1. Field of the Invention
This invention relates generally to plasma arc torches, and more particularly to the design and construction of an improved collimator component of such plasma arc torches.
2. Discussion of the Prior Art
Plasma arc torches are known in the prior art and comprise a device which can efficiently convert electrical energy into heat energy. Plasma arc torches, as the name implies, generate a plasma plume exhibiting a high specific enthalpy coupled with low gas requirements. As is set out in the Camacho et al. U.S. Pat. No. 4,559,439, there are basically two types of plasma arc torches. The first type is referred to as a non-transferred arc torch and the second is referred to as transferred arc torches. In the non-transferred arc type, there is a rear electrode, a front electrode-and a gas vortex generator that is coaxially placed between the front and rear electrodes. This assembly is contained within a water-cooled housing along with other components necessary for generating an electrical arc. The arc extends from the rear electrode past the gas vortex generator location and to an attachment point on the front electrode.
In the transferred-arc type of plasma generator, a collimating nozzle is mounted in coaxial alignment with the rear electrode and vortex generator. In this type of operation, the electrical arc attaches between the rear electrode and an external work piece that is being worked upon after passing through the collimating nozzle.
Transferred arc generators are described in U.S. Pat. No. 3,194,941 to Baird, and in U.S. Pat. No. 3,818,174 to Camacho. The present invention is directed to an improved collimator for a transferred arc-type plasma arc torch and is deemed to be an improvement over the prior art, such as the collimator shown in
Referring to
The gas injected into port 28 becomes ionized and is rendered plasma by the arc 32 and is injected onto the work piece 30. The collimator 22 includes a longitudinal bore having a frusto-conical taper 34 and serves to concentrate the plasma into a beam, focusing intense heat that speeds up melting of and chemical reaction to the work piece in a furnace in which the plasma torch is installed.
Keeping in mind that the exposed toroidal face 36 of the collimator 22 is exposed to corrosive chemicals given off from the melting/gasification of the work material 30 as well as to secondary arcs, especially in the tapered zone 34 of the collimator, it is imperative that the collimator not be allowed to deteriorate to the point where cooling water can escape the normal channels provided in the torch and flow out onto the work piece that may typically be at a temperature of 2000° F. or more. Resulting superheated steam could create an explosive force within the confines of the plasma arc heated furnace. To avoid such an event, it becomes necessary to shut down the process and replace the collimator at relatively frequent intervals.
Referring to
Located directly below the threaded zone 42 on the holder member is a plurality of bores, as at 44, the bores being regularly spaced circumferentially about the periphery of the holder member. An integrally formed annular collar 46 is provided at the proximal end of the collimator.
The prior art collimator 22 further includes a tubular insert 54 machined from a copper alloy billet. It has a central lumen 56 and an outer wall 58 whose diameter is dimensioned to fit within the central bore 48 of the holder member with a predetermined clearance space between the wall defining the central bore of the holder member and the outer diameter of the tubular insert. The insert is also formed with a circular plate-like flange 60 at its distal end that surrounds the lumen 56. Further, the cross-sectional view of
In the prior art collimator assembly shown in
As is explained in the Hanus, et al. '939 patent, supra, cooling water is made to flow through a first annular passageway in the torch housing, through the radial bores 44 of the collimator and through the clearance space between the bore 48 and the outer tubular wall 58 of the insert 54 and from there through radial bores 66 and out through an annular port to another passageway contained within the housing 12 and leading to the water outlet port 26 seen in
The weld made at the joint between the counterbore 50 and the periphery of the flange 60 have proven to be problematic. Extensive corrosive action from the furnace gases corrodes the material on either side of this weld ring and of the e-beam weld itself The life of the collimator is thereby limited by either the integrity and precision of the e-beam weld itself or by the loss of material due to corrosion. This corrosive loss of material may be a result of both galvanic and non-galvanic corrosion. The galvanic corrosion, of course, is due to the presence of dissimilar materials in contact within an electrically conductive medium, such as the gas given off by the reaction of the arc flame with the work piece. The non-galvanic, standard corrosion is due to chemical reaction between the corrosive gases given off by vaporization of the work piece within the plasma arc heated furnace.
As is apparent from
A need, therefore, exists for a collimator design having an increased working life and safety improvements over the prior art. The present invention satisfies this need.
In accordance with the present invention the improved collimator comprises an annular holder member formed from an electrically conductive alloy that has an outer diameter with threads over a predetermined surface thereof. The threads are adapted formating with the threads on the inner surface on a plasma arc torch housing. The holder member has a central bore of a predetermined diameter extending from a first end to a second end thereof. The collimator further includes an insert member adapted to fit within the central bore of the holder member. It, too, is formed from an electrically conductive alloy. The insert member has a tubular stem portion concentrically disposed and integrally formed with a generally circular, radially extending faceplate. The tubular stem portion has an outer diameter that is less than the predetermined diameter of the central bore in the holder member. Hence, insertion of the tubular stem portion of the insert member into the central bore of the holder member defines an annular cooling water passage there between. The faceplate of the insert member has an annular, proximally-extending flange that engages the outer diameter of the holder member at locations offset and remote from a front surface of the faceplate. Rather than having an e-beam weld ring on the exposed face of the collimator as in the prior art depicted by
The foregoing features, objects and advantages of the invention will become apparent to those skilled in the art from the following detailed description of a preferred embodiment, especially when considered in conjunction with the accompanying drawings in which:
Certain terminology will be used in the following description for convenience in reference only and will not be limiting. The words “upwardly”, “downwardly”, “rightwardly” and “leftwardly” will refer to directions in the drawings to which reference is made. The words “inwardly” and “outwardly” will refer to directions toward and away from, respectively, the geometric center of the device and associated parts thereof. Said terminology will include the words above specifically mentioned, derivatives thereof and words of similar import.
Referring first to
Fitted into the central bore 108 of the holder member 104 is an insert member 118. The insert member is also preferably formed from an electrically conductive alloy, e.g., a copper alloy. The insert member has a tubular, longitudinally extending stem portion 120 that is concentrically disposed and integrally formed with a generally circular radially extending faceplate 122 at one end of the stem portion.
As with the prior art, the tubular stem portion has an outer diameter that is less than the predetermined diameter of the central bore 108 of the holder member 104. Hence, when the tubular stem portion 120 of the insert member 118 is placed within the central bore of the holder member, an annular gap 124 is created that leads from the obliquely extending circumferentially-spaced, radial bores 114 to the front end 110 of the holder member 104.
With continued reference to
The insert member is joined to the annular holder member by forming a continuous e-beam weld between a collar 130 at the proximal end of the holder member 104 and a slightly raised annular collar 132 formed at the proximal end of the insert member 118. Further, the flange 126 is e-beam welded to the bosses 128 at locations that are offset from the front surface 100 of the faceplate 122 in a proximal direction.
When the collimator 102 of the present invention is screwed onto the distal end of the torch housing 12 (
The improved collimator of the present invention also provides a continuous, smooth, annular cooling water flow passage from deep inside the collimator bore to a transition near the taper at 134, and the radially outward from the taper along the obverse side of the faceplate 122. In the prior art collimator of
By way of summary, the collimator constructed in accordance with the present invention offers several important improvements in terms of collimator life and overall safety. The present invention is of a simpler construction than the prior art and offers the opportunity for the high heat duty sections of the collimator, i.e., the face plate, to be fabricated from a single material with no welded seams exposed. Also, the collimator of the present invention offers a simpler and more effective cooling water passage to be implemented, thus providing the opportunity of achieving lower collimator material temperature. The single material construction of the exposed face avoids any possible galvanic corrosion contribution to the overall corrosion to which the collimator is exposed to in use and may reduce the overall corrosion due to the wall temperature sensitivity to chemical corrosion reaction rates. The combination of minimal galvanic activity and lower wall temperatures in critical, high heat load locations provides additional life to the collimator. Finally, and of significant importance, is the fact that the collimator design of the present invention provides a greater margin of safety, compared to the prior art design as it relates to the e-beam welding-related water leakage from the collimator.
This invention has been described herein in considerable detail in order to comply with the patent statutes and to provide those skilled in the art with the information needed to apply the novel principles and to construct and use such specialized components as are required. However, it is to be understood that the invention can be carried out by specifically different equipment and devices, and that various modifications, both as to the equipment and operating procedures, can be accomplished without departing from the scope of the invention itself.
This application is a continuation of prior PCT Application PCT/US2005/035927, filed 06 Oct. 2005. This application claims priority to provisional application Ser. No. 60/616,797, filed Oct. 7, 2004, the contents of which are hereby incorporated by reference.
Number | Name | Date | Kind |
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3194174 | Coberly et al. | Jul 1965 | A |
3818174 | Camacho | Jun 1974 | A |
4559439 | Camacho et al. | Dec 1985 | A |
5362939 | Hanus et al. | Nov 1994 | A |
Number | Date | Country | |
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20070175870 A1 | Aug 2007 | US |
Number | Date | Country | |
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60616797 | Oct 2004 | US |
Number | Date | Country | |
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Parent | PCT/US2005/035927 | Oct 2005 | US |
Child | 11732430 | US |