U.S. patent application number 10/073386 was filed with the patent office on 2002-08-15 for method for softening a selected portion of a steel object by heating.
Invention is credited to Finkl, Charles W., Underys, Algirdas A..
Application Number | 20020108683 10/073386 |
Document ID | / |
Family ID | 26857316 |
Filed Date | 2002-08-15 |
United States Patent
Application |
20020108683 |
Kind Code |
A1 |
Finkl, Charles W. ; et
al. |
August 15, 2002 |
Method for softening a selected portion of a steel object by
heating
Abstract
A method and apparatus for tempering the shank portion only of
die blocks which comprises subjecting the shank portion of a die
block or other large metal part to electrical energy derived from
induction heating or infrared heating to a controlled depth,
preferably just sufficiently deep to temper the shank portion but
not sufficiently deep to temper the hardened working portion of the
part.
Inventors: |
Finkl, Charles W.;
(Evanston, IL) ; Underys, Algirdas A.; (Arlington
Heights, IL) |
Correspondence
Address: |
James G. Staples
A. Finkl & Sons Co.
2011 North Southport Avenue
Chicago
IL
60614
US
|
Family ID: |
26857316 |
Appl. No.: |
10/073386 |
Filed: |
February 12, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10073386 |
Feb 12, 2002 |
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09160895 |
Sep 25, 1998 |
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09160895 |
Sep 25, 1998 |
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08582373 |
Jan 11, 1996 |
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Current U.S.
Class: |
148/526 |
Current CPC
Class: |
Y02P 10/25 20151101;
Y02P 10/253 20151101; B21J 13/00 20130101; C21D 1/63 20130101; C21D
1/34 20130101; C21D 1/10 20130101; Y10S 148/903 20130101; C21D
9/0068 20130101; C21D 2221/10 20130101; B21K 5/20 20130101 |
Class at
Publication: |
148/526 |
International
Class: |
C21D 001/10 |
Claims
What is claimed is:
1. In a method of reducing the incidence of cracking at the
shank-body junctions of hardened die blocks, the steps of placing
an electric heat source in close, operative proximity to the
shank-body junction of a die block to be softened, directing the
heat generated by the electric heat source only to the body-shank
portion of the die block, and terminating the operation of the
electric heat source after the body-shank portion of the die block
has been drawn.
2. The method of claim 1 further characterized in that the electric
heat source is in abutting contact with the shank-body junction
surfaces formed in the die block.
3. The method of claim 2 further characterized in that the
thickness of the electric heat source equals the height of the
shank of the die block.
4. The method of claim 3 further characterized in that the electric
heat source is induction heating coils.
5. The method of claim 1 further characterized in that the electric
heat source is spaced from the body-shank portion of the die
block.
6. The method of claim 5 further characterized in that the electric
heat source is infrared heating means.
7. The method of claim 6 further characterized in that the infrared
heating means are tungsten halogen lamps arranged to direct
infrared energy onto a defined area of a die block to be
softened.
8. The method of claim 6 further characterized in that the tungsten
halogen lamps operate in the short wave division of the
electromagnetic spectrum.
9. Apparatus for reducing cracking at the body-shank junctions of a
hardened die block, said apparatus including, in combination an
electric heat source in close proximity to the body-shank junction
portion of the die block, said electric heat source being arranged
to direct heat to the body-shank junction portion of the die block,
and in an amount such that the body-shank portion, only, of the die
block is softened to a level at which subsequent cracking at a
shank-body junction of the die block is substantially eliminated,
and means for confining the heat from the electric heat source to
the body-shank junction portion of the die block.
10. The apparatus of claim 9 further characterized in that the
electric heat source is induction heating coil means.
11. The apparatus of claim 10 further characterized in that the
means for confining the induction heating currents generated by the
induction heating coil means includes at least partial envelopment
by non-magnetic material of those portions of the induction heating
coil means which are not in operative relationship with the shank
or body portion of the die block.
12. The apparatus of claim 11 further characterized in that the
means for confining the induction heating currents are substances
selected from the group consisting essentially of non-magnetic
rock, rock-type and ceramic materials which are capable of
withstanding, without substantial distortion, the temperatures
generated during treatment by the induction heating coil means.
13. The apparatus of claim 12 further characterized in that the
induction heating coil means are in abutting contact with the
shank-body junction surface of a die block.
14. The apparatus of claim 13 further characterized in that the
thickness of the induction heating coil means equals the height of
the shank of a die block.
15. The apparatus of claim 9 further characterized in that the
infrared heating means are tungsten halogen lamps.
16. The apparatus of claim 14 further characterized in that the
tungsten halogen lamps are spaced closely to the body-shank
junction portion of the die block.
17. The apparatus of claim 15 further characterized in that the
tungsten halogen lamps are arranged to operate in the short wave
division of the electromagnetic spectrum.
Description
[0001] This invention relates to a method and apparatus for
eliminating or at least drastically reducing the cracking which
today frequently occurs at the junctions of the body and shank of
ferrous alloy die blocks and similar parts.
BACKGROUND OF THE INVENTION
[0002] Die blocks are well known forging implements which, after
the sinking of an impression therein to thereby form a die, are
used in forging machines such as hammers. A hammer die, after final
machining and heat treatment, is then fitted to a die holder in the
hammer. A typical hammer die has a large thick body (to provide for
one or more resinkings of the impression) and, usually, a
relatively short, dovetailed shaped shank located in the middle of
one side of the body and extending the length of the body. A
typical shank is about 2" in height.
[0003] In operation a hammer die is exposed to extremely rugged
conditions. In normal operations with all machine components
properly positioned and secured, tremendous shock loads are
transmitted to all portions of the die. Such loads, which are
derived from the many tons of impact forces resulting from the
weight of the downwardly driven ram portion of the hammer die
striking the workpiece resting in the die holder of the hammer die,
have their greatest effect on the weakest portion of the die which,
as is well known, is the junction of the shank and body of the
hammer die. All too frequently the dies, which may range in
hardness from about 28 Rc to about 54 Rc, are cracked or fractured
at the shank-body junction of the die and this can lead to
catastrophic failure.
[0004] Many forging die applications require a tool steel die block
that has been heat treated to a high hardness level to optimize the
wear resistance of the working face. At the same time the shank
portion of the die block requires a lower hardness level to
facilitate machining and prevent cracking of the filet radius
during the forging process. The "composite" design is achieved by
heat treating the entire block to the high face hardness and then
selectively tempering the shank portion at a tempering temperature
higher than that used to temper the entire block.
SALT BATH SHANK TEMPERING
[0005] In the current practice the shank is tempered by immersing a
portion of the previously heat treated and hardened die block into
a bath of molten metal salt containing barium chloride (BaCl.sub.2)
at a temperature of 1250.degree. F. (677.degree. C.). Heat from the
molten salt is conducted into the submerged portion of the die
block, is transmitted through the block, and is lost through
radiation and convection from the portion of the block exposed to
the ambient air above the salt. After approximately 180 minutes a
steady state heat transfer condition is established where the
highest temperature of approximately 1250.degree. F. (677.degree.
C.) is present at the submerged corner. The temperature decreases
to approximately 1050.degree. F. (566.degree. C.) at the salt
immersion depth. The temperature continues to decrease toward the
top surface of the die block exposed to the ambient air. The final
temperature at the top (working face) of the die block depends on
the depth immersion and total height of the die block. It is
imperative that the working portion of the die block remain below
the original die block tempering temperature to prevent softening
of the working face. The metallurgical effectiveness of the shank
tempering process depends on the combination of the temperature
achieved and time held at that temperature. The current practice
specifies a total salt bath treatment of 6 hours (3 hours after
steady-state is reached) to allow for sufficient tempering of the
shank portion.
PROBLEMS WITH SALT BATH SHANK TEMPERING
[0006] Technical, maintenance, environmental, and safety problems
limit the commercial success of the current process. Technically
the process is limited by the relatively slow rate of heat input
generated by the molten salt at 1250.degree. (677.degree. C.). The
slow heat input rate coupled with the heat lost due to radiation
and convection from the portion of the block exposed to the ambient
air limits the maximum temperature within the block, at that salt
immersion depth, to approximately 1050.degree. F. (566.degree. C.).
The extent to which the shank is selectively tempered is limited by
the temperature achieved in the shank portion of the die block and
the time held at temperature. The maximum temperature of the top
(working face) must remain below the original tempering temperature
of the parent block to prevent softening. This maximum working face
temperature depends on the depth of immersion into the salt bath
(heat input) and the height of the block above the salt bath (heat
output). For small blocks it is impossible to sufficiently temper
the shank portion without softening the working face due to the
relatively small portion of the block above the salt bath. Further
the process is somewhat time consuming requiring a batch processing
time of six hours. It is possible to increase the effective
tempering temperature at the salt immersion depth and decrease the
batch processing time by increasing the temperature of the molten
salt bath, however, this only increases the maintenance,
environmental, and safety problems associated with the process.
[0007] Several maintenance problems hinder the commercial success
of the salt bath shank tempering process. Costly stainless steel
pots are used to contain the molten salt used for the shank
tempering process. These pots are corroded by the salt and require
replacement approximately every eight months resulting in an annual
cost of $5,700. Any increase in salt pot operating temperature will
significantly reduce the life of the salt pots. The actual metal
salt must be replenished at a cost of approximately $2,000
annually. In addition to the cost of these consumables is the
annual cost of approximately $21,000 for the natural gas used to
heat the pot. Additional costs are associated with the maintenance
of the burners, themocouples, and the control systems.
[0008] Several environmental and safety problems plague the use of
the salt bath shank tempering process. The barium chloride
contained in the salt is considered a hazardous waste under the
Resource Conservation and Recovery Act due to its barium content
which is a heavy metal and requires special disposal procedures.
Overexposure to this salt can lead to several varied health risks.
Skilled operators are required to conduct the salt bath processing
due to the many safety hazard associated with the molten salt.
Extreme care must be taken to avoid the introduction of water into
the molten salt. Condensation or ice that may have accumulated on
the die blocks will become explosive upon contact with the molten
salt if not thoroughly removed prior to immersion in the bath. If
moisture is introduced the rapid conversion to steam can splatter
the molten salt onto adjacent personnel. Care must also be taken
when placing blocks into the salt bath to avoid inhalation of the
powdered metal salt when loading the pot. Because of these
environmental and safety concerns it is required that any salt bath
tempering process must be located in a specialized shop area.
[0009] Following the salt bath treatment the blocks must be stored
until cool. Next, the salt that adheres to the sides of the block
must be removed prior to the moving the blocks to the next
operation. Again this is required to contain the metal salt and
prevent contamination of other locations. The same precautions must
be maintained when handling the salt that is removed from the sides
of the block.
[0010] The results of such treatment, while better than no
treatment, are, in a sense, marginal since the process is difficult
to regulate and measure with precision and a substantial element of
judgment enters into the practice of the process, even on a
day-in-day-out routine basis. Further, the process is lengthy,
often requires the use of cranes or other auxiliary equipment to
manipulate, hold and control the position of the die block during
the salt bath treatment. The blocks, which are custom made, are of
different sizes, shapes and widths, and this non-uniformity makes
it even more difficult to properly reduce the hardness at the
inside corner of the shank cut-out.
[0011] In summary the operating drawbacks to the salt bath system
may be summarized as follows:
[0012] 1. Salt pot has to be replaced twice a year at a cost of
approximately $4,000.
[0013] 2. The salt bath is a toxic waste and disposal is
difficult.
[0014] 3. Salt pot is labor intensive.
[0015] 4. Salt pot has to be in a special, protected location.
[0016] 5. Splash and inhalation from the salt is dangerous to the
operator.
[0017] 6. Periodic cleaning is necessary.
[0018] 7. Salt sticks to sides--has to be washed off.
[0019] 8. There is a danger of explosion due to the presence of
water or ice on the die block.
[0020] There is therefore a need for a method and apparatus for
preventing cracking at the shank-body junction of die blocks which
is speedy in application, requires minimal handling of the die
block to be treated, minimal auxiliary equipment during processing,
eliminates the use of hot, liquid salt baths with their above
described drawbacks, and gives predictable and duplicatable results
over the range of sizes, shapes, and compositions of die blocks
currently produced.
SUMMARY OF THE INVENTION
[0021] The invention is a shank-body drawing or tempering system
utilizing electric heat that eliminates the need for the currently
used salt-baths with their attendant drawbacks as described above,
yet which can process all shapes, sizes and compositions of die
blocks in a speedy, efficient and reproducible manner with
consistent results, while requiring only a fraction of the cost of
capital equipment and operating costs of salt baths, including
savings in manpower, space and consumable materials.
[0022] In a first embodiment of the invention paddle shaped
induction heater means are placed in operative contact with a
ferrous workpiece and an enclosure which does not transmit
induction currents, said paddle including induction heating coil
means having a capacity to heat the critical areas of the die block
to any desired depth and any degree of softness using well known
operating parameters currently utilized in induction heating
devices. Preferably a die block is placed, in a shank down
position, on a non-magnetic base and an induction heating paddle is
placed in contact with the shank the exposed portion of the paddle
being blocked off with non-magnetic material. The water cooled
copper tube induction coil, which is encased in a non-magnetic
jacket, is activated for a sufficient period of time, depending on
size, shape and composition of the workpiece, to draw the
shank-body to a condition in which cracking is either eliminated or
drastically reduced as contrasted to the results currently achieved
with salt baths or other means.
[0023] In another embodiment of the invention the die block after
hardening but either before or after a shank is formed in the back
side (i.e.: the non-working surface) of the die block is subjected
to infrared heat. The infrared heat is preferably generated by
tungsten halogen lamps which are arranged to direct the radiant
energy at the surface to be treated. While no limits on the length
of the waves of the electromagnetic spectrum have been positively
established, good results have been obtained with short wave
radiation, i.e.: 0.78 to 2.0 .mu.m.
DESCRIPTION OF THE DRAWING
[0024] The invention is illustrated more or less diagrammatically
in the accompanying drawings wherein:
[0025] FIG. 1 is a view of a current prior art salt bath process
and system for eliminating cracking at the shank-body junctions of
die blocks;
[0026] FIG. 2 is a top plan view of the system of the invention
showing a die block being treated;
[0027] FIG. 3 is a front view of FIG. 4 with parts omitted for
clarity;
[0028] FIG. 4 is a view of a die block with which this invention
may be used, the die block being illustrated in a final machined,
shank up position;
[0029] FIG. 5 is a perspective, partly diagrammatic view of the
induction heating paddle used in the invention;
[0030] FIG. 6 is a perspective view, in an open position, of a
simple non-insulated infrared furnace utilizing linear tungsten
halogen tubes arranged in a rectangular shape corresponding to the
shape of the surface of the illustrated die block which is to be
softened;
[0031] FIG. 7 is a perspective view of the infrared furnace of FIG.
6 in an operating position;
[0032] FIG. 8 is an infrared heating profile in a non-insulated
furnace with a surface hold at 1320.degree. F. for 3.5 hours;
and
[0033] FIG. 9 is a hardness profile for an infrared heat treated
die block.
DETAILED DESCRIPTION OF THE INVENTION
[0034] In the following detailed description of the invention like
reference numerals will be used to refer to like parts from Figure
to Figure in the drawing.
[0035] Referring first to FIG. 1 the current procedure, labeled
Prior Art, for reducing cracking at the shank-body junction of a
die block is there illustrated. A die block is indicated generally
at 10, the die block having a shank 11 and a body indicated
generally at 12. The die block is shown positioned shank down on a
special basket 13 in a salt bath 14 held in tank 15. If the
vertical dimension of the shank is about 2 inches, which is a
conventional shank dimension of ferrous alloy die blocks currently
intended for impact forging, such as hammer machines, it will be
noted that the depth of the bath is about 3-4 inches, and thus
about 1-2 inches of the body 12 of the die block 10 is submerged in
the bath 14. The depth to which the block is submerged can be
adjusted as needed by adjustment mechanism 16. Since the block 10
can be quite large, for example two feet or more in width together
with lengths into double figures, the block represents a very
substantial heat sink. As a result, to heat a block, or several
blocks if the tank 15 is used to capacity, a large number of
calories will be absorbed by the blocks from the hot liquid and
hence temperature measuring equipment must be used to continuously
monitor the temperature of the bath, and provisions made to add
heat to the bath, usually gas burners located beneath the tank. It
will be seen that the shank-body junction on either side of the
shank has had a fillet formed therein, indicated at 17 and 18. Even
with such procedures and precautions, cracking remains a problem. A
typical notch crack, as it is called, is indicated at 19. If the
crack is severe enough it may extend all the way through to the die
face 20 in which event the die is either a total loss or a large
amount of rework, including welding and possibly even banding, must
be performed, to put the die back into working condition. Even if
the crack extends only part way into the body 12 and assuming the
operator is alert enough to notice it after it begins, the die must
be immediately taken out of production and reworked. Hence down
time with all the well known adverse consequences of lost
production, are encountered. It should be understood that, more
often than not, the block 10 will not have a shank 11 when salt
bath treated. A shanked block has been shown for ease of
understanding and particularly to illustrate crack 19.
[0036] Referring now to FIGS. 2, 3 and 5 a table is indicated
generally at 25, said table being composed of a material which does
not conduct induction heating currents. A stainless steel or even a
granite or suitable ceramic material may be used in the
construction of table 25. The table has a front edge 26, left edge
27, right edge 28 and rear edge 29. A backing plate is indicated
generally at 30, the lower portion of which, in this instance, is
butted against rear edge 29 of the table 25. As can be best seen in
FIG. 3, backing plate 30 extends upwardly a substantial distance so
that its front face 31 forms an abutment wall of considerable
height.
[0037] Referring now to FIG. 5 an indication heating means which
may be referred to as a paddle is indicated generally at 35. Paddle
35 is an induction heating coil system composed of a length of
continuous, hollow copper tubing, indicated generally at 36, said
tubing having an inlet 32, an entry run 37, a bend 39, a return run
40 and an outlet 41. The hollow, fluid tight tubing is enclosed in
a steel jacket, indicated generally at 42, whose width and length
dimensions can be of virtually any desired measurements and whose
height can vary to a considerable extent. It will be understood
that the longer the length the greater will be the heat generated,
and hence either the greater must be the cooling water flow rate
through the tubing, or the larger must be the diameter of the
tubing so as to carry enough coolant to remove the heat generated
during the process. It will be understood that the paddle may, if
desired, be made in two longitudinal sections so that one or more
intermediate, mating sections, each with its own length of copper
tubing may be added to the paddle to increase or decrease its width
as desired, the short lengths of tubing in the added sections being
mated to ends of the copper tubing in bend 39. The top end face of
the paddle is indicated at 33.
[0038] Referring now to FIGS. 2 and 3 particularly, the paddle 35
is shown laying flat on the upper surface 32 of table 25, and
butted against the front face 31 of backing plate 30 at the
table-backing plate junction. The relationship of the front edge 43
and the rear edge 44 of the paddle 35 to the backing plate 30 is
shown best in FIG. 2.
[0039] A through hardened die block is indicated generally at 50
resting upon the right end portion of paddle 35. The die block,
which, in this instance, does not have a shank formed in it, is
defined by front side 51, rear side 52, left edge 53, right edge
54, bottom 55 and top 56. As can be appreciated form FIG. 3, the
entire surface area of the bottom 55 of block 50 is in surface
abutting contact with the top surface 33 of the paddle 35.
[0040] It will be noted that the surface area of paddle 35 is
considerably larger in both length and width directions than the
dimensions of block 50. In this condition, and in order to ensure
efficient operation of the induction heating coil paddle 35, the
exposed surfaces of paddle 35 are covered with blocks of material
which do not conduct induction heating currents. In this instance a
large block 60 is placed on the left end portion of the paddle 35.
The right edge 61 of block 60 is placed on the left end portion of
the paddle 35. The right edge 61 of block 60 butts against the left
edge 53 of the die block and the rear edge 62 butts against front
face 31 of the backing plate 30. As can be best seen in FIG. 2, the
left edge 63 and front edge 64 or block 60 slightly overlap the
rear edge 44 and the front edge 43 of the paddle.
[0041] A second block, or blocker, is indicated generally at 68.
The bottom 69 of block 68 overlies, in surface abutting engagement,
the portion of the right portion of paddle 35 which is not covered
by die block 50.
[0042] It will thus be seen that the surface of die block 50 which
is to be drawn is in contact over its entire surface area with
paddle 35, and all portions of the upper surface 33 of paddle 35
which are not covered by the die block have been covered by a
blocker so that the upper surface 33 of the paddle is not exposed
to the atmosphere.
[0043] In FIG. 4 the block 50 has been removed following treatment,
and a shank machined into the non-working face thereof.
Specifically, the shank 21 may, for example, have a width 23 of
about 4 inches with the left and right sides thereof having a
dimension of about 2 inches, and shoulders, or die wings, 71, 72 or
about 101/2 inches, so that the total width of the block is about
25 inches. The left and right sides 73, 74 may be about 9-11
inches, for example, and the length of the sides 16 inches, though
in actuality the length will vary widely. The above dimensions are
only exemplary, and all of them may vary, though a typical range of
the left and right sides of block 70 are on the order of about 2
inches to 31/2 inches. The length dimension of sides 75 and 76 may
be of virtually any size, up to and including 8 or 10 feet.
Alternatively, fillets may be formed at the shank-body
junctions.
[0044] By way of comparison, in the salt bath system a rack is
usually required for pieces up to about 8,000 pounds during
treatment. Above this weight and size tongs, which are controlled
by a crane, must be used. As a consequence, for processing which
requires a rack the piece dimension should have practical optimum
measurements of about 26 inches wide by 48 inches in length by 22
inches in height, with an absolute maximum of about 28 inches wide
and 50 inches long. If no rack is used the preferred optimum
dimensions are about 38 inches wide by 48 inches long with an
absolute maximum of 40 inches wide by 50 inches long. Although the
above figures may vary to some degree form installation to
installation they illustrate the fact that there is a practical
maximum limit to the size dimensions which can be accommodated in
the prior art salt bath system.
[0045] In operation, when the induction coil is energized the
induction current acts only in the metal components, and
specifically only in that portion of the block 50 which overlays
paddle 35. A coolant system, including a pump P, is indicated
generally at 80 for circulating coolant under suitable and
conventional pressures in the copper tubing 37-41. The runs of the
copper tubing are connected to the Power Source in a conventional
manner. As an example, the application of 60 cycle current for from
15-30 minutes will usually be sufficient to raise the temperature
to about 1130.degree. F., which temperature, while sufficient to
adequately draw the shank-body junction area, will not overheat a
cavity which has been previously sunk in the die block. It will be
understood that the term "draw" or "drawing" is used in this
application synonymous with tempering which is carried out
fundamentally for the purpose of precipitating iron carbide from
martensite.
[0046] Although a single paddle which, in this instance spans the
entire distance between the right side of the body and the shank
has been shown, it will be understood that it may be more
convenient in other set-ups to use two small paddles.
[0047] When the system is not in use, no equipment must be
maintained and no special precautions need be taken to ensure the
safety of personnel in the area. The paddle 30 will promptly cool
down to near room temperature after the power is shut off and the
coolant circulated for a few minutes, and the heat pick-up by the
large granite non-magnetic base 25 and the blockers 60, 68 will be
minimal.
[0048] The infrared energy embodiment of the invention is
illustrated in FIGS. 6-10.
[0049] Factors of importance in the use of infrared energy are: (1)
the absorption characteristics of the material being heated; (2)
the power density of the radiating area on the part; (3) the ratio
of convected heat to radiant heat; (4) the geometry of infrared
emitters and reflectors including furnace design; and (5) the type
of control required.
[0050] Infrared energy is the portion of the electromagnetic
spectrum between 0.78 and 1000 .mu.m. The infrared electromagnetic
spectrum can be divided into three divisions: (1) short wave 0.78
to 2.0 .mu.m, (2) medium wave 2.0 to 5.0 .mu.m, and (3) long wave
5.0 .mu.m to 1 mm. The actual emission spectrum of a given source
is dependent upon its temperature. Increasing the source
temperature will result in shorter overall wavelengths of the
energy. This also corresponds to an increase in the overall
emissive power. Increased temperature rise of the part can be
achieved by increasing the heat transfer, dwell time, or the amount
of infrared incident on the target. The wavelength of light
utilized in the herein described system, approximately 1.2 .mu.m,
will allow for maximum percent emissive power. This wavelength is
produced by glowing the tungsten halogen filaments at approximately
4892.degree. F. (2750.degree. C.).
[0051] The infrared furnace of FIG. 6 is a cold wall furnace; i.e.:
only the sample is heated to the desired temperature, and the
furnace utilizes 100 W per linear inch elements. Due to the low
thermal mass of the heating elements, the furnace is capable of its
full heat flux in approximately 2 seconds after start-up Also, due
to its cold wall design, the furnace cools extremely quickly.
[0052] In one demonstration, approximately 12 infrared heat
treatments were performed on 18-.times.22-.times.12-in.-thick steel
block instrumented with 12 thermocouples located at various depths
and locations throughout the block. A maximum of 51.2 kW was
utilized on the top surface (22 by 18 in.) of the steel block with
an infrared flat panel for 47 minutes prior to cutting back the
power to maintain the surface temperature of the block at
1320.degree. F. (716.degree. C.). After 1 hour and 18 minutes, the
furnace had to be held at 21.4 kW to maintain the given
temperature.
[0053] A series of experiments were performed in order to see the
effects of several variables, including: (1) surface oxide--(a)
unoxidized, and (b) heavily oxidized (i.e.: scale); (2) block
insulation--(a) insulating the upper 2.5 in. of the block, and (b)
insulating the entire block; (3) edge heating effects; and (4)
modeling was also accomplished in order to observe approximate
efficiencies.
[0054] The block was initially heated with a heavy oxide scale in
order to observe the effects of this heavy loose scale on the
infrared heating. A second experiment was performed with the
surface of the block ground revealing unoxidized steel. It was
observed that this had little effect on the overall heating due to
a couple of factors. The furnace was positioned over the steel
block as showing in FIG. 7 or that any light not absorbed by the
block would be reflected back by the highly nonabsorbing body and
reflected back to the steel block. The surface of the steel block
exceeded 752.degree. F. (400.degree. C.) in less than 10 minutes
which is the temperature at which oxidation of the steel will occur
and the surface will absorb over 90% of the incident light.
[0055] Due to installation of a new multichannel data acquisition
system and the need for real time power output of the furnace for
modeling, an additional experiment was performed. As can easily be
observed in Table 1, the surface of an approximately 1500-lb die
block can be brought to the upper tempering temperature in less
than 48 min, utilizing less than 52,000 W, and then has to
continuously be decreased to 21,000 W to maintain the surface
temperature.
1TABLE 1 Infrared power flux profile during heat treatment of a die
block Infrared power flux Time at power flux (W) (min, s) 51,525
47, 40 49,625 2 46,841 1 45,181 1 42,933 1, 50 41,809 1, 10 40,685
2, 40 39,614 2, 10 38,704 1, 50 36,830 2 33,725 3, 10 36,402 4, 20
33,136 10, 30 30,995 7, 20 30,246 8 29,443 9 27,837 3, 30 26,980
22, 50 25,695 5, 20 25,321 1, 40 23,554 15, 10 22,483 49, 10 21,413
31, 50
[0056] In a subsequent procedure, a hardened block was treated to
preferentially soften the back 2.5 in. Three thermocouples were
attached to the block to monitor temperature during the softening
process at the surface, 2.5 in. down the side and on the back side.
This block was about two-thirds the size of the block utilized for
all of the temperature profiling of FIG. 7. The block with a
2.5-in. insulation wrap was heat treated at 1320.degree. C. for
31/2 hours with the infrared furnace, and the temperature profile
is shown in FIG. 8.
[0057] The foregoing results indicate that infrared sources can
effectively reduce the hardness of a prehardened die block. The
block hardness was 2.95 BID (429 HB). To verify the softening
effect of the infrared heat source, the following procedure was
used: (1) 0.5 in. of material was removed, and (2) Brinnel hardness
tests were taken over the surface using a 2-by 2-in. grid. This
procedure was performed until the hardness was measured at a
distance of 2 in. below the heated surface. As can be seen in FIG.
9, the hardness 2 in. below the surface is an average of 3.26 BID
(350 HB). The "crowned" shape of the hardness distribution could be
due to the loss of infrared energy from the sides of the block or
from the natural hardness distribution from edge to edge of the
block.
[0058] In conclusion it can be seen that infrared can be readily
utilized to preferentially soften die steel to a given depth.
Results to date suggest efficiencies on the order of almost 86%.
Therefore, combining the fact that the infrared system can be
readily turned on and off in seconds and results in no
environmental hazards, the infrared system has very considerable
cost savings over the conventional salt bath system.
[0059] It will thus be seen that a method and apparatus utilizing
electrical energy has been disclosed for preventing cracking at the
shank-body junction of die blocks which is speedy in application,
requires minimal handling of the die block undergoing treatment,
eliminates the need for the use of auxiliary equipment during
treatment, eliminates the use of hot, liquid salt baths with their
attendant drawbacks-including environmental concerns, and which
gives predictable, and duplicatable, results over a wide range of
sizes, shapes and compositions of ferrous alloys.
[0060] Although a preferred embodiment of the invention has been
illustrated and described, it will at once be apparent to those
skilled in the art that modifications may be made within the scope
of the invention. Accordingly it is intended that the scope of the
invention not be limited by the foregoing exemplary description but
solely by the hereafter appended claims when interpreted in light
of the relevant prior art.
* * * * *