GB2271842A

GB2271842A - Method of igniting a fuel-gas/heating-oxygen mixture

Info

Publication number: GB2271842A
Application number: GB9314525A
Authority: GB
Inventors: Joachim Klisch; Georg Roeder; Horst Thorandt
Original assignee: Messer Griesheim GmbH
Current assignee: Messer Griesheim GmbH
Priority date: 1992-10-23
Filing date: 1993-07-13
Publication date: 1994-04-27
Also published as: IT1272737B; DE4235856A1; FR2697319A1; ITMI932216A1; GB9314525D0; ITMI932216A0

Abstract

The invention relates to a method of igniting a fuel-gas/heating-oxygen mixture of a thermal processing tool, in particular of a cutting torch, with an ignition flame. In order to reduce the noise emission during ignition, the fuel-gas/heating-oxygen mixture has a smaller proportion of fuel gas relative to a neutral setting. The ignition gas is formed inside the processing tool from a branched-off partial quantity of the lean mixture and is ignited with an ignition device (26) Fig 2 (not shown). When the ignition flame has emerged from the nozzle (33) of the tool, the lean mixture flowing in the vicinity is ignited and the quantity of fuel gas required for the normal setting is then fed to the fuel-gas/heating-oxygen mixture. This method significantly reduces the noise caused during ignition. <IMAGE>

Description

- 1 2271842 Method and thermal processing tool foi: igniting a

fuelgas/heating-oxygen mixture The invention relates to a method of igniting a fuel -gas/ heating- oxygen mixture according to the preamble

of Claim 1 and to a thermal processing tool according to the preamble of Claim 5.

Using thermal processing tools, in particular cutting torches, individual work-pieces are cut out of large-area metal sheets, the cutting operation being carried out by a fuel-gas/heating-oxygen flame and cutting oxygen. Using the fuel-gas/heating-oxygen flame of the cutting torch, the work-piece is preheated to its ignition temperature which lies below the melting point. Oxygen is supplied under pressure by opening a valve, whereupon the material burns.

The fuel-gas/heating-oxygen mixture and the stream of cutting oxygen is set at valves on the cutting torch. In the normal setting of the f uelgas /heatingoxygen mixture, fuel gas (acetylene) and oxygen are mixed at a ratio of 1:1. In the injector, the fuel gas is sucked in through the flowing heating oxygen and mixes in the fuel-gas/heating-oxygen line. After ignition, this gas mixture burns as a flame at the cutting-torch nozzle.

To ignite the fuel-gas/heating-oxygen mixture, ignition devices arranged inside the cutting torch have proved to be advantageous since these become less soiled and, with these internal ignition torches compared to so called external ignition torches, there is no risk at all of collision with work-pieces or work-piece devices.

A multiplicity of internal ignition devices have been disclosed, which each have specific advantages and disadvantages. For example, a cutting torch has been disclosed in US Patent Specification 3,255,803, in which the ignition gas flows into the cutting-oxygen duct via a cross-bore between the duct of the f uel-gas /heatingoxygen mixture and the cutting-oxygen duct and is ignited at that point via an ignition device. The aisadvantages involved with a cross-bore of this type, namely arcing of the ignition flame into the duct of the fuel -gas/ heating oxygen mixture and one-sided effect on the heating in the case of flowing cutting oxygen, are to be prevented according to the German Offenlegungsschrift 3f516F511 of the generic type by a threaded screw arranged in the cross-bore.

The advantage of these ignition devices consists in that the device expenditure is small since the line for the fuel-gas/heating-oxygen mixture is used simul taneously for transporting the ignition gas, and no regulating devices are required for the ignition gas.

Furthermore, ignition devices have been dis closed, in which separate ignition-gas mixture feedlines are connected to ignition-gas quantity regulating devices (German Patent Specification 3,52-7,955), or in which ignition gases are taken from the supply lines for the fuel gas and the heating oxygen and are mixed in a separate mixer (German Offenlegungsschrift 3,941,370).

Upon ignition of the fuel-gas/heating-oxygen mixture set to neutral, an ignition detonation of the explosive fuel-gas/heating-oxygen mixture of 90 to 110 decibels occurs in all the known ignition devices, which detonation has led to considerable iMpairments of the operating personnel and people present in the production works.

The invention is therefore based on the object of reducing the noise emission during zhe ignition of a fuel-gas/heating-oxygen mixture of a thermal processing tool.

This object is achieved in a method of the

Claims

generic type by the characterising features of Claim 1 and in a thermal

processing tool of the generic type by the features of Claim 5.

By the f eatures of Claim 2. the noise emission of the ignition detonation is lowered by 6 to 12 decibels as a function of the nozzle size.

By the features of Claim 3, on the one hand the noise emission of the ignition flame is reduced and, on the other hand, it is made possible for the ignition-gas mixture to be taken from the fuel-gas/heating-oxygen mixture. Separate ignition-gas mixture regulating devices or ignition-gas mixture feedlines are not required.

By the features of Claim 4, backflashing in the fuel-gas/heating-oxygen line is advantageously avoided.

A cost-effective setting of the fuel-gas /heatingoxygen mixture with reduced proportions of fuel gas (leaned fuel-gas/heating-oxygen mixture) is achieved with a thermal processing tool, in particular a cutting torch.

according to the features of Claim 5. After the ignition of the leaned fuel-gas/heating-oxygen mixture, the full quantity of fuel gas can be added via the additional valve.

To automate the ignition sequence, the valve is connected via a control line to a control. preferably the control of the cutting-torch machine, which control switches the valve settings open and closed.

Via the features of Claim 7, a leaned fuelgas/heating-oxygen mixture is defined as a function of the type of fuel gas. In this casei a particularly cost- effective variant of the device is achieved by a bypass line which is always open. Further developments of the invention are specified in the subclaims. 25 The advantages achieved by the invention consist, in particular, in that the noise emission of the ignition detonation is reduced by 6 to 12 decibels relative to the ignition of a neutral f uel- gas /heating -oxygen mixture due to the reduced proportion of fuel gas in the fuel- gas/heating-oxygen mixture and the ignition-gas mixture which is branched off from the latter. Additionally, due to the slower ignition reaction of the leaned fuelgas/heating-oxygen mixture. flam arcing into the duct of the fuel-gas/heating-oxygen mixture and backflashing are far less critical than in a neutral f uel-gas /heatingoxygen mixture formation.

Furthermore. due to the leaned fuel-gas/heatingoxygen mixture. the consumption of fuel gas s reduced in the thermal processing of workpieces since the tool can be moved to cutting sites between two work-pieces or f rom the parking position of the cutting torch with a leaned fuel-gas/heating-oxygen flame, that is to say with the additional valve closed.

The method according to the invention can advantageously also be used in the pre-heating and postheating for welding and cutting, in annealing, tempering and f lame-hardening and the like in conjunction with heat burners.

An exemplary embodiment of the invention is illustrated in the drawing and described in greater detail below. Figure 1 shows a gas connecting block of a cutting torch with an additional valve, arranged. in the fuel- is gas line with a bypass line.

Figure 2 shows a sectional illustration of the torch head of a cutting torch with an internal ignition device.

In Figure 1. the gas connecting block 10 of a cutting torch is illustrated in partial sectionf to which gas connecting block lines 14, 15, 16, provided on the input side with setting valves. for cutting oxygen, fuel gas and heating oxygen are connected. According to Figure 1, the setting valves 11, 12, 13 are constructed as manually actuated valves. Arranged in the gas connecting block 10 is an injector 17 which is connected via connec tion ducts 18, 19 to the lines 15, 16 f or fuel gas and heating oxygen. On the output side, the injector 17 is connected via connection duct 20 and line 21 to the torch head 22 illustrated in Figure 2. Line 14 for the cutting oxygen is likewise connected to the torch head 22 via connection duct 23 and line 24. Furthermorer the electric lead 25 (illustrated only diagrammatically) for the ignition device 26 illustrated in Figure 2 is fed through the gas connecting block 10. The electric lead is connected on the gas connecting block 10 to a connection element 27 which is connected to an ignition source via electric leads (not illustrated in detail)..The ignition device 26 is advantageously constructed as an ignition plug.

Arranged ahead of the setting valve 13 in the fuel-gas line is an additional valve 28 with a bypass line 29. The valve 28 is connected to a control 31 via a control line 30. The control 31 is the cutting-torch machine control which is known per se.

The non-return safeguards arranged furthermore in the lines 141 151 16 as well as access and shutoff valves and the distributor pipes and gas regulating devices are known per se and therefore do not need to be illustrated and described in greater detail.

The torch head 22 is illustrated in greater detail in Figure 2. The torch head is connected to the gas connecting block 10 via the lines 21,, 24 and the guide pipe 32. Cutting-torch nozzles 33 can be connected to the torch head. The nozzle illustrated in Figure 2 is preferably constructed as a two-part slot nozzle. The heating nozzle 34 is screwed into the internal thread 36 of the torch head 22 by means of the external thread 35 constructed at the upper end.

It isr of course. also possible to construct the heating nozzle 34 to be integral with the cutting nozzle 37 or to attach it to the torch head 22 by means of a compression screw (not illustrated in detail).

The internal thread 36 of the torch head 22 bounds an annular space 38 which is constructed in the form of an annular groove at the end of the torch head 22 facing the nozzle 33. When the nozzle 33 has been screwed into the torch head 22, the annular space 38 is partially closed by the front 39 of the heating nozzle 34 so that the annular space 38 communicates on the outlet side with all the heating slots of the heating nozzle 37. on the inlet side, the annular space 38 communicates via the duct 44 with the line 21 for the fuel-gas/heating-oxygen mixture. The cutting nozzle 37 is screwed with its end opposite the outlet side into a threaded bore of the central pin of the torch head 22 constructed in the centre of the annular space 38. The cutting duct 42,, arranged in the centre of the cutting nozzle 37, communi- cates with the cutting-oxygen duct 43 of the torch head 22. The line 24, not illustrated in detail in Figure 2, is connected to the cutting-oxygen duct 43.

The annular space 38 communicates via a connec- tion duct 45 with a branch duct 46 which opens out into the cutting- oxygen duct. Constructed in the connection duct 44 is a nut thread 47 into which is screwed a threaded screw 48 with a bolt thread. It is sealed off gas-tightly towards the atmosphere at the screw cap by an annular seal 48.1. The threaded screw is accessible from the outside for servicing purposes.

The device works as follows:

Prior to ignition. the setting valves 11, 12, 13 are opened. The ignition operation is then initiated via the control 31 by triggering an ignition signal. The ignition operation is started manually. After startingy the heating oxygen flows with a quickly burning fuel gas as a function of the nozzle size, f or example at a pressure of 2.5 bar and, with a slowly burning fuel gas, as a function of the nozzle size, for example at a pressure of 3 bar via the line 16 and fuel gas at a pressure of. f or example. 0. 5 or 1 bar or greater via the bypass line 29. which is always open, into the injector 17 in which an ignitable, lean gas mixture is formed. The fuel-gas/heating-oxygen mixture has an empirically determined proportion of fuel gas which is smaller than 1 equal to 50 % relative to the normal setting for slowly or quickly burning fuel gases. The reduced quantity of fuel gas is set via different cross-sections in the bypass line 29. The values for the passage-opening of the bypas s line 29 are 0.25 to 0.65 mm, preferably 0.3 to 0.45 mm for the quickly burning fuel gas acetylene, and for the following slowly burning fuel gases propane 0.35 to 0.8 mm, preferably 0.5 to 0.6 mm.

Mapp 0.35 to 0.8 mm, preferably 0.5 to 0.6 mm, natural gas 0.55 to 0.9 mm, preferably 0.7 to 0.8 mm, Grieson 0.35 to 0.8 mm, preferably 0.5,to 0.6 mm This leaned mixture flows via connection duct 20 r and line-21 into the torch head 22 and then via duct 44 into the annular space 38. The leaned fuel-gas/heating oxygen mixture flows out of the nozzle 33 via the heating slots 40 of the heating nozzle 34. A small quantity of leaned fuel-gas/heating-oxygen mixture flows through the thread clearance of the connection duct 45 into the branch duct 46 and from there into -:he cutting-oxygen duct 43. After a given initial flow time of the leaned fuel-gas/heating-oxygen mixture, t1fte ignition is triggered by the control 31, thus resulting in a high voltage spark at the ignition device 26. This high voltage spark ignites the leaned ignition-gas mixture in the branch duct 46. The flame front then forming moves in the direction of the cutting duct 42 of the nozzle 33. It emerges from the cutting duct 42 into the open air at the f ront of the nozzle 33 and, in doing so, ignites the leaned f uel-gas/heating-oxygen mixture flowing out of the heating slots 40. Simultaneously with Ithe starting of the ignition, the cutting oxygen is activated by the control during a brief interval, e. g. via a remote-controlled access valve. The cutting oxygen reaches the ignition site at a point in time at which the f lame front has already emerged from the nozzle 33. The brief flow of cutting oxygen partially enters the branch duct 46 and connection duct 45 and extinguishes any groups of flames remaining at the threaded screw 48 or in the connection duct or branch duct. Flame arcing into the heating slots and backflashing into the duct 44 are reliably avoided by this surge of cutting oxygen. The proportion of fuel gas in the leaned fuel-gas/heating-oxygen mixture and the ignition-gas mixture is reduced by this flow of cutting oxygen without the ignition flame going out. After the leaned fuel-gas/heating-oxygen mixture has been ignited, the valve 28 is switched to "OPEN" by the control 31. The valve 28 opens so that the full proportion of the fuel gas required for a normal setting flows via the valve 28 and the bypass line 29 to the injector and from there into the annular space 38. A full flame is formed, generally with a neutral setting.

According to a further exemplary embodimentf the throughflow opening of the valve 28 can be adjusted continuously or discontinuously by means of the control 31 so that it corresponds to the passage-openings of the bypass lines for the different fuel gases. This design results in a simple adaptation to the type of fuel gas.

By the ignition of a leaned f uel-gas /heatingoxygen mixture with a proportion of fuel gas which is smaller than / equal to 50 % relative to the normal setting. the noise emission of the ignition detonation is reduced by 6 to 12 decibels down to 78 to 98 decibels due to the slower reaction of the mixture.

Claims 1. Method of igniting a fuel-gas/heating-oxygen mixture of a thermal processing tool, in particular a cutting torchr with an ignition flame, characterised in that the fuel-gas/heating-oxygen mixture has a smaller proportion of fuel gas relative to a neutral setting.
2. Method according to Claim 1, characterised in that the fuel- gas/ heatingoxygen mixture has a proportion of fuel gas which is smaller than / equal to 50 per cent relative to the normal setting of slowly or quickly burning fuel gases.
3. Method according to Claim 1 or 2, characterised in that the ignition gas is formed inside the processing tool from a branched-off partial quantity of the lean fuel-gas/heating-oxygen mixture and is ignited with an ignition device (26) and,, when the ignition flame has emerged from the nozzle (33) of the processing tool, the lean fuel-gas/heating-oxygen mixture flowing in the vicinity is ignited and the quantity oi fuel gas required for the normal setting is then JEed to the fuelgas/heating-oxygen mixture.
4. Method according to Claim 1 or 2. characterised in that,, for a given period, cutting oxygen is connected downstream of the ignition gas mixture.
5. Thermal processing tool, in particular cutting torch,, consisting of a gas connecting block (10) with an injector (17), to which gas connecting block lines, provided with valves (11, 121 13) on the input side for fuel gas (15), heating oxygen (16) and cutting oxygen (14) are connected, and which is connected on the output side to a torch head (22) via lines f or cutting oxygen (24) and fuel-gas/heating-oxygen mixture (21)r and the torch head (22) can be connected to cutting-torch nozzles (33) via ducts for cutting oxygen (43) and fuelgas/heating-oxygen (44),, an ignition device (26) connected to the cutting-oxygen duct (43) being arranged in the torch head (22), to which ignition device an ignition-gas mixture can be fed via a connection duct (45) with a threaded screw (48) through the thread clearance, characterised in that an additional valve (28), preferably with a bypass (29), is arranged in the fuel-gas line.
6. Thermal processing tool according to Claim 1,, characterised in that the valve (28) is connected to a control (31) via a control line (30) and the valve settings open/closed can be switched by the control (31).
7. Thermal processing tool according to Claim 5 or 6, characterised in that the bypass line (29) is provided as a path which is always open, and the passage-opening is constructed as a function of the type of fuel gas.
8. Thermal processing tool according to one of Claims 6 to 7, characterised in that the cutting-oxygen duct (43) is connected to the ignition device (26) via a branch duct (46), and the connection duct (45) connected to the line (21) for the fuel-gas/heating-oxygen mixture opens out into the branch duct (46).
9. Thermal processing tool according to one of Claims 5 to 8, characterised in that the values for the passage-opening of the bypass line (29) are 0.25 to 0.65 mm, preferably 0. 3 to 0.45 mm for the quickly burning fuel gas acetylene, and for the following slowly burning fuel gases propane 0.35 to 0.8 mm, preferably 0.5 to 0.6 mmr Mapp 0.35 to 0.8 mm, 0.5 to 0.6 mm, 0.55 to 0.9 mmi 0.7 to 0.8 mm, 0.35 to 0.8 mm, 0.5 to 0.6 Em.
10. Thermal processing tool according to Claim 5j, characterised in that the valve (28) is connected to a control (3 1) via a control line (3 0). and the throughf low opening of the valve _. (2 8) can be sez between OPEN and CLOSED by means of the control (31).

natural gas preferably preferably preferably t,