US2175160A

US2175160A - Nozzle for cutting blowpipes

Info

Publication number: US2175160A
Application number: US135766A
Authority: US
Inventors: Zobel Theodor; Noetzlin Ulrich
Original assignee: Linde Air Products Co
Current assignee: Linde Air Products Co
Priority date: 1935-07-02
Filing date: 1937-04-08
Publication date: 1939-10-03
Anticipated expiration: 1956-10-03

Description

Oct. 3, 1939. T. ZOBEL ET AL 2,175,160

NOZZLE FOR CUTTING BLOWPIPES Filed April 8, 1937 Patented Oct. 3, 1939 UNITED STATES PATENT OFFICE many, assig ors, by insane The Linde Air Products Company, New York. N. Y,

a corporation of Ohio Application April 8,

In Germa This invention relates to nozzles for cutting blowpipes and, more particularly, to improvements in the shape of the cutting oxygen passages in such nozzles.

Nozzles or tips heretofore used for oxygen or autogenous" cutting of metal have been formed with either straight cylindrical or stepped cylindrical bores, the latter shape representing the improved form and being almost exclusively in use at present for this reason. However, even a nozzle of this kind is imperfect from a physical and aerodynamic standpoint as it still leaves very much to be desired with respect to the devel opment and utilization of the dynamic energy and the form of the oxygen jet produced. The oxygen jets from such nozzles or tips at pressures greater than subject to .npulse losses which rapidly increase with increasing pressure, thus considerably decreasing the cutting eiliciency.. Attempts have been made in practice to overcome this deficiency by designing each cutting tip for only a very small pressure range and thus also for a very small cutting range, maintaining the oxygen at the optimum working pressure for each size of tip. In this case it is necessary to tips of diiferent sizes for covering a wide cutting range. However, with increasing thickness of material the conditions get more and more unfavorable inasmuch as besides the lack of economy in the use of large tips it is necessary to increase the pressure which of necessity implies a deterioration of the flow conditions in the cutting jet,

Therefore, it would be advantageous to make use in cutting tips of the Laval effect which is known from other fields of technique. As is well known, the Laval nozzle under certain conditions renders it possible to convert gas pressure into gas 40 velocity, in a divergently tapered portion following the smallest cross section of the cutting oxygen passage of the nozzle,

It has been suggested already in the literature to use the Laval nozzle in its known simple form 45 for cutting torches. However, due to the fact that the Laval nozzle is extremely sensitive to even slight inaccuracy in the pressure adjustment and that diiferent nozzles are required for diilerent working pressures, the Laval nozzle 50, hitherto has been a failure in its application to cutting torches. The ideal cutting torch should permit a transformation of gas pressure into gas velocity substantially without losses, and should possess this' property for a very wide or even 55 any range of working pressures, delivering an the critical pressure is use a number of our nozzle as distinct 1937, Serial No. 135,766 y'July 2,1935

8 Claims- (Cl. 58-211) approximately parallel. compact gas jet having a maximum velodty with minimum cross sectional area of the jet.

Our novelncmle due to the particular design and shape" of the oxygen passage meets with these Ii ideal requirements and, therefore, differs fundamentally in its aerodynamic efiect and operation from the ordinary Laval nozzle.

In the oxygen passage of our cutting nozzle the transitional portions at the throat of the pas- 1 sage and at its smallest cross section are gently curved or well rounded, and the surfaces of these, portions are convex relative to the longitudinal axis of thenofl epassage. In contradistinction to the ordinary Laval nozzle, a conical portion" of our oxygen pwsage is followed by a transitional arched portion, the surface of which is concave relative to the longitudinal axis of the passage, and this arched portion is so shaped as to terminate in a cylindrical end portion. It is 20 also possible to design the nozzle in such a manner that the two arched or curved portions at the inlet or throat and the exit or discharge mouth of the nozzle passage or bore pass over, directly into one another in a turning point 01125 the profile curve, i. e., in a point representing a common tangent to both of the arches,

A very favorable form of the oxygen passage of our novel nozzle is obtained if the portions following the smallest'cross-section merge into a curved portion, concave relative to the longitudinal axis of the nozzle, and which terminates in a cylindrical portion at the exit of the oxygen passage and corresponds approximately to a portion of a flat ellipse ending at the short axis of the ellipse, while the tangents contacting the said portion following the smallest cross section do not exceed an angle of 10 with respect to the center axis of thenozzlepassage and if the expansion ratio resulting by dividing the largest 40,

diameter by the smallest diameter of the nozzle passage does not exceed 2.

An important element of the oxygen passage of from that of the ordinary Laval nozzle is the conical portion which diverges at a relatively greater angle. By this curved section it is possible to induce the stationary Machs waves produced in the case of a velocity beyond the velocity of sound-which waves penetrate each other and are reflected according to ,deflnite laws at the boundaries of the jet-4o adopt a flowing direction such that the jet having a velocity above that of sound, when leaving the nozzle, takes the form of a parallel or cylindrical jet, or at least a curved section following the 45 3o nozzles.

very close approximation thereto without being the sake of completeness the outer annular duct subjected to a compression shock or impulse. for the preheat gases, has been indicated at 4 in The same phenomenon will result in case or any this figure, but has been omitted from Figs. 2 and other pressure conditions: within the nozzle, the 3 as it has nothing to do with our invention.

is changed, which latter factor has no he the circular are n and the circular arc T2 around however, on the further shape of the jet. With a center point M (which is shown at a still further 10 nozzle of this type it is possible to obtain a comreduced length).

pact cutting oxygen jet of a cylindrical or nearly Referring to Fig. 3, the arc of a circle BC of cylindrical shape within a wide range of working Fig. 1 has been replaced by an arc of an ellipse pressures. This phenomenon, although not in B'D, the rest of the left half of the ellipse being accordance with the former aerodynamic theory, indicated in dotted lines in order to show what 15 mental w rk, the profile of the nozzle bore or oxygen passage.

With nozzles of this kind, it is possible to pro- Refe ring to any of Figs. 1-3 it will be seen duce, in the effective cutting portion of an oxythat the ratio between the maximum diameter may be employed and a relatively wider range of 2. 1= plate thicknesses may be cut with a, given size With regard to the angle a between the divernozzle than with prior commercially employed gent conical porti n and h no zl axi a l up to =10 may be used, but the efliciency of zle having a straight conically extending oxygen sion. Generally the curved portion should not passage terminating in an arc of a circle; be shorter than about A, of the total length of Fi 2 i a, longitudinal ection of a i il r nozthe nozzle. Preferably, the nozzle of the invenzle, the straight conical portion between the arcs tion is t uc wi h an y n pa e probeing reduced, however, to a transition point; vided with a throat, the wall between said throat 40 and and the discharge mouth of the passage having Fig. 3 is a longitudinal section of a nozzle i 1- an initially wide divergence or included angle of t t t of 1 t conical portion t m t- 14 or more followed by a curving section that jng, however, in an arc of an ellipse, 813121086113 a cylinder at the mouth. The ter- Referring now to the drawing, and first to Fig. mination of the curved section at the nozzle 1, D1 is the diameter of the narrow constriction mouth is necessary, n c njunction with the short zle. It will be seen that the inlet portion l of the which is an optimum value n many instan es. nozzle passage is shaped to the arc of a circle hav- It will be noted that the angle of divergence ing a radius n, and terminates, in the direction of the forms of nozzles illustrated is considerably of flow, in a straight conical profile portion, greater than that ordinarily used in divergent which extends from point A to point B and this nozzles of the so-called "'Laval" type, while the 55 7 axis and an intermediate section comprising a The reason for this, as previously explained, is

convex and concave surfaces oi revolution. For tion 01' pressure above orbelow that theoretically 75 phere. When the theoretical pressure is exceeded the stream remains approximately parallel within a relatively large range.

Practical experiments have shown that the linear cutting speeds attainable with our novel nozzle are to higher than the maximum linear cutting sp ds attainable with other up-todate cutting blowpipe nozzles, while the oxygen consumption is not higher and the cut faces are very clean and smooth. Another advantage of our novel nozzles resides in their high adaptation to different cutting conditions. For in-.

stance,- practical experiments have shown it possible to cut objects of any thickness up to 200 mm. with a single nozzle having a mouth of 1.5 mm. minimum diameter with very good eflieiency, whereas different nozzles or tips having a wide range of mouth diameters would have been required for different thickness of the material if using ordinary nozzles.

If the nozzle is made of copper or a similar soft material it is preferable to produce it by chipless shaping" so as to attain the highest precision of the polished surface and shape of the profile of the nozzle bore. This may be effected, for example, by forcing one or several calibrated mandrels into a piece of material having a cylindrical bore corresponding approximately to the smallest cross section of the nozzle profile.

It is also possible to produce the profile by starting from a cylindrical bore corresponding approximately to the maximum diameter of the nozzle profile and reducing the nozzle diameter by rolling or drawing the nozzle piece over one or more calibrated mandrels representing the inner shape of the nozzle.

We claim:

1. A nozzle for cutting metals having an oxygen passage therethrough, said passage comprising an inlet portion having a restricted throat, an outlet having a greater cross-sectional area than said throat, and a portion between said throat and said outlet having a wall diverging at a rate that diminishes with respect to length toward said outlet, said wall comprising a surface of revolution including a frusto-conical portion of relatively wide divergence adjacent to and smoothly joining said throat and a portion between said conical portion and the outlet generated by an arcuate element revolved about the axis of said oxygen passage, said surface substantially approaching a cylindrical form adjacent the outlet, the length of said last named portion being greater than about one-third the total length of said nozzle.

2. A nozzle for cutting metals having an oxygen passage extending therethrough, said passage comprising an inlet portion, a throat. a discharge mouth and an intermediate portion joining said throat to said discharge mouth; the wall of said throat comprising a surface of revolution coaxial with but convex relatively to the axis of said passage; and the wall of said intermediate portion comprising another surface of revolution coaxial with but concave relatively to the axis of said passage, the wall of said intermediate portion smoothly joining said convex surface to said discharge mouth.

3. A nozzle for cutting metals, as claimed in claim 2, in which said transition portion comprises a conical surface of revolution coaxial with the axis of said passage, said conical surface being disposed between and having every element thereof substantially tangent to both said convex and said concave surfaces.

4. A nozzle for cutting metals, as claimed in claim 2. in which the angle between the axis of said passage and every common tangent to said curved surfaces at said transition portion is less than about 20, and the ratio of the diameter'of the mouth of said passage and the smallest diameter of said throat is less than three.

5. A nozzle for cutting metals, as claimed in claim 2, in which said concave surface of revolution is substantially semi-elliptical and terminates adjacent the mouth of said passage in a plane perpendicular to the axis of said passage and containing the minor axis of the ellipse generating said concave surface of revolution.

6. A nozzle for cutting metals having an oxygen passage therethrough, said passage comprising an inlet portion having a restricted throat, an outlet having a greater cross-sectional area than said throat, and a portion intermediate said throat and said outlet having a wall diverging at an initially relatively high rate that diminishes constantly with respect to length toward said outlet, said wall comprising a surface of revolution joining said throat in a smooth transitional curve and approaching substantially a cylindrical form adjacent the outlet, said intermediate portion being free of abrupt transitional zones.

7. A nozzle for cutting metals'having an oxygen passage and a preheating gas passage extending therethrough, said oxygen passage comprising an inlet portion having a restricted throat, an outlet having a greater cross-sectional area than said throat, and a portion intermediate said throat and said outlet having a wall diverging from said throat at an initially relatively high rate that diminishes with respect to length toward said outlet, said wail comprising a surface of revolution approaching substantially a cylindrical form adjacent said outlet, said intermediate portion being free of abrupt transitional zones.

8. A nozzle as claimed in claim 7, in which said surface of revolution is generated by a portion of an ellipse rotated about an axis of the ellipse.

THEODOR ZOBEL. ULRICH NOE'IZLIN.