GB1576576A

GB1576576A - Pressed carbon brush with at least one embedded cable

Info

Publication number: GB1576576A
Application number: GB1844/78A
Authority: GB
Original assignee: Hoffmann and Co Elektrokohle AG
Current assignee: Hoffmann and Co Elektrokohle AG
Priority date: 1977-01-18
Filing date: 1978-01-17
Publication date: 1980-10-08
Also published as: FR2377719A1; FR2377719B3; DE2701829A1; AT359159B; ATA931177A

Description

(54) PRESSED CARBON BRUSH WITH AT LEAST ONE EMBEDDED CABLE (71) I, PETER HOFFMANN, an Austrian citizen trading as HOFFMANN & Co. ELEK- TROKOHLE KG, of Hallstatter See, 4823 Steeg, Austria, do hereby declare the invention, for which I pray - that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to carbon brushes for electrical equipment with embedded cables, and also to apparatus for the manufacture of these brushes. The term "carbon brushes" as used herein includes both those which are free of metal and those with a metal content, e.g. of from 5% to 95%.

For supplying an electric current to a carbon brush the brush requires a connecting cable, e.g. in the form of a stranded copper wire, which cable has to be securely connected to the carbon brush. Particularly in the case of low voltage equipment, the carbon brush has to carry a very high current and its operation is to a large extent dependent on the quaIity of the connection of the current-supply cable to the brush.

For many decades it has been known and customary to connect this supply cable to the carbon brush by rivetting, embedding by means of a metal powder, or by soldered connections. The connections thus produced fulfil their purpose completely, but necessitate expensive mechanical treatment of the carbon brushes, Consequently, there has been no lack of attempts to introduce this connecting cable directly during the pressing of the carbon brush, whereupon during the thermal treatment (sintering) following the pressing step n secure connection between cable and brush body is obtained. This type of connection is of great importance nowadays for the carbon brushes which are produced in large quantities.

When compressing the powdery starting mixtures to form carbon brushes anisotropy arises in the brush, i.e. at least one more or less thick lamination at right angles to the pressing force is formed. The location of these lamination planes within- the finished carbon brush has to be taken into considers tion when attaching the cable and when using the carbon brush. It is necessary to prevent the lamination planes ftoni extend; ing parallel to the surface a X t,. i.e. the tubbing surface on the commutator or the like, since relatively high carbon-brush wear occurs due to the relatively low strength bez tween the iamination planes.

Theoretically it is readily possible to introduce the stranded copper wire at any point into the mould. When introducing the stranded copper wire perpendicularly to the pressing force, i.e. through the mould difficulties arise, however, both regarding the optimum compression and with regard to deformation of the stranded where, as well as structural difficulties regarding the design of the mould. Preferably,- therefore, the stranded copper wire is introduced though one of the two punches, i.e. pressed in paralleI to the pressing force.

Now if the pressing direction is to be identical to the dimension t of the carbon brush, it is therefore necessary for the cable outlet in the finished carbon brush to lie in the surface nxr. If the pressing- direction is to be identical to the dimension a of the carbon brush, the cable outlet must lie in the surface t X r.

In the brush-holder designs which have already been devised for the use of carbon brushes with embedded cables; this has been already taken into account: although- rt is associated with a serious - disadvantage: in order to provide space for the cable it is necessary for one will of the brush holder -to- -include a recess which not only increases the cost of the brush holder but also; reduces the stability of the holder casing Irreslp;ec- tive of this, in most cases it, is thus possible only with difficulty to change over from brushes and bmsh-holder arrangements, which were so designed- at the outset for mnulded brushes, to the brushes with- embedded cables which are conside'rabfr more economical. As a solution to tliis, brushes have been produced in which the cabl:e is in fact embedded in the dimension t or dimension a, However the cable-outlet point lies in a recess moulded therewith and the cable is bent at the outlet point through an angle of 90" in the direction of dimension r with a radius which is determined by the possible depth of this recess. Quite apart from the fact that this design is limited to brushes with a relatively large t-dimension or a-dimension, since only in these brushes can a sufficiently deep recess be accommodated so as to allow a suitable bending radius, the bending of the stranded wire through 90" constitutes, whatever the radius, a considerable stress on the stranded wire, particularly with large cable crosssections, so that during subsequent use cable breakages can occur at this point.

The disadvantages of the known methods described -above are eliminated, or at best mitigated, by the present invention.

In - accordance - with the present invention there is provided a carbon brush having at least - one lamination in a lamination plane perpendicular to the rubbing face of the brush, and having at least one embedded cable, wherein the end of the cable which is embedded in the carbon brush extends at an angle of from 10C to 800 to the lamination plane, and wherein the cable is embedded in the brush by pressing and sintering the brush.

The invention also provides a moulding apparatus for the manufacture of a carbon brush of the invention comprising a mould and at least one punch which, for admitting the brush cable, has a guide aperture opening into its end face, wherein the axis of the guide aperture at its outlet extends at an angle of from 100 to 80" to the direction of displacement of the punch.

The- invention is characterised in that for carbon brushes, which from the holder structure have the cable outlet provided in the surface axt, it -is possible to retain the dedesired lamination direction a X r or t x r.

The cables can be embedded with the punch and, -nevertheless, the cable is subjected to little bending stress, whereby the danger of cable breakages at the outlet point can be largely - eliminated.

This is achieved in accordance with the invention in that the end of the cable embedded in the carbon brush extends at an angle of -from iO to 80G to the lamination planes! while at the outlet point of the cable the carbon brush is - preferably bevelled at an 'angle"'of" from, 10" to 80 , preferably about 45 .

In ,the -rna"nufactur'e of the carbon brush acceding to the invention, the cable to be embedded is introduced through a bore in the '-p"'unch 'w'hid'h, bore is inclined at an angle of - frb''m' 1()0 to 88) to the direction of the pressing force. According to a preferred embodiment of the apparatus in accordance with the invention, a punch is used whose surface is not flat but has in the zone of the desired cable outlet a projecting shoulder whose front face is bevelled at an angle of from 10 to 80 , e.g. about 45".

In the manufacture of the carbon brush in accordance with the invention by means of the apparatus according to the invention, the flow processes occurring within the moulding powder during compression will divert the cable further in the direction of the lamination planes disposed perpendicularly to the pressing direction. After the final pressing or after the subsequent thermal treatment (sintering), the cable will in this example extend at an angle of at least 45" to the pressing direction, usually at a larger angle, and therefore, it is possible for the cable to be bend over easily (benefitting from the oblique recess which, moreover, is imparted by the punch to the carbon brush and formed therein) and through an angle which is less than 90 , perpendicularly to the pressing direction and parallel to the direction of the dimension r. By suitable choice, which is dependent in each case on the application and the size of carbon brush used, both of the angle of the inclined shoulder of the punch and of the angle which the bore opening into this inclined surface and serving to guide the stranded copper wire has in relation to the pressing direction, it is possible to obtain ideal compression conditions so that not only is the stranded wire securely anchored in the carbon brush but damage is obviated as far as possible, which could lead to breakage of the stranded wire at the outlet point and the bending point. This can be facilitated substantially in that, additionally, instead of a round stranded wire having the same bending resistance in all directions, a stranded wire is used which differs from the circular cross-section, e.g. a fiat stranded wire, whose breadth is disposed substantially perpendicular to the bending plane.

The invention is, of course, not only applicable to brushes having - one connecting cable. The bevelled face, imparted to the carbon by the punch and in which the outlet for the wire is located, can be recessed during the embedding of one or even several cables, so that it is limited only to the vicinity of the cable outlet. However, it may also extend over the entire edge of the carbon brush.

Various embodiments of the present invention will be described in detail by way of example, with reference to the accompanying drawings, in which : Figure 1 shows the designations of the brush dimension in accordance with IEC standards' and : as 'also used herein, i.e.

a=axial, t=tangential and r=radial with respect to the rotating commutator against which the carbon brush is applied. Furthermore, parallel to the surface sxr there is shown one of the desired laminations which are obtained by pressing in the direction of dimension t; Figures 2a and 2b show a carbon brush of a currently known type; Figure 3 shows in section a press die for manufacturing a carbon brush according to one embodiment of the invention Figures 4a and 4b show in section two different embodiments of a punch for the press die shown in Figure 3; and Figures 5 and 6 show a finished, pressed carbon brush according to one embodiment of the invention, before and after bending of the cable.

In the case of the known carbon brushes illustrated. in Figures 2a and 2b, whose pressing direction P is directed, for example, in the direction of the dimension t, the cable 2 is embedded into the carbon brush 1 parallel to the pressing direction, i.e. parallel to dimension t. A recess 3, formed by means of the punch in the carbon brush 1 in the vicinity of the cable outlet, makes possible the subsequent bending of the cable 2 through 90" so as to reach the condition ready for installation, as shown in Figure 2b. It is readily apparent that the cable undergoes considerable stress at the bending point and that this embodiment is suitable only for carbon brushes with a relatively large t-dimension or a-dimension and not for very large cable cross-sections.

The press die illustrated in Figure 3, which serves to manufacture a carbon brush according to the invention, has a mould 4, a punch 5 and a lower punch 6, between which the powder mixture 7 is pressed. A shoulder 9 projects from the end face 8 of the punch 5, the front face of which shoulder is inclined at an angle p of from 10 to 80 , preferably about 45 , to the end face 8. A passage 11 for admitting the cable extends through the punch 5, which passage opens as a bore into the front face 10 of the shoulder 9. The axis of this bore is inclined to the guide direction of the punch 5, i.e.

to the direction of the pressing force, at an angle a of from 10 to 80". The angles a and p can, but need not, be the same.

Figure 4a and 4b show two possible cable guides in the punch 5. As shown in Figure 4a, it is possible for the cable guide to extend further within the punch 5 in the form of a passage constituting a continuation of the outlet bore. However, as shown in Figure 4b, it can also leave the punch 5 as a direct extension of the guide bore at the angle a.

It is necessary, of course, in this latter case to ensure that the cable emerging from the punch is not crushed in the moulding process.

Figure 5 shows a carbon brush 1, according to one example of embodiment of the invention, after pressing. The angle a, which is formed after pressing between the axis of the cable 2 and the pressing direction, i.e. the normal to the lamination planes, will be of the same magnitude as the angles a and ,, , but will usually be greater. The angles a and are chosen so that a is as large as possible.

Figure 6 shows the carbon brush of Figure 5 ready for installation, i.e. with the cable 2 having been subsequently aligned so as to extend at an angle of approximately 90" to the pressing direction and thus lie parallel to dimension r of the carbon brush. It is readily apparent here that a considerable reduction in the bending stress of the cable has occurred when compared to the cable shown in Figure 2b. In particular, this also results from the presence of the bevel 12 on the carbon brush 1, and it is evident that this embodiment is suitable for substantially smaller t-dimension or dimension and also for larger cable cross-sections than was possible heretofore.

WHAT I CLAIM IS:- 1. A carbon brush having at least one lamination in a lamination plane perpendicular to the rubbing face of the brush and having at least one embedded cable, wherein the end of the cable which is embedded in the carbon brush extends at an angle of from 10 to 80" to the lamination plane, and wherein the cable is embedded in the brush by pressing and sintering the brush.

2. A carbon brush as claimed in claim 1 wherein the brush has a bevelled portion at the outlet point where the cable leaves the brush.

3. A carbon brush as claimed in claim 2 wherein the bevelled portion extends approximately at right angles to the axis of the cable.

4. A carbon brush as claimed in any one of claims 1 to 3 wherein the cable has a non-circular cross-section.

5. A carbon brush as claimed in claim 4 where the cable is in the form of a flat, standed wire, wherein the maximum breadth of the cable is disposed perpendicularly to the plane of the angle between the cable end and the lamination plane.

6. A carbon brush as claimed in claim 1 substantially as hereinbefore described with reference to and as illustrated in Figure 5 or 6 of the accompanying drawings.

7. A moulding apparatus for the manufacture of a carbon brush as claimed in any one of the preceding claims comprising a mould and at least one punch which, for admitting the brush cable, has a guide aperture opening into its end face, wherein the axis of the guide aperture at its outlet ex

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. respect to the rotating commutator against which the carbon brush is applied. Furthermore, parallel to the surface sxr there is shown one of the desired laminations which are obtained by pressing in the direction of dimension t; Figures 2a and 2b show a carbon brush of a currently known type; Figure 3 shows in section a press die for manufacturing a carbon brush according to one embodiment of the invention Figures 4a and 4b show in section two different embodiments of a punch for the press die shown in Figure 3; and Figures 5 and 6 show a finished, pressed carbon brush according to one embodiment of the invention, before and after bending of the cable. In the case of the known carbon brushes illustrated. in Figures 2a and 2b, whose pressing direction P is directed, for example, in the direction of the dimension t, the cable 2 is embedded into the carbon brush 1 parallel to the pressing direction, i.e. parallel to dimension t. A recess 3, formed by means of the punch in the carbon brush 1 in the vicinity of the cable outlet, makes possible the subsequent bending of the cable 2 through 90" so as to reach the condition ready for installation, as shown in Figure 2b. It is readily apparent that the cable undergoes considerable stress at the bending point and that this embodiment is suitable only for carbon brushes with a relatively large t-dimension or a-dimension and not for very large cable cross-sections. The press die illustrated in Figure 3, which serves to manufacture a carbon brush according to the invention, has a mould 4, a punch 5 and a lower punch 6, between which the powder mixture 7 is pressed. A shoulder 9 projects from the end face 8 of the punch 5, the front face of which shoulder is inclined at an angle p of from 10 to 80 , preferably about 45 , to the end face 8. A passage 11 for admitting the cable extends through the punch 5, which passage opens as a bore into the front face 10 of the shoulder 9. The axis of this bore is inclined to the guide direction of the punch 5, i.e. to the direction of the pressing force, at an angle a of from 10 to 80". The angles a and p can, but need not, be the same. Figure 4a and 4b show two possible cable guides in the punch 5. As shown in Figure 4a, it is possible for the cable guide to extend further within the punch 5 in the form of a passage constituting a continuation of the outlet bore. However, as shown in Figure 4b, it can also leave the punch 5 as a direct extension of the guide bore at the angle a. It is necessary, of course, in this latter case to ensure that the cable emerging from the punch is not crushed in the moulding process. Figure 5 shows a carbon brush 1, according to one example of embodiment of the invention, after pressing. The angle a, which is formed after pressing between the axis of the cable 2 and the pressing direction, i.e. the normal to the lamination planes, will be of the same magnitude as the angles a and ,,ss, but will usually be greater. The angles a and ss are chosen so that a is as large as possible. Figure 6 shows the carbon brush of Figure 5 ready for installation, i.e. with the cable 2 having been subsequently aligned so as to extend at an angle of approximately 90" to the pressing direction and thus lie parallel to dimension r of the carbon brush. It is readily apparent here that a considerable reduction in the bending stress of the cable has occurred when compared to the cable shown in Figure 2b. In particular, this also results from the presence of the bevel 12 on the carbon brush 1, and it is evident that this embodiment is suitable for substantially smaller t-dimension or dimension and also for larger cable cross-sections than was possible heretofore. WHAT I CLAIM IS:-

1. A carbon brush having at least one lamination in a lamination plane perpendicular to the rubbing face of the brush and having at least one embedded cable, wherein the end of the cable which is embedded in the carbon brush extends at an angle of from 10 to 80" to the lamination plane, and wherein the cable is embedded in the brush by pressing and sintering the brush.

tends at an angle of from 10 to 80" to the direction of displacement of the punch.

8. An apparatus as claimed in claim 7 wherein at the outlet point of the guide aperture the punch has a projecting shoulder with a front face inclined at an angle of from 10 to 80" to the end face of the punch.

9. An apparatus as claimed in claim 8 wherein the inclined shoulder is limited to the vicinity of the cable outlet.

10. An apparatus as claimed in claim 8 wherein the inclined shoulder extends along the entire length of one edge of the punch.

11. An apparatus as claimed in claim 8 "'wherein the angle a as hereinbefore defined of the guide aperture and the angle > ss as hereinbefore defined of the front face of the inclined shoulder areunequal.

12. An apparatus as claimed in claim 7 substantially as hereinbefore described with reference to and as illustrated in Figures 3, 4a or 4b of the accompanying drawings.

13. A method of manufacturing a carbon brush which comprises operating a moulding apparatus as claimed in any one of claims 7 to 12.

14. Electrical equipment including at least one carbon brush as claimed in any one of claims 1 to 6.