US2794755A - Flat powder stream forming process - Google Patents

Description

June 4, 1957 F. MOESINGER, JR

FLAT POWDER STREAM FORMING PROCESS Original Filed April 18, 1950 WORK INVENTOR FRED MOESINGER,JR.

ATTORNEY United States Patent FLAT PowoER STREAM FORMING PROCES Fred Moesinger, in, Morristown, N. 3., assignor to Union Carbide and Carbon Corporation, a corporation of New York Original application April 18, 1950, Serial No. 156,652, now Patent No. 2,622,048, dated December 16, 1952. Divided and application April 11, 1952, Serial No. 281,841, new Patent No. 2,743,964, elated May I, 1956. Again divided and this application June 23, 1955, Serial No. 517,448

4 (Ilaims. (Cl. 148-9.5)

This invention relates to flat powder stream forming processes, and more particularly to such processes for supplying an external relatively large fiat stream of powder to a thermochemical scarfing reaction zone.

The present application is a division of my copending application Serial No. 281,841, filed April 11, 1952, which is in turn a division of its copending application Serial No. 156,652, filed April 18, 1950, now Patent No. 2,622,048 granted December 16, 1952, for External Powder Scarfing Process, Product and Apparatus.

In prior attempts to thermochemically scarf stainless steel with the aid of powdered iron, the latter was fed to the reaction zone internally, i. e., along with the scarfing oxygen stream. When internal powder feed equipment was used for scarfing stainless steel slabs, the process was expensive, and the surface quality of products rolled from scarfed slabs was not satisfactory in that a type of defeet called a shiner was found to have frequent occurrence upon the rolled scarfed product. A shiner is a slightly depressed area of higher reflectivity with substantially the same composition as the base material. 'It is believed that heavy scale rich in admixed iron and possibly covering a metallic deposit on the plate itself is rolled into intimate contact with the underlying metal, thereby protecting it from furnace gases and air. pickling, the thin rolled-in, metallic-scale layer is removed, exposing the protected zone which is the Shiner. Thus, it was necessary to mechanically grind the resulting surface in order to avoid undesirable shiners in the final product, thereby considerably increasing the cost. 1

In scarfing with an internally fed stream of powder a in the past, such stream was usually round. As a result, a relatively deep groove was formed in each scarfing pass, so that it was necessary to subsequently remove considerable metal, which was expensive, in order to obtain a desired relatively flat, scarfed surface. accentuated due to the fact that the edges 'or borders of the groove were uneven, which was highly objectionable. In attempting to scarf with parallel streams of scarfing oxygen containing internally fed powder, in one pass, the adjacent streams interfered with one another, and the resulting scarfed surface had fused powder globules on the ridges between the grooves or cuts, which made the product obviously unacceptable for subsequent rolling.

Another difliculty with prior atempts to scarf stainless steel was due to inherent limitations in the available powder dispensing equipment. Control of the powder flow was restricted to a critical range. Furthermore, a single bleeder valve was used to adjust both the powder carrier gas back-pressure and the carrier gas powder-injector pressure, which objectionably restricted the range of adjustment. The control was critical and the powder flow was non-uniform and limited in quantity.

Upon 4 This trouble was Patented June 4, 1957 Also, prior to the invention, powder distribution across a single or a multiple stream scarfing out was non-uniform, due to the inherent concentration of the powder in the center of a single round stream, as well as nonuniform blending of the powder in adjacent streams.

Prior to the present invention, therefore, it was necessary to mechanically grind or chip stainless steel slabs, for example, to condition the surface for subsequent treatment. This was expensive, slow, and not entirely satisfactory for all grades of stainless steel. Prior attempts to thermochemically scarf stainless steel shapes were even more expensive.

The main object of this invention, therefore, is to provide an improved process which overcomes such problems. Another object of the invention is to provide apparatus for dispensing powdered solid fuel, which is efiicient and effective; substantially increasing the speed of scarfing while, at the same time, considerably reducing the consumption of powder. A further object is to provide means for discharging a relatively flat stream of powder in which the powder is substantially uniformly distributed thereacross.

According to the invention of my application Serial No. 156,652 there is provided a novel process for thermochemically scarfing hard-to-scarf metal work with the aid of powdered solid fuel, which comprises applying a relatively flat stream of commercially pure oxygen against the work surface at an acute dihedral angle, applying preheat to the work adjacent such oxygen stream; directing at least one separate, relatively fiat stream of a suitable carrier gas containing relatively fine powdered solid fuel toward such oxygen stream at an acute dihedral angle therewith, at a lower velocity than that of the oxygen stream, so that the powder merges with the leading fringe only of the oxygen stream on the way of the latter toward the work; and relatively moving the work and such streams along the path to be scarfed. The powdered solid fuel is uniformly distributed across the relatively flat carrier-gas stream, but does not enter into the main layer or core of the oxygen stream due to the higher velocity of the latter.

As a result, substantially all of the powdered solid fuel is heated to ignition temperature, and the so-heated particles burn in the oxygen and liberate energy in the form of heat. Such liberated energy heats the metal being scarfed land the burning powder attacks such metal, raising the temperture and lowering the melting point of the surface material. As a result, the subsequent core of pure oxygen efficiently and effectively attacks the metal chemically and physically, removing a portion of the work surface. The reaction zone is then moved along a desired path to be soarfed at a relatively rapid rate, so that the work is thermochemically desurfaced.

Scarfing passes up to six times wider than was heretofore possible are accomplished by the invention at scarfing speeds which are two to three times faster, and with 25 to percent less powder consumption. Production operations also show that the cost has been reduced as much as 50 percent compared with grinding.

More specifically, according to the invention of my application Serial No. 156,652, there is provided apparatus for thermochemically scarfing hard-to-scarf metal work with the assistance of powdered solid fuel, which comprises the combination of a blowpipe nozzle having a relatively flat continuous slot for discharging a stream of commercially pure oxygen against the work, and upper and lower rows of ports for discharging preheating flame supporting jets of gas adjacent such scarfing oxygen stream, and a novel powdered solid fuel nozzle mounted adjacent the blowpipe nozzle. Such powdered solid fuel nozzle is provided with a relatively flat continuous slot for discharging the powered solid fuel in a relatively flat Means are associated with the powdered solid fuel nozzle for assuring uniform transverse distribution of the powder in the carrier gas upon its dischange.

According to the present invention there isprovided a process of forming a relatively flat or thin stream of relatively fine metallic powder in which the powder is substantially uniformly distributed across such stream, which comprises mixing the metallic powder with a stream of carrier gas, confining such stream to a longitudinal path, abruptly changing the direction of flow of the stream, confining the stream to a path of increasing width and decreasing thickness, and subsequently discharging the resulting flat stream in which the powder is uniformly distributed transversely thereof, at an exit velocity of' between 30' and 350 feet/ second through 'a relatively narrow shot which is between 0.0150 and 0.0625 inch thick.

Adjustable powder dispenser means are also provided for supplying a selected amount of powdered solid fuel in a carrier gas, at a selected flow rate of the carrier gas, such rate and amount being independently adjustable over relatively wide ranges.

In the drawing:

Fig. l is a view mainly in side elevation, parts being broken away and shown in section, of a scarfing machine illustrating the invention;

Fig. 2 is a view mainly in front elevation of the apparatus shown in Fig. 1;

Fig. 3 is an enlarged fragmentary perspective view of the nozzle portion of such apparatus; and

Fig. 4 is an enlarged fragmentary detail, mainly in cross-section, showing how the gas mixture is supplied to the preheating gas ports.

As shown in the drawings, the illustrated machine scarfing apparatus S is mounted on a suitable support F above the path of the work W, such as a cold slab of stainless steel, to be scarfed. The apparatus S includes a relatively flat powder nozzle mounted on a modified scarfing nozzle 12 of conventional construction. The nozzle 12 is preferably of the wide-continuous-slotted type having a relatively wide slot '14 for discharging a relatively flat stream of commercially pure oxygen against the work W, as well as upper sand'lower rows of ports 16 and 18 for discharging preheating-flame supporting jets of premixed oxy-acetylene gas adjacent such scarfing oxygen stream. The burning gas jets merge into preheating flames 22 and 24 which extend above and r below the oxygen stream 20, forming dihedral angles with the work surface 25.

Oxygen is supplied to the nozzle 12, for example, from a suitable source of oxygen under pressure, by way of a supply pipe 26, a manifold 28 and a battery of tubes 30. At the same time, a suitable combustible mixture of oxygen and acetylene, or other fuel gas, is supplied to the preheating flame ports 16 and 18 by way of gas pipes 32 which are connected to suitable gas mixers and supplies of oxygen and fuel gas under pressure.

The powder nozzle 10 is mounted by a suitable bracket 33 directly on the blowpipe nozzle 12, and comprises a metal base 34 and a metal cover 36 secured together by bolts 38. The base 34 and the cover 36 are provided with a channel, or mating channels, forming a slot 40 for discharging a suitable relatively flat powder-laden carrier gas stream 39, which can be any suitable gas, such as air, or nitrogen, or oxygen, for example. The discharge face of the powder nozzle 10 is tapered and positioned on the blowpipe nozzle 12 so that slot 40 discharges the separate powder-laden carrier gas stream 39 from a flat orifice 41 located directly above the frontupper edge of the nozzle 12. The powder-laden gas stream 39 forms a dihedral angle with the oxygen stream 20, and with the work surface 25.

The upper and lower walls of the slot 40 diverge slightly upstream, and the upper end of the slot is in communication with the outlet end of a novel powder distributor 42 made of sheet-metal in the form of a fishtail which is supported in front of the oxygen manifold 28 by a bracket 44. The interior of the powder distributor 42 has side walls 46 which diverge in the direction of the powder flow, and front and rear walls 48 which gradually converge in the direction of such flow.

The illustrated powder distributor 42 is provided at the upper end thereof with an angulated tubular inlet 50 for assisting in the proper distribution of powder transversely of the carrier gas stream. Such inlet'50 is connected by a hose 51 to a novel powder-laden carrier-gas supply system.

As pointed out above, the powder distributor 42 is provided with a tubular shaped inlet 50 which is angulated with respect to the distributor, so that the powder flow impinges at an abrupt angle against the back wall of the fan-shaped body proper of such distributor. This change of direction plus the flattening out of the passage, distributes the powder uniformly across the confined stream. The distributor contains a fan-shaped interior approach section terminating in an exit slot which is in communication with the inlet end of the slot 40 in the powder nozzle 10, the parts being secured together in gas-tight relation by an escutcheon 112. Thepowder nozzle 10 which receives the powder which has been uniformly spread out by the action of the distributor 42 has downwardly convergent upper and lower walls in the slot 40 which discharges the powder through the exit orifice 41 which, in the illustrated apparatus, is about 0.03 inches by 6.00 inches in size, and then through the upper preheating fiames 22 of the scarfing nozzle 12. In the present example the scarfing nozzle 12 is provided with a scarfing oxygen slot 14 which is also about 6.00 inches wide.

The following table discloses typical performance data for 6-inch and 2-inch wide scarfing equipment.

The following table discloses ratios for different units.

fi-IN. UNIT Cut Depth, In. Cu. Ft. Air/ Lb. Powder 2-IN. UNIT In the illustrated apparatus (6" unit), at an exit velocity of between 30 and 350 feet/second, the impingement angle alpha of the powder stream on the preheating flames, i. e., the optimum included angle between the powder nozzle 10 and the continuous slotted oxygen nozzle 12 is about 40, when the exit velocity of the latter is between 500 and 850 feet/ second. In other words, the slotted scarfing nozzle makes an optimum dihedral angle beta of 30 with the top surface of the work, and the powder nozzle makes an optimum dihedral angle of 70 with the top surface of the work. i

The following table discloses optimum nozzle arrangements in connection with actual performance data of various units.

OPTIMUM DIHEDRAL AND PERFORMANCE The following tables illustrate the composition and size of an example of the iron powder which has been used successfully according to this invention. Other examples can be found in Wagner 2,451,422.

CHEMICAL COMPOSITION Percent Free iron At least 85.00 Total carbon Not over .30 Residual material Balance PHYSICAL PROPERTIES Free from any contaminating materials as, for example, wooden splinters, fibers, or non-ferrous alloys of brass and bronze.

SCREEN SIZE Percent l00 on 200 mesh 25 200 on 325 mesh 25 325 50 Scarfing speeds (i. e., relative movement between the work and the scarfing unit) obtained according to this invention, that is to say, -50 feet/minute, are up to six times faster than when using a prior single nozzle powder scarfing machine with internal powder feeding. This is accomplished with 25 to 75% less powder consumption per unit of scarfed surface. The invention also eliminates shiners in stainless steel sheets rolled from slabs scarfed with powder consisting essentially of iron, without mechanically grinding the scarfed surface before final rolling. The invention, furthermore, results in a surface of good quality in the as-scarfed condition, i. e., such that it may be rolled into a finished shape, requiring a minimum of additional conditioning.

The scale that remains adhering to the base metal, has a very high degree of oxidation. There is practically no FeO, and substantially or mainly all of such scale is F6304. The oxidation products are substantially free of admixed metal (particularly iron or iron-rich metallic compounds). The scale layer may be classified as light. When the base metal is stainless steel, its surface is relatively free of slag and shows only a typical melted condition of the surface on the order of magnitude of 0.005 inch, or less, in thickness. The base metal also is substantially free of metallic particles, deposited on, or adhering to its surface.

The scale adhering to the base metal is not tightly bonded; and has little tendency to adhere during subsequent heating, rolling and processing. Further, the scale is quite uniform in distribution, composition and adherance, and is of such a nature that subsequent heating and rolling produces practically no tendency to force the scale into intimate contact with the base metal. Thus, the resulting product, when rolled, is free of shiners, the mechanical grinding step being entirely eliminated. Furthermore, this is accomplished with considerably less powder at a much faster rate and substantially less cost than was possible prior to the invention.

1 claim:

1. In the art of thermochemically scarfing work composed of metal having a refractory oxide surface, such as stainless steel, with the aid of ferrous metal powder, by directing at an exit velocity of between 500 and 850 feet per second a relatively fiat stream of commercially pure oxygen against a surface portion of the work to be scarfed at an acute dihedral angle with respect to such surface portion; the improvement which comprises forming a relatively flat stream of relatively fine powder in which the powder is substantially uniformly distributed across a stream of gas, which comprises confining such stream to a path of relatively round cross-section, abruptly changing the direction of flow of the stream, confining the stream to a path of increasing width and decreasing thickness, and subsequently discharging the resulting flat stream at an exit velocity of between 30 and 350 feet per second through a relatively wide and thin slot which is between 0.150 and 0.0625 inch thick toward the leading edge of such oxygen stream and such surface portion.

2. Process of forming a relatively fiat stream of relatively fine powder as claimed in claim 1, in which said slot is form two to more than six inches wide.

3. Process of forming a relatively fiat stream of relatively fine powder as claimed in claim 1, in which the abrupt change in direction of the flow of the stream is accomplished by impinging the stream of round cross section against a flat surface disposed transversely to the direction of flow of the round stream.

4. Process of forming a relatively flat stream of relatively fine powder as claimed in claim 1, in which the abrupt change in direction of the flow of the stream is accomplished by discharging the powder stream out of a passage of round cross section into a separate chamber of rectangular cross section disposed at a sharp angle to said round passage, and impinging the entire stream of round cross section against a flat surface on the far side of said chamber of rectangular cross section disposed at said sharp angle to the direction of flow of said entire round stream.

References Cited in the file of this patent UNITED STATES PATENTS 1,677,726 Nagel July 17, 1928 2,235,542 Wenzel -2 Mar. 18, 1941 2,674,210 Holub Apr. 6, 1954

Claims (1)

1. IN THE ART OF THERMOCHEMICALLY SCRAFING WORK COMPOSED OF METAL HAVING A REFRACTORY OXIDE SURFACE, SUCH AS STAINLESS STEEL, WITH THE AID OF FERROUS METAL POWDER BY DIRECTING AT AN EXIT VELOCITY OF BETWEEN 500 AND 850 FEET PER SECOND A RELATIVELY FLAT STREAM OF COMMERCIALLY PURE OXYGEN AGAINT A SURFACE PORTION OF THE WORK TO BE SCARFED AT AN ACUTE DIHEDRAL ANGLE WITH RESPECT TO SUCH SURFACE PORTION; THE IMPROVEMENT WHICH COMPRISES FORMIN A RELATIVELY FLAT STREAM OF RELATIVELY FINE POWDER IN WHICH THE POWDER IS SUBSTANTIALLY UNIFROMLY DISTRIBUTED ACROSS A STREAM OF GAS, WHICH COMPRISES CONFINING SUCH STREAM TO A PATH RELATIVELY ROUND CROSS-SECTION, ABRUPTLY CHANGING THE DIRECTION OF FLOW OF THE STREAM, CONFIDING THE STREAM TO A PATH OF INCREASING WIDTH AND DECREASING THICKNESS, AND SUBSEQUENTLY DISCHARGING THE RESULTING FLAT STREAM AT AN EXIT VELOCITY OF BETWEEN 30 AND 350 FEET PER SECOND THROUGH A RELATIVELY WIDE AND THIN SLOT WHICH IS BETWEEN 0.150 AND 0.0625 INCH THICK TOWARD THE LEADING EDGE OF SUCH OXYGEN STREAM AND SUCH SURFACE PORTION.

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