Abstract:
A graphite electrode and a holder for the electrode for use in a metal disintegrator, the electrode having a hollow columnar body with a skirt wall open at one end, the skirt wall having a plurality of holes extending between one end and an opposite end, the holes being adapted to conduct liquid coolant from said opposite end to said open end, the holder being proportioned to engage and support the electrode at its opposite end when the electrode is installed on a metal disintegrator, the electrode and holder being constructed and arranged to vent a portion of the volume of said liquid coolant through a space between a part being disintegrated and an interior surface of the skirt wall.

Description:
The invention relates to improvements in metal disintegrating machines and processes. 
     BACKGROUND OF THE INVENTION 
     Metal disintegrators have been used for decades to cut metal components that, typically, are too hard, inaccessible or otherwise impractical for more conventional cutting techniques such as drilling, milling, sawing, abrading or oxygen acetylene torching. Metal disintegrators vibrate a graphite electrode into and out of contact with a metal part to be cut. Electrical current supplied at the cutting end of the electrode turns local areas of the part being cut molten and water or other liquid coolant solidifies and fractures the local molten areas into small free particles when the electrode cyclically pulls away from the part. The process cycles many times a second, e.g. 60 or 50 Hz until a cut is completed to the desired depth. 
     When parts of large cross-section are to be severed from a surrounding body such as a stud locked in a hole, it is known to use a tubular electrode having an outside diameter slightly smaller than the stud. The electrode is used to burn through the operative length of the stud leaving a disembodied core. This technique greatly reduces the total energy required for burning the stud free of its surrounding solid compared to what would be required if a solid or coreless electrode was used. In practice, tubular electrodes of the prior art experience limitations in the size or included cross-section and length or depth of a cut. Beyond certain electrode included cross-section size and length combinations, cutting action is slowed or eventually stopped and accuracy is compromised or lost. 
     SUMMARY OF THE INVENTION 
     The invention advances the art of contact arc thermal shock metal cutting machines, commonly known as metal disintegrators, by providing hollow electrodes with a coolant vent path for the interior of the electrode. It has been discovered that continuous coolant flushing action of the interior of the hollow electrode through its holder end greatly improves cutting performance. The vent path permits the interior of the electrode to be continuously flushed with liquid coolant to carry away metal particles that would otherwise re-arc at random sites so as to accelerate wear of the electrode and lose precision of the cut. Moreover, venting, in accordance with the invention, avoids excessive back pressure of the liquid coolant that otherwise interferes and eventually stops necessary vibration of the electrode induced by the head of the machine into and out of contact with the part being disintegrated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a somewhat diagrammatic illustration of a metal disintegrator machine including a vertical cross-section of an electrode holder and electrode taken in the offset planes indicated at  1 - 1  in  FIG. 2 ; and 
         FIG. 2  is an axial view of the electrode holder and electrode taken in the plane  2 - 2  indicated in  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawing, a metal disintegrator machine  10  includes a head  12  carried and horizontally adjustable on an arm  13 . The arm  13 , in turn, is vertically adjustable on a vertical post  14 . The mounting of the head  12  on the arm and the mounting of the arm on the post  14  provide angular adjustments about horizontal and vertical axii. Those skilled in the art will recognize that the head  12  can be supported in other orientations beyond that shown and can be mounted on special hardware or bracketry to suit a particular job. The head  12  is vertically slidable on a vertical guide  16  and the majority of the weight of the head, including a vibration inducing solenoid contained in the head, an electrode holder  17 , and an electrode  18  is largely counterbalanced with an air cylinder  19  aligned vertically with the guide  16  and supplied from a regulated source of air pressure above atmospheric pressure. 
     A power supply  21  delivers alternating current at relatively low voltage, e.g. 32 volts, and relatively high current, e.g. 300+ amps to the head  12  through a cable  22  to the head and a cable  23  serving to ground a body in which the part to be disintegrated is located. A source  24  of coolant, commonly water, can be a pump or connected to a utility line with suitable pressure controls. 
     The illustrated electrode holder  17  comprises a circular generally flat plate  28  with an integral central upstanding stud  29  on its upper side. The holder is preferably made of aluminum so that it is highly electrically conductive. The stud  29  is received in a socket on an armature of the vibration solenoid located in the head  12  as is known in the art. The stud  29  can be fitted with a bronze sleeve  31  to be gripped in the socket. The power supply, through the cable  22  is connected to the solenoid socket to conduct electrical power to the holder  17 . 
     A lower face  32  of the holder  17  is machined or otherwise formed with a circular pocket  33  to receive a mounting end  34  of the electrode  18 . An annular groove  36  is formed adjacent the periphery of the pocket  33  and communicates with two ports  37  through an upper face  38  of the holder plate connected to the source  24  of coolant through supply lines  39 . 
     In its illustrated form, the electrode  18  is a hollow, circular unitary body that includes a cylindrical thin wall tube  41  and an end wall  42  that represents part of the mounting end  34  of the electrode. The outside diameter of the electrode  18  fits within the pocket  33  on the lower face of the holder plate  28  so that the outer face of the end wall  42  abuts a base surface  43  of the pocket  33 . A bolt  44  assembled through a central hole  46  in the end wall  42  is threaded into a central blind hole  47  in the holder  17 . The bolt  44  compresses a spring washer  48  to retain the electrode end wall  42  in the pocket  33  of the holder  17 . 
     A plurality of preferably uniformly angularly spaced coolant passages  51  are drilled or otherwise formed through the electrode tubular wall  41  from a lower cutting end  52  of the tube wall to the outer face of the end wall  42 , i.e. the mounting end  34  of the electrode. The passages or holes  51  at the holder end lie under and communicate directly with the annular groove or channel  36  enabling the channel to serve as a manifold for the holes. A set of angularly spaced aligned holes  56 ,  57  and  58  are provided in the spring washer  48 , electrode end wall  42  and holder plate  28 , respectively. 
     In operation, coolant, such as plain water, from the source  24  is directed through the supply lines  39  to the ports  37  and into the annular groove or channel  36 . The channel  36  distributes the coolant to the coolant passages  51  in the electrode tube wall  41 . The solenoid in the head  12  vibrates the electrode holder  17  and electrode  18  to alternately contact and draw away from a workpiece  61 .  FIG. 1  illustrates the electrode  18  after it has partially burned into the workpiece  61  shown as a threaded metal bolt received in a threaded hole in a large body  62 . Either the body  62 , if it is electrically conductive, or the workpiece  61 , is grounded relative to the power supply  11 . The solenoid vibrates at the frequency of the current applied to it, i.e. 60 or 50 Hz for example. The electrode  18  is typically sized so that its outside diameter is slightly smaller than the root diameter of the threads of the bolt or workpiece  61 . 
     When the cutting end  52  contacts a workpiece  61  it turns local areas of the workpiece molten from the resistance heating that results from the application of the large electrical current. When the cutting end  52  moves away from the workpiece  61 , an electrical arc is extinguished and coolant discharges through the holes  51  to suddenly chill the molten metal causing it to shatter into small solidified particles. In this manner, the electrode  18  burns a path through the workpiece  61  slightly larger than the cross section of the electrode itself. That is, the major diameter and the minor diameter of a groove being cut into the workpiece  61  are respectively larger and smaller than the corresponding outer and inner surfaces of the electrode  18 . The clearance created between the wall surfaces of the electrode  18  and the wall surfaces burned into the workpiece  61  affords annular channels for the coolant to escape and carry with it the metal particles being created in a flushing action. 
     The size and number of the coolant passages or holes  51  will depend on the size of the electrode  18 . The aligned holes  56 ,  57  and  58  in the spring washer  48 , electrode end wall  42  and holder plate  28  have the unique function of venting the interior of the electrode  18 , permitting flow of coolant along the path generally indicated by the arrows  66 . Venting of the interior of the electrode afforded by the vent holes  56 ,  57  and  58  at the holder end  34  of the electrode has been found to produce dramatic increases in the performance of a disintegrator. 
     It has been discovered that by venting the interior of the electrode  18  back through the end  34  of the electrode being held, electrodes of much greater diameter and/or length beyond what has heretofore been used are not only practical but work remarkably well in terms of speed and quality of cut. Still further, it is has been found that results are improved when the total vent or open area afforded by the holes  58 ,  56 , and  57  in the washer  48 , end wall  42  and holder plate  28  are related to the total cross sectional area of the coolant passages or holes  51 . Depending on the size and configuration of the electrode, this relationship can range between about 50% to about 150%. In most instances, it is desirable to adjust or restrict the vent open area for the interior of the hollow electrode  18  so that more than half of the coolant flow flushes the exterior wall of the electrode. 
     The coolant passages  51  can have a diameter of about 3/32″ to about ⅛″. Holes or bores of this size will leave no core or minimal core as the electrode  18  cuts through a workpiece. Where a core might be left by coolant passages, either because they are of a larger size or because of other conditions, these cores can be eliminated by simply rotating the electrode a few degrees about its longitudinal axis. 
     It will be understood that the hollow columnar electrode can take other cross-sectional shapes such as that of a square, rectangle, or hexagon. Still further, it is contemplated that the electrode can be formed without an end wall at its end opposite the cutting end. In such a case, a holder or its equivalent can be used to throttle and thereby limit coolant flow back through the interior of the electrode. 
     The electrode  18  will cut material within about 1/32″ of its interior and exterior wall surfaces. With the present invention, a much improved uniformity of the cut and life of the electrode have been experienced because of the flushing action on the exterior and interior of the electrode and the consequent avoidance of re-arcing of the particles which can otherwise be trapped between the exterior and interior walls of the electrode and the adjacent walls of the workpiece being cut. 
     It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.