US1807794A

US1807794A - Biuish ajjd current collector

Info

Publication number: US1807794A
Authority: US
Publication date: 1931-06-02
Anticipated expiration: 1948-06-02

Description

June 2, 1931. H. D. MUNDAY 1,807,794

BRUSH AND CURRENT COLLECTOR Filed May 1a, 1928 Fi -1 E2 30 Brush containing /approxi.mately abrasive INVENTOR. BY [170mm flMzmday u ATTORNEY Patented June 2, 1931 HORACE D. MUNDAY, OF SCHENEG'IADY, N WV YDR-K BRUSH AND CURRENT COLLECTOR Application filed May 18, 1928.

This invention relates to current collectors for dynamo electric machines, and one object of the invention is to provide an improved v.,truin; device for connnutators or slip rings of such machines. further object is to provide an improved means for stabilizing the operation of collectors, particularly for preventing chattering or vibrating of the collector brushes and connected parts. A further bject of my invention is to provide an abrave brush which will act as a truing or stabilizing device for connnutator or collector rings. A. further object is to provide an im- .uprovcd brush which will automatically true 11p a commutator or collector ring and will then keep it true.

Many commutators or collector rings from one cause or another sooner or later get out of ,round. .Vhcn the rotor part of the machine is small it is generally removed from the frame of the machine and the commutator turned in a lathe. hen the rotor is large, some form 01 portable grinding wheel or lathe turning tool is used to true up the com- "mutator without removal of the rotor from its frame. In either case the machinemust be idle for a considerable length of time.

Sand paper and abrasive blocks applied to the commutator by hand are expedients that will help commutation to some extent, principally by cutting down the high mica that generally appears at the flat spot of the commutator, but having little or no elfect so far .as the elimination of the flat spot is concerned. Also, it is usually necessary to repeat this expedient every few days.

Undercutting of the mica to a depth of of an inch or more is of some help in avoiding the formation of flat spots in the commutator. In small machines, however, there is a tendency for dirt to collect in the slots of the commutator and burn out the armature, thus making the slotting of the commutator-s of small machines of doubtful value.

Another way for preventing formation of flat spots in commutators is to carefully or experimentally select a brush to fit each particular machine. This, however, is obviously uneconomical and in many cases unsuccess- 50 ful.

Serial No. 278,749.

Excessive pressure on the brush has some tendency to prevent the formation of flat spots, but this remedy causes heating of the commutator with a considerable loss of power through brush friction.

lVhen a portable turning tool is used to turn the commutator of armature, without removal of the armature fromthe machine, the turning speed employed is considerably lower than the normal running speed of the armature. This may cause the commutator, though true at the turning speed, to be out of true at the running speed. Even when the commutator is turned in a lathe it is often found to be out of true at the running speed.

lVhen a. commutator is trued with a grinding wheel, in accordance with the methods heretofore employed, there is a tendency for the wheel to cut alittle deeper as it passes from one commutator bar to .anothe This makes the bar relatively high in the middle and low on the edges. Vhen such a commutator in use there is at first a burning at the rear edge of the bar, due to the breaking of the current at that edge. Due to the fact that the surface ofthe bar inclines inwardly toward the axis of the commutator near the edge of the bar, the current between the brush and the bar is interrupted with a slow, arcing break instead of a quick, snappy break. This causes the bar to burn away much faster than it would if it had a true cylindrical outer surface.

None of such devices in use at the present time are automatic, at least in the sense that they can be left alone for hours or days at a time.

By employing a brush formed in accordbeen trued up by my improved brush, the brush may be removed from the machine and an ordinary brush substituted therefore, or, if desired in certain cases, my improved brush may be allowed to remain in the machine, in which case it will continue to function as a current collector and will also serve to maintain the commutator true.

In the embodiment of my inventionherein disclosed, my improved brush is formed of conducting material, such as carbon, and abrasive material, such as carborundum, mixed in certain proportions with the conducting material. The carborundum or similar material causes the brush to have an abrasive action on the commutator which, if the brush contains a sufiicient amount of abrasive, has a truing action on the commutator. In case, for example, the commutator has a fiat spot, the brush when used in the usual brush holder will press more lightly on the low spots of the commutator than on other parts, with the result that, while all parts of the commutator may be ground downto some extent by the abrasive brush, the high parts of the commutator will be ground down faster than the low parts, and the commutator will ultimately become true. The different grinding effect on different parts of the commutator is believed to be due for the most part to the friction between the brush and the brush box or between the stationary and moving or brush feeding parts of the brush holder. The brush, acting under the influence of the brush feeding means, tends to remain in contact with the commutator surface and to move down into the low spots as the low spots pass on to the brush and to move up on to the high spots as the high spots pass under the brush. Both the inward and outward motions of the brush are opposed by the friction above referred to. With the brush feeding means exerting a constant force tending to press the brush against the commutator, the reaction force which the low spot of the commutator exerts on the brush to stop its further motion into the low spot is the difference between the force feeding the brush forward and the friction, whereas when the brush rides up onto a high spot of the commutator the force exerted by the commutator to push the brush back is the sum of the feeding force and the friction. In other words, to stop the forward motion of the brush, a force of one value is necessary, and to cause a backward motion of the brush a force of greater value is necessary. Each time a high spot of the commutator passes under the brush the pressure of the brush against the commutator and the abrasive action of the brush is increased, with the result'that the high spots of the commutator are ground faster than the low spots.

In certain cases the mass or inertia of the brush and moving parts of the brush holder may have a beneficial truing efiect, as when it is desired that a forwardly moving brush shall hurdle a flat spot in a commutator; in other cases the mass or inertia may favorably afiect the action of a backwardly moving brush, as when the brush is being used to cut down a high commutator bar.

The above described actions result in a clifferential grinding effect which tends to true the commutator. Due to the fact, however, that the brush is also used as a current collector, there is an opposing tendency, due to sparking or arcing between the brush and commutator, to cause the commutator to become more out of round, and when the abrasive action of the brush is relatively slight I find that the tendency of the commutator to become out of round more than counteracts the truing effect due to the abrasiveness of the brush. However, with brushes of greater abrasive content, the truing effect predominates and the commutator ultimately becomes true. In practice I find'that a brush containing of carbon and 30% of carborundum will serve, when employed in the usual brush holders, to true a commutator or collector ring and maintain it true. Other desirable effects may be obtained in brushes whose composition varies from somewhat less than 10% of abrasive to somewhat more than 70% of abrasive. With brushes whose abrasive content is considerably less than 10% there is, or is likely to be, difficulty in truing a commutator in a satisfactory time limit, as the grinding down of the high partof the commutator may be scarcely greater than the burning deeper of the flat spot, unless the corrective process is speeded up (as by the substitution of a stiffer spring for the ordinary brush-holder spring), or the rate of deterioration reduced (as by taking off a portion of the load of the electric machine). l/Vhen the brush is formed from a homogeneous mixture of carbon and abrasive, the presence of a very large proportion of abrasive has the effect of rendering the brush, made by some manufacturing processes, soft so that it wears away quickly. With brushes prepared inthis manner it is therefore advisable to limit in some cases the proportion of abrasive employed, particularly where the brush is intended to remain in the machine after the truing operation is completed; however, in other cases the softer brush resulting from a larger abrasive content may be of distinct advantage. For instance, a hard abrasive brush in a brush holder with a weak spring may give an undesirably slow abrasive action; the substitution for the hard abrasive brush of a softer abrasive brush resulting to the greater softness that is the result of the greater number of abrasive particles. I am aware that brushes containing a small percentage of abrasive have been employed for cleaning a commutator but so far as I am aware no brush has ever'been employed with sufiicient abrasiveness to permit its use for truing a commutator. A brush containing 10 parts abrasive and 90 parts carbon is believed to contain about 100% more abrasive than has been employed in present practice.

Other objects and advantages of my invention will appear from the following description taken in connection with the accompanying drawings wherein Figure 1 shows, in side elevation, one form of abrasive brush, the brush being mounted in a brush holder.

Figure 2 is a view similar to F i 'ure 1, but showing a modified form of brush.

Figures 3 and 4 show, in side elevations taken respectively at right angles to one another, a preferred and still further modified brush mounted in a brush holder of the same general type as that shown in Fi ure 1, and

Figure 5 shows, in side elevation, a still further modified form of brush in nintcc. in a brush holder of a different type from that shown in Figures 1 to 1.

The brushes shown in the drawings contain conducting material and abrasive material in approximately the propoztions above set forth. The brush is preferably formeo of a homogeneous consolidated llllfltlll'G of those materials, although it is essential only that the active end, that is, the end which bears against the commutator 10. be formed of these materials. For the conducting material I may employ carbon or graphite and in certain cases I may employ a composition consisting of copper and graphite formed in a manner well known in the art. As the abrasive ingredient of the composition, I may employ carborunduin, alundum or other suitable material.

Figure 1 shows a brush 12 having its upper end 13 at right angles to the side 14 and to the walls of the brush box 15. This end 13 is engaged by the pressure finger 17 which forces the lower end against the commutator 10. It will be noted that the brush in Figure 1 is positioned at a considerable inclination to the radius of the commutator. The reaction of the commutator against the active end 18 of the brush forces the abrasive brush against the right hand side of the brush box 15, as viewed in Figure 1, and the friction between the brush and brush box results in the differential grinding effect as described. If desired, suitable means may be provided for increasing the friction'between the brush and brush holder, as by coating the brush with material which forms a friction surface.

In Figure 2 the top end of the brush,

which is engaged by the pressure finger 17,

is inclined, so that the finger not only forces the brush downwardly through the brush box but also forces the brush laterally against the side of the brush box and supplies the requisite friction for the differential rinding operation.

In the brush shown in Figures 3 and 4c the inclined upper surface 34 against which the fin gcr 17 presses is formed by a metal member 35 secured by a rivet or other s table means to the upper part of one of the wider sides of the body portion of the brush. The men'iber 35 has an upwardly extending ton ue 36 which is engaged by the pressure linger 17. If desired, the member 35 may be formed of deformable metal, so that the tongue 36 may be bent to any inclination desired, thereb" adjusting the f *iction between the brush and brush holder. The inclination of the tongue to the sides of the brush may vary from 30 to In the form of brush holder illustrated in Figure 5, the pressure finger 10, shown in transverse section, of a type which extends entirely over the brush, and the brush ll, employed in this type of brush holder, comprises a member l2 secured to one of the narrower sides of the brush body portion.

In certain cases, instead of employing an abrasive brush, I may employ a block of abra sive material dimensioned to fit the brush holder box or other brush guide. Such an abrasive block would not be a conductor and would therefore not be employed as part of the current collector. If, however, the machine is provided with four or more brushes the abrasive block may be substituted for one of the brushes and the machine may continue to function, the remaining brushes carrying the load.

Imake no claim herein broadly to the idea of truing a commutator by causing an abrasive member to be pressed with greater pressure against high parts of the commutator than against low parts as this is made the subject of my Patent No. 1,727,112, granted September 3, 1929. Other forms of the generic invention herein disclosed are described in my copending applications of even date herewith, namely: Serial No. 278,748, wherein the abrasive or truing memher is caused to move tangentially of the commutator during the truing operation; Serial No. 278,751, wherein among other embodiments of the invention wedge shaped members are employed in the brush box for securing the desired greater pressure on the high parts of the commutator; Serial No. 278,752 wherein utilization is made of a canting or locking engagement betwee" two cooperating members for effecting the high abrasiy e pressure on the high parts and Serial No. 278,7 50 wherein a number of other embodiments of the generic invention are disclosed.

Having now described my invention, what I claim and desire to secure by Letters Patent is:

1. In a current collecting device designed automatically to eliminate flat spots from a commutator, the combination with said commutator of a brush containing, in excess of 10 7 structed and arranged as to cause said brush to press against low spots of said commutator with substantially less pressure than against high parts of the commutator, whereby during rotation of said commutator the high parts thereof are abraded to the level of the low parts.

2. In a current collecting device designed automatically to eliminate fiatspots from a commutator the combination with said commutator, of a brush having an abrasive action greater than that of a brush composed of a consolidated mixture of about 90 per cent. graphite and 10 per cent. carborundum, a brush holder supporting said brush and pressing the same into contact with the commutator, the brush, brush holder and commutator being so constructed and arranged as to cause said brush to press against low spots of said commutator with substantially less pressure than against high parts of the commutator, whereby during rotation of said commutator the high parts thereof are abraded to the level of the low parts.

3. In a device for truing a'commutator, the combination with an eccentric commutator, of a brush holder having a brush box and a pressure finger, a brush in said brush box, said brush being composed of a consolidated mixture of carbon and 25 per cent. carborundum and being formed with an inclined outer end, and said pressure finger engaging said end and forcing said brush toward said commutator and laterally into substantial frictional engagement with a sidewall of said box, with the efiect that'a substantially less reaction thrust of the commutator is required merely to stop the advance of the brush than to press the brush backward, whereby there is less abrasive effect on a low spot of the commutator than on the high parts.

4t. In combination with a rotary collector, an abrasive brush consisting of from 80 to 90 per cent carbon and to 10 per cent carborundum, a brush holder and means for causing the brush to be pressed by said holder with lower pressure against the low parts of the commutator and with higher pressure against high parts of the commutator, whereby said brush has a substantial abrasive effect on the copper of said commutator at high pressures and has substantially negligible abrasive effect on the copper at low pressures. Y

5. In combinationwith a commutator, a device for automatically eliminating flat parts therein, said device comprising a member having an abrasive action greater than that of a body composed of a consolidated mixture of about 90 per cent graphite and 10 per cent carborundum, a brush holder for supporting said member and means for causing said member to be pressed with substantially greater pressure against the high parts of the commutator than against the low parts, whereby there is substantially greater abrasive effect on the high parts than on the low parts.

6. In a dynamo electric machine having an eccentric commutator, a grinding device comprising in combination a stationary brush holder having a brush box, an abrasive member mounted in and dimensioned to slidably fit said box, said member being of integral construction and of more abrasiveness than a consolidated mixture of about 90 per cent graphite and 10 per cent carborundum, means for automatically advancing said member against the commutator and means for causing substantial friction between the abrasive member and brush box with the effect that a substantially less reaction thrustof the commutator is required merely to stop the ad vance of the abrasive member than to push the abrasive member backward, whereby there is substantially less abrasive effect on the low parts of the commutator than on the high parts. I

Signed at New York in the county of New York and State of New York this 17th day of May A. D. 1928. a

' HORACE 'D. MUNDAY.