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Патент USA US2130420

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Sept. 20, 1938.
c. B. FERREE
2,130,420
DRAW OVEN
Filed Nov. 18, 1956
2 Sheets-Sheet 1
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BY
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‘ATTORNEYS
Sept. 20, 1938.
c. B. FERREI:4
2,130,420
DRAW-OVEN
Filed Nov. 18, 1936
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Patented Sept. 20, 1938
2,130,420
UNITED STATES
PATENT OFFICE
2,130,420
DRAW OVEN
Cliüord B. Ferree, Pittsburgh, Pa.
Application November 18, 1936, Serial No. 111,408
2 Claims. (Cl. 26E-5)
'I‘his invention relates to the production of time successfully and advantageously to “draw” r`
forged steel rolls, and consists in a method of ' a forged roll in “ain”
procedure, and an apparatus, whereby the possi
In the accompanying drawings Fig. I is a view
bility is realized of tempering a forged roll by in plan from above of an oven of the invention,
actually built and used industrially, from which Cil “air drawing,” with benefits and advantages to
be described. This application is a continuation
in part of an application for Letters Patent filed
by me August 28, 1935, Serial No. 38,195.
In the production of forged-steel rolls, after a
roll has been machined and hardened and before
polishing for delivery to the user, it is subjected
to an ultimate tempering step.
This ultimate
tempering step, commonly called “drawing” (in
that extreme hardness is in some degree reduced
or drawn from the metal), consists in raising the
roll from atmospheric temperature to a tempera
ture that in different cases may range from as
low as 290° F. to as much as 425°, or, in extreme
cases, even to 700 or 800°, and cooling it again
in the open air. This heating of the roll is a very
20 nice operation: it must be accomplished inl very
uniform manner, that the quality of the finished
roll shall be uniform throughout all its extent.
Heretofore this ultimate heating has beenV per
formed in a bath of oil. Alternative methods
25
of tempering, practised upon other bodies in
tended for other uses involve, one, the employ
ment of a bath of molten lead, and, another,
heating in the gaseous atmosphereof an oven;
30 these two other methods are characterized “lead
drawing” and “air drawing.” The latter term is
inaccurate, in that the atmosphere is not atmos
» pheric air, but krather a gaseous furnace atmos
phere; but the term has gained acceptance, and is
CIO Ol understood.
I shall useV it in accepted manner
and my use of it will not be misunderstood. Lead
drawing is not appropriate to the ultimate tem
pering step in the production of a forged roll, be
-cause the melting-point of lead is beyond the
temperature range that is requisite; air drawing
has not hitherto been .made practical, because of
the wide disparity in thermal capacity per unit of
volume between steel and “air” (i. e., furnace
atmosphere) and because of the great mass of a
45 roll body, in relation to surface area.
I have discovered that by providing an oven so
constructed that the gas burning within shall
build up a super-atmospheric pressure in the oven
chamber, by forming the furnace walls of mate
v50 rial of low heat conductivity, and by burning
Within the chamber a gas of high heat value
mingled with air in relative quantities such as to
effect perfect combustion, I am able for the first
time to overcome the diñiculties and for the first
the roof has been removed; Fig. II is a view of
the same unroofed oven in side elevation; and Fig.
III is a view of it in vertical and transverse sec
tion, with the roof in place. And in Fig. III a roll
is shown in end elevation, in place Within the`A 10
oven.
Fig. IV is a chart showing comparatively '
the heat losses of the apparatus of my invention
and those of a tank for oil-drawing.
'I‘he oven is essentially an oblong chamber of
approximately square cross-section, and of such¿
particular dimensions as to receive the rolls to be
treated. The chamber within is, but for a parti
tion Wall that affords longitudinal subdivision,
free of any screen: there is no baille nor flame
diverting nor flame-confining partition between,
the burner and the article under treatment. The
flame has free access to the naked roll surface.
Such a chamber I characterize a free chamber.
In ordinary circumstances a plant will be required
to produce rolls of various dimensions, and the „
oven will be of suii'icient size to receive the `
largest. In this instance the oven measures, in
ternally, 16 feet 11 inches in length, 5 feet in
breadth, and 5 feet in height. There are within
the oven chamber guides that define a space that _
is 3 feet 9 inches wide; so that this oven is adapt- "
ed to receive any roll not substantially exceeding
16 feet in length nor 3 feet 6 inches in maximum
diameter. I have successfully treated in this
oven, having the characteristics herein described,
and by following the procedure herein set forth, '
rolls that ranged in size from 28x55 inches down
ward. The size given is not a limitation; it hap
pens merely to be the size of the largest rolls I
have hitherto had occasion to produce,
I have y
found it advantageous to provide a removable
partition or curtain Wall, subdividing the oven
chamber, to the end >that for relatively short rolls
a portion only of the oven structure need be used;
and I have found it convenient thus to reduce the 45
size of the oven by half. Rolls of the maximum "
size indicated have volume approximately one
fourth that of the furnace chamber.
The side walls I and the end Walls 2 are con
tinuous and unbroken and stand permanently
fixed upon the floor 3. The roof 4 is preferably
made in sections longitudinally of the oven; and
it, as has been said, is removable. It rests when
in place upon the side and end walls; and it
too is
substantially continuous.
The oven _y
3
2,130,420
seams in the roof) tight walled, it will be per
ceived that the play of the ñames tends to build
up pressure within the oven chamber and to ex
clude atmospheric air. The practical and actual
effect is that an inert atmosphere of high tem
perature is maintained within the oven; that the
actual temperature may by the adjustment of the
supply Valves be varied and brought to the de
sired degree; and that within all the oven cham
10 bei` from floor to roof the temperature may be
maintained uniform, within a permissible toler
ance of ten degrees F.
If natural gas be used, the oven atmosphere
will, with inconsiderable variation, be carbon
15 dioxide,
10%; water vapor, 18%; nitrogen,
'72%. If fuel gas be used, while the components
of the oven atmosphere will be the same, the
proportions will be somewhat different.
When in continued operation the roll within
20 the oven has come to furnace temperature, the
completion of the heat treatment, the empty oven
will in the course of one or two hours have cooled
sufñciently to allow it to receive another roll for
treatment. No such speed of operation is at
tainable in the oil-drawing procedure.
It is desirable, in order to gain toughness, that
a relatively high peak temperature be attained;
but a relatively high peak temperature is, in the
oil-drawing procedure, gained only with loss of
hardness. Actual experience shows that it is pos 10
sible in my “air-drawing” procedure to attain
higher peak temperatures than in the old oil
drawing procedure while maintaining a like de
gree of hardness.
The oil-drawing procedure is limited, in the 15
matter of peak temperature, by the necessity of
operating below the flash-point of the oil. No
Such limitation attends my “air-drawing” pro
cedure.
There are serious disadvantages attendant 20
case the nozzles of the holding burners are all
upon the oil-drawing procedure, from which the
“air-drawing” procedure of my invention is free.
The ñrst and most serious of these is the fire
horizontally placed, the holding burners may have
hazard.
heating-up burners may be shut off, and the
holding burners only continued in action.
In
25 been cooperating with the heating-up burners
in their essential function; but in case some of
the nozzles of the holding burners are vertically
directed, the holding burners will be brought
into service in alternation with the heating-up
30 burners.
When the roll has been held at peak tempera
ture the desired length of time (typically four
teen hours), the burners are shut oiî, the oven is
opened, and the roll removed. While the roll
35 may be brought into the open air at any preferred
point in the course of its cooling, it ordinarily
will be removed without delay, when the heat
treatment is completed. The emptied oven will
cool rapidly and will without long delay be avail
40 able for operation upon another roll.
I have found that at a peak temperature of
350° F., that is to say, with a temperature dif
ference on opposite sides of the wall of 250° or
somewhat more, the heat loss in my oven is
45 55,000 B. t. u. per hour. The heat loss in a tank
of comparable size for oil-drawing is 220,000
B. t. u. per hour.
A comparative showing of heat
loss in the apparatus of the two types throughout
the range of ordinary operation is given in the
50 chart, Fig. IV.
The heat generation in my oven to effect what
is termed a “low” draw (the usual procedure)
is at a rate that ranges from 45,000 B. t. u. per
hour to 226,000, and the average is approximately
55 80,000 B. t. u. per hour. The saving in heat ex
penditure over the heretofore prevailing oil
drawing practice is about seventy per cent. For
high draw in the practice of my invention the
heat generation ranges from 45,000 B. t. u. per
60 hour to 457,000. It then will be manifest that in
normal operation the heat penetrability of the
Operation is in any case and of neces
sity dangerously near the flash-point of the oil; 25
and because there is variability here that can
not be wholly eliminated, accidents occur, with
injury to men and property. It happens inevi
tably that a roll often carries water to the oil tank,
and when this occurs the fire hazard is increased. 30
The roll as it comes from the oil bath in the
oil-drawing operation is coated with oil, and the
oil coating delays its cooling to room tempera
ture-and cooling to room 4temperature is neces
sary, before work upon the roll can be resumed. 35
Furthermore, when at length the roll comes to
the grinding wheel, the heavy coating of oil upon
its surface clogs the wheel, and necessitates wheel
dressing. From all such embarrassments pro
cedure under my invention is free.
I believe myself to be the ñrst successfully to
draw a rolling-mill roll in “air”.
I claim as my invention:
1. A draw oven for the heat treatment of a
rolling-mill roll, including floor, side walls, and 45
roof, the side walls and roof being formed of
heat-insulating material of low heat-absorption
capacity, the roof being removable and the seams
incident to the removable-roof construction af
fording the sole exit for gas from the chamber
within the closed oven, means for supporting by 50
its necks within the chamber and with its face
free end enveloped throughout all its extent in
the atmosphere within the oven a roll to be treat
ed, and means for projecting into the otherwise 55
free chamber from opposite sides and in a hori
zontal plane below the lower limb of curvature
of a roll supported within the oven chamber two
lines of name.
2. A draw oven for the heat treatment of a 60
rolîïig-mill roll, including floor, side walls, and
walls of my furnace is less than 200 B. t. u. per
roof, the side Walls and roof being formed of
square foot per hour, and that the heat genera
tion within the chamber exceeds 200 B. t. u. per
65 square foot per hour and very considerably ex
ceeds the rate of loss through wall permeability.
The control of temperature is more accurate in
the practice of my invention than is possible in
heat-insulating material of low heat-absorption
the oil-drawing procedure. By actual observa
70 tion it is found that the variation in peak tem
perature in the practice of my invention averages
12 degrees F., whereas in the oil-drawing pro
cedure the variation amounts to 22 degrees.
When, as ordinarily will be the case, the roll
75 is removed from the oven immediately on the
40
capacity, the roof being removable and the seams
incident to the removable-roof construction af 65
fording the sole exit for gas from the chamber
within the closed oven, means for supporting by
its necks within the chamber and with its face
free and enveloped throughout all its extent by
the atmosphere within the oven a roll to be treat 70
ed, and means for developing in the otherwise
free chamber in a horizontal plane below the
lower limb of curvature of a supported roll an
outspread substantially uniform layer of ñames.
CLIFFORD B. FERREE.
76
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