CA1103568A - Method and apparatus for reducing smoke and preventing secondary fins during scarfing - Google Patents

Abstract

ABSTRACT

A thermochemical scarfing process and apparatus capable of reducing the amount of smoke discharged to the atmosphere and/or of preventing the formation of "secondary"
fins when spot scarfing, comprising:
(a) scarfing oxygen is directed against a reaction zone of molten metal on the surface of the workpiece to produce a scarfing reaction, and (b) relative movement is provided between the oxygen stream and the workpiece, said reaction forming a molten puddle in front of the reaction zone that grows larger as the cut progresses, wherein the improvement comprises:
(c) directing at least one stream of non-reactive fluid to form a fluid, sheet-like curtain that provides a cover over the reaction zone and at least the rear portion of the molten puddle in such manner that said curtain forms a pocket with the surface of the workpiece.

Description

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~BACKGROUND
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This i~e~ion relates to the thermochemica~
desurfacing of metal bodies, commonly called scarf$~g. More particularly9 this ~nven ion comprises a method ~nd apparatus for preventing fin ~orma~ion along ~he boundaries of a scarfing cut, and for substantially reduc~ng the amou~t of smoke discharged i~to the atmosphere during scarfing.
The comm~n practice in scarfing is to flrst form a molten metal puddle or "hot spo~" on the surface of the wor~-pieee by direc~ing preheat 1ames at a relatively ~mall area of ~he surface until it xeaches its ~gnition tempera~ure.
Thereater, a stream of oxygen is dlrected obliquely against the molten pu~dle to produce a thennochemical reac~ion on the me~al ~urface. Relat~ve mo~ement is then produced between the oxygen stream and the workpiece which contlnues the thenmo-chemical rezc~ion along the metal surface, thereby producing the desired desurfacing along the leng~h of the metal body.
~uring the scarfing reac~ion, a puddle of molten slag, fonmed dnwns~ream o the scarfing reactio~ zone, continually precedes the advancing reaction zone alon~ the work ~urface. This slag puddle preheats the metal surface before ~t is raised to its ignition temperature by ~he ~carfing oxygen streamO Thus, ~he oxygen stream has a two-fold purpose: firs~ to effec~ua~e the thermochemical r action with the me~al, and second, ~o

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continually push the molten puddle of metal and sl~g forward to expo~e fresh metal or the scarfing reaction.
There are two seemingly unrelated problems associ~ted with conventional scarfing: (1) fonmation of fins when less than ~he full surface of the workpiece is scarfed and ~2) forma~ion of smoke, regardless of whether the full surace or less than the full su~face is scarfed. Surprls-ingly1 the preferred ernbodiment o~ ~he prese~t invention is o substantial beneflt in mlnimizi~g the adver~e efec~s of both of these problems, each o~ which will be discussed separa~e ly .
One problem associated with scarfing less than the ful~ width of a metal surface, a process commonly referred to ~8 "spot scarfing", is the fo~mation o "flns" at the edge of the scaring pass. The term "fin" as used herein refers to a thin flash or wash of pure or sllghtly oxidized base metal ~:
which is solidly ~oined to the surface of the metal workpiece at the bou~d~y of a scarfing cut; the ~lns being undesirable deects on ~he me~al body wh~ch must be remo~ed before rolling.
Fins may be produc~d by either or both of two unrelated causes~
Fins may be producecl directly ~rom the primary reaction zone i molten metal is driven laterally out of sald zone by the force o~ ~he scarfi~g oxygen stream, causing the molten metal to adhere to the edge of ~he scarfing cut where it solidifies in plaee. This type of in forma~ion (referred ~o herein, for purposes o conveniencel as "primary" ins~ can be prevented ~ D 9664-1

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by us~ng a specially shaped di~char~e orifice for the scarfing oxygen stream wh~ch gradually diminlshes the intensity of ~he o~ygen stream at the ends of the orifice to the point where the stream cannot sustain ~ scarf~g reaction along the boundaries of the scarfing cut, bu~ can oxidize molten me~al at BUCh boundaries before i~ solidifies. ~ozzles h~ving orifices of the special type described above that are partlcularly suited for spot scarfing in individual and gang arrangement are desrribed in U.SO Patent Nos. 4,078,950 and 4,013,486.

Fins m y alqo be formed by ~ ~o-called "secondary"
effect which arises when the molten puddle of slag ~rows progressi~ely larger ahead of the primary reaction zvne to the polnt where the advancing oxygen stream can no longer move the entire puddle forward, and therefor pushes only the center :~
portion of ~he puddle forward, thereby forcing some of the molten metal at the edges of the puddle laterally beyond ~he boundaries o the scarfing cut where ~t ~olidifies in an un-oxidized ~ate. One problem wi~h which ~he presen~ disclosure ~s concerned is a method and apparatus for preventing such " secondary'~ fin formation~

~ The use of fluid streams to help remove the slag ;~ produced by the scarfing reaction is well known. Thus3 for example, U.S~ Patent Nos. ~873,224 and 3,163~5S9 to Thompson et al disclose, respectively, solid and hollow streams of high ~ ~"

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pressure water directed transversely to skim across the work surface just ahead of the scarfing reaction zone to wash away ~he slag. U.S~ Patent No. 3,354,002 to Gingerich et al discloses a plurality of high velocity water je~s positioned slightly downstream of the reaction zone, perpendicular to ~he direction o~ travel of the scarfing reaction, to ~rap the slag spray and to wash it off the work surface into a slag chute. While the use of such water jets, positioned trans-verse to the work surface, commonly referred to as "cross-fire, slag-water" jets, is effective for removing slag from the surface of the metal, it is nevertheless incapable of preventing fins. This is due primarily to the fact that cross-fire slag~water jets are positioned on one side of the - -- workpiece to blow molten slag from the near side of the cut into a slag receptacle located along the opposite side of ~he workpiece. This has ~he effect of minimizing ~in-format;on on the n~r side of the cut, while tending to aggravate the problem o fin-:~ormation on the far side.
The second problem caused by conventional scarfing 20 operations is the large amount of smoke, i.e., fume~ or vapors ~
and fine particulate matter formed by the scaring reaction.
Prior art techniques for the collection and removal of smoke ; from the vicini~y of the scarfing reaction zone are relatively cunbersome, requiring an inordinate amount of auxiliary `~
cleaning equipment. In scarfing machine installations where the wo~kpiece moves pas~ a stationary machine, the smoke is normally collected ~n large stationary hoods and removed 5. `

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~hrough ducts maintained under negative pressure by fans. The trapped smoke is thereafter sent through scrubbers and precipitators for removal of contaminants prior to being vented to the atmosphere. In installations where the scarf-ing machine moves past a stationary workpiece, traveling ducts are used in place o~ a stationary smvke hood ~o collect the smoke. In both cases 9 h~wever, the equipment required for collecting and cleaning the smoke is relatively large, expensive and difficult to maintain.
In addition to preventLng secondary ins and reducing the amount of smoke emitted to the atmosphere~ the present invention produces a third beneficial result, namely reduction of nOLSe. It is also apparent from comparing scarf-ing operations with and without the practice of this inven-tion, that practice of the invention reduces the amount of noise emanating from the scarfing reaction.
OBJECTS

Accordingly, it is an object of the present inven-tion to provide a method and apparatus for spot scarfing the surface of a metal workpiece in such manner as to prevent the formation of "secondary" fins along the boundaries of spot scarfing cu~s I~ is still a~other objec~ of the present invention to provide a scarfing method and apparatus which substantially reduces the amo~nt of smoke that escapes into the a~mosphere from the scarfing reaction.

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I~ is a further object of the present invention to provide a method and apparatus for spot scarfing the surface of a metal workpiece in such manner as to prevent the forma-tion of "secondary" fins along the boundaries of the scarfing cut and at th~ same time substantially reducing the amount of smoke that escapes into the atmosphere from the scarfing reaction.
~ SUMMARY OF THE INVENTION -;~ These and other objects, which will become apparent from the detailed disclosure and claims to follow, are achieved ~:~ by ~he present invention,~one aspect of which comprises:
: A thermochemical scarfing process wherein (~) a stream of scarfing oxygen is directed against a reaction~zone of molten metal on the surface of a metal workpiece to produce ~ -~
:~ a thermochemical reaction thereon and (b) relative movement is provided between the oxygen stream and the workpiece to continue the reaction along the length o metal surace to produce the desired scarfing cut, said reaction tending to forming a molten puddle in front of the advancing reaction æone that tends to grow larger as the cut progresses, wherein the improvement comprises:
~; ~c) directing at least one stream of non-reactive : fluid so as to form a fluid sheet-like curtain that provides . ~
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; a cover over the reaction ~one and at least the rear portion of the molten puddle in such ma~ner ~hat said fluid curtain ~ forms a pocket with the surface of tb~ workpiec~

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Although the fluid curtain may intersect the work surf~ce directly to form the pocket, it m~y al50 fon~ the pocket indirectly by hav~ng ~he leading edge o the curtain intersect one of the cross-fire slag-water jets, i.e., one of the ~treams of water directed perpendioular to the direction of the ~carfing pass which skim the work surface ~ust ahead of ~he scarfing puddl~.
The ~luid curtain may be directed either rom ~bove and in substantially the same direction as the oxygen ~tream, and down at an oblique angIe to the work surface, or it may be directed at an oblique ~ngle to the work surface from the side of and substant~ally perpendicular to ~he oxygen stream. In either case, ~he curtain will intercept the smoke emanating from the scarfing reaction, thereby substantially reducing the amou~t of ~moke emitted to the surrounding abmosphere~
If the stream nr streams forming the fluid cu~tain are directed down fr~m above the oxygen stream and in : sub~tantially the ~ame direction as the oxygen stream so that the stream impinges upon the molten puddle across it~ entire width, and at A sufficient distance upstream of ~he leading edge of ~aid puddle with ~uficient intensity ~hat the leading portion of said puddle is granulated and pushed orward in the direction of the ~carfing path, it w~11 keep ~he puddle ~ufficiently small ~o be readily pushed forward by ~he scarfing : ~xygen ~tream wi~hou~ deflecting ~ portion of the puddle ::
laterally ~eyond ~he boundaries of ~he scaring cu~. By so doing, ~he ormation of "second~ylr fins will be prevented.

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Another aspeet of the present invention comprises:
Apparatus for scarfing the surface of a metal body comprising in combination: (a) means for discharging a stream of oxygen and dîrecting it against a reactlon zone o molten metal on the surface of said me~al body to produce a thermo-chemical reaction thereon, and (b) means for producing relative ; movement between the workpiece and said means for discharging oxygen, wherein the improvement comprises:
(c) means for discharging at least one stream of non-reac~ive fluid such that i~ forms a shee~-like curtain directed to form a cover over the reaction zone and at least the rear portion of the molten puddle in such manner that said fluid curtain forms a pocket with the surface of the workpiece, said means being capable o preventing the formation o secondary fins along the boundaries of a spot scarfing cut a~d/or ~f substantially reducing the ~mount of smoke prod~ced by a s~arf- :
ing reaction from being discharged into the atmosphere.
A preferred embodiment of the apparatus includes cross- ~
ire, slag-water jets. In such case, the nozzles forming the ~ .
fluid cuxtain are directed such that the leading edge of the curtain in~ersect one of the cross-fire, sla~-water jets.
Said r~ozzle means may be d~rected either from above the means for d~recting said oxygen stream, down at an oblique angle to the work surface in substantially ~he same direction as the oxygen stream or said nozzle means may be direc~ed from the side of the means for directing said oxygen stream, at an oblique angle to the work sur~ace and subst~ntially perpendicul~r ,, to the oxygen stream. In either case the curt~in will inter-cept vapors and particulate matter emana~ing from the scarfing reaction, thereby causing substantial reduction in the amount o smoke emitted to the surrounding atmosphereO
If the nozzle means for fonming the cur~ain are directed down from above the oxygen stream and in substantially the same direction as the oxygen stream at an oblique angle to the work surface, so that the stream impinges ; upon the molten puddle across its entire width and at a sufficient distance upstream of the leading edge of said puddle with sufficient intensity that the leading portion of said puddle is granulated and pushed forward in the direction of the scarfing path by said fluid stream, it will keep the puddle sufficiently small to be readily pushed forward along the metal surface by the scarfing oxygen stream without deflecting a portion of the puddle laterally beyond the boundaries of the scarfing cut. By so do~ng, the formation of secondary fins - will be prevented.
The term "non-reactive fluid" as used throughout the ~peciication and claims is in~ended to mean a fluid that will not react rapidly with the metal workpiece. Water is the preferred non reacti~e fluid for accomplishing both objectives, i.e., secondary fin prevention a~d smoke-controlO However, other useful non-re~ctive fluids include~ for example: ste~m, water mist ~i.e.~ a mix~ure of water and air), or mix~ures ~ of water and an inert gas such as nl~rogen or argon~
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IN Illl~ Dl/~l~IGS
Figure 1 is a ~chematic illustration, in side view, of a conventional spot scarfing cut in which the molten meta1 and slag puddle has been formed.
Figures 2 and 3 are top and cross-s~ctional ~lews, respectively ~llu~tra~ing a steel sl~b which has been spot scarfed with a conventional noæzle producing f~ns.
Figures 4 and 5 are top and cro~s-sectional v~ews~
respectl~ely illustrating a steel slab which has been ~pot scarfed by nozzle means capable of preventing prlmary fino formation, but incapable of preve~ting secondary f~n-formation along the boundaries of the cut.
Figure~ 6 and 7 are top and cross-sectional views, ~ respectively illustrating a steel slab which has been spot : æcarfed in accordance with the present i~ent~on, i.e., which produces a cut free of secondary fins as well as prlmary fins~
Figure 8 is a perspective view illustrating a : preferred embodiment of the present invent~on, how a metal slab may be spo~ scarf~d to produce a fin~free cut, while the amount of smoke ~mitted to ~he a~mosph2re is simultaneously reduced.
Figure 9 is a side view of the ~nvention, illustrating the relat~ve orientation of the wa~er stream and ths ox~gen stream to obtain both smoke reduction and el~minating secondary ~ins.
Figure 10 is a side view of ~he invention, illustrating a-fluid cur~ain tha~ will reduce the amount of smoke emit.~ed ,, ~
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to the atmosphere, but will not necessarily prevent secondary fins.
Figure 11 is a side view of the invention illustrat-ing a fluid stream that is useful for preventing the formation of secondary fins, but not the reduction o smoke emitted to the atmosphere.
Fîgure 12 is a top view of another embodiment of the lnvention i~l~strating a 1uid ~urtain directed from the side of the workpiece perpendicular to the oxygen stream that w.ill reduce the amount of smoke emitted to the atmosphere, but will not prevent secondary ins.
Figure 13 is a side view of the present inven~ion illustrating how the pocket for smoke control can be formed :; by directing the fluid curtain in the direction of the oxygen stream so as to intersect the cross-fire slag-water jets.
- Figure l4 is a side view of the present invention ` ~ illustr~ting how the pocket ~or smoke control can be fonmed by directing the fluid curtain perpendicular to the oxygen stream so as to intersect the cross-~ixe slag-water jets.
DETAILED DESC~IPTION OF THE INVENTION ~.
The present i~vention is predicated in part on the ~; discovery that "secondary" fins can be prevented from forming along the edges of a scarfing cut by directing a stream of non-reactive fluid at ~he workpiece to effectively control the ~, . .
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size of the molten puddle in front of the reaction zone. A
stream of fluid striking the molten puddle upstream, or behind its leading edge, maintains the puddle size below the limit beyond which the puddle can no longer be pushed forward along the surfaee of the metal by the scarfing oxygen stream w1thout deflecting portisns of ~aid puddle beyond the scarfing cut boundaries. The term "upstream" is used with :-reference to the stream of scarfing oxygen. Hence, "upstream"
: means toward the scarfing nozzle. The permissible puddle :~ 10 length may vary, depending upon ~he scarfing oxygen pressure, scarfing speed a~d depth o~ cut. For a spot scarfing operation on cold steel, a stream of fluid striking the slag puddle at a distance of about 35 cm in front of the reaction ~,r zone has proven effective for secondary fin prevention. For - fln control the fluid stream is preferably a water jet at a -. `
pressure of at leas~ 8.8 kg/cm2 (gage) positioned above the scarfing oxygen stream to strike the slag puddle at an angle ::
o about 45 relative ~o the w~rk surface and directed in the direction of the oxygen stream. The angle of inclination of the water stream and i~s location relative to the puddle may, however, vary widely provided it granulates the leading portion of the slag puddle and moves it in the same direc~ion as the advancing scarfing reaction zone. Thus, the angle between the fluid stream and the workpiPce may vary from 20 ;`
to 80 and still be effective for fin prevention.
It has also been discovered that a fluid curtain ~hich covers the reaction zone and at least the rear portion 13.

of the molten puddle so that the curtain forms a pocket with the work surface or the cross~fire slag removal jets serves as a barrier and absorbs large quantities of the smoke formed by the scarfing reaction~ The liquid stream "scrubs"
the unde~ired vapors and particulate matter, preventing their escape into the atmosphere surrounding the scarfing reaction.
- As a result, the undesired contanimants in the smoke are concentrated in a fluid stream which can be purified with far less effort and expense than purification o~ relatively large ~: 10 volumes of air containing the contaminants in dilute form.
Referring to Figure 1, a single spot scarfirlg nozzle N is shown producing a cut in the direction shown by arrow A of depth D on workpiece M. The zone of primary reaction R is produced between the cutting oxygen stream discharged from scarfing nozzle N and the workpiece M.
During a typical scarfing pas~ volatile by-products of the scarfing reaction (i.e., smoke F)~s discharged from the reaction zone R as well as from the rearward portion of the slag puddle S. The forward portion of puddle S is cooler and 20 forms less s~oke. In addition~ the forward portion is generally removed by cross -fire water j ets 9 (as shown in Figures 13 and 14), Some molten ma~erial frQm puddle S is blown out of ~eaction zone R to the edge of the scaring cut.
If nozzle N is a conventional round or rectangularly shaped ~ozzle, the melt thus blown aside would su~sequently resolid-ify, adher~ng to the workpieee M, as shown in Figures 2 and 3, along the boundaries ll of scarfing cut 12 ~o for~ fins 13.

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In addition to being formed from metal blown out of the primary reaction zone, fins 13 are formed independently from :;
a second source, namely from a por~ion of the molten slag puddle S in front of the reaction zone; the fins formed from the latter being referred to herein as "secondary" fins. In all cases~ fins 13 must be removed before the metal body is subsequently rolled.
Figures 4 and S illustrate how secondary fins 20 form on the surface of a workpiece M during spot scarfing in ~;.
the direction shown by arrow A, when a specially shaped nozzle only capable of preventing the fonmatlon of primary r fins is used. The resulting scarfing cut 22 is fin-ree or a distance "d" from the start or front edge 23 of ~he cut, ;
while the remaLnder of the cut is characterized by secondary ;~
fins 20 along the boundaries of the cut 24. The partially fin-free cut 22 reflects the fact that the molten slag puddle was readily pushed forward along the work surface for a distance "dt' by the stream of scarfing oxygen emanating from the scarfing oxygen no~æle and primary fin formation was prevented by the specially shaped nozzle. However5 when the size o the puddle in front of the advancing reaction zone becomes unduly large~ portions of the puddle are deflected to ~he sides of the cut by the scarfing oxygen stream forming the secondary fins.
Figures 6 and 7 illustrate the smoothly contoured cut 30, fi~-free along boundaries 31, produced when workpiece M 1s spo~ scarfed using the specially ~happed nozzles referred . ~5. .

, D-9664-1 to above and in accordance with the invention wherein the formation of secondary as well as primary fins has been prevented .
- Figure 8 shows a spot scarfing pass in progress wherein a single w~ter nozzle 40, located above scarfing unit 41, is shown directîng a high pressure stream of water which fans ou~ to produce a water cur~a;n 44 that strikes the s lag puddle 46 at a distance e upstream or behind the leading edge 42 of the puddle. The leading portion 43 of the puddle ; 10 is cooled and granulated by the water curtain 44, and the granulated slag 45 is swept forward in substantially the direction of the scarfing path shown by arrow A, To reduce `
the amount of smoke that enters the atmosphere from the scarfing reaction, the water curtain 44 must have a width a~
least equal to that of the reaction zone as it passes above it.
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Note that ~he inclined water curtain 44 forms a pocket with the workpiece M that traps the rising smoke by absorbing it.
For purposes of secondary fin prevention, the stream of water 44 must be at least the width W of the molten puddle .~.
w~en it strikes the puddle to insure that the leading portion ; of the puddle 43 is granulated across its entire width and swept forward by the high pressure water curtain 44. The ::~
remainder of the puddle 46 is ~hereby maintained small enough to be moved forward by the oxygen stream) bu~ large enough to still provide sufficient preheating of the workpiece M. In order to prevent primary fin formation, as well as secondary fin for~ation, the scarfing oxygen uni~ 41 must be of ~he 16~

specially-shaped type described in U.S. Patent No. 4,040,871 if an individual fin free cut is to be made; or of the specially-shaped type described in U.S. Patent No. 4,0137486, ~f a plurality of side-by-side cuts is to be made.
Allthough a single water nozzle 40 which faras out is shown in Figure 8, ~t will be apparerlt to those skilled in the ;: ar~ that a plurali~y of such no~zles or a wide ~Lot type of nozzle could be used ~n its place. A pluraliPy of ~aozzles would be preferred if more complete smoke control were nece~sary ~:
10 or desirable to produce a fluid ~urtain that more completely - blanketed the area above~ the smoke producing reaction zoIIe~ that is the primary reaction zone and th~ hot, back end of the molten slag puddle .
Figure 9 i9 a side-view of apparatus simllar ~o that shown in Figure 8, except that a single nozzle scarfing oxygen torch N is u~ed in place of a scarfing un~t 410 Nozzle N directs a stream of scarfing oxygen B, in the direction of the axis o:E
; nozzle N, at workpiece M t:o form the scarfing reaction zone R~
D represents the depth of the cut and arrow A the direct~on in 20 w~ich th0 scarfing cut progresses. Water curtain J discharged from water nozzle 50 s~rikes slag puddle S a distance L ahead of reac~ioIl zone R at an angleff~ relative ~o the wo~cplece M. ~ote that the water curtain J does not and must not ~mpinge on the reaction zone R ~ince ~:o do so would interf~re with the scarfing reaction ~nd could kill i~ completely.
In accordance with the pre~ent invention, smoke 17.

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con~rol and secondary fin prevention may both be achieved u~ ing apparatus illustrated in Figures 8 or g by using the following preferred operating conditions for scarfir~
cold steel traveling at about 9 rs~eters/minute to a dept~ of , about 3/16". In such case the distance L should be absut 35 cm, and the angle~ formed by the water stream J and the surface of the ~orkpiece should be ~etween 30 and 45. The gage pressure of the fluid should. be from about 8 kg/cm2 to about 11 ~/cm2. The prefexred fluid is water. The puddle S
is prF~vented ~rom growing. larger than length L, a slze wh~ch the scarfing oxygen stream B is able to move forward, since ~: tha~ portion of puddle 51 which would norm~lly form ahead of ~he wa~er s~ream J is gramllated and swept :~orward and away from the scarfing cut . Like the apparatus shown iIl F~ gure 8, the apparatus o~ F~guxe 9 may also be used in combination with means for pre~entirlg the :IEormation of primary finsO In order to do so, it is necessary to use as the nozzle N" ~ special : `
nozzle which pre~ents the formation of primary fins, such as described in previously referred to U.S. Paten~ Nos.

4,040,871 and 4,013,486 It w~ll be appzrent that ~he water curtain J will .
not only prevent the ~ormation of secondary ins, but by covering the ~rea s:l~ver tlhe reaction ~one rom which smcske is emi~ted, ~ will al~o ac~ as a smoke absorbing curtain since the smoke ~ends to travel upwards and is thus trappQd by the wa~er curtain J. The smoke is con~posed o~ ixon oxide fumest vaporized metal, ine particles of sl g and the like.

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Figure 10 illustrates the effect o:E direc~ing the water stream J further upstream so that it intersects the workpiece M ahead of the slag puddle S. Here, ~he water curtain formed by stream J will reduce the amount of smolce ~-.
discharged to a~mosphere,, but will not prevent the formation of secondary fins9 since the water curtain ~et J doe~ n~t impinge upon carfing puddle~S, so ~hat prevention of secondary fins by keeping the size o the puddle small is not accompli~ed,. However, as lorlg as the f`luid curtain p~sses over ~he reactiorl s:one, a~ a width at least equal to that of the reaction zone, the amou~t of smoke emitted to the ~tmosphere will be substantially reducedO The angle ~
as previously defined, can vary from t) to 60 and still be effecti~Te for smoke co~trol, wit~h an angle o~ 30 being preferred~ The water pressure may ~ary from abo~t 3 Icg/cm~
gage to as high as practic~l. Alr-water mixtures can be used .
: at lower pres~ure bec~use the air tends to atomize the water, producing finer mists of water over the reaction zone. Steam or mixtures o~ an inert gas such as nitrogen or argon with water will also effectively trap the smoke. The fluid eon~aining ~he ~rapped smoke is ordinarily collected together with the water from the cross-fire, slag-~ets~ in a drainage system under the workpiece rom whence i~ is piped to a wa~er ~reatmen~ system.
Figure 11 is a side view of an embodiment of the invention that will prevent secondary fins, but will ~ot substantially reduce the amount of smoke discharged to the atmosphere. Here, water nozzle 50 is positioned such that the fluid stream does not pass over the reaction zone R, thereby failing to accomplish effective smoke control.
However, since the water stream J impinges on the puddle S
along its ent~re width, at a sufficient distance upstream of its leading portion to granulate and push forward the leadîng portion of the puddle, prevention of secondary fins ~s accomplished. For preventing secondary fins, the angle~
- can vary fxom about 20~ to about 80 with 45 being preferred. A fluid pressure of at least 8 kg/cm~ gage is preferred.
Figure 12 illustrates an alternative embodiment for : practicing the present invention, one that is capable o~
substantially reducing the amoun~ of smoke emitted to the atmosphere, but not of preventing secondary fins.Scarfing unit :~
51 is shown making a spot scarfing cut on workpiece M. Arrow A

indicates the direction of the scarfing cut or path. Water nozzle 60 fàns out to produce a sheet-Like stream of water 54, wide enough to blanket the entire molten puddle 56 and ; 20 reaction zone R. Although the preferred method o~ directing the fluid stream is from above t~e scarfing oxygen stream down at an oblique angle to the workpiece and in substantially the same direction as the scarfing oxygen stream, the fluid :~.
may originate from either side of the workpiece as shown in Figure 12, as long as it forms a curtain that covers the reaction zone R and at least the rear portion of molten puddle 56 so as ~o form a pocket with the work surface that 2~.

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intercep~ the smoke emanating the scarfing reaction. In Figure 12, fluid stream 54 is directed from the right side of ~he oxygen stream 61 and perpendicular to ~he direction of the scarfing oxygen stream ~1. Although for purposes of illustration only one water nozzle 60 is shown, a plurality of nozzles may be used Figure 13 illustrates how the pocket for trapping the smoke may be ormed by combining the sheet-like fluid curtain 11 with cross-fire, slag-water jets 9. Such jets are described in greater detail in, for example, U.S. Patent Nos 2,465,297, 3~163?559 and 3,354,002. Scarfing unit 5 is one of several such units (only one of which is shown) -:~
in abutting relationship for scarfing the entire surface of the workpiece. In such cases, formation of fins along the edges of ~he scarfing cut is not a proble~. In Figure 13, .. . ..
the scarfing units:5 direct a sheet-like stream of scarfing oxygen 6 ~t the surface of the metal workpiece ~ to produce the thermochemical reaction. A molten slag puddle 8 is formed in front of the reaction zone R. The three cross-fire, slag-water jets 9 which skim the surace of the workpiece M areused to granulate3 trap and remove the slag. A header 10 is used to discharge a fluid curtain 11 over the top of the reaction zone R. I~e leading edge of curtain 11 intersects the cross-fire, slag~water jet~ 9 to form the pocket for trapping the smoke.

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Figure 14 illustrates an alternative embod~ment of the inventionO It :Ls similar in :Eunction ~o that shown in Figure 13 except that the fluid curtain is for~ed by a plur~
àlity of stre~ms directed by nozzles 12 from the side of the - work~7iece M perpendicular ~o the dlrec~lon of lthe oxygen stream 6. Nozzles 12 are located in a plane inclined `~ down from above the scarfing oxygen stream toward ~che work-pI eee M. The leadin~g edge of the :Eluid curta~ inter~ects one of the three cross-fire, slag-jets 9 to form ~he pocke~ ~or 10 trapping the smoke F.
Although ~he drawings all illustrate 'the 1uid curtain of thi.s inventioTI as a fl~t plane, it will be apparent to those skilled in ~he art, that it can h~ve any shape tha~
~: ulfills its function requirement~ e curtain could, or `~ example, be curved down to the work surface to pre~ent even ~he small amounts of smoke that normally escape a~ the open sides of a planar curtain, (such as illustrated in Figures 10 and 13) from escaping~ Alternatively, the curtain could be formed of several, for example, three planar streams, iOe., ~ne 20 over the top and one on each side of the react~ on zone and slag puddle O
If smoke control is sought to be achieved on a four sided scarfing machine, 8uch as shown in U.S. Paten'c No,.
2,465~2~7~ where a scarfi~g reaction takes place on all four sides of the workpiece, a fluid curtain would be requ~red on each of the four sides to trap ~he smoke. For optimum smoke reduction, the entire clrcumferential area surrounding the 22.
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~-9664-1 ,8 workpiece should be enclosed by a water curtain. This could be accomplished by a one~piece, i.e., frusto-conically shaped curtain or by a plurality of individual curtains surrounding all four sides of the workpiece. Less complete but adequate smoke reduction can be achieved by having a planar fiuid cur~ain on each side of the work surface being scarfed. If only two surfaces are being scarfed, say top and on~ side, then only those two surfaces require a fluid curtain.

~3~ :

Claims (24)

WHAT IS CLAIMED IS:

1. In a thermochemical scarfing process wherein (a) a stream of scarfing oxygen is directed against a reaction zone of molten metal on the surface of the metal workpiece to produce a thermochemical reaction thereon, and (b) relative movement is provided between the oxygen stream and the workpiece to continue the reaction along the metal surface to produce the desired scarfing cut, said reaction forming a molten puddle in front of the advancing reaction zone that tends to grow larger as the cut progresses, the improvement comprising:
(c) directing at least one stream of non-reactive fluid so as to form a fluid sheet-like curtain that provides a cover over the reaction zone and at least the rear portion of the molten puddle in such manner that said curtain forms a pocket with the surface of the workpiece.

2. The process of claim 1 wherein said stream is directed from above and in substantially the same direction as the oxygen stream and down at an oblique angle to the work surface, whereby said curtain intercepts the smoke emanating from the scarfing reaction and thereby substantially reduces the amount of smoke discharged to the surrounding atmosphere.

3. The process of claim 1 wherein said stream is directed from the side of and substantially perpendicular to the oxygen stream, and at an oblique angle to the work surface,whereby said curtain intercepts the smoke emanating from the scarfing reaction and thereby substantially reduces the amount of smoke discharged to the surrounding atmosphere.

24.

4. The process of claim 2 wherein the leading edge of said fluid curtain intersects a jet of water directed substantially perpendicular to the direction of the scarfing cut to skim across the work surface ahead of the scarfing puddle.

5. The process of claim 3 wherein the leading edge of said fluid curtain intersects a jet of water directed substantially perpendicular to the direction of the scarfing cut to skim across the work surface ahead of the scarfing puddle.

6. The process of claim 1 wherein the non-reactive fluid is water.

7. The process of claim 1 wherein the non-reactive fluid is a gas-water mixture.

8. The process of claim 1 wherein the non-reactive fluid is steam.

9. The process of claim 1 wherein said stream is directed from above and in substantially the same direction as the oxygen stream,and down at an oblique angle to the work surface, so as to impinge said stream upon said puddle across its entire width, at a sufficient distance upstream of the leading edge of said puddle and with sufficient intensity that the leading portion of said puddle is granu-lated and pushed forward in the direction of the scarfing path 25.

by said fluid stream to keep the puddle sufficiently small that the scarfing oxygen stream can readily push it forward along the metal surface without deflecting the puddle laterally beyond the boundaries of the scarfing cut, thereby preventing the formation of secondary fins.

10. The process of claim 9 wherein the non-reactive fluid is water.

11. The process of claim 9 wherein the non-reactive fluid is a gas-water mixture.

12. The process of claim 9 wherein the non-reactive fluid is steam.

13. In apparatus for scarfing the surface of a metal body comprising in combination: (a) means for discharging a stream of oxygen and directing it against a reaction zone of molten metal on the surface of said metal body to produce a thermochemical reaction thereon, and (b) means for producing relative movement between the workpiece and said means for discharging oxygen, the improvement comprising:
(c) means for discharging at least one stream of non-reactive fluid such that it forms a sheet-like curtain directed to form a cover over the reaction zone and at least the rear portion of the molten puddle such that said fluid curtain forms a pocket with the surface of the workpiece.

14. The apparatus of claim 13 wherein said means for discharging said fluid curtain is directed from above and in 26.

substantially the same direction as the axis of said means for discharging oxygen, and directed down at an oblique angle to the work surface, thereby rendering said fluid curtain capable of intercepting smoke emanating from the scarfing reaction and substantially reducing the amount of smoke discharged to the surrounding atmosphere.

15. The apparatus of claim 13 wherein said means for discharging said fluid curtain is directed at an oblique angle to the work surface, from the side of and substan-tially perpendicular to the axis of said means for dis-charging oxygen, thereby rendering said fluid curtain capable of intercepting smoke emanating from the scarfing reaction and substantially reducing the amount of smoke discharged to the surrounding atmosphere.

16. The apparatus of claim 14 which includes means for directing a jet of water substantially perpendicular to the direction of the scarfing cut to skim across the work surface ahead of the scarfing puddle, and wherein said means for discharging said fluid curtain is directed to intersect said jet of water.

17. The apparatus of claim 15 which includes means for directing a jet of water substantially perpendicular to the direction of the scarfing cut to skim across the work surface ahead of the scarfing puddle, and wherein said means for discharging said fluid curtain is directed to intersect said jet of water.

27.

18. The apparatus of claim 13 wherein said means for discharging said fluid curtain is directed from above and in substantially the same direction as the axis of said means for discharging oxygen, and directed down at an oblique angle to the work surface to impinge said stream upon said puddle across its entire width, at a sufficient distance upstream of the leading edge of said puddle and with sufficient intensity that the leading portion of said puddle is granulated and pushed forward in the direction of the scarfing path by said fluid stream to keep the puddle sufficiently small that the scarfing oxygen stream can readily push it forward along the metal surface without deflecting the puddle laterally beyond the boundaries of the scarfing cut, thereby preventing the formation of secondary fins.

19. In apparatus for scarfing the surface of a metal body comprising: (a) means for discharging a stream of oxygen and directing it against a reaction zone of molten metal on the surface of said metal body to produce a thermo-chemical reaction thereon, the improvement comprising:
(b) means for discharging at least one stream of non-reactive fluid such that it forms a sheet-like curtain directed to form a cover over the reaction zone and at least the rear portion of the molten puddle such that said fluid curtain forms a pocket with the surface of the workpiece.

28.

20. The apparatus of claim 19 wherein said means for discharging said fluid curtain is directed from above and in substantially the same direction as the axis of said means for discharging oxygen and directed down at an oblique angle to the work surface, thereby rendering said fluid curtain capable of intercepting smoke emanating from the scarfing reaction and substantially re-ducing the amount of smoke discharged to the surrounding atmosphere.

21. The apparatus of claim 19 wherein said means for discharging said fluid curtain is directed at an oblique angle to the work surface,from the side of and substantially perpendicular to the axis of said means for discharging oxygen, thereby rendering said fluid curtain capable of intercepting smoke emanating from the scarfing reaction and substantially reducing the amount of smoke discharged to the surrounding atmosphere.

22. The apparatus of claim 20 which includes means for directing a jet of water substantially perpend-icular to the direction of the scarfing cut to skim across the work surface ahead of the scarfing puddle, and wherein said means for discharging said fluid curtain is directed to intersect said jet of water.

23. The apparatus of claim 21 which includes means for directing a jet of water substantially perpend-icular to the direction of the scarfing cut to skim across the work surface ahead of the scarfing puddle, and wherein said means for discharging said fluid curtain is directed to intersect said jet of water.

29.

24. The apparatus of claim 19 wherein said means for discharging said fluid curtain is directed from above and in substantially the same direction as the axis of said means for discharging oxygen, and directed down at an oblique angle to the work surface to impinge said stream upon said puddle across its entire width, at a sufficient distance upstream of the leading edge of said puddle and with sufficient intensity that the leading portion of said puddle is granulated and pushed forward in the direction of the scarfing path by said fluid stream to keep the puddle sufficiently small that the scarfing oxygen stream can readily push it for-ward along the metal surface without deflecting the puddle laterally beyond the boundaries of the scarfing cut, thereby preventing the formation of secondary fins.

30.