WO2024002944A1

WO2024002944A1 - Torch for an oxy-fuel welding and cutting system and method of operating the torch

Info

Publication number: WO2024002944A1
Application number: PCT/EP2023/067261
Authority: WO
Inventors: Axel Vogelsang
Original assignee: Messer Cutting Systems Gmbh
Priority date: 2022-06-27
Filing date: 2023-06-26
Publication date: 2024-01-04

Abstract

Known torches, in particular injector torches, comprise a torch base body (4), a torch head (2) connected to the torch base body (4) and a torch tip (2.1) held therein, wherein flow paths are defined in the torch base body (4), at least one of which is a fuel gas path (7) extending from a fuel gas inlet (5. 2), and at least one other being an oxygen path (8) extending from an oxygen inlet (5.1), and wherein the fuel gas path (7) and at least a conduit portion of the oxygen path (8) join at a venturi nozzle (33; 33.1) to form a common outlet path (34) leading through the torch tip (2.1). In order to provide a torch with which a leak or blockage in the fuel gas line and/or in the oxygen line can be reliably detected, it is proposed that the venturi nozzle comprises a pressure nozzle (33.5) fluidically connected to the oxygen line (8) and having a nozzle outlet (33.6), wherein the outlet path comprises a mixing nozzle (34) and a mixing nozzle inlet (34.1) for generating an oxygen-fuel gas mixture, and wherein the venturi nozzle (33; 33.1) and the mixing nozzle (34) are adapted to generate in operating mode a negative pressure P_negative of at least -0.3bar relative to atmospheric pressure in the fuel gas path (7).

Description

TORCH FOR AN OXY-FUEL WELDING AND CUTTING SYSTEM AND METHOD OF OPERATING THE TORCH

FIELD OF THE INVENTION

This invention relates to a torch, and more particularly, but not exclusively to a torch for use in an oxy-fuel system. In particular, the invention relates to an oxy-fuel torch that can be hand-held or that can be removably connected to machines for cutting, welding, brazing or heating.

BACKGROUND TO THE INVENTION

The applicant’s provisional patent application No. ZA 2022/07073 entitled “Oxy-fuel welding and cutting system” filed on the same date as this provisional patent application and its provisional patent application No. ZA 2022/07075 entitled “Demand valve for an oxy fuel welding and cutting system”, are both included herewith, in their entirety, by way of reference.

As known in the industry, oxy-fuel welding, brazing, heating and cutting are processes that use fuel gases and oxygen. Fuel gases are for example acetylene, natural gas, propane, hydrogen and MAPP gas.

The equipment used in oxy-fuel welding, brazing, heating, soldering and cutting requires an oxygen source and a fuel gas source (usually contained in cylinders), two pressure regulators, two flexible hoses (one for each source of gas), a torch and where mandatory, a flashback arrestor.

Some regulators allow to use or set the pressure of the gas from the gas cylinders in accordance with EN-ISO:2503. The volume required for the task to be performed is then adjusted by the operator turning needle valves at the torch. Accurate flow control with a needle valve relies on a constant supply pressure from the regulator to the torch.

The hoses are manufactured to be compatible to the gases used. A double hose or twinned design hose is sometimes used, meaning that the oxygen and fuel hoses are joined. However, beads of molten metal given off by the cutting process can become lodged between the hoses, and burn through, releasing the pressurized gas inside, which in the case of fuel gas, usually ignites.

Fuel gas such as acetylene is not just flammable; in certain conditions it is explosive. Although it has an upper flammability limit in air of 81 %, acetylene's explosive decomposition behavior makes this irrelevant. If a detonation/deflagration wave enters the acetylene cylinder, the cylinder may be blown apart by the subsequent decomposition. Ordinary check valves I non-return valves that normally prevent backflow I reverse flow are not capable to stop a flashback as they do not contain flame quenching components.

Between the regulator and hose, and ideally between hose and torch on both oxygen and fuel lines, a flashback arrestor and/or non-return valve (check valve) may be installed to prevent flame or oxygen-fuel mixture being pushed back into either regulator at the cylinder and damaging the equipment or causing a cylinder to explode. A check valve lets gas flow in one direction only. It is usually a chamber containing a ball that is pressed against one end by a spring. Gas flow one way pushes the ball out of the way, and a lack of flow or a reverse flow allows the spring to push the ball into the inlet, blocking it.

The torch is the tool that the operator uses to perform the appropriate tasks required. It has a connection and valve for the fuel gas and a connection and valve for the oxygen, a handle for the operator to grasp, and gas mixing facilities where the fuel gas and oxygen mix, with a nozzle where the flame exits. Two basic types of torches are in use; (i) nozzle mixing torches and (ii) premix - injector type torches.

Acetylene, LPG and other fuel gases are highly flammable, and form explosive mixtures with the surrounding air and/or oxygen. A major cause of accidents with gas equipment is leaking connections or poorly maintained equipment and the subsequent ignition of the leaking fuel gas which is extremely flammable can create an explosion. Even small leaks can cause a flash fire or explosion, particularly when the equipment is used in poorly ventilated areas or confined spaces such as in underground mining operations where the gases can accumulate. During the operations, sparks and spatter can be generated which are a major cause for ignition. To detect leaks in the hoses or connections, leak detection spray is applied to all fuel gas and oxygen connections starting at the cylinder valve, regulator including all other connections up to the torch nozzle. Leaks will be clearly indicated by foaming bubbles at the point of leakage. A user will then know that it would be dangerous to light the gases at the nozzle and/or gas system before the leak is stopped or the leaking component is replaced. It is especially user unfriendly when an entire length of hose needs to be sprayed and checked.

This could be quite hazardous as a lot of this gas equipment is used underground or in confined spaces and the risk of explosions and the effect thereof can be devastating.

OBJECT OF THE INVENTION

It is an object of this invention to provide a torch for an oxy-fuel system which, at least partially, alleviates or assists to alleviate some of the abovementioned hazards.

In particular, it is the object of the invention to provide a torch with which a leak or blockage in the fuel gas line and/or in the oxygen line can be reliably detected.

Furthermore, it is a technical problem of the invention to provide a method for operating the torch which enables immediate detection of a leak or blockage in the fuel gas line and/or in the oxygen line in a reproducible manner.

SUMMARY OF THE INVENTION

In accordance with this invention there is provided a torch comprising: a body defining flow paths therethrough, two inlet flow paths being a fuel and an oxygen flow path extending from fuel and oxygen inlets, the flow paths combining at a venturi to form a single outlet path terminating in an outlet opening, the venturi being configured to, under operational pressures and flows open a demand valve upstream from the fuel flow path inlet. The torch is used in an oxy-fuel system to generate a heat source for heating brazing, welding or cutting. When a breach of the fuel line occurs, the demand valve will close.

These and other features of the valve are described in more detail below.

Torches that use the Venturi effect are also referred to as injector torches, with the Venturi nozzle usually being a gas-mixing nozzle or an injector insert in the torch base body or torch head.

The torch according to the invention, preferably is an injector torch, comprises a torch head connected to the torch body and a torch tip held therein, wherein flow paths are defined in the torch body, at least one of which is a fuel gas path extending from a fuel gas inlet and at least one other being an oxygen path extending from an oxygen inlet, and wherein the fuel gas path and at least a portion of the oxygen path join at a venturi nozzle to form a common outlet path leading through the torch tip,

• wherein the venturi nozzle comprises a pressure nozzle fluidically connected to the oxygen line and having a nozzle outlet,

• wherein the outlet path comprises a mixing nozzle and a mixing nozzle inlet for producing an oxygen-fuel gas mixture,

• and wherein the venturi nozzle and the mixing nozzle are configured to generate in operating mode a negative pressure Pnegative of at least -0.3bar relative to atmospheric pressure in the fuel gas path.

In so-called "injector torches", the oxygen is supplied at a higher pressure than the fuel gas. The oxygen flowing into the injector creates a negative pressure, as a result of which the fuel gas is sucked in and entrained. Oxygen and fuel gas mix in the mixing tube. This negative pressure is not defined, but only the overall system must meet the requirements of DIN EN ISO 5172 in order to permit a corresponding approval. In order to ensure that a negative pressure is established in the injector torch, this DIN standard prescribes the performance of a "suction test". The "suction test" is still considered to have been passed if the pressure measured on the fuel gas side does not exceed 0.5 times the fuel gas pressure specified by the manufacturer. That means, that this condition is also fulfilled if the pressure on the fuel gas side is above atmospheric pressure, i.e. the pressure in the fuel gas line is greater than zero; this is not a “negative pressure” in the sense that the pressure is below atmospheric pressure. Nonetheless, the inventors have measured the pressure in the fuel gas line of injector torches available on the market. They found that they usually have a pressure at the fuel gas connection of -0.05 to -0.2bar (this means an absolute pressure of 0.8 to 0.95bar).

But this reduced pressure is, on the one hand, not exactly defined and may also fluctuate into the positive pressure range as process conditions or torch designs change, and, on the other hand, the pressure, although reduced, may not be low enough to detect a (small) pressure change caused as a result of a (small) leak if it is not sufficient to cause reliable closing of the connected demand valve.

That is, one of the merits of the invention is to have recognized that the "negative pressure" in prior art systems was undefined and too low for reproducible functionality. This means that one focus of the invention is the generation of a defined negative pressure in order to ensure the function of the overall system in conjunction with the negative pressure demand valve and thus to produce an absolutely leakage-free and safe system. The fulfilment condition of ISO 5172 2 are thus also fulfilled by the way, but do not represent the main focus.

The torch creates a sufficient Venturi effect to ensure the opening of a demand valve in an upstream fuel line. Upon breach of the fuel line, the demand valve will close rendering the torch and connected system safe.

The torch base body is connected to the torch head, which is supplied with oxygen, fuel gas and/or an oxygen-fuel gas mixture. The torch tip is usually replaceable and comprises one or more nozzles, such as a cutting nozzle and a heating nozzle.

The nozzle referred to above as the "mixing nozzle" forms a "single-outlet path" in which the fuel gas mixture is fed to the torch head.

Due to the Venturi effect, the oxygen flow exiting the pressure nozzle outlet and entering the mixing nozzle inlet creates an effective negative pressure Pnegative in the fuel gas path and entrains fuel gas into the mixing nozzle. The decisive factor for the Venturi effect is the (effective) negative pressure Pnegative present at the mixing nozzle inlet. This negative pressure continues into the fuel gas chamber and throughout the fuel gas supply line to the demand valve. The demand valve suitable for the torch according to the invention is vacuum-controlled and opens only when the negative pressure Pnegative in the fuel gas path has a setpoint value of -0.3bar or more (relative to atmospheric pressure), for example -0.4bar (relative to atmospheric pressure). If there is a leak in the upstream fuel gas supply line between the demand valve and the mixing nozzle inlet, the setpoint cannot be reached because of the fuel gas escaping there, so the demand valve will not open. The same applies if there is a leak in the oxygen line so that the Venturi effect is not sufficient to set the negative pressure setpoint or if one of the two lines mentioned is blocked.

The effective negative pressure Pnegative is defined as the pressure measured in the fuel gas path when the torch is in its operating mode. That means, a nozzle is inserted in the outlet path for the oxygen fuel gas mixture, e.g. a cutting, welding or heating nozzle is inserted in the torch head. The effective negative pressure Pnegative must be reached in the upstream fuel gas supply line regardless of the specific nozzle currently used. In the idle state, that means, when no nozzle is inserted in the outlet path for the fuel gas mixture, the negative pressure difference must be even higher (more negative relative to atmospheric pressure) than the effective negative pressure Pnegative. The values given for Pnegative are always differential pressures relative to atmospheric pressure (i.e. 1 bar), regardless of whether they are preceded by a minus sign or not. A higher value for Pnegative means a larger difference to 1 bar, i.e. a lower absolute pressure. In this sense, for example, -0.4bar is a "higher value" than -0.3bar.

The invention essentially differs from the current state of the art of the injector torches in that, on the one hand, it fulfills the requirements of DIN EN 5172, but in addition generates a defined negative difference pressures relative to atmospheric pressure (1 bar) lower than -0.3bar. This negative pressure makes it possible to open a corresponding vacuum controlled demand valve (e.g. a so called S.A.T. valve - Safety Advanced Technology) and is able to deliver the required amount of fuel gas in order to optimally adjust the flame and can thus also generate a fuel gas surplus.

The invention optimizes the injector, mainly pressure and mixing nozzle in their ratio and dimensions so, that for the first time an appropriately defined negative pressure more than -0.3bar can be generated in the fuel gas supply line. The suction effect at the fuel gas connection, which is achieved by the Venturi effect, serves primarily to provide safety against gas backflow into the fuel gas line under all operating conditions for the corresponding torch or application.

The Venturi nozzle and the mixing nozzle are preferably designed so that an effective negative pressure Pnegative of at least -0.4bar, preferably in the range of -0.4 to -0.8bar, and particularly preferably in the range of -0.42 to -0.6bar relative to atmospheric pressure can be set in the fuel gas path.

The higher the range lower limit is selected, the more sensitive the leak detection responds; but the more difficult and costly it is to set the negative pressure setpoint reproducibly. Therefore, negative pressure differences more than -0.8bar are technically feasible but not preferred in practice.

There are several design and process parameters for adjusting the negative pressure setpoint. A particularly preferred design parameter is that a distance A in the range between 0.2mm and 2mm, preferably between 0.25mm and 1.5mm and especially preferably between 0.3mm and 1.2mm is set between the nozzle outlet of the pressure nozzle and the mixing nozzle inlet.

If the distance A is too narrow, the oxygen flow exiting the narrow pressure nozzle outlet can impede the inflow of the fuel gas. If the distance A is too large, the oxygen flow upstream of the mixing nozzle inlet may fan out to such an extent that it mixes noticeably with the fuel gas even before the mixing nozzle inlet and the setpoint for the effective negative pressure Pnegative in the fuel gas path is not achieved.

Another preferred design measure for achieving a sufficient Venturi effect is that the mixing nozzle inlet has a diameter D, and that the nozzle outlet of the pressure nozzle has a diameter d, and that the following applies for the diameter ratio d/D: 0.1 < d/D < 0.8, preferably 0.15 < d/D < 0.5, particularly preferably 0.2 < d/D < 0.4.

At a very small diameter ratio d/D of less than 0.1 , the flow rate of oxygen is low and thus the amount of fuel gas and the power of the torch are also low. With a very large diameter ratio d/D of more than 0.8, the Venturi effect and thus the suction power becomes smaller and smaller.

It has proved useful if the venturi nozzle comprises at least one injector insert in which or on which a fuel gas chamber is formed which is fluidically connected to the fuel gas path and is adjacent to the mixing nozzle inlet, the nozzle outlet of the pressure nozzle being opposite the mixing nozzle inlet.

The at least one injector insert is inserted, for example, into the torch base body or into the torch head. It contains at least one channel and/or cavity for the inflowing oxygen flow. It also contains at least one channel and/or cavity for the inflowing fuel gas, or it forms the at least one channel and/or cavity for the fuel gas together with the surrounding torch base body or torch head.

The nozzle outlet of the pressure nozzle communicates with the fuel gas chamber, for example, by being adjacent to the fuel gas chamber. The oxygen flow exiting the pressure nozzle outlet and entering the opposite mixing nozzle inlet passes through the combustion gas chamber, generates the effective negative pressure Pnegative there due to the Venturi effect and entrains fuel gas into the opposite mixing nozzle.

In the diagram in Figure 7, the oxygen pressure at the inlet of the pressure nozzle (in bar) is plotted against the outlet pressure (in bar) at the oxygen pressure regulator for a cutting torch without a cutting nozzle as well as for different cutting nozzle sizes inserted therein (the numbers in columns 4 to 9 indicate the thickness range of the metal sheets for which the cutting nozzle is designed).

Table 1 shows the measured values on which the diagrams of Figure 7 and of Figure 8 are based.

Table 1

It can be seen that the pressure drop is essentially independent of the type of cutting nozzle used, and that the pressure at the pressure nozzle scales with the pressure at the pressure regulator.

The oxygen pressure at the pressure regulator is preferably designed for operation with an oxygen pressure P02 at the pressure regulator in the range between 1 bar and 10bar.

With regard to the method of operating the torch according to the invention, the above technical problem is solved according to the invention by a method comprising the following method steps: a fuel gas is supplied to the fuel gas chamber via a fuel gas path with a nominal fuel gas pressure PH2 in the range of 0.5 to 2bar, oxygen is supplied to the pressure nozzle via an oxygen line with an oxygen nominal pressure P02 in the range of 2 to 10bar, the injector and the mixing nozzle being designed such that a negative pressure Pnegative of at least -0.3bar relative to atmospheric pressure is set in the fuel gas path.

Due to the Venturi effect, the oxygen flow leaving the outlet of the pressure nozzle and entering the mixing nozzle inlet creates an effective negative pressure Pnegative in the fuel gas path and entrains fuel gas into the mixing nozzle. The decisive factor for the Venturi effect is the (effective) negative pressure Pnegative present at the mixing nozzle inlet. This continues into the fuel gas chamber and throughout the fuel gas path to the demand valve. The demand valve suitable for the torch according to the invention is vacuum-controlled and opens only when the negative pressure Pnegative in the fuel gas path has a setpoint value of -0.3bar or more (relative to atmospheric pressure), for example -0.4bar (relative to atmospheric pressure). If there is a leak in the fuel gas path between the demand valve and the mixing nozzle inlet, the setpoint cannot be reached because of the fuel gas escaping there, so the demand valve will not open. The same applies if there is a leak in the oxygen line so that the Venturi effect is not sufficient to set the negative pressure setpoint or if one of the two lines mentioned is clogged.

In a particularly preferred process variant, a negative pressure Pnegative of at least -0.4bar, preferably in the range of -0.4 to -0.8bar, preferably in the range of -0.42 to -0.6bar relative to atmospheric pressure is set in the fuel gas path.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now further explained with reference to the figures. The figures and figure descriptions are exemplary and are not to be considered as limiting the scope of the invention. In detail shows

Figure 1 a torch with a longitudinal injector in a three-dimensional representation in a view of the front of the torch head,

Figure 2 shows the torch of Fig. 1 in a three-dimensional representation in a rear view of the top side, Figure 3 a first embodiment of the torch according to the invention with a longitudinal injector in a longitudinal section through the torch head,

Figure 4a a second embodiment of the torch according to the invention in the form of a cutting torch with a gas-mixing nozzle acting as an injector in the torch base body in a longitudinal section,

Figure 4b a third embodiment of the torch according to the invention in the form of a cutting torch with a gas-mixing nozzle acting as an injector in the torch head in a longitudinal section,

Figure 5 a fourth embodiment of the torch according to the invention with an angled torch head with a longitudinal injector inserted therein in three- dimensional representation,

Figure 6 a fifth embodiment of the torch according to the invention with a stretched torch head with a longitudinal injector inserted therein in three-dimensional representation,

Figure 7 a diagram explaining the relationship between the oxygen pressure set at the pressure regulator and the pressure applied to the pressure nozzle,

Figure 8 a diagram explaining the relationship between the oxygen pressure set at the pressure regulator and the suction pressure applied in the fuel gas path, and

Figure 9 a three-dimensional representation of a longitudinal injector integrated in a torch head, partially in section.

DETAILED DESCRIPTION OF THE DRAWINGS

The torch 1 shown in Figure 1 is an injector torch as is generally known in the art to create a heat source for heating, cutting, braising or welding. In the preferred example, it is designed as a cutting torch and comprises a torch head 2 with an injector 3 designed as a longitudinal injector, a base body 4 and a handle 5.

On the handle 5 there is a hose connection 5.1 for oxygen, and a hose connection 5.2 for the fuel gas (such as acetylene). The valves required for shutting off and regulating are usually located on the base body 4, namely a heating oxygen regulating valve 4.1 , a fuel gas regulating valve 4.2 and a trigger arm 4.3 for setting the volume flow for the cutting oxygen. A cutting oxygen line 6 leads from the base body 4 to the torch head 2; and a fuel gas path 7 and a line 8 for heating oxygen (see Figure 2) lead to the injector 3. A nozzle assembly is inserted into the torch head 2, comprising a heating nozzle 2.1 and a cutting nozzle 2.2. The base body 4 with the operating parts 4.1 , 4.2 and 4.3 can be made in one piece with the handle 5 of the torch 1 .

Figure 2 shows the known injector cutting torch 1 in a top view. The injector 3 is suitable to create a Venturi effect, which is suitable to cause a pressure reduction in the fuel gas path 7. For this purpose, the known injector torches are operated so that the heating oxygen is supplied at a higher pressure than the fuel gas. The heating oxygen flowing into the injector creates a negative pressure, as a result of which the fuel gas is drawn in and entrained. Heating oxygen and fuel gas mix in the mixing tube and flow out via the cutting nozzle 2.2.

As explained above, the reduced pressure generated by the known injector nozzles is not defined, but only the overall system must meet the requirements of DIN EN ISO 5172 in order to permit a corresponding approval. The inventors have measured the pressure in the fuel gas line of injector torches available on the market. They found that they usually have indeed a negative pressure at the fuel gas connection of -0.05 to -0.2bar (this means an absolute pressure of 0.8 to 0.95bar). In the features visible in Figs. 1 and 2, the known injector torch 1 does not differ from an injector torch of the invention. The features belonging to the invention relate to the design of the injector nozzle and are explained in more detail below with reference to Figures 3 to 8.

Figure 3 shows a torch head 32 of an injector torch 30 according to the invention in longitudinal section.

The torch of the invention is designed to produce sufficient Venturi effect to ensure the opening of a vacuum-controlled demand valve in an upstream fuel line that only responds to a comparatively high negative pressure. In the event of even a minor leak in the fuel gas line, much less a rupture, the demand valve will close, making the torch and connected system safe. Therefore, the invention differs from the current state of the art in that, on the one hand, it fulfills the requirements of DIN EN 5172, but in addition generates a defined high negative pressure difference of at least -0.3bar, preferably at least -0.4bar, which is able to deliver the required amount of fuel gas in order to optimally adjust the flame and can thus also generate a fuel gas surplus, and which makes it possible to open a corresponding negative pressure demand valve, which is inserted into a fuel gas supply line (also referred to as “supply path”) between the main pressure reducer and the torch of the invention. .

The invention optimizes the area of the injector, mainly pressure and mixing nozzle in their ratio and dimensions so, that for the first time an appropriately defined negative pressure of at least -0.3bar, preferably at last -0.4bar, can be generated at the fuel gas inlet.

The suction effect at the fuel gas connection, which is achieved by the Venturi effect, serves primarily to provide safety against gas backflow into the fuel gas line under all operating conditions for the corresponding torch or application.

This means that one focus of the invention is the generation of the defined negative pressure in the fuel gas line in order to ensure the function of the overall system in conjunction with the negative pressure demand valve and thus to produce an absolutely leakage-free and safe system. By the way, the provisions of ISO 5172 2 are thus also fulfilled, but do not represent the main focus.

This further improvement of the prior art is explained in more detail below with reference to Figures 3 to 8. Where the same reference numerals are used as in Figures 1 and 2, these designate identical or equivalent components or constituent parts of the torch according to the invention.

The injector of Figure 3 is designed as a longitudinal injector 33. A mixing nozzle 34 is formed in the torch head 32. An injector 33 is inserted between the mixing nozzle 34 and the oxygen and fuel gas paths (7; 8) opening into the torch head 32. Oxygen flows from the oxygen line 8 into a pressure nozzle 33.5 at a pressure of, for example, 2.5bar (preferred range: 2 to 8.5bar). The fuel gas flows from the fuel gas path 7 at a lower pressure of, for example, 1 bar (preferred range: 0.4 to 1 ,7bar) into an annular fuel gas chamber 33.7, which is flu idical ly connected on the one hand to the pressure nozzle 33.5 via the narrow nozzle outlet 33.6 and on the other hand to the mixing nozzle 34.

The pressure nozzle 33.5 (oxygen) opens into the annular fuel gas chamber 33.7 via a bore 33.8 with a narrow nozzle outlet 33.6. The oxygen flows at high pressure from the pressure nozzle 33.5 into the annular fuel gas chamber 33.7 and enters the opposite located mixing nozzle 34. The oxygen flow thus generates a negative pressure in the annular fuel gas chamber 33.7, so that the fuel gas is drawn from the fuel gas chamber 33.7 at an effective negative pressure Pnegative, oxygen and fuel gas mix in the mixing nozzle 34 and the gas mixture enters the cutting nozzle 2.2 via a mixing channel 34.2 and adjoining settling area 34.3.

The effective negative pressure Pnegative present in the annular fuel gas chamber 33.7 is at least -0.3bar (under atmospheric pressure) according to the invention, preferably it is at least -0.4bar and more preferably in the range between -0.4 and - 0.9bar, particularly preferably between -0.42 and -0.8bar. This effective negative pressure Pnegative can be established - apart from a negligible pressure drop of the order of up to 10% - in the entire fuel gas path 7, up to a demand valve inserted in the fuel gas path 7. This may, for example, be a vacuum-controlled demand valve designed to open the fuel gas path 7 only at a negative pressure of at least -0.3bar for the fuel gas and to close it otherwise.

The effective negative pressure Pnegative is determined to a large extent by the distance A between the outlet (nozzle outlet 33.6) of the narrow bore 33.8 and the nozzle inlet 34.1 of the mixing nozzle 34. This distance corresponds to the width of the annular fuel gas chamber 33.7. If the distance A is too narrow, the oxygen flow flowing out of the narrow nozzle outlet 33.6 can obstruct the entry of the fuel gas into the annular fuel gas chamber 33.7. If the distance A is too large, the oxygen flow may fan out too much upstream of the nozzle inlet 34.1 of the mixing nozzle 34, so that it already mixes appreciably with the fuel gas upstream of the mixing nozzle 34 and the setpoint for the effective negative pressure Pnegative in the fuel gas path 7 is not reached. In the preferred example, the distance A is 0.65mm.

Another design parameter that affects the effective negative pressure Pnegative is the diameter ratio d/D between the diameter d the narrow pressure nozzle outlet 33.6 and the diameter D at the nozzle inlet 34.1 of the mixing nozzle 34. The diameter of the narrow nozzle outlet 33.6 is always smaller than the diameter D at the nozzle inlet 34.1 of the mixing nozzle 34, so that the diameter ratio d/D is smaller than 1. Particularly preferably, it is in the range between 0.1 and 0.8, preferably between 0.14 and 0.5, and most preferably in the range between 0.2 and 0.4. If the diameter ratio d/D is very small, e.g. less than 0.1 , the flow rate of oxygen is low and thus the amount of fuel gas and the power of the torch are also low. With a large diameter ratio d/D, e.g. more than 0.8, the Venturi effect and thus the suction power becomes small so that there is a risk that the effective negative pressure Pnegative cannot be generated and maintained in the fuel gas path.

These above-mentioned diameter d/D ratios apply to typical pressure nozzle diameters in the range of 0.3 to 5mm. If both d and D become equally smaller, the diameter ratio remains the same and the suction power increases, but a pressure nozzle diameter of less than 0.3mm results in a low gas flow volume and thus a low burner performance.

In the preferred example, d is 0.57mm and D is 1.9mm, and the diameter ratio d/D is 0.3.

The effective negative pressure Pnegative is also influenced by the oxygen pressure applied to the pressure nozzle 33.5. This can be in the range of 1 to 10bar, for example, and is typically in the range of about 2 to 5bar. The diagram of Figure 8 shows this dependence using the example of the cutting torch shown in Figure 3, when this is fitted with cutting nozzles of different sizes. The x-axis shows the pressure range P02 between 1 and 10bar, which corresponds to the oxygen pressure at the pressure regulator (and which correlates linearly with the pressure at the pressure nozzle 33.5, as shown in Figure 7). On the y-axis is plotted the effective negative pressure Pnegative (in bar) measured in the fuel gas path (more precisely: in the area of port 5.2). From this it can be seen that the effective negative pressure Pnegative decreases with increasing oxygen pressure, whereby the smaller and thinner the cutting nozzle, the smaller the decrease at the same oxygen pressure. For example, in the case of a cutting nozzle for a sheet thickness in the range of 200 to 300mm, an effective negative pressure Pnegative of -0.3bar already results at an oxygen pressure of about 3bar; whereas when using a cutting nozzle for a sheet thickness in the range of 3 to 10mm, an effective negative pressure Pnegative of -0.3bar requires an oxygen pressure of more than 3bar. Irrespective of this, an effective negative pressure Pnegative of -0.3bar can be set with the cutting torch according to the invention using the usual oxygen pressures.

In the schematically illustrated embodiment shown in Figure 4a, the torch 40 is also designed as a cutting torch. It comprises a torch head 2 and a base body 4, which also serves as a handle. On the base body 4 there is a hose connection 5.1 for oxygen, which is connected to an oxygen line 8, a hose connection 5.2 for fuel gas, which is connected to a fuel gas path 7, an oxygen regulating valve 4.1 , a fuel gas regulating valve 4.2 and a trigger arm 4.4. In the area of the oxygen regulating valve

4.1 , the oxygen line 8 splits into a heating oxygen line 8.1 and a cutting oxygen line 4.7. The trigger arm 4.4 is used to simultaneously open and close both the heating oxygen line 8.1 and the cutting oxygen line 4.7. In the area of the fuel gas regulating valve 4.2, the fuel gas path 7 merges into a fuel gas bore 7.1 , which opens into an annular fuel gas chamber 7.2. The annular fuel gas chamber 7.2 is connected to a mixing nozzle 44 via an annular channel 7.3. In the region of the mixing nozzle inlet

44.1 , the heating oxygen line 8.1 also opens into the mixing nozzle 44, its opening cross section tapering in the direction of the mixing nozzle inlet 44.1 and the flow velocity of the heating oxygen flow increasing as a result. At the mixing nozzle inlet

44.1 , the opening cross section of the heating oxygen line 8.1 is smaller than the opening cross section of the annular channel 7.3 and the flow velocity of the heating oxygen flow is greater than that of the fuel gas flow. As a result, a negative pressure relative to atmospheric pressure is generated in the annular channel 7.3, in the annular fuel gas chamber 7.2, in the fuel gas bore 8.1 and in the fuel gas path 8, which causes fuel gas to be drawn into the mixing nozzle 44 in accordance with the Venturi effect. The mixing nozzle 44 is a gas-mixing nozzle acting as an injector. The design in the area of the mixing nozzle 44 as well as gas pressures and flows are such that a negative pressure of at least -0.3bar compared to atmospheric pressure is established at the mixing nozzle inlet 44.1 and in the annular channel 7.3, which thus also prevails in the fuel gas path 7.

In the schematically shown embodiment of the cutting torch 41 in Figure 4b, the same or equivalent components as in the cutting torch of Figure 4a are designated with the same reference numerals. It differs from that of Figure 4a essentially in that the mixing nozzle 44a is annular and is displaced into the torch head 2, and that the heating oxygen line 8.1 opens into an annular space 8.4 which opens into an annular mixing nozzle 44b via a tapering annular channel 8.5. The fuel gas bore 7.1 opens into an annular fuel gas chamber 7.4, which merges into the annular mixing nozzle 44b via an annular channel 7.5. The design in the area of the mixing nozzle 44b as well as gas pressures and flows are such that a negative pressure of at least -0.4bar compared to atmospheric pressure is established in the fuel gas chamber 7.4.

The embodiment of the torch according to the invention shown in Figure 5 is designed as a cutting torch with an angled torch head 2 in which a cross injector 53 is inserted. The design of the cross injector 53 and the gas pressures and flows are such that a negative pressure of at least -0.4bar compared with atmospheric pressure is established in the fuel gas path 7.

The embodiment of the torch according to the invention shown in Figure 6 is designed as a cutting torch with an elongated torch head 2 in which a cross injector 63 is inserted. The design of the cross injector 63 and the gas pressures and flows are such that a negative pressure of at least -0.4bar compared with atmospheric pressure is established in the fuel gas path 7.

The partial sectional view of the cutting torch 90 of Figure 9 serves to explain the injector principle using the example of a longitudinal injector insert inserted into the torch head. The following components can be identified:

91 : inlet area of the heating oxygen

92: annular combustion gas chamber

93: pressure nozzle

94: pressure nozzle bore

95: mixing nozzle inlet. Here the negative pressure Pnegative is present, which sucks in the fuel gas.

96: mixing nozzle

97: mixing channel (upstream section): Here, the oxygen flows in centrally at high velocity. This is how the negative pressure is created in the mixing nozzle inlet area 98: mixing channel (downstream area): Calming section - here the oxygen mixes further with the fuel gas

99: torch head: Mixing section of both gases

Under typical operating conditions, the torch can generate a negative pressure Pnegative relative to atmospheric pressure of at least -0.3bar, for example a negative pressure Pnegative of -0.4bar.

An example of an embodiment of the process according to the invention is explained in more detail below with reference to Figure 3.

A cutting torch 30 configured according to the embodiment of Figure 3 is used. Oxygen and a fuel gas are supplied to the cutting torch 30. The oxygen pressure at the pressure reducer of the oxygen cylinder is set to 5bar, which is the pressure established in the oxygen line 8 and which is the nominal oxygen pressure P02. The pressure at the pressure reducer of the acetylene cylinder is set to 0.7bar. This is the nominal fuel gas pressure PH2. A demand valve (e.g. a so-called S.A.T valve) is inserted in the fuel gas line downstream of the pressure reducer. The demand valve is vacuum-controlled and it opens only when the negative pressure difference (relative to atmospheric pressure) in the fuel gas path is -0.3bar or more.

Before inserting the cutting nozzle into the torch head, a pressure of 4.1 bar is present at the pressure nozzle. Due to the Venturi effect and the configuration of injector and mixing nozzle, a negative pressure of -0.44bar compared to atmospheric pressure is established in the fuel gas path (measured at the connection hose 5.2).

After inserting into the torch head a cutting nozzle for cutting metal sheets with a thicknesses of 10 to 100 mm, a pressure of 4.1 bar is still present at the pressure nozzle. Now, an effective negative pressure Pnegative of -0.41 bar compared to atmospheric pressure is established in the fuel gas path (measured at the connection hose 5.2). This effective negative pressure Pnegative is present in the entire fuel gas line 7 up to the demand valve (except for a small decrease due to line resistance). The demand valve is vacuum-controlled and configured to have a pressure setpoint to open the demand valve, e.g. the pressure set point is -0.3bar. Since this negative pressure is higher (more negative) than the set point of -0.3bar, the demand valve opens, so that the cutting process can begin.

As a result of the comparatively high negative pressure, the fuel gas pressure can even be increased and additional fuel gas can be supplied to the cutting process. This allows a cutting process to be operated even with an excess of fuel gas, which can be useful for cutting particularly thick sheets, for example.

In the event of a leak in the fuel gas path between the demand valve and the mixing nozzle inlet, the setpoint of -0.3bar for the effective negative pressure cannot be reached because of the fuel gas escaping there, so that the demand valve inserted in the fuel gas path does not open. Also, in cases that the flow of fuel through the fuel gas path is interrupted, or the pressure inside the fuel gas path drops, the pressure set point cannot no longer be reached so that the demand valve will stop the fuel flow.

It will be appreciated by those skilled in the art that the invention is not limited to the precise details as described herein.

Claims

PATENT CLAIMS

1 . Torch, in particular injector torch, comprising a torch base body (4), a torch head (2) connected to the torch base body (4) and a torch tip (2.1 ) held therein, wherein flow paths are defined in the torch base body (4), at least one of which is a fuel gas path (7) extending from a fuel gas inlet (5. 2), and at least one other being an oxygen path (8) extending from an oxygen inlet (5.1 ), and wherein the fuel gas path (7) and at least a conduit portion of the oxygen path (8) join at a venturi nozzle (33; 33.1 ) to form a common outlet path (34) leading through the torch tip (2.1 ),

• wherein the venturi nozzle comprises a pressure nozzle (33.5) fluidically connected to the oxygen line (8) and having a nozzle outlet (33.6),

• wherein the outlet path comprises a mixing nozzle (34) and a mixing nozzle inlet (34.1 ) for generating an oxygen-fuel gas mixture,

• and wherein the venturi nozzle (33; 33.1 ) and the mixing nozzle (34) are adapted to generate in operating mode a negative pressure Pnegative of at least -0.3bar relative to atmospheric pressure in the fuel gas path (7).

2. Torch according to claim 1 , characterized in that a negative pressure Pnegative of at least -0.4bar, preferably in the range from -0.4 to -0.8bar, and particularly preferably in the range from -0.42 to -0.6bar relative to atmospheric pressure can be set in the fuel gas path (7).

3. Torch according to claim 1 or 2, characterized in that the mixing nozzle inlet (34.1 ) has a diameter D, and that the nozzle outlet (33.6) of the pressure nozzle (33.5) has a diameter d, and that for the diameter ratio d/D applies:

0.1 < d/D < 0.8, preferably 0.15 < d/D < 0.5, particularly preferably 0.2 < d/D < 0.4.

4. Torch according to one or more of the preceding claims, characterized in that the venturi nozzle comprises at least one injector insert (33.1 ) in which or on which is formed a fuel gas chamber (33.7) fluidically connected to the fuel gas path (7) and adjacent to the mixing nozzle inlet (34.1 ), the nozzle outlet (33.6) of the pressure nozzle (33.5) being opposite the mixing nozzle inlet. Torch according to one or more of the preceding claims, characterized in that between the nozzle outlet (33.6) of the pressure nozzle (33.5) and the mixing nozzle inlet (34.1 ) a distance A is set in the range between 0.2mm and 2mm, preferably between 0.25mm and 1.5mm and particularly preferably between 0.3mm and 1.2mm. Method of operating a torch according to any of claims 1 to 5, comprising the method steps:

• a fuel gas is supplied to the fuel gas chamber via a fuel gas path (7) with a nominal fuel gas pressure PH2 in the range of 0.5 to 2bar,

• oxygen is supplied to the pressure nozzle (33.5) via an oxygen line with an oxygen nominal pressure P02 in the range from 2 to 10bar,

• the injector and the mixing nozzle being designed in such a way that a negative pressure Pnegative of at least -0.3bar with respect to atmospheric pressure is set in the fuel gas path (7). Method according to claim 6, characterized in that a negative pressure Pnegative of at least -0.4bar, preferably in the range from -0.4 to -0.8bar, and particularly preferably in the range from -0.42 to -0.6bar relative to atmospheric pressure is set in the fuel gas path (7).