US2645733A - Commutator - Google Patents

Description

y 4, 1953 P. A. MARSAL 2,645,733

COMMUTATOR Filed Oct. 23, 1950 2 Sheets-Shee l INVENTOR PAUL AMARSAL ATTORNEY P. A. MARSAL July 14, 1953 COMMUTATOR 2 Sheets-Sheet 2 Filed Oct. 25, 1950 INVENTOR PAUL A. MARSAL Patented July 14, 1953 UNITED STATES PATENT. OFFICE COMMUTATOR;

Paul A. Marsal, Rocky River, Ohio, asslgnor to Union Carbide and Carbon Corporation, a corporation of New York Application October 23, 1950, Serial No. 191,533

Claims.

ductivity is required of the segments, copper is' most frequently used. However, metal segment materials do not forma sufficiently strong bond with the molded insulating material to withstand the forces exerted thereon under operating conditions which may include a commutator speed as high as 15,000 R. P. M. and a. temperature as high as 200 C. For this reason, the segments, or the cylindrical body of segment material from which the segments are subsequently cut, are provided with inwardly projecting fin, ribs, or tongues which are of dove-tail or other mechanical keying configuration, and extended radially into the mass of molded insulating material in order to securely fasten the segments thereto.

While mechanical keying is reasonably effective in securing the commutator segments, it has several disadvantages. It requires machining the tongues or other mechanical lockingdevice, This not only adds considerable expense to the construction cost, but constitutes a. difiicult operation where the machining must be done on the inner surface of a small cylindrical body of segment material against which the insulating mass is to be molded. This machining operation increases in difficulty as the commutator decreases in size or the number of segments increase. In addition, any machining must be done accurately because a poor segment weight distribution is very detrimental to commutator life at vhigh speeds.-

One object of this invention is to provide a commutator of the type described wherein no special mechanical configuration is necessary to secure the segments to the mass of insulating material, the segments being secured solely by the bond between the segment material and the insulating material. I I v An additional object is to provide a commutator which, while efl-lcient and durable in use, is simple and'economical to construct.

This invention is based on the discovery that when carbon is useda a segment material and a phenol-formaldehyde condensation resin is employed as an insulating material, the resin may be molded against the carbonby the application of heat and pressure to. form a joint which is mechanically and thermally stable, even'under high-speed commutator operating conditions, without any mechanical keying.

In the drawings:

Fig. 1 i a perspective view of a cylindrical tube of carbon commutator segment material.

Figs. 2 and 2A are perspective views of two types of metal bushings suitable for use in the proposed commutator.

Fig. 3 is a perspective view of the cylindrical body of carbon commutator segment material with the metal bushing coaxially aligned therein and the interstice filled with a mas of 'molded, heat-hardened, insulating resin.

Fig. 4 is a perspective view of the assembly of Fig. 3 with the commutator segments cut therein.

Fig. 5 is an end view of the commutator shown in Fig. 4 with aportion thereof cut away.

Fig. 6 is a section on lines 6-6 of Fig. 5. Fig. 7 is a view of one type of terminal which may be employed in soldering leads to the individual segments.

Fig. 8 is a view,'parts being broken away, showing the parts of a. modified commutator assembled in preparation for the introduction of the resin into th opening around the bushing.

Fig. 9 is a sectional view, taken along the line 9-9 shown in Fig. 10, of the modified cominu tator.

Fig. 10 is an end view, parts being broken away along the line l0-I0-shown in Fig. 9, of the modified commutator.

Fig. ll i a perspective view of the fully assemf' bled modified commutator.

Referring to the drawings, a cylindrical carbon tube IU of suitable diameter is cut to the desired length of the proposed commutator segments. Preferably, the carbon tube has one side longi- I tudinally slit at H to enable it to be compressed secured within a mold and the space between the bushing and carbon tube filled with insulating material I l. The insulating material employed in this invention is .a heat-hardenabla phenolformaldehydecondensation resin, which may be combined with the usual amount of fillers, such as asbestos, paper, carbon and the like, if desired. the amount and technique of employing fillers being well known in the resin molding art.

The insulating mass M is subjected to sufficient heat and pressure to convert it to an infusible state. Preferably, the-insulating material is preformed and heated to the smoking point by means of high frequency induction heating. The

preform are then loaded into a hot transfer cylinder and forced into the mold by means of a hydraulic press. A'satisfactory molding was obtained for a commutator 1% inches in diameter and 1 inch long using the following procedure:

Insulating material Asbestos-filled,

formaldehyde molding compound (about Go% by weight asbestos) Preform weight 78 grams Mold temperature 380 Transfer cylinder temperature 380l00 F.

Plunger temperature 180 F.

Compression time 30 seconds 7 Curing time 2 minutes Curing pressure 3500 pounds gauge on a 20 ton Elmes press After removal from the mold, the unit is out longitudinally to form the commutator segments l6, separated by the slots l5. If the carbon tube Ii] was cut initially (I l) to facilitate insertion in the mold, one slot l5 should be made to coincide with this cut. A carbon commutator thus made is very strong and the segments are securely fastened to the phenolic insulating material despite the absence of mechanical keying.

Since electrical leads can not be attached to the carbon segments readily, some provision must be made for fastening the leads thereto. One method is to cut notches 2| in one end of the cylindrical carbon tube it! prior to assembling the commutator, one such notch being provided for each proposed segment lead. Each notch area is coated with molybdic acid which is allowed to dry and then fired in a reducing atmosphere at about 1200 C. for about one minute. The molybdic carbide formed is readily wet by a solderwettable metal, preferably copper 22. This copper coated notch provides an excellent terminal for soldering leads.

In the modified commutator shown in Figs. 8, 9, 1 0, and 11, a metal flang 3!, preferably of brass, is provided asa means for connecting the secure good electrical contact between the flange 3| and the'carbon segmentsSii, the flange 3| is attached to or made integral with a thin metal tube 33, preferably of brass, which fits snugly into the carbon tube In the preferred embodiment of the invention, an annular groove 35 is cut in the inner surface of the carbon tube 30, and the metal tube 33 is extended along the carbon tube 34 covering, atleast in par'uathe annular groove 35. The metal tube 33, being thin 'and'of-a malleable metal in the preferred embodiment, is made to conform to the annular groove 35 in the carbon tube 34 when the insulating, phenol-formaldehyde resin 36 is introduced under pressure into the interstices between the bushing 37 and the carbon tube 34 and metal tube 33. This serves to lock the metal tube 33 and flange 3i in place and insure good electrical contactbetween the flange 3| and carbon tube 34. When the commutator set,- ments 32 are cut, as shown in Fig. 11, the cut portions or segments 38 of the flange 3! provide a surface which can be wet by solder and to which leads may be conveniently attached.

A joint of suificient strength for most commutating conditions is obtained by hardening the phenol-formaldehyde resin, as described, against the relatively smooth inner surface of the carbon tube. If additional strength is required, annular grooves 39 may be providedin the carbon tube 34. These grooves increase the area of contact between the carbon tube and the resin, thus increasing th strength of the joint.

This application is in part a continuation of phenoldrical tube of carbon a bushing, the outer diameter of said bushing being smaller than the inner diameter of the carbon tube, filling the interstice between the bushing and tube with a phenolformaldehyde condensation resin and subjecting the same to heat and pressure until it becomes infusible, after said resin has been rendered infusible, radially slicing through the carbon tube in a longitudinal direction to form the commu tator segments, positioning a substantially annular, solder-wettable conductor, prior to the step of slicing through said carbon tube, in electrical contact with one end of said tube and in fixed relationship with said tube, and, when the carbon tube is sliced, cutting said conductor into a number of segments each of which is in electrical contact with one and no more than one carbon commutator segment.

2. A method of manufacturing commutators which comprises coaxially aligning within a cylindrical tube of carbon a bushing, the outer diameter of said bushing being smaller than the inner diameter of the carbon tube, filling the interstice between the bushing and tube with a i phenol-formaldehyde condensation resin and subjecting the same to heat and pressure until it becomes infusible, after said resin has been rendered infusible, radially slicing through the carbon tube in a longitudinal direction to form the commutator segments, coating one end of said carbon tube, prior to the step of slicing through said carbon tube, with a layer of molybdic carbide, superimposing on the molybic carbide a layer of solder-wettable metal, and, when the carbon tube lead Wires and the commutator segments 31 To is sliced, cutting said layers of molybdic carbide sulatingcore of a heat-hardened phenol-formaldehyde condensation resin, and carbon commutator segments, one end of said segments being disposed in electrical contact with a conductor capable of bein Wet by solder and adapted to receive electrical leads.

4. A commutator comprising a bushing, an insulating core of a heat-hardened phenol-formaldehyde condensation resin, and carbon commutator segments, at least a portion of one end of each commutator segment being coated with molybdic carbide on which a coating of solderwettable metal is superimposed.

5. A commutator comprising a bushing, an insulating core of a heat-hardened, phenol-form aldehyde condensation resin, and carbon commutator segments, one end of said segments being held in electrical contact with metal segments by said insulating core, said metal segments presenting a suitable surface for the attachment of leads.

PAUL A. MARSAL.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 520,264 Hoffman May 22, 1894 866,262 Coleman Sept. 17, 1907 1,757,393 Schmid May 6, 1930 2,236,257 Borchers Mar. 25, 1941 2,297,464 Fleischman Sept. 29, 1942

Claims (1)

1. A METHOD OF MANUFACTURING COMMUTATORS WHICH COMPRISES COAXIALLY ALIGNING WITHIN A CYLINDRICAL TUBE OF CARBON A BUSHING, THE OUTER DIAMETER OF SAID BUSHING BEING SMALLER THAN THE INNER DIAMETER OF THE CARBON TUBE, FILLING THE INTERSTICE BETWEEN THE BUSHING AND TUBE WITH A PHENOLFORMALDEHYDE CONDENSTATION RESIN AND SUBJECTING THE SAME TO HEAT AND PRESSURE UNTIL IT BECOMES INFUSIBLE, AFTER SAID RESIN HAS BEEN RENDERED INFUSIBLE, RADIALLY SLICING THROUGH THE CARBON TUBE IN A LONGITUDINALLY DIRECTION TO FORM THE COMMUTATOR SEGMENTS, POSITIONING A SUBSTANTIALLY ANNU-

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