Heat retaining curtains for reheat furnace discharge openings and charging openings

A discharge opening for a reheat furnace is shielded with a pair of metal woven wire mesh curtains each secured above the discharge opening and hanging to the bottom of the opening. Each curtain preferably is formed from multiple parallel coplanar ribbons, each extending from above the discharge opening to the bottom of the discharge opening. The mesh curtains are fabricated from a sag resistant metal alloy. Embodiments are described for accommodating slots which receive discharge lifter members for removing heated metal workpieces from the furnace. A preferred mounting apparatus employs one or more fibrous thermal insulation strips above the discharge opening. A counterweight mounting apparatus urges the fibrous thermal insulating strips against the outer wall of the furnace.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a closure for the discharge opening of a 
steel reheat furnace comprising sag-resistant metal alloy mesh curtains 
formed from plural steel mesh ribbons. The metal alloy mesh curtains also 
may be employed in the charging opening of certain reheat furnaces. The 
purpose of the metal alloy mesh curtains is to retain heat energy within 
the reheat furnace by reducing the opportunities for heat to leave the 
furnace. 
2. Description of the Prior Art 
Steel reheat furnaces are employed to reheat steel workpieces to a 
temperature at which the steel may be mechanically worked outside the 
reheat furnace. U.S. Pat. Nos. 3,148,868; 3,716,222; 3,749,550; 4,427,371. 
The steel workpieces are heated to temperatures of 2000.degree. F. and 
higher. The reheat furnaces have refractory ceilings, side walls and 
floors and include plural heat sources such as gas burners or radiant gas 
burners. Horizontal rails are mounted within the furnace to support steel 
workpieces as they move through the furnace from a charging opening at one 
end to a discharge opening at the other end. The temperature gradient 
across most reheat furnaces develops the highest temperatures adjacent to 
the discharge opening and usually significantly lower temperatures 
adjacent to the charging opening. A refractory slab customarily is 
positioned within the furnace adjacent to the discharge opening. Multiple 
slots are presented within the refractory slab to receive fingers for 
directing and withdrawing the forward-most workpiece from the refractory 
slab through the discharge opening. 
With the advent of high temperature radiant heaters, it is now possible to 
develop high temperatures within a reheat furnace adjacent to the charging 
openings. Reheat furnaces provided with high temperatures adjacent to the 
charging openings will benefit from the curtains of this invention. Such 
installation will be separately discussed in this specification which is 
principally concerned with discharge openings. 
Heated steel workpieces are removed from the reheat furnace through the 
discharge opening, and new workpieces are introduced through the charging 
opening whereby a continuous inventory of steel workpieces at gradually 
increasing temperatures is maintained inside the reheat furnace. 
Customarily the discharge opening is in line with the movement of steel 
workpieces through the furnace; however the discharge opening may be 
angled with respect to the line of movement, e.g., U.S. Pat. No. 
4,492,565. 
Customarily one or more vertical steel or composite assemblies are provided 
to function as doors at the charging opening and at the discharge opening. 
U.S. Pat. No. 4,669,939. The doors are raised vertically by cables to 
expose the charging opening or discharge opening and the doors are 
maintained in an elevated position until a steel workpiece or workpieces 
enters the charging opening or is withdrawn through the discharge opening. 
Immediately thereafter the doors are lowered to obstruct heat loss through 
the openings. A significant heat loss occurs during the time when the 
doors are elevated and the openings are exposed. The heat loss is usually 
greatest at the discharge opening where the temperatures the highest in 
the structure. 
It is known to employ steel mesh curtains at the charging opening of a 
reheat furnace which heretofore experienced elevated temperatures of the 
order of 1500.degree. F. At these temperatures, woven mesh curtains of 
ordinary steel are not adversely affected by the temperature exposure. 
However steel mesh curtains have not been employed at the discharge 
opening of reheat furnaces where the furnace heat loss can be severe. 
Some reheat furnaces may experience much higher temperatures as a result of 
recently available radiant heat sources which can be located adjacent to 
the charging opening of reheat furnaces. In such reheat furnaces, the 
curtains of this invention will provide reliable heat retention. 
STATEMENT OF THE PRESENT INVENTION 
According to this invention metal alloy wire mesh curtains can be 
fabricated from plural ribbons of high temperature, sag-resistant metal 
alloy wire, formed from chromium/iron/aluminum alloys, e.g., Kanthal APM, 
the Tradename of a chromium/iron/aluminum alloy of Kanthal, AB. Such 
curtains may be employed at the discharge openings of reheat furnaces and 
at the charging openings of certain reheat furnaces. A discharge opening 
normally includes a water-cooled lintel defining the horizontal top of the 
discharge opening. 
The curtains are fabricated from multiple, substantially co-planar vertical 
ribbons of metal alloy wire mesh, each secured at its top adjacent to the 
water-cooled lintel. Each ribbon is freely suspended, terminating at or 
adjacent to the bottom level of the furnace discharge opening. The ribbons 
are secured to a horizontal steel conduit through which cooling water is 
delivered. In a preferred embodiment, two distinct curtains are mounted in 
horizontally-spaced-apart relation so that the exiting workpieces engage a 
first curtain and thereafter engage a second curtain while moving through 
a reheat furnace discharge opening. Preferably the interior metal alloy 
mesh curtain confronting the heat source is fabricated from thin wire and 
has relatively small mesh openings. The exterior metal alloy curtain is 
fabricated from thicker coarse wire and has larger mesh openings. Thus the 
interior metal alloy curtain is less permeable to gas flow and more 
resistant to heat transmission than the exterior metal alloy mesh curtain. 
The advancing workpieces displace the metal alloy mesh curtains in the 
direction of movement of the workpiece with the result that the bottom 
portions of the metal alloy mesh ribbons are draped or dragged across the 
upper surface of the exiting steel workpieces, providing limited openings 
for facile heat loss through the furnace openings. 
In furnaces having slots adjacent to and beneath the discharge openings, 
means are provided for separately sealing the slot openings to retard heat 
loss through the slot openings. A preferred slot opening means is a ribbon 
of the mesh material corresponding in width to the slot width, extending 
from above the discharge opening to the bottom of a slot. Alternatively a 
wide curtain may be provided with one or more depending curtain sections 
which correspond dimensionally to a slot opening. 
Means are provided to raise a slot opening curtain above the top of the 
slot prior to entry of a lifter into a slot to preclude engagement of the 
lifter with a slot opening curtain during entry of a lifter into a slot. 
An alternative slot cover is a counter-weighted, heat resistant sheet which 
is pivoted about a horizontal axis outboard and beneath a slot exterior 
opening. This sheet permits use of discharge opening curtains having a 
straight, horizontal bottom edge. The heat resistant sheet pivots in 
advance of a lifter, rests beneath a lifter during workpiece extraction, 
and is restored to a slot-opening cover position as the lifter is 
withdrawn from the slot. Preferably the pivot means includes water-cooling 
capacity. 
Accordingly a principal object of this invention is to provide metal alloy 
wire mesh ribbons to form one or more vertical curtains which normally 
substantially entirely cover the discharge opening of a high temperature 
reheat furnace and resist heat loss through the opening. 
Another object of this invention is to provide high temperature, 
sag-resistant metal alloy wire mesh ribbons forming a curtain for 
discharge openings of a high temperature reheat furnace, together with a 
water-cooled beam from which the steel wire mesh ribbons are suspended. 
A still further object of this invention is to provide novel structure for 
securing metal alloy wire mesh curtains in heat retaining relation with a 
discharge opening of a high temperature reheat furnace. 
Another object of this invention is to provide means to cover slot openings 
in those furnaces which employ slots and correlated lifters to extract 
heated workpieces through a discharge opening. 
A still further object of this invention is to provide a heat resistant 
curtain structure outboard of the charging opening of those reheat 
furnaces which have high temperatures developed adjacent to the charging 
opening.

FIG. 1 illustrates a typical reheat furnace 10 having a refractory top wall 
11 and floor 12, refractory side walls 13 and refractory end walls 14, 15. 
The refractory end wall 14 has a charging opening 16. The refractory end 
wall 15 has a discharge opening 17. Extended through the furnace is a 
horizontal beam assembly 18 which supports steel workpieces as they move 
through the furnace from the charging opening 16 to the discharge opening 
17. Multiple heat sources such as gas burners 19 are mounted at selected 
locations on the top walls of the furnace. Additional gas burners 19' are 
provided beneath the horizontal beam assembly 18. A flue 20 receives the 
gaseous products of combustion which are generated within the furnace 10. 
Thermal energy in the combustion gases is usually recovered in heat 
regenerators. A removable closure member 21 is provided to obstruct the 
charging opening 16 to permit introduction of steel workpieces which are 
to be heated in the furnace. A removable closure member 22 is provided to 
obstruct the discharge opening 17 except when heated workpieces are 
removed through the discharge opening 17. The temperature within the 
reheat furnace 10 increases from the charging opening 16, where steel 
workpieces at ambient temperature are introduced into the furnace, to a 
maximum temperature at the discharge opening 17 where steel workpieces, 
heated to an appropriate working temperature are withdrawn from the 
furnace 10. A refractory hearth 80 is usually provided adjacent to the 
discharge opening 17 to support the steel workpieces prior to withdrawal 
from the furnace 10. Slots 81 are presented in the refractory hearth 80 to 
accommodate extending fingers 82, called "lifters", (FIGS. 5, 9, 10) of a 
typical workpiece withdrawal device which elevates a finished workpiece 
above the refractory hearth 80 and removes the finished workpiece through 
the discharge opening 17. Because the temperature of the reheat furnace 10 
adjacent to the discharge opening 17 is a maximum temperature, 
substantially more heat energy is lost from the furnace through the 
discharge opening 17 than through the charging opening 16. Temperatures as 
high as 2500.degree. F. are common in reheat furnaces adjacent to the 
discharge opening 17. The removable closure members 21, 22 are frequently 
formed from rectangular slabs of refractory materials in appropriate metal 
frames. Supporting means (not shown) are required to lift the closure 
members 21, 22 up and away from the furnace opening 16, 17, respectively. 
According to the present invention, two horizontally spaced-apart curtains 
are presented at the discharge opening 17 to serve as a closure for the 
opening 17 to retard loss of heat energy through the discharge opening 17. 
The spaced-apart curtains are formed from aligned metal alloy woven mesh 
ribbons which are secured at their top in a common vertical plane and can 
move and drape over a steel workpiece moving outwardly from the furnace 
through the discharge opening 17. 
Woven metal alloy mesh ribbons are illustrated in FIGS. 2 and 3. The 
ribbons 30, 31 include helical wire warp elements 33, 34 and straight wire 
woof elements 35, 36. The warp elements 33, 34 are nested to establish 
aligned passageways through which the woof elements 35 may be positioned. 
The exposed ends 37, 38 of the straight wire woof elements 35, 36 
respectively, are deformed to establish suitable heads which prevent 
withdrawal of the woof elements in either direction from the aligned 
passageways established by the nested, modified helical warp elements 33, 
34. Such woven mesh is readily available in ordinary carbon steel and 
other specialty metal alloys. Steel mesh ribbon similar to the ribbons 30, 
31 have been employed in steel reheat furnaces to provide double steel 
mesh curtains at the charging opening of the furnaces where conventionally 
the existing temperatures will not adversely affect the curtains. 
The metal alloy woven mesh ribbons of the present invention are fabricated 
from sag resistant metal alloy, typically an alloy of 
aluminum/chromium/iron and more particularly from a specific 
aluminum/chromium/iron alloy known as Kanthal APM. The APM alloy has 
significant sag resistance at temperatures of 2500.degree. F. and higher. 
The warp elements 33 of FIG. 2 are larger than the warp elements 34 of FIG. 
3. Similarly the woof elements 36 of FIG. 2 are larger than the woof 
elements 35 of FIG. 3. As a result the metal alloy woven mesh ribbon 30 
(FIG. 2) is more porous, i.e., has larger openings, than the steel woven 
mesh ribbon 31 of FIG. 3. 
TYPICAL INSTALLATION 
Referring to FIGS. 4 and 5, the discharge end of a reheat furnace 10 has a 
refractory end wall 15 with a generally rectangular discharge opening 17. 
A water-cooled lintel 40 (FIG. 5) customarily is provided along the top of 
the opening 17 to provide structural support for the end wall 15. A 
typical water-cooled lintel construction is illustrated in FIG. 8 wherein 
a lintel 40a is formed from a horizontal beam 41 having a web 42 and 
flanges 43. Steel sheets 44 are welded to the flanges 43 by means of 
continuous welds 45 to define water passageways 46 through which cooling 
water is delivered when the reheat furnace is at operating temperatures. 
Reverting to FIGS. 4 and 5, a steel mesh curtain support assembly 50 is 
suspended from pivot blocks 51 which are secured to the outside of the 
furnace end wall 15, above and spaced from the discharge opening 17. The 
curtain supporting assembly 50 is urged into contact with the furnace 
lintel 40 by means of a counterweight 52 secured to the distal end of a 
shaped steel bar 53 which is pivotally secured to the pivot block 51. In 
one embodiment, FIG. 7, the curtain supporting assembly 50 includes a 
generally horizontal beam 54 and a pair of generally rectangular steel 
tubes 55, 56 which are spaced-apart and secured along their top edge to 
the bottom flange 57 of the beam 54. Unobstructed pipes 58, 59 are secured 
through the vertical walls of the conduits 55, 56 at spaced locations. 
Water passageways 60, 61 are presented along the conduits 55, 56 
respectively. A strip of thermal insulation 62 as shown in FIG. 6, is 
secured to the curtain supporting structure 50 by means of a metal alloy 
strip 63 and a metal alloy rod 64 which extends through the tubes 55, 56 
respectively and is secured by an appropriate means such as a threaded nut 
65. The thermal insulation strip 62, as seen in FIG. 6, includes randomly 
oriented refractory fibrous material 66 which is wrapped with a thin 
cylindrical fibrous mesh 67 and is obtained as a cylindrical strip. The 
steel bar 63, when compressed against the insulation 62, deforms the 
circular cross-section to a bean shape as illustrated in FIGS. 6, 7. 
An alternative to the bean-shaped thermal insulation strip 62 is 
illustrated in FIG. 12 as a "tadpole" shape strip 69a formed from a 
cylindrical strip of refractory fibers 66a deformed by a metal alloy rod 
63a secured through the insulation strip 62a by means of bolts 64a. 
It will be observed from FIG. 7 that the insulation strip 62 abuts the 
water-cooled lintel 40 along two edges 68, 69. As a result of the 
mounting, the thermal insulation 62 or 69a prevents stingers from 
appearing at the top of the discharge opening 17. Stingers are known in 
the reheat furnace art to be finger-like flames of burning gas and 
incandescent air-borne particles. 
It will be observed from FIG. 7 that curtains 70, 71 are secured to and 
depend from the supporting structure 50. The interior curtain 70 is 
retained at its upper end between the water-cooled conduit 56 and the 
thermal insulation strip 62. The exterior curtain 71 is retained at its 
upper end between the two water cooled tubes 55, 56. The exterior woven 
mesh curtain 71 is formed from relatively coarse woven ribbons and the 
interior woven mesh curtain 70 is formed from less coarse metal alloy 
woven mesh. Accordingly the interior curtain 70 is less permeable that the 
exterior curtain 71. 
FIGS. 9 and 10 illustrate steel workpieces 75 supported on horizontal rail 
18. A forward steel workpiece 75a has entered the discharge opening 17 and 
has engaged the interior curtain 70a. It will be observed that the forward 
pieces 75a are supported above the refractory hearth 81 by lifters 82 
which elevate and withdraw the workpiece 75a. The lifter 82 is shown 
partially withdrawn from the slot 80. 
The exiting workpiece 75a advances the interior curtain 70a which begins to 
drape over the exiting workpiece 75a. The exiting workpiece is identified 
as 75b in FIG. 10 where a substantial portion of the exiting workpiece 75b 
has advanced through the discharge opening 17 and engages both steel 
curtains 70b and 71b which are flexible in the direction of movement and 
readily drape over the exiting workpiece 75b. 
It will be observed from FIGS. 9 and 10 that the workpieces 75 are in 
end-to-end contact in the manner of a pusher furnace when supported on the 
horizontal beam 18. It should be apparent that the steel workpieces 75 may 
be spaced-apart as they would be presented in a walking-beam furnace. 
EXTRACTOR SLOT ACCOMMODATION 
In those reheat furnaces having slots for receiving lifters, additional 
means may be provided for retaining furnace heat which might otherwise 
escape through the slots when the lifters are inactive. 
In one embodiment the curtains of FIGS. 4, 5 are comprised of wide ribbons 
70, 71 and narrow ribbons 83 having extensions 83a which cover the slot 
81. Some means must be provided to elevate the narrow ribbon extension 83a 
prior to entry of a lifter 82 into the slot 81. One means is a chain 84 
adapted to elevate the narrow ribbon extensions 83a (not seen in FIG. 4) 
and 86a as particularly shown by the chain 84a on the right hand slot of 
FIG. 4. As more clearly seen in FIG. 5, the chain 84 is connected to an 
appropriate connector 85 which is secured to the narrow ribbon extension 
83a of the outer ribbon 83. A corresponding inner ribbon 86 has a narrow 
ribbon extension 86a which is joined to the narrow ribbon extension 83a by 
an appropriate connector 87. Thus when the chain 84 is pulled upwardly, 
the narrow ribbon extensions 83a, 86a will rise above the top level of the 
slot 80 and permit the lifter 82 to enter into the slot 80 without 
interfering with the curtains. It should be observed that the remainder of 
each curtain 83, 86 remains in a heat shielding position (FIG. 5) while 
the lifter 82 is in the slot 80. 
In FIG. 13, an embodiment of the invention is illustrated wherein the 
external curtain 71 comprises multiple wide ribbons 71' and multiple 
narrow ribbons 83. The narrow ribbons have a narrow ribbon extension 83a 
which corresponds in profile with the oven slots (not see in FIG. 13). 
An alternative embodiment for retarding loss of heat from the furnace 
through the slots is illustrated in FIGS. 14, 15, 16, 17 where a generally 
flat sheet 90 constitutes a heat shield which covers the furnace slot 80 
when the lifter 82 is inactive. The curtains 83, 86 terminate above the 
top of the lifters 82. FIG. 14 illustrates the normal orientation of the 
components with the lifter 82 in an inactive position. The sheet 90, 
preferably a flat sheet, may be equipped with appropriate reinforcing 
strips 91 for rigidity and is preferably secured in a pivotal manner below 
and outside the discharge opening 17. A water carrying pipe 92 is secured 
to the furnace wall by means of brackets 93. The sheet 90 is rotatably 
secured to the pipe 92 by brackets 94. An appropriate counterweight 95 
normally maintains the sheet 90 in a generally vertical, slot shielding 
position as shown in FIG. 14. The leading workpiece is indicated as 75c in 
FIG. 14; as 75d in FIG. 16; and as 75e in FIG. 17. 
When the lifter 82 enters the slot 80, the sheet 90 is pivoted by contact 
with the under surface of the lifter 82 with the upper edge of the sheet 
90 and thereby the slot 80 is unobstructed to the entry of the lifter 82. 
When the lifter 82 is extracted together with a forward workpiece 75e, the 
heat shielding sheet 90 commences to return to its normal, generally 
vertical position as shown in FIG. 17 through the gravity effect of the 
counterweight 95. After the lifter 82 has completely withdrawn from the 
discharge opening 17, the heat shielding sheet 90 is automatically 
restored to its heat shielding disposition of FIG. 14. 
Referring to FIG. 18, there is illustrated a charging opening of a reheat 
furnace similar to that illustrated in FIG. 1 where corresponding numerals 
indicate corresponding elements. 
The furnace chamber 13 is enclosed, in part, by a floor 12 and vertical 
wall 14. A charging opening 16 is provided in the vertical wall 14. Within 
the furnace chamber 13, steel workpieces 75f are supported on generally 
horizontal rails 18. A supporting table 96 provides generally horizontal 
support for incoming steel workpieces 75g. It will be observed that the 
incoming steel workpiece 75g has its leading edge in contact with the 
trailing edge of the steel workpiece 75f which has already entered into 
the oven chamber 13. Pusher means (not shown) are provided to advance the 
steel workpieces 75g, 75f and the other steel workpieces which are in the 
pusher advancement mode. 
A curtain supporting structure 97 includes a mounting block 98 secured to 
the outer surface of the vertical wall 14 above the charging opening 16. A 
crank arm 99 is pivotally connected to the mounting block 98 at one end 
and pivotally connected at the other end to a water cooled curtain holder 
100 which includes a tubular member 101 adapted to receive cooling water 
through a water receiving conduit 102 and to discharge heated cooling 
water by means (not shown). The curtain holder 101 has secured to one 
surface a fibrous thermal insulation batt 103, similar to the batt 62 of 
FIG. 6. The batt 103 engages the outer surface of the vertical wall 14 to 
retain heat within the chamber 13 and to preclude "stingers" which are 
blowing gas-borne particles. The vertical wall 14 also may include a water 
cooled lintel 104 similar to the lintel 40a described in connection with 
FIG. 8. 
The curtain holder 101 supports two alloy mesh curtains 105, 106 which 
correspond respectively with the curtain 70, 71 previously described. That 
is, the curtain 105, adjacent to the furnace wall 14, has a finer mesh and 
is less gas pervious than the other curtain 106 which is remote from the 
vertical wall 14. 
As the steel workpieces 75f and 75g advance into and through the furnace 
chamber 13, the curtains 106, 105 drape over the top surfaces of the steel 
workpieces 75f, 75g and serve to retain heat within the chamber 13. The 
curtains 105, 106 in their normal depending position, i.e., when there are 
no workpieces in the opening 16, will hang to a level near the bottom wall 
of the opening 16. 
While similar structural devices have been employed heretofore to retain 
heat at the discharge openings 16 of reheat furnaces, the composition has 
not heretofore been critical because prior reheat furnaces had a 
relatively low temperature in the chamber 13 adjacent to the charging 
opening 16. With the advent of radiant heaters, substantial elevated 
temperatures may exist within a reheat furnace, even adjacent to the 
charging opening 16. The metal alloy mesh proposed in this invention will 
permit the use of prior art curtain structures for the charging openings 
of such reheat furnaces. The alloy is described as a high temperature, 
sag-resistant metal alloy wire, formed from chromium/iron/aluminum alloys, 
e.g., Kanthal APM, the trademark of a chromium/iron/aluminum alloy of 
Kanthal, AB.