US1736988A - Commutator cylinder - Google Patents

Description

Nov. 26, 1929. F, TUPPER 1,736,988

COMMUTAT-OR CYLINDER Filed March 18, 1927 l I 1'3 3| WITNESSES: 3O 36 I2 32 INVENTOR FranK H.Tupper MM Y A'TTORNEY Patented Nov. 2 1929 UNITED STATES PATENT OFFICE FRANK H. TUPPER, OF WILKINSBURG, PENNSYLVANIA, AS SIGNOR WESTINGHOUSE ELECTRIC d: MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA COMMUTATOR CYLINDER Application filed March 18, 1927. Serial No. 176,565.-

My invention relates to commutator cylinders and particularly to commutator cylinders in which the assembled segments are held in position'by molded insulating material.

More particularly, my invention relates to a commutator cylinder of the above-mentioned type in which the segments have a shape particularly adapted to prevent the destruction, thereof when the cylinder is rotated at high speeds.

One of the objects of my invention is to provide a method of fastening commutator segments together and so holding the segments firmly in place that the body of molded insulating material will not be destroyed as a result of the centrifugal action.

Another object of my invention'is to pro- "vide a means for increasing the mechanical strength of molded commutator cylinders and for holding the reinforcing members in place during the molding operation. v

' In the accompanying drawing,

Fig. 1 is a plan view, partly in longitudinal section, of a complete commutator cylinder embodying my invention,

Fig. 2 is an enlarged fragmentary sectional view of a portion of a commutator segment similar to those heretofore commonly used,

Fig. 3 is a similar view of a portion of a commutator segment embodying my invention, and v a Fig. 4 is a cross sectional view of the mould, one half of the commutator cylinder being shown in elevation as it lies in the mould.

Referring to Fig. 1, a plurality of segments of conducting material 1 and insulating'material 2 are alternately disposed in annular relation to form a hollow cylinder 3. Each of the segments 1 and 2 is provided with a downwardly projecting portion 40f inverted.

- ,T shape, having, in each side, a slotlike notch'or necess 5 which is substantially semicircularin shape. The recesses provide annular grooves 6 to which access is'provided by means of anentrance space 7 adjacent to the overhan 'ng outer end of the bottom crossarm 8 of the inverted T-shape portion 4. Disposed in the circular innerportion of the groove 6, and adjacent to-the active portions 1 Beef the commutator segments 1 and 2, are a plurality of fibrous flexible, reinforcing members 9, such as impregnated cord rings. The reinforcing members-9 prevent the radial displacement of the commutator segments 1 and 2, which would otherwise occur owing to centrifugal action when the commutator cylinder is rotated at high speeds.

The assembled commutator segments 1 and 2 and reinforcing members 9 are disposed around a hollow cylinder 11 of metallip material, co-axial therewith and spaced therefrom. Disposed between the cylindrical member and the assembled commutator segments is a quantity of molded insulating material 12 such as bakelite.

In the construction of a commutator cylin der according to my invention, the commutator segments l and 2 are assembled and held together by an expansible sleeve 13 (Fig. 1), which is clamped around the cylinder 3 formed by the assembled segments 1 and 2.'

of the groove 6 and cause them to be tightened, thereby still further increasing the rigidity of the cylinder 3 formed by the commutatorsegments 1 and 2.

The cylinder 3 and reinforcing members 9 are placed in a metallic mould 14 (Fig. 4). so

A quantity of moldable insulating material 12 is placed in the space between the bushing 11 and the assembled commutator segments 1 and 2. Heat and pressure are then applied, causing the moldable insulating material 12 to become solidified, thereby securing the as sembled segments 1 and 2 to the bushing 11 and forming the commutator cylinder 3. The mould 14 and the expansible sleeve 13'are then removed.

'The commutator bar most commonly used heretofore is similar in shape to the one which is shown, in part, at 1a in Fig. 2. A dovetail portion .15 of wedge sha is employed for securing or anchoring the if, thereby providing an annular portion of molded insulating material of substantially triangular section, as indicated at 16. It will be apparent, from the drawing, that this sha e of commutater bar requires only a sin quantity of molded insulating material with which to anchor the bar in place.

The shapeof commutator bar heretofore utilized frequently caused the destruction of the body of the molded insulating material when the commutator cylinder was subjected to stresses caused by centrifugal force at the operating speed of the motor. It is'apparent, from Fig. 2, that the bond between the wedgelike molded insulating material 16 and the adj acent sloping edge 18 of the end of the commutator bar 1a is subjected to a shearing stress caused by the commutator bar let being forced out radially by centrifugal action when the commutator cylinder is rotated at high speeds. The centrifugal action causes the commutator bar 1a to exert a stress nor mal to the sloping edge 18, thereby forcing the molded insulating material 16 away from the commutator bar 1a.

By my invention, I provide a recess 5 of such shape that substantially the only force upon the body of molded insulating material 21 is normal to the end surface 22 of the commutator bar and in a radial direction.

Heretofore, it has been difiicult to correctly position the reinforcing members in the grooves provided therefor since the said mem- .bers were often displaced during the'molding of the commutator bod By my invention, provide an annular groove, the entrance to which is smaller than the main portion of the groove, thereby substantially preventing the reinforcin members from bein forced out of the sai groove during the mo ding operation. In addition, the particular shape of grooveprovided by my invention permits a greater quantity of reinforcing material to be utilized than heretofore.

The commutator designer is very strictly I limited as tothe size and shape of the comof the commutator cylinder, the total depth mutator bars. The diameter and the length of the bars, and the minimum thickness of the bars at the inner or bottom side are. usually all fixed by otherconsiderations, so that they cannot be varied. I Even the depthof the' solid portion of the commutator bar, above the side rooves 6 for holding the insulating and bin ing material, is usualy predetermined by considerations respecting a reason able life of the commutator cylinder, which is limited by the depth to which the material may be worn away before the device becomes useless. Sometimes the ends of the commutator cylinder are .used for a short-circuiting device,

as in a motor which starts as a repulsion motor and then has the commutator bars short- 7 circuited to produce an induction motor during normal-running conditions and, in such case, thecommutator engineer must provide the necessary depth of commutator bar,'at

.the, edg e, as specified by the machine designer, in order to provide for the proper operation of the short-circuiting apparatus.

In other cases, the commutator cylinder maybe of the samediameter as the armature, so that commutator necks may not be utilized, and it is necessary to have a certain depth of bar in order to permit the use of large, deep slots which are milled therein to receive the soldered ends of thecommutator leads.

It is apparent, therefore, that the side notches 5 and the inverted T-shaped extension 4: at the bottom of the commutator bar 1 must occupy a very limited space in a radial direction. In view of considerations such as the foregoing, and the necessity for obtaining a suflicient amount of molded material in the notch, the triangular notch shown in Fig. 2 has been widely utilized in the past.

It will be understood that the commutator bar is'thinnest and weakest at the bottom, the very place where the inverted T-shaped projection 4 must be provided. The depth of this'projection, at a section below the inner end 23 of the slot, must be suflici'ently great to provide the necessary mechanical strength to withstand the shearing shresses imposed thereon and to' prevent the projecting portions 24 at the bottom of the commutator segments from bending sideways and producing short-circuits. It will be obvious that a in my drawings, I have shown a roundednotch, wherein the stresses are gradually transmitted to the projecting portion 24, and wherein the cross-sectional area of the extendin portion 24, at a point below the extreme 1nner end 23 of the notch, is as'great as possible.

An im ortant feature of my invention is that the ottom edge 22 of my notch is substantially horizontal, or parallel with the motor .axis, the same being preferabl assist in the retention of the portion of' the molded material filling the slot, although a very slight downward inclination in the opposite direction wouldnot be very objecun der-cut at a very slight angle in or er to" maximum strength of the pro'ecting\portions -shaped tionable-if the departure from the horition, indicated at 25 in Fig. 2. Moreover,

any slight longitudinal shifting of the insulating body 16 will produce loose bars, even though it does not cause breakage. At the same time, the rounded inner end of my slot materially increases the strength of the projecting portion 24- at the bottom of the commutator bar.

Another important feature of my invention is that the upper edge 26 of the slot is under-cut to catch the ring of cord, as well as that part of the molded material which fills the slot, so that it cannot be expelled from the slot and so that the cord ring, in particular, cannot drop out of the slot during the molding operation, as will be more specifically described hereinafter. In the preferred construction, the entire upper side 26 of the slot is under-cut at a uniform rate, so as to provide a straight side at an angle to the horizontal axis, by means of which the inner end of the slot is raised,

permitting the utilization of a deeper projecting portion 24 at the bottom of the commutator bar. 4

By the use of the under-cutting 26 in the thicker, or upper, portion of the commutator segment 1, I have materially reduced the weight of the commutator cylin der, thereby decreasing the centrifugal forces and enabling the device to withstand higher speeds than heretofore.

In making a. commutator cylinder in accordance with my invention, the cord which is intended to be used for forming the reinforcing cord rings 9 is preferably first impregnated with a synthetic phenolic resin or an equivalent substance. A suitable number of turns of the cord are then wound to formthe ring 9. The commutator segments 1 are assembled, with alternating spacers, or similar shaped mica segments 2, to form Ia cylinder which is' temporarily held in place by means of the split steel retaining ring 13.

Preferably, the assembled commutator segments are heated, as bybeing placed on a steam table (not shown), and the cord rings 9 are putin place, one end at a time, and pressed home .by means of a pressing tool (not shown), which may also be previouslyf heated,flwhereby the strands are compressed ,sufliciently to hold the same in place. By this'treatment, the resin is softened and caused to adhere, so that the cord ring is; held together and stays in place and, when cooled,'will be hard, and, moreover, such treatment compacts the cord ring and makes it possible to use more turns of cord.

- The preheating of the ring, as just demain body of moldable material 12 around the commutator, as is illustrated in Figf 4 of the drawing. I

The commutator cylinder, .with its temporary split-steel retaining ring 13, is assembled, in the form of apparatus shown in Fig. 4, in a split sleeve 30, which is usually in two parts, and is provided with an inclined seat 31 adapted to receive the correspondingly inclined outer surface 32 of the retaining ring 13 around the commutator cylinder. The split sleeve 30, containing the commutator cylinder, is then dropped into a matrix 33 having an inclined inner opening 34 to receive the inclined outer sides of the split sleeve; and the parts are firmly pressed into position, the commutator cylinder being held down by means of a hollow nut 35 engaging threads on the split sleeve.

A bottom spacing collar 36 is provided at the bottom of the matrix and a centrally disposed pin 37 extends through the whole. The metal bushing 11 is then placed on top of the collar 36 and inside of the commutator cylinder; and a carefully weighed quantity of moldable material is inserted in the mould and pressed home by means of a plunger 39, the entire aparatus being placed in a heated press and subjected to heat and pressure for a desirable length of time in order to compress and harden the moldable material.

It will be evident, from the explanation just given, that the two cord rings 9 are disposed in the slots before the commutator cylinder is stood on end and placed in the mould. Thus, one of the cord rings is so placed that it tends to drop out of the slot, and, moreover, the moldable material itself, as it enters the space from the top and flows around the bottom of the inverted T-shaped portions 4 at the bottom of the commutator bars, tends, by its movement, to drag the bottom cord ring out of its slot and dispose it ultimately at the bottom of the mould, far

to cause the cord ring to contract, thereby increasing the effectiveness of the same. It

is important that the cord ring shall fill at least enough of the inner end of the slot to obtain a purchase on the substantially horizontal bottom portion 22 of the slot, to prevent the development of outward thrusts tending to expel the molded material from the inside of vthe slot when centrifugal forces develop tending to move the inverted T-shaped extensions of the bar radially outwardly.

' By my invention, I provide a commutator cylinder of improved design which has a greatly increased mechanicai strength and which may be rotated at much higher speeds than any molded commutator heretofore invented. 1

Allhough I have herein described my invention with reference to a specific example of the construction thereof, it is apparent that my invention is not limited to the exact details shown and I desire, therefore, that only such limitations shall be placed thereupon as are imposed by the prior art or specifically set forth in the appended claims.

I claim as my invention:

1. A molded commutator member comprising a body of molded insulating material having a plurality of segments of conducting material embedded therein, said segments having circular recessesalined to provide an annular slot and a plurality of reinforcing members disposed in the said slot providing a reinforcing ring having a little more than semi-circular cross-section thereby retaining the segments against centrifugal action, said slot being of such shape that the reinforcing members are prevented from becoming displaced during the molding of the commutator.

2. A conmiutator cylinder fora dynamoelectric machine comprising a drum of phenolic condensation product having a plurality of conducting members secured thereto, said conducting members having a plurality of notches positioned to constitute an annular groove, and a plurality of retaining windings of fibrous material disposed in the said groove, thereby securing the conducting members against displacement caused by centrifugal action, said groove having apartly closed entrance whereby the retaining windings' are prevented from being accidentally displaced during the molding operation.

3. A molded commutator cylinder comprising a plurality of conducting segments and insulating segments alternately disposed to form a cylinder, a cylindrical member-of heat-hardened molded insulating material fasteningthe segments together, said segments having a plurality of recesses arranged iniannular relation to form grooves, a plurality of reinforcing members disposed in the said grooves, thereby securing the segments against radial displacement, said grooves having projecting lip portions disposed at the entrances thereof, whereby the reinforcing members are retained therein durin the molding of the device.

4. l commutator cylinder comprising bars having side grooves and inverted T-shape botposed at the inner end of each side groove,

and a cylindrical body of molded insulating material enclosing said grooves and inverted T-shaped bottom extensions. 7

In testimony whereof, I have hereunto subscribed my name this 12th day of March,

FRANK TUPPER.

my I i

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