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Title:
APPARATUS AND METHODOLOGIES FOR BATCH ANNEALING
Document Type and Number:
WIPO Patent Application WO/2017/115187
Kind Code:
A1
Abstract:
An annealing furnace and methodologies for batch annealing. The annealing furnace includes a base for stacking one or more coils, a vertically extended outer cover having a first heat source for directly heating the surface of the outer cover and indirectly heating an inner cover. The inner cover is enclosed by the outer cover. The inner cover heats a stack of the one or more coils contained within the inner cover. The annealing furnace also includes a control chamber for circulating a heating media. The control chamber is an enclosed closed space defined by the base and the inner cover. A second heat source is disposed on the top of the outer cover. The second heat source increases the temperature of the heating media near the top end of the stack of the one or more coils.

Inventors:
BAYATI, Hamid (SABIC Technology Center - Jubail, P.O. Box 11669Jubail, 31961, SA)
AL-HARBI, Mansour (SABIC Technology Center - Jubail, P.O. Box 11669Jubail, 31961, SA)
AL-SHAHRANI, Saeed (SABIC Technology Center - Jubail, P.O. Box 11669Jubail, 31961, SA)
Application Number:
IB2016/057441
Publication Date:
July 06, 2017
Filing Date:
December 08, 2016
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
SABIC GLOBAL TECHNOLOGIES B.V. (Plasticslaan 1, 4612 PX Bergen op Zoom, 4612 PX, NL)
International Classes:
C21D9/663; F27B11/00; F27D99/00
Foreign References:
US5380378A1995-01-10
US4621794A1986-11-11
EP0109185A11984-05-23
US20120018931A12012-01-26
US4596526A1986-06-24
US5419699A1995-05-30
US20150001769A12015-01-01
Other References:
None
Download PDF:
Claims:
CLAIMS

1. An annealing furnace comprising:

a base for stacking one or more coils;

a vertically extended outer cover having a first heat source for directly heating the surface of the outer cover and indirectly heating an inner cover,

the inner cover enclosed by the outer cover and wherein the inner cover provides heat to a heating medium to heat a stack of the one or more coils contained within the inner cover;

a control chamber in which the heating media is circulated, wherein the control chamber is an enclosed closed space defined by the base and the inner cover; and

a second heat source disposed at the top of the outer cover, wherein the second heat source increases a temperature of the heating media near a top end of the stack of the one or more coils.

2. The annealing furnace of claim 1, further comprising:

a thermocouple for detecting the temperature of the heating media near the top end of the stack.

3. The annealing furnace of claim 2, wherein the thermocouple is disposed through the center of the stack of the one or more coils.

4. The annealing furnace of claim 1, wherein the second heat source is an electrical resistance element.

5. The annealing furnace of claim 1, wherein the second heat source is a gas fired burner.

6. The annealing furnace of claim 1, wherein the heating media is an inert gas.

7. The annealing furnace of claim 1, further comprising:

a sensor for sensing a composition of the heating media.

8. The annealing furnace of claim 1, further comprising:

a fan to circulate the heating media through the control chamber.

9. The annealing furnace of claim 1, further comprising:

convector plates, wherein the convector plates separate edgewise the one or more coils and provide radial flow of heat between the coils,

10. An apparatus for batch annealing comprising:

a batch annealing furnace having an inner cover and an outer cover having a heat source for heating the inner cover, wherein the inner cover provides heat to a heating medium to heat a stack of one or more coils,

an auxiliar' heat source placed on top of the batch annealing furnace, wherein the auxiliary heat source heats a circulated media near the top section of the stack; a thermocouple disposed near the top section of the stack for detecting a temperature of the circulated media; and

a microcontroller configured to control the auxiliary heat source as a function of the temperature collected via the thermocouple.

1 1. A method for batch annealing, the method comprising:

stacking one or more coils onto a base,

covering the one or more coils with an inner cover of an annealing furnace, wherein the inner cover is enclosed by a vertically extended outer cover having a heat source for heating the inner cover;

depositing an auxiliary heat source on top of the annealing furnace; and controlling a temperature of a heating media near the top section of a stack of the one or more coils using the auxiliary heat source.

12. The method of claim 11, further comprising:

sensing a composition of the heating media; and

controlling the auxiliary heat source as a function of the composition.

13. The method of claim 1 1 , further comprising:

sensing a temperature of the top section of the heating media via a thermocouple; and

controlling the auxiliary heat source as a function of the temperature.

Description:
APPARATUS AND METHODOLOGIES FOR BATCH ANNEALING

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of U.S. Provisional Application No. 62/272,953, filed December 30, 2015. The contents of the referenced application are incorporated into the present application by reference,

TECHN ICAL FIELD

[0002] The present disclosure relates to a batch annealing furnace with auxiliary heat source.

BACKGROUND

[0003] Annealing coiled steel is desirable because cold reduction during manufacture of coiled steel tends to lead to elongation of the grains of the stainless steel thereby greatly distorting the crystal lattice and inducing heavy internal stresses. The steel that results from the cold reduction process is typically very hard and has little ductility. Annealing techniques include batch operations, such as conventional box annealing (also known as batch coil annealing furnaces or bell shaped furnaces) and continuous operations. SUMMARY

[0004] The present disclosure relates to an annealing furnace comprising a base for stacking one or more coils; a vertically extended outer cover having a first heat source for directly heating the surface of the outer cover and indirectly heating an inner cover; the inner cover enclosed by the outer cover and wherein the inner cover provides heat to a heating medium to heat a stack of the one or more coils contained within the inner cover; a control chamber in which the heating media is circulated, wherein the control chamber is an enclosed closed space defined by the base and the inner cover; and a second heat source disposed at the top of the outer cover, wherein the second heat source increases a temperature of the heating media near a top end of the stack of the one or more coils. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] FIG. 1 is a schematic that shows an annealing furnace according to one example;

[0006] FIG. 2 is a schematic that shows an annealing furnace with an electrical auxiliary heat source according to one example;

[0007] FIG. 3 is a flow chart for hatch annealing according to one example;

[0008] FIG. 4 is a graph illustrating variations in temperature during an annealing process of steel coils according to one example, and

[0009] FIG. 5 is an exemplar)' block diagram of a computer according to one example.

DETAILED DESCRIPTION

[0010] Batch annealing is used to improve the ductility of cold rolled steel coils (e.g., coiled steel). Annealing is employed to impart softness, machinability, and metal-working properties to the metal by removing stresses previously imparted to the metal, usually by previous cold rolling operations in which the metal was stressed. Coils are heated to a temperature slightly above the transformation critical temperature range and the coils are held at the critical temperature until the coils have been uniformly heated to the transformation temperature then the coils are cooled. The heat treatment is carried out in an annealing furnace with a protective atmosphere. Purging is another critical step in the annealing process and should take place when the workload is cold. Nitrogen or lean (noncombustible) Exothermic gas are common choices for purging. Dew point, infrared (three-gas analyzers) and oxygen probes may be used to monitor the protective atmosphere. The protective atmosphere is preferably oxygen starved or oxygen free (e.g., less than 1% oxygen).

[0011] Batch annealing is used in a plurality of industries such as steel mill, automotive (exposed as well as unexposed parts), appliances (e.g., refrigerators, washing machines, and dryers), and furniture. A problem encountered through batch annealing of coils is to obtain a uniform temperature. [0012] FIG. 1 is a schematic that shows an annealing furnace 100 according to one example. The annealing furnace 100 includes a base 102 upon which one or more coils 104 may be stacked vertically as shown in FIG. 1 , an inner cover 106, an outer cover 108, a heat source 110, and a fan 112. The coils can be of steel strips, steel wires, steel sheet, and/or any other shape. The inner cover 106 encloses the one or more coils 104. The outer cover 108 encloses the inner cover 106. The inner cover 106 and/or the outer cover 108 preferably form a seal with the base 102 to define an inner sealable space. The inner cover 106 and/or the outer cover 108 are sealable at the base 102 and removable. The outer cover 108 has the heat source 1 10 positioned thereon. The heat source 110 (e.g., which sources heat from one or more of a gas fired burner, electrical resistance elements, and oil fired burner) heats the outside surface of the inner cover 106 which in turn radiates heat to the one or more coils 104 inside the enclosed space. In one example, the heat source 110 may be pipes positioned in a predetermined arrangement along the vertical sides of the outer cover 108. Compressed air which may be heated by natural gas burners is circulated through the pipes. The base 102 has sufficient strength to support at least one coil wherein each steel coil has an axial opening (also known as axial passage or eye of the coil) and an outside surface. For example, the base 102 may be secured to the ground. The base 102 may be of any desired conventional shape such as circular, square, or rectangular. The base 102 may also include insulation materials such as wool fiber refractor}' insulation. The coils are stacked coaxially upon one another on the base 102 wherein the axial passage of each coil (eye) are aligned to form a central axial path. The axial passage is substantially horizontal to the base 102. That is, when one or more coils are stacked, the axis of the axial passage is perpendicular to the base 102, As described further below, the axiai path allows the flow of the heating media through the coils.

[0013] The inner cover 106 is sealed to the base 102 to prevent contamination of the heating media in the inner cover 106. That is, to prevent the heating media from leaking out and to keep atmospheric air from leaking in. A plurality of sealing techniques may be used such as using an O-ring seal, resilient pads, an elastomer bag seal, or the like. The seal is made from heat resistant materials. In addition, the seal is cooled to minimize stress from repeated heat cycles which may lead to thermal fatigue failure.

[0014] Further, a gas inlet (not shown) may be provided to introduce a furnace atmosphere into a control chamber 114 which is an enclosed space defined by the inner cover 106 and the base 102 during the annealing process. The furnace atmosphere is introduced through the gas inlet after an initial atmosphere has been discharged through a gas outlet. The gas inlet and the gas outlet may be used to draw a vacuum in the control chamber 1 14. The furnace atmosphere may be either inert (e.g., nitrogen), hydrogen or some combination of hydrogen and inert (e.g., HNX™). The type of gas or gas mixtures (e.g., endothermic, exothermic, dissociated Ammonia, Hydrogen, Nitrogen-DA, Nitrogen-Hydrocarbon, Nitrogen-H 2. and Nitrogen-Methanol) depends on the metal being treated, the treatment temperature, part contamination limits, and the surface requirements of the product being annealed. The protective gas atmosphere is for preventing surface oxidation in order to meet the high demand on the surface of the cold rolled steel. For example, a 94% nitrogen content loaded with a 6% hydrogen may be introduced to the control chamber through the gas inlet at a rate of 1800 cubic feet per hour.

[0015] In one example, a fan 1 12 may be included in the base 102. The fan 1 12 functions to cool the one or more coils or convectively heat the one or more coils by movement of the heating media (furnace atmosphere) within the control chamber 1 14. That is, the fan 112 circulates the atmosphere within the control chamber 1 14 to allow a transfer of heat to and from the one or more coils 104 to and from the heating media. The base 102 may also include a diffuser member which radially distributes the heating media from the fan 112. [0016] In one example, the fan 112 may be a radial fan. The fan 112 is aligned with the axial path. In one example, the radial fan has a 24 inch diameter capable of a flow of about 5,000 cubic feet per minute up to about 10,000 cubic feet per minute. The radial fan forces the heating media radially away from the center of the inner cover through a base space which communicates from the fan 112 to the annular space between the stack of coils and the inner cover wall. As the atmosphere rises and encounters the top of the control chamber, the atmosphere is directed radially inward by the inner surface of the top of the furnace and then downwardly through the axial path (formed by the aligned eyes of the coils) in the center of the stack of coils under the influence of the fan 112 as shown in FIG. 1.

[0017] In one example, the outer cover 108 may have heat-insulating properties (e.g., ceramic fiber insulation) to retain the heat within an enclosed space defined by the outer cover and the base; on the other hand, the inner cover 106 preferably has heat-transferring properties to transfer the heat to the control chamber 1 14 and ultimately to a stack of coils within the furnace. The coils may be heated to a temperature between 550 °C to 700 °C.

[0018] The use of the fan 1 12 in the base 102 is to circulate heating media in the control chamber 114 and contact the heating media with the stacked coils to heat the one or more coils. The circulating by the fan heats ensures temperature uniformity during the heating process. However, there may still be some non-uniform heat transfer which limits the rate at which heat transfer can take place and/or leads to an inhomogeneous heat profile across the stack of coils. Thus, the annealing furnace 100 includes a second heat source 116.

[0019] The second heat source 116 provides additional heat for an upper section of the stack of one or more coils. That is, the second heat source 116 heats the outer cover which in turn heats the inner cover near the top of the control chamber 114. The heat provided by the second heat source 1 16 results in an increased temperature at the top of the outer and inner covers and consequently a heat patch at the top of the control chamber. The heating media has a temperature spike at the top of the control chamber in comparison to the heat at other locations within the control chamber. As the heating media is directed downwardly through an axial path in the center of the stack the heating temperature at the inner surface of the stacked coils is more uniform than in the absence of the second heat source 1 16. The second heat source 116 may be included inside the annealing furnace 100, e.g., mounted or disposed on an inner surface of the outer cover, disposed on top of the outer cover and/or penetrate through bot the outer and inner covers. The second heat source 116 may be, for example, a gas-fired burner, an electrical resistance element, or other type of heat sources as would be understood by one of ordinary skill in the art.

[0020] In one embodiment, a second axial fan (not shown) may be placed near the top of the outer cover 108 to force the hot atmosphere through the axial path.

[0021] A plurality of thermocouples may be used to monitor the temperature of the heating media within the inner cover 106 and within the control chamber. The thermocouples may be connected to a microcontroller 1 18. The readings from the thermocouples are recorded and stored in the microcontroller 118. A thermocouple 120 may be placed near the top of the control chamber 1 14 to provide temperature measurements of the atmosphere near the upper section of the one or more coils 104.

[0022] The microcontroller 118 controls the heat source 110 and the second heat source 1 16 as a function of the readings. In particular, based on the readings from the thermocouple 120 the microcontroller 1 18 controls the second heat source 16. For example, the second heat source 1 16 may be activated once the thermocouple 120 detects a predetermined temperature. In one example, the heat source 1.10 and the second heat source 116 are activated simultaneously. In addition, the second heat source 116 may be controlled as a function of the heat transfer coefficient of the atmosphere composition detected using sensors. [0023] In addition, the microcontroller 118 may control the admission of the atmosphere through the gas inlet (not shown) into the control chamber 114.

[0024] The annealing furnace 100 also includes a cooling mechanism (not shown) to be activated once the one or more coils need to be cooled during the annealing process as would be understood by one of ordinary skill in the art. For example, the cooling mechanism may be finned cooling tubes carrying water or another heat transfer medium cooled by a heat exchanger and are provided near the base 02.

[0025] The one or more coils 104 may be separated edgewise from one another by one or more diffuser plates 122 or convectors inserted between the top edge of one coil and the bottom edge of an adjacent coil. The diffuser plates permit the atmosphere to flow radially inward through flow paths between the exposed top and bottom edges of adjacent coils as would be understood by one of ordinary skill in the art. The convector plates or diffuser plates have an axial opening which is coaxial with the axial path. Convector plate styles include radial-wedge bar, wedge bar, X-bar, tear drop, or the like. Each convector plate has concentric inner and outer diameters. Flow paths are defined by convector plate formations that extend radially between the inner and outer diameters. The flow paths facilitate the flow of the heating media between adjacent end region (i.e. flow in a radial direction) of the stacked coils during the operation of the annealing furnace 100 which help to achieve uniform heating.

[0026] FIG. 2 is a schematic that shows an exemplar' annealing furnace with an electrical auxiliary heat source according to one example. In FIG. 2, the auxiliary heat source is electrical heater elements 200 such as sinuously shaped resistor ribbons. The electrical heater elements 200 are positioned in the center of the top of the outer cover 108 aligned with the axial path. As described previously herein, the auxiliary heat source heats the atmosphere near the top section of the control chamber 1 14 which in turn heats the inner surface of the coils.

[0027] FIG. 3 is a flow chart for batch annealing according to one example. The process starts by stacking one or more coils onto the base 102, at step S300. More specifically, coils are stacked coaxiaily upon one another with the axial passage of each coil aligned to form a central axial path. Then, the one or more coiis are covered with the inner cover of the annealing furnace at step S302. Alternatively, the annealing furnace may include a door to place the coils to be treated. At step S304, an auxiliary heat source is deposited on top of the annealing furnace. At step S306, the temperature of a heating media near the top section of a stack of the one or more coils is controlled using the auxiliary heat source. The second heat source (auxiliary heat source) allows better control of the heat distribution in the furnace. The auxiliary heat source is activated as a function of readings from thermocouples deposited throughout the furnace. For example, the auxiliary heat source may be activated when the temperature of the top section is within a predetermined range. In one example, the second heat source is activated as a function of the size and number of the coils. In addition, the auxiliary heat source may be controlled as a function of the atmosphere type.

[0028] FIG. 4 is a graph illustrating variations in temperature during an annealing process of steel coils according to one example. Trace 400 shows the variation of temperature with time in a conventional annealing furnace. Trace 402 shows the variation in temperature with time when the annealing furnace includes an auxiliary heat source. As shown in FIG. 4, the annealing furnace with the auxiliary heat source reaches the annealing temperature 602 C faster than the conventional annealing furnace. The exemplary data, shown in FIG. 4, are for furnaces with four steel coils having an average weight of 20.9 t. One advantage of the annealing furnace described herein is the homogeneity of the heat treatment. [0029] FIG. 5 is an exemplary block diagram of a computer 528 according to one example. Alternatively or additionally, the functionality of the microcontroller 118 may also be provided by the computer 528.

[0030] Next, a hardware description of the computer 528 according to exemplary embodiments is described with reference to FIG. 5. In FIG. 5, the computer 528 includes a CPU 500 which performs the processes described herein, for example the algorithm shown in FIG. 3. The process data and instructions may be stored in memory 502. These processes and instructions may also be stored on a storage medium disk 504 such as a hard drive (HDD) or portable storage medium or may be stored remotely. Further, the claimed advancements are not limited by the form of the computer-readable media on which the instructions of the inventive process are stored. For example, the instructions may be stored on CDs, DVDs, in FLASH memory, RAM, ROM, PROM, EPROM:, EEPROM, hard disk or any other information processing device with which the computer 528 communicates, such as a server or computer.

[0031] Further, the claimed advancements may be provided as a utility application, background daemon, or component of an operating system, or combination thereof, executing in conjunction with CPU 500 and an operating system such as Microsoft Windows 7, UNIX, Solaris, LINUX, Apple MAC-OS and other systems known to those skilled in the art.

[0032] In order to achieve the computer 528, the hardware elements may be realized by various circuitr' elements, known to those skilled in the art. For example, CPU 500 may be a Xenon or Core processor from Intel of America or an Opteron processor from AMD of America, or may be other processor types that would be recognized by one of ordinary skill in the art. Alternatively, the CPU 500 may be implemented on an FPGA, ASIC, PLD or using discrete logic circuits, as one of ordinary skill in the art would recognize. Further, CPLI 500 may be implemented as multiple processors cooperatively working in parallel to perform the instructions of the inventive processes described above.

[0033] The computer 528 in FIG. 5 may include an optional a network controller 506, such as an Intel Ethernet PRO network interface card from Intel Corporation of America, for interfacing with a network that may connect one or more annealing furnaces. As can be appreciated, the network (not shown) can be a public network, such as the Internet, or a private network such as LAN or WAN network, or any combination thereof and can also include PST or ISDN sub-networks. The network can also be wired, such as an Ethernet network, or can be wireless such as a cellular network including EDGE, 3G and 4G wireless cellular systems. The wireless network can also be WiFi, Bluetooth, or any other wireless form of communication that is known.

[0034] The computer 528 further includes a display controller 508, such as a NVIDIA GeForce GTX or Quadro graphics adaptor from NVIDIA Corporation of America for interfacing with display 510, such as a Hewlett Packard HPL2445w LCD monitor. A general purpose I/O interface 512 interfaces with a keyboard and/or mouse 514 as well as an optional touch screen panel 516 on or separate from display 510. General purpose I-'Q interface also connects to a variety of peripherals 518 including printers and scanners, such as an OfficeJet or DeskJet from Hewlett Packard .

[0035] The general purpose storage controller 524 connects the storage medium disk 504 with communication bus 526, which may be an ISA, EISA, VESA, PCI, or similar, for interconnecting all of the components of the computer 528. A description of the general features and functionality of the display 510, keyboard and/or mouse 514, as well as the display controller 508, storage controller 524, network controller 506, and general purpose I/O interface 512 is omitted herein for brevity as these features are known.