US2373309A - Divergent-outlet cutting torch - Google Patents

Description

April 10, 1945. J. K. HAWL TON 2,373,3

DIVERGENT-OUTLET CUTTING TORCH Filed May 26, 1942 IN V EN TOR.

JAMES K HAM/L TON I A;TORIVEY Patented Apr. 10, 1945 DIVERGENT-OUTLET CUTTING TORCH James K. Hamilton, Plainfield, .N. J., assignor to Air Reduction Company, Incorporated, New York, N. Y., a corporation of New York Application May 26, 1942, Serial No. 444,544

'7 Claims.

This invention relates to oxygen cutting'torches, and especially to torches that have a divergent outlet for the cutting oxygen.

In standard cutting tips of the prior art in which the oxygen stream is discharged from a cylindrical passage and at a pressure higher than. atmospheric, the gas stream expands suddenly at the discharge end of the tip to about atmospheric pressure. This sudden expansion results in extreme turbulence. It may be shown by static pressure measurements and other means that the oxygen upon leaving the tip may actually expand to a pressure below one atmosphere, later be compressed above atmospheric pressure, and then go through numerous repetitions of this cycle. The expansion of the oxygen stream increases the width of the kerf and thus increases the amount of metal that is removed in making a cut.

. In a cutting tip that is constructed with a properly designed divergent outlet, the oxygen expands from a value in the throat of 0.53 of the initial pressure at the throat entrance to atmospheric pressure within the confines of the divergent portion of the tip. The pressure at the end of the tip is one atmosphere and the only turbulence in the emerging stream is the result of imperfections in the tip proper.

The velocity of a gas discharging from a nozzle is givenby the following relationship In which V-vel. in .ft./sec. at section where gas has expand-ed to P2 -ac celeration of gravity K-speci fic heat ratio R-universal gas constant T1-ir1itial absolute temperature-degrees F.

Pa-pressure on discharge end of nozzle pounds/sq. in. absolute P1DTSSSU1' on inlet side of nozzlepounds/sq.

absolute For oxygen the above equation may be reduced to the following T=530 F. absolute The velocities of these equations are not exactly those obtained in practice because of heat transfer, friction, and some initial upstream velocity, but the equations do establish that the maximum velocity with a divergent tip approaches a value of about 2400 ft./sec., as the initial pressure is increased. With an initial pressure of 100 pounds/sq. in. the discharge velocity is about- 1600 ft./sec. with a tip designed to discharge at a pressure of one atmosphere.

These velocity relations do not apply when standard tips having cylindrical outlet passages are considered. Since the pressure in thedischarge end of a standard tip is always about 0.53 of the initial pressure, the exit velocity will always be the same regardless of what initial pressure is used. Thevalue may be computed as about 1000 ft./sec. This does not imply that it is impossible to obtain higher velocities with standard tips after the stream leaves the tip. Sudden expansion does result in higher velocities which are less, however, than obtained with divergent tips.

Because of the higher velocity of the divergent outletv tip, sufficient oxygen for cutting a given thickness of metal can be obtained with a narrower jet than is the case with a standard tip; and the jet from a divergent outlettip'has little or no tendency to spread out since the pressure of the stream is approximately the same as that of the surrounding atmosphere. In the case of a standard tip, it is impossible to obtain a parallel stream except at very low pressures, because the discharge pressure is greater than atmospheric, thus giving a spreading exit stream.

The theoretical shape of the throat and discharge passage of a divergent outlet tip involves curved surfaces that are difiicult and expensive to obtain in manufacture of the tips. I have dis- 1 covered that if certain relationships are kept within determined ranges, such curved surfaces are not necessary, and that cylindrical and frustoconical surfaces are sufiicient. Some of these relationships are opposed to what would be expected from theoretical considerations. For example, I

. have found that'better results are obtained with vergent outlet cutting torch that is less expensive to manufacture.

Other objects, features and advantages of the invention will appear or be pointed out as the specification proceeds.

The drawing is a sectional view taken on a central plane through the tip end of a torch embodying the invention.

The drawing shows a tip III with a centrally located, diverging outlet passage II for the cutting oxygen. The passage II is in axial alinement with a throat I2. straight sides that comprise a frusto-conical surface that meets a straight cylindrical wall of the throat I2.

Oxygen flows to the throat I2 through an approach passage I4 that is in axial alinement with the throat. The passage III is cylindrical, and of larger diameter than the throat. At the downstream end of the passage I4 there is a tapered surface I5 left by the end of the drill that is used to make the passage I4. The included angle of the surface I5 is of the order of 120 degrees when a standard drill is used, and this surface provides a transition from the full diameter of the approach passage I4 to the diameter of the cylindrical throat I2. The use of this angular surface left by the drill in the transition between the approach passage and the reduced-diameter pas- H,

sage through the throat gives good results if the diameter of the approach passage I4 is from oneand-a-half to two-and-a-quarter times as great as the diameter of the throat. This range in The passage II has diameter makes the area of cross-section of the throat between and /9 of the cross-sectional area of the approach passage.

It is important that there be no burrs left at either the inlet or outlet ends of the throat where the tapered or frusto-conical surfaces meet the cylindrical throat surface.

In theory, a long throat would impair the performance by increasing the friction in the tip. Contrary to theory, better results are obtained by increasing the length of the throat. A length 1 throat the gas stream becomes stabilized before it expands in the diverging outlet passage.

The ratio of the diameter of the outlet end of the passage I I to the diameter of the throat I2 With everything else the same in the tip is the expansion ratio of the tip. I find an expansion ratio of from 1.20 to 1.35 to be most advantageous, and a range from 1.15 to 1.40 practical. This permits the torch to be used with an upstream pressure around 100 pounds per sq. in. and the gas stream discharged at approximately atmospheric pressure. This obtains a jet velocity close to 1600 ft./sec. Because of the shape of the velocity curve an increase in the pressure of gas supplied to the torch to 500 pounds/sq. in. will obtain an increase in jet velocity of only about 300 ft./sec. High expansion ratios are therefore not advantageous in practice because the benefit of the slight velocity increase is more than offset by the necessity of using regulators adjustable for high pressure, by considerations of hose strength and flexibility, and by the fact that existing oxygen installations are not generally equipped for supplying gas at such high pressure.

Although a tip constructed to operate with a supply pressure of pounds/sq. in. will not deliver gas at a pressure of exactly one atmosphere with any other supply pressure, I find that some variation in supply pressure can take place Without destroying the parallel sides of the jet. In describing the pressure as around 100 pounds, sq. in., a range of pressure from about 70 pounds/sq. in. up to about pounds/sq. in. is contemplated.

The angle of divergence of the passage I I is the angle included between the surfaces of the passage diametrically opposite each other. This angle is preferably between 4 and 10 degrees.

It is advantageous to employ the smaller expansion ratios and the larger angles of divergence with tips of larger size. Conversely, the larger expansion ratios and the smaller angles of divergence are better with tips of smaller size.

The following examples give these relations on a small and a large size tip.

The tip I!) fits into a socket in a torch body It and is held in the torch body by a tip nut II. The cutting oxygen flows from a conduit I8 into a passage I9 at the upper end of the tip. The passage I9 merges into the approach passage I I. The reasons for the different diameter passages 69 and M are practical. A single large-diameter passage I9 extending all the Way to the throat I2 would have the disadvantage of producing too abrupt a change in section; above the range previously specified for the ratio of approach passage cross-section to throat cross-section. To extend the small-diameter passage I 4 all the way to the top of the tip would make the drilling of the tip more diificult. The approach passage It should have a length ten or more times as great as the length of its diameter. With a short tip, a portion of the length of the approach passage can be in the torch body.

The tip I0 has preheating jet passages 26 arranged in a circle around the central cutting oxygen outlet I I. Oxygen and fuel gas for preheating flames are supplied to the jet passages 20 from annular chambers 2I and 22 that the tip forms with the torch body when the tip is positioned in its socket in the torch body.

It is not essential that the passages in the tip be round, and where the passages are described as round it wil be understood that others of noncircular cross-section may be considered mechanical equivalents. Terms of orientation are, of course, relative, and some features of the invention can be used without others.

I claim:

l. A cutting tip having a diverging outlet oxygen passage with a straight side Wall throughout its length from its inlet end to the end of the tip, and a throat through which gas flows to the divergin passage, the ratio of thediameter of the delivery end of the diverging passage to the diameter oi the throat being between 1.40 and 1.15, said throat having a straight side wall and being of uniform cross-section substantially throughout its length and being of substantially the same (11- I ameter as the adjoining end of the diverging passage, and the length of said straight side wall of the throat being equal 'to more than three times the diameter of the opening through the throat.

' 2. An oxygen cutting torch having an approach passage, a throat that is of cylindrical crosssection and approximately fifteen to twenty times as long as its diameter, and a diverging outlet passage beyond the throat having a straight side wall throughout its length from the throat to the end of the tip, the diameter of the throat being substantially the same as the diameter of the adjoining end of the diverging passage and the ratio of the diameter of the delivery end of the diverging passage to the diameter of the throat being between 1.40 and 1.15.

A diverging-outlet cutting tip having a conduit that is of reduced diameter at one region to provide a throat whose length is greater than three times its diameter and that is of uniform section substantially throughout its length, said conduit being of uniformly increasing cross-section from the throat to the end of the tip and forming an outlet passage having a straight side wall throughout its length from the throat to the end of the tip, the ratio of the diameter of the delivery end of the outlet passage to the diameter of the throat being between 1.40 and 1.15, and the included angle of divergence of the uniformly in creasing cross-section of the outlet passage being between 4 and degrees.

4. A tip for an oxygen cutting torch, said tip having a diverging oxygen passage of frustoconical form with a straight side wall throughout its length from its inlet end to the end of the tip,

and a throat whoselength is greater than three times its diameter andthat is of cylindrical section substantially throughout its length and that connects with the small-diameter end of the diverging passage, the diameter of the throat being same as the diameter of the adjoining end of the diverging passage, the ratio of the diameter of the delivery end of the diverging passage to the diameter of the throat being between 1.40 and 1.15,

and a generally cylindrical approach passage leading to the throat, the approach passage having a diameter between 'one-and-a-h'alf and twoahd-a-quarter times as great as the diameter of the throat and a straight frusto-conical portion connecting with the throat.

6. A cutting tip for delivering a high velocity and parallel-side oxygen stream into a kerf, said tip having an oxygen passage therethrough with a throat intermediate the ends of the tip, a diverging outlet passage on the discharge side of the throat and an approach passage on the supply substantially the same as the diameter of the adjoining end of the diverging passage and the raside of the throat, the diverging outlet passage havin a straight frusto-conical wall surface with an included angle between 4 and 10 degrees and a diameter at the discharge end of the outlet passage that is between 1.40 and 1.15 times as great as the diameter of the throat; the throat being cylindrical and communicating directly with the diverging outlet passage and having a length more than three times as great as its diameter, the approach passage havinga convergin portion that connects with the throat and a cylindrical portion that is from 1 to 2% times as large in di- 'fameter as the throat, the length of the cylindrical times as great as its diameter.

portion of the approach passage being 10 or more 7. A cutting tip for delivering a high velocity :and parallel-side oxygen stream into a kerf, said ftip having an oxygen passage therethrough with a throat intermediate the ends of the tip, a diiverging outlet passage on the discharge side of the throat and an approach passage on the supply "'side of the throat, the diverging outlet passage having a straight frusto-conical wall surface with an included angle between 4 and 10 degrees and a diameter at the discharge end of the outlet passage that is between 1.40 and 1.15 times as great as the diameter of the throat, the throat being cylindrical and communicating directly with the diverging outlet passage and having a length more than three times as great as its diameter, the

approach passage being cylindrical and from 1% to 2%; times as large in diameter as the throat, the length of the cylindrical approch passage being 10 or more times as great as its diameter.

JAMES K. HAMILTON.

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