Abstract:
A contactor device used in a wire-feeder employed in a welding system is disclosed. The contactor uses oversized nuts, increased torque and surface features to increase the heat dissipation of the contactor. This solution is an economical way of increasing heat dissipation to extend the life of contactors that are subject to failure due to heating and increased internal resistance.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to the art of welding with wire-feeders and improved heat dissipation on a contactor used in welding systems with wire-feeders. 
         [0003]    2. Background 
         [0004]    Modern wire-feeders in welding systems employ an electromechanical switch known as a “contactor” to electrically connect a welding gun to its power supply at the appropriate time. For the welding gun to operate, the contactor (or switch) is closed as the operator depresses the trigger of the welding gun. That is, pulling the trigger on the gun causes a solenoid in the contactor to move a bridge that brings the welding gun in electrical connection with the welding power source. Because of the high currents used in welding, arcs form in the contactor as the solenoid opens and closes the electrical circuit. Over time these arcs erode the metal at the point of electrical contact, resulting in increased resistance within the contactor. This increased resistance is the primary cause of heat dissipation problems and overall contactor degradation—ultimately resulting in device failure for the contactor. 
         [0005]    In practice, the solution to contactor degradation has been to make the contactor inexpensive and easy to replace. This solution, however, cannot avoid the problems caused when a contactor fails in the middle of a weld process. Depending on the weld, a contactor failure during the middle of a weld may force the partially welded pieces to be scrapped. Accordingly, a contactor with a longer lifetime before failure is desired. Contactors, however, are price sensitive products where inexpensive improvements extending the life of contactors are highly desired. For example, solid state contactors last longer than electromechanical contactors, but are not used as widely because they cost significantly more than electromechanical contactors. 
         [0006]    Over the lifetime of an electromechanical contactor, the internal resistance increases as a result of the arcing that occurs when the contactor is switched on and off. This resistance impedes current flow, reduces the voltage supplied to the welding gun, and creates significant heating problems. Because of the high currents passing through the contactor, the heating problems often lead to device failure. As such, an economical solution for improving heat dissipation is needed in the market. 
       SUMMARY 
       [0007]    In one embodiment, an electromechanical contactor apparatus used in a wire-feeder employed in a welding system comprises: a first and second threaded electrical post; a first and second bus line in electrical connection with the first and second threaded electrical posts, respectively; a first and second locking nut connected to the first and second threaded electrical posts, respectively; and a first and second oversized nut in electrical connection with the first and second threaded electrical posts, respectively, wherein each oversized nut is in electrical contact with and between its respective bus line and locking nut. 
         [0008]    In another embodiment, an electromechanical contactor apparatus used in a wire-feeder employed in a welding system comprises: a first and second threaded electrical post; a first and second bus line in electrical connection with the first and second threaded electrical posts, respectively; a first and second locking nut connected to the first and second threaded electrical posts, respectively; and a first and second oversized nut in electrical connection with the first and second threaded electrical posts, respectively, wherein each oversized nut is in electrical contact with and between its respective bus line and locking nut, and wherein at least one oversized nut is over-torqued. 
         [0009]    In another embodiment, an electromechanical contactor apparatus used in a wire-feeder employed in a welding system comprises: a first and second threaded electrical post; a first and second bus line in electrical connection with the first and second threaded electrical posts, respectively; a first and second locking nut connected to the first and second threaded electrical posts, respectively; and a first and second oversized nut in electrical connection with the first and second threaded electrical posts, respectively, wherein each oversized nut is in electrical contact with and between its respective bus line and locking nut, and wherein at least one oversized nut is over-torqued and contains ridges on at least a portion of the oversized nut&#39;s top surface. 
         [0010]    In another embodiment, an electromechanical contactor apparatus used in a wire-feeder employed in a welding system comprises: a first and second threaded electrical post; a first and second bus line in electrical connection with the first and second threaded electrical posts, respectively; a first and second locking nut connected to the first and second threaded electrical posts, respectively; and a first and second oversized nut in electrical connection with the first and second threaded electrical posts, respectively; wherein each oversized nut is in electrical contact with and between its respective bus line and locking nut; wherein the width of at least one oversized nut is at least 1.5 times the width of its respective locking nut; and wherein the torque of the at least one oversized nut is between 10.0 foot-pounds and 85.0 foot-pounds. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a typical arrangement for a welding system with a wire-feeder. 
           [0012]      FIG. 2  is an expanded view of the common elements in a contactor used in wire-feeder. 
           [0013]      FIG. 3  is a modified contactor with improved heat dissipation features according to an embodiment of the present invention. 
           [0014]      FIGS. 4   a - 4   c  depict an oversized nut with ridges according to an embodiment of the present invention. 
           [0015]      FIGS. 5   a - 5   d  provide examples of various patterns of ridges from a “top down” perspective according to embodiments of the present invention. 
           [0016]      FIGS. 6   a - 6   g  provide examples of various patterns of ridges from a cross section perspective according to embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Welding systems with the consumable wire supplied by a wire-feeder, as shown in  FIG. 1 , are commonly used to weld metals. These welding systems can be operated manually or automatically where a robot is programmed by a machine. Welding system  10  includes a power source  12 , wire-feeder  18 , contactor  20 , wire spool  28 , welding gun  36 , electrode  40 , and workpiece  42 . Power source  12  connects to wire-feeder  18  via lead  14 . Wire-feeder  18  connects to welding gun  36  via lead  30 . Wire-feeder  18  also controls roller motor  24  via lead  22  and contains contactor  20 . Contactor  20  is an electrical switch that is typically called “contactor” rather than “switch” in the industry. Contactor  20  is typically an electromechanical contactor, which switches on and off using a solenoid to physically move a bridge into electrical connection at a contact point. In another embodiment, contactor  20  is a solid-state type contactor, where it is switched on and off using solid-state circuitry rather than electromechanical switching. By way of lead  22 , wire-feeder  18  controls roller motor  24 , which operates rollers  26 . Rollers  26  are used to feed wire  34  to welding gun  36 . Wire  34  is stored in wire spool  28 . Welding gun  36  contains trigger  37  and contains electrical contact tip  38  where wire  34  is fed through. In addition, welding gun  36  is supplied electrical power via lead  30  and exposes electrode  40  to workpiece  42 . Power source  12 , wire-feeder  18 , and workpiece  42  are connected to electrical ground via leads  16 ,  32 , and  44 , respectively. 
         [0018]    Welding system  10  creates a weld on workpiece  42  when an operator depresses trigger  37  in welding gun  36 . When trigger  37  is depressed, contactor  20  closes (i.e. turns on) to allow current to flow from power source  12  to welding gun  36 . As the weld is created, rollers  26  feed wire  34  to welding gun  36 . Wire  34  is ultimately deposited on workpiece  42  at electrode  40  to create the weld. Welding ceases when the operator releases trigger  37 , which causes contactor  20  to open (i.e., turn off) preventing the flow of current from power source  12  to welding gun  36 . In one embodiment, welding gun  36  and trigger  37  are operated by an automatic robot rather than a human. 
         [0019]    Welding system  10  in  FIG. 1  depicts a wire feeder used in an arc welding system. Clearly, wire-feeder  18  can be used in any welding system that requires consumable wire to be fed to create the weld. According to additional embodiments of the invention, therefore, wire feeder  18  and contactor  20  are used in a variety of welding systems (in addition to arc welding systems) where consumable wire is fed with a wire feeder. 
         [0020]      FIG. 2  demonstrates a typical contactor  20 . Contactor  20  switches on when control signals force solenoid  106  to physically move an internal bridge to electrically connect post  105   a  and post  105   b . Post  105   b  is attached to bus  102   b , which is connected to power source  12  via lead  14 . Post  105   a  is attached to bus  102   a , which is connected to welding gun  36  via lead  30 . Thus, switching contactor  20  into the on position allows current to flow from power supply  12  to welding gun  36  through contactor  20 . Bus  102   a  and bus  102   b  are respectively attached to posts  105   a  and  105   b  with several nuts. Specifically, bus  102   a  is between nut  101   a  and nut  103   a , with locking nut  104   a  placed on top of nut  103   a . Similarly, bus  102   b  is between nut  101   b  and nut  103   b , with locking nut  104   b  placed on top of nut  103   b.    
         [0021]    The high currents used in welding result in electrical arcs inside contactor  20  as solenoid  106  brings the internal bridge into and out of contact with posts  105   a  and  105   b . That is, arcs of electricity appear in the gap between the internal bridge and posts  105   a  and  105   b  as the internal bridge is moved up or down by solenoid  106 . These arcs erode the metal in the internal bridge and posts  105   a  and  105   b  and increase the electrical resistance at their interface. Thus, current flowing from power source  12  to welding gun  36  meets increased resistance the longer contactor  20  is used. This increased resistance impedes current flow, reduces the voltage supplied to welding gun  36 , and generates significant thermal heating. Further, heat alone will increase the resistance in a conductor. In the end, the heat generated in contactor  20  impairs performance significantly and is often the ultimate cause of failure for contactor  20 . 
         [0022]      FIG. 3  illustrates contactor  20  with improved heat dissipation ability according to one embodiment of the present invention. Here, oversized nuts  107   a  and  107   b  replace nuts  103   a  and  103   b , respectively. Oversized nuts  107   a  and  107   b  are larger than nuts  103   a  and  103   b  and serve to dissipate heat more rapidly. Nuts  103   a  and  103   b  are typically the same size or close to the same size as locking nuts  104   a  and  104   b . The additional surface area of oversized nuts  107   a  and  107   b  allows the heat generated in contactor  20  to dissipate more rapidly. This results in lower internal resistance, better conduction of current, and a longer lifetime for contactor  20 . The improved heat dissipation can benefit electromechanical and solid state contactors alike because both types demonstrate improved performance with greater heat dissipation. Using oversized nuts  107   a  and  107   b  provide an economical manner of improving heat dissipation because one can use “off the shelf” oversized nuts  107   a  and  107   b  or manufacture custom oversized nuts  107   a  and  107   b  for little additional cost over standard size nuts  103   a  and  103   b . In one embodiment oversized nuts  107   a  and  107   b  are the same size as each other and in another embodiment the oversized nuts  107   a  and  107   b  differ in size. 
         [0023]    In one embodiment, oversized nuts  107   a  and  107   b  are at least 28 mm wide and nuts  103   a  and  103   b  are 16 mm wide. In another embodiment, oversized nuts  107   a  and  107   b  are between 20 mm and 100 mm wide. In still another embodiment, oversized nuts  107   a  and  107   b  are at least 1.5 times larger than nuts  103   a  and  103   b.    
         [0024]    In another embodiment, oversized nuts  107   a  and  107   b  are over-torqued. That is, the torque applied to oversized nuts  107   a  and  107   b  is greater than the torque normally required. This increased torque allows greater contact with buses  102   a  and  102   b , which promotes improved heat transfer. Because the metal surfaces of oversized nuts  107   a  and  107   b  and buses  102   a  and  102   b  are irregular and not perfectly flat, gaps typically exist where the two separate surfaces do not contact each other. Over-torquing reduces these gaps by forcing the metals closer together. In addition, the increased compression at the interface promotes heat transfer. The improved heat flow allows for greater heat dissipation from oversized nuts  107   a  and  107   b . Accordingly, increased torque on the oversized nuts results in greater heat dissipation and improved contactor performance. In one embodiment, each oversized nut  107   a  and  107   b  is over-torqued by being set to a torque value of between 10.0 foot-pounds and 35.0 foot-pounds. In another embodiment, each oversized nut  107   a  and  107   b  is over-torqued by being set to a torque value of between 10.0 foot-pounds and 85.0 foot-pounds. 
         [0025]    In another embodiment, oversized nuts  107   a  and  107   b  are manufactured with features to create greater surface area. Greater surface area in contact with the ambient air allows for increased heat dissipation capabilities. Accordingly, the top surface of oversized nuts  107   a  and  107   b  (i.e., the surface opposite the electrical bus and partially touching the locking nut) can have ridges or deformations to increase the surface area exposed to ambient air. Ridges or deformations on at least part of the top surface of oversized nuts  107   a  and  107   b  allows the ambient air to draw away additional heat from contactor  20 .  FIGS. 4   a  to  4   c  show an oversized nut with ridges  202 .  FIGS. 4   a  and  4   b  illustrate two views of an oversized nut with ridges on the entire top surface of the oversized nut.  FIG. 4   c  illustrates an oversized nut with ridges covering only a portion of the top surface of the oversized nut. Section  204  is an area on the top surface of an oversized nut without ridges and is shown in a circular pattern centered in the middle of the oversized nut, but can be a variety of shapes and located in other locations on the top of the oversized nut.  FIG. 5  demonstrates some examples of non-linear patterns of ridges. The ridges  202  do not need to be aligned linearly as depicted in  FIGS. 4   a  to  4   c . Rather, the ridges can accomplish the same goal of increasing surface area and improving heat dissipation even where the ridges  202  do not align linearly across the entire surface. It follows, therefore, that many patterns of ridges or deformations can increase the surface area and improve heat dissipation. These patterns of ridges can vary from a “top down” perspective as seen in  FIG. 5  or vary as seen in the examples depicted in the cross section views of ridges in  FIG. 6 . 
         [0026]    It is noted that although the present invention has been discussed above specifically with respect to welding applications, the present invention is not limited to this and can be employed in any similar applications. While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.