US3501665A - Plasma torch - Google Patents

Description

United States Patent Int. Cl. Hin N88 US. 'Cl. 313146 6 Claims ABSTRACT OF THE DISCLOSURE In a plasma torch for spectrum analysis examination processes a bar-shaped cathode and an annular anode are disposed in a casing which is subdivided by two discshaped apertured arc stabilizers into three chambers. At least the two outer chambers are provided with tangential inlet apertures for a protective gas, while the central chamber has a viewing aperture in front of which a spectrum analysis examination device is arranged.

The disc-shaped arc stabilizers are disclosed to be made of graphite and to be mounted in discs having cavities through which a cooling medium flows. The protective gas may, for example, be argon.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to a plasma torch for spectrum analysis examination processes.

Description of the prior art During recent years plasma torches for spectrum analysis examination have been disclosed in which the substance to be analyzed is introduced into an electric arc. With an electric are considerably higher temperatures can be'obtained than with chemical flames as previously used for such examination purposes. The use of higher temperatures, however, is advantageous because by these temperatures more energy is provided for dissociation and stimulation of the substances to be analyzed. As a result considerably more substances as before may be examined by spectrum analysis processes.

A number of different types of plasma torches are already known to those skilled in the art. Of these torches those have proven to be particularly suitable wherein the plasma of the electric arc is stabilized by diaphragms disposed between the arc cathode and anode. Said diaphragms, therefore, serve as are stabilizers.

By applying slight pressure above the atmospheric a plasma jet is forced in perpendicular direction to the axis of the electric are through an aperture in the cham ber wall wherein the electric arc burns. Examination is then performed in this plasma jet. In the axis of the jet temperatures of up to 6,500" K. can be obtained. However, with these prior art devices major difficulties are encountered in introducing the substances to be analyzed into the center of the jet.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a novel plasma torch which overcomes the above mentioned disadvantage. It is another object to provide a plasma torch wherein still higher temperatures can be obtained than with the known devices. It is a further object to provide a plasma torch which can be easily dismounted and thus allows ready access to all its parts.

These objects are attained by arranging the cathode and the annular anode in a casing that is subdivided by two disc-shaped apertured arc stabilizers into three chambers, of which at least the two outer chambers are provided with tangential inlet apertures for a protective gas. The central chamber has a viewing aperture in front of which a spectrum analysis examination device of known design is positioned.

The annular arc stabilizers consist of graphite rings mounted in brass or copper discs. The latter are provided with cavities through which a cooling liquid passes.

The annular anode preferably consists of spectrally pure carbon and may also be disposed in a disc-shaped holder through which a cooling medium flows. The cathode may consist of a throiated tungsten pencil which is fastened in a bar-shaped metal holder. The latter may be mounted axially slidably in an extensible spring housing.

Preferably at least part of the guide for the bar-shaped holder of the cathode consists of a hollow metallic disc through which also a cooling medium flows and which at the same time serves to provide electrical connection of the cathode to a cable connected to a DC. source.

In order to ensure easy dismantling of the torch and simple interchangeability of all parts the torch is constructed of disc-shaped and annular individual components which are held together by means of two clamp connectors.

DESCRIPTION OF THE DRAWINGS The objects and advantages of a plasma torch according to the invention will be more fully comprehended from the following description when taken in conjunction with the appending drawings, wherein- FIG. 1 is a cross-sectional view of the plasma torch along line II in FIG. 2, and

FIG. 2 is a plan view of the plasma torch.

Referring to the drawings, a plasma torch in accordance with the inevention comprises two discs 1 and 2, each of which has a central bore and which are made of electrically non-conductive, thermal insulating material. The two discs are held together by means of two clamp connectors 3 and 4. The clamp connectors 3 and 4 swivel around pin 3a and are hooked behind locking pins 3b. Four hollow discs 5, 6-, 7 and 8 through which a cooling medium flows are positioned between the discs 1 and 2. They are separated from one another by insulating rings 12, 13, 14, made of a material capable of withstanding heat, for example asbestos cement. The discs 6, 7 and 8 are provided with central bores, in each of which carbon rings 9, 10 and 11 are respectively mounted. The carbon rings 9 and 10 serve as apertured stabilizers, while the carbon ringe 11 serves as an anode and is connected electrically by means of a cable 11a to a terminal 11b for the current supply.

In the interior of an extensible spring housing, a barshaped cathode holder 17 is mounted in a cover 16 which closes the housing 15 and which is made of electrically non-conductive material, said cathode holder being guided in a tube 18 of insulating material which is inserted in the disc 1 and further guided by metal disc 5. The cathode holder 17 extends through a central bore in the metal disc 5 and at its inner end carries a thoriated tungsten pencil 19, which in addition is surrounded up to the height of its conical tip by a brass ring 20. The metal disc 5 is connected by means of a cable 21 to the other pole 21b of the direct current supply. The brass ring 20 serves on the one hand to improve the electrical connection of cathode pencil 19 to the disc 5 and on the other hand provides better transfer of heat.

The cavities containing coolant 35 in the discs 5, 6, 7 and 8 are connected serially together through hose connections 22, 23, 24, 25, 26 and 27 with a source of coolant, for example tap water. The electrical conductivity of water is so slight that it does not impair the arc current which may be between 30 and 60 amperes. It is advantageous for the coolant to be allowed to flow first 3 through the cavity in the cathode disc 5 and thenthroug the other cavities, since the cathode is subjected to the greatest thermal load. The coolant is fed into the disc 5 by the hose connection 25 and led out the opposite side by connection 26. Connection 26 is now connected with hose connection 22. Water enters the hollow area of disc 6 through connection 22 and leaves through connection 27. Connection 27 is now connected by a hose to 23 so that the coolant now flows into the hollow area of disc 7 from which it flows out through another connection which is under hose connectin 27. This lower hose connection is finally connected by a flexible hose with connection 24 of the hollow area of disc 8. From disc 8 the water is finally led off through a pipe connection underneath hose connection 27. This completes the circulation beginning with inlet connection 25, passing through four hollow areas to the outlet from the hollow areas of disc 8.

Beneath the annular anode 11 there is disposed, concentrically to its bore, an atomiser 28 (shown in broken lines) for the introduction of the analysis material into the plasma of the are burning between the cathode 19 and anode 11. Bores having tangential inlet apertures 29 and 31 are provided in the annular insulating discs 12 and 14 and are in communication with gas admission connections 32 and 34 respectively. During operation a protective gas, for example argon, is injected through these bores into the chambers containing the cathode or anode. The

tubular extension of the disc 7 is provided with cooling ribs and likewise has a bore having a tangential inlet aperture, which is in communication with a gas inlet connection 33. In the tubular extension of the disc 7 there is in addition provided a viewing aperture 50 through which it is possible to view the central chamber of the burner. The direction of viewing is indicated in FIG- URE 2.

The arc in the plasma torch is ignited by moving the cathode holder axially in the direction of the anode against the pressure of the spring of the extensible housing 15 until the brass ring 20 surrounding the cathode 19 makes contact with the annular anode 11. The spring then 'brings the cathode 19 back into the operative position, while the electric arc is formed between the cathode 19 and the anode 11.

It is advantageous to provide an adjustable apertu ed plate in the spectrophotometric viewing device, in order thereby to permit a selection of the v ewing point inside the plasma.

The above described plasma torch will permit observations in the plasma core at temperatures of up to 17,000 K.

What is claimed is:

1. A plasma torch for spectrum analysis examination processes comprising in combination a casing;

a bar-shaped cathode and an annular anode disposed in said casing along a common axis;

a cathode holder;

an anode holder;

electrically conductive means adapted to connect said cathode to one pole of a D.C. source;

electrically conductive means adapted to connect said anode to the other pole of said D.C. source;

two disc-shaped apertured arc stabilizers subdividing said casing into three chambers;

a holder for each of said are stabilizers;

means adapted to cool said holders;

inlet apertures for a protective gas being provided in the outer two of said chambers; and

a viewing aperture being provided in the central chamber in front of which a spectrum analysis examination device can be disposed.

2. A plasma torch for spectrum analysis examination processes comprising in combination and along a common aXlS a bar-shaped cathode and an annular anode;

an electrically conductive disc-shaped holder whereon said annular anode is mounted, said disc being provided with cavities through which a cooling medium flows;

electrically conductive means adapted to connect said anode holder to one pole of a D.C. source;

a bar-shaped holder whereto the cathode is fastened,

said holder being axially displaceable;

means adapted to guide said bar-shaped cathode holder,

said guide means comprising an electrically conductive disc provided with cavities through which a cooling medium flows;

electrically conductive means adapted to connect said disc to the other pole of a D.C. source;

two disc-shaped apertured arc stabilizers;

two metallic discs wherein said are stabilizers are secured, said discs being provided with cavities through which a cooling medium flows;

three insulating rings inserted between said discs and two insulating apertured discs being positioned in front and to the rear of said discs and rings; clamping means adapted to press said discs and rings together so as to form a solid block, the latter constituting a casing which is subdivided by said are stabilizers into three chambers; an electrically non-conductive hose connection adapted to connect serially said cavities in said discs; tangential inlet apertures for a protective gas being provided in the outer two of said chambers; and

a viewing aperture in the central chamber through which the substance to be analyzed may be observed.

3. A plasma torch according to claim 2, wherein said protective gas is argon.

4. A plasma torch according to claim 2, wherein said apertured arc stabilizers comprise graphite rings.

5. A plasma torch according to claim 2, wherein said annular anode consists of spectrally pure carbon.

6. A plasma torch according to claim 2, wherein said cathode consists of a thoriated tungsten pencil.

References Cited UNITED STATES PATENTS RAYMOND F. HOSSFELD, Primary Examiner US. Cl. X.R. 313 231 315-111

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