MXPA99002362A - Induction heaters to improve transitions in continuous heating systems, and method - Google Patents

Abstract

A heating system (50) and method for heating a metal strip (40) to within a predetermined temperature tolerance range while the metal strip (40) serially travels through the heating system (50). The heating system (50) has at least one preceding heating section (52), at least one induction heating section (54), and at least one following heating section (56), with the heating sections (52, 54, 56) being serially arranged. The metal strip (40) is heated to below the Curie point of the metal strip (40) in the preceding heating section (52). Next, the metal strip (40) is heated to, at a maximum, approximately the Curie point in the induction heating section (54). Then, the metal strip (40) is heated to above the Curie point and to within the predetermined temperature tolerance range in the following heating section (56).

Description

INDUCTION HEATERS TO IMPROVE THE TRANSITIONS IN CONTINUOUS HEATING SYSTEMS AND METHOD BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the heating of metal strips that pass through a continuous heating system. More specifically, this invention relates to the heating of metal strips to predetermined temperature tolerance scales. 2. Description of the Prior Art Generally, continuous heating furnaces are used for continuous or galvanized annealing of strip, strip or metal plate, which will be referred to collectively as "strip". Specific heating procedures are established to impart the desired characteristics to the strip. Each heating method has a predetermined peak metal temperature tolerance scale at which the strip must be heated upon leaving the furnace regardless of the dimensions of the strip. Such furnaces can be broadly classified into those that are electrically heated and those that are heated by combustion gas. Gas-fired furnaces can be subclassified in the type of irradiating tube and the type of direct ignition. Considering energy efficiency, cost of operation, initial investment and other factors, gas-fired furnaces can be much more advantageous than electrically heated furnaces. When strips of metal of different dimensions are treated by continuously heating, it is common practice to practice the serial passage of the strips through the furnace. Often, but not always, the strips are welded together before being fed continuously through the furnace. The region between the strips is referred to as a transition. Transitions can be classified into categories for changes in strip thickness, strip width, thermal cycle, strip velocity, or any combination of the four previously mentioned parameters from one order, or coil to the next. When transitions pass through the furnace system, special control techniques are required to change furnace conditions due to the large thermal mass of the furnace system. Ovens of the prior art have been limited in the scale of allowable transitions. If the transition is very large, the furnace will produce a large amount of strip that does not meet the tolerances (usually ± -6.6 ° C) above the desired peak metal temperature. This strip outside the tolerance is a generally slag product because the physical properties of this strip will not be those of the specification.

The prior art describes various techniques used to improve furnace performance for transitions. The simplest of these techniques is to use the direct feed control to prepare the oven for the incoming coil. This has typically been done with mathematical models that simulate the heat transfer between the furnace and the strip to predict the optimum operating conditions of the furnace for the transitions. This method is auxiliary, although it is still subject to the relatively slow response speed of a furnace ignited by a main fuel or heated by electrical resistance and the associated thermal mass. Another prior art is to have a type of preheating system that can respond relatively quickly, such as convection, direct ignition, cross-flow or induction. Those units can then be used to add heat to one of the coils in the transition to produce a peak metal temperature that is not normally possible with the conditions that exist within the furnace at the time of transition. All of these units have been installed at the entrance of the main heating section and all have been used, in various ways, to improve the response capacity of the process. See U.S. Patent No. 4,239,483 (lida) (induction heaters). These units are generally used in conjunction with the previously mentioned model formation to extend the range of transitions. However, the strip is subject to the conditions of the furnace, which results in the preheating section having a very limited impact on the peak metal temperature. In theory, the ideal location for such a rapid response heating device would be where the oven strip comes out so that the oven does not limit the utility of the device. However, this is not practical with the technology currently available. Most induction heaters are limited to raising the temperature of a strip to its Curie point, which is approximately 704.4 ° C-760 ° C. Since the typical peak metal temperature is greater than the Curie point, those induction heaters are not useful at the end of the furnace. Induction heaters that heat the metal strip higher than the Curie point are not practical in continuous annealing due to very small coil openings and / or large losses in heating efficiencies. Cross-flow heaters can be used at these temperature scales, although they are not practical from a physical point of view. Convection heating on this temperature scale is also impractical from a mechanical and maintenance point of view. Direct-ignition heaters can not be used at the higher peak metal temperatures due to the tendency to oxidation of the strip surface.

Therefore, there is a need for a way to reduce or eliminate metal strips outside the specification that occur when transitions travel through the furnace.

BRIEF DESCRIPTION OF THE INVENTION The present invention is directed to a continuous strip heating system and the method of operation thereof, the heating system having induction heaters placed between a plurality of heating sections of a continuous strip heating system, wherein the Inclusion of the induction heaters allows for less strip slag as long as the heating system has changed its temperature to accommodate changes in dimensions and other heating requirements of the strip. Accordingly, it is an object of the invention to provide a heating system and the method for heating a metal strip to within a predetermined temperature tolerance range as long as the metal strip travels serially through a system of heating. The heating system has at least one preceding heating section, at least one preceding heating section, at least one induction heating section, and at least one subsequent heating section, with the heating sections that are placed in series. The metal strip is heated to below the Curie point of the metal strip in the previous heating section. Next, the metal strip is heated to a maximum of about the Curie point in the induction heating system. Then, the metal strip is heated above the Curie point and within the predetermined temperature tolerance range in the later heating section. Other objects and additional advantages will appear in the future.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an elevation view of the heating system comprising an induction heating section between the front and rear heating sections. Figure 2 is a perspective view of a combined strip comprising two strips of different dimensions. Figure 3 is a schematic representation of the connection between the heating system and programmable control means. Figure 4 is a sectional view of a W type tube heater used in the heating sections. Figure 5 is a flow diagram of a method for heating a metal strip in a heating system comprising an induction heating section. Figure 6 is a flow chart of a method for optimally locating an induction heating section in a heating system. Figures 7 to 10 are graphs of the temperatures of the heating system during the change of the temperature of the heating system to accommodate a change in strip dimensions.

DESCRIPTION OF THE PREFERRED MODALITY (S) MODEL (S) Referring to the drawings, in which similar reference numerals designate similar components, Figure 1 illustrates the heating system 50, or furnace, for heating a continuously moving combined strip 40 within a tolerance range of Peak metal temperature or some other predetermined temperature tolerance range. The heating system 50 is located upstream of a wetting section and downstream of a pre-heating section in a continuous steel strip annealing line. Other embodiments of the invention are useful in the process requiring heat treatment of a metal strip, such as continuous strip galvanizing lines or continuous plate furnaces. The heating system 50 has an upper section 86 and a lower section 88 which extend through an anterior heating section 52, an induction heating system 54. and a subsequent heating section 56 placed in series. Other embodiments of the invention have a plurality of anterior and / or posterior heating sections. Additional embodiments of the invention have the heating sections 52-56 positioned vertically. Even other embodiments have the heating sections in a plurality of housings or in a single housing. Those arrangements allow the combined strip 40 to enter the previous heating section 52 at the inlet 53, pass through three heating sections, and exit through the outlet of the subsequent heating section 57. The combined strip 40 of moves through the heating sections 52, 54 and 56 in steps 60, 62 and 64 respectively. A passage is a space that extends from the upper section 86 to the lower section 88 or vice versa, through which the combined strip 40 passes. In the embodiment of Figure 1, there are ten steps in the previous heating section 52 , a step 62 in the induction heating section 54, and thirteen steps 64 in the rear heating section 56. While the steps in the embodiment of FIGURE 1 are vertically oriented, other embodiments of the invention may have oriented steps in other directions, such as horizontal. Additional embodiments of the invention may have a single horizontal passage extending from the entrance of the previous heating section to the outlet of the subsequent heating section. In the negotiation of the steps, the combined strip 40 is moved on the rollers 70, the rollers of the tensiometer meter 72, the clamping rollers 74 and the steering rollers 76, which are located in the upper and lower sections 86 and 88. While all the rollers hold the combined strip 40 as it travels through the passages, some of the rollers have additional purposes. The tensiometer rollers measure the tension in the combined strip 40 while the clamping rollers 74 change the tension in the same. Steering rollers 76 control the direction of the combined strip 40. Referring now to Figure 2, the combined strip 40, comprising a first strip 10 and a second strip 16, have been processed in the heating system 50. he understands that the strip refers to a length of metal that is, although not limited to, a strip, at least one band, or at least one plate. The first strip 10 has a front end 18 and a rear end 20. The rear end 14 of the first strip 10 and the front end of the second strip 16 are welded together in a transition 22. In other embodiments of the invention, the first and second strips 10 and 16 can be joined through suitable means or they can be separated. In embodiments of the invention processing separate strips, the strips are at least close to each other, with a region from the rear end 14 to the first end which is the transition 22. The recessed portions 36 and 38 of the first and second strips 10 and 16, respectively, are adjacent to the transition 22 and are the portions of the strips that were not heated within approximately the peak metal temperature tolerance range. This results in the recessed portions 36 and 38 being out of specification material, and therefore slag. The rest of the first and second strips 10 and 16 are larger portions 32 and 34 of the strips respectively. Larger portions 32 and 34 are within the peak metal temperature tolerance range and are material within the specification. A main objective of the heating system 50 is to minimize the size of the smaller portions 36 and 38 and maximize the size of the larger portions 32 and 34, thereby maximizing the production of the material within the specification. Referring now to Figure 3, in the preferred embodiment of the invention a programmable control mechanism 300 directs the heating of the previous heating section 52 and the subsequent heating section 56 and the use of the induction heating section. 54. In other embodiments of the invention, the control mechanism may not be programmable. The programmable control mechanism 300 directs the heating by means of a programmable control system 302 which is interconnected with the previous heating section 52, the induction heating section 54 and the subsequent heating section 56 through the duct 304 to direct the operations of the heating system 50. In other embodiments of the invention, a wireless transmission system (not shown) can be placed in place of or in conjunction with the conduit 304. The instrumentation in the heating system 50 measures at least one portion of the variables (described below) of the combined strip 40 and of the heating system 50 and generates variable signals 310. The conduit 304 sends the variable signals 310 from the heating sections to the programmable control system 302. The additional variables that are not measured by the instrumentation are determined by an operator of the ac system and are manually entered into the programmable control system 302 by means of an input device 306. There are numerous variables that are received by the programmable controller 302. Some of the variables of the first strip are length 24, width 28 and thickness 29. Some of the variables of the second strip are the length 26, the width 30 and the thickness 31. Other important variables in the heating of the first and second strip 10 and 16 include the initial temperature of the strips, the speed of the strips through the heating system 50 and the outlet temperature of the strips. Instrumentation can be used to measure a portion of these variables, ie thermocouples, distance indicators, speed indicators, etc. The heating system also has variables that influence the heating of the strip, such as the temperature at different locations of the first and subsequent heating sections 52 and 56. In the embodiment of Figure 1, the first and subsequent heating sections they are divided into twelve combustion zones 101-112. Other embodiments of the invention may have more or less combustion zones. At least one thermocouple (not shown) located near the middle of each zone 101-112 measures the zone temperatures, generates a signal 310. and transmits the signal to the control system 302. The preferred embodiment of the invention has two or more thermocouples in each combustion zone. Other embodiments of the invention may have different variables. The programmable control system 302 analyzes the variable signals 310 and the variables manually entered in the context of a thermal model 308 to determine the new operating parameters for the heating system 50. The thermal model 308 is a mathematical model that simulates the transfer of heat between the heating system 50 and the combined strip 40 and the results of the changes in the operating conditions of the heating system to determine the new operating parameters. After the analyzes, the programmable control system 302 transfers the new operation parameters within the operation parameter signals 312 which are sent to the heating system 50 via the conduit 304 to direct the operations thereof. In other embodiments of the invention, the operating parameters are determined by an operator of the heating system who manually, or by means of a control system, directs the operations of the heating system 50. The operating parameters of the system direct different components of the heating system. Referring now to Figures 1 and 4, the heating components of the first and subsequent heating sections 52 and 56 are type W radiant tube heaters, ignited by gas 80. Those heaters are operated in an atmosphere of 0-100% of hydrogen, the remainder being nitrogen or another designated prepared atmospheric gas. A tube heater is comprised of a hollow tube 150 formed in the orientation and shape of a "W" with an upper member 152 and a lower member 154. A pilot burner 156 and a main gas inlet 158 extend into the member upper, provided gas 159 which enters tube 150 and which is ignited with a fiame 160, generating combustion products 162. Pilot burner 156 is a premix type pilot burner designed for automatic operation. The combustion products 162 move through the interior of the tube 150 and out of the lower member 154 within an exhaust gas manifold 164. Since the burners are suction-type burners, the exhaust fans (not shown) extract the combustion products 162 within the exhaust gas collector 164. The air 166 enters the lower member 154 through an air inlet 168. The air 166 is heated by the combustion products 162 through the use of a recuperator 170 in the lower member 154, thereby generating air 172 heated to 315.5 ° C to 426.6 ° C in the preferred embodiment of the invention. The heated air 172 is moved towards the upper member 152 by means of a vertical hollow member 174 which extends between the upper and lower members, the heated air 172 is used in the combustion gas 158. Other embodiments of the invention use other types, dispositions and quantities of heaters.

The tube heaters 80 are heated on both sides of the passages 60 and 64 to heat the combined composite strip 40 traveling therethrough. The tube heaters 80 are oriented such that the tubes 150 are parallel to the combined strip 40 as it travels through the passages. The tube heaters 80 are placed up to about eleven tube heaters on each side of a passage. The placement and control of the tube heaters 80 are designed around twelve independent combustion zones 101-112 in the first and second heating sections 52 and 56, as shown in Figure 1. The combustion products 162 may be through additional heat recovery steps after being collected by the exhaust gas harvester 164. In one embodiment of the invention, the combustion products from the zones 101-112 come out in two separate exhaust systems. The first exhaust system discharges zones 101-106 and the waste heat in this stream is used in the preheating section. The second exhaust system discharges the zones 107-112 and the wetting section to a heat recovery system. Other embodiments of the invention may not recover the waste heat in the preheating zone or in a waste heat recovery system. The operation parameter signals 312 direct the ignition speed of the tube burners 80 by means of a control valve in the gas supply of each zone (not shown). The signals 312 also control a damper position to control the negative pressure in the exhaust gas collector 164 (not shown). In addition, the signals 312 vary the speed of the exhaust fans to control the main suction pressure in the exhaust gas collector 164. All of these operations result in the control of temperatures in the combustion zones 101-112 by the mechanism control 300 through the direction of the signals 312. The operation parameter signals 312 also direct the components of the induction heating section 54, which is induction heaters 82. In the preferred embodiment of the invention, the induction heaters 82 are soienoid induction heaters. In the embodiment of the invention shown in Figure 1, the induction heating section 54 is comprised of five induction heaters 82 through which the combined strip 40 passes. In other embodiments of the invention, the heating section Induction can be an individual induction heater. Induction heaters are well known in the art and are described in U.S. Patents 4,678,883 (Saitoh, et al.) 4,585,916 (Rich), 4,054,770 (Jackson eta l), 3,444,346 (Russell et al) and 2,902, 572 (Lackner, et al), which are incorporated in their totalities. In the induction heater 82, the combined strip passes longitudinally through a magnetic field, inducing electric currents therein. Those induced electric currents heat the strip 40 as a result of the electrical resistance of the strip. The magnetic field is generated by the electric current moving through coils in the induction heaters 82 placed around the combined strip 40 (not shown). The control mechanism 300, through the signals 312, directs the electric current to be supplied to the induction heaters 82. In one embodiment of the invention, the overall length of each coil is approximately 91.44 cm, with a minimum of approximately 60.96 cm of space between the adjacent coils. The internal coil dimension is approximately 20.32 cm by approximately 254 cm. The induction heaters 82 are cooled by a closed-cycle cooling water system designed to provide a liquid cooling medium at 32.2 ° C. The cooling system comprises an evaporation-type cooling tower, a cooling tower fan, a tower circulation pump, and a pump and supply system for providing the liquid cooling medium to the induction heaters 80. Other embodiments of the invention include different induction heaters, others configurations of induction heaters and other means for cooling induction heaters. Before the first strip 10 enters the heating system 50. the programmable control mechanism 300 sends the operation parameter signals 312 to the first and subsequent heating sections 52 and 56 to heat the different zones in the sections to obtain a first temperature profile. The first temperature profile is established by the temperatures of the combustion zones 101-112 in which the first strip 10 can exit the heating system 50 within a first predetermined temperature tolerance range. Likewise, a second temperature profile allows the second strip 16 to exit the heating system 50 within a second predetermined temperature tolerance range. The temperature profiles are set in the first and subsequent heating sections 52 and 56 and not in the induction heating section 54 because the first and subsequent heating sections transfer the heat to the strip and the heating section, the which allows temperature measurements in the heating sections and, therefore, a temperature profile that is indicative of the transfer of heating to the strip in a specific zone. Since the induction heaters heat the strip directly, the temperature in the induction section is not indicative of the amount of heat transfer to the metal strip and does not constitute a part of the temperature profiles established by the control mechanism 300 However, the programmable control mechanism 300 can not direct the heating system 50, or more specifically the first and subsequent heating sections 52 and 56, to the transition between two temperature profiles instantaneously. While the variables of the strips do not change appreciably, there is little need for the programmable control mechanism 300 to direct the combustion zones 101-112 to make rapid changes in the temperature profile. However, the large thermal masses of the heating sections restrict the speed at which the programmable control mechanism 300 can make the transition of the combustion zones between the two temperature profiles. The more drastic the differences in the variables of the first strip and the variables of the second strip, the greater the difference in the two temperature profiles and the smaller the transition. While the programmable control mechanism 300 is transitioning the heating system 50 between the first and the second temperature profile, part of the first strip 10 and the second strip 16 leaving the heating system are not within the first or second temperature tolerance range, respectively, thereby creating relatively large minor portions 36 and 38 and leading to more slag strip material. However, the programmable control mechanism 300 can direct the induction heaters 82 to rapidly heat the combined strip 40, albeit with much higher energy costs compared to the tube heaters 80. Rapid heating is useful for supplying heating to the strip combined while the programmable control mechanism 300 is transitioning the heating system 50 between the two temperature profiles. This supplemental heating by the induction heating section 54 results in reduced sizes or removal of smaller portions 36 and 38 and reduced or eliminated amounts of off-spec material. When the first strip 10 requires a temperature profile hotter than the second strip, the programmable control mechanism 300 begins to make the transition from the heating system to the second temperature profile, colder while the first strip 10 is still passing through it. To compensate for the increasingly cold temperature profile of the heating system 50 and, therefore, its ability to completely heat the strip, the programmable control mechanism 300 directs the induction heating section 54 to boost the temperature of the first strip 10 so that it leaves the heating system 50 within the first predetermined temperature tolerance range. Ideally, when the transition 22 passes through the heating system 50, the programmable control mechanism 300 has completed the transition of the system between the first and the second temperature profile, thereby eliminating the smaller portions 36 and 38. In practice, the smaller portions 36 and 38 can only be reduced. When the first strip 10 requires a colder temperature profile than the second strip 16, the programmable control mechanism 300 starts to make the transition from the heating system 50 to the second temperature profile, hotter while the first strip 10 is still passing through the same As the transition 22 passes through the heating system, the programmable control mechanism 300 complements the heating of the second strip 16 with the induction heating section 54 until the second temperature profile is reached will reduce or eliminate the out-of-spec material, resulting in a minimization or elimination of the smaller portions 36 and 38 of the first and second strips 10 and 16 The induction heating section 54 is limited to raising the temperature of the combined strip up to the Curie point of the metal, which is about 7044 ° C to 760 ° C for the steel However, the pull a combined 40 requires a peak metal temperature of greater than the Curie point when leaving the rear heating section 56 Referring to Figure 5, in one aspect of the invention it involves heating a metal strip within a tolerance range of predetermined temperature The metal strip is moved serially through a heating system 50 along a path 41 through at least one preceding heating section 52, at least one induction heating section 54 , and at least one subsequent heating section 56, with the heating sections that are placed in series as shown in Figure 1. Typically the length of the path 41 through the previous heating section 52 is about 40% at 50% of the path length through the complete heating system 50. In the first stage 401, the metal strip is heated below the Curie point in the previous heating section. In the next step 402, the metal strip is heated to a maximum of about the Curie Point in the induction heating section. In the next step 403, the metal strip is heated above the Curie point in the subsequent heating section. In the preferred embodiment of the invention, the metal strip is heated to approximately the Curie point in the induction heating section in step 402. As previously stated, the heating system can be located downstream of a preheating section and upstream of a wetting section in a continuous strip annealing line, in a continuous strip galvanizing line, or be another process. Another aspect of the invention optimally locates the induction heating section 54 within the heating system 50 to have an efficient and flexible heating system 50. The location of the induction heating section is determined by where it is capable of raising rapidly the temperature of the combined strip to the Curie point would be more efficient in the continuous production of the combined strip 40 within the tolerance range of peak temperature and, therefore, minimizing the size of the smaller portions 36 and 38 of the combined strip 40 Referring now to Figure 6, the determination of the location of the induction heating section is based on a strip design. metal traveling serially at a design speed through the heating sections serially placed in a pre-induction heating section heating system (not shown) is executed as follows. The first step 501 is to determine a plurality of design strip temperatures at a plurality of locations of the pre-induction heating section heating system, respectively. This determination can be achieved in an appropriate manner, including taking temperature measurements of the strip in the real system, or a similar one, or calculating the theoretical temperatures for each location based on the mathematical model of the system. The next step 402 is to determine a maximum design metal strip temperature increase that is obtained by the design metal strip that travels through the induction heating section at the design speed. The next step 503 is to subtract the maximum design metal strip temperature increase from the Curie point of the design metal strip, thereby defining an optimum design metal strip entry temperature. The successive step 504 is to determine a specific system location having a corresponding strip temperature equal to the optimum design metal strip entry temperature, thereby identifying an optimum design metal strip entry location. the induction heating section. The next step 505 is to insert the induction heating section between two adjacent heating sections and close to the optimum design metal strip inlet location. The induction heating section may be inserted either before or after the metal strip entry location of optimum design, depending on how the heating sections may be separated to accommodate the induction heating section. Preferably, the upstream sections of the induction heating system, also known as the above heating sections, comprise about 40% to 50% of the heating system. In the preferred embodiment of the invention, the above heating section 52 comprises about 40% to about 50% of the heating system 50, and is followed by the induction heating section 54 and the subsequent heating section 56.

EXAMPLE The first strip 10 is a strip of steel 0.119 cm thick and 152.4 cm. The second strip 16 is 0.0762 in thickness and 152.4 cm in width. Both strips have a peak metal temperature tolerance range of 843 ° C ± -6.6 ° C for strips that fall within the specification. However, the first strip 10 requires more heat input to raise its temperature to 843 ° C than the second strip 16 due to its greater mass per length. Referring now to Figure 7, a graph 220 illustrates a steady-state heating condition of the heating system 50 with the first strip 10 passing therethrough. On the horizontal axis 208, the percentage of the length of the heating system is marked, while the vertical axis 209 marks the temperature. The graph 200 has a first temperature curve 202 of the first strip 10, an ideal temperature curve 204, and a heating system temperature curve 206. The first strip temperature curve 202 is a plot of the actual temperature of the first pulls in a plurality of locations in the heating system. The ideal temperature curve 204 is a plot of the ideal temperatures of the first strip at a plurality of locations in the heating system. The temperature curve of! heating system 206 is a graph of the temperatures of the heating system at a plurality of locations in the heating system. The temperature curve of heating system 206 is 804.4 ° C at the inlet of the heating system and 915.5 ° C at the outlet. The temperature curves of the first and ideal strips 202 and 204 are almost superimposed, with an initial temperature of 176.6 ° C and a peak metal temperature of 843 ° C. note that there is a flat portion 203 of the curves 202 and 204 near the middle of the heating system. The flat portion 203 corresponds to a specific location of the induction heating section 54 in the heating system that is approximately 40% of the distance of the heating system. The entire location of the induction heating section is in the above heating section 52 and all locations following the induction heating section are in the following heating sections. Since the induction section is not in use, there is no change in temperature for the current strip or the ideal strip in the flat portion 203. The temperature curve of the heating system 206 is similar to the first temperature profile. However, the temperature curve of the heating system 206 illustrates the temperatures of the heating system at different locations in the heating system. The first temperature profile is distinguishable from the curve in which the profile is the temperatures of the heating zones 101-112 in the heating system 50 which allows the first strip 10 to be heated within the first predetermined temperature tolerance range. Referring to Figure 8, a graph 210 illustrates the heating system 50 when the programmable control mechanism 300 begins the transition from the temperature profile in anticipation to the second strip 16. The graph 210 has a first strip temperature curve 212 , an ideal temperature curve 204, a temperature curve of the heating system 216 and the same axes 208 and 209 as the graph 200 in Figure 5, which are analogous to the curves in graph 200.

The second strip 16, which are significantly thinner, requires lower temperatures in the front and rear heating sections 52 and 56 to reach a peak metal temperature in the range of 843 ° C. Therefore, those heating sections are starting to be cooled as shown by the heating temperature curve of the system 216 which is only 760 ° C at the inlet and only 888.2 ° C at the outlet. Nevertheless, as the strip 10 is passing, the induction heating section 54 is turned on, raising the first temperature curve of the strip 212 from 843 ° C to 704.4 ° C as shown in a portion 213 of the curve. Using the induction heating section 54 allows the exit temperature of the strip 10 to be within the 837.7 ° C specification. Referring now to Figure 9, the graph 220 illustrates the heating system 50 after the transition 22 passing through the heating system 50 but before the heating system reaches the steady state. The graph 220 has a second strip temperature curve 222, an ideal temperature curve 204, a heating system temperature curve 216, and axes 208 and 209, which are analogous to the curves in graphs 200 and 210. Being smaller, the second strip temperature 222 rises rapidly from 93.3 ° C to 648.8 ° C approximately the first 40% of the heating system. Since the induction heaters 80 are off, the second strip temperature curve 222 is flat in a portion 223, which corresponds to the induction section 54. The curve 222 continues to rise to an exit temperature of 854.4 ° C, which is within the specification. In this example, the size of the smaller portions 36 and 38 were essentially eliminated. In other transitions, the sizes of the smaller portions are only reduced. Referring now to Figure 10, the graph 230 illustrates a heating system 50 in a steady state with the second strip 16 passing therethrough. The graph 230 has a second strip temperature curve 232, an ideal temperature curve 204, a temperature curve of heating system 236, and axes 208 and 209, which are analogous to the curves in graphs 200, 210, 220. The heating system temperature curve 236 is less than the curves 206 and 216 since the second strip 16 requires less heat input than the first strip 10 due to its relatively thinner state. The temperature of curve 236 is 693.3 ° C at the entrance to the heating system, compared to 804.4 ° C for curve 206. Similarly, the temperature of curve 236 is 871.1 ° C at the exit of the system. heating, compared to 915.5 ° C for curve 206. Since the induction heaters 80 are turned off, the second strip temperature curve 232 is flat in a portion 233 corresponding to the location of the induction heating section 54 The temperature curve of the heating system 236 is similar to the second temperature profile. However, the curve of the heating system 236 illustrates the different locations of the temperatures of the heating system in the heating system. The second temperature profile is distinguishable from the curve 236 in that the profile is the temperatures of the heating zones 101-112 in the heating system 50 which allows the second strip 16 to be heated to within the second temperature tolerance range . Therefore, by placing the induction heating section 54 between the first and second sections 52 and 56 of a heating system 50, a greater percentage of the combined strip 40 leaves the heating system 50 within the temperature tolerance range peak metal, thereby minimizing the smaller portions 36 and 38 of the combined strip. Other embodiments of the invention can heat a strip of more than two strips. The present invention may be presented in other specific forms without departing from the spirit or essential attributes thereof and. accordingly, reference is made to the appended claims, rather than to the above specification, to indicate the scope of the invention.

Claims (26)

1. A method of heating a metal strip within a temperature tolerance range while the metal strip is moved serially through a path in a heating system, the method comprising the steps of: providing a heating system comprising at least one preceding heating section, at least one induction heating section, and at least one subsequent heating section which are placed in series; locating the current heating system below a pre-heating section and upstream of a wetting section in a continuous strip annealing line, in a continuous strip galvanizing line, or in a continuous plate oven; heating the metal strip below the Curie point in the previous heating section; heat the metal strip to a maximum of about the Curie point in the induction heating section; and heating the heating strip above the Curie point in the subsequent heating section.

The method of claim 1, wherein the path has a length and a portion extending through the preceding heating section, the portion having a length of about 40% to 50% of the length of the trajectory.

3. An optimal location method of an induction heating section in a pre-induction heating section heating system comprising a plurality of heating sections placed in a serial manner to heat a moving metal strip in a serial manner at a design speed through a path, comprising the steps of: a) determining a plurality of strip temperatures at a plurality of system locations in the pre-induction heating section heating system, respectively, b ) determining a maximum design metal strip temperature increase achievable by moving the design metal strip through the induction heating section at a design speed; c) subtracting the maximum design metal strip temperature increase from a Curie point of the design metal strip, thereby defining an optimum design metal strip entry temperature; d) determining a specific system location having a corresponding strip temperature approximately equal to the optimum design metal strip entry temperature, thereby identifying an optimum metal strip entry location; and e) inserting the induction heating section between two heating sections adjacent to and close to the optimum design metal strip entry location.

The method of claim 3, further comprising the step of inserting the induction heating section before or after the metal strip entrance location of optimum design.

The method of claim 3, further comprising the step of inserting the induction heating section before or after one or more previous heating sections of the heating system, wherein the path has a length and a portion that is extends through the above heating section, the portion having a length of about 40% to 50% of the length of the path after inserting the induction heating section therein.

A heating method of first and second metal strip within a first and second predetermined temperature tolerance range, respectively, each strip of metal having an initial portion, a final portion, a front edge and a trailing edge, the trailing edge of the first metal strip that is at least close to the front edge of the second metal strip, comprising the steps of: a) providing a heating system comprising at least one preceding heating section, at least one induction heating section, and at least one subsequent heating section which are placed in series; b) serially passing the first and second metal strips through the heating system; c) insofar as the initial portion of the first metal strip is passing through the heating system, it heats the anterior and posterior heating sections to a first temperature profile; d) while the final portion of the first metal strip the initial portion of the second metal strip is passing through the heating system, making the transition of the heating of the previous and subsequent heating sections to obtain a second profile of temperature therein, including the complement of heating the final portion of the first metal strip and / or the initial portion of the second metal strip with the induction heating section; and e) while the final portion of the second metal strip is passing through the heating system, heating the previous and subsequent heating sections to a second temperature profile.

The method of claim 6, wherein the trailing edge of the first metal strip is attached to the front edge of the second metal strip.

The method of claim 7, further comprising the steps of: a) entering the variables of the first strip of metal, the variables of the second strip of metal, and the variables of the heating system within a control system; and b) directing the operation of the above heating section, the induction heating section, and the subsequent heating section based on the first and second predetermined temperatures, a thermal model, the variables of the first metal strip, the variables of the second metal strip, and the variables of the heating system with the control system.

The method of claim 8, wherein the steering and / or introduction steps are executed at least in part by an operator of the heating system.

The method of claim 8, wherein: a) the variables of the first metal strip comprise length, width, thickness, speed of the strip through the heating system, the initial temperature and the final temperature of the strip; b) the variables of the second metal strip comprise length, width, thickness, speed of the strip through the heating system, the initial temperature and the final temperature of the strip; c) the variables of the heating system comprise a real temperature profile of the previous and subsequent heating sections.

The method of claim 10, wherein the step of introducing further comprises the steps of a) measuring at least a portion of the variables of the first metal strip, at least a portion of the variables of the second strip of metal, and at least a portion of the variables of the heating system with instrumentation; b) generate variable signals from them; and c) transmitting the variable signals to the control system.

The method of claim 7, wherein the step step in serial form further comprises passing the first and second metal strips serially; a) a plurality of heaters placed in steps in the above heating section; b) at least one induction heater placed in at least one passage; and c) a plurality of heaters placed in steps in the subsequent heating section.

The method of claim 12, wherein the steps are oriented vertically or horizontally.

The method of claim 12, wherein the heaters of the anterior and posterior sections are type W radiant tubes ignited by gas.

The method of claim 7, further comprising the step of passing the first and second metal strip through a wetting section of a continuous strip annealing line after serially passing the first and second strip to through the heating system stage.

16. A heating system for heating a first and a second metal strip within a first and a second temperature tolerance range, respectively, each metal strip having an initial portion, a final portion, a leading edge and a rear edge, the trailing edge of the first metal strip that is at least close to the front edge of the second metal strip, comprising: a) at least one preceding heating section; b) an induction heating section; c) at least one subsequent heating section, wherein the heating sections are placed in series to allow the first and second metal strips to pass serially therethrough; and d) a metal strip temperature control mechanism connected to the first, second and subsequent induction heating sections for: (i) reaching a first temperature profile in the previous and subsequent heating sections; (ii) achieve a second temperature profile in the previous and subsequent heating sections; and (ii) complementary heating of the final portion of the first strip and / or the initial portion of the second metal strip in the induction heating section while transitioning the previous and subsequent heating sections between the first and second temperature profiles.

The heating system of claim 16, wherein the trailing edge of the first metal strip is attached to the front edge of the second metal strip.

The heating system of claim 16, wherein the temperature control mechanism of the metal strip comprises: a) input means for inputting the variables of the first metal strip, the variables of the second metal strip, and the variables of the heating system in a control system; and b) a thermal model; wherein, the control system directs the operation of the heating sections based on the first and second temperatures, the thermal model, the variables of the first metal strip, the variables of the second metal strip, and the system variables of heating.

The heating system of claim 18, wherein: a) the variables of the first metal strip comprise length, width, thickness, strip velocity through the heating system, the initial temperature and the final temperature of the strip. strip; b) the variables of the second metal strip comprise length, width, thickness, speed of the strip through the heating system, the initial temperature and the final temperature of the strip; and c) the variables of the heating system comprise a real temperature profile of the previous and subsequent heating sections.

The system of claim 19, wherein: a) the front and rear heating sections comprise a plurality of heaters placed in steps; b) the induction heating section comprises at least one induction heater placed in at least one passage; and c) the steps of the heating section are placed in series to allow the first and second metal strips to pass serially therethrough.

The method of claim 20, wherein the steps are oriented vertically or horizontally.

22. The method of claim 21, wherein the heaters of the anterior and posterior sections are type W radiant tubes ignited by gas.

The heating system of claim 22, wherein: a) the input means comprises the instrumentation for measuring at least a portion of the variables of the first metal strip, at least a portion of the variables of the second metal strip, and at least a portion of the variables of the heating system, which generate variable signals from them, and which send the variable signals to the control system; and b) the control system comprises means for receiving the variable signals.

24. The heating system of claim 18, wherein the control system is programmable.

The heating system of claim 17, wherein the heating system is located: a) current below a pre-warming section and upstream of a wetting section in a continuous strip annealing line; b) on a continuous strip galvanizing line; or c) in a continuous plate oven.

26. The heating system of claim 17, wherein the metal strip temperature control mechanism is at least partially controllable by a heating system operator.