US3231431A

US3231431A - Post-mixed fuel gas preheat scarfing

Info

Publication number: US3231431A
Application number: US377666A
Authority: US
Inventors: Allmang William
Original assignee: Union Carbide Corp
Current assignee: Union Carbide Corp
Priority date: 1964-06-24
Filing date: 1964-06-24
Publication date: 1966-01-25
Anticipated expiration: 1983-01-25

Description

Jan. 25, 1966 w L AN 3,231,431

POST-MIXED FUEL GAS PREHEAT SCARFING Filed June 24, 1964 INVENTOR.

WILLIAM ALLMANG BY kw- ATTORNEY nite This application is a continuation-in-part of my then pending but now abandoned application Serial No. 117,724, filed June 16, 1961, which is, in turn, a continuation of my then pending but now abandoned application Serial No. 843,651, filed October 1, 1959, which is, in turn, a continuation of my then pending but now abandoned application Serial No. 682,103, filed September 5, 1957.

This invention relates to post-mixed fuel gas preheat scarfing, and more particularly to method of thermochemical removal of metal from a surface thereof with a wide continuous stream of cutting oxygen preheated by a fuel gas selected from the group consisting of natural gas, propane, methane and coke oven gas.

In the use of natural gas for preheat flames such as in hand operated oxyfuel blowpipes, the natural gas has been premixed with oxygen. Heretofore, it has been an unsolvable problem to employ post-mixed natural gas flames with continuous slot scarfing units.

Mainly, the problem is to have a post-mixed preheat flame adhere to the face of the flame ports. The precise reasons for this problem are not known. Several reasons are put forth as explanations. To obtain the same preheat effect with natural gas, it is necessary to use several times the amount of gas that would be required if acetylene were used. As a result, natural gas must be used at higher pressures and velocities. A high velocity flow may cause the natural gas preheat flame to blowoff the preheat block.

Secondly, natural gas has a lower rate of flame propagation. That is, natural gas will not burn back fast enough to keep the flame on the tips.

It is therefore the main object of the present invention to provide a scarfing process having a continuous slot oxygen stream and post-mixed natural gas preheat flames.

According to the present invention the efliuent natural gas is confined to a path substantially parallel to the cutting oxygen stream and the natural gas is shielded to prevent mixture with atmospheric air. For some unknown reason, when the natural gas is so confined and shielded, a stable, uniform post-mixed preheat flame is obtained. Without this shielding, it is impossible to keep the flames on the tip. The probable explanation is that the bafl le strips confine the gas and produce better mixing with the cutting oxygen.

Also, the invention comprises an improvement on continuous slot scarfing units which comprise securing a baffle strip to the upper and lower preheat blocks. The same results are obtainable using one-piece preheat blocks machined to the same contour.

In the drawings:

FIG. 1 is a side elevation of a scarfing head provided with post-mixed natural gas preheat according to the present invention;

FIG. 2 is a front elevation of the same normal to the oxygen slot; and

FIG. 3 is a view similar to FIG. 1 showing a modified construction.

As shown in the drawing, the oxidizing gas is projected in a wide continuous stream S at an acute angle of impingement onto the reaction zone R, which extends transversely across the entire width of the work W. The stream is confined by an outer surface T and an inner surface B.

States Patent 0 The outer surface T extends smoothly and continuously forwardly along the stream S toward the reaction zone beyond the inner surface B for a distance greater than the thickness of the stream S. This extension of the outer surface T forms an overhanging lip L, the front edge of which is close to the horizontal projection of the front edge of the inner surface B.

An outer transverse row of jets of preheat fuel gas P is projected inwardly at an acute angle against the outside of the stream S beyond the front edge of the lip L, and an inner row of preheat fuel gas jets F is projected outwardly at an acute angle against the inside of the stream S beyond the front edge of the inner surface B. The outer preheat jets are thus located nearer along the stream to the zone of reaction than the inner preheat jets for a dis tance greater than the thickness of the stream.

The confining of the upper surface of the stream of oxidizing gas beyond the lower surface thereof and nearer to the reaction zone prevents the tendency of the gas to expand and escape, and also prevents contamination of the stream by outside air. In operation, the stream of oxidizing gas tends to hug or cling to and follow the underside of the overhanging lip L, and so be projected in a straight line continuing onto the reaction zone with a decreased amount of turbulence.

The location of the outer preheat jets nearer to the reaction zone increases the heat transfer to and temperature rise of the reaction zone, greatly facilitating starting, and increasing the efliciency of the reaction, because the hottest part of the preheat flame is brought nearer to the reaction zone. Also, the outer preheat flames themselves tend to confine the oxidizing gas stream and shield it from contamination.

The location of the inner preheat jets facilitates heat transfer to the stream of oxidizing gas, which arrives at the reaction zone in a highly heated condition.

According to the present invention natural gas is suppiled to the preheat fuel passages P and F. A baffle strip 10 is secured to the front face of the upper preheat block above the preheat fuel passage P, and a similar baffle strip 12 is secured to the front face of the lower preheat block below the preheat fuel passages F. The thickness M of these strips are preferably one half inch as shown in FIGS. 1 and 3. The lower surface of bafiie strip 10 attached to the upper preheat block and the upper surface of baffle strip 12 attached to the lower preheat block should each be located as close to the preheat ports P and F as possible As shown in the drawings, the distance D from the lower surface of baflie strip 10 to the surface T of the upper preheat block is approximately of an inch. Similarly, the distance D measured from the upper surface of the baflie strip 12 to the surface B of the lower preheat block is approximately of an inch. Consequently, the actual distance from the surface of each baflie strip to each row of preheat ports P and F is less than A; of an inch.

Baflle strips

10 and 12 act to confine both sides of the post mixed stream formed from the natural gas issuing from the upper and lower preheat ports P and F and the preheat flow of oxygen issuing as a wide continuous stream S. It is believed that this confining action of the baflie strips upon both sides of the oxygen-fuel mixture prevents atmospheric air from aspirating thereinto at a point adjacent each row of preheat ports.

It has been found to be a critical requirement of this invention that the

baffle strips

10 and 12 be contiguous with respect to each preheat block as shown in the drawing. In FIG. 1, for example, it is important to note that

baflies

10 and 12 are in contact with the edge of the upper and lower preheat blocks, respectively. In FIG. 3, of course, the

baflie strips

10 and 12 are formed as an integral part of the upper and lower preheat blocks, respectively. The effect of having the baifie strips contigous with respect to each preheat block is that it prevents atmospheric air from being aspirated through any spacing between the baffle strips and the preheat blocks into the oxygen-fuel mixture at a point close to the preheat ports P and F. The aspiration of even a minute quantity of air at this point will cause instability of the post-mixed oxygen-natural gas flame. Even a spacing of a few thousandths of an inch between the rear surface I and the edge of the preheat block will have a substantial effect on the stability of the post-mixed oxygen-natural gas flames issuing from the preheat ports P and F.

In the form shown in FIG. 1, the battle strip 12 is secured to the lower preheat block by bolts 15 countersunk into the strip, and all gaps filled with silver solder. The surface is then machined to a 45 degree angle as at 17. This triangular construction avoids forming a pocket between the strip 12 and the lower preheat block in which slag could build up. Instead, this construction causes the slag to slide forward and be blown away by the preheat gases.

As shown in FIG. 3, the bafiles are formed integral with the preheat blocks. The upper preheat block is extended forward and machined to form a surface 14 spaced outwardly from the oxygen slot S and extending parallel thereto forwardly from the natural gas jets P. The lower preheat block is similarly machined to form a similar surface 16 to confine the natural gas from the jets F.

While the invention has been described in connection with the use of natural gas as a fuel, it is equally applicable when the fuel gas is propane, methane or coke oven gas.

What is claimed is:

1. In a process of thermochemically scarfing a metal body by discharging a sheet-like stream of oxidizing gas onto a reaction zone extending across the metal body and at an acute angle of impingement to the work surface thereof, and wherein fuel gas is discharged from orifice means and directed against at least one side of said stream of oxidizin gas, the improvement which comprises shielding the effluent fuel gas from its point of discharge to prevent aspiration of atmospheric air thereinto immediately adjacent said point of discharge by a baflie surface extending forwardly from immediately adjacent the point of discharge toward the reaction zone whereby a stable post-mixed fuel gas-oxidizing gas preheat fiame will be maintained.

2. In a process for thermochemically scarfing a metal body by discharging a sheet-like stream of oxidizing gas onto a reaction zone extending across the metal body and at an acute angle of impingement to the work surface thereof, and wherein fuel gas is discharged from orifice means and directed against each side of said stream of oxidizing gas, the improvement which comprises shielding the effluent fuel gas from its point of discharge against aspiration of atmospheric air thereinto by a surface extending forwardly from immediately adjacent said orifice means toward the reaction zone whereby stable postmixed fuel gas-oxidizing gas preheat flames will be maintained.

3. A process as claimed in claim 1 wherein oxygen comprises said oxidizing gas and a member selected from the group consisting of natural gas, propane, methane and coke oven gas comprises said fuel gas.

4. In a continuous slot scarfing unit wherein a central passage is provided for discharging a sheet-like stream of oxygen for reaction with a metal surface to be scarfed and wherein orifice means are provided for discharging fuel gas against at least one side of said stream of oxygen, the improvement which comprises means for shielding the efiluent fuel gas from its point of discharge from said orifice means to prevent aspiration of atmospheric air thereinto adjacent said point of discharge, said means having a baffie surface extending forwardly from immediately adjacent said point of discharge toward the reaction zone whereby a stable post-mixed oxygen-fuel gas preheat flame will be maintained.

What is claimed is:

5. In a process for thermochemically scarfing metal bodies by confining the inside and outside of a supply of oxidizing gas to form a stream of substantially uniform thickness, discharging said sheet-like stream of oxidizing gas onto a reaction zone extending across a metal body and at an acute angle of impingement to the work surface of said metal body and continuing the confinement of the outside of said stream of oxidizing gas smoothly and continuously farther along the stream toward the reaction zone than the inside of said stream for a distance greater than the thickness of the stream, and discharging fuel gas from orifice means directed against both sides of said discharge oxidizing gas stream beyond the confinement thereof on its way to said reaction zone at an acute angle of impingement therewith, the improvement which comprises continuing the flow of said discharged fuel gas at the same acute angle but in the same general direction as the oxidizing gas stream without interruption into admixture with the oxidizing gas stream, and confining the outer sides of the commingled effluent fuel gas and oxidizing gas mixture beyond the confinement of said stream of oxidizing gas on its way to said reaction zone by a surface substantially parallel to each side of said oxidizing gas stream, and extending forwardly from immediately adjacent said orifice means smoothly and continuously farther along the commingled stream toward the reaction zone to shield the flow of said efliuent and prevent aspiration of atmospheric air thereinto at a point immediately adjacent said orifice means, whereby post-mixed fuel gasoxidizing gas preheat flames will be maintained.

6. A process as claimed in claim 5 wherein oxygen comprises said oxidizing gas and a member selected from the group consisting of natural gas, propane, methane and coke oven gas comprises said fuel gas.

7. In a process for thermochemically scarfing metal bodies by discharging a sheet-like stream of oxidizing gas onto a reaction zone extending across a metal body and impinging at an acute angle to the work surface of said metal body, confining said sheet-like stream of oxidizing gas between surfaces respectively nearer to and farther from said work surface, said farther surface extending smoothly and continuous forwardly and terminating in a front edge beyond the front edge of said nearer surface in overhanging relation thereto for a distance measured along said stream and greater than the distance between said surfaces, to bring the front edge of said farther surface close to the horizontal projection of the front edge of said nearer surface and discharging fuel gas from orifice means directed against at least one side of said discharged oxidizing gas stream at an acute angle of impingement therewith, the improvement which comprises continuing the flow of said discharged fuel gas at the same angle but in the same general direction as the oxidizing gas stream without interruption, and confining the outer side of the commingled effluent fuel gas-oxidizing gas mixture beyond said farther surface in the direction of said reaction zone by a surface substantially parallel to the outside of said oxidizing gas stream, and extending contiguou'sly from said edge of said farther surface and immediately adjacent said orifice means smoothly and continuously farther along the commingled stream toward the reaction zone to shield the flow of said commingled stream to prevent aspiration of atmospheric air thereinto at a point immediately adjacent said orifice means, whereby a post-mixed fuel gas-oxidizing preheat flame will be maintained.

8. In a continuous slot scarfing unit wherein said slot is formed between an upper preheat block and a lower preheat block in spaced relation to one another and wherein means are provided for discharging an oxygen stream through said slot for reaction with a metal surface to be scarfed, the improvement which comprises orifice means for discharging a stream of preheat fuel gas from a point adjacent the edge of each of said preheat blocks, and means comprising a 'batfie strip contiguously extending from said edge of each of said preheat blocks in a direction substantially parallel to the axis of said slot and immediately adjacent said orifice means.

6 References Cited by the Examiner UNITED STATES PATENTS 10/1936 Rendleman 148--9.5 X 6/1954 Bucknam et a1. 266-23

Claims

1. IN A PROCESS OF THERMOCHEMICALLY SCARFING A METAL BODY BY DISCHARGING A SHEET-LIKE STREAM OF OXIDIZING GAS ONTO A REACTION ZONE EXTENDING ACROSS THE METAL BODY AND AT AN ACUTE OF IMPINGEMENT TO THE WORK SURFACE THEREOF, AND WHEREIN FUEL GAS IS DISCHARGED FROM ORIFICE MEANS AND DIRECTED AGAINST AT LEAST ONE SIDE OF SAID STREAM OF OXIDIZING GAS, THE IMPROVEMENT WHICH COMPRISES SHIELDING THE EFFLUENT FUEL GAS FROM ITS POINT OF DISCHARGE TO PREVENT ASPIRATION OF ATMOSPHERE AIR THEREINTO IMMEDIATELY ADJACENT SAID POINT OF DISCHARGE BY A BAFFLE SURFACE EXTENDING FORWARDLY FROM IMMEDIATELY ADJACENT THE POINT OF DISCHARGE TOWARD THE REACTION ZONE WHEREBY A STABLE POST-MIXED FUEL GAS-OXIDIZING GAS PREHEAT FLAME WILL BE MAINTAINED.