US1746208A - Electric-arc cutting - Google Patents

Description

P. P. ALEXANDER I 1,746,203

. ELECTRIC ARC CUTTING Original Filed Aug. 26, 1925 Inventor Peter P Alexandef,

His Attorhgy.

Patented Feb. 4, 1930 UNITED STATES PATENT OFFICE PETER I. ALEXANDER, OF MARBLEHEAD, MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A. CORPORATION OF NEW YORK ELECTRIC-ARC CUTTING Application filed August 26, 1925, Serial No. 52,663. Renewed October 3, 1927.

My invention relates to the cutting of metals by means of the electric are.

An object of my invention is to provide an improved process and an improved apparatus utilizing an arc of relatively high potential and great heating capacity to cut metals. Although not limited thereto my invention finds particular application to the cutting of cast iron and non-ferrous metals.

The are voltage using a carbon electrode in air is on the average of 37 volts and the current values used are high, in some cases as high as 1500 amperes. The width of the groove cut depends on the size of the electrode which in turn depends on the value of the current used. As the cutting is essentially a melting process the speed is determined by the amount of metal to be removed and the energy supplied for that purpose.

As pointed out in my application, Serial No. 758,082, filed December 26, 1924, for methods and apparatus for electric arc welding, and assigned to the same assignee as the present application, the voltage of the arc in a hydrogen atmosphere is greatly in excess of that of the corresponding are in air. The

high normal voltage of such an arc makes it possible to secure a much greater heating effect with this are in the hydrogen atmosphere than in air for the same current and with this high are voltage and a high current value the energy available by the employment of such an arc is tre nndous. Furthermore, the are in hydrogen has its largest fall of potential in the gaseous layer next to the positive crater; that is a large proportion of the energy is produced at the exact place Where it is needed when the work to be cut is made the positive side of the circuit.

, Because of the high voltage great energy may be derived with low current values and thus one generator may be used both for welding and cutting. If the necessary high striking voltageof about 120 voltsfor an 31011 1 a hydrogen atmosphere be obtained by the 1nsertion of a properly predetermined reactance in the circuit any suitable source of current may be used, for example a enerator such as shown in Letters Patent to ergman, No. 1,340,004 wound for about 80 volts on open circuit has been found to give satisfactory operation. The minimum arc voltage in hydrogen is about 40 volts, but it is to be understood that are voltages greatly in excess of this may be used where a suitable supply circuit is used. The arc voltage depends upon the arc length. I have successfully used are voltages in excess of 7 5 volts and higher voltages may be used if desired.

My invention is to be distinguished from cutting arrangements and processes wherein the heating effect of an arc is supplemented by the chemical reaction of combustion of gases such for example as oxygen and hydro gen. In accordance with my invention the gaseous medium is not oxidizing but actively reducing in its nature. The gas need be supplied in relatively small quantities. The method of cutting may be such as to allow a free flow of the melted metal from the cut or section but preferably the gaseous medium is supplied in the form of a blast which removes the molten metal.

The cost of hydrogen per cubic foot is at the present time from two and one half to three times lower than that of oxygen or acetylene. In large industrial plants hydrogen is available as a by-product. In such a case its cost is only one twentieth that of acetylene. Tlie reducing gaseous mediumneed not be pure hydrogen but I deem it preferable to use a medium which contains or is decomposed in the arc to produce a considerable percentage of hydrogen. For example, I have found illuminating gas may be used. Illuminating gas contains around 30 to 40% of hydrogen and a somewhat smaller amount of carbon monoxide. The hydrocarbons and carbon dioxide of illuminating gas are decom osed and recombined when the arc is con ned in the kerf with the further liberatron of hydrogen. The presence of carbon monoxide in substantial proportions tends to cost of my gas are cutting process using il1uminating'gas will be comparable to or lower than that of the previous gas cutting means and it is much more satisfactory for cast iron and non-ferrous metals. 7

By my process I have cut cast iron and steel plates of one and two inches in thickness with. a current of 130 amperes; at speeds of 30 and 40 feet per hour and the edges of the cuts have been clean and sharp and compare favorably with the cuts made with the oxy-hy: drogen torch. The reducing gas flame protects the metal during the operation and the edges are not oxidized as is the case in oxyhydrogen or oxy-ace'tylene cutting where the basic principle of the process rests upon the oxidization and burning of the metal. Furthermore, since the gas flame entirely surrounds the electrode its consumption is greatly lessened.

Aside from these advantagesof low cost 'ofoperation, the possibility of using a single standard generator as above pointed out for both welding and cutting purposes 1s a great advantage. Atthe present time cutting .by the carbon arc necessitates machines capable of developing from 600 to 1000 amperes or more.-

The single figure of the drawing illustrates an automatic machine for .carrying out my invention. In the figure, 10 is a graphite or carbon electrode which is mounted insliding engagement within a tube 11 located in the face of the nozzle 12. The electrode 10 may be adjusted in the tube 11 by means of a screw 13. The end of the tube 11 is enameled to prevent accidental short circuiting of the arc when the electrode is in a deep narrow cut.

A heavy copper tube 14 conducts the gas and the current simultaneously to the nozzle 12. Gas is supplied to the tube by a pipe 15 and one terminal of the source of welding current is connected at 16 to this tube. Tube 14 slides in the steel block 17 so that the height of the electrode above the work can be adjusted. The block 17 slides freely within a sleeve 18 which is supported by a carriage 19. Block 17 is also provided with arms 20 carrying at their extremities cam followers 21. These cam followers are forced into engagement'by gravity with cams 22 adjustably located by means of splined joints to axles 23 of the carriage 19.

' The carriage 19 is arranged to move on rack rails 24 and is positivel driven by a motor 25 mounted on a brac et 26- secured to the carriage by a gear train 27 which drivesone of the axles of the carriage. The motor 25 may be a constant speed motor or as shown in the drawing it may have its terminals connected across the arc in which case the speed of cutting will be regulated automatically. If the arc length is shprtened by the metal not being removed at a rate corresponding to the speed of propulsion of the move more metal.

carriage the voltage impressedon motor 23 will be lessened and the carriage slowed in its travel so that the energy in the arc may re-- len' 'th which is determined by the rate of re- 11103211 of metal. a

As the motor advances the carriage along the rack rails the rotary movement of the earns 22 secured to the axles 23 of the carriage causes the block 17 by means of arms 20 and the cam followers 21 to oscillate thereby oscillating the electrode vertically in the plane of the kerf.

lVhen operating the machine it is preferable to keep the arc between the electrode 10 and the work 28 within the kerf, since if the are be brought to the surface of the work there is a tendency for it to wander about over the surface of the Work and produce a rough and irregular kerf.

The application of Irving Langmuir, Serial No. 7 29,185, filed July 30, 1924:, for heating process and apparatus, assigned to the same assignee as the present application, discloses and claims method and apparatus for producing atomic hydrogen and carrying it over to the work Where it is recombined, lib crating heat. WVhether or not heating of the work by the recombination of dissociated hydrogen may under certain circumstances be present to some extent when my invention is used, I make no claim to such subject matter since the Langmuir invention is earlier than my invention.

While I have described and illustrated an apparatus particularly adapted for carrying out my process where a certain class of work is to be cut, it is apparent that for many classes of work a hand tool maybe preferable. It will also be apparent to those skilled in the art that as far as the broader aspects of my apparatus are concerned it is immaterial whether the machineoperates on rails over the work or rolls directly upon the work or remains stationary While the Work moves. I therefore, aim in the appended claims to cover all such modifications and constituting the other electrode and supply ing a blast of a reducing gaseous medium containing hydrogen to envelop the are and remove the molten metal.

2. The method of cutting metal work by the electric are which comprises maintaining a cutting are within the kerf in the work between a negative electrode and the work constituting the positive electrode and supplying a blast of illuminating gas to envelop the arc and remove molten metal.

3. A gas are cutting machine wherein the arc is between an electrode and the work, comprising means for producing relative movement between the arc and the work along the section to be cut, means for oscillating. the electrode in the plane of the cut, and means for supplying a blast of gaseous medium to envelop the arc and remove molten metal.

4. A gas are cutting machine wherein the arc is between an electrode and the work, comprising means for producing relative movement between the arc and the work along the section-to be cut, means for oscillating the electrode in the plane of the cut and within the kerf, means for supplying a blast of gaseous medium to envelop the arc and remove molten metal, and means for controlling the rate of movement along the work in response to an electrical characteristic of the are which varies with the arc length.

5. A gas are cutting device comprising a gas delivery nozzle, an electrode mounted in said nozzle, a support for said nozzle, and means for vertically oscillating said nozzle relatively to the work.

6. An are cutting machine wherein an arc is maintained between a substantially non-consuming electrode and the work comprising means for producing relative movement between the arc and the work along the section to be cut, means for oscillating the electrode in the plane of the cut, and means for controlling the rate of movement along the work in response to an electrical characteristic of the are which varies with the arc length.

7. The method of cutting metals by the electric arc which comprises maintaining a cutting are between a negative electrode and the work constituting the positive eletrode and supplying a reducing gaseous medium containing hydrogen about the arc and molten metal.

In witness whereof I have hereunto set my hand this 12th day of August, 1925.

PETER P. ALEXANDER.

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