US2962318A - Magnetic catch - Google Patents

Description

Nov. 29, 1960 M. o. TEETOR 2,962,318

MAGNETIC CATCH Filed Jan. 19, 1956 2 sheets-sheet 12y 52 IN1/EN TOR.

Nov. 29, 1960 M., o. TEETQR 2,962,318

A MAGNETIC CATCH Filed Jan. 19, 1956 2 SheetsSheet 2 nited States PatentMAGNETIC CATCH Macy 0. Teetor, 24 Orpheum Ave., Metaire, La.

Filed Jan. 19, 1956, Ser. No. 560,176

16 Claims. (Cl. 292-2515) This invention relates to improvements in magnetic catches for cabinet doors and the like and more particularly to a novel permanent magnet assembly for use in such catches.

Magnetic door catches of various types have been suggested heretofore in which cooperating magnet and armature units are mounted in coacting positions on door and frame members. In my prior Patents Nos. 2,508,305 and 2,690,348 I have shown one type of magnetic catch which is highly effective and provides a number of important advantages over other magnetic and non-magnetic catches heretofore suggested. One of the principal features of my prior inventions involves the movable mounting of one of the catch elements, i.e. either the magnetic element or the armature element, and also the use of a spring operatively coacting with the movable catch element for normally urging it into retracted position inwardly of its supporting door or frame member.

The present invention is directed to an improved magnetic-catch including a movable magnet assembly having a unique design which results in enhanced magnetic holding power and a highly effective catch opera-tion. As will hereinafter appear, the catch of the present invention is particularly adapted for and has been specially designed to utilize a sintered ceramic magnet material such as the composite of barium and iron oxides available commercially under the trademark Indox. Magnet materials of this type have important advantages over metallic alloy magnets for many applications of permanent magnets such as in magnetic catches. For example, Indox magnets are lighter in weight than metallic alloy magnets, have certain superior magnetic characteristics including high coercive force, are easily magnetized but difficult to demagnetize, and are made from readily available non-critical raw materials, namely, barium carbonate and iron oxide. Moreover, the catch of Ithe present invention is comparatively inexpensive but at the same time has extremely good holding power and is simple to manufacture and install.

Accordingly, a primary object of the present invention is to provide a novel and improved magnet assembly for use in magnetic catches.

A further object of the invention is to provide a novel and improved magnet unit for a magnetic catch utilizing the aforementioned magnet assembly.

Another object of the invention is to provide a novel permanent magnet assembly for a magnetic catch which is specially adapted for utilization of a powerful sintered ceramic magnet material such as the composite of barium andiron oxides known commercially as Indox.

An additional object of the invention is to provide a novel highly simplified, and inexpensive magnetic catch.

Other objects and advantages of the invention will become evident from the subsequent detailed description taken in conjunction with the accompanying drawings, wherein:

showing a catch comprising one specific embodiment of the invention as mounted in one position thereof;

Fig. 2 is a view similar to Fig. l but showing a different mounting arrangement for the catch;

Fig. 3 is an end elevational view on an enlarged scale as seen along theline 3 3 of Fig. 2;

Fig. 4 is a sectional view taken along the line 4-4 of Fig. 3;

Fig. 5 is a sectional view taken along the line 5-5 of Fig. 4;

Fig. 6 is a plan view of a blank or stamping from which the housing of the catch is formed;

Fig. 7 is a perspective view of the partially formed catch housing;

Fig. 8 is a fragmentary front elevational view of a cabinet provided with a catch comprising a second embodiment of the invention;

Fig. 9 is a large scale perspective view of the magnet assembly contained in the catch shown in Fig. 8;

Fig. 10 is an enlarged front elevational view of the complete magnet unit shown in Fig. 8;

Fig. l1 is a longitudinal sectional view taken along the line 11-11 of Fig. 10;

Fig. l2 is a transverse sectional view taken along the line 12-12 of Fig. 10;

Fig. 13 is a top plan view of a magnet assembly comy prising another embodiment of the invention;

Fig. 1 is a fragmentary sectional view of a cabinet Fig. 14 is an end elevational view of the device shown in Fig. 13; l?

Fig.' l5 is a sectional view taken along theline 15--15 of Fig. 13; and

Fig. 16 is a sectional view similar to Fig. l5 but show:- ing still another embodiment of the invention.

Referring first to Figs. 1-7, this embodiment of the invention comprises a two-way or dual acting magnet unit adapted to be mounted in several different ways. For example, in Fig. l the magnet unit designated generally at 20 is secured to the underside of acabinet shelf 21 for coaction with an armature unit in the form of asteel plate 22 secured by ascrew 23 to the cabinet door designated at 24. In Fig. 2, themagnet unit 20 is secured to lthe inner edge of the door frame designated at 26 and thearmature plate 22 is mounted in coacting relation at the inner face of thedoor 24.

Themagnet unit 20 comprises a non-magnetic housing with a permanent magnet assembly loosely retained therein for limited movement. For simplicity and economy, the housing is preferably formed from a one-piece sheet metal stamping or blank, e.g. brass or aluminum, as shown at 27 in Fig. 6. The blank 27 is folded along the dotted lines shown in Fig. 6 to provide a generally rectangular open-ended magnet-receiving recess defined by afront wall 28, a rea-r wall 29 formed from the butted edges of the folded blank, and a pair ofside walls 31. Within the recess of the housing is mounted a generally rectangular permanent magnet assembly indicated generally at 32 and comprising a laminar structure including a relatively thin rectangular wafer or plate-like magnet element 33 and a pair of thin rectangular soft steel plates orpole pieces 34 at its opposite sides.

Themagnet element 33 has a central bore oraperture 36, and the pole pieces are formed in this instance with inwardly extending depressed portions providing a pair of opposed integral bosses 37 extending into the opposite axial ends of theaperture 36 and coacting therewith for locating the magnet element and loosely retaining the same in assembled relation with the pole pieces. Theentire magnet assembly 32 is loosely disposed in the rectangular recess of -the housing for limited movement toward either of the open ends of the recess. Eachpole piece 34 extends at its opposite edges beyond the correspondingedge of themagnet element 33 to delinea pair of elongatededgewise grooves 38 therebetween, and a pair ofelongated bar springs 39 of non-magnetic spring material a-re disposed in thesegrooves 38 for resilient coaction with themagnet element 33. A pair of integral retaining ears orlugs 41 are provided at each open end of the housing recess extending inwardly 'from theside walls 31 and engaging the end 'portions of thesprings 39 thereby loosely retaining the entire magnet assembly in the housing.

As will readily be understood from Fig. 7, in assembling themagnet unit 20 one pair ofears 41 may first be bent inwardly, followed by successive endwise insertion in the recess of one of thesprings 39, themagnet assembly 32, and theother spring 39, and finally the remaining pair ofears 41 are bent over to complete the operation.

As best seen in Fig. 7, theears 41 are spaced bynotches 42 from the adjacent front andrear walls 28 and -29 so that the projecting edge portions of thepole pieces 34 may extend beyond theears 41 and the open ends of the recess for magnetically contacting thearmature element 22 in either of the mounting arrangements shown in Figs. l and 2. Thus, as shown in Fig. 4, when thedoor 24 is in closed position adjacent theframe 26, the right-hand projecting edges of thepole pieces 34 are drawn into magnetic holding contact with thearmature 22 so that theentire magnet assembly 32 is shifted toward the door thereby exing the right-hand bar spring 39 outwardly. As a result thedoor 24 is held in closed position solely by the resilient inward retracting effect of thespring 39 in the same general manner described in my aforemem tioned prior Patents Nos. 2,508,305 and 2,690,348. By reason of the slightly loose mounting of themagnet assembly 32 within the housing recess, as is evident from the clearance shown in Figs. 4 and 5, it will be understood that the magnet assembly can undergo limited angular or cooking movement in order to align the contact faces of thepole pieces 34 with thearmature 22 and thereby compensate for any slight misalignment between the door and frame members due to warpage or other causes. To facilitate such rocking self alignment of the magnet assembly, the opposite recessed longitudinal edges of themagnet element 33 which are engaged by thesprings 39 have an outwardly bulged or generally convex curvature, as at 43 (Fig. 4). As will readily be apparent, the curved edges 43 also allow thesprings 39 to bend or iiex as shown in Fig. 4 so as to permit outward movement of the magnet element for a predetermined distance.

As also seen in Fig. 4, thearmature element 22 is preferably an elongated rectangular steel plate having a singlecentral aperture 44 which receives in countersunk relation the head of thescrew 23. A pair of barbs or points 45 are formed in the armature plate at opposite 'sides of thescrew 23 to facilitate accurate and speedy installation of the armature plate while using only a single screw.

Because of the unique magnetic characteristics of Indox, it is desirable that the magnet material be proportioned to provide a relatively large magnetic area and a relatively short magnetic length. For this reason, the generally rectangular wafer-like configuration of themagnet element 33 is desirable and the element is preferably magnetized along an axis extending transversely or through the thickness of the wafer, i.e. in a vertical direction as theelement 33 is viewed in Fig. 5. Consequently, themagnet element 33 has a relatively large magnetic cross-sectional area extending along the curved edges 43 and at the same time the pole-to-pole distance or the dimension of the magnet in the direction of its magnetized axis is relatively small.

As heretofore mentioned, themagnet unit 20 comprises La two-way or dual acting unit whereby the catch can be 4mounted for operation in a plurality of diierent posi- ,tions as shown -by way of illustration in Figs. 1 and 2.

4 Thus, the catch has a wide degree of utility and is adapted to meet varying installation requirements. The sheet material forming the buttedrear Wall 29 extends integrally beyond the magnet-receiving recess of the housing and is formed with a parallel off-set bend to provide a mountingflange 46 having a plurality ofapertures 47 whereby the catch unit is rigidly mountable byscrews 48 on the door frame or other supporting structure. As previously mentioned, in the Fig. 1 installation, themovable magnet assembly 32 moves toward one of the open ends of the housing recess to contact thearmature 22, and in the Fig. 2 installation themagnet assembly 32 moves vtoward the opposite open end of the housing recess in order to contact thearmature 22. However, in each case one or the other of thespring members 39 provides the desired resilient inward retracting action which is essential to proper non-rattling operation of the catch. Another advantage of the double spring arrangement is found in the shock-absorbing action when the catch is released. For example, in Fig. 4, when thedoor 24 is opened the magnetic contact between thepole pieces 34 and thearmature 22 is disrupted whereupon the tensioned spring member 39 (at the right-hand side as viewed in Fig. 4) causes rapid resilient retraction of the magnet assembly within the housing. However, the left-hand spring member 39 cushions the inward movement of the magnet assembly thereby avoiding noisy and objectionable impact which is sometimes encountered in magnetic door catches.

Because of the somewhat limited impact resistance of magentic materials of the sintered ceramic type such as Indox, it is important to provide means for protecting the magnet material against severe impact such as might be encountered when a cabinet door is slammed. In the present embodiment of the invention, I provide abutment means or locating projections designed to insure accurate positioning of the magnet unit relative to its supporting structure and the cooperating armature unit. Thus, the sheet material forming thewall 29 has another laterally offsetintegral extension 49 which functions as an end abutment in the installation arrangement shown in Fig. 1 thereby insuring a predetermined minimum spaced relation between thearmature plate 22 on the door and themagnet assembly 32 within the housing. Thus, even if thedoor 24 is slammed with considerable force, the stop action of theabutment 49 prevents undesirable forceful impact of thearmature 22 against the magnet assembly. In fact, themagnet assembly 32 must move outwardly against the action of one of thespring members 39 in order to complete magnetic contact with thearmature 22.

For the Fig. 2 mounting arrangement, the mounting ange `46 is provided with an outwardly struck integral tang or `abutment 51 which is adapted to engage the inner edge of thedoor frame 26, as best seen in Fig. 5, thereby insuring the desired spaced relation between themovable magnet assembly 32 and thearmature plate 22 on the door. As seen in Fig. 6, thetang 51 is conveniently formed by providing partially sheared areas S2 in the housing blank 27 which are adapted to abut in continuous edgewise relation to form the tank S1 when the housing is completely formed.

Referring now to Figs. 8 to l2, the invention is illustrated in connection with a single acting or one-way catch having a non-magnetic housing (in this instance plastic) which is generally similar to the housing shown in my prior Patent No. 2,690,348. Thus, in Fig. 8 the magnet unit, designated generally at S3, is mounted on thesill 54 of a cabinet frame, and an armature element in the form of an apertured washer 55' is rigidly mounted on thecabinet door 56 by means of ascrew 57. The magnet housing has an elongatedbody portion 58 with a mountingflange having slots 59 for adjustable mounting of the unit by means of a pair ofscrews 60. Thebody 58 of the magnet housing has a centrally locatedsocket portion 61 which in this instance is generally rectangular' in shape. The movable magnet assembly (Fig. 9) ,com-

seagate a prises awaferlike element 63 of Indox or the like having acurved edge 64 and a pair ofsteel plates 66 providing pole pieces which project beyond thecurved edge 64 of the magnet element to define a spring-receiving groove in the same general manner as heretofore described. This magnet assembly is held in assembled relation by means of a non-ferrous or non-magnetic tubular pin orbushing 67 which extends through anaperture 68 in themagnet element 63 and has its opposite end portions received in a pair of sockets orcavities 69 in thepole pieces 66. In the illustrated embodiment, thesockets 69 are formed by providing integral outwardlybulged portions 71 in theplates 66. Thebushing 67 serves to locate thepole pieces 66 relative to themagnet element 63 and holds the parts in assembled relation.

As best seen in Figs. and 12, this embodiment of the invention has particular utility in situations where it is desired to utilize existing magnetic catch housings with the relatively powerful and compact Indox magnet assemblies. With magnetic catches using magnetic alloy magnet elements such as Alnico, the size of the magnet unit has been appreciably larger and, therefore, the size of the recess 6l in thehousing 58 is somewhat greater than is required for a small size Indox magnet assembly. However, by means of the oppositely extendingrounded protuberances 71 at the opposite sides of the magnet assembly, a spacer or filler effect is realized so that the relatively smaller magnet assembly can effectively be used in the relatively larger size magnet housing. In other words, theprojections 71 serve to fill the extra space within therecess 61 and locate the magnet assembly within the enlarged recess.

An elongated non-magneticbar spring member 72 extends through the groove between thepole pieces 66 of the magnet assembly and the ends of thebar spring 72 are received within the interior of thehousing 58 in abutnient with a pair ofshoulder portions 73. When the cabinet door is closed, the magnet assembly moves outwardly against the retracting action of thespring 72 to permit magnetic contact between thepole pieces 66 and the armature 53 as clearly seen in Figs. ll and 12. Otherwise, the operation of the catch is generally similar to the previously described embodiment and also similar to the catch described in my prior Patent No. 2,690,348..

In Figs. 13, 14 and 15 a slightly differentembodiment of the magnet assembly is shown comprising a wafer-like magnet element 74 andcompanion pole pieces 76 provided with aligned apertures 77 and 7S, respectively. In this case, a non-magnetictubular bushing 79 extends through the alignedapertures 77 and 78 and the ends ofv A pair` the bushing project beyond thepole pieces 76. of plastichemispherical caps 81 are tightly secured to the projecting ends of thetubular bushing 79 for holding the parts in assembled relation, thecaps 81 havinginternal socket portions 82 for receiving the ends of thebushing 79. As will readily be understood, thecaps 81 may be of any desired size in order to provide the required spacer or filler effect.

In Fig. 16 still another slight modification of the magnet' assembly is shown comprising an apertured magnet element 83 and a pair ofapertured pole pieces 84. In this instance the magnet element and the pole pieces are retained in assembled relation by means of a solidnonmagnetic pin 86 rather than a tubular pin or bushing as previously described. Also, in this instance, the external' I claim: 1. For use in a magnetic catch unit including a non magnetic housing adapted to be mounted rigidly on a supporting structure, the combination of a spring member and a permanent magnet assembly adapted to be movably contained in the housing for coaction with an armature unit, said assembly comprising a plate-like magnet element having an aperture therethrough, a pair ofv plate-like pole pieces at opposite sides of said magnet Telement, said pole pieces extending beyond at least one edge of said magnet element thereby defining a recess between the pole pieces, and means extending transversely between said pole pieces and said aperture for retaining the pole pieces in assembled relation with said magnet element, said spring member being disposed in said recess in engagement with said one edge of said magnet element and said spring member being adapted to coact with the housing for resiliently retaining the magnet assembly within the housing.

2. The combination of claim l further characterized in that said one edge of the magnet element has a generally convex curvature.

3. The combination of claim l further characterized in that said magnet element comprises a relatively thin wafer of a sintered ceramic composite of barium and iron oxides.

4. The combination ofclaim 3 further characterized in that said wafer is generally rectangular in shape with its magnetized axis extending along the thickness of the wafer whereby to provide a relatively large cross-sec.

tional magnet area with a relatively short magnet length in the direction of said magnetized axis.

5. For use in a magnetic catch unit including a non-.

magnetic housing adapted to be mounted rigidly on a supporting structure, the comb-ination of a spring member and a permanent magnet assembly adapted to be movably contained in the housing for coaction with an armature unit, said assembly comprising a plate-like magnet` element having an aperture therethrough, a pair of platelike pole pieces at opposite sides of said magnet element, said pole pieces extending beyond at least one edge of said magnet element thereby defining a recess between the pole pieces, and a pin disposed transversely in said aperture with its opposite ends extending into said pole pieces for retaining the latter in assembled relation with the magnet element, said spring member being disposed in said recess in engagement with said one edge of said magnet element and said spring member being adapted to coact with the housing for resiliently retaining the magnet assembly within the housing.

6. For use in a magnetic catch unit including a nonmagnetic housing adapted to be mounted rigidly on a supporting structure, the combination of a spring member and a permanent magnet assembly adapted to be movably contained in the housing for coaction with an armature unit, said assembly comprising a pair of parallel plate-1ike pole pieces, a plate-like magnet element interposed between said pole pieces and having an aperture therethrough, said pole pieces extending beyond at least one edge of said magnet element thereby defining a` recess between the pole pieces, means at the outer sides of said pole pieces defining a pair of outwardly projecting protuberances and a pair of inwardly opening socketv and said spring member being adapted to coact with. the housing for resiliently retaining the magnet assembly within the housing.

7.` The combinationr of claim 6v further charaeteriaada.v

7 in that said pole pieces comprise relatively thin plates having integral outwardly bulged portions providing said protuberances and said socket portions.

8. The combination of claim` 6` further characterized in that said pole pieces comprise relatively thin plates having apertures aligned with the aperture in said magnet element and with the ends of said pin extending through the apertures in the pole pieces and projecting beyond the outer sides of said plates, and said means comprises a pair of cap elements secured to the projecting ends of said pin.

9. In a magnetic catch, a magnet unit mountable on one of a pair of door and frame members for coaction with an armature unit mounted on the other of said members, said magnet unit comprising a non-magnetic housing having coacting front, rear, and side walls deiining an open-ended generally rectangular magnetreceiving recess, a generally rectangular magnet assembly loosely and movably disposed in said recess and having oppositely extending pole pieces adapted to project through either open end of said recess for contact with the armature unit, a pair of spring members within said recess extending across the open ends thereof in coacting relation with said assembly, retainer means on said housing for engaging said spring members and thereby retaining the spring members and the magnet assembly in said recess, said spring members resiliently urging the magnet assembly within said recess but said magnet assembly being movable in either direction against the action of the respective spring members for contacting the armature unit, a mounting ilange on said housing adjacent one open end of said recess for mounting the unit on a supporting structure, a first abutment means on said ange cooperable with the supporting structure for accurately positioning the magnet assembly relative to the armature unit when the magnet unit is mounted for operative movement of the magnet assembly toward said one open end of said recess, and a second abutment means on said housing adjacent thte other open end of said recess for accurately positioning the magnet assembly relative to the armature unit when the magnet unit is mounted for operative movement of the magnet assembly toward said other open end of said recess.

10. In a magnetic catch, a magnet unit mountable on one of a pair of door and frame members for coaction with an armature unit mounted on ythe other of said members, said magnet unit comprising a non-magnetic housing having coacting front, rear, and side walls deining an open-ended generally rectangular magnet-receiving recess, a generally rectangular magnet assembly loosely and movably disposed in said recess and having oppositely extending pole pieces adapted to project through either open end of said recess for contact with the armature unit, a pair of spring members within said recess extending across the open ends thereof in coacting relation with said assembly, and a pair of retaining ears extending inwardly from said side walls at each open end of said recess for engaging said spring members and thereby retaining the spring members and the magnet assembly in said recess.

11. In a magnetic catch, a magnet unit mountable on one of a pair of door and frame members for coaction with an armature unit mounted on the other of said members, said magnet unit comprising a non-magnetic housing having coacting front, rear, and side walls dening an open-ended generally rectangular magnet-receiving recess, a generally rectangular magnet assembly loosely and movably disposed in said recess, said magnet assembly including a plate-like magnet element and a pair of platelike pole pieces at the opposite at sides of said magnet element, said pole pieces extending beyond said magnet element at opposite edges of the latter thereby defining oppositely disposed elongated grooves in the magnet assembly adjacent the opposite open ends of said recess, a -pair of retaining ears extending inwardly from said side walls at each open end of said recess and adapted. to lit between said pole pieces, and a pair of elongated spring members disposed within said grooves and retained at their ends by said ears whereby said magnet assembly and said spring members are retained in said recess, said spring members resiliently urging the magnet assembly within the recess but said magnet assembly being movable in either direction against the action ot the respective spring members for projecting said pole pieces through either open end of said recess for contact with the armature unit.

12. In a magnetic catch, a magnet unit mountable on one of a pair of door and frame members for coaction with an armature unit mounted on the other of said mem bers, said magnet unit comprising a non-magnetic housing having a magnet-receiving recess, a magnet assembly movably disposed in said recess and having oppositely extending pole pieces adapted to project from said recess at opposite sides of said housing for contact with an armature unit, and a pair of spring members coacting with said housing and with said assembly for retaining the latter in the housing, said magnet assembly being movable in opposite directions against the action of the respective spring members for projecting said pole pieces into contact with the armature unit, one of said spring members resiliently urging the magnet assembly inwardly into the recess and the other of said spring members serving as a resilient cushion for the inwardly retracted magnet assembly upon disengagement thereof from the armature unit.

13. In a magnetic catch, a magnet unit mountable on one of a pair of door and frame members for coaction with an armature unit mounted on the other of said members; said magnet unit comprising a non-magnetic housing having a generally rectangular magnet-receiving recess with oppositely disposed open ends; a permanent magnet assembly movably disposed in said recess, said assembly including a plate-like magnet element having an aperture therethrough, a pair of plate-like pole pieces at opposite sides of said magnet element, and means projecting inwardly from said pole pieces into said aperture at opposite axial ends thereof for retaining the pole pieces and the magnet element in assembled relation, said pole pieces projecting from said recesses through said open ends for contact with the armature unit whereby to provide a double set of Operative pole faces; and retaining means coacting between said housing and said assembly for retaining the latter in the housing.

14. In a magnetic catch, a magnet unit mountable on one of a pair of door and frame members for coaction with an armature unit mounted on the other of said members; said magnet unit comprising a non-magnetic hous ing having a generally rectangular magnet-receiving recess with oppositely disposed open ends; a permanent magnet assembly movably disposed in said recess, said magnet assembly having oppositely extending pole pieces adapted to project from said recess through both of said open ends for contact with an armature unit in a plurality of dierent mounted positions of the magnet unit; and retaining means coacting between said housing and said assembly for retaining the latter in the housing,

l5. In a magnetic catch, a magnet unit mountable on one of a pair of door and frame members for coaction with an armature unit mounted on the other of said members, said magnet unit comprising a non-magnetic housing defining an open-ended generally rectangular magnet receiving recess, a generally rectangular magnet assembly loosely and movably disposed in said recess and having oppositely extending pole pieces adapted to project through either open end of said recess for Contact with an armature unit, a pair of spring members within said recess extending across the open ends thereof in coacting relation with said assembly, and means coacting between said housing and said spring members for retaining said spring members and said magnet assembly in said recess.

16. In a magnetic catch, a magnet unit mountable on one of a pair of door and frame members for coaction with an armature unit mounted on the other of said members, said magnet unit comprising a non-magnetic housing defining an open-ended generally rectangular magnetreceiving recess, a generally rectangular magnet assembly loosely and movably disposed in said recess, said magnet assembly including a plate-like magnet element and a pair of plate-like pole pieces at the opposite flat sides of said magnet element, said pole pieces extending beyond said magnet element at opposite edges of the latter, thereby defining oppositely disposed elongated grooves in the magnet assembly adjacent the opposite open ends of said recess, a pair of elongated spring members disposed within said grooves, and means coacting between said housing and said spring members for retaining said spring members and said magnet assembly in said recess, said spring members resiliently urging the magnet assembly 10 within the recess but said magnet assembly being movable in either direction against the action of the respective spring members for projecting said pole pieces through either open end of said recess for contact with an armature unit.

References Cited in the le of this patent UNITED STATES PATENTS 2,240,035 Catherall Apr. 29, 1941 2,508,305 Teetor May 16, 1950 2,690,348 Teetor Sept. 28, 1954 2,701,158 Schmitt Feb. 1, 1955 2,862,752 Heppner Dec. 2, 1958 FOREIGN PATENTS 607,148 Great Britain Aug. 26, 1948 631,523 Great Britain Nov. 4, 1949

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