GB2048457A - Plasma burner with contact protection - Google Patents

Plasma burner with contact protection Download PDF

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Publication number
GB2048457A
GB2048457A GB8007556A GB8007556A GB2048457A GB 2048457 A GB2048457 A GB 2048457A GB 8007556 A GB8007556 A GB 8007556A GB 8007556 A GB8007556 A GB 8007556A GB 2048457 A GB2048457 A GB 2048457A
Authority
GB
United Kingdom
Prior art keywords
nozzle
cap
plasma burner
plasma
burner
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
GB8007556A
Other versions
GB2048457B (en
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Mansfeld Kombinat Wilhelm Pieck VEB
Original Assignee
Mansfeld Kombinat Wilhelm Pieck VEB
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Mansfeld Kombinat Wilhelm Pieck VEB filed Critical Mansfeld Kombinat Wilhelm Pieck VEB
Publication of GB2048457A publication Critical patent/GB2048457A/en
Application granted granted Critical
Publication of GB2048457B publication Critical patent/GB2048457B/en
Expired legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K10/00—Welding or cutting by means of a plasma
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H1/00—Generating plasma; Handling plasma
    • H05H1/24—Generating plasma
    • H05H1/26—Plasma torches
    • H05H1/32—Plasma torches using an arc
    • H05H1/34—Details, e.g. electrodes, nozzles
    • H05H1/3473—Safety means
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H1/00—Generating plasma; Handling plasma
    • H05H1/24—Generating plasma
    • H05H1/26—Plasma torches
    • H05H1/32—Plasma torches using an arc
    • H05H1/34—Details, e.g. electrodes, nozzles
    • H05H1/36—Circuit arrangements
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H1/00—Generating plasma; Handling plasma
    • H05H1/24—Generating plasma
    • H05H1/26—Plasma torches
    • H05H1/32—Plasma torches using an arc
    • H05H1/34—Details, e.g. electrodes, nozzles
    • H05H1/38—Guiding or centering of electrodes

Landscapes

  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Plasma & Fusion (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Mechanical Engineering (AREA)
  • Plasma Technology (AREA)
  • Arc Welding In General (AREA)
  • Discharge Heating (AREA)
  • Investigating, Analyzing Materials By Fluorescence Or Luminescence (AREA)

Abstract

A plasma burner has contact protection means for protecting the operator against impermissibly high voltage and the burner head itself against destruction. The burner comprises a nozzle 1 attached to a nozzle holder 2 and surrounded by a nozzle cap 3, with cooling water flowing between the nozzle 1 and cap 3. Disposed over the nozzle cap 3 and insulated therefrom by an air gap 9 is an electrically conductive protective cap 8 which is mounted on the burner shaft by means of two contact pieces 7 constructed as half rings. Each of the two contact pieces 7 is connected via a cable to a fault current protective circuit. The operating conditions are monitored by means of voltage indicators which effect switching functions, and resistors, capacitors and diodes connected in correspondence thereto, and if malfunctions occur, switching operations are triggered which protect the plasma burner and the installation. <IMAGE>

Description

SPECIFICATION Plasma burner with contact protection This invention relates to a plasma burner which has contact protection means for pro ,acting the operator against impermissibly high voltage and the burner head itself against destruction. Preferably the arrangement is used for burners which have a transmitted arc and in which the nozzle, nozzle cap or other metallic nozzle-attaching elements carry a voltage in relation to the workpiece.
Known plasma burners, more particularly manual plasma burners, have variously operating arrangements to protect the operator, but they fail to ensure complete protection. It is known to provide the nozzle with a ceramic cap or to coat the nozzle with a ceramic or enamel layer. The splashes or metal vapours produced during a cutting operation coat the protective caps with a relatively thin metal layer, so that contact is made to the nozzle.
As a result, large voltage-carrying areas may be produced on the burners and be accidentally touched during operation.
The aforementioned protective arrangements must be regarded as dangerous, since although they are called protective arrangements, they can lose their protective function during burner operation.
A more effective contact protection arrangement is known which is free from the aforementioned defects but has technical disadvantages. In that arrangement the nozzle cap is separated from the nozzle by a ceramic insulator and a resilient seal. The protective cap is connected to the workpiece or earth potential via a fault current protective circuit. If the switching threshold of the protective circuit is exceeded by a suddenly occurring voltage potential, the plasma current source is switched off (German Democratic Republic Patent Specification 63 823).
One disadvantage is that the fault voltage monitoring system fails if the nozzle cap contacts the workpiece in difficult cutting positions such as occur, for example, in angle plates or elbows. If in that case an arc flashover or a metal bridge formation takes place on the ceramic insulator, as a rule the insulator is destroyed by thermal overloading.
Another disadvantage is that the nozzle cap is liable to electrolytic decomposition caused by the high voltage potential between the nozzle and the nozzle cap, the cooling water acting as an electrolyte. As a result of this decomposition the nozzle caps lose sealing tightness at the places where they are clamped.
It is an object of the invention to obviate the disadvantages of the prior art and to provide a plasma burner which exactly meets the requirements as regards electric contact protection.
The invention aims at providing a plasma burner which enables the nozzle and a protective means to be readily exchanged, although they are both so insulated from one another electrically as to obviate electrolytic processes which may destroy the nozzle cap due to corrosion. In addition to providing contact protection for the operator, it must ensure that the protective circuit operates even if the protective means or the nozzle contact the workpiece.
Accordingly, the present invention consists in a plasma burner comprising a burner shaft, a nozzle and a nozzle cap surrounding said nozzle, with cooling water flowing between them, a cathode disposed coaxially in the nozzle, a fault current protective circuit, and a voltage indicator, effecting switching functions, arranged, in use, between a workpiece and the nozzle to monitor the nozzle for the presence of a voltage potential in relation to the workpiece, characterised in that disposed over the nozzle cap and insulated therefrom by an air gap is an electrically conductive protective cap, that to attach the protective cap to the plasma burner shaft at least two contact pieces are provided, each of which is connected via a cable to the fault current protective circuit, and that connected in series to the voltage indicator is a resistor to which is connected in parallel at least one capacitor having a diode connected in series.
The voltage indicators effecting switching functions are connected in known manner between the workpiece and the nozzle to monitor the nozzle for the presence of a voltage potential in relation to the workpiece.
According to the invention a resistor, preferably a relay, is connected in series to the voltage indicator, a series connection consisting of at least one capacitor and one valve being connected in parallel to such resistor.
The capacitor is charged by the nozzle potential. By means of its accumulated electric charge the satisfactory operation of the plasma burner in various operating conditions can be checked by comparison and by connection to switching contacts of the plasma installation. The installation is therefore enabled to distinguish whether a plasma burner with indirect (non-transmitted) arc or with direct (transmitted) arc is connected. In the case of an indirect arc the nozzle is not monitored, since in this operational mode the nozzle is at earth potential.
If the fault current circuit responds in the direct operational mode, the plasma installation is immediately switched off. If the nozzle potential suddenly fails, only the cutting operation is interrupted. The operator can switch on the plasma burner by pressing the button again. If therefore the nozzle voltage remains zero, the plasma installation is then switched off by means of the previously obtained capacitor comparison voltage. This indicates to the operator that there is a fault in the plasma burner or faulty operation. For example, a bridge formation between the nozzle and the protective cap must be eliminated, or operation with nozzle-workpiece contact must be corrected.If the plasma burner is switched off by the operator, or the arc discharge tears off at the end of the workpiece, the voltage indicator responds with a delay, due to the capacitor connected in parallel via the resistor.
Faulty recording is prevented by a plasma installation relay contact which opens earlier.
In the case of plasma burners having power turnovers greater than 20 kW, advantageously the protective cap is formed with narrow apertures, to avoid the possible damming of heat.
Advantageously the protective cap is not completely flush with the nozzle in one plane, but the nozzle projects slightly out of the protective cap. This does not restrict vision during operation.
Conveniently the protective cap is con nected by means of screwthreading or resil ient cams to the contact pieces, which are disposed on an insulating member of the plasma burner.
Relays, semiconductor relays or semiconductor circuits can be used to indicate the fault current and nozzle potential.
In order that the invention may be more readily understood, reference is made to the accompanying drawings which illustrate diagrammatically and by way of example an embodiment thereof, and in which: Figure 1 is an axial section through a plasma burner in the zone of the nozzle and nozzle cap; and Figure 2 is a circuit arrangement constructed with relays.
A nozzle 1 is retained centrally in a nozzle holder 2 by means of a nozzle cap 3. A cooling water space 4, required for cooling the nozzle 1, is metallically sealed between the nozzle 1 and the nozzle cap 3, while the nozzle holder 2 is sealed by a rubber ring 5.
During operation the nozzle cap 3 and nozzle 1 carry a voltage potential in relation to a workpiece 11 (Fig. 2). The nozzle holder 2, nozzle 1 and nozzle cap 3 are electrically separated from the plasma burner casing via an insulating member 6. Located in the insulating member 6 are two contact pieces 7 in the form of half-rings, to each of which a protective cable extends for the fault current monitoring of the plasma installation. Machined into the surface of the contact pieces 7 is a screwthread which retains an electrically conductive protective cap 8 at the inner wall of its top end (as viewed in Fig. 1). Alternatively, the protective cap 8 may be connected to the contact pieces 7 by means of resilient cams (not shown). The two contact pieces 7 are electrically connected to one another by the protective cap 8 which may be provided with apertures (not shown).An air gap 9 insulates the nozzle cap 3 and protective cap 8 from one another. The plasma burner is built up coaxially around a cathode 10.
Fig. 2 shows a circuit arrangement constructed with relays and having a known fault current protective circuit. The plasma burner is shown by its specific constructional elements the cathode 10, nozzle 1 and protective cap 8. The workpiece 11 is connected to the circuit via a workpiece cable 12.
Two protective conductors, which can be short-circuited by the protective cap 8, extend therefrom via an on-off switch 13 to a low voltage transformer 14, rectifier 15 and relay 16. By means of its contacts the relay 16 controls the on-off circuit of the plasma installation. The protective cap 8 is also connected via diode 17 to a fault current relay 18. If a fault current flows via the protective cap 8 to the fault current relay 18, the latter closes and its contacts trigger the emergency stoppage of the plasma installation.
The nozzle 1 is connected to a relay 19 via a resistor 20 and also to capacitors 21; 22, a resistor 23, diode 24 and contact 25. (The contact 25 is in the plasma installation). If the plasma burner is operating correctly, the nozzle 1 carries a voltage potential in relation to the workpiece 11. This voltage causes relay 19 to close and at the same time charges capacitors 21; 22. If the cutting process is interrupted, the relay 19 opens with delay, due to the discharge of the capacitor 22. As a result, the contacts of the relay 19 cannot operate in the plasma installation on-off circuit.However, if during the operation of the plasma burner, splashes cause a short circuit bridge to build up between the nozzle 1 and protective cap 8, the fault current monitoring system of the protective cap 8 cannot operate, since the protective cap 8 is lying directly on the workpiece 11, the relay 19 immediately opens and switches the plasma burner off. In that case the delay does not come into operation. This event is stored by the closing of the relay 26.
The contacts 19' and 19" are closed-circuit contacts which are opened when the relay 19 closes. The contacts 27' and 27" are associated with relays belonging to the plasma installation control circuit. The contacts 27'; 27" are closed during the cutting process but open at different times. With a smooth start of cutting, the contacts 26'; 26" open earlier than the contacts 27'; 27" close. If after a malfunction the operator switches the plasma burner on again, and the malfunction continues, via the contact 25, which is closed during the pilot arc burning period, the capacitor 21 is discharged via the bridge formed between the nozzle 1 and the protective cap 8. As a result of the discharge, the relay 19 briefly closes, and when it opens, the contacts 26'; 26"; 21; 19" and the diode 28 operate the fault current relay 18, thus triggering the emergency stoppage system.
By means of additional diode wiring of the relay 19 in the form of diodes 17 and 28, further monitoring of the plasma installation such as, for example, workpiece contact or thermal overload protection, can be connected. In the absence of the protective cap 8, the plasma burner cannot be switched on since it is also switched on and off via this protective circuit. At the same time the nozzle 1 and therefore the nozzle cap 3 also are monitored during cutting for the presence of a voltage potential in relation to the workpiece 11.

Claims (6)

1. A plasma burner comprising a burner shaft, a nozzle and a nozzle cap surrounding said nozzle, with cooling water flowing between them, a cathode disposed coaxially in the nozzle, a fault current protective circuit, and a voltage indicator, effecting switching functions, arranged, in use, between a workpiece and the nozzle to monitor the nozzle for the presence of a voltage potential in relation to the workpiece, characterised in that disposed over the nozzle cap and insulated therefrom by an air gap is an electrically conductive protective cap, that to attach the protective cap to the plasma burner shaft at least two contact pieces are provided, each of which is connected via a cable to the fault current protective circuit, and that connected in series to the voltage indicator is a resistor to which is connected in parallel at least one capacitor having a diode connected in series.
2. A plasma burner according to claim 1, wherein the protective cap is adapted to the shape of the nozzle cap and provided with apertures.
3. A plasma burner according to claim 1 or 2, wherein the nozzle projects slightly out of the protective cap.
4. A plasma burner according to any of claims 1 to 3, wherein the protective cap is connected to the contact pieces by means of a screwthread or resilient cams.
5. A plasma burner according to any of claims 1 to 4, wherein the voltage indicator is a semiconductor circuit, a semiconductor relay or an electromechanical relay.
6. A plasma burner, substantially as herein described with reference to and as shown in the accompanying drawings.
GB8007556A 1979-03-06 1980-03-05 Plasma burner with contact protection Expired GB2048457B (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DD21141479A DD142267B1 (en) 1979-03-06 1979-03-06 Plasma torch with contact protection

Publications (2)

Publication Number Publication Date
GB2048457A true GB2048457A (en) 1980-12-10
GB2048457B GB2048457B (en) 1983-02-02

Family

ID=5517031

Family Applications (1)

Application Number Title Priority Date Filing Date
GB8007556A Expired GB2048457B (en) 1979-03-06 1980-03-05 Plasma burner with contact protection

Country Status (9)

Country Link
JP (2) JPS55146894A (en)
AT (1) AT374717B (en)
BG (1) BG39109A1 (en)
DD (1) DD142267B1 (en)
DE (1) DE3005894A1 (en)
FR (1) FR2450659A1 (en)
GB (1) GB2048457B (en)
SE (1) SE444629B (en)
SU (1) SU1046982A1 (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3810620C1 (en) * 1988-03-29 1989-09-21 Messer Griesheim Gmbh, 6000 Frankfurt, De Plasma burner
DE4300942A1 (en) * 1992-01-17 1993-07-22 Esab Welding Products Inc
CN107441897A (en) * 2017-07-26 2017-12-08 永康市广多环保设备科技有限公司 A kind of guard method of waste gas treatment equipment and equipment

Families Citing this family (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2534107A1 (en) * 1982-10-01 1984-04-06 Soudure Autogene Francaise ARC WORK FLASH WITH REMOVABLE COIFFE
DE3328777A1 (en) * 1983-08-10 1985-02-28 Fried. Krupp Gmbh, 4300 Essen PLASMA TORCHER AND METHOD FOR OPERATING IT
IT1204121B (en) * 1986-02-27 1989-03-01 Cebora Spa WELDING TORCH OR PLASMA CUTTING WITH NON-TRANSFERRED ARC
WO1988001218A1 (en) * 1986-08-11 1988-02-25 2-I Moskovsky Gosudarstvenny Meditsinsky Institut Device for plasma-arc cutting of biological tissues
US4916283A (en) * 1988-04-26 1990-04-10 Daihen Corporation Water cooling plasma arc working apparatus
DE10124013A1 (en) * 2001-05-17 2002-11-21 Isphording Germany Gmbh Burner head of a gas burner
FR2983674B1 (en) * 2011-12-01 2014-09-26 Air Liquide ARC PLASMA TORCH WITH ENHANCED ELECTRICAL INSULATION

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DD63823A (en) *
DE1615352B2 (en) * 1967-11-02 1971-09-02 VEB Mansfeld Kombinat Wilhelm Pieck, χ 4250 Lutherstadt Eisleben CIRCUIT ARRANGEMENT AND DEVICE FOR PLASMA HAND TURNERS
DD87361A1 (en) * 1970-10-23 1972-01-20 Electric discharge system for oxidizing gases
DD132706A3 (en) * 1974-10-08 1978-10-25 Jochen Boehme METHOD AND DEVICE FOR PROTECTING THE DUTIES OF WORK-PLASTERED PLASMA ROLLERS

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3810620C1 (en) * 1988-03-29 1989-09-21 Messer Griesheim Gmbh, 6000 Frankfurt, De Plasma burner
DE4300942A1 (en) * 1992-01-17 1993-07-22 Esab Welding Products Inc
CN107441897A (en) * 2017-07-26 2017-12-08 永康市广多环保设备科技有限公司 A kind of guard method of waste gas treatment equipment and equipment

Also Published As

Publication number Publication date
AT374717B (en) 1984-05-25
FR2450659B1 (en) 1984-04-06
JPS55146894A (en) 1980-11-15
DD142267B1 (en) 1980-12-24
DD142267A1 (en) 1980-06-11
BG39109A1 (en) 1986-04-15
SE8001733L (en) 1980-09-07
SE444629B (en) 1986-04-21
DE3005894C2 (en) 1989-10-12
GB2048457B (en) 1983-02-02
FR2450659A1 (en) 1980-10-03
ATA83380A (en) 1983-10-15
DE3005894A1 (en) 1980-09-18
JPS6258894U (en) 1987-04-11
SU1046982A1 (en) 1983-10-07

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Legal Events

Date Code Title Description
732 Registration of transactions, instruments or events in the register (sect. 32/1977)
PCNP Patent ceased through non-payment of renewal fee

Effective date: 19940305