Abstract:
A diffuser ( 24 ) for an annealing furnace has a plurality of radially extending generally and vertically oriented vanes ( 40 ) for radially directing furnace gases. The vanes have top edges ( 42 ) defining a generally planar support and the top edges of the vanes have a notch ( 38 ) therein for receiving a conduit ( 34 ) preferably ring shaped that extend substantially around a center portion of the diffuser plate. The conduit ( 34 ) is connected to an inlet ( 32 ) for receiving enriching gases and exit ports ( 50 ) circumferentially space about said conduit ( 34 ) passing the enriching gases into the diffuser ( 24 ) to be mixed with ambient furnace gases.

Description:
TECHNICAL FIELD 
   The field of this invention relates to heat treatment apparatus and to improvement in a diffuser with an improved inlet for furnace washing gases. 
   BACKGROUND OF THE DISCLOSURE 
   Bell type annealing furnaces have long been used to anneal and spheroidize stacks of coils such as steel strip, wire or rod. The annealing furnace includes an outer cover with a heat source for example gas burners or electrical heating elements that heats the space within outer cover. An inner cover is positioned in the heated space and seals a charge, commonly stacks of metal coil, in a controlled chamber. Ambient initial atmosphere that contains undesirable gases such as oxygen is discharged from the chamber and is continuously replaced with substantially inert furnace gases supplied from an inlet. These furnace gases, commonly referred to as washing gases, for example nitrogen, are ladened with small percentages of hydrocarbons. The gas is used to promote, transfer and circulate heat transferred through the inner cover and provide washing of the stacks of coils as the coils are heated. The hydrocarbons are used to bond to any free oxygen within the furnace in order to prevent the oxygen from attacking the carbon in the annealing metal. 
   To promote circulation of the furnace gases, a fan is centrally mounted at the base of the furnace. A diffuser plate helps diffuse the furnace gases radially from the central fan radially toward the inner cover of the furnace. Any gases that have been heavily ladened with moisture and other contaminants travel downward and are discharged out through a lower positioned discharge port. Fresh incoming replacement washing gas often referred to as enriching gas is further supplied from the inlet near the bottom of the furnace to be mixed with the previously heated furnace gases. As these gases pass along the inner cover, they are heated up and travel upwards and mix with the previously heated furnace gases. 
   It has been discovered that the relatively cool enriching gases which have an initial temperature of approximately 100° F. often do not adequately mix and heat up with the previously heated furnace gas which are often at temperatures of approximately 1400° F. If the enriching gases in some cases do not reach a minimum adequate cracking temperature of approximately 900°, concentrated forms of hydrocarbons may be deposited on some coils within the chamber. Furthermore, the cooler gases may prevent some metal coils to reach the desired temperature adequate for proper annealing and spheroidizing. These coils within the annealing furnace may undergo an undesirable phenomenon known as carbon pickup which results in an embrittled metal. 
   Statistically, most of the above noted problems occur with the coil stacks closest to the enriching gas inlet. The present inlet for the enriching gases is located under the coil stacks. The coil stacks which are round are positioned on the diffuser plate within a round furnace inner cover of substantially larger diameter. If the diffuser plate does not have an upper plate cover, the enriching gases from the inlet can follow an undesirable flow route directly upwardly within the gap that is present between the round inner cover wall and the round coil stacks to prematurely come into contact with the coil stacks located in proximity above the inlet. 
   What is needed is an improved delivery of furnace enriching gases which will properly be heated and mixed with the previously heated furnace gases to achieve proper mixing, diffusing, and heating before coming into contact with the charge. What is further needed is a diffuser plate which accommodates the improved distribution of enriching gases and provides for the improved diffusion, mixing, and heating of these introduced enriching gases. 
   SUMMARY OF THE DISCLOSURE 
   In accordance with one aspect of the invention, an annealing furnace has an inner cover and base. This inner cover and base define an interior control chamber for heating a charge, for example a stack of coils. The interior chamber has an inlet for receiving enriching gases and an outlet for discharging gases. The furnace has a central fan for circulating furnace gases and a diffuser member for radially distributing furnace gases from the fan. 
   A ring shaped conduit is fluidly connected to the inlet. A plurality of exit ports are circumferentially spaced about the ring shaped conduit for distributing incoming enriching furnace gases from the inlet about the diffuser member. 
   Preferably, the exit ports have varying sizes and becoming larger farther downstream from the inlet. In one embodiment, the conduit has a circular shape in cross-section and the exit ports are positioned at a radially outer section of the ring shaped conduit and set at an angle between a vertical and horizontal position. The vertical position being defined at the radially outer portion of the ring shaped conduit. For example, the angle can be approximately 45° below the vertical position. It is desirable that the diffuser has a plurality of vanes with a top edge for providing generally planar support for the charge. The top edges have notches therein for nesting the ring shaped conduit therein such that the ring shaped conduit lies wholly below the top edges of the diffuser vanes. 
   It is desirable that the diffuser member has a sliding connection with the inlet to allow for relative radial movement of the ring member with the inlet as the ring member expands and contracts during heating and cooling cycles of the annealing furnace. 
   According to another aspect of the invention, a diffuser for an annealing furnace has a plurality of radially extending generally and vertically oriented vanes for radially directing furnace gases. The vanes have top edges defining a generally planar support. The top edges of the vanes have a notch therein for receiving a conduit that extends substantially around a center portion of the diffuser. The conduit has an inlet for receiving enriching gases and exit ports circumferentially spaced about the conduit for passing the enriching gases into the diffuser to be mixed with ambient furnace gases. 
   Preferably, the conduit is arcuate and may be ring shaped. Also preferably, the conduit has a circular shape in cross-section and the exit ports are positioned at a radially outer section of the ring shaped conduit and set at an angle between a vertical and horizontal position. For example, the angle is approximately 45° below the vertical position. In one embodiment the exit ports have varying size and become larger farther downstream from the inlet. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Reference now is made to the accompanying drawings in which: 
       FIG. 1  is an elevational segmented view of an annealing furnace in accordance with one embodiment of the invention; 
       FIG. 2  is plan view of the diffuser plate and ring assembly shown in  FIG. 1 ; 
       FIG. 3  is an enlarged side elevational view showing the ring shaped conduit nested in the diffuser plate; 
       FIG. 4  is a fragmented enlarged top plan view showing the slide connection of the ring shaped conduit member with the inlet member; 
       FIG. 5  is a bottom plan view of the ring shaped conduit illustrating the exit ports; and 
       FIG. 6  is a top plan view illustrating the diffuser and ring shaped conduit under a charge of coil stacks. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to  FIG. 1 , an annealing furnace  10  has an outer cover  12  and an inner cover  14 . Heating sources  16  are installed on the outer cover  12  to provide heat in the space  17  between the inner and outer covers. The heating sources for example may be in the form of gas burners or electrical resistance elements. The inner cover  14  rests on a seal  18  at the floor  21  to seal off the interior chamber  20  within cover  14  from the ambient exterior. While outer cover  12  may have heat insulating properties to retain the heat within, inner cover  14  has heat transferring properties to expeditiously transfer the heat from the space  17  to the interior control chamber  20 . 
   A squirrel cage fan  22  is centrally positioned at the floor  21  of the interior chamber  20  to provide radially outward flow of furnace gases through a diffuser plate  24 . The furnace gases are directed radially outwardly through the diffuser plate  24  until they encounter the inner cover  14  where the gases are heated and then rise along the inner cover  14 . As the gases approach the top of the interior chamber  20 , they are directed then radially inward and then downwardly through an open center channel  26  formed between the stacks of coils  28  that are to be heat treated, e.g. annealing, or spheroidizing. 
   The initial atmosphere within the chamber  20  present when the chamber is sealed is discharged through discharge port  30  and replaced by a mix of incoming furnace gases, for example, a 94% nitrogen content ladened with a 6% hydrocarbon content in the form of propylene. The furnace gases are provided from inlet  32  at continuous flow rates of approximately 1800 cubic feet per hour. 
   As shown more clearly in  FIGS. 2 and 3 , the inlet  32  is connected to a ring shaped conduit  34  through leg  36 . The ring shaped conduit  34  is nested in notches  38  cut within the vanes  40  of the diffuser plate  24 . The vanes  40  extend generally in a vertical plane and extend radially to direct gas flow from the central fan  22  toward the inner cover  14 . The conduit is sized such that that the top portion of the conduit does not extend above the top edges  42  of the vanes  40  and a gap  54  is formed below conduit  34  and floor  21 . The top edges  42  are substantially planar and are used as a planar support for the coil stacks  28 . The coil stacks  28  as shown in  FIGS. 1 and 6  may be mounted about a central spindle  44  that has a lower end plate  46  that functions to hold the coils of metal from falling off the spindle and forms a relatively generally planar surface that can rest on the top edges  42  of the vanes  40 . 
   As shown in  FIG. 4 , the incoming leg section  36  has a sliding sleeve connection with inlet  32 . This sliding or slip connection may be formed by having the inlet  32  and the incoming leg  36  made from 3 inch pipe both received in opposite ends of a 3½ inch sleeve  48 . A gap  49  is provided between the inlet  32  and leg  36  to allow for outward radial expansion of the ring shaped conduit  34  during heating cycles within the furnace. 
   As shown in  FIGS. 3 and 5 , the ring shaped conduit  34  has a plurality of exit ports  50  circumferentially spaced about the conduit ring. The exit ports  50  have varying sizes, being smaller closer to the inlet  32  and increasing in size as they become farther downstream from the inlet port  32 . The sizing should be arranged such that the each exit port  50  provides for the same flow rates of gas therethrough. The exit ports  50  are positioned to be approximately 45° canted down from the radially outer vertical position about the cross section of the ring as clearly shown in  FIG. 3 . 
   In operation, when the furnaces in initially closed, furnace gases pass at a rate of about 1800 cubic feet per hour through inlet  32  and then is forced to go through conduit  34  before it enters into the interior chamber  20  to mix with and help displace the initial atmosphere through discharge port  30 . The furnace gases, often referred to as washing gases are heated and circulate via the fan  22 . The gases are displaced radially outward through the diffuser plate  24  and through the gap  54  provided below ring shaped conduit  34  toward the inner cover  14  where the gases then rise. As the furnace gases approach the top section of the chamber  20 , they generally flow radially inward and then downward through central channel  26  to return to the fan and repeat the cycle. 
   Heavily laden gases with moisture and contaminants sink to the bottom and are discharged through discharge port  30 . As enriching gases from inlet  32  continuously flows in. Enriching gases have an initially relatively cool temperature of 100° F. The enriching gases must pass through the leg  36  and the longer conduit ring  34  and is relatively evenly distributed out through all the exit ports  50 . Because the leg  36  and ring  34  are within the heated interior chamber  20 , the conduit  34  and leg  36  can provide for a significant heat transfer to the enriching gases flowing within. The incoming enriching gas is heated as it travels through the conduit  34  and is further heated and diluted with a larger portion of furnace gases in the diffuser plate as the enriching gases leave the exit ports  50 . The enriching gases further mix and heat with the furnace gases as they flow radially outward through the diffuse place until they encounter the inner cover  14 . They rise along the inner cover  14 . The enriching gases that were initially at a cool approximately 100° F. are now adequately mixed and heated with the existing furnace gases before they encounter contact with the coil stacks  28 . 
   The introduction of the enriching gases through the exit ports  50  is controlled by the sizing of the exit ports  50  about the conduit ring  34  and their canted position about the cross-sectional circumference of the conduit. The 45° angle provides for an exit port  50  which has the gas flow neither encountering a venturi effect from the surrounding flow of the furnace gases nor encounter resistance from back pressure from furnace gas turbulence about the conduit. The minimization of any venturi effect or back pressure allows for a controlled and predictable flow of enriching gas. 
   Flow of the enriching gases about a full 360° about the diffuser plate  24  under the stacks of coil  28  prevents a concentration of cool enriching gases against the coil stacks and thus prevents carbon pickup on the stacks and also provides for adequate annealing temperatures for all stacks. 
   In this fashion and improved diffuser plate with a conduit ring substantially reduces of the amounts of carbon pickup and improperly or inadequately annealed and spheroidized coil stacks. A more efficient annealing process with a higher yield and less waste is thus provided. 
   Variations and modifications are possible without departing from the scope and spirit of the present invention as defined by the appended claims.