U.S. patent number 3,752,460 [Application Number 05/227,147] was granted by the patent office on 1973-08-14 for oxygen trap scarfing apparatus.
This patent grant is currently assigned to Union Carbide Corporation. Invention is credited to Thomas James Lytle.
United States Patent |
3,752,460 |
Lytle |
August 14, 1973 |
**Please see images for:
( Certificate of Correction ) ** |
OXYGEN TRAP SCARFING APPARATUS
Abstract
The time required for scarfing the surface of a metal body is
decreased by shortening the preheating time. This is accomplished
by directing a row of "trap" oxygen streams from ports located
above the upper preheat fuel gas ports so that the oxygen streams
form a plane which intersects the surface of the metal body in such
way as to form a wedge shaped pocket to confine the burning
preheating gases. This results in faster puddle formation and
causes the puddle to be formed at a location just ahead of the
projected converging point of the fuel and oxygen gas streams,
rather than in back of the converging point where it would be
formed by prior art methods.
Inventors: |
Lytle; Thomas James (West
Orange, NJ) |
Assignee: |
Union Carbide Corporation (New
York, NY)
|
Family
ID: |
26921211 |
Appl.
No.: |
05/227,147 |
Filed: |
February 17, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
836233 |
Jun 25, 1969 |
3647570 |
Mar 7, 1972 |
|
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Current U.S.
Class: |
266/53; 148/202;
266/74 |
Current CPC
Class: |
B23K
7/06 (20130101) |
Current International
Class: |
B23K
7/06 (20060101); B23K 7/00 (20060101); B23k
007/00 () |
Field of
Search: |
;148/9.5
;266/23R,23H,23T |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Dost; Gerald A.
Parent Case Text
This is a continuation of copending application Ser. No. 836,233
filed June 25, 1969, now U.S. Pat. No. 3,647,570 issued Mar. 7,
1972.
Claims
What is claimed is:
1. In a continuous slot, post-mixed fuel-oxygen scarfing apparatus
wherein said slot is formed between an upper preheat block and a
lower preheat block which are in spaced relation to one another,
wherein means are provided for controllably discharging a
sheet-like stream of oxidizing gas through said slot for reacting
with a metal surface to be scarfed as well as for burning preheat
fuel gas, and wherein said scarfing apparatus is provided with a
row of ports communicating with supply passages for discharging a
plurality of parallel streams of preheat fuel gas from at least the
upper preheat block to converge with said stream of oxidizing gas,
the improvement comprising: a row of oxygen ports located in said
upper preheat block above said row of fuel gas ports communicating
with oxygen supply passages, means for controlling the flow of
oxygen through said oxygen supply passages independently of the
flow of said sheet-like stream of oxidizing gas, said row of oxygen
ports being capable of discharging a plurality of parallel streams
of oxygen gas which form a sheet-like oxygen gas curtain, said
oxygen ports being directed at the converging point of the straight
line projections of the oxidizing gas and fuel gas streams so as to
cause the oxygen curtain streams emanating therefrom to form a
wedge shaped pocket between the planes formed by said curtain
oxygen stream and the surface of said metal body, thereby confining
the fuel and oxidizing gases discharged from their respective
ports.
2. The scarfing apparatus of claim 1 wherein said lower preheat
block also is provided with a row of ports communicating with
supply passages for discharging a plurality of parallel streams of
preheat fuel gas.
Description
BACKGROUND
This invention relates to the thermochemical conditioning of
ferrous metal bodies, commonly referred to as scarfing; and more
particularly to apparatus capable of decreasing the time required
for a complete scarfing cycle with post-mixed, fuel-oxygen preheat
gas scarfing units by decreasing the time required for preheating
the metal workpiece to be scarfed. The present invention is
applicable to scarfing of hot as well as cold metal workpieces.
According to present post-mixed scarfing practice, as exemplified
by U.S. Pat. No. 3,231,431, a scarfing reaction is caused to take
place by first raising the temperature of the metal surface to be
scarfed to the ignition temperature of the metal in an oxygen
atmosphere. This temperature, which may be lower than the melting
point of the metal in air, is referred to as the "reaction
temperature." When the reaction temperature is reached, a puddle of
molten metal is formed. The metal is removed -- that is, the
thermochemical scarfing reaction is caused to take place -- by
impinging a stream of oxygen on the puddle. In other words, in
order to initiate a scarfing reaction a puddle must be formed
before the scarfing oxygen stream can be turned on for the
thermochemical scarfing reaction to begin.
A complete scarfing cycle consists of four steps. First, the
workpiece is positioned in register with the scarfing machine.
Second, the scarfing units are closed, either automatically or
manually, around all the sides of the workpiece which are to be
scarfed. Third, preheating of the workpiece is caused to take place
by means of fuel-oxygen preheat flames so that a puddle of molten
metal is formed on the stationary workpiece; and fourth, the
scarfing reaction is carried out by initiating the flow of scarfing
oxygen and setting the workpiece in motion. For example, when
scarfing a 30 foot slab at 2,000.degree.F, positioning takes about
3 seconds, closing about 5 seconds, preheating about 10 seconds,
and scarfing the length of the slab about 20 seconds. Thus, the
total scarfing cycle for the 30 foot slab requires approximately 38
seconds.
The time required for a complete scarfing cycle results in a
scarfing rate or speed that is in some cases slower than the rate
at which steel is rolled in a conventional mill. It is therefore
desirable to decrease the time required to complete a scarfing
cycle in order that the scarfing operation keep up with the
production of the mill. Reduction in scarfing time may obviously be
accomplished by reducing the time required for any of the above
mentioned four steps which take place during a complete scarfing
cycle. Since positioning and closing require a total of only about
8 seconds, the amount of improvement possible in these two steps is
relatively small. Consequently, the logical steps to shorten in
order to improve the speed of a scarfing cycle are the preheating
and/or scarfing steps.
The seemingly simple expedient of increasing the flows of fuel and
oxygen to decrease preheating time and increase scarfing speed,
does not work. If greater than normal quantities of either fuel or
oxygen are supplied, preheating time fails to improve. For example,
if more fuel gas than conventionally used is provided, it tends to
pinch off the supply of oxygen to the workpiece with a consequent
decrease in heating capacity, thereby slowing down the preheating
reaction. Similarly, increasing the preheating oxygen decreases the
heating potential of the upper preheat flames by placing an
intervening layer of cold oxygen between the upper preheat flames
and the workpiece. Additionally, the increased oxygen acts as a
cooling medium which draws heat from the workpiece. The
simultaneous and proportional increase in both preheat fuel gas and
oxygen offers little improvement, since the excess amounts of
oxygen and fuel cannot be mixed and burned efficiently in a
post-mixed system.
THE DRAWINGS
In the drawings:
FIG. 1 is a side elevation of a scarfing unit according to the
present invention which is provided with a row of "trap" oxygen
orifice ports located in the upper preheat block above the row of
preheat fuel gas ports.
FIG. 2 is a front elevation of the scarfing unit shown in FIG.
1.
FIG. 3 is a graph comparing the preheat times obtained by the use
of the "trap" oxygen stream in accordance with the present
invention as compared to a scarfing unit without such "trap" oxygen
streams.
In accordance with the prior art, in order to maximize heat input
into the workpiece at the reaction zone, the upper and lower
preheat fuel gas streams 11 and 12 in FIG. 1, as well as the
scarfing oxygen stream 9 emanating from the central slot 8, are all
directed so that their straight line projections converge at point
A on the surface of the workpiece W. However, due to the
aerodynamics of the system, caused by the flow of hot reacting
gases and cooling from the surrounding area, as well as the
pressure drop caused by the flow of high velocity gases, the puddle
20 forms not at the point A, but rather in back of it by several
inches at point B. Consequently, it has been necessary, in
accordance with prior art practice, as shown for example in U.S.
Pat. No. 3,322,578, to back up the scarfing unit or the workpiece
(in a direction opposite to the arrow) by several inches before the
scarfing oxygen stream was turned on, so that when it was turned
on, the scarfing oxygen stream would impinge upon the puddle rather
than ahead of it. This backing up of either the scarfing unit or
workpiece between preheating and starting of the scarfing reaction
has been responsible in part for the excessive time required for
preheating.
OBJECTS
It is the primary object of this invention to decrease the time
required for a complete scarfing cycle.
It is another object of this invention to decrease the time
required to preheat the workpiece prior to initiation of the
scarfing reaction.
It is still another object to avoid the necessity for backing up
the scarfing unit or workpiece before scarfing oxygen is turned
on.
SUMMARY OF THE INVENTION
These and other objects, which will become apparent from the
detailed disclosure and claims to follow are achieved by the
present invention, which comprises a continuous slot, post-mixed
fuel-oxygen scarfing apparatus wherein said slot is formed between
an upper preheat block and a lower preheat block which are in
spaced relation to one another, wherein means are provided for
controllably discharging a sheet-like stream of oxidizing gas
through said slot for reacting with a metal surface to be scarfed
as well as for burning preheat fuel gas, and wherein said scarfing
apparatus is provided with a row of ports communicating with supply
passages for discharging a plurality of parallel streams of preheat
fuel gas from at least the upper preheat block to converge with
said stream of oxidizing gas, the improvement comprising: a row of
oxygen ports located in said upper preheat block above said row of
fuel gas ports communicating with oxygen supply passages, means for
controlling the flow of oxygen through said oxygen supply passages
independently of the flow of said sheet-like stream of oxidizing
gas, said row of oxygen ports being capable of discharging a
plurality of parallel streams of oxygen gas which form a sheet-like
oxygen gas curtain, said oxygen ports being directed at the
converging points of the straight line projections of the oxidizing
gas and fuel gas streams so as to cause the oxygen curtain streams
emanating therefrom to form a wedge shaped pocket between the
planes formed by said curtain oxygen stream and the surface of said
metal body, thereby confining the fuel and oxidizing gases
discharged from their respective ports.
DETAILED DESCRIPTION OF THE INVENTION
The oxygen curtain or plane above the preheat fuel gas streams
formed by the "trap" oxygen streams causes a wedge shaped pocket to
be formed between itself and the surface of the metal being
scarfed. The oxygen curtain is formed by a parallel row of oxygen
ports 23 located above the row of upper preheat block fuel gas
ports 15. High velocity fuel gas from both upper and lower preheat
blocks 1 and 2 is directed into the pocket, becoming trapped in the
pocket and consequently forced to mix intimately with the oxygen 9
emanating from the continuous slot 8. This permits considerable
improvement to be made in preheat time by increasing the flows of
fuel and oxygen that can be adequately mixed for combustion while
precisely fixing the location of the puddle at the point where it
is desired.
The oxygen curtain provides a two-fold effect; first, it acts as a
physical barrier to contain or trap the fuel and oxygen preheat
gases causing them to burn in place; and second it permits an
increase in the total amount of oxygen, thereby causing a hotter
flame to be produced. The combination of these two effects improved
heat transfer to the workpiece and concentrates the heat at a
particular spot.
An unexpected but very beneficial result of this invention is that
the molten puddle is formed not at point B behind point A, but
rather at point C forward of point A. As a result of the fact that
point C is just ahead of the projection of the scarfing oxygen
stream 9, backing up of the workpiece or scarfing unit prior to
starting of the cutting oxygen flow is eliminated. This, in turn,
provides additional beneficial results in the speed of
preheating.
Reference to FIGS. 1 and 2 will show that the scarfing unit is
comprised of an upper preheat block 1, a lower preheat block 2, a
head 3 and a shoe 4 which rides on skids 6. The lower surface 6 of
upper preheat block 1 and the upper surface 7 of lower preheat
block 2 form a continuous slot passage 8 for the oxygen stream 9.
The rear end 10 of oxygen passage 8 communicates with an oxygen
supply manifold 25, to which the supply of oxygen is controlled by
valve 26. During preheating, passage 8 is used to provide oxygen
for combustion of the upper and lower preheat fuel gas streams 11
and 12. After the puddle 13 has been formed, the oxygen flow in
stream 9 is increased to provide sufficient oxygen for the scarfing
reaction. Upper preheat block 1 is provided with a plurality of
preheat fuel gas passages 14 which terminate at the front face of
the preheat block 1 in a row of fuel gas ports 15. Gas passages 14
communicate with a fuel gas header 24 located in head 3 from which
they receive their supply of fuel gas. Natural gas is the preferred
fuel gas; however, other fuel gases may also be employed such as,
for example, methane, propane or coke oven gas. Lower preheat block
2 contains a plurality of fuel gas passages 17 which communicate
with and receive a supply of fuel gas from header 18 located in
head 3. Passages 17 terminate at the front face of the lower
preheat block 2 in a row of lower preheat fuel gas ports 19. Both
the upper preheat fuel gas ports 15 and the lower preheat fuel gas
ports 19 are directed so that the straight line projections of the
gas streams 11 and 12 emanating therefrom will converge with the
straight line projection of the sheet-like stream of oxygen 9 at
the converging point A on the surface of the metal workpiece W. Due
to the aerodynamic effect of the hot gas streams as previously
explained, the puddle 20 is formed upon the surface of the
workpiece W at point B by prior art methods, i.e., without the use
of the "trap" oxygen stream 21.
In accordance with the present invention, the upper preheat block 1
is provided with a plurality of oxygen passages 22 which terminate
at the front face of said preheat block in a row of "trap" oxygen
ports 23. Oxygen is supplied to passages 22 from an oxygen header
16 located in head 3. The "trap" oxygen streams 21 emanating from
ports 23 are also directed to converge with the fuel gas stream
projections 11 and 12 and oxygen stream projection 9 at point A.
The plane formed by the plurality of "trap" oxygen streams 21 forms
a wedge shaped pocket between itself and the surface of the
workpiece W to confine the preheating gas streams 11 and 12 and the
oxygen stream 9 thereby improving heat transfer to workpiece W and
concentration of the heat within the wedge shaped pocket formed
thereby. It has been found that when the "trap" oxygen stream 21 is
used, the puddle 13 is formed at point C just ahead of converging
point A, rather than at point B where it would have been formed
without the use of the "trap" oxygen streams. This is apparently
caused by the change in the flow dynamics of the system resulting
from use of the "trap" oxygen streams. In other words, due to the
aerodynamics of the system, the streams of fuel gas and oxygen do
not follow the straight lined projections 9, 11, 12 and 21, but
rather follow a path indicated generally by flow lines F.
Consequently, when the scarfing reaction is to begin, after puddle
13 has been formed at point C, the oxygen stream 9 is simply
increased to the flow rate required for scarfing by adjustment of
valve 27 or other conventional flow control means, and the
workpiece W is then set in motion toward the right as indicated by
the direction of the arrow, without the need for backing up the
workpiece or scarfing unit. This would have been necessary had the
puddle been formed at point B, in order that the scarfing reaction
might begin by having the scarfing oxygen stream 9 impinge upon the
puddle. After the preheat step has been completed, and the scarfing
reaction started, the "trap" oxygen flow may be kept on, shut off
completely, or lowered just to "bleed" slightly in order to prevent
ports 23 from becoming plugged by the splatter of molten metal and
slag. This can be effectuated by adjustment of valve 26 or other
conventional flow control means. Keeping the "trap" oxygen on at
full flow rates during the scarfing step has not been found to
produce any beneficial results.
FIG. 3 is a graph comparing preheating time using a post-mixed
fuel-oxygen scarfing unit of the prior art with a unit in
accordance with the present invention containing a row of "trap"
oxygen ports above the upper preheat fuel gas ports to provide the
oxygen curtain of the present invention. The flow rates of preheat
fuel gas (natural gas) were approximately 3,500 C.F.H. in both
cases. The total amount of oxygen was likewIse the same in both
cases, i.e., about 7,500 C.F.H. However, the distribution of the
oxygen was different. In the case of the prior art scarfing unit,
all of the oxygen was discharged through the center slot, while in
the case of the scarfing unit of the present invention,
approximately half of the oxygen was discharged through the center
slot and the other half through the "trap" oxygen ports. It can be
seen from the graph that preheating time depends upon the
temperature of the steel work surface and that the hotter the work
surface, the shorter the preheating time. Curve X shows the results
obtained in using a scarfing unit of the present invention, while
curve Y shows the results obtained using a standard post-mixed
scarfing unit of the prior art. Comparison of curves X and Y shows
that at steel temperature of 2,000.degree.F, it required only about
3 seconds to preheat the workpiece in accordance with the present
invention, whereas it required 10 seconds to preheat the workpiece
WiJh the prior art unit. This constitutes a reduction of about 7
seconds, or better than a three fold improvement. A similar result
can be observed at 1,500.degree.F where it required about 5 seconds
to preheat in accordance with the present invention, whereas it
required about 27 seconds with the prior art unit.
The significance of the faster preheat time obtained in accordance
with this invention is that it improves the prehating time at
2,000.degree.F, for example, by about 7 seconds, thereby cutting
the scarfing cycle described previously from 38 seconds to about 30
seconds. This is an improvement of over 20 percent in the scarfing
cycle and is sufficient to enable the scarfing machine to keep up
with a higher production rate than was formerly possible. It should
be noted that the present Invention also provides a saving in
preheating time by elimination of the need for backing up the
workpiece or scarfing unit prior to initiation of the scarfing
oxygen reaction, in addition to the shortening of the preheating
time as shown in FIG. 3.
* * * * *