US2290295A - Method and apparatus for desurfacing metal - Google Patents

Description

METHOD AND APPARATUS Fon nEsURFAcING METAL Filed Nov. 8'. 1940 INVENTOR ARTHUR P. SCHELLER ATTORNEY f//gw Patented July 2l, 1942 2,290,295 d ME'rnoD AND APPARATUS Foa nEsUnrAc- ING tion .of Ohio METAL Arthur P. Scheuer, Irvington, N. J., The Linde .AirProducts Company,

assigner to a corpora- Application November 8, 1940, Serial No. 36l823 .(Cl. 26S-23) 11 Claims.

This invention relates to a method of and apparatus for desurfacing metal bodies, and more particularly to blowpipe nozzles, and the using thereof, which are especially useful in connection with surface metal removal'by effecting a progressive thermochemical reaction of such metal with an oxidizing medium.

When an oxidizing gas stream o'f suitable character is directed obliquely against a work surface, such as that of a ferrous metal body suitably heated to an ignition temperature, and moved along said surface, a thermochernical reaction takes place between the oxygen and the ferrous surface metal, which leaves a bright, clean area. Part of the metal removed is oxidized to form a molten slag and part of the metal is melted by the heat of the reaction. A wave of such mixed molten metal and slag is advancedioy the force of the oxidizing uid stream over the surface metal to be removed and assists in properly heat- -ing the surface portions of the base metal immediately prior to the actual desurfacing reaction. In desurfacing a relatively wide area, it has been customary to arrange two or more blowpipe nozzles to direct oxidizing fluid jets against the work surface. Such nozzles had circular oxygen orices and produced substantially cylindrical oxygen jets flowing with a relatively low veloclty, i. e., a velocity below about 1000 feet per second. Each such jet makes an individual groove in the work surface, so that a ridge is formed between adjacent grooves by the desurfacing operation.

Such ridge formation conceals and often contains defective metal which it was intended to eliminate by the desurfacing operation. Also surface defects intended to be removed by the desurfacing, while removed completely within the channels, are only partially or removed not at all in the region of the ridges. Subsequent working or rolling of the metal body causes the flaws or defects in the ridges to appear in the product and result in rejections, or they are further concealed, resulting in unsound steel or a product of poor quality.

In the desurfacing of blooms, billets, ingots and the like, it is thus highly desirable that the entire surface undergoing treatment be removed, with the elimination of substantially all ridge formation, so that the desurfaced area is substantially flat. l

Conventional desurfacing blowpipe nozzles have a relatively large central cylindrical oxidizture of fuel gas, such as acetylene, and combustion supporting gas, such as air or oxygen. Thus, in operation, a series of heating flame jets issue from such preheat gas passages. 'I'he oxidizing iiuid supplied to the central passage is preferably oxygen. The oxygen passage of such nozzles have generally been formed in a manner to cause expansion of the oxygen stream and a reduction of the velocity of flow to a value below about 1000 feet per second or below the so-called acoustic velocity. The walls of such oxygen passages are either cylindrical or constantly expanding from the inlet end toward the outlet end of the nozzle and it has been found that, for satisfactory metal removing eiiiciency, the range of variation in the rate of gas ow through such nozzles is relatively limited. With' nozzles having cylindrical orifices it has not been possible to remove surface metal efficiently so as to produce smooth channels with gas velocities substantially exceeding the acoustic velocity. The use of a row of such nozzles for desurfacing a wide area produces transversely concave grooves divided by objectionable ridges, as pointed out above.

Therefore, the main objects of this invention are to provide: an improved method of and apparatus for removing surface metal from ferrous metal bodies adapted to overcome the disadvantages and objectionable features of the prior art in the matter of ridge formation; a method of efficiently removing surface metal with oxygen streams flowing with velocities exceeding the acoustic velocity; and apparatus for carrying out such method for removing a wide layer of surface metal to a substantially constant depth to produce a new surface substantially free from. ridges.

The above and other objects and novel features of this invention will 'become apparent from the following description taken with the accompanying drawing in which:

Fig. 1 is a fragmentary perspective view of a desurfacing unit embodying the principles of this invention in operation; I

Fig. 2 is a view in front end elevation on an enlarged scale of a blowpipe nozzle constructed f* according to the invention;

Fig. 4 is asimilar view in longitudinal section -of a,modiiled form of nozzle according to the ing fluid outlet passage surrounded by a concenl tric series of equally spaced preheat gas passages. The latter are supplied with a. combustible mixinvention;

Fig. 5 is a fragmentary perspective view showing the location of the inserts in the nozzle the end portion of the nozzle being indicated by brokenlines.

Fig. 6 is a fragmentary view of a longitudinal section taken on the line 6-6 of Fig. 3 showing an insert and the lateral slots.

In general the improved blowpipe nozzle according to the invention is particularly adapted for a multiple nozzle desurfacing head or unit as illustrated in Fig. l. Each nozzle has the outlet portion of its desurfacing oxygen passage shaped so that it changes smoothly from a circular passage to a slot-like exit orifice having substantially flat top and bottom edges and the passages are so shaped as to produce a uniform velocity distribution. Such nozzles make individual grooves that are substantially ilat, and when suitably spaced in a row in` a desurfacing head, the edges of the adjacent oxygen streams merge to produce a substantially continuous wide desurfacing-stream thereby to eliminate or greatly reduce the objectionable ridges and remove all the defective surface metal.

coincides with the discharge end face II, and the oblique planes of which are equally inclined relatively to the ax-is of the bore I3 and intersect along a line which intersects said axis perpendicularly at an external point in front of the face II. The inserts I 6 taper inwardly topoints I1 on elements of the bore I3 spaced at 90 from the elements of the bore on which are located The cross-sectional -area ofthe slot-like exit orifice, for best results, may be the same as, or slightly less than, the cross-sectional area of the circular passage adjacent to the altered portion. The cross-sectional area of the altered portion is either constant oruniformly reduced, so that the passage is streamlined and has no abrupt changes in its cross-sectional area.

According to this invention, the nozzle N may be produced from a. blank of a conventional blowpipe nozzle having an axial oxygen passage 0 by forming a concentric series of suitably spaced longitudinal preheat passages?, in the nozzle blank and modifying the orifice end portion of the passage O. Diametrically opposed divergent slots or grooves I0, III are then machined in the body of the nozzle in the walls of the oxygen passage O. The slots I 0 are of greatest depth at the end face I I of the nozzle andvextend inwardly to a point I2 where their depth tapers tozero. The walls of the slots III are preferably in the shape of sections of oblique cylinders the bases of which lie in the plane of the face II and theaxes of which are inclined at equal angles relatively to the axis of the passage O and intersect at a point on said axis within the nozzle.

The nozzle blank employed for the form of nozzle illustrated in Figs. 2, 3, 5, and 6 has an oxygen passage O comprising cylindrical bore changed smoothly from a cylindrical flow to a portion I3 extending back from the face Il, a.

constricted inlet portion Il and a tapered portion I5 joining the inlet Il and the bore Il. The inlet Il is of a diameter to pass the desired volume of oxygen' when the oxygen is supplied at a suitable head pressure through a supply passage S in a blowpipe head indicated at H. The blowpipe head H is preferably of a type suitable for receiving a closely spaced row of desurfacirlti` blowpipes and has nozzle receiving openingsof the customary construction adapted to receive and hold the nozzles N, the nozzles N being retained by ring nuts R acting against a shoulder K adjacent the inlet end` of the nozzles.. The preheating gas passages P of the nozzles are supplied with mixed combustible gas by a channel C in the head H with which they communicate.

To form, with the slots III, the delivery orifice of the nozzle according to the invention, a pair of tapered inserts I6, I6 are then secured within the bore I3 adjacent the face II opposite each other. The inserts Ilpreferably comprise oblique sections of a right cylinder the cylindrical surface portion of which coincides with and is in contact with the bore I3, the base of which insert h points I2.

The inserts I6, I6 are disposed so that their straight base edges are alined with the slots III;

In the form ofenozzle illustrated in Fig. 3 the I oxygen flow is metered by the inlet restriction I4. The stream`of oxygen then expands in the portion I5 at a rate suflicient to effect a. reduction of velocity. In the portion I3 the stream becomes substantially non-turbulent and in the portion of the passage between the faces of the inserts I6 and beyond the points I1, the flow is sectionally oval flow, the stream "becoming ribbon-like at the exit facel I I, that is, like a ribbon of substantial thickness having non-parallel edges since the stream continues to expand in width at a substantial rate as well as slightly in thickness after leaving the nozzle. In the portion of thelpassage from points I1 to points I2 the cross-sectional area gradually decreases and the flow velocity increases. the end face I I, the upper and lower walls of the passage continue to converge but the side walls of the passage which are now formed by the slots I0, diverge. 'I'he rate of such divergence is so chosen that the cross-sectional arca of the passage in the plane of the face II is substantially equal to the cross-sectional area of the passage in the region of the points I2. With such relation betweenv the upper and lower' and side walls of the passage, it is found that the ribbon-like stream of oxygen produced by the nozzle flows with a substantially uniform velocity throughout the entire width of the stream. It is important that the velocity be uniform in order to produce substantially flat desurfacing cuts. Furthermore the stream expands very little'in the vertical direction but will expand edgewise or laterally just the right amount to merge properly with adjacent streams when several such nozzles Fig. 1.

In the modified form of no zzle illustrated in Fig. 4 and which has an end. view appearance similar to Fig. 2, the cylindrical bore llis oi substantially constant diameter to the inlet end of the nozzle N' and the slots I0' taper to points I2' which are substantially in the same transverse right plane as the points I1 of the inserts I6. The oxygen passage in this form of nozzle is substantially of constant cross-sectional area throughout. The control of the quantity of oxygen flowing may be eiected by a metering passage in the blowpipe head or by controlling the flow rate to the nozzle. The diversion of the side walls of the passage from the points I2' to the face II is preferably such as to balance the convergence of the top and bottom walls from the points I1 to the face II so that the crosssectional area of the passage in the plane of From the points I2 to l as the area of the slotted end orifice. If desired, the nozzle N may also be provided with an inlet restriction similar to passage I4.

The resulting arrangement is preferably such that there is provided a streamlined oxidizing fluid flow passage at least the end portion of which is of substantially constant cross-sectional area and has a cross-sectional shape that gradually changes from circular to oblong shape at the discharge face II of the nozzle. The long sides of the oblong shape are straight and substantially parallel, and the short sides thereof are preferably curved.

The above-described method of making the nozzles is simple and relatively inexpensive because the parts are readily available and there results a precision instrument. However, various changes may be made in the detailed method of construction disclosed therein without departing from the principles of the invention provided that substantially the same shape of oxygen passage results. For example, the nozzle may beformed from a single piece of metal.

'Ihe blowpipe nozzles N or N are assembled in a desurfacing apparatus indicated fragmentarily at A and comprising a head plate I9 through which the individual nozzles pass and are supported in' a row for longitudinal and rotational adjustment. The nozzles are preferably positioned with the long sides of the orifices in parallel relation to the surface 20 of the work W which may be the top surfaceof a steel billet,-

ingot or slab. The axes of the nozzles are held at an acute angle to the surface 2l) in order to impinge the oxidizing streams 2l along and obliquely against the surface. The slot-like exit orifices of the passages O and O' are arranged in transverse alinement for normal operation and the nozzles are spaced so that the oxygen streams 2| combine or merge smoothly into one Wide substantially continuous fiat sheet at the zone of reaction indicated at Z, thus, advancing the molten metal and slag in a uniform wave 22 and leaving a clean, fiat, new surface 23 cn the work.

The desurfacing apparatus A may be normally stationary while the work W is moved relatively thereto toward the plate I 9, but, if desired, the Work may be stationary while the apparatus A is advanced for the desurfacing operation. The lower surface of the plate I9 preferably is guided on the surface 23 to maintain the nozzle orifices at a constant elevation from the work surface. The preheating flame jets issuing from the preheat passages P operate inthe usual way to assist in maintaining the thermochemical reaction of the oxygen with the ferrous surface metal undergoing treatment.

In some cases the surface defects may be deeper and more concentrated along certain portions of a surface, such as along the edges of billets. When it is desirable to remove a greater depth of metal along certain portions of the surface, one or more of the nozzles is fractionally turned about its axis so that the lower edge of its orifice is not parallel with the work surface. Each such nozzle with a non-parallel orifice will produce a substantially fiat bottcmed groove the depth of which varies transversely f the groove. The nozzles also may be staggered in their distances from the work surface, as desired.

The use of blowpipe nozzles of this invention in a multiple nozzle desurfacing head results in the removal of a uniform layer of metal from the Work surface, leaving a surface that is free of ridge formation. Thus, all surface defects and fiaws which are no deeper than the depth of the desurfacing operation are removed. The desurfaced area may be of uniform or uniformly varied depth, as desired, and more of the defective surface metal is removed than is possible with conventional nozzles.

With conventional round nozzles it is usually necessary to remove metal to a greater depth at the center of the channels produced than the depth of the defects in order to remove most of the defective surface metal. When a uniform layer of metal is removed the depth of removal need not be as great in order to remove all defects and therefore the employment of nozzles according to this invention will provide greater over-all economy.

Good results have been' obtained with a nozzle embodying the principles of this invention `and having an oxygen passage provided with an inlet restriction of about .277 inch diameter, a maximum cross-sectional area of about .135 square inch and aV cross-sectional area at the end orifice of about 0.067 square inch, the width of the slot being about 1/8 inch. Such a nozzle will produce an oxygen stream effecting eiiicient surface metal removal with a relatively wide range of gas ow rates between about 1500 cubic feet per hour to 3500 cubic feet per hour and stream velocities of from about 600 feet per second to about 2000 feet per second or considerably in excess of the acoustic .velocity. These velocities are on the basis of normal temperature and pressure conditions as the conditions in the stream are diicult to measure.

It will be noted that the narrow sides of the oxygen passage of the'nozzle of this invention diverge or fiare outwardly. The angle of di` vergence preferably should be such that the oxygen streams where they strike the work surface merge' to form a sheet of oxygen of substantially uniform depth transversely ofthe surface. If there is-too much overlapping of the oxygen streams there will be a gouging effect so that instead of removing undesirable ridges, grooves may be produced which are also undesirable.

With the specific example of nozzle disclosed above and having the orifice side walls diverging to include an angle of about 24, the center-tocenter spacing of the nozzle orifices in the head A should be about l; inches. It has been found that substantially fiat surfaces are produced when thespacing is between 111g inches to about 11A inches. It has also been found that a divergence of the side walls of the outlet passage in conjunction with a convergence of the top and bottom walls is essential to produce a uniform distribution of velocity of flow of the stream throughout the width of the ribbon-like stream. If the divergence is too small or too great, the velocity distribution becomes uneven and a nonuniform depth of cut will result.

` The oxygen streams from the desurfacing nozzles are directed downwardly and obliquely onto the work surface in the general direction of advance and the reaction puddle formed by each jet or stream lis proportional to the size and shape of the cross-sectional area. of the surface metal removed by the desurfacing operation. The length of the individual puddles or of the combined puddle, measured in the direction of advance, must be appreciable, to maintain the stability of the desurfacing operation. 'Ihat is to say, if the puddle or wave of molten metal and slag is too short the desurfacing operation may be -lost or'be deflected by irregularities of the 'original surface. 'Ihe length of puddle is dependent on the thickness of the stream..and therefore the oxygen stream must be of suiiicient thickness to maintain a puddle oi' sumcient length. The' vertical or shortest dimension of the .oxygen stream also must not be too narrow or the` stream will tend to deform and become feathery. 'I'his is probably due to the friction effects of the sidewalls of the orifice and turbulence caused by the surrounding air. l

It has alsorbeen discovered that for the purpose of making a substantiallyflat cut, it is essential that the bottom surface of the stream .shall be fiat. v'1'herefore,` the lower edge of the surface removal with smaller loss of surfacei metal, stability of operation, and excellent economy.

Other uses for the nozzle disclosed herein may be found and it will be apparent that modifications of the nozzle may be made and in the process of making and using the nozzle and that certain features can be used independently of others without departing from the spirit and scope of the invention as set forth in the claims. For example, the upper insert might be omitted altogether or there may be substituted for the upper insert I6 an insert which does not have a fiat oblique surface but one that is higher in` its center portions. Where oxygen is named in the claims it should be understood to include not only substantially pure oxygen but also oxygen containing mixtures.

I claim:

1. A method of thermochemically removing surfacev metal from ferrous metal bodies which comprises heating at least a portion of the metal to be removed to an ignition temperature; forming a ribbon-like oxygen stream to flow with a velocity of flow substantially exceeding the acoustic Yvelocity and with substantially uniform velocity throughout its width, said stream having a relatively flat bottom surface and diverging lateral sides; directing said stream obliquely against and along .said heated portion of surface metal and with said.bottom surface adjacent said surface of the body; and relatively moving said stream and said body to advance said stream along said surface in the direction of surface metal to ybe removed.

2.- In a method of. thermochemically removing surface metal fr m ferrous metal bodies by applying obliquely ainst and along a surface of said body heated v the ignition temperature, a stream of oxygenv and relatively moving such stream and said body, the steps comprising increasing the velocity of flow of said stream to values substantially exceeding the acoustic velocity. and so forming said stream that a substantially uniform layer of surface metal is removed by effecting a gradual conversion of the form of the streamfrom substantially round in cross section to a laterally wide form having divergent lateral edges and a substantially at lower side adjacent the surface of said body.

3. A method of thermochemically removing surface metal from ferrous metal bodies which v comprises heating at least a portion of the metal to be removed to an ignition temperature; forming a row of ribbon-like oxygen streams,- each to flow with substantially uniform velocity throughout its width, said streams having nat lower sides substantially in alinement and latl eral diverging sides; spacing said streams so that adjacent diverging sides thereof merge suiliciently to form in effect a substantially uniform wide desurfacing stream; directing said streams obliquely against and along said heated portion of surface metal and with said flat sides adjacent the surface of said body," and relatively moving said desurfacing stream and said body to .advance said stream along said surface in the direction of surface metal to be removed.

4. A method of thermochemically removing surface metal from ferrous metal bodies according to claim 3 in which the velocities of flow of said streams are .increased to values substantially exceeding the acoustic velocity.

5. A method of thermochemically removing surface metal-from ferrous metal bodies according to claim 3 including the step of so spacing said streams with respect to the angle of divergence of said sides that the surface removing action of ysaid row of streams is substantially uniform across the entire width of surface impinged, whereby the surface metal is removed to a constant depth..

6. A method, of thermochemically removing surface metal from ferrous metal bodies which comprises heating at least a pou-tion of the metal to be removed to an ignition temperature; providing a stream of oxygen of suitable volume and pressure; effecting a reduction of the velocity of flow of said stream by expansion; re-

ducing the. turbulence of said stream; increasing the flow velocity of said stream by gradually decreasing its cross-sectional area; then converting said stream to a substantially ribbonlike form having an increased ilow velocity by effecting a simultaneous reduction of the thickness andan increase of the width of the stream without substantial change of its cross-sectional area; and directing such ribbon-like oxygen stream obliquely against and Aprogressively along said h'eated portion of surface metal whilev a wide side of said stream is maintained adjacent said surface, to remove a layer 'of surface metal having a substantially flat contour.

7. A method o f thermochemically removing surface metal from ferrous metal bodies which comprises heating at least a portion of th'e metal to be removed to an ignition temperature; providing a-relatively voluminous stream of oxygen to flow at a relatively low velocity; reducing the turbulence of said streams; increasing the flow velocity of said stream by gradually but slightly decreasing the cross-sectional area of said stream: then converting said stream to a substantially ribbon-like form having an inface metal while a wide side of said stream is maintained adjacent said surface, to remove a layer of surface metal having a transversely fiat contour.

8. Desurfacing apparatus comprising a plurality of blowpipe nozzles arranged in a row to impinge oxidizing fluid streams along and obliquely against a ferrous metal body for thermochemical reaction with heated surface metal, said nozzles each having smooth oxidizingl fluid flow passages including an intermediate portion, a slot-like exit oriiice, upper and lower wall portions that smoothly converge from said intermediate portion toward said exit orifice, and side wall portions that diverge from the width of said intermediate portion to the width of said orifice, the cross-sectional area of the passage where said side divergence begins being substantially equal to the cross-sectional area of said exit orice and the exit orifices of said nozzles being alined to produce a sheet-like oxidizng gas stream of substantially even thickness, and means associated with said oxidizing gas 'exit orifices for heating at least a portion of said surface metal to the ignition temperature.

9. Desurfacing apparatus as defined by claim 8 in which the center-to-center spacing of said nozzles are correlated with thedivergence of said side walls to insure the removal of surface metal to a substantially constant depth.

10. Desurfacing apparatusV as defined by claim 8 including means supporting each of said blowpipe nozzles lfor rotational adjustment.

l1. Desurfacing apparatus as defined by claim 8 in which the divergence of said side wall portions of said oxidizing gas passage is such as to include an angle of about 24 degress and the center-to-center spacing of said nozzles is between l; inches to 11A inches.

ARTHUR P. SCHELLER.

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