Diffuser system for annealing furnace with water cooled base

A convection diffuser and charge support system for an annealing furnace utilizes a diffuser base assembly that includes a vane-carrying center casting which underlies a charge support plate, and which is perimetrically surrounded by a pair of outer and inner cooling rings. The components of the diffuser base assembly cooperate to define an array of horizontally extending gas circulation passages that are shielded from above by the charge support plate. The horizontal passages extend among a plurality of upstanding heat exchange fins that are carried by the inner cooling ring, and terminate in upwardly extending outer end regions that are defined by grooves formed in the outer cooling ring. A centrifugal fan draws hot gases through a central opening in the charge support plate and conveys the gases radially outwardly through the horizontally extending gas flow passages. The gases flow outwardly through the horizontal passages, among the fins of the inner cooling ring, and are diverted upwardly by the grooves of the outer cooling ring for movement along generally helical flow paths about a charge of material being annealed. The outer cooling ring is provided with a depending, perimetrically extending skirt. In an annealing process, cooling of the hot gases within the furnace enclosure is carried out in a two stage procedure that is initiated sufficiently gradually to avoid collapse of the positive pressure atmosphere within the furnace enclosure.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to the heat treating process known 
as annealing, and, more particularly, to a convection diffuser and charge 
support system with fluid cooled base components for use in an annealing 
furnace, and to methods for carrying out an annealing process by operating 
a water cooled convection diffuser and charge support system in a 
particularly advantageous manner to provide a controlled cooling of gases 
that are circulated within the closed environment of the annealing furnace 
during an annealing process without causing collapse of the positive 
pressure atmosphere of the furnace. 
2. Prior Art 
Annealing is a heat treatment process whereby a charge of material is 
heated to and held at an elevated temperature for a sufficient length of 
time to assure that metastable conditions in the material, such as 
frozen-in strains, dislocations, vacancies, and the like are permitted to 
achieve thermodynamic equilibrium. With ferrous materials, the term 
"annealing" is usually used in the sense of a "full" annealing process 
which involves a change of phase, whereby the metal is heated into the 
austentic region, and thereafter cooled back to ambient temperature to 
develop a softened structure of pearlite and ferrite within the metal. 
Where the charge of ferrous material being annealed has been cold-worked, 
the annealing process is used to soften the material to relieve such 
hardness as has been induced during cold working. Cold-working tends to 
increase the dislocation density of a metal manyfold. By way of example, a 
cold-worked piece of metal may have a dislocation density that is 10.sup.6 
greater than that of an unworked specimen of the same material. Since 
dislocations within cold-worked metal are surrounded by strain fields, the 
greater the number of dislocations, the greater is the magnitude of the 
"free energy" which is stored in these strain fields and which can be 
released during annealing to furnish a driving force that will assist in 
bringing the dislocation density back to within a desired range. 
In order to properly anneal a charge of ferrous material, it is important 
to confine the charge within an enclosure wherein a non-oxidizing 
environment is maintained. The gases which define the non-oxidizing 
environment must be circulated within the enclosure during annealing to 
assure that convection heat transfer takes place efficiently to enable the 
annealing process to be carried out in a reasonable period of time. 
Similarly, during cooling of the charge, proper gas flow is important to 
effect convection cooling. 
Where the charge of material to be annealed takes the form of a plurality 
of coils of rolled steel, the enclosure utilized to surround and support 
the charge conventionally includes an annular base structure atop which a 
vertical stack of the coils of steel to be annealed is supported, with the 
coils positioned coaxially one atop another. The enclosure also includes a 
generally cylindrical shroud which cooperates with the base structure to 
contain the stacked charge of coils and to define an enclosed environment 
within which hot gases of the controlled environment are caused to 
circulate. 
In conventional practice, a fan is disposed in a centrally located chamber 
or hole formed through the base structure for forcing circulation of the 
gases of the non-oxidizing atmosphere throughout the enclosure. The 
conventional flow path for circulation includes a flow of gases downwardly 
through the stack of coils, and upwardly along the outer surfaces of the 
coils. Convector plates are interposed between adjacent ones of the 
stacked coils to provide convection flow paths for diverting some of the 
circulating gases between the ends of adjacent coils. The base structure 
on which the lowermost coil rests is provided with vanes for directing 
gases discharged from the fan outwardly and upwardly about the stack of 
coils. 
While the gas circulation passages of a newly built diffuser base may 
provide a gas flow pattern that is relatively effective in disbursing 
gases throughout the enclosure, once the newly built base has been in 
service for several months, its flow passages often become deformed due to 
thermodynamically induced stress which results in creep growth that 
requires trimming, with the result that the passages no longer operate as 
intended to properly direct gas flow. 
Moreover, inasmuch as the structures which define the vanes of present day 
diffuser bases are traditionally formed as weldments of relatively soft 
steel, the vanes tend to become deformed and/or broken during use, thereby 
further adding to the inefficiency and unpredictability of a diffuser base 
after it has been in use for a significant period of time. Thus, present 
day diffuser bases not only fail to operate efficiently and effectively 
over long periods of time, but also require frequent checking for 
structural integrity, cleaning and repair. 
While proposals have been made to utilize water cooled heat exchanger 
equipment of various types to expedite the cooling of the heated gases 
that are present in an annealing furnace enclosure after a charge of metal 
has been heated sufficiently to anneal it, problems have arisen in efforts 
to implement these proposals. In many instances, the heat exchanger 
equipment has been found to interfere with proper flow of the gases within 
the furnace enclosure. In most instances, the initiation of a flow of 
cooling fluid through the heat exchanger equipment has been found to cause 
so rapid a temperature drop in the gases within the enclosure that the 
positive pressure atmosphere of the gases is "collapsed" such that a 
negative pressure results. The tendency toward creation of a negative 
pressure within the furnace enclosure (the pressure is "negative" in 
comparison to the pressure of surrounding ambient air) has the very 
undesirable effect of causing ambient air to be drawn into the enclosure. 
With the introduction of ambient air, and the oxygen it contains, 
deleterious effects are encured by the charge of metal being annealed. 
In order to overcome the deleterious effects of an unwanted introduction of 
ambient air into the annealing furnace enclosure, it has been found 
necessary, in implementing most prior proposals for the use of water 
cooled heat exchanger equipment in an annealing furnace, to initiate 
operation of the heat exchanger equipment while the gas temperature within 
the furnace enclosure is sufficiently high that the resulting collapse of 
the positive pressure atmosphere within the furnace (and the attendant 
drawing of oxygen containing ambient air into the furnace enclosure) can 
be overcome by re-establishing a positive pressure, non-oxygen-containing 
atmosphere while the charge of metal being annealed is still sufficiently 
hot to permit that the deleterious effect that is occasioned by the action 
of oxygen on the metal to be treated and overcome (i.e., reversed) before 
the charge of metal has cooled to an extent that the deleterious effect is 
retained by the treated metal. 
The need to "turn on" previously proposed heat exchanger equipment while 
the temperature within the closed environment of an annealing furnace is 
relatively high causes the heat exchanger equipment to be subjected to a 
wrenching thermal shock that significantly diminishes the life expectancy 
that this equipment would otherwise enjoy if it were not necessary to 
initiate its cooling function while the temperature within the annealing 
furnace enclosure is so high. Due to the enormity of the thermal shock to 
which the heat exchanger equipment is subjected, its construction must be 
significantly strengthened and enhanced to guard against shock induced 
failure, whereby the physical size of this equipment and the attendant 
extent to which the equipment interferes with the proper flow of gases 
within the furnace enclosure are undesirably increased, and the overall 
performance of the furnace suffers. 
Stated in another way, the implementation of prior proposals for the use of 
fluid cooled heat exchange equipment in the environment of an annealing 
furnace has been found to encounter more problems, and problems of greater 
severity, than would be expected; moreover, many of these implementation 
efforts have been found to fail as the result of components being 
subjected to excessive thermal shock, and/or to be unacceptable in view of 
the deleterious effect that the components have on desirable operating 
characteristics of an annealing furnace. 
3. The Referenced Diffuser System Patent 
The invention of the Diffuser System Patent addresses the foregoing and 
other drawbacks of the prior art by providing a durable, novel and 
improved convection diffuser and charge support system. In preferred 
practice, the invention of the Diffuser System Patent utilizes charge 
support system components that are formed from highly durable, shock 
resistant nodular cast iron, with selected ones of the components 
incorporating cast-in-situ cooling conduits. 
In accordance with the preferred practice of the invention of the Diffuser 
System Patent, a diffuser base, a base-encircling ring, and a plurality of 
charge-support convector plates are all formed as castings of a 
particularly durable material known as nodular iron. Nodular iron is cast 
iron which has been treated while in a molten state with an alloy that 
contains an element such as magnesium which favors the formation of 
spheroidal graphite when the cast iron solidifies, whereby the resulting 
product is more ductile and durable than normal cast iron. 
The casting or castings of the diffuser base define a set of horizontally 
extending gas circulation passages that are shielded from above by an 
integrally formed overlying top wall. The top wall also serves to 
strengthen a plurality of upstanding gas directing vanes that are formed 
as integral parts of the diffuser base casting or castings, whereby there 
is much less tendency for deformation and breakage of the vanes. The 
casting or castings which form the base-encircling ring define an array of 
curved, upwardly opening passages that cooperate with the primary flow 
passages of the diffuser base to direct the gases of the non-oxidizing 
atmosphere along particularly advantageous, substantially helical flow 
paths about the periphery of the stack of coils. 
By forming the base-encircling ring as a structure which is separate and 
apart from the diffuser base, the base and the ring are easily separated 
one from the other for occasional cleaning. Moreover, this feature of 
separability enables the primary gas flow passages formed in the diffuser 
base to extend almost entirely horizontally and to thereby be shielded 
from above by the top wall of the base to prevent debris from falling into 
these carefully configured passages. The passages formed in the 
base-encircling ring comprise, in effect, upwardly curved extensions of 
the horizontally extending primary flow passages formed in the base. When 
the diffuser base is separated from the ring, the passages of both of 
these structures are rendered readily accessible for cleaning and 
maintenance. 
Other features of the invention of the Diffuser System Patent lie in the 
optional use of (1) one or more cast-in-situ cooling conduits provided in 
the base-encircling ring, and (2) a continuous, depending skirt wall that 
is formed as an integral part of the base-encircling ring. The cooling 
conduit or conduits may be utilized during the cool-down part of an 
annealing cycle to assist in cooling such gases as are circulated within 
the controlled environment. The depending skirt extends into an upwardly 
facing annular groove that is conventionally provided in the furnace base. 
The skirt engages a fibrous refractory sealant positioned in the groove 
and thereby assists in effecting a gas-tight seal that prevents ambient 
air from entering the closed controlled environment of the annealing 
furnace. The skirt also shields the surrounded portion of the furnace from 
deterioration. 
SUMMARY OF THE INVENTION 
The system of the present invention provides a convection diffuser and 
charge support system having water cooled base structure components, 
wherein the system incorporates improvements and refinements of features 
that form the subject matter of the referenced Diffuser System Patent. The 
system of the present invention preserves the high degree of efficiency 
with which the system of the referenced Diffuser System Patent circulates 
gases in the closed controlled environment of an annealing furnace, and 
yet provides an enhanced capability for cooling the gases in an 
accelerated but controlled manner once the heating portion of an annealing 
cycle has been completed. 
The present invention provides a convection diffuser and charge support 
system having a water cooled heat exchange capability that functions 
without causing collapse of the positive pressure atmosphere within the 
furnace enclosure, whereby the water cooled components of the system (1) 
may be brought into operation at lower temperatures than is possible with 
systems embodying many prior proposals, and (2) need not be constructed to 
withstand the extraordinary degree of thermal shock to which heat 
exchanger structures of prior proposals are subjected by virtue of their 
need to initiate operation at relatively high temperatures. 
In accordance with the preferred practice of the present invention, a 
charge support structure (which may take the form of either a single 
casting such as is described in the referenced Diffuser System Patent, or 
a mated arrangement of two or more castings as is described later herein) 
is perimetrically surrounded by a pair of outer and inner cooling rings. 
The outer and inner cooling rings preferably are brought into fluid cooled 
operation in a sequential manner when the temperature within the closed 
controlled environment of the annealing furnace has reached predetermined 
relatively low values, whereby the cooling rings are subjected to minimal 
thermal shock but nonetheless function quite effectively to expedite the 
cooling of gases in a particularly desirable manner. Features of the 
invention reside not only in the provision and structural arrangement of 
the outer and inner cooling rings, but also in preferred method of their 
use in an annealing process, as will be explained. 
In accordance with the preferred practice of the present invention, a 
convection diffuser and charge support system for an annealing furnace 
utilizes a diffuser base assembly that is perimetrically surrounded by a 
pair of outer and inner cooling rings. In preferred practice, the 
components of the diffuser base assembly include a vane-carrying center 
casting which underlies a charge support plate, and which cooperate to 
define an array of horizontally extending gas circulation passages that 
are shielded from above by the charge support plate. The horizontal 
passages extend among a plurality of upstanding heat exchange fins that 
are carried by the inner cooling ring, and terminate in upwardly turned 
outer end regions that are defined by grooves formed in the outer cooling 
ring. A centrifugal fan draws hot gases through a central opening in the 
charge support plate and conveys the gases radially outwardly through the 
horizontally extending gas flow passages. The gases flow outwardly through 
the horizontal passages, among the fins of the inner cooling ring, and are 
diverted upwardly by the grooves of the outer cooling ring for movement 
along generally helical flow paths about a charge of material being 
annealed. The outer cooling ring is provided with a depending, 
perimetrically extending skirt. Where the charge of metal being annealed 
takes the form of a vertical stack of coils, convector plates are 
interposed between end regions of adjacent ones of the coils to provide 
flow paths for ducting gases therebetween, and for cooperating with the 
base assembly to provide an apparatus that enables a particularly 
advantageous type of controlled cooling to be carried out as the charge is 
being annealed. 
Especially significant features lie in the provision and utilization of a 
pair of outer and inner cooling rings that perimetrically surround a 
centrally located charge support structure, whereby a dual staged 
implementation of a fluid cooled heat exchange process can be employed, 
with the outer ring (which is preferably formed as a bolted-together 
assembly of relatively heavy castings) can be gradually cooled to start 
the heat exchange process without causing the positive pressure atmosphere 
within the furnace to be collapsed, and with the inner ring being brought 
into cooling operation at a lower temperature whereby its relatively 
lightweight construction is not subjected to so great a thermal shock as 
is the more heavily constructed outer cooling ring. 
Still other features reside in the provision of a charge support structure 
that includes a charge support plate which overlies a central casting, 
with upwardly extending vanes being formed on the central casting for 
cooperating with the charge support plate to define horizontally extending 
gas flow passages through which flows of gases are maintained by a 
centrally located fan; the provision on the central casting of a 
perimetrically extending lip formation for supporting the inner cooling 
ring; and the utilization of interlocking formations on the charge support 
plate and the central casting so that, if radial cracks develop in the 
charge support plate (preferably along radially extending lines of 
weakness that are provided in the casting that forms the charge support 
plate), the segments of the charge support plate will be held in place 
atop the central casting.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, a heat-treating apparatus embodying features of the 
preferred practice of the present invention is indicated generally the 
numeral 10. The apparatus 10 includes a conventional, generally 
cylindrical enclosure 12 having a closed upper end 14 and an open lower 
end defined by a rim 16. The rim 16 extends into an upwardly-opening 
annular groove 18 defined by a conventional support structure 20. The 
groove 18 is provided with a seal 22 of suitable material such as ceramic 
fiber refractory to prevent leakage of such gases as are supplied (in a 
conventional manner by conduits which are not shown) to the interior of 
the enclosure 12 to provide a positive pressure, non-oxidizing atmosphere 
within the enclosure 12. Housed within the enclosure 12 is a charge 30 of 
material to be annealed, depicted in FIG. 1 as including a vertical stack 
30 of three coils of steel 32, 34, 36. 
In accordance with features of the present invention, a diffuser base and 
support structure of novel and improved design, indicated generally by the 
numeral 50, underlies and supports the lowermost coil 32. A convector 
plate 70 is positioned between the coils 32, 34, and an identical 
convector plate 70' is positioned between the coils 34, 36. 
A fan 90 having a rotary impeller 92 is disposed substantially centrally 
with respect to the diffuser base 50 for circulating non-oxidizing gases 
within the closed environment of the enclosure 12. The improved diffuser 
base and support structure 50 is shown somewhat schematically in FIGS. 1 
and 2 as defining gas flow passages 52 which extend horizontally outwardly 
from the vicinity of the fan 90 to the vicinity of a pair of outer and 
inner cooling ring structures 110, 210. The outer cooling ring structure 
110 has grooves 111 formed therein that cooperate to define curved, 
upwardly turned gas flow passages 112 for receiving gases that discharge 
radially outwardly from the passages 52 under the influence of the fan 90, 
and for directing these gases outwardly and upwardly along helical flow 
paths about the outer surfaces of the stack 30 of coils 32, 34, 36, as is 
indicated generally by arrows 115. The inner cooling ring structure 210 
has heat exchange fins 211 that project into the paths of gases that 
discharge from the passages 52 for cooling these gases as they travel 
toward the passages 112, as will be explained. 
The diffuser base 50 includes a center casting 51 that has a central 
opening 54 which surrounds the impeller 92 of the fan 90, and an overlying 
charge support plate 53 which has a relatively smaller diameter central 
opening 55 located atop the impeller 92 of the fan 90. The center casting 
51 and the charge plate 53 cooperate to protectively shield portions of 
the impeller 92 of the fan 90, and to facilitate establishing efficient, 
directionally controlled flows of gases within the environment of the 
furnace enclosure 12. 
Referring to FIGS. 4, 5, 10 and 11 the center casting 51 of the diffuser 
base 50 includes a bottom wall 56 of annular, substantially planar 
configuration. A perimetrically extending lip 57 projects radially 
outwardly along the circumference of the bottom wall 56 to define an 
upwardly facing ledge for receiving and supporting the inner cooling ring 
210. A plurality of curved vane formations 60 extend vertically upwardly 
from the bottom wall 56 and are formed integrally therewith. 
Referring to FIGS. 4, 5, 12 and 13, the charge support plate 53 defines a 
generally planar top wall 58 that rests atop the vane formations 60 and 
cooperates therewith to define the flow passages 52 that are curved (as 
viewed from above), shielded, horizontally-extending channels through 
which gases from the fan impeller 92 flow as they are directed rapdily 
outwardly. As is best seen in FIGS. 1, 2 and 13, the charge plate 53 has 
an annular dependency 61 that surrounds the central opening 55 and 
projects a short distance into the space that is centrally located among 
the inner ends of the vanes 60 of the center casting 51. The dependency 61 
has a circumferentially extending shoulder 63 that engages the inner ends 
of at least some of the vanes 60 to interlock the charge support plate 53 
and the center casting 51 and to prevent undesired relative movement 
thereof. The top wall 58 extends radially outwardly for a distance that is 
slightly farther than does the bottom wall 56 (i.e., the outer diameter of 
the top wall 58 is greater than the outer diameter of the bottom wall 56), 
whereby the top wall 58 serves to shield not only the inner cooling ring 
structure 210 but also radially inward portions of the outer cooling ring 
structure 110 (including the inner end regions of the curved passages 112 
which are formed as grooves 111 in the outer ring structure 110). The top 
wall 58 of the charge support plate 53 serves to engage and support the 
lowermost coil 32 of the charge 30 of metal to be annealed. 
Referring to FIGS. 4-6, the outer cooling ring structure 110 extends 
perimetrically about portions of the center casting 51 and provides a 
spaced array of the grooves 111 (located at spaced locations extending 
along substantially the entire length of the ring 110). Referring to FIGS. 
4, 5, 14 and 15, the inner ring structure 210 resides atop the ledge 57 
such that it closely perimetrically surrounds the center casting 51 at a 
location that is spaced radially inwardly from the outer cooling ring 110. 
The inner cooling ring 210 has a plurality of fins 211 that are arranged 
in groups (typically of eight or nine relatively closely spaced fins), 
with the groups of fins 211 being spaced along the circumferential length 
of the underlying tube 212. The fins 211 cooperate with the vanes 60 of 
the center casting 51 and with the grooves 111 of the outer cooling ring 
structure 110 to duct gases that discharge horizontally from the passages 
52 into the curved, upwardly turned passages 112. The vanes 60, the 
grooves 111, and the fins 211 cooperate to effect an advantageous 
directing of the flows of gases from the fan 90 so that these gas flows 
travel radially outwardly among the vanes 60 of the center casting 51, 
among the fins 211 of the inner ring 210, through the grooves 111 of the 
outer cooling ring 110, and then upwardly along substantially helical flow 
paths extending about the stack of coils 30, as is indicated in FIGS. 1 
and 2 by the arrows 115. 
As is best seen in FIGS. 2, 3, 5, 7 and 7B, the base-encircling outer 
cooling ring structure 110 is preferably formed as a bolted-together 
assembly of castings 113 that take the form of identical arcuate segments. 
Each of the castings 113 has embedded integrally within it a fluid cooling 
conduit 114. The conduits 114 have end portions 116 which depend for 
connection to a conventional fluid circulation unit (not shown). The 
cooling conduits 114 are utilized during the cooling part of an annealing 
cycle to diminish the temperature of the castings 113 of the outer ring 
110 so that the outer ring 110 can likewise serve to reduce the 
temperature of the gases being circulated within the closed, controlled 
environment of the enclosure 12, as will be explained in greater detail. 
As is best seen in FIGS. 2, 3A, 5, 14 and 15, the tube 212 of the inner 
ring structure 210 defines a cooling conduit 214 that has end portions 216 
which depend for connection to a conventional fluid circulation unit (not 
shown). The conduit 214 and its heat conductive fins 211 are utilized 
during the cooling part of an annealing cycle to reduce the temperature of 
the gases being circulated within the closed, controlled environment of 
the enclosure 12, as will be explained in greater detail. 
In accordance with the preferred practice of the present invention, the 
cooling conduits 114 that extend through the outer ring segments 113 are 
formed by pre-forming lengths of steel pipe to assume the desired 
configurations of the cooling conduits 114, filling the pipes with mold 
sand, positioning the pipes in sand molds which are configured to form the 
desired shapes of such nodular iron castings as are required to form the 
segments 113 of the outer ring structure 110 with the pipes positioned in 
the molds in the exact positions where it is desired to provide cooling 
conduits, and with end portions 116 of the pipes projecting beyond the 
mold cavities defined by the molds), whereafter molten iron is poured into 
the molds in the conventional manner to form the castings 113. After 
pouring and cooling, the castings 113 are removed from their molds, the 
sand is removed from the interior of the cooling conduits 114, and the 
cast segments 113 of the ring structure 110 are then connected by bolts 
119, as shown in FIGS. 5, 6, 6A and 7, to form the completed outer ring 
structure 110. 
If necessary to accomodate the diameter of a particular center casting 51, 
metal spacer blocks (not shown) may be installed between the 
bolted-together ends of the segments 113. By forming the outer cooling 
ring or "heat sink" 110 as cast segments that are bolted together, ring 
segments 113 having a given radius of curvature can be utilized, either 
with or without suitable space blocks (not shown) positioned between their 
bolted-together ends, to function about the periphery of center casting 51 
of a range of outer diameters. 
As is best seen in FIGS. 1, 2, 5, 6A, 7 and 7B, the outer ring structure 
110 has, depending from its perimeter, a substantially continuous skirt 
118 which extends into the upwardly opening groove 18 for engaging and 
sealing with the ceramic fiber refractory material 22 carried within the 
groove 18. The skirt 118 not only assists in preventing ambient air from 
entering the closed, controlled environment of the apparatus 10, but also 
serves to surround and shield from deterioration such portions of the 
furnace as underlie the ring structure 110. 
Referring to FIGS. 8 and 9 in conjunction with FIG. 1, the convector plate 
70 is shown as being formed from a one-piece cast structure, having a 
generally annular configuration. Spaced, radially-extending support ribs 
72 extend between spaced, radially-extending open sectors 74. Curved inner 
and outer formations 76, 78 are provided at the inner and outer ends of 
the open sectors 74, respectively, for facilitating the flow of 
non-oxidizing gases between adjacent end regions of the stacked coils 32, 
34. A central opening 80 defines a restricted flow orifice, the size of 
which is selected to assist in providing the desired type of gas flow 
circulation within the controlled, closed environment. The convector plate 
70' is identical to the plate 70 and operates in a similar manner to 
facilitate the desired type of gas flow between the ends of the coils 34, 
36 as well as downwardly through the stack 30 of coils 32, 34, 36. 
Features of the plate 70' which correspond to the described features of 
the plate 70 are indicated in FIG. 1 with "primed" numerals that are 
otherwise the same as the numerals used in conjunction with the plate 70. 
An important aspect of the practice of the present invention resides in the 
use of the outer cooling ring 110 which can be thought of as a relatively 
rugged, very durably constructed "heat sink," in combination with the use 
of the much more lightly constructed inner cooling ring 210 that can be 
thought of as being a very efficient supplemental heat exchange device. 
The nodular iron castings 113 from which the outer ring 110 is formed will 
withstand the rigors that are encountered as the ring 110 is employed to 
withdraw heat energy from hot circulating gases, and to transfer this heat 
energy to flows of cooling fluid that are circulated through the conduits 
114. The durable character of the outer ring 110 enables it to be "turned 
on" (i.e., to have flows of cooling fluid initiated through its conduits 
114) at relatively high temperatures of about 600.degree.-900.degree. F., 
a most preferred temperature being about 800.degree. F. The outer cooling 
ring 110 acts as a "heat sink" that will, in a gradual and unobtrusive 
manner, serve to initiate the expedited withdrawal of heat energy from 
gases being circulated within the confines of the enclosure 12. The flows 
of cooling fluid through the conduits 114 of the outer ring 110 are 
continued until the temperature of the gases within the enclosure 12 has 
been reduced to a predetermined temperature, typically within the range of 
about 150.degree.-300.degree. F., a most preferred temperature being about 
220.degree. F., at which temperature the enclosure 12 can be opened 
without causing deleterious effects to the annealed coils 32, 34, 36 that 
comprise the charge 30. 
The inner cooling ring 210 performs a very efficient transfer of heat 
energy from gases that are circulating within the enclosure to such 
cooling fluid as is circulated through the conduit 214. Preferably the 
inner ring 210 is "turned on" (i.e., has its coolant flow initiated) when 
gases within the enclosure 12 have reached a relatively lower temperature 
than is present when the coolant flows in the outer ring 110 are 
initiated, whereby the inner cooling ring 210 is subjected to a lesser 
"shock" than is incurred by the outer cooling ring 110. Typically the gas 
temperature at which coolant flow is initiated in the inner cooling ring 
210 is within the range of about 400.degree.-600.degree. F., a most 
preferred temperature being about 500.degree. F. The flow of cooling fluid 
through the conduit 214 of the inner ring 210 is continued until the 
temperature of the gases within the enclosure 12 has been reduced to a 
predetermined temperature, typically within the range of about 
150.degree.-300.degree. F., a most preferred temperature being about 
220.degree. F., at which temperature the enclosure 12 can be opened 
without causing deleterious effects to the annealed coils 32, 34, 36 that 
comprise the charge 30. 
While the inner ring 210 is shown as having a single conduit 214 that 
defines a single coolant flow path, this ring too can be formed as an 
assembly of segments (or otherwise) to provide a plurality of cooling 
conduits that define a plurality of coolant flow paths. 
The fins 211 of the inner cooling ring 210 are oriented and structured to 
minimize aerodynamic obstruction, to aid in directing gas flows along 
desired paths, and to maximize heat exchange surface area. Preferably the 
fins 211 are formed from carbon steel but are copper coated or copper 
covered to maximize their heat exchange effectiveness. Because the inner 
ring 210 is subjected to a lesser thermal shock than the outer ring 110, 
the inner ring 210 can have its conduit 214 formed from stainless steel, 
to which the copper covered carbon steel fins 211 are welded. 
The center casting 51 is preferably formed as a single member, using 
nodular cast iron. The charge support plate 53, however, is preferably 
formed from gray iron. While a charge support plate 53 formed from gray 
iron will almost always experience some radial cracking in the environment 
of an annealing furnace, gray iron is nonetheless preferred because it 
tends to retain its configuration, i.e., its top surface will tend to 
remain desirably planar. Other materials, such as nodular cast iron, tend 
not to crack and could be used in place of gray iron; however, gray iron 
is preferred inasmuch as other materials such as nodular iron may tend to 
warp or otherwise distort such that the top support surface they would 
provide to support the charge of metal 30 to be annealed could become 
undesirably non-planar. 
Radial cracking of a charge support plate 53 can be partially controlled or 
at least confined by providing the charge support plate 53 with radially 
extending lines of weakness 59, as is best seen in FIGS. 4, 12 and 13. By 
this arrangement, if radial cracks do form, they will tend to form along 
the lines of weakness 59 thereby, at worst, tending to cause the charge 
support plate 53 to be divided along the lines of weakness 59 into two or 
more segments. The resulting segments are prevented from moving relative 
to the underlying central casting 51 by virtue of the extension of their 
depending formations 61 into the space located among the inner ends of the 
vanes 60 of the central casting 51, and by virtue of the abutting 
engagement of the shoulder 63 with inner ends of the vanes 60. 
While features of the present invention (e.g., the provision of a center 
casting 51, a charge support plate 53, a pair of outer and inner cooling 
rings 110, 210, and convector plates 70, 70') have been described and 
illustrated as being used in combination with each other, it will be 
understood that these features may also be used independently one from 
another. 
Although the invention has been described in its preferred form with a 
certain degree of particularity, it is understood that the present 
disclosure of the preferred form is only by way of example and that 
numerous changes in the details of construction and the combination and 
arrangement of parts may be resorted to without departing from the spirit 
and scope of the invention as hereinafter claimed. While orientation terms 
as "upwardly," "downwardly," "inwardly," "outwardly" and the like have 
been utilized in describing the invention, these terms should not be 
interpreted as being limiting. It is intended that the patent shall cover, 
by suitable expression in the appended claims, whatever features of 
patentable novelty exist in the invention disclosed.