BACKGROUND OF THE INVENTION In the iron and steel industry, very large cutting torches are used to cut metal objects having a very large thickness into small pieces, e. g. so called skulls, i. e. sediments in metallurgical vessels, which have been allowed to freeze and which will be reused in the metallurgical process. Other typical objects are so called mischarges, which have been cast and proved to have the wrong composition, and therefore the ingots will be returned to the process. In order to make it possible to charge the melting furnaces with such large objects, they must first be cut into small pieces. Another field of application for cutting torches of this kind is cutting of continuous ingots to slabs or blooms.

Today, such cutting torches are mainly used, which work with acetylene and oxygen gas. Acetylene is, however, expensive. Mainly for financial reasons, natural gas and LPG (Liquid Petroleum Gas, which in Sweden is most commonly known as"gasol") are more attractive, in spite of the lower energy content of such gases. Further, those torches which work with acetylene and oxygen gas are not suitable for natural gas or LPG, and therefore great efforts have been made to develop cutting torches, which can work with natural gas or LPG, and which can give at least as good cutting results as acetylene torches. Those torches which have so far been constructed and which have been used in the iron and steel industry, with LPG as fuel, which has been mixed with oxygen gas in front of the torch nozzle, have, however, unsatisfactory cutting ability.

The high sound level caused by said type of torches is also very troublesome.

DISCLOSURE OF THE INVENTION The purpose of the invention is to attack the above mentioned problems. The characteristic features of the invention is that the torch, in addition to petroleum gas and oxygen gas, is provided to work also with air and that it therefore comprises an air drum

surrounding said first unit, said air drum extending at a distance from said first unit along at least substantially its whole length, said air drum having a suction port for air in its rear end, and an outlet in its front end for ejecting air through said outlet in the form of an air flow in the longitudinal direction of the torch, said air flow surrounding the flame formed in front of the torch nozzle. It has been noticed that through this arrangement the cutting ability of the torch is essentially improved compared to known technique. Without limiting the function of the torch to any special theory, it may be assumed that the surrounding air flow, which has the same direction as the gas mixture and the flow of oxygen gas leaving the nozzle, counteract the combustible gases and the flame being spread, i. e. maintaining a high degree of laminarity and hence are kept substantially concentrated up to the cutting spot. A sign that the surrounding air flow has said effect is that the flame becomes intensively white, which points to a much higher temperature, which in its turn can be assumed to depend on a very efficient combustion. At the same time an unexpected, heavy reduction of the sound level is achieved. Another effect is that a cooling of the unit inside the air drum is achieved.

The characteristic features of a preferred embodiment of the torch according to the invention are further : -that the torch head is provided at a considerable distance from the mixing unit; -that at least one petroleum gas channel is provided in the mixing unit, which channel may be connected to a supply conduit for petroleum gas; -that at least one oxygen gas channel is provided in the mixing unit, which channel may be connected to a supply conduit for oxygen gas; -that at least said one petroleum gas channel and said at least one oxygen gas channel are joined with each other in a mixer in the mixing unit to form a mixture of petroleum gas and oxygen gas; -that the torch head comprises a rear portion and a front portion; -that the torch nozzle is removably connected to the torch head in its front portion; -that the torch nozzle has a central channel ending in the front end of the nozzle, and around the central channel, at a radial distance therefrom, a nozzle slit or a great number of channel lying close to each other, which also end in the front portion of the nozzle; and -that in the rear portion of the torch head there is a bas mixing channel between said gas mixing conduit connected to the torch head and said slit or tightly lying channels, as well as a oxygen gas channel between said oxygen gas conduit and said central channel in the nozzle.

Further features and advantages, which can be achieved with the invention, will be apparent from the appending patent claims and from the detailed description of a preferred embodiment of the invention.

BRIEF DESCRIPTION OF DRAWINGS In the detailed description below of a preferred embodiment reference will be made to the enclosed drawings, of which Fig. 1 shows a side view of a cutting torch according to a preferred embodiment, but an air drum included in the torch is shown schematically in cross section; Fig. 2 shows schematically a side view of a unit included in the cutting torch ; Fig. 3 is a perspective view of a nozzle sleeve; and Fig. 4 shows a perspective view of a nozzle insert intended to be provided in the nozzle sleeve.

DESCRIPTION OF A PREFERRED EMBODIMENT With reference first to Fig. 1, a unit is generally designated 1. The unit 1 is surrounded of an air drum 2 extending essentially along the entire length of the unit 1. The unit 1 comprises in its rear end a mixing unit 3 and in its front end a torch head 4 and a nozzle 5. A oxygen gas conduit 6 and a gas mixture conduit 7 for a mixture of oxygen gas and LPG extend between the mixing unit 3 and the torch head 2. Specifically, a mixture is used as LPG, which is marketed in Sweden under the trade name LPG-Mix, consisting of 33 weight-% (38 volume-%) propan, 4.5 weight-% (7.6 volume-%) ethane, 1.5 weight-% (1.0 volume-%) pentanes and heavier, totally less than 1 % methane and olefins, balance butane. Also LPG, which in Sweden is marketed under the trade name Propan 95, can be used but it is not as good as LPG-Mix. The distance between the mixing unit 3 and the torch head 4 should be at least 50 cm. For a manufactured and used cutting torch the distance was about 90 cm, but it may also be longer. The longer the distance is, the better the cooling effect from the air flowing through the air drum 2 will be, which will be explained below. In the rear end of the mixing unit 3 there are three connections 10,11,12, namely for a first oxygen gas hose 13, a second oxygen hose 14, and a hose 15 for the supply of LPG. Said hose connections 10 through 12 and conduits 6 and 7 are uninsulated and exposed to the air inside the air drum 2 and can therefore be effectively cooled by the air in the air drum 2.

The mixing unit 3 and the torch head 4 are joined with each other through two bars 16, which in their turn are joined with each other through a pair of transverse bars 17, so

that the mixing unit 3, the conduits/tubes 6 and 7, and the torch head 4 with the torch nozzle 5 are kept together in said integrated unit 1. This one in its turn is attached to the air drum 2 by means of an mounting plate 18, which is welded to the transverse bars 17.

Finally, the air drum 2 is attached to a not shown stand or to another firm carrier via brackets 19 or via other mounting means.

In the mixing unit 3, Fig. 2, there is a first through, straight oxygen gas channel 21 extending through the mixing unit and connecting the first oxygen gas connection 10 with the oxygen gas conduit 6. A second oxygen gas channel 22 extends though a nipple in the rear end of the mixing unit 3, which channel is connected to the connection 11 of the second oxygen gas hose 14 and further up to a mixing nozzle 25. This one is exchangeable and shows in its front portion, around the periphery of the mixing nozzle, a lot of beams and therebetween longitudinal grooves surrounded by, along a portion of the front part of the mixing nozzle, an annular slit 26. A channel 23 for LPG gas extends from the connection of the hose 15 to said slit 26. The LPG gas is distributed in the slit 26 and mixed therein by being ejected by the oxygen gas flow from the channel 22, which flow is distributed in said peripheral grooves, so that a mixture of LPG gas and oxygen gas is obtained in the gas mixing conduit 7, which mixture is mixed further in the gas mixing conduit 7 while the mixture is kept comparatively well cooled through cooling effect from the air flow in the air drum 2.

The nozzle 5 consists of a first, exchangeable nozzle insert 30 in a exchangeable nozzle sleeve 31. The nozzle insert 30 extends through the entire length of the nozzle sleeve 30. In its rear end it is provided with a threaded portion 32, which is screwed into a threaded boring 33 in the torch head 4. The nozzle sleeve 31 has in its rear end a collar 34 fitting in a larger boring in the torch head 4,. In the region of the rear end of the torch head 4 the nozzle sleeve 31 has an inwardly facing, annular shaped portion 35, against which a nut 36 is pressed, said nut being screwed into said boring in the torch head 4, which threaded boring is surrounding the portion 36 of the nozzle sleeve between the collar 37 and the inwardly facing portion 35.

From said inwardly facing portion 35 the nozzle sleeve 31 has the shape of a straight cylinder. Said cylindrical portion has been designated 38. The first nozzle insert 30 has a front part 40, Fig. 4, which around its periphery has longitudinal grooves 41 extending along the whole of said front portion 40 and also somewhat into the tubular portion 42 of the nozzle insert 30 behind the front part 40, which tubular portion 42 has smaller

outer diameter than the outer diameter of the longitudinal beams 44 between the grooves 41 in the front portion 40 of the nozzle insert 30.

The beams 44 in the front portion of the nozzle insert abuts against the cylindrical inside of the front cylindrical portion 38 of the nozzle sleeve 31, so that the grooves 41 of the front portion of the nozzle insert 30 form longitudinal, tightly adjacent channels 43 in the nozzle 5, said channels being entirely axial and hence giving a laminar flow to the gas mixture which shall flow through the nozzle and leave the nozzle in its nose.

Behind the front portion of the nozzle insert 30 there is an annular slit 46 between the inside of the nozzle sleeve 31 and the outside of the tubular portion 42 of the nozzle insert. Said slit 45 communicates with the channels 43 between the beams 44 and extends backwards to an annular chamber 46 between said central portion 36 of the nozzle sleeve 31 and the tubular portion 42 of the nozzle insert 30. An oxygen gas channel 47 extends from the oxygen gas conduit 6 to the chamber 33 being formed by the inner boring in the torch head 4, which in its turn communicates with an axial, central nozzle channel 48 through the first nozzle insert 30. The central channel 48 extends also through the front portion 40 of the nozzle insert 30 up to a second, exchangeable nozzle insert 49 in the nose of the nozzle. Said second nozzle insert 49 has a central, straight blow-out channel 50 for oxygen gas. On the face of the nozzle insert 49 there is a couple of small cavities 51 providing grips for a tool, by means of which the threaded nozzle insert 49 can be screwed out of and into a corresponding, threaded central hole in the front portion of the first nozzle insert 30.

A gas mixture channel 53 extends through the torch head 4 and connects the gas mixture conduit 7 with the annular chamber 46 and then also via the slit 45 with the blow-out channels 43 between the beams 44.

A tube 70 extends through the air drum 2, which tube ends in front of the nozzle 5 for the supply of a metal powder, particularly iron powder for intensifying the cutting ability of the cutting torch.

The above described cutting torch works in the following way. Clean oxygen gas is driven from a now shown, pressurized oxygen gas source through the first oxygen gas hose 13, through the first oxygen gas channel 21 in the mixing unit 3, through the oxygen gas conduit 6 between the mixing unit 3 and the torch head 4, through the oxygen gas channel 47 in the torch head 4 to the chamber 33, and through the central

channel 48 I the first nozzle insert 30 up to the second nozzle insert 49 to finally being blown out as a forwardly directed, axial oxygen gas flow through the central blow-out channel 50 for oxygen gas.

Oxygen gas is also pressed through the second oxygen gas hose 14, through the second oxygen gas channel 22 in the mixing unit 3 to the mixing nozzle 25 and further through the peripheral channels thereof. LPG-gas is carried through the hose 15 to the channel 23 for LPG gas in the mixing unit 3 and through said channel up to the annular slit 26 to be ejected by and mixed with the oxygen gas flow coming through the mixing nozzle 25. The LPG gas mixture, which has thus been well mixed, is then driven further through the gas mixture channel 53 in the torch head 4 up to the chamber 46 and further through the slit 45 and the axially directed blow-out channels 43. As soon as the gas mixture is left the nozzle, the gas flows from the individual blow-out channels 43 are brought together to form a curtain of a combustible gas mixture, which has the same axial direction as the oxygen gas flow leaving the central blow-out channel 50 for oxygen gas. The mixture is ignited in front of the nozzle.

The flows of oxygen gas and gas mixture leaving the nozzle 5 bring through an ejector effect air with them into the air drum 2. To enhance said ejector effect and to give the ejected air flow an axial, essentially laminar flow picture the air drum 2 is funnel shaped at its front portion showing a smaller part or spout 60, which surrounds the nozzle 5.

The annular blow-out opening of the air drum 2 around the nozzle 5 has been designated 61, Fig. 1, and the slit between the front portion 60 of the air drum and the nozzle 5 has been designated 62. The main portion 63 of the air drum 2 is essentially wider and need not necessarily have a shape of a circular cylinder. Also a in cross section rectangular shape is conceivable. The distance between the walls of the drum in the main portion 63 of the drum and the mixing unit 3, the conduits 6 and 7, and the torch head 4 can also be considerably larger than what is shown in Fig. 1. The air volume in the region of the main portion 63 of the drum is therefore essential, which give the air in the air drum a considerable dwell time in the drum in the region of its main portion 63, which is positive to achieve the desired cooling effect. The air is sucked into the drum 2 in its upper end, which is funnel shaped. The funnel shaped portion has been designated 65. The lower portion of the drum surrounding the nozzle 5 and comprising the pipe 60 can me loosened from the main portion of the drum to make the nozzle 5 accessible for the exchange of nozzle and/or nozzle parts.

Metal powder, preferably iron powder, can me supplied through the tube 70. Said powder is brought together with the gas glows in front of the nozzle 5 and increases essentially the temperature in the cutting spot. It has been calculated that the temperature increase can amount to about 300°C. Hereby it is possible to cut also large blocks of stainless steel with a good result, which blocks normally are very difficult to cut.

As mentioned in the preamble the cutting torch has a very good cutting effect. Without limiting the invention to any special theory it may be assumed that, in order to achieve said good effect, it is of essential importance that all gas flows leaving the torch, i. e. the oxygen gas flow which is blown out through the central blow-out channel 50 for oxygen gas, the gas mixture which is blown out through the surrounding blow-out channels 43, and the air which flow out through the opening 61, are axial and parallel to each other, which initially gives laminar flows, and that the laminar flow picture of the oxygen gas flow and the flame, which is formed by the gas mixture, essentially maintain their laminar flow pictures up to the focal spot. It is also very likely that the essential sound attenuation is provided by the laminar air flow leaving the torch and counteracting turbulence.

It is also advantageous that the nozzle sleeve 31, the first nozzle insert 30, and the second nozzle insert 50 are exchangeable. Through the choice of components with suitable dimensions the effect of the torch may be adjusted.

It is also considered to be important that the mixture of oxygen gas and LPG gas does not take effect in front of the nozzle, when the gases has left it but within the torch itself and at a considerable distance from the nozzle. It is not been theoretically analysed why this gives a better effect of the cutting torch. Conceivable explanations can be that one achieves a better mixture between oxygen gas and LPG gas or that the cooling of the combustible mixture, which is obtained through the location of the mixing unit far back in the torch with efficient cooling thereof and of the conduits up to the torch head, or a combination of said circumstances is of essential importance.

It should be understand that the invention may be varied and that the invention is not limited to the shown embodiment. The blow-out channels 43 may for instance have the shape of tightly adjacent, drilled channels in the first nozzle insert 30 instead of consisting of milled grooves between peripheral beams on the nozzle insert. The latter construction is, however, most favourable, not at least from a manufacturing point of view.