US2105038A - Brush for dynamo-electric machines - Google Patents

Description

' Jan. 11, 1938. w. o. HELWIG 2,105,038

BRUSH FOR DYNAMO-ELECTRIC MACHINES Filed Nov. 20, 1936 iNVENTOR 1444.4 m? 0. fifth l6 Z24 flwa ATTORNE Patented Jan. 11, 1938 UNITED STATES PATENT 2,105,038 BRUSH roa DYNAMO-ELECTRIC maclmms Walter O. Helwig, Milwaukee, Wis. Application November 20, 1936, Serial No. 111,763

4 Claims. (Cl. 171-325)) OFFICE This invention relates to brushes for dynamo electric machines for use on slip rings or on commutators.

Various attempts have been made to provide dinary brushes. For example, in cold dry weather there is much more rapid wear for the old style of brush than when other atmospheric conditions obtain.

5 some means of lubricating brushes on dynamo However, this invention has for a further ob- 5 electric machines to increase the life and reduce iect to provide a brush which has substantially the wear and friction, but these attempts have no variation in wear, irrespective of changes in not proven wholly satisfactory. atmospheric conditions. v

One expedient has been to insert rods of ma- This invention in its broadest aspects contemterial in holes drilled in the metal portions of plates not only the use of purely lubricating 10 the brushes, but these brushes have been unsatmeans but also the use of lubricating means to isfactory as they still did not greatly reduce the which a small percent of abrasive material has wear and also as there was considerable danger been added. of the rods slipping out of place and short-cir- It is a common practice to form these brushes cuiting the live portions of the machine to the either as an alloy metal type or as a non-alloy 5 framework of the machine or to the framework type of brush. In the alloy type of metal brush of the brush holders. it is the usual practice to have only a small per- A very peculiar phenomenon has been observed cent of graphite, whereas in the non-alloy type where a plurality of brushes are employed on a higher percent of graphite is employed.

5 each slip ring. It has been found that the wear In practicing this invention with the alloy type is unequal and the contact between the several of brush substantially a pure lubricating or treatbrushes and the slip ring is unequal. The result ing means is employed, such, for example, as of this is that one brush will suddenly carry graphite with a binder, such as pitch. With the considerably more current than another brush non-alloy type of brush it is still desirable to 35 and this sudden increase in current will cause have lubricating material, but if this alone were the leaders from the brushes to be violently agiemployed, it has been found that the slip rings tated or shaken from an electromagnetic effect. or the commutators become somewhat fouled by Almost immediately another brush will suddenly material removed from the brush. This invenstart carrying more current as the wear on the tion, however, contemplates means for preventan brush is faster when there is no current than ing this condition. For instance, under these when there is current flowing at the contact conditions the treating material not only has its between the brush and slip'ring. The result of lubricating properties, but to the main body of this is that there is almost a continuous tremgraphite a very small percent of abrasive matebling or shaking of the leaders and consequent rial is added so that the treating material acts shaking of the brushes with machines employing not only as a suitable lubricating agent but also a plurality of brushes on each slip ring. as a cleaning agent so as to keep the slip ring This invention is, among other things, deor the commutator bright and clean. It is theresigned to relieve the real cause of this defect as fore intended that the treating material as hereit provides brushes whose wear is substantially inafter referred to be interpreted as meaning 40 the same, in which the selective action of current either of these general types of materials. 40 flow for certain of the brushes with sudden shift- A further and specific object of this invention ing to certain other of the brushes is avoided, is to provide a brush in which the treating maand in which a very smoothly operating brush is terial is mechanically interlocked with and, if provided. I desired, may also be cemented to the body of the Further objects are to provide a brush for brush so that the mechanical interlock either 45 dynamo electric machines in which the addiwith or without the cement insures a permanent tional material, such as the lubricating material, grip or interlocking between the body of the is interlocked and rigidly retained by the body brush and the treating material, irrespective of of the brush so that this additional material the gradually decreasing length of the brush due cannot fall out of the brush and cannot become to wear thereon. 50

dislodged therefrom so that all danger of shortcircuiting or other damage due to this cause is avoided.

It has been found also that the atmospheric conditions materially alter the operation of or- Further objects of this invention are to provide a novel form of brush which avoids local heating due to uneven bearing of the brush and which when used with commutators materially reduces the short-circuit current and acts as if it were two very closely associated brushes with a resistance path between the brushes.

An embodiment of the invention is shown in the accompanying drawing, in which:

Figure 1 is a view of the brush with a part of the leaders cut off, the direction of rotation of the commutator or slip ring being indicated by the arrow.

Figure 2 is a view of the body of the brush with the treating material as it appears while it is being forced laterally or inserted into the slot of the brush.

Referring to the drawing, it will be seen that the body of the brush is indicated by the reference character I. This brush has flexible leaders 2 attached thereto in any suitable manner, as by means of the bolt 3, the nut or head thereof being preferably set down within the opening 4.

The body of the brush is provided with a transverse dovetail shaped slot 5, cut completeLv therethrough from one side to the other side, and the treating material 6 is carried within this slot and is rigidly gripped and held by the brush.

This treating material is preferably formed of graphite to which a suitable binder, such as pitch, has been added. It is subjected to a high pressure and then baked without contact of air. The brush is usually formed oi bronze, copper, or brass powder to which a certain percent of graphite has been added, and this body is compressed and thereafter machined.

Subsequently the treating material 6 is inserted by means of a press by sliding it laterally into the slot. It dovetails with the slot and thus interlocks with the body of the brush. This particular form of interlocking is preferred, though obviously other means of interlocking may be followed.

It is preferable to coat the sides of the wedge of treating material and the sides of the slot with a cement, such as a phenolic condensation compound cement, which after the wedge has been pressed into place hardens and additionally holds the wedge of treating material in place.

Where an alloy type of metal brush is emplayed, the treating material is preferably composed wholly of a lubricating material, such as graphite, to which a suitable binder, such as pitch, has been added. On the other hand, if the brush is of non-alloy type and has a higher percent of graphite in the body of the brush itself, the treating material may have added thereto, in addition to the ingredients stated, a small percent of abrasive material. This, as stated hereinabove, is for the purpose of keeping the slip ring or commutator clean. The relative proportions or the addition or omission of the abrasive material may be varied depending also on the composition of the slip ring or commutator or of the brush body.

It is apparent that this invention provides a treating material, such as a lubricating means, which etxends uniformly completely across the face of the brush and thus uniformly lubricates or conditions the entire face of the brush and the entire cooperating face of the contact ring or commutator, so that there is no unequal wear but, on the other hand, so that there is a uniform and smooth action.

It is to be noted also that when the brush is used with a commutator, there is a relatively high resistance path from one portion of the brush to the other portion of the brush due to the interposition therebetween of the graphite material. This materially reduces short-circuit currents between adjacent commutator bars passing below a brush. Any substantial amount of short-circuit current that passes through the body of the brush would have'to pass up, over and around the inserted treating material and thus would have a longer path of travel and consequently more resistance would be offered thereto. whe it is considered that the voltage inducing these short-circuit currents is very small, it is apparent that this increase in resistance is ample to greatly reduce the flow of short-circuit current.

The brush in actual practice has been found to operate smoothly, to have a very much increased length of life, to operate quietly without the selective sudden flow of current through one or another of the brushes, and to greatly reduce the wear not only on the brush but on the slip ring or commutator as well.

Although this invention has been described in considerable detail, it is to be understood that such description is intended as illustrative rather than limiting, as the invention may be variously embodied and is to be interpreted as claimed.

1 claim:

1. A brush for a dynamo electric machine comprising a body portion having a slot extending transversely therethrough, and a transverse, wedge-shaped body of treating material positioned within said'slot and interlocking with said body portion.

2. A brush for a dynamo electric machine comprising a body portion, said body portion having a wedge-shaped slot cut transversely therethrough from one side to the other side and through its operating face, a wedge-shaped block of treating material held rigidly within said slot,

" and cementing means between said treating material and the body of said brush.

3. A brush for a dynamo electric machine having a moving contact member, said brush comprising a body portion formed of conducting material, and a section of treating material extending completely across the operating face of the brush transversely of the direction of motion of said moving contact member, said section of treating material being presented at the active face of the brush substantially uniformly across the entire face of the brush and being mechanically interlocked with said body portion.

4. A brush for a dynamo electric machine comprising a body portion having an active face and having a slot extending transversely of the body portion and opening through the active face of the brush, a transverse, laterally elongated body of treating material positioned within said slot, said brush including interlocking means for positively locking the treating material to the body of the brush, whereby unequal expansion and contraction between the body of the brush and the treating material will not cause loosening of the treating material.

WALTER 0. HELWIG.

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