US3373308A

US3373308A - Negative electrodes for carbon arc lamps

Info

Publication number: US3373308A
Application number: US575203A
Authority: US
Inventors: Perrin Jean Adrien
Original assignee: Carbone Lorraine SA
Current assignee: Mersen SA
Priority date: 1963-10-31
Filing date: 1966-07-05
Publication date: 1968-03-12
Anticipated expiration: 1985-03-12
Also published as: FR1383904A; GB1021984A; DE1285622B

Description

March 12, 1968 A. PERRIN 3,373,308 NEGATIVE ELECTRODES FOR CARBON ARC LAMPS Filed July 5. 1966 2 SheetsSheet l 1 1 13a 1 f I Inventor JEAN A. PERRIN A [to s March 12, 1968 J. A. PERRIN 3,373,308

NEGATiVE ELECTRODES FOR CARBON ARC LAMPS Filed July 5. 1966 2 Sheets-Sheet 2 Fig.5.

Inventor J. A- ERRM Attorneys United States Patent 3,373,308 NEGATIVE ELECTRODES FOR CARBON ARC LAMPS Jean Adrien Perrin, Pagny-sur-Moselle, France, assignor to Societe le Carbone Lorraine, Paris, France, a French body corporate Continuation-impart of application Ser. No. 337,763, Jan. 15, 1964. This application July 5, 1966, Ser. No. 575,203

Claims priority, application France, Oct. 31, 1963, 952,421, Patent 1,383,904 Claims. (Cl. 313-357) ABSTRACT THE DISCLOSURE A negative electrode for a high-intensity carbon arc lamp has a male end of truncated conical shape terminating in a conical point of greater apical angle. This male end fits into the complementarily-shaped female end of a preceding electrode. The electrode burns from the male towards the female end and at the junction the cathodic spot of the arc is constrained to pass to the point so minimising risk of dowsing the arc.

This is a continuation-in-part of my copending application, Ser. No. 337,763, filed January 15, 1964.

The present invention relates to carbon arc lamps and to an improved method for the operation thereof Negative electrodes for such are lamps are usually made from a carbonaceous composition, e.g. an artificial graphite or a coke bound with tar or a resin, or a mixture of artificial graphite and coke bound with tar or a resin. Such a composition is extruded from a press in the form of cylindrical rods which are then baked at high temperature. The rods thus obtained are known as graphitised.

Negative electrodes of such compositions are consumed at such a speed that it is necessary to advance them gradually by roller wheels and after a certain period of operation to extinguish the arc lamp and to replace the negative electrode by a new electrode.

It is an object of the invention to avoid the necessity of extinguishing the arc lamp to replace the negative electrode.

In conventional and relatively low intensity carbon arc lamps using currents of about 8 to 17 amperes, stability of the position of the cathodic spot of the arc has not been an important requisite. Disturbance of the arc at the moment of its passage across an electrode joint did not present any major problems, since the length of the arc was very short, 3 to 5 mm. Also absolute maintenance of the cathodic spot along the axis of the negative electrode was not rigorously necessary. On the passage of the joint, there could be displacements of the cathodic spot without risk of causing an extinction of the arc. This was because the low intensity used by the arc lamps for public lighting in 1884 did not induce a magnetic field sufiiciently intense to cause as a result during the passage of the joint, displacements of the are which could be aggravated by the magnetic field and result in the extinction of the are. High intensity arc lamps, on the other hand, function at intensities of 200 to 400 amperes. The length of the are for these lamps is distinctly greater than that used for are lamps for public lighting: 14-21 mm. for the high intensity arcs as against 3 to 5 mm. for the arc lamps for public lighting. The magnetic field induced by the passage of the high current is so intense that when there is a slight displacement of the cathodic spot away from the axis of the negative electrode, the displacement is aggravated as a result of the action of the magnetic field on the plasma, which results in an extinction of the arc.

.It is known to make joints between positive carbons ice.

for are lamps operating on direct current, which allow arc projectors having a magazine of positive carbons to operate for long periods. However, although the negative carbons are used up much more slowly than the positive carbons, it is still necessary to replace them by new negative carbon electrodes and for this it is necessary to switch off the lamp.

It is an object of the invention to provide a negative electrode for carbon arc lamps operating on direct current, said electrode being of such nature as to allow an uninterrupted operation of the lamp, the electrode being replaceable without cutting the input current and without the are being fortuitously extinguished when the cathodic spot passes from the end of the negative carbon used up guring operation to the beginning of the replacement car- It is a further object of the invention to provide an improved negative electrode for carbon arc lamps which is so fashioned as to enable a joint to be effected which avoids extinctions of the arc, by maintaining the cathodic spot on the axis of the negative electrode at the moment of passage of the arc across the joint.

It is another object of the invention to provide an improved method of operating a carbon arc lamp.

It is also an object of the inventionto provide a high intensity carbon arc lamp using negative electrodes which may be replaced simply without extinction of the arc.

Other objects will become apparent from the description which follows.

Accordingto the invention there is provided a negative electrode for a high intensity carbon are lamp, said electrode having a male end formed to fit into a complementarily-shaped female end of another electrode and being adapted to burn from said male end towards said female end, said male end being in the form of a truncated conical portion terminating in a pointed portion, the angle of taper of said pointed portion being greater than that of said truncated conical portion.

The essential advantage of the invention is that the replacement of the negative electrodes may be effected quickly by hand, mechanically or automatically without a binder, cement or similar jointing means, the junction between two adjacent electrodes being effected by the fitting of a male end of the new electrode into a female end of the nearly-exhausted electrode.

The negative electrodes according to the invention are preferably used without copper coating and in an arc lamp the current input of which is located near the end of the cathodic point, that is to say at a distance of 35 to 40 mm.

The relative dimensions and the taper angle of the mating parts are so dimensioned as to insure a good mechanical solidity of the joint without exaggeratedly diminishing the thickness of the skin electrode wall at the location of the joint, as this could cause a breakage.

- In order that the invention may be more clearly understood, reference will now be made to the accompanying drawings which show by way of example, two embodiments of known negative electrodes having truncated joints, and one embodiment of a negative electrode in accordance with the invention, and in which:

FIGURE 1 shows an axial section through the end portions of two known negative electrodes having a truncated male spigot and a truncated female socket,

FIGURE 2 shows a similar section of a second known arrangement,

FIGURE 3 shows a similar section through a negative carbon electrode according to the invention, and

FIGURE 4 shows the co-operating ends of a pair of conjoinable electrodes according to the arrangement of FIGURE 3, but in the separated state, the left hand electrode being in axial section and the right hand electrode in elevation;

FIGURE shows in partial longitudinal vertical section a high intensity carbon arc lamp in operation having joined negative electrodes according to the invention, and

FIGURE 6 shows in partial longitudinal vertical section the arc lamp of FIGURE 5 when the burning negative electrode is almost consumed.

The negative electrode is provided with a male fitting at one end and a female fitting at the other end, which fittings are arranged to couple so that the normal passage of the electric current through the coupling is facilitated.

Referring to the drawings, and firstly to FIGURE 1, a known negative carbon 1 shown in solid outline, eventually becomes consumed during operation and wears down to a pointed shape shown by the chain-dotted line 2. The end is socketed at 3 to receive a truncated tapered spigot 4 of a replacement electrode 5, in a sleeve joint. The thickness of the wall between the exterior surface of the used electrode at 2 and the internal surface of the female recess 3 steadily decreases during the consumption of the electrode.

If the diameter d of the minimum cross-section of the tapered spigot 4 of the male end of electrode 5 is too great in relation to the diameter of the concentric crosssection of the end 2 of a carbon 1, i.e., the Wall thickness as referred to above, there is a risk that the end 2 shown by chain-dotted lines will break off and since the arc strikes at this part the arc would become extinguished.

As the new electrode commences to burn away, its contours form continuations of the part 2, as indicated by the dotted line 5a.

FIGURE 2 shows in axial section known negative carbon electrodes similar to those of FIGURE 1. Here again the nearly consumed electrode 6 and a new carbon 7 are connected by a sleeve joint in the form of a tapered spigot 8 fitting into a socket 9 in the end of electrode 6. The diameter of the minimum cross-section d2 of the spigot 8 is less than the diameter d1 of spigot 4 of FIG- URE 1. The remaining part 10 of the electrode 6 is defined by the chain-dotted line. The breaking off of part 10 cannot be avoided, but the part 10 is shorter than the part 2 of FIGURE 1, and the arc re-strikes immediately on the new electrode without becoming extinguished. In fact the temperature of the remaining part 10 of the used-up electrode or of the male spigot 8 is sufficiently high that the ionisation level at this place aids the restriking of the arc. However the arc is disturbed by the placement of the cathodic area on the plane surface of the cross-section of the tapered portion. The dotted line 7a indicates the burn-off portion of the new electrode. The spigot 8 is joined to the socket 9 by a disc of a thermo-setting resin such as Bakelite which melts during operation and runs, which is a nuisance so far as good operation is concerned.

FIGURE 3 shows in axial section two negative carbon electrodes somewhat similar to the negative electrodes shown in FIGURES 1 and 2, but connected by a sleevejoint according to the invention which is a combination of -a tapered point and truncated taper. The female or socketed end 11 of the used-up electrode 12 is joined to the male end of the new electrode 13 by means of a sleeve joint comprising a taper 14 extended to a small tapered point 15, the end of which, because of its advance location in the part 16 (indicated by chain-dotted lines) of the used-up carbon, is brought to a temperature near that of the cathodic area before the part 16 is broken. At that moment the arc is immediately re-struck without difliculty, to the end of the small tapered point 15, the shape of which favours the fixation of the cathodic area and the ionisation level of which is very slightly different from the normal ionisation level of the cathodic area. The burn-ofi portion of the new electrode is indicated at 13a.

FIGURE 4 shows one end of each of the two electrodes according to the invention and of the kind shown in FIGURE 3, but in the separated condition. On the left is the female or socketed end, shown in section, the truncated tapered part 11 being extended by a tapered recess 17 and on the right the male or spigoted end.

FIGURES 5 and 6 show schematically a carbon arc lamp utilising continuous combustion negative carbon electrodes according to the invention with the anode 20 and its current lead-in and holder. The light emission is mainly from the spot at the anode. According to'the direction in which it is desired to project the light the anode may be arranged at various angles in a vertical plane. The angle of the cathode may be suitably adapted is known manner.

FIGURE 5 shows the negative electrode 12 in the course of combustion, partially sectioned at its base in order to show the female fitting 11. The new electrode 13 is shown fitted in the electrode 12 in the course of combustion. The operation of fitting one electrode into the other may be carried out manually or mechanically. The conical part 11 is arranged to provide adherence for the forward electrode 12 to carry with it the electrode 13 in its arc-ward movement.

FIGURE 6 shows the negative electrode 12 when nearly consumed, the new electrode 13 having already been taken by the feed rollers 18. The quantity of carbonaceous material of the electrode 12 remaining around the female fitting 11 is sufiicient to allow the passage of the electric current. The distance between the cathodic spot 25 and the apex of the conical part 15 of the fitting is relatively small, this small distance permitting the transmission of the heat from the cathodic spot to the apex of the cone 15 so that the arc is regenerated without interruption on this same apex of the cone 15. The cathodic spot is thus maintained along the axis of the negative electrode.

It will be understood that the male or spigoted end is inserted into the female or socketed end of an electrode already in operation before the latter is used up or completely consumed. It will also be appreciated that an electrode according to the invention preferably has one end formed with a male spigot and its other end with a female socket. Essentially, however, the electrode only has the rear end formed with a female socket-the other end may be the same as a conventional electrode. This is of use for initially striking an are where a shaped end is not necessary and may even be undesirable.

The tapered sleeve joints operate to best advantage if the degree of taper of the female and male parts is the same. The preferred taper angle is from 4 to 7.

The ratio between the diameter of the cross-section at the widest part of the taper to the exterior diameter of the generally cylindrical negative carbon may vary between 0.45 and 0.55. The ratio between the length of the taper to the exterior diameter of the cross-section of the negative carbon may vary between 0.75 and 0.91.

The taper angle of the tapered point 15 of the male spigot 15 of FIGURES 3 and 4 is at least and the tapered end recess 17 of the female socket 11 is also 90".

The provision of the tapered point 15 has the advantage of ensuring the rapid passage of the are from the end in the course of combustion to that of the new carbon without exaggerated heatin at the junction.

The taper angle of the two tapering parts of the joint should not exceed 7, because the axial cleavage stress between the male and female extremities must be greater than that produced by the expansion of the air and of the gases trapped in the bottom of the cavity of the female part, otherwise there may be premature projections of the piece of the female sleeve and extinguishing of the are.

It is clear that the invention applies to negative carbons of all lengths operating with direct current whatever their rate of wear.

The external oxidation of the negative electrode produces a tapered shape 16, the cross-sectional area of which decreases from the current lead-in part 19 up to the location of the cathodic spot 25. The dimensions of the male and female conical parts are arranged to be such that the above-mentioned tapering does not lead to a premature fracture of the female rearward part of the electrode in the course of combustion. This premature fracture would involve undesirable extinction of the arc.

Moreover, it is important to ensure the maintenance of the cathodic spot 25 along the axis of the negative electrode when the arc has to pass from the electrode in the course of combustion to the following electrode; to this end, the truncated part of the joint is prolonged by the conical part 15.

The male and female sleeve junctions may be formed by any appropriate machine-tool means, e.g. a lathe, particularly a screw-cutting lathe after having square-cut the graphitic or graphitised cylindrical rods. Suitable dimensions for a negative electrode with a diameter of 11 mm. are given below:

Length of truncated conical portion 14 mm Length of pointed portion 15 mm 2.1 Diameter of base of truncated conical portion 14 mm 5 Diameter of base of pointed portion 15 mm 4.26 Apex angle of pointed portion 15 degrees 90 Angle of conical portion 14 do 4 These negative electrodes operated effectively at the following parameters:

240 amp., 56 volts (13.44 kw.) 350 amp, 70 volts (24.5 kw.) 400 amp, 80 volts (32 kw.)

For these conditions, the length of negative electrode emerging from the current lead-in 19, in other words the protrusion, was between 25 mm. and 35 mm.

At the moment when the arc passes, in the course of combustion, from the remnant 12 to the new electrode 13, a small fragment of the electrode 12 is observed to drop off, this fragment comprising a portion between the cathodic spot 25 and the tip of the cone 15. The tip of the cone 15 of the male fitting being thus heated sulficiently to raise its temperature to a high value, the arc is immediately restarted on said tip 15.

It should be understood that the foregoing description of specific embodiments is for the purpose of illustration only and that various modifications may be made without departing from the scope of the invention as defined in the appended claims.

I claim:

1. A negative electrode for a high intensity carbon arc lamp, said electrode having a male end formed to fit into a complementarily-sha'ped female end of another electrode and being adapted to burn from said male end towards said female end, said male end being in the form of a truncated conical portion terminating in a pointed portion, the angle of taper of said pointed portion being greater than that of said truncated conical portion, said electrode having a female socket at one end in the form of a truncated conical bore extended by a tapered recess, the angle of taper of said truncated conical bore and of said truncated conical portion lying between 4 and 7.

2. A negative electrode for a high intensity carbon arc lamp as set forth in claim 1, wherein the ratio between the largest width of said truncated conical portion and the exterior width of the electrode in the same radial plane lies between 0.45 and 0.55.

3. A negative electrode for a high intensity carbon arc lamp, said electrode having a male end formed to fit into a complementarily-shaped female end of another electrode and being adapted to burn from said rnale end towards said female end, said male end being in the form of a truncated conical portion terminating in a pointed portion, the angle of taper of said pointed portion being greater than that of said truncated conical portion, the ratio of the length of said truncated conical portion and said pointed portion to the diameter of the electrode lying between 0.75 and 0.91.

4. A negative electrode for a high intensity carbon arc lamp, said electrode having a male end formed to fit into a complementarily-shaped female end of another electrode and being adapted to burn from said male end towards said female end, said male end being in the form of a truncated conical portion terminating in a pointed portion, the angle of taper of said pointed portion being greater than that of said truncated conical portion, the angle of said pointed portion being at least 5. A negative elect-rode for a high intensity carbon arc lamp, said electrode having a male end formed to fit into a complementarity-shaped female end of another electrode and being adapted to burn from said male end towards said female end, said male end being in the form of a truncated conical portion terminating in a pointed portion, the angle of taper of said pointed portion being greater than that of said truncated conical portion, said electrode having a female socket at one end in the form of a truncated conical lbore, extended by a tapered recess, having an angle of taper of 90.

References Cited UNITED STATES PATENTS 863,674 8/1907 Tone 313357 1,253,572 1/1918 Buchanan 313357 2,024,445 12/ 1935 Gatehouse 3 l3357 2,693,498 11/1954 Penberthy 313-357 3,030,544 4/1962 Gambooldi et a1. 313357 3,131,290 4/1964 Stepath 313355 FOREIGN PATENTS 1,383,904 11/1964 France.

3,315 1878 Great Britain. 8,781 6/1884 Great Britain.

JOHN W. HUCKERT, Primary Examiner.

A. J. JAMES, Assistant Examiner.