US2470999A - Thermochemical metal removal - Google Patents

Description

May 24, 1949. E. MEINCKE THERMOCHEMICAL METAL REMOVAL 2 Sheets-Sheet 1 Filed July 28, 1944 INVENTOR' EDWARD MEINCKE BY ATTORNEY May 24, 1949. E. MEINCKE I THERMOCHEMICAL METAL REMOVAL 2 Sheets-Sheet 2 Filed July 28, 1944 INVENTOR EDWARD MEINCKE ATTORNEY Patented May 24, 1949 THERMOCHEMICAL METAL REMovArL Edward Meincke, Scotch Plains, N. J., assignor to The Linde Air Products Company, a corporation of Ohio Application July 28, 1944, Serial n fsimca;

3 Claims.

This invention relates to the thermochemical removal of metal from readily combustible ferrous metal bodies as by cutting, flame machining, boring, deseaming, desurfacing and similar operations. More particularly it relates to an improved method for rapidly initiating a thermochemical reaction between a .jet of oxygen and a ferrous metal body which is readily amenable to ordinary thermochemical metal-removing procedures wherein only a jet of oxygen and a preheating flame are progressively applied against initial and successive portions thereof.

In the art of thermochemically removing metal from readilyoxidizable ferrous metal bodies, such as carbon steel slabs, bars, billets, or blooms, a heating flame is directed against a portion of the surface to raise the metal to itsloxygen ignition temperature. After. a suitable time delay a stream of oxygen is directed against the heated portion of the surface to oxidize the heated ferrous metal, forming a molten mixture of iron oxide and metal which is driven out of the reaction zone by the force of the oxygen stream. The heating flame and oxidizing gas stream thereupon are moved relatively to the body along a path suitable for extending the metal removal operation in a desired direction.

When heating flames alone are used to heat a portion of a ferrous metal body for initiating athermochemical metal removing operation, a substantial time interval elapses before the ignition temperature isreached. When such a metal removing operation is to be initiated on a round bar having no sharp edges, or within the boundaries of a cold metal body, it is an especially slow procedure to heatthe metal to its ignition temperature, and undesirable gouging of the surface often occurs. Such gouging occurs even on hot steel if the movement of the blowpipe and the opening of the cutting oxygen valve are not so synchronized as to prevent it. As an illustration, the preheating time for starting a desurfacing operation at a square cut edge of a billet, using multiple nozzles, generally varies from 12 to 30 seconds for a cold steel billet and from 3 to 8 seconds for a hot steelbillet. In an effort to decrease the preheating time there have been used heating flames of greater size and heating intensity than are normally required to maintain the metal removing reaction after its initiation, but this increases the operating cost with only a slight decrease in starting time.

Likewise, in the severing of a steel body such as a billet, bar, or slab, ithas been necessary to pause at the edge of the body to preheat the edge to its ignition temperature. This has been especially annoying when periorming cutting operations on a large scale with a. plurality of such steel bodies arranged side by side because preheating time must be, lost at theedge .of each successive body. One procedure has been to employ two operators, one for cutting and the other to preheat the edges in advance of the cutting operation.

In another procedure of the prior art for increasing the speed of starting a thermochemical reaction on a ferrous metal body, a short length of iron rod is positionedin frontof the preheating flame and, when this length of rod has been raised to its ignition temperature, cutting oxygen is directed against the heated portion to ignite it. The burning portion of rodis blown against the surface of the bodyand the latter is thereby heated to its oxygen ignition temperature sufficiently rapidly that the. cutting oxygen stream soon begins to attack the metal body. Once the metal removing actionhas been initiated, it proceeds normally without the addition of more iron rod, while relative movement is efiected between th oxygen stream and the body.

While the starting rod method for initiating a thermochemical metal removing reaction has proved to be an important advance in the art, it has several disadvantages-which are avoided by the method of the present invention. The feeding of a starting rod involves skillful coordination of the movements of the blowpipe operator for success in starting the removal of the metal. If insufficient time for preheating is allowed, the iron rod may not be up to the ignition temperature when the oxygen flow is started; or if too much time is allowed, the heated end of the iron rod may melt, fall ofi, and be blown away before the cutting oxygen flowis started. In eithercase there is a failure to initiate the metal removing operation. Also important isthe fact that a delay of several seconds is required to bring the end of the starting rod to its ignition temperature before the oxygen flow can .be started, so that running starts cannot be effected. Another disadvantage of the startingrod method is the need for a mechanical rod feeding device mounted in close proximity to the blowpipe nozzle for guiding the rod into the preheating flame. Such a device is exposed todamage; and sometimes complicates or prevents entirelythe insertion of a blowpipe nozzle into-a confined space. Moreover, in multiple nozzleworl-:, suoh as desurfacing or multiple cutting, starting rods are not entirely dependable because -it'is -,not always possible to heat-each'rod to the ignition temperature in exactly the same interval of time; and if too little or too much time elapses for preheating a particular rod it becomes impossible to initiate the oxidizing action of the oxygen stream from the corresponding nozzle. Another disadvantage of the starting rod procedure is that it cannot be efi'ectivelyapplied tononhorizontal surfaces such as the side orzbottomsurfaces of ferrous metal bodies because the force of gravity tends to cause the preheated and ignited portion of the rodeither to flow away from the reaction region or to drop away entirely from the surface.

Therefore, among the important objects of this invention are to provide a novelmeth'odforu starting the thermochemical reaction of a" jet of oxygen with a readily oxidizable ferrous metal temperature in a flame, and igniting and burning body more rapidly than has heretofore-beenpos sible; and to provide such a starting method which is dependable and=simple. are to provide such a. method which can be used Other objects to start rapidly aithermocheinical reaction on" both horizontal "and non-horizontal "surfaces such as, the top; side; and bottom surfaces'of 'afer rous metal body; which makes it possible to" effect running starts in"cutting,flamemachining,

desurfacingand like proceduresy'which can be used in: confined -locations;--which is dependable for starting multiple 'nozzle metal removing operations such as desurfacingl; and which permits the employment of asirnplified mechanical con-' struction; havingibut few moving-parts to get out of order. "Another,object""is"to provide a" novel method whereby a single operator can out continuously. across atplurality of. ferrous metal bodies'arranged sideby side without pausing to" preheatthe edge'of each successive body.

The above and other'objects,'and the novel features of the invention, will become'apparent from the, following detailed description having referenceto the accompanying drawings, where- Fig. 1 is a schematic side elevational view of one form of apparatus. forv performinghthernethod of .theinvention, shownin position for cutting acrosslasteelbillet;

Fig. 2-,is an enlarged vertical mid-sectional view of apart ofltheaapparatusuof Fig.1.showing a cutting nozzle in: position forcutting a kerf in a ferrousmetahbody; 4

Fig-43 is -.an end v (view shown in Fig. 2;-

Fig. "41 is amend view of a modified form of cutting; nozzle;.. 1

Fig::-5,.is-a side elevational view of a part of a modified form of-apparatusfor cutting ferrous metal: by. the method of :the invention;

Fig.6 is aobottom end view ofthe apparatus shown in-Figa5; r: z" I Fig. 7: is a side elevational view showing a modified arrangementofthe apparatus of Fig.15;

Rig; 8v is-avertical mid-sectional viewof the front end of .one-rtyperof :deseaming 'or' flame machiningblowpipeproperly positioned for de-'- which has been nickedby the-method of the subsequent breaking by impact; 1

invention I for and 4 blowpipe properly-positioned for boring a hole of the cutting nozzle Fig. 11 is a side elevational view showing a the powder b'y directing a jet of oxygen against both the body. and the applied powder within such regionfto' propagate the heat of combustion of the powdento the body. A portion of the ferrous metal body in the starting region is in this way promptlyraised to its oxygen ignition temperature and is ignited in the flowing stream of oxygen. After ignition of the body the application of powder is stopped and the flame and the flowing oxygen jet are advancedrapidly *ove'r a selected path relatively to theferrous t metal body, thereby oxidizin'g successive portionsof the 3 body? As 'in' ordinary thermochemical metal re-" moving operations, a 'fiuid*mixtu're- "of oxide slag by he an'd'molten metal forms and is-"displac'ed kinetic energy of' the oxygen stream? The adj uvant powder" can be introduced into the region of the oxidizing reaction "in any suit able manner, but I have" found it advantageous to entrain the powderin a gas; such as com pressed air, and to direotthe' powderlaiden gas stream into the cuttingoxygen jet Whichblows able procedure for introducing'the powdered ad juvant material is to suspend 'it injth'e metal 're"- moving oxygen'strear'n" before discharge from the lowpipe nozzle;

The adjuvant or helping powder ordinarily used to perform the method described above, de-

sirabl-y comprises ahighly'combustiblemetal such as powdered iron, low carbon steel, cast iron, or

ferromanganese, and mixtures of suchmetals with one another and with'othenmate'rials, such as aluminum -or' manganesel A'djuv ant' 'powde'rs comprising about-%"ste'el and '20 %"fer'rorrianganese or-80% steel and 20% aluminum are" wur suited for my'novel method" It is"to' befu'n'der' stood, however, that my invention is not'l'iniited" to the use ofthese specific metal'powders nor even to metal powders as a"class,-'since"other'com. bustible powdered materials 'can bu'sed successfully for performing the methodi" Therefore, the

term adjuvant materia is used-herein'to 'de:

note any suitable combustible powder which permits an increase-in therate of starting thermochemical metal-removal by my novel method.

More speoifically in rapidly cutting a deep narrow kerf along-a'selected path or cutting line on i a readily oxidizableferrous-metal body by--the method ofmy inventionfajetof oxygen, a stream-- of combustible metal powder; and a preheating medium such as an oxy-ac'etyleneflamehaving' sufiicient 1 heating intensity toheat at- 'least' the powder to its= oxygen ignition temperature; are directed concurrently against the regionuof' the" surface" where the out is- -to be started. The" powder quickly ignites andpropagatesits heat of combustion to the metal body, raising" apertion' Of the-bodyto its' igniti'o n tem erature. In"

order to carry the' combustion-'01:" the body to a suitable depth, usually completely through the body, the oxygen jet is so directed as to penetrate deeply into the body, for example at an angle of 90 to the surface or at some other somewhat smaller angle. Once the oxidizing reaction has started the powder flow is shut off and the preheating medium and the jet of oxygen are advanced in unison relatively to the body in a direction substantially parallel to the surface along the desired path of cut, to ignite and burn successive portions of the body along the cutting line, leaving a deep kerf.

Most cuts are carried completely through the ferrous metal body with the object of severing the two portions on opposite sides of the kerf. However, by moving the jet of oxygen and the preheat medium so rapidly relatively to the body that the oxygen jet penetrates only partly through its thickness, heavy steel billets can be nicked at high speed as in Fig. for subsequent impact breaking.

In the flame machining of a readily oxidizable ferrous metal body by the method of my invention, the reaction is initiated by concurrently directing against a region on the surface of the body from a suitable source a jet of oxygen flowing obliquely relatively to the surface in the direction of the path, a preheating medium such as an oxy-acetylene flame, and a stream of combustible adjuvant powder. As in cutting, the burning adjuvant powder propagates its heat of combustion to the base metal to ignite the latter, the powder flow is interrupted and the jet of oxygen and the preheating medium are advanced in unison relatively to the body along the selected path in a direction substantially parallel to the surface to ignite and remove successive portions of the body to a shallow depth. The jet of oxygen should be flowing with sufiicient velocity and should be inclined at a small enough angle to the surface that the molten metal and oxide slag are blown forward along the selected path to assist in preheating successive portions of the metal. This procedure can be carried out with only a single nozzle as when deseaming a billet, or a bank of nozzles can be arranged side by side to remove a shallow layer from part or all of the surface of a billet, bloom, or slab.

My novel method for thermochemically removing metal from readily oxidizable ferrous metal bodies by using a powdered adjuvant material to initiate the reaction, as described in detail above, involves an extremely rapid initiation of the thermochemical reaction, far more rapid than has been possible heretofore. For example, in flame cutting a readily oxidizable ferrous metal body the out can be started without any pause for preheating, by moving the cutting blowpipe toward the body at full running speed with the preheating gas burning, and the cutting oxygen jet and powdered adjuvant material flowing.

Alternatively, a cutting blowpipe can be positioned above the exact point on the body at which the cut is to be initiated with the preheat gas burnin and the cutting oxygen flowing, and by promptly thereafter applying a burst of powdered adjuvant material to the metal surface the cut is initiated instantly and relative movement between the body and the blowpipe can be started simultaneously with the application of powder. Such instantaneous starts are possible regardless of the shape or type of surface, so that bodies having round surfaces can be cut as expeditiously as vvthose having sharp corners. My

starting procedure is a big improvement over both ordinary oxy-acetylene cutting, wherein preheating to the ignition temperature is accomplished solely by the oxy-acetylene flame, and over the starts obtained with a starting rod which must be preheated for several seconds before the cutting operation is actually initiated.

In cutting and deseaming, a burst of powder causes the metal removing operation to start immediately even if the starting point is within the boundaries of the metal body or is on a rounded surface havin no sharp corners. In a desurfacing operation using my starting method, metal removal from a cold steel billet can be started inabout to 2 seconds elapsed time with nine blowpipe nozzles arranged side by side and a powder flow between and 2 lbs/min, whether the start is made at a square out edge or within the boundaries of the billet. In contrast, if powder is not used the starting time varies from about 10 seconds in the case of a cold billet or slab having a square corner to 30 seconds or more if the start is made within the boundaries of the metal body. The cost of starting a multiple nozzle desurfacing operation is about the cost of starting such an operation without any auxiliary material. Even using steel starting rods, the starting time for initiating desurfacing is 6 or 7 seconds. Moreover, starting a thermochemical desurfacing operation with powdered adjuvant material is more dependable than methods employing a plurality of starting rods, because there is involved in heating the powder to its ignition temperature no variable time element, such as is encountered when iron rods are heated at different rates.

When using powder solely for making a running start in the cutting of a metal body which can subsequently be out fast enough without powder, I provide a thermochemical cutting nozzle adapted to direct both a preheating flame and a cutting oxygen jet against successive regions on the surface of the body alon a selected cutting line or path, and continuously advance the nozzle, the flame, and the cutting jet to the body from a point short of where the flame and the cutting jet first impinge against the body, and then along the cutting line. At the instant of initial impingement of the flame and cutting jet, and while maintaining the advance of the nozzle, I deliver only against the region of initial impingement a small quantity of powdered adjuvant material oxidizable by the cutting oxygen to supplement the heat applied by the flame and substantially instantaenously heat the region of initial impingement to its ignition temperature, thereby avoiding interruption of the advance of the nozzle when starting the cutting operation. Thereafter the nozzle is advanced to cut the metal without the further introduction of powdered material.

Trials have indicated that running or instantaneous cutting starts can be made on rounds of various diameters and square cornered and rounded cornered blooms, billets, and slabs. Tests have also indicated that under most circumstances the speed of approach can equal the cutting speed. When powder is not used the time required for preheating prior to the starting of the out will vary depending upon the shape of the material to be cut, being considerably longer in the case of a large diameter round than a small one and shortest for a relatively square cornered billet.

caseof a start within the-boundaries.otthematerial. Tests have indicated thata powder flow rate of vfromz to oz.. per minute. will producea successful. start.

.In. the. thermochemical .deseamingof ,hot steel bodies .thepractice has been .topreheatwiththe v flame .for aperiod varying from 2 to.5. seconds. With-my novelmethod, instantaneous starts are possible, and .in.mu1tiple. nozzle .desurfacing -flyingstarts can be madeby positioning the nozzles oil the end ofthe steel body, effectin relative moyementbetween the nozzles and the {body toward one another at arreduced rate withtheheatingfflames, oxygenjets, and powder streams flowing, and increasing the speed of movement to a normal. desurfacing speed after initiation of the thermochemical reaction. The established practice of preheatingwithout powder has-required that-the steel body beheld stationary-during the preheat period.

---My-methocl provides several otheradvantages in addition to' increased starting speed. Thepreheating fiame need only'be of the'relatively small size-and heating intensity needed forcontinuing the operation after its initiation, rather than the excessively large and hot flame ordinarily used. Sucha startin procedure-does not requiresuch a skillful coordination of the operators movements. as is necessary when using a starting rod. *Moreover, the initiation of a metal-removing operation is not limited to the horizontal top surface of a metal body, as is the case-with astarting:rod,"butmay =be employed on-the side and bottom surfaces as well.

In Figs, 1, 2 -and 3 of the drawings,- a cutting *blowpipe H is shown in deep narrow kerf E3 in a squart readily oxidizable :steel billetld having rounded corners. Oxygen and acetylene are supplied to the blowpipe through the hoses l7 andlll'controlled by the .valves' fll and .23, respectively. A-portion of the oxygen is mixed with the acetylene within the blowpipe, in a well-known manner,- to form a combustible gas mixture which flows through the :COHdHitYZB to the nozzle 21, fromwhich itis discharged and 'bu-rned to form a preheating 'fiame. Thezb'allance of the oxygen is employed for the cutting action. and .flows to the nozzle -21'Lthrough a conduitwEShaving-a shutofi" valve (not shown) controlled ;by. a valve lever 3 I 3A.:2110Wd'611di5136fi5811 3.3 :containing a .supply I of .suitablecombustible adjuvant powder, such 1 as steel, iron or mixtures of steel with ferroman- .ganese or aluminum; has .a gas :inlet;.-:3 5...and. an :1outl1et: -3l :forzpowder laden gas connected -.to .a

long hoserlflfor conducting the powder-ladengas tothe .bl'oWpipe I! l. dispenser is. =shown One. suitablestype of'wpowder in Eatent 12,327,337 granted August/24; $943,170 C. J'..Burch and- .G. "Ed-- vwards. The powder laden ;.g'as then passes :through :the.:conduit 113 to the nozzle EM and is tdischargedtoaid the cutting operation. Elow -.o..-the powderrladen gas through the conduit-.43 lislcontrolled bya valve .45 in the head-Hmonrnectedsbyi a 110111-49 :to:a thumb :lever: .5 Lon-the handle of the blowpipe.

position for cutting a @As shown in detail .in Fig-2,. the- -nozzle:2-1-:is similar to ordinarycutting:nozzles-in havingua central cutting oxygen-passage 53.and1a;plurali ty ofpreheat gas-passagesfifi with outlets arranged onan annular zone surrounding. the centralpassage for providingna ring of :=pr,eheating flames .56- aroundthe central cutting oxygen jet 58. In addition, the nozzle 21 hasva plurality oflongitudinal powder. passages .51 having inlets earranged in a ring of larger. diameterthanthe ring of preheat passages and outlets arranged in a ring of smaller diameter than. the preheatring between. the latter and theoutlet otthe oxygen passage. 53. Suitable gas-tight seats 59, 6,.l,.and Etseparate thethree sets of .passages.53,. 5.5 and 5'1 .il'om one another and the .atmosphere,..and permit each set-of passages to communicate-exclusively with the correspondingone..of..the supply conduits 28,125 and' l3, respectively, through suitablepassages in .the head '41.

In operatin the blowpipe shown in.Figs. 1,2 and 3.tl1e valves 2i and 2.3. are adjustedto provide a pleheatl'ng gas mixture which, when ignited, will'formflames 56 of sufii-cient heating intensity tc'heat at least the. adjuvant powder to its oxygen ignition temperature. The preheatingflamesSB are then directed againstxthe edge of the billet i5 and the oxygen and powder controllevers 3| and'fihrespectively, are depressed, by the operatcrwhile he holds the blowpipe at alarge angle to the surface such that the oxygen jet 58 will penetrate deeply into the billet. The padjuvant powder streams instantly ignite andburn' in contactwith the surface of the billet [5;thereby heating a small portion of the latter toits oxygen ignition temperature almost instantaneously and initiating combustion. Immediately-thereafter thevalve- H5 is closed by releasinglever 5| to interrupt powder flow and'the blowpipe l l is moved across the billet 55 parallel to itstop surface to advance the jet of oxygen and the preheat flames in'unison, thereby igniting andburning-succes- .sive portions ofithe body and leaving .a Keri-13.

Fig.4 shows the end of a modified nozzle -66 wherein-only a single adjuvantpowder outlet 61 is locatedbetween the centraloxygen passage-69 and the preheat ring 68 in a position tolead or lag the cutting oxygen jet. Itisapparent' that the numberof powderoutlets may bevariedat willin accordance with the particular-purpose for which eachnozzle is designed.

Figs. 5 and 6 show an ordinarycutting'nozzle .1|,-of well known construction; used inconjunction with a separate adjuvant =powder supply nozzle 1.3. The lower portion of the powder nozzle :73 is inclined toward the nozzle ILandhas itS outlet closely adjacent thelower end of thelatter zinlposition for discharging the stream of powder glibetween. two of the preheat orifices flata sufficient velocity to penetrate the preheat fiame :envelope 18. and impinge against 'the central .oxygen stream 19.

nozzleacetylene gas from a ring-of passages-89 and zox'ygenfrom the central passage 91. -Pow- .deredladjuvant material is introduced intothe .central passage .9 I through ports-i 93 =in 'commu 'nication with a supply passage 94 controlled-by a valve 96. When startinga deseaming operation,

the externally: :mixedstype ifiame 88. is ldirected obliquely against the surfaceof the slab 81 while the nozzle 85 is held at an acute angle thereto. Immediately thereafter, the cutting oxygen and adjuvant control levers (not shown) are depressed by the operator, thereby increasing the rate of flow of oxygen and causing the powder laden gas to flow through the powder inlet ports 93 into the passage 9|. When the adjuvant powder impinges against the slab 81, it ignites and burns instantly, propagating its heat of combustion to the surface of the slab and heating the latter almost instantly to its oxygen ignition temperature to start the thermochemical reaction. Thereafter, powder flow is discontinued and the jet of oxygen and the preheating flame are advanced in unison relatively to the slab 81 substantially parallel to the surface along a selected path to ignite and remove successive portions of the billet to a shallow depth. Powder starting is especially advantageous for spot deseaming wherein the metal removing operation must be started within the boundaries of a steel body. Powder starting is also highly advantageous for flame machining a groove in the side edge of a plate to prepare it for welding to another plate, because the powder impinges against the plate directly. With a starting rod, the metal melted off by the flame tends to drop away under the influence of gravity. It is apparent that a nozzle designed for projecting premixed type flames toward the slab 81 can be used, if desired.

Fig. 9 shows a motor-propelled carriage 9'! mounted upon a track 99 and carrying a machine cutting blowpipe MI in proper position to out a kerf I02 along a cutting line extending transversely across each of a plurality of elongated readily oxidizable ferrous metal bars or billets I08, I I0, and H2 arranged side by side with their top surfaces in substantially the same plane. The incoming acetylene and oxygen streams for the heating flame are controlled by the two valves I03 and I05, the cutting oxygen stream by the valve I01, and the adjuvant powder flow by the valve I09. Anozzle III identical with that shown in Fig. 2 is attached to the lower end of the blowpipe for directing a heating flame and a cutting oxygen jet against successive regions on the surfaces of the bodies. When starting a cut with this cutting machine, the blowpipe IOI is usually positioned with the nozzle III spaced a small distance from the edge of the billet I08 at a point short of where the flame and oxygen jet initially impinge against one of the two outside bodies I08 and H2, with the preheat gases burning and the cutting oxygen jet and powder stream flowing. The cutting machine 91 is then started and advances continuously at full running speed (or some lower or higher speed) toward the billet I08 and, at the instant when the nozzle reaches the edge of the billet I08 the burning adjuvant powder and the flame cause the edge to ignite and the cut to start, no pause in the movement of the cutting machine being necessary. Powder flow is discontinued when the out has started.

When cutting a series of bodies I08, H0, and H2 as shown in Fig. 9 by employing adjuvant powder only for increasing the starting speed, it is an important feature of this invention to deliver adjuvant material to the region of initial impingement of the heating flame and cutting oxygen jet against each succeeding body while continuing the advance of the nozzle without interruption along the several cutting lines in succession. By this procedure, I avoid interrupting the advance of the nozzle when starting the cutting operation on the outside body, and when starting the cutting operation on each of the succeeding bodies of the side by side arrangement. In the arrangement shown in Fig. 9, for example, powder is delivered momentarily to the regions of initial impingement of the heating flame and oxygen jet against the initial edges of the steel billets I08, I I0, and H2 in succession, but the powder flow is discontinued immediately after the thermochemical action begins at the initial edge of each billet so that the major portion of the kerf in each billet is out without benefit of adjuvant powder. This procedure can be carried out on bars, billets, slabs, and like bodies of various shapes, such as round, square, or rectangular.

Running starts in flame machining and desurfacing operations can be accomplished with a procedure similar to that described above for cutting, using an appropriate propelling device.

Fig. 11 shows a blowpipe I I3 positioned with its nozzle I I5 close to the end of a-billet I It in which a hole H8 is being bored. Shallow holes can be drilled with the nozzle stationary, but deeper holes sometimes require movement of the nozzle along the axis of the oxygen stream. A blowpipe identical with that shown in Figs. 1 and 2 can be used for this purpose, and the powdered adjuvant material is discontinued after ignition of the billet metal has started.

Specific examples of the method of the invention have been described herein by way of example only. It is to be understood that changes in the method can be made within the scope of the invention, as defined in the claims appended hereto.

What is claimed is:

l. A method of rapidly initiating and efiecting a thermochemical metal-removing reaction along a selected path on a ferrous metal body which is readily amenable to ordinary thermochemical metal-removing procedures wherein only a jet of oxygen and a preheating flame are progressively applied against initial and successive portions of said metal body, said method comprising first heating to its oxygen-ignition temperature a selected region of said body at which said metalremoving reaction is to begin by concurrently directing together against said region a jet of metal-removing oxygen, 2. preheating flame, and finely-divided burning combustible metallic adjuvant powder to cause said powder to impart its heat of combustion to saidregion whereby said body is heated substantially instantaneously to the oxygen-ignition temperature thereof in said region; then interrupting the supply of adjuvant powder to said region immediately after said body has become ignited therein; and thereafter continuing the thermochemical metal-removing reaction by directing only said jet of metal-removing oxygen and said preheating flame against successive portions of said body along said path in a direction away from said region.

2. A method in accordance with claim 1 which also comprises continuously advancing said preheating flame and said oxygen jet to said body and then along said path without interruption from a point short of where said flame and jet first impinge against said body; and, at the instant of initial impingement of said flame and jet against said body, blowing said burning finelydivided combustible metallic adjuvant powder against the region of such initial impingement.

3. A method in accordance with claim 2 wherein said adjuvant powder is advanced as a flowing stream together with said preheating flame

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