EP0177423A1 - Cutting torch nozzle with an internal mixture - Google Patents

Abstract

This nozzle includes an outer case (1) and a core (2) which define in succession: a series of passageways (15) having a zone for the injection of fuel gas and comburent gas, a mixing zone of small section and a primary homogenization zone of larger section; an annular secondary homogenization zone (16) whose section is substantially equal to the total section of the preceding zone; a single acceleration passage (17) having a decreasing section; and a single outlet conduit (18) having a constant section. Application in oxyacetylene torches consuming a few cubic meters per hour acetylene.

Description

The present invention relates to a torch nozzle with internal mixture, of the type comprising an outer annular casing and a core disposed in this casing, the casing and the core defining a series of channels each of which successively comprises, starting from the upstream, an injection zone adapted to be supplied with combustible gas and oxidizing gas, a mixing zone of small cross-section then a homogenization zone of clearly larger cross-section, the outer casing extending beyond the end of the core and forming at its downstream end a single outlet pipe for the mixture.

• - dans les premiers, le mélange combustible-comburant est effectué très en amont de la buse, à plusieurs dizaines de centimètres de l'orifice de sortie, lequel délivre un dard unique. Ces chalumeaux offrent un avantage de simplicité de réalisation, notamment en ce qui concerne la buse, qui est une pièce vulnérable. Par contre, en cas de rentrée de flamme (initiée par exemple par une obstruction partielle de l'orifice de sortie de la buse), le front de flamme pénètre à l'intérieur du chalumeau et peut se stabiliser au niveau de l'injecteur. C'est le phénomène dit de "prise à l'injecteur", susceptible de détruire le chalumeau et, dans le cas d'un appareil manuel, de brûler la main de l'opérateur ;
• - dans les seconds, l'injection, le mélange et l'homogénéisation du mélange sont regroupés à l'intérieur de la buse. Comme il est difficile de mélanger et d'homogénéiser des débits supérieurs à 500 1/h sur une longueur aussi faible que celle d'une buse (quelques dizaines de mn) , ce principe a conduit, pour atteindre plusieurs m³/h, à fractionner le débit total en le répartissant dans plusieurs canaux fraisés identiques régulièrement répartis autour de la buse.

We know that there are two main families of blowpipes: blowpipes with global pre-mixing and blowpipes mixing in the nozzle:

• - In the first, the fuel-oxidizer mixture is carried out very upstream of the nozzle, several tens of centimeters from the outlet orifice, which delivers a single dart. These torches offer an advantage of simplicity of construction, in particular with regard to the nozzle, which is a vulnerable part. On the other hand, in the event of reentry of flame (initiated for example by a partial obstruction of the outlet orifice of the nozzle), the flame front penetrates inside the torch and can stabilize at the level of the injector. This is the so-called "injector" phenomenon, capable of destroying the torch and, in the case of a manual device, of burning the operator's hand;
• - In the second, the injection, mixing and homogenization of the mixture are grouped inside the nozzle. As it is difficult to mix and homogenize flows greater than 500 1 / h over a length as short as that of a nozzle (a few tens of minutes), this principle has led, to reach several m ³ / h, to split the total flow by distributing it in several identical milled channels regularly distributed around the nozzle.

The main advantage of the second family torches lies in a very high safety of use: in case of reentry of flame, this generally only concerns one channel, and like the distance between the flame front and the injector is small, the volume of detonating mixture concerned is considerably lower than with a pre-mixing torch. In any case, even in the event of a general reentry of flame (which is improbable), the operator's hand, away from the nozzle by several tens of cm, risks absolutely nothing.

In most known nozzles with internal mixing, the principle of flow division has led to the production of channels extending to the front end of the nozzle, so that they are multidard nozzles, which excludes certain applications, for example the withdrawal heat, which require occasional heating. Furthermore, US Patent 1,940,343 proposes a monodard nozzle with internal mixing, which is of the type indicated above. However, this nozzle has certain disadvantages, in particular with regard to the design of the homogenization zone and its connection with the outlet pipe of the mixture.

The object of the invention is to provide a monodard nozzle which, for a moderate total length, ensures the ejection under excellent conditions of a well homogeneous mixture, for flow rates up to several _m ³ _{/ h} .

To this end, the invention relates to a torch nozzle of the aforementioned type, characterized in that the channels open into an annular space delimited between the outer casing and the core and having a section approximately constant and equal to the total section of the channels, this annular space in turn opening into a single passage with decreasing section delimited by the outer envelope and the downstream end of which forms said single outlet pipe for the mixture.

• - la figure 1 est une vue en coupe longitudinale d'une buse de chalumeau conforme à l'invention ;
• - la figure 2 est une demi-vue partielle en coupe longitudinale illustrant un détail de réalisation de cette buse ; et
• - la figure 3 est une demi-vue partielle en coupe longitudinale illustrant une variante.

An embodiment of the invention will now be described with reference to the appended drawing, in which:

• - Figure 1 is a longitudinal sectional view of a torch nozzle according to the invention;
• - Figure 2 is a partial half-view in longitudinal section illustrating a detail of embodiment of this nozzle; and
• - Figure 3 is a partial half-view in longitudinal section illustrating a variant.

The torch nozzle shown in Figure 1 consists of two elements: an outer casing 1 and an inner core or "core". It is essentially of revolution around an axis XX; for the convenience of the description, it will be assumed that this axis is horizontal and that the gases circulate from the right end (upstream end) to the left end (downstream end) of the nozzle; we will refer in the following to abscissas x counted from right to left along the axis XX, of an origin (x = 0) corresponding to the lover end plane of the envelope 1 to a value x = x ₇ corresponding to its downstream end plane.

The inner wall of the envelope 1 has two parts: over most of its length, from x = 0 to x ₆ , a converging frustoconical part 3, then a cylindrical part 4 extending from x ₆ to x ₇ .

Externally, the casing 1 has in its upstream part a thread 5 for connection to a torch head (not shown), then a hexagon 6 for tightening, then it has a convergent shape up to its downstream end.

• - une partie divergente 7, extérieure à l'enveloppe 1, adaptée pour s'appliquer de façon étanche contre une portée conjuguée de la tête de chalumeau ;
• - jusqu'à l'abscisse x₃, située à peu près à mi-longueur de la partie 3 de l'enveloppe, une partie tronconique 8 convergente conjuguée de cette partie 3 ;
• - de x₃ à x_4' une courte zone tronconique 9 plus fortement convergente ; et
• - de x₄ à x₅, un nez 10 d'allure parabolique qui se termine par une pointe arrondie 11, par exemple suivant un rayon de 0,3 mn, comne on le voit mieux à la figure 2.

The core 2 has the general shape of a conical needle with the same angle at the top as the part 3 of the recess of the envelope, which allows it to be positioned and to be fixed in the latter by simple wedging. More precisely, this core comprises, from upstream to downstream:

• - A divergent part 7, external to the casing 1, adapted to be applied in leaktight manner against a combined surface of the torch head;
• - Up to the abscissa x ₃ , located approximately mid-length of part 3 of the envelope, a frustoconical convergent part 8 conjugate of this part 3;
• - from x ₃ to x _{4 '} a short frustoconical zone 9 more strongly convergent; and
• - From x ₄ to x ₅ , a parabolic-looking nose 10 which ends in a rounded point 11, for example along a radius of 0.3 min, as can be seen better in FIG. 2.

From a point located outside the envelope to the abscissa x ₄ , the core 2 comprises a series of longitudinal grooves 12 regularly distributed over its periphery. It also comprises, from its upstream end face, a blind axial bore 13 and, from this, a series of conduits 14 each of which opens into a groove 12 at a certain distance x ₁ from the plane of upstream end of envelope 1.

From the abscissa x 0, the grooves 12 delimit with the wall part 3 of the envelope as many channels 15 whose passage section, defined by the depth of the grooves, varies: this section, after having increased by x = 0 to x ₁ (fuel injection), is small from x ₁ to x ₂ , then much larger from x ₂ to x ₃ . The grooves 12 then gradually disappear in the area 9, which constitutes a transition zone where the channels open into an annular space 16 delimited between the core and the envelope from x ₃ to x ₅ .

If s denotes the section of each channel 15 to the abscissa x ₃ , n the number of channels and S the section of the annular space 16 to the abscissa x ₄ , we have substantially S = ns, to within + 10% .

From x ₄ to x ₅ , the parabolic profile of the core 2 is chosen so that the section of the annular space 16 remains substantially constant and equal to the value S defined above.

From x ₅ to x ₆ , the wall part 3 of the envelope 1 alone delimits a single passage 17 with decreasing circular section; from x ₆ to x ₇ , the wall part 4 delimits a single duct 18 with a constant circular section which is connected to the passage 17.

• - sous l'effet de sa propre pression d'alimentation et de l'aspiration créée par l'oxygène, le gaz combustible pénètre dans le conduit 14 et se jette dans le canal 15 à l'abscisse x₁ ;
• - de x₁ à x₂, une vitesse élevée de la veine gazeuse (faible section de passage) favorise la création de turbulences propices à un brassage des filets d'oxygène et de gaz combustible. Cette zone est une zone de mélange des deux gaz ; et
• - de x₂ à x₃, l'augmentation considérable de la section offerte au passage du gaz ralentit la vitesse du mélange afin de lui donner le temps de s'homogénéiser. Cette zone constitue une zone d'homogénéisation primaire du mélange.

In operation, the nozzle thus described is fixed to the head of a torch; combustible gas, for example acetylene, is sent into the bore 13 of the core, and oxygen is injected into the upstream end of the grooves 12. The following phenomena then occur in each channel 15:

• - under the effect of its own supply pressure and the suction created by oxygen, the combustible gas enters the duct 14 and flows into the channel 15 at the abscissa x ₁ ;
• - From x ₁ to x ₂ , a high speed of the gas stream (small passage section) promotes the creation of turbulence conducive to mixing of the oxygen and fuel gas streams. This zone is a zone for mixing the two gases; and
• - From x ₂ to x ₃ , the considerable increase in the cross-section offered to the passage of the gas slows down the speed of the mixture in order to give it time to homogenize. This zone constitutes a primary homogenization zone of the mixture.

The gas streams meet in the transition zone 9 and then flow into the annular space 16. The section of this space being constant, there is simply a continuation of the homogenization, that is to say that the space 16 constitutes a secondary homogenization zone.

Then, the mixture crosses the passage 17, where it undergoes an acceleration until reaching, at the entry of the conduit 18, a speed sufficient to balance, at the exit of the nozzle, the speed of deflagration of the mixture.

In the variant of FIG. 3, the nose 10 of the core is modified so as to facilitate its realization: instead of having a rigorously parabolic profile, this nose consists of a trunk of upstream cone 19 followed by a downstream cone 20 more strongly convergent, which ends with the same rounded point 11 as above.

The connection circle of the truncated cone 19 and the cone 20 is located on the abscissa x ₈ , intermediate between x4 and x ₅ , for which the gas passage section would be maximum if the nose 10 was a single cone 21 s' extending from x ₄ to x ₅ , as shown in phantom in Figure 3.

With such an embodiment of the nose 10, we see that we still have: S (x ₄ ) ⁼ S (x ₅ ) ₌ S (x ₈ ) ₌ n. s to within + 10%, so that the behavior of the mixture in space 16 remains practically the same as with the configuration in FIGS. 1 and 2.

The Applicant has successfully tested an oxy-acetylene nozzle with internal mixture in accordance with the variant of FIG. 3, for acetylene flow rates up to ³ m ³ / h. For oxygen / acetylene consumption ratios close to stoichiometry, no sensitivity to "injector intake" was found.

Claims (8)

1 - Torch nozzle with internal mixture, of the type comprising an outer annular casing (1) and a core (2) disposed in this casing, the casing and the core defining a series of channels (15) each of which successively comprises, from upstream, an injection zone adapted to be supplied with combustible gas and fuel gas, a mixing zone of small cross section then a homogenization zone of clearly larger cross section, the outer casing (1) is extending beyond the end of the core (2) and forming at its downstream end a single conduit (18) for outlet of the mixture, this nozzle being characterized in that the channels (15) open into an annular space (16) delimited between the outer casing (1) and the core (2) and having an approximately constant section (S) equal to the total section (ns) of the channels (15), this annular space in turn opening into a single passage (17,18) with decreasing section delimited by the outer envelope (1) and the downstream end of which forms said single conduit (18) for leaving the mixture. 2 - torch nozzle according to claim 1, characterized in that, in the region of said annular space (16), the outer casing (1) has an internal profile (3) frustoconical and the core (2) has a profile ( 10) roughly parabolic. 3 - torch nozzle according to claim 1, characterized in that, in the region of said annular space (16), the outer casing (1) has an internal profile (3) frustoconical and the core (2) has a profile formed an upstream truncated cone (19) followed by a downstream cone (20) of greater angle at the top. 4 - torch nozzle according to claim 3, characterized in that the connection between the truncated cone (19) and the cone (20) is at the location (x ₈ ) where the passage section would be maximum if the trunk cone and the cone were replaced by a single cone (21). 5 - torch nozzle according to any one of claims 1 to 4, characterized in that between the end (11) of the core (2) and said single outlet conduit (18), said single passage (17) has a circular section. 6 - torch nozzle according to any one of claims 1 to 5, characterized in that said single outlet duct (18) is cylindrical. 7 - torch nozzle according to any one of claims 1 to 6, characterized in that the outer casing (1) has an inner profile (3) frustoconical to said single outlet conduit (1). 8 - torch nozzle according to any one of claims 1 to 7, characterized in that the end (11) of the core (2) forms a rounded tip.

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