. The outer pole shoe is welded to the outer pole projection, thus completing the all-welded construction.

Generally, in order to obtain a joint of low magnetic reluctance between two pieces of iron, the abutting surfaces of the pieces are very accurately machined; Heretofore, the joint between the pole shoes and pole pieces of large lifting magnets has not been of as low reluctance as desired because of the excessive cost of accurately machining such large castings. The novel magnet construction of this invention whereby a portion of the inner pole shoe is fitted tightly into and extends through an axial opening in the magnet frame not only permits the pole shoe to be easily and securely welded to the magnet frame, but also, by virtue of the same cooperative relation between the inner pole shoe and the magnet frame, results in a joint of lower reluctance between the pole shoe and the inner pole piece of the magnet frame than can be obtained without accurate machining. Both the drive fit obtained as a result of the cooperation between the cylindrical portion of the inner pole shoe and the cylindrical portion of the axial central opening in the magnet frame and the wedge fit obtained as a result of the cooperation between the tapered surfaces of the two parts cooperate in producing an extremely low reluctance joint substantially through the major flux path of the magnet. Only an extremely small portion of the mutually engaging surfaces of the inner pole piece and the inner pole shoe are in contact with the. usual butt joint.

An object of this invention is to provide a new and improved electromagnet suitable for use as a lifting magnet.

Another object is to provide an electromagnet in which the inner pole shoe is attached to the magnet frame in such a manner that the attachment will resist all the forces likely to damage it and wherein the magnetic reluctance of the joint between the inner pole shoe and the magnet frame is minimized.

A more specific object is to provide a substantially all-welded lifting magnet.

Another object is to provide a lifting magnet in which the coil unit is sealed and protected without the use of bolts or screws.

A correlative object is to provide a circular lifting magnet in which both the inner and outer pole shoes are Welded to the magnet frame.

Another object is to provide a lifting magnet in which a portion of the inner pole shoe extends into and substantially through an axial opening in the magnet frame.

Another object is to provide a lifting magnet in which an inner pole shoe is welded to the top of the magnet frame.

Other objects and advantages will become apparent from the following specification wherein reference is made to the drawings, in which Fig. 1 is a side elevation, partly in vertical section, of a lifting magnet embodying the invention;

Fig. 2 is an enlarged fragmentary vertical section of the central portion of a modification of the lifting magnet of Fig. 1, and

Fig. 3 is a diagrammatical sectional view showing an assembly step preliminary to welding.

The lifting magnet illustrated in Fig. 1 comprises a circular magnet frame Ill having integral therewith a cylindrical inner pole piece l2 and. an annnular outer pole piece M. The pole pieces l2 and M form downwardly projectin concentric extensions of the frame l0 and define an annular winding space l6 therebetween which is open at the bottom to receive an annular coil unit la. The pole pieces l2 and l 4 are formed integral with the frame Ill since greater strength and a better magnetic circuit are thereby obtained. The inner p-o-le piece i2 is in the form of a hollow cylinder with a central axial opening l9 extending through the magnet frame It. Suitable supporting lugs I! may be cast integral with the magnet frame If) as shown.

The coil unit is may be of any suitable type, and, for purposes of illustration, comprises a sleeve 20 which fits over the periphery of the inner pole piece l2, an annular flange 22 welded to the upper end of the sleeve 20, and a plurality of suitably insulated windings 24, each of said windings being formed of strap copper, the turns of which are insulated in the usual manner. The sleeve '23 and the flange 22 are preferably of magnetic iron or steel so that they add to the area of the magnetic circuit of the magnet.

The coil unit 58 is supported and sealed in the winding space l6 by an annular sealing plate 26 which has its inner peripheral edge fastened in a shouldered recess in the lowerouter peripheral edge of the pole piece [2 by a continuous weld 28 and which has its outer peripheral edge fastened in a similar shouldered recess in the lower inner peripheral edge of the outer pole piece M by a continuous weld 3B. The sealing plate 26 may be made of non-magnetic metal such as brass or a chromium steel alloy or it may be made of magnetic iron or steel to facilitate welding. The total flux shunted by a magnetic steel inner bottom plate of sufilcient thickness to support the coil unit has been found to be very small.

A conventional terminal and sealing arrange; ment for the coil unit i8 is illustrated. A pair: of circumferentially spaced current conducting leads 3|, only one of which is shown in Fig. 1, extend from the windings 24 into a chamber 32 of a terminal box 34 formed integral with the frame In and are attached respectively to circumferentially spaced bolts 36 which pass through an integral dividing wall 38 into a chamber 40 of the terminal box 34. Suitable electrical connections (not shown) are made to the bolts 35 in the chamber 40 from a source of power through a pair of circumferentially spaced water tight plugs 42. After the coil unit 18 is in place and the sealing plate 26 is attached, the chamber 32 and the winding space It around the coil unit l8 are preferably filled in a well-known manner with a suitable water-proof insulating compound (not shown). Openings in the top of the terminal box 34 which provide access to the chambers 32 and 48 are closed by pipe plugs 44 and 45, respectively.

An annular non-magnetic protective plate 43 preferably cast from high manganese steel has annular finished areas on its upper surface near its inner and outer peripheries which abut against the inner and outer marginal areas of the bottom of the sealing plate 26 and is held in position by the clamping action of an inner pole shoe 48 and outer pole shoe 5!). The protective plate 4'5 is preferably of hollow ribbed construction as suggested at the left in Fig. 1 to provide greatest strength and rigidity for unit weight and to insure a sound casting, and clearance 52 is provided at the top of the ribs so that finishing of the entire top surface of the plate 46 is not required.

The top inner marginal portion of the outer pole shoe El! is cut away to form an annular shouldered recess 54 which receives the outer marginal portion of the protective plate 45, and has an upwardly extending annular flange 55 around its outer periphery which fits into an annular shouldered recess 58 cut in the outer periphery of the outer pole piece l4 adjacent its lower face. A suitable Welded connection 65 is made between the pole shoe 59 and the pole piece l4 along the top of the flange 56. The top surface of the pole shoe 50 thus is held tightly against the face of the pole piece l4 while the shouldered recess 54 assists in holding the protective plate 45 against the sealing plate 26. Bolt carrying flanges and bolts around the periphery of the magnet are thereby rendered unnecessary.

The inner pole shoe 4% comprises a lower cylindrical or central disc portion 62 the top outer marginal area of which is cut away to form an annular shouldered recess 53 which receives the inner marginal portion of the protective plate 48 and also comprises a centrally disposed, upwardly extending projection 64 which fits into the axial opening [8 in the center of the magnet frame id. The projection 54 comprises a lower upright frusto-conical portion 68 which fits tightly and wedges into a complementary frusto-conical portion iii of the opening 59. Above the frusto-conical portion 63 of the pole shoe the projection ea has a substantially cylindrical portion 1! which fits tightly with a drive fit into a complementary upper cylindrical portion '53 of the opening 49. The diameter of the opening I9 at the lower face of the pole piece I2 is preferably just slightly smaller than the outside diameter of the pole piece [2 so as to leave as small a butt joint as possible between the pole shoe 48 and the frame ID.

A suitable welded connection '52 is made be tween the top of the portion 64 of the inner pole shoe 48 and the magnet frame I 0 substantially at the top of the opening IS. The pole shoe 48 has a small central axial bore 14 which assists in cooling, permits drainage from the top of the magnet frame, and serves as a bolt opening during assembly in a manner to be described.

Because of the wedge and drive fits between the inner pole piece l2 and the inner pole shoe 48, forces due to transverse and upward blows against the pole shoe 48 are not transmitted to the welded connection 12, and because of the drive fit alone, the weight of the inner pole shoe 48 is not supported entirely by the welded connection i2. When the magnet is energized and the pole shoe 48 is subjected to the strongest downward forces, the pole shoe 43 is, of course, held strongly against the magnet frame It} by magnetic attraction and no downward forces are transmitted to the weld T2. Furthermore, even though the pole shoe 48 is only attached to the magnet frame ii) near the center, the outer marginal portion of the pole shoe 48 cannot be bent away from the protective plate 46 as a result of the strongest forces likely to be encountered in service since the thickness of the pole shoe 43 increases progressively inwardly due to the frusto-conical portion 68.

The welded connection 12 can be made strong enough to support the weight of the pole shoe 48 without the drive fit. For example, in the modification: Fig. 2, an inner pole shoe it has a lower cylindrical portion 48 and an upwardly extending centrally disposed portion entirely of upright frusto-conical shape which is inserted in a cooperating frusto-conical axial opening 82 through an inner pole piece 83 integral with a magnet frame 84. The magnet of Fig. 2 differs from that of Fig. 1 principally in that the complementary frusto-conical surfaces of the inner pole shoe and the inner pole piece are relatively larger in Fig. 2 and in that the complementary cylindrical surfaces for a drive fit are omitted.

It may be noted in Fig. 2 that the lesser angle of convergence upwardly of the complementary frusto-ccnical surfaces eliminates the necessity for fitted cylindrical surfaces such as on the portion Ii and adjacent frame portion of Fig. l. in order to prevent horizontaliy applied forces on the inner pole shoe l6 from tending to break the weld l2. trated in directions approximately normal to the frusto-conical surfaces.

Referring to Fig. 3, which shows one method by which the inner pole shoe 48 may be positioned against the magnet frame it": preparatory to making the weld it, a bar 86 laid across the top of the magnet frame :8 supports the pole shoe 48 during assembly by means of a threaded bolt 88 which passes through the axial bore 14 in the pole shoe 48 and opening 89 in the bar 86. A head 96 of the bolt 83 abuts against the lower surface of the pole shoe i8 and a nut 92 is threaded onto the end of the bolt 88 above the bar 88. By turning the nut 92 the inner pole shoe 48 is lifted into position and great pressure between the pole shoe 48 and the magnet frame i5 is thereby exerted.

Due to the large force by which the pole shoe and the frame It are urged together by this procedure, full advantage is taken of the wedge fit between the complementary tapered portions 68 and m of the projection 64 and the opening IS respectively, and the drive fit is easily made between the cooperating portions ii and E3 of the Such forces in Fig. 2 would be concenprojection 66 and the opening l9, respectively. The tight fitting of the projection 65 into the Opening l9 not only prevents the transmission of all destructive forces to the weld 12, but also greatly reduces the reluctance of the magnetic circuit of the magnet. After the pole shoe 63 and the magnet frame I i] are tightly clamped together by the action of the bolt 83, part or parts of the weld 72 are made and then the bar 85 is removed. The weld l2 then can be completed. The same method of assembly, of course, is applicable to the modification of Fig. 2, it being noted that in Fig. 2 it is essential, due to the absence of a drive fit, to have the car 86 so shaped that the weld 12 can be partially effected before the bar 85 is removed.

Removal of the inner pole shoe 48 and the outer pole shoe 59 can be accomplished by chipping or otherwise machining out the welds 60 and 72, respectively. It has been found that such prooedure is much simpler than the loosening of a great many nuts which have become firmly attached to the usual pole shoe bolts during the period of service of the magnet.

We claim:

1. A lifting magnet comprising a magnetic frame member having an annular peripheral flange projecting downwardly therefrom, an axially directed opening through said frame within and spaced from said flange and having a tapered portion, an inner or central pole unit projecting downwardly from said frame and having a tapered portion fitting tightly into said tapered portion of said opening, said pole unit fitting into the other portion of said opening, the peripheral walls of said portions constituting the major fiux path between the frame member and the inner pole unit, and a welded connection between said pole unit and said frame at the top of said pole unit.

2. An electromagnet having an inner pole piece, an outer annular pole piece surrounding said inner pole piece and defining a winding space therebetween, an axially directed opening through said inner pole piece and having a tapered portion, and pole shoes associated with said pole pieces respectively, the pole shoe associated with the inner pole piece having a tapered portion extending into said tapered portion of said open ing and in firm face to face contact therewith and having a projection fitting into the other portion of said opening, and means located at the end of said projection remote from the face of said inner pole piece for holding said pole shoe and said inner pole piece together in flux conducting contact.

3. An electromagnet comprising a frame having spaced inner and outer polar projections defining a winding space therebetween, an axially directed opening in said inner polar projection extending through said frame, at least a part of said opening being tapered with the largest area of said opening nearest the face of said inner polar projection, and a pole shoe associated with said inner polar projection and having a portion fitting into said opening, at least a part of said pole shoe being tapered and fitting tightly into the tapered part of said opening with its peripheral wall constituting a principal flux path between the frame and said pole shoe.

l. A lifting magnet comprising a frame having concentrically arranged inner and outer polar projections defining a winding space therebetween, a frusto-conical opening in said inner polar projection extending through said frame, the

largest cross-sectional area of said opening being nearest the lower face of said inner polar projection, a pole shoe extending below the lower face of said inner polar projection and having a frusto-conical portion fitting tightly into said opening, and means at the upper end of said pole shoe for securing said frame and said pole shoe in flux conducting contact.

5. A lifting magnet comprising a frame having concentrically arranged inner and outer polar projections extending downwardly therefrom and defining an annular winding space therebetween, an axially directed cylindrical opening extending through said inner polar projection and said magnet frame, said opening having a tapered counterbore extending inwardly from the lower face of said inner polar projection, a pole shoe associated with said inner polar projection and having a tapered portion extending into and fitting tightly against the counterbored portion of said opening and a cylindrical portion fitting into the remainder of said opening, and a securing connection between said frame and the top of said pole shoe.

' 6. A lifting magnet comprising a magnetic frame member provided with an inner depending pole piece having a bottom working face, a winding surrounding said pole piece and having its lower face surface above the lowermost portion of said bottom working face, an axially directed opening through said pole piece, a homogeneous and unitary magnetic pole shoe having a portion extending outwardly from the lower peripheral edge of said opening and below the said bottom working face and also having a portion fitting into said opening and with its peripheral surface in intimate flux conducting relation to surfaces defining said opening, said surfaces constituting the major flux path between the frame member and pole shoe, and a securing connection entirely located at the end of said pole shoe remote from said working face and holding said pole shoe and said pole piece together in said flux conducting relationship.

7. A lifting magnet comprising a magnetic frame member provided with an inner or central depending pole piece, an axially directed opening extending through said pole piece and said frame member, a homogeneous and unitary pole shoe having a cylindrical portion fitting snugly into said opening and a lower portion extending outwardly from the periphery of said opening, and a welded connection entirely located substantially at the outer marginal portion of said cylindrical portion at the end thereof remote from said lower portion for holding said pole shoe and said frame member together in fiux conducting relationship, said cylindrical portion having a diameter which is at least equal to one-fourth of the diameter of said lower portion thereby preventing stretching of said cylindrical portion due to the weight of said pole shoe and the attracted magnet load and reducing the loading per lineal unit of said welded connection.

8. A lifting magnet comprising a frame having spaced inner and outer polar projections defining a winding space therebetween, an axially directed opening in said inner polar projection extending through said frame, a homogeneous and unitary pole shoe extending into said opening and in drive fitted fiux conducting relation to surfaces defining said opening to provide a principal flux path from the inner polar projection to the unitary pole shoe for conducting to. a load efficiently the flux created by said magnet, and means further se- 9 curing said pole shoe to said frame and located at the inner end of said pole shoe.

9. A lifting magnet comprising a magnetic frame member having upper and lower face surfaces, an opening in said frame member extending between said surfaces, a homogeneous and unitary pole shoe forming the principal means for conducting flux i mm the central region of the magnet to a load and having a first portion extending into said opening and in drive fitted flux conducting relation to surfaces of said frame defining said opening, said surfaces constituting the major flux path from the frame to the unitary pole shoe, a second portion extending outwardly from the axis of said opening in flux conducting relation to said lower surface, and a securing connection between said first portion and said frame member located at the top of said first portion and holding said pole shoe and said frame member together in said flux conducting relation.

10. A lifting magnet comprising a frame having spaced inner and outer polar projections defining a winding space therebetween, an axially directed opening in said inner polar projection extending through said frame and having a tapered portion and cylindrical portion, a homogeneous and unitary pole shoe extending into said opening and having a cylindrical portion and a tapered portion, said tapered portions of the opening and pole shoe fitting together in fiux conducting relation, and the wall of said cylindrical portion of the opening and the cylindrical wall of the pole shoe being drive fitted together, and constituting a principal flux path for conducting to a load substantially all of the flux created by said magnet.

DAVID C. VJ RIGHT. ARTHUR L. WARD.

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