Abstract:
An apparatus ( 10 ) and method for preheating welds uses a centered induction plate ( 12 ) having preferably a plurality of induction coils ( 30, 32 ) to impart the generation of heat in the materials to be welded ( 14 ), being interactively controlled by at least a temperature sensor ( 90, 92 ) and power supply control loop ( 16 ) so that even preheating can be obtained for a selected length of time given the parameters of the weld desired.

Description:
CLAIM OF PRIORITY  
       [0001]     Priority is claimed based upon Provisional Patent Application Ser. No. 60/209,030, filed Jun. 2, 2000, which is incorporated by reference as if fully set forth herein. 
     
    
     STATEMENT OF INVENTORSHIP  
       [0002]     Assignee, Holland Company, believes that the subject matter was the invention of Richard F. Miller.  
       FIELD OF THE INVENTION  
       [0003]     Some welding techniques require precise consistent and controlled heating, which is difficult or impossible to obtain with torches, gas burners or other electric devices. Instead, this is achievable through the use of induction heating wherein a plate or other locating and holding device is placed in a gap between work pieces to be welded, the plate containing an array of induction heating elements which, when energized, produce shaped, varying electromagnetic fields which link with and induce a voltage in the work pieces which in turn results in eddy current flows and subsequent power losses, as well as hysteresis losses, so that the workpiece temperature is raised to a desired, uniform level prior to welding.  
       BACKGROUND OF THE INVENTION  
       [0004]     1. Summary of Invention  
         [0005]     The preferred embodiment is adapted to use in welding railroad rails, however, other difficult to weld work pieces could be advantageously preheated with the invention. The descriptions herein of rail welds should be considered with this more expansive use in mind.  
         [0006]     Induction type heat allows for precise heating at ideal locations and can be used to control heat gradients. This control is possible though use of a feedback system, controller, coil arrangement and a positioning mechanism. This eliminates the human element, resulting in an automated high quality weld preheat method.  
         [0007]     The use of an automated electrically powered and computer controlled induction heating system using the induction heating coils and heating plate with sensitive temperature control and feedback interfaced within the power supply enables higher quality and more consistent welds of difficult to weld pieces such as railroad rails and similar high strength and complex shaped generally ferric items. One advantage in this regard is the ability to manipulate the heat gradient. Also included in advantages over prior art methods are the facts that no consumables are required, there is no need for gases or fuel on board or during transportation and cleanliness—in that there are no combustion byproducts. The invention provides consistent heat through a wide range of ambient temperatures. Another advantage is that of use in different rail geometry, rail chemistries and welding methods. In addition to heating, an analogous plate or array can be used to control cooling after welding.  
         [0008]     In the preferred and alternative embodiments, the invention envisions the use of independent, single or multiple coils and/or power units. Independent, single or multiple coils and/or power units enable the precise location of heating, subdivides locations of heating and provides flexibility in the control of heating areas. An added benefit of using an independent preheating unit, as compared to including the welder or portions of the welder&#39;s power supply or the like is that of efficiencies gains due to multi tasking during welding process. While preheating is occurring, the welder itself can be independently set up for welding operations, or, indeed, one rail may be welded while the adjacent rail is preheated, should the rail gaps be proximate the rail welder&#39;s cable runs.  
         [0009]     2. Description of Related Art  
         [0010]     While preheating of metal pieces for welding as a general concept is well known, heretofore generally manual application of heat has been used. The use of items such as gas or other torches, gas burners or electrically powered devices. Field welding in the past commonly preheated with torches and gas burners. Such methods introduce human intervention positioning, timing or estimating heat input and temperature. Combustion variables including fuel, air, pressure, position and shape of a flame relative to rails, ignition steps, initial temperature of the workpieces and even weather contribute to imprecision in temperature control in the prior art. Resistance electrical devices have power and conductivity variables including both electrical and thermal limitations that also contribute to imprecision in temperature control. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a schematic view showing the layout of the components of the invention.  
         [0012]      FIG. 2  is an elevational view showing the induction plate of the invention.  
         [0013]      FIG. 2A  is an elevational view showing an induction coil with ferrite core.  
         [0014]      FIG. 3  is a wiring diagram showing the control wiring of the invention.  
         [0015]      FIG. 4  is a wiring diagram showing the power supply wiring to control separate heating zones.  
         [0016]      FIG. 5  is a side elevational view showing the induction plate of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     Weld quality and consistency can be improved with precise control of heating (temperatures, location zones and heat gradients). Heating becomes more critical when dealing with certain alloying, geometry or ambient temperatures. This is more of an art gained through experience or a routine that must be followed carefully to attempt to produce consistent, quality welds.  
         [0018]     An induction heating system  10  uses a tool or plate  12  to heat a railroad rail  14 . Power control  16  is operatively connected to a pair of power supplies  18 , 20 . Power supplies  18 , 20  are in turn operatively connected to a heat zone control unit  22  using control output connections  24 ,  26 . Cables (not shown) interconnect power supplies  18 , 20  to plate  12 , generally, and to heating elements  30 ,  32  specifically through connectors  34 ,  36 .  FIG. 2A  shows the heating element  32  in more detail. Each element  30 ,  32  is generally broken out into a separate heating module  38 ,  40  using the elements  30 ,  32  and other features more fully described below to provide a unitary heating module  38 ,  40 . The heating system  10  is a 5 Kw, 25 Khz induction heating system broken out in the form of two 2.5 Kw modules  38 ,  40 . While this is the preferred capacity of the system, different welding operations could advantageously be accommodated through the use of a heating system with a different heating capacity. These are capable of independent heating of two heat zones,  42 ,  44 . Each module  38 ,  40  is connected to a heating element  30 ,  32  with ferrite cores  46 ,  48  in a common housing in plate  12  capable of being inserted in an approximate one inch gap between rails  14 . It will be understood that the rails  14  are shown in section and in the field there will be to rails  14  with a gap between them intended to be welded.  
         [0019]     For preheating of normal section railroad rails  14  for gas shielded arc welding, the preferred heat zones  42 ,  44  consist of two heating locations  50 ,  52  generally near the bottom flanges  54 ,  56 . The preferred embodiment will be further described below after general description of the field that requires induction preheating.  
         [0020]     Gas shielded arc welding without the preheating taught by the invention in this application has been practiced under controlled laboratory and/or workshop conditions but is believed unsuitable for use in the field. One method used under controlled conditions is generally taught by U.S. Pat. Nos. 5,773,779 and 5,877,468, which are incorporated by reference as if fully set forth herein. It is believed that one reason the method described in these two patents is inoperative in field conditions is inadequate control of preheating. Delivery of gas shielded arc welding equipment and the alignment and restraint of railroad rails and the deployment of a weld containment unit for application of weld beads is taught in published International Application No. WO 99/31322 published 16 Dec. 1998 entitled “Mail Welding Apparatus Incorporating Rail Restraining Device, Weld Containment Device and Weld Delivery Unit.” The teachings of this application are also incorporated by reference. It is believed that the apparatus and method taught herein are essential in effective practice of gas shielded arc welding of rails.  
         [0021]     Additionally, other welding methods are believed to be capable of enhancement through the use of the invention taught here. Other weld methods, such as thermite, on site foundry and even certain flux-based arc welding may prove suitable for high strength welds of complex shapes with adequate and well controlled preheating.  
         [0022]     While the preferred embodiment of induction heating for rail welding using gas shielded arc welding anticipates using two heating modules  38 ,  40 , other uses could use fewer, more or differently arranged heating modules. Thus, for certain rail welding or joining methods it may prove advantageous to heat the entire rail section simultaneously. The invention is not limited to rail welding using two heating modules.  
         [0023]     Plate  12  is formed to fully support and contain heating elements  30 ,  32 . Accordingly plate  12  has a body portion  60  ending in a protective ceramic cover  62  which fully covers ferrite cores  46 ,  48  and the corresponding conductors of elements  30 ,  32 . Side edges  64 ,  66  of plate  12  are fitted with centering bar assemblies  68 ,  70 . Assemblies  68 ,  70  use centering adjustment mechanism  72  to adjust bars  74 ,  76  outwardly or inwardly to fit the rail gap. It will be understood that assemblies  68 ,  70  are symmetric and accordingly only one assembly  70  is shown and illustrated in  FIG. 5 .  
         [0024]     Precise cutting of rails in the field is quite difficult, thus there is often variation in the size of gaps and the orientation of their faces. The adjustable and expandable centering bar assembles enabling side to side and top to bottom centering are important in aligning plate  12  as close to the center of the gap as practicable to maximize the uniform heating of the rail ends. In this manner the assemblies  68 ,  70  are aligned for maximum effectiveness and uniformity, being centered between faces that may themselves be non-parallel due to the difficulty of cutting in the field.  
         [0025]     Each heating element  30 ,  32  is fitted with a respective pair of water/power connections  80 ,  82  illustrated in  FIG. 2A . These enable both the electrical power connection necessary to energize the ferrite core  46 ,  48  and provide conduits for the transmission of cooling fluid to dissipate the heat radiantly transmitted from the preheated rails  14  to the plate  12 . Spring clips  84 ,  86  are used to retain elements  30 ,  32  in place in plate  12 .  
         [0026]     Temperature measuring devices such as spring loaded thermocouples  90 ,  92  are used as an integral part of both plate  12  and heat zone control unit  22 . Thermocouples  90 ,  92  are operatively connected to heat zone control unit  22  which is in turn used to control power supplies  18 ,  20 . Power supplies  18 ,  20  receive signals from unit  22  interconnected through connections  24 ,  26  which provide power on or power off control signals depending on the heat measured at thermocouples  90 ,  92 . It will be observed, particularly from  FIG. 1  and  2  that thermocouples  90  and  92  are positioned proximate ferrite cores  48 , thereby providing an accurate temperature reading from rails  14  which are heated as a result of the energizing of elements  30 ,  32  and particularly cores  46 ,  48 . The general principles of induction heating will be recognized, namely the providing of a sufficiently large energy output at elements  30 ,  32  and cores  46 ,  48  will create heat in adjacent steel rails  14 .  
         [0027]     In this manner heat zones  42 ,  44  are interactively controlled so that a controlled heat results although a variety of factors, whether an imprecise gap, power, magnetic fluctuations, unequal temperature differential or even environmental factors such as a crosswind, impact the actual temperature and heat distribution in the rails. As noted above while locating heat zones  42 ,  44  near the rail flanges is advantageous for gas shielded arc welding other types of welding may require the use of different heat zones such as heating the entire rail section including flanges, web and head, or for the welding of different shapes such as I-beams and the like. In these other uses and applications, the number of heat zones and their orientation can be controlled consistent with the principles of this invention. The use of one or more coil elements  30 ,  32  gives flexibility in applying the two preferred heat zones  46 ,  48 . In other, particularly non-rail welding applications, a single heat zone or multiple heat zones could be used. A plurality of coil elements, two or more, also provide flexibility in temperature differentials that may be required by particular metallurgical or welding considerations.  
         [0028]     The invention enables precision controlling of the heat gradient in the pieces to be welded. The interactive control between elements  30 ,  32  and thermocouples  90 ,  92  in zones  42 ,  44  enables the ability to manipulate the effects of applied heat to the particular metallurgy of the rails  14  and weld material and method used.  
         [0029]     Control unit  22  can also be interconnected to corresponding additional fixtures or controls. The invention contemplates a feedback system that enables, but is not limited to input from a robot or positioner or a controller/computer that calculates heat soak/rail temperature for particular conditions. With this data compared to the induction heat inputs directly supplied by unit  22  and temperature measurement enabled by thermocouples  90 ,  92 , control unit can be modified for particular time and energy parameters, given known metallurgical and welding requirements.  
         [0030]     This full feedback system maximizes the quality control of the welding process so that it will be repeatable and monitored. The full feedback system also records actual temperatures and adjusts automatically. The fill feedback system is further programmable for various materials, conditions and methods. With greater and better data regarding when the weld pieces reach correct temperature(s) in singular and/or multiple zones fully integrated with weld delivery controls, the user is provided a seamless system with no additional mechanisms, components required, such as the prior art burners or torches, and welding materials requiring multiple unrelated and uncontrolled steps. Finally, the fully integrated system can be manipulated by robot for deployment, movements during heating process and retractment.  
         [0031]     In operation, the steps of the invention are premised on the step in which each heat zone is monitored by a temperature measuring device which checks temperature on one side of the zone. Even heating is achieved on either side of the zone because the inductor is centered between the rails with a mechanical centering device, which independently and exactly centers the inductor relative to side one and side two. By so doing each side is brought up to a preferably preheat temperature even though the rails may have a variable gap. It will be noted that the temperature may, of course, vary based on the materials welded and the method of welding used.  
         [0032]     Rail ends are preheated by induction heating for preparation of welding. The ideal temperature and heat gradient is controlled by a feedback system. The feedback system uses temperature-measuring devices like thermocouple&#39;s, pyrometers, and other heat sensors with or without a controlling device. During the pre-heating, different zone(s) of rail ends can be simultaneously heated independently of each other. Frequency, proximity and number of cycles allow for control of the heat gradient. This is complemented though coil designs in the tool and/or power inputs. This tool fits between the rail ends in the gap and can be manipulated by a robotic arm or manually. The gaps between rails are approximately ¼″ and up. Material and mechanical designs of this tool enhance durability and efficiencies. Process requirements are monitored and recorded for quality control. Parameter measurements give a go/no go signal to proceed with welding or intervene with corrections to meet parameters. In addition post-heating enjoys many of the same benefits. The complete system is mobile and portable.  
         [0033]     In operation, each zone begins heating simultaneously. Should one zone reach temperature prior to the other the heater output is reduced so as to maintain at temperature until the second zone also achieves required temperature. Only at this time does the controller send a signal to the weld controller indicating that welding can commence.