Patent Publication Number: US-6911089-B2

Title: System and method for coating a work piece

Description:
FIELD OF THE INVENTION 
   The present technique relates generally to systems and methods for applying a coating to a work piece. More specifically, the present technique relates to a system and method for applying heat to facilitate the application of a coating to a work piece. 
   BACKGROUND OF THE INVENTION 
   In many areas of manufacturing, products are coated with a protective coating. The protective coating may be used to prevent corrosion, damage from scratching, etc. Some protective coatings are air-dried to cure the coating. However, heat may also be used to cure a coating. There are many types of coating materials and types. For example, there are liquid coatings and dry granular coatings. Coatings may require heat to set/cure the coating. The heat may be applied before or after the coating is applied. 
   Methods of heating a work piece to set/cure a coating include flame heating, resistive heating elements, and induction heating. With flame heating, a torch is used to apply heat to the work piece. However, it is difficult, if not impossible, to accurately control the temperature of the work piece/coating using this method. Therefore, the coating may not cure or set properly. Resistance heating methods produce a flow of electrical current through a heating element to produce the heat. Typically, the resistive heating element is placed on the work piece to enable heat to be transferred to the work piece by conduction. Thus, the resistive heating elements must be removed before applying the coating to the surface. In addition, once the resistive heating elements reach their steady-state temperatures, they typically must be allowed to cool before they can be removed from the work piece. This may add considerable time to the coating process. Typically, induction heating systems utilize a clam-shell design that extends over the work piece. However, these clam-shell design typically are large and cumbersome and also must be removed to enable the coating to be applied. 
   There is a need, therefore, for a technique for coating a work piece and for applying heat to cure or set the coating that does not have the problems associated with the techniques described above. Specifically, there is a need for a technique to enable a work piece to be heated and a coating applied “on-the-fly.” 
   SUMMARY OF THE INVENTION 
   The present technique provides a novel approach designed to respond to some or all of these needs. The technique provides an induction heating system adapted to heat a work piece “on-the-fly.” The technique also may provide a system having an applicator adapted to apply a coating to the work piece. In one embodiment of the present technique, the system is adapted to apply a wet coating to the work piece. In another embodiment, the system is adapted to provide a dry coating to the work piece. The technique also may be adapted to apply heat to heat shrink a coating onto a work piece. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
       FIG. 1  is a coating system adapted to travel around a work piece, such as a section of pipeline to heat the section and apply a layer of coating thereto, according to an exemplary embodiment of the present technique; 
       FIG. 2  is an electrical schematic diagram of an induction heating system, according to an exemplary embodiment of the present technique; 
       FIG. 3  is a front elevational view of a temperature controller, according to an exemplary embodiment of the present technique; 
       FIG. 4  is an alternative embodiment of the coating system, illustrating a coating roller adapted to dispose a layer of coating onto the section of pipeline; 
       FIG. 5  is a second alternative embodiment of the coating system, illustrating a coating system adapted to extend across a desired portion of a work piece to heat the section and apply a layer of coating thereto; and 
       FIG. 6  is a third alternative embodiment of the coating system, illustrating a system adapted to travel around a work piece to apply heat to heat shrink a coating onto the work piece. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring generally to  FIG. 1 , a system  20  for heating and applying a coating to a work piece on-the-fly is illustrated. In the illustrated embodiment, the work piece is a section of pipeline  22 . However, the present technique may be used with a work piece other than a pipeline. In the illustrated technique, rather than heating an entire section of a pipeline and then applying a coating to the section of the pipeline  22 , the illustrated system  20  is adapted with a movable applicator  24  adapted to travel around the pipeline  22 , preheating a region of the pipeline  22  and then applying a layer of coating to the region as the applicator  24  is moved around the pipeline  22 . In this embodiment, the applicator  24  is adapted to preheat the pipeline  22  prior to applying the coating. However, the applicator  24  may also be adapted to apply the coating to the region of the pipeline  22  before the heat is applied to the pipeline  22 . With work pieces other than a pipeline, the system may be adapted to rotate the work piece, rather than the applicator  24 . 
   The system  20  also comprises a heating system  26  coupled to the applicator  24  to enable the applicator  24  to heat the pipeline  22 . In the illustrated embodiment, the heating system  26  is an induction heating system. However, other types of heating systems may be used, such as an infrared heating system adapted to radiate infrared energy into the work piece. In this embodiment, the heating system  26  comprises a temperature controller  28  and an induction heating power source  30 . In addition, the system  20  also comprises a coating reservoir  32  coupled to the applicator  24  to provide the coating for the pipeline  22 . 
   As illustrated, during assembly, the pipeline  22  has a coated portion  36  and an uncoated portion  38 . The uncoated potion  38  is comprised of the uncoated ends of adjoining pipe sections. The uncoated portion  38  also comprises the weld  40  joining the adjacent pipe sections. The applicator  24  is adapted to provide a layer of coating to the uncoated portion  38  of the pipeline  22 . In this embodiment, the applicator  24  has a track band  42  that is disposed circumferentially around the pipeline  22 . This embodiment of the applicator  24  also comprises a carriage or bug  44  adapted to travel circumferentially around the pipeline  22  on the track band  42 . General examples of carriages and bugs adapted to travel around a pipeline are presented in U.S. Pat. No. 5,676,857, entitled “METHOD OF WELDING THE END OF A FIRST PIPE TO THE END OF A SECOND PIPE,” issued on Oct. 14, 1997; U.S. Pat. No. 5,981,906, entitled “METHOD OF WELDING THE ENDS OF PIPE TOGETHER USING DUAL WELDING WIRES,” issued on Nov. 9, 1999; and U.S. Pat. No. 6,265,707 B1, entitled “METHOD AND APPARATUS FOR INDUCTIVE PREHEATING AND WELDING ALONG A WELD PATH,” issued on Jul. 24, 2001, which are hereby incorporated herein by reference. In this embodiment, a motor  46  is disposed on the carriage  44  to drive the carriage  44  around the pipeline  22 . A power cable  48  is coupled to the induction heating power source  30  to provide power to the motor  46 . However, power may be provided to the motor  46  from another source of power. The illustrated system  20  may be assembled to coat one uncoated portion of a pipeline and then disassembled and moved to coat another uncoated portion of the pipeline  22 . 
   The induction heating system  26  also comprises an induction head  50  that is secured to the carriage  44  and coupled to the induction heating power source  30  by an induction heating cable  52 . The induction heating power source  30  provides a flow of AC current through the induction heating cable  52  and induction head  50  to produce a varying magnetic field. The varying magnetic field produces eddy currents in the uncoated portion  38  of the pipeline  22 . The eddy currents, in turn, increase the temperature of the uncoated portion  38  of the pipeline  22 . In this embodiment, the induction head  50  is adapted to extend over the uncoated portion  38  of the pipeline  22 . In addition, the induction head  50  comprises a coil adapted to direct the magnetic field toward the uncoated portion  38  of the pipeline  22 . The coil may be comprised of a solid metal coil. The coil also may be formed from a cable or be non-circular. 
   The induction heating power source  30  produces a current having a high frequency, such as a radio frequency. However, at high frequencies the current carried by a conductor is not uniformly distributed over the cross-sectional area of the conductor, as is the case with DC current. This phenomenon, referred to as the “skin effect”, is a result of magnetic flux lines that circle part, but not all, of the conductor. At radio frequencies, approximately 90 percent of the current is carried within two skin depths of the outer surface of a conductor. For example, the skin depth of copper is about 0.0116 inches at 50 KHz, and decreases with increasing frequency. The reduction in the effective area of conduction caused by the skin effect increases the effective electrical resistance of the conductor. In the illustrated embodiment, the induction heating cable  52  utilizes a litz wire (not shown) to produce the magnetic fields. The litz wire is used to minimize the effective electrical resistance of the induction heating cable  52  at high frequencies. A litz wire utilizes a large number of strands of fine wire that are insulated from each other except at the ends where the various wires are connected in parallel. The individual strands are woven in such a way that each strand occupies all possible radial positions to the same extent. In the illustrated embodiment, the induction head  50  and cable  52  are air-cooled. However, the induction head  50  and induction heating cable  52  may be adapted to be fluid-cooled. The induction heating power source  30  may be adapted to provide a cooling fluid for the induction head  50  and induction heating cable  52 . 
   In the illustrated embodiment, the temperature controller  28  receives temperature data from a temperature detector  54  adapted to measure the temperature of the region of the pipeline  22  being heated by the induction head  50 . However, the temperature detector  54  may be adapted to detect temperature from another portion of the pipeline  22 , such as the area forward of the coating applicator. Preferably, the temperature detector  54  is a non-contact temperature detector, such as an infrared-sensing temperature detector. In this embodiment, the temperature data is coupled to the temperature controller  28  by a cable  56 . The temperature controller  28  may be programmed to produce a desired temperature in the region of the pipeline  22  being heated. 
   There are a number of ways of operating the system to establish a desired temperature in a portion of the pipeline  22 . In this embodiment, the induction heating power source  30  is adapted to provide a constant output and the temperature controller  28  is adapted to establish the desired temperature in the portion of the pipeline  22  by controlling the movement of the induction head  50  relative to the pipeline  22 . For example, for a given output from the induction head  50 , the slower the movement of the induction head  50  around the pipeline  22 , the greater the increase in temperature of the region of the pipeline  22  proximate to the induction head  50 . The motor  46  may be operated to provide a relatively constant speed around the pipeline  22  or the motor  46  may be selectively started and stopped to achieve a desired temperature in the pipeline  22 . Alternatively, the temperature controller  28  may be adapted to vary the output of the induction power source  30  to achieve a desired temperature in the portion of the pipeline  22  prior to applying the coating. Indeed, the system  20  may be designed for open-loop operation, that is, it may not have a temperature detector  54  and temperature controller  28 . For example, the output of the induction power source  30  may be established to produce a desired temperature in the pipeline  22  for a given speed of the motor  46 . In addition, the motor  46  may be provided with a motor controller, such as a potentiometer, that allows the speed of the carriage to be manually set to a desired speed. 
   In the illustrated embodiment, the applicator  24  also comprises a coating applicator  58  adapted to deposit a layer of coating  60  on the pipeline  22 . In this embodiment, the coating  60  is a liquid and the coating applicator  58  is adapted to spray the liquid coating  60  onto a portion of the uncoated portion  38  of the pipeline  22 . A pump  62  is provided to pump the liquid coating  60  from the coating reservoir  32  to the coating applicator  58 . However, the pump  62  may be disposed in another location, such as the coating reservoir  32 . A hose  66  is provided to couple the coating  60  from the reservoir  32  to the pump  62 . However, the coating  60  may also be a dry powder coating. In addition, the coating reservoir  32  may be secured to the applicator  24  to travel with the carriage  44 . In the embodiment illustrated, the track band  42  and carriage  44  are oriented on the pipeline  22  so that the induction head  50  leads the coating applicator  58  as the carriage  44  travels around the pipeline  22 , to enable the induction head  50  to preheat the pipeline  22  before the application of coating  60  to the pipeline  22 . However, the track band  42  and carriage  44  may be disposed on the pipeline  22  to enable the coating applicator  58  to lead the induction head  50 , to enable the induction head  50  to heat the pipeline  22  after the coating  60  has been applied. Alternatively, the motor  46  may be adapted to change the direction of travel of the carriage  44  around the track band  42 . 
   Referring generally to  FIG. 2 , an electrical schematic of a portion of the induction heating power system  26  is illustrated. In the illustrated embodiment, 460 Volt, 3-phase AC input power is coupled to the power source  30 . A line source or a generator may provide the input power. A rectifier  76  is used to convert the AC power into DC power. A filter  78  is used to condition the rectified DC power signals. A first inverter circuit  80  is used to invert the DC power into desired AC output power. In the illustrated embodiment, the first inverter circuit  80  comprises a plurality of electronic switches  82 , such as IGBT&#39;s. Additionally, in the illustrated embodiment, a controller board  84  housed within the power source  30  controls the electronic switches  82 . Control circuitry  86  within the controller  28  in turn, controls the controller board  84 . 
   A step-down transformer  88  is used to couple the AC output power from the first inverter circuit  80  to a second rectifier circuit  90 , where the AC is converted again to DC. In the illustrated embodiment, the DC output from the second rectifier  90  is, approximately, 600 Volts and 50 Amps. An inductor  92  is used to smooth the rectified DC output from the second rectifier  90 . The output of the second rectifier  90  is coupled to a second inverter circuit  94 . The second inverter circuit  94  converts the DC output into high-frequency AC signals. A capacitor  96  is coupled in parallel with the induction heating cable  52  across the output of the second inverter circuit  94 . The induction head  50 , represented schematically as an inductor  98 , and capacitor  96  form a resonant tank circuit. The capacitance and inductance of the resonant tank circuit establishes the frequency of the AC current flowing from the power source  30  to the induction head  50 . The current flowing through the induction head  50  produces a varying magnetic field that induces current flow, and thus heat, in the pipeline  22 . 
   Referring generally to  FIG. 3 , as discussed above, the temperature controller  28  may control the system  20  automatically. In the illustrated embodiment, the temperature controller  28  comprises a programmable control unit  100  operable to receive programming instructions to heat the pipeline to a desired temperature. The control unit  100  comprises a display  102  adapted to display the desired temperature  104  and the actual temperature  106  as detected by the temperature detector  54 , where provided. The temperature controller  28  also comprises a parameter display  108  adapted to provide induction heating system operating parameter data. For example, the illustrated parameter display  108  is operable to provide a user with the power available from the induction power source  30  and the power currently being provided by the power source  30 . The parameter display  108  also is operable to provide a user with an indication of the output current and the output voltage of the power source  30 . The parameter display  108  also is operable to provide a user with an indication of the frequency of the AC output current to the inductive head  50 . The illustrated temperature controller also is adapted with a digital display  110  adapted to provide temperature data. This embodiment also comprises a hard drive  112  operable to record temperature data. 
   The temperature controller  28  also comprises a run button  114 , a hold button  116 , and a stop button  118 . Once the system  20  is assembled, the run button  114  may be operated to direct the system  20  to drive the applicator  24  around the pipeline  22 , heating the pipeline and applying a layer of coating thereto as the applicator  24  is driven around the pipeline  22 . The temperature controller  28  may vary the speed of the applicator  24  to achieve the desired temperature. The hold button  116  may be operated to pause operation of the system  20 . The stop button  118  may be operated to halt operation of the system  20 . 
   Referring generally to  FIG. 4 , an alternative embodiment of a coating applicator  120  is illustrated. In this embodiment, the coating applicator  120  is adapted to roll a dry powder coating onto the uncoated portion  38  of the pipeline  22 . However, the coating applicator  120  may also be adapted to roll liquid coating onto the pipeline  22 . The induction head  50  is adapted to preheat a section of the uncoated portion  38  of the pipeline. The temperature detector  54  senses the temperature of the pipeline section and directs the movement of the carriage  44  in response to the temperature data. The temperature controller  28  may be programmed to achieve an optimal temperature in the pipeline for setting the coating. 
   Referring generally to  FIG. 5 , an alternative embodiment of an applicator mechanism  122  is illustrated. In the illustrated embodiment, the applicator mechanism  122  is adapted to be supported on both sides of an uncoated portion  38  of a pipeline  22 , rather than on a single side. This embodiment utilizes two circumferential track bands  42 , one on each side of the uncoated portion  38  of the pipeline  22 . A first carriage  124  is disposed on one track band  42  and a second carriage  126  is disposed on the other track band  42 . In this embodiment, an induction head  128 , a coating applicator  130 , and a temperature detector  131  are secured to the first and second carriages  124 ,  126 . Thus, preventing any bending stress in the induction head  128 , coating applicator  130 , or temperature detector  131  that may be present when only a single carriage is used. In addition, the two-carriage embodiment illustrated may enable a wider region of a work piece to be coated, set, or cured than a single carriage embodiment. 
   Referring generally to  FIG. 6 , an alternative embodiment of a coating system  132  is illustrated. In this embodiment, the applicator  134  is adapted to heat shrink a section of heat shrink material  136  over an uncoated portion  38  of the pipeline  22 . Consequently, the illustrated applicator  132  does not have a coating applicator. A strip of heat shrink material  136  may be disposed over the uncoated portion  38  of the pipeline and heated to join the ends of the strip into a band around the uncoated portions of the pipeline  22 . The system  132  may then be operated to heat the pipeline  22  to produce heat to cause the band of heat shrink material  136  to shrink onto the pipeline  22 , forming a coating. 
   It will be understood that the foregoing description is of preferred exemplary embodiments of this invention, and that the invention is not limited to the specific forms shown. Modifications may be made in the design and arrangement of the elements without departing from the scope of the invention as expressed in the appended claims.