The invention relates generally to the spraying of a substance onto a surface. More specifically, the invention is a plasma transferred wire arc (“PTWA”) system, apparatus, and method for deflected thermal spraying (collectively, the “system”).
A. Plasma
There are four “states of matter” in physics. Matter can take the form of: (1) a solid; (2) a liquid; (3) a gas; or (4) a plasma. Plasma is an ionized gas consisting of positive ions and free electrons in equal proportions resulting in essentially no overall electric charge. Like a gas, plasma does not have a definitive shape or volume. It will expand to fill the space available to it. Unlike gases, plasmas are electrically conductive. Plasma conducts electricity, produces magnetic fields, and responds to electromagnetic forces. In plasma, positively charged nuclei travel in a space filled of freely moving disassociated electrons. These freely moving electrons allow matter in a plasma state to conduct electricity.
Although the term “plasma” is not commonly used outside the context of science and engineering, there are many common examples of plasma that people encounter in everyday life. Lightning, electric sparks, fluorescent lights, neon lights, and plasma televisions are all examples of plasma. Gas is typically converted into a state of plasma through heat (e.g. high temperatures) or electricity (e.g. a high voltage difference between two points).
B. Thermal Spraying
Thermal spraying is a process by which a material is sprayed onto a surface with the purpose of improving the surface that is being sprayed. There are many different types of thermal spraying, including, but not limited to: plasma spraying; detonation spraying; wire arc spraying; plasma transferred wire arc spraying; flame spraying; high velocity oxy-fuel coating spraying (“HVOF”); warm spraying; and cold spraying.
Two of these thermal spraying techniques involve the use of plasma, plasma spraying and plasma transferred wire arc spraying. Plasma spraying involves the introduction of feedstock, which can be in the form of a powder, a liquid, a ceramic feedstock that is dispersed in a liquid suspension, or a wire that is introduced into a plasma jet created by a plasma torch. Plasma transferred wire arc (“PTWA”) spraying is plasma spraying when the feedstock is electrically part of the circuit and is in the form of a wire.
C. PTWA—Plasma Transferred Wire Arc technology
PTWA can be used to enhance the surface properties of components. Treated components can be protected against extreme heat, abrasion, corrosion, erosion, abrasive wear, and other environmental and operational conditions that would otherwise limit the lifespan and effectiveness of the treated component. Overall durability is enhanced, while at the same time PTWA can also be used to achieve the following advantages with respect to treated components: (1) reductions in weight; (2) cost savings; (3) reduction in friction; (4) and a reduction of stress. In the context of vehicles such as automobiles, PTWA treatment of engine components such as cylinder bores can result in increased fuel economy and lower emissions. PTWA can also be useful in refurbishing old parts as well as in enhancing new parts.
The inputs of a PTWA system are electricity, gas, and consumable feedstock. The consumable feedstock is. the wire that is atomized by a plasma arc created between the cathode and the free end of the wire. The output of a PTWA system is a plasma arc between a cathode and an anode, where the anode is an open end of a consumable wire. The plasma spray is what enhances the surface properties of a component or surface being treated. Feedstock in a PTWA system is delivered to the plasma torch in the form of the wire. Electric current travels through the wire as the free end of the wire is moved to where the generated plasma exits the nozzle of the plasma torch. In many PTWA systems, the torch assembly revolves around a longitudinal axis of the wire feedstock while maintaining an electrical connection, a plasma arc, between the cathode of the plasma torch and the open end of the wire feedstock. In some embodiments, there is an offset between the longitudinal axis of the wire feedstock and the center of revolution (from the perspective of a cathode revolving around a center point) or the center of rotation (from the perspective of a cathode and surrounding empty space rotating around a center point). See U.S. Pat. No. 8,581,138 which discloses a thermal spray technology “wherein the method includes the steps of offsetting the central axis of a consumable wire with respect to an axial centerline of a constricting orifice.”
PTWA technology can provide highly desirable benefits in the treatment of components used in a wide variety of different industries, including but not limited to: aerospace; automotive; commercial vehicles; heavy industrial equipment; and rail.
D. Operating Parameters
The correct functioning of a PTWA system typically requires the tight coordination of three key parameters: (1) a straight and rapidly traveling feed wire between about 100-500 inches/minute; (2) stable current traveling through the rapidly traveling feed wire; and (3) a consistent gas flow/pressure sufficient for sustaining stable plasma temperatures typically between 6,000 and 20,000 degrees Celsius. If one or more of the parameters of a PTWA system fall outside the desired ranges, inconsistent melting of the feed wire can result. Such inconsistency can negate the desired advantages of PTWA spraying.
The correct functioning of a PTWA system requires the coordination of different variables under substantially tight constraints. Operations outside those constraints are not necessarily visible to the human eye unless the undesirable effects are severe. For example, a PTWA system functioning outside of desired parameters can result in “spitting” because the system will project large molten globules instead of finely atomized particles onto the surface being treated by the PTWA system. Even before visible “spitting” occurs, the operation of a PTWA system with even one parameter outside of an acceptable range can be highly undesirable.
E. Use of Secondary Gas
Prior art PTWA systems utilize secondary gas such as air to direct the particle stream in manner so that the particle stream impacts the targeted surface in the desired manner. In most instances, secondary gas is directed through the nozzle to a help shape the particle stream in a substantially symmetrical and collimated manner, with the sprayed particle stream being perpendicular to the wire. The centerline of the particle stream is typically in line with the horizontal plane (the plane that is perpendicular to the wire). The particle stream is typically directed in the same direction as the center vector.
The prior art presumes that the symmetrical direction of secondary gas to the particle stream is the optimal approach for quality coatings. The prior art affirmatively teaches away from the concept that the horizontal deflection of the particle stream is desirable. Such deflection significantly reduces collimation in the spray pattern and changes the geometry of the spray pattern. In the context of a cathode that rotates around the wire, it is counter-intuitive in the prior art to purpose deflect the particle stream against the direction of the cathode rotation or even in the same direction as the rotation of the cathode. Despite the teachings and assumptions of the prior art, horizontal deflection can be highly desirable.
The system can be further understood as described in the Summary of the Invention section set forth below.
The invention relates generally to the spraying of a substance onto a surface. More specifically, the invention is a plasma transferred wire arc (“PDA/A”) system, apparatus, and method for deflected thermal spraying (collectively, the “system”).
The system can be conceptualized and implemented as an improvement to a wide range of prior art spraying devices and plasma torches, but is particularly useful, novel, and non-obvious in the context of PTWA technology.
In many embodiments, the deflection of the particle stream is effectuated by non-symmetrical passageways of secondary gas within the nozzle. In other embodiments, the non-symmetrical passageways are attributable to another component such as an air baffle or other form of secondary gas director. other components possess the non-symmetrical. Deflection can occur horizontally (left or right in the plane that is perpendicular to the wire), vertically (up or down relative to the wire), or both horizontally and vertically at the same time.
The system can be implemented in a wide variety of different ways using a wide variety of different components and configurations. Virtually any PTWA system in the prior art can incorporate and benefit by horizontally deflecting the particle stream in certain contexts.
Many features and inventive aspects of the system are illustrated in the Figures which are described briefly below. However, no patent application can disclose all potential embodiments of an invention through text descriptions or graphical illustrations. In accordance with the provisions of the patent statutes, the principles and modes of operation of the system are explained and illustrated with respect to certain preferred embodiments. However, it must be understood that the components, configurations, and methods described above and below may be practiced otherwise than is specifically explained and illustrated without departing from its spirit or scope. Each of the various elements described in the glossary set forth in Table 1 below can be implemented in a variety of different ways while still being part of the spirit and scope of the invention.
The drawings described briefly above can be further understood in accordance with the Detailed Description section set forth below.
The invention relates generally to the spraying of a substance onto a surface. More specifically, the invention is a plasma transferred wire arc (“PTWA”) system, apparatus, and method for deflected thermal spraying (collectively, the “system”).
All element numbers referenced in the text below are listed in Table 1 along with an element name and definition/description.
The system 100 can be implemented and used with respect to virtually any prior art PTWA apparatus 50. Implementation of the system 100 involves will often involve use of a nozzle 220 that includes a non-symmetrical nozzle passageway configuration 249. However, other components of the system 100 such as an air baffle 578 or some other secondary gas director 576 can be implemented to possess the structural attributes effectuating the non-symmetrical passageway configuration 549.
The non-symmetrical nature of a non-symmetrical passageway configuration 549 can be grounded in a variety of different attribute configurations. By way of example, such a configuration can result from even one of the following attributes:
The deflection of particle stream 70 can also be influenced by other factors acting in concert with a non-symmetrical passageway configuration 549, such as the pressure, quantity, temperature, and density of the secondary gas 518.
Whether the source of non-symmetry resides within the nozzle 220, outside the nozzle 220, or both within and outside of the nozzle 220, such a non-symmetrical configuration 549 can be implemented to deflect the particle stream 70 horizontally 91 and/or vertically 92. Horizontal deflection 91 in the direction that is opposite to the rotational movement 280 of the cathode 212 as it rotates around the wire 310 can be particularly desirable, but horizontal deflection 91 with the direction in which the cathode 212 rotates around the wire 312 may desirable in certain contexts.
Secondary gas 518 (typically air, but other secondary gases 518 are known in the prior art) is directed towards the particle stream 70 to shape and direct the particle stream The particle stream 70 is created by the plasma arc 70 across a gap 61 between the cathode 212 and the free end 370 of the wire 310. In the prior art, the secondary gas 518 is directed in a symmetrical manner towards to the particle stream 70. This results in a particle stream 70 that is highly symmetrical and collimated. The spray pattern in such a particle stream 70 can be relatively narrower in comparison to the spray pattern resulting from a non-symmetrical passageway configuration 549.
Particle streams 70 that are not deflected have a center line 76 that is horizontally perpendicular to the free end of the wire 370 and in line with the center vector 78. Such a center line 76 protrudes mostly straight out from the plasma arc 60, from the center point in the opening 224 of the nozzle 220 along the center vector 78. A particle stream that is deflected can be referred to as a deflected particle stream 90.
Deflection can occur in a vertical up/down direction (which is referred to as vertical deflection 92), a horizontal left/right direction (which is referred to as horizontal deflection 91), or in both directions simultaneously. It is believed that horizontal deflection 91 is particularly useful, and the horizontal deflection 91 is against the direction of at which a cathode 212 rotates around the free end 370 of the wire 310 is potentially more useful than horizontal deflection 91 that is in the same direction in which the cathode 212 rotates.
A deflected particle stream 90 differs in several respects from a non-deflected particle stream 70. A deflected particle stream 90 increases the porosity of the coating on the surface 80 being sprayed. Such a particle stream 90 is less collimated, with a wider and non-symmetrical spay pattern. Also, by creating a less collimated spray pattern there is less localized heating of the surface 80. Not all of the particles in the particle stream 90 will adhere to the surface 80. Particles that do not adhere will be deflected and/or splash off the surface 80. With a deflected particle stream 90 these particles not adhering to the surface 80 are less likely to build up on the face of the nozzle 220. In addition, by performing horizontal deflection 91 as opposed to vertical deflection 92, there will be less buildup of these particles not adhering to the surface on the torch body 202 above the nozzle 220.
In the context of horizontal deflection, the deflection angle 79 is an angle in the left/right plane. The deflection angle 79 can be less than 5 degrees, up to 10 degrees, in excess of 10 degrees, or even in excess of 20 degrees depending on the specific nature of the material making up the surface 80 to be treated with the particle stream 70.
In the context of vertical deflection, the deflection angle 79 is an angle in the up/down plane. The deflection angle 79 can be less than about 5 degrees, up to about 10 degrees, in excess of about 10 degrees, or even in excess of about 20 degrees depending on the specific nature of the material making up the surface 80 to be treated with the particle stream 70.
The system 100 can implement non-symmetrical passageway configuration 549 that includes one or more passageways 540 in a variety of different ways. In many embodiments, the non-symmetrical passageway configuration 549 is a non-symmetrical nozzle passageway configuration 249, but the non-symmetry can also be based on the structure of the secondary gas director 576, such as an air baffle 578.
Attributes of the nozzle 220 and/or secondary gas director 576 can result in a deflected particle stream 90 without changing the orientation of the nozzle 220 or the orientation of the wire 310 that is used to form the plasma arc 60.
Any non-symmetrical passageway configuration 549 of one or more passageways 540 in the system 100 can potentially result in the directing of secondary gas 518 in a non-symmetrical manner such that the particle stream 70 is a deflected particle stream
A. Passageway Attributes
B. Prior Art
C. Size
D. Shape
E. Angle
F. Locations
Non-symmetry in locations 544 can be achieved through the omission of one or more passageways 540 in an otherwise symmetrical configuration or by having at least one passageway 540 at a non-symmetrical location 544.
1. Omission
2. Non-Symmetrical Location
G. Inlets
Some embodiments of the method 900 can involve a single passageway 540 that is non-symmetrical on the basis of shape 541, size 542, or angle 543 with respect to different portions of the passageway 540 (the passageway 540 is an aggregated single passageway that is fed through one or more inlets 545).
At 910, plasma gas 512 is moved towards the cathode 212. Plasma gas 514 is necessary for creating a plasma arc 920 necessary to atomize the free end 370 of the wire 310.
At 920, the plasma arc 60 is ignited. This is sometimes done across the gap 61 between the cathode 212 and the wire 310. The plasma arc 60 can also be ignited between the cathode 212 and the nozzle 220 and then the plasma arc 60 can be transferred to the wire 310. The required inputs for the plasma arc 60 are plasma gas 514 and electricity 490.
At 930, a particle stream 70 is created by the melting/atomizing of the free end 370 of the wire 310 by the plasma arc 60.
At 940, the particle stream 70 is deflected with secondary gas 518 such as air so that the particle stream 70 is a deflected particle stream 70. Deflection can be horizontal deflection 91 (left/right), vertical deflection 92 (up/down), or both at the same time. Deflection can be implemented through a wide range of different non-symmetrical passageway configurations 549 based on differences in one or more configuration attributes. The magnitude of the deflection of the particle stream 70 can also be influenced by the secondary gas pressure, temperature, and other factors.
Deflection is particularly interesting when it is done horizontally on a system 100 that involves a cathode 212 that rotates around a wire 310 in a trajectory that can be referred to as an orbit or rotation 280.
The system 100, which includes the nozzle 220 with a non-symmetrical passageway configuration 249 can be implemented in a variety of different ways using a variety of different assemblies, with each assembly having a variety of different viable operating environments.
A. Component Views
As illustrated in
The illustration of
B. Schematic Views
The apparatus 110 includes a torch assembly 200 containing a plasma gas port 532 and a secondary gas port 534. The torch body 202 is typically formed of an electrically conductive metal. The plasma gas 512 is connected by means of a plasma gas port 532 to a cathode holder 214 through which the plasma gas 512 flows into the inside of the cathode subassembly 210 and exits through gas ports 216 located in the cathode holder 214. The plasma gas 512, which typically forms a vortex flow between the outside of the cathode subassembly 210 and the internal surface of the plasma nozzle 222, and then it exits through the constricting orifice 224. The plasma gas vortex provides substantial cooling of the heat being generated by the functioning of the cathode 212.
Secondary gas 518 enters the torch assembly 200 through secondary gas ports 534 which direct the secondary gas 518 to a gas manifold 550 (a cavity formed between a baffle plate 578 and the torch body 202 and then through bores 556 in the baffle 578. In a symmetrical configuration, the secondary gas 518 flow is uniformly distributed through the equiangularly spaced passageways 540 concentrically surrounding the outside of the constricting orifice 224. In a non-symmetrical passageway configuration 549, the flow of the secondary gas 518 is not uniformly distributed.
Wire feedstock 320 is used supply the plasma arc 60 with the material that is sprayed onto the surface 84. The wire 310 is directed by rollers 340 that are powered by a speed-controlled motor 350. The wire 310 moves through a wire contact tip 422 which is in electrical contact to the wire 310 as it slides through the wire contact tip 422. In this embodiment, the wire contact tip 422 is composed of two pieces, 422A and 422B, held in spring or pressure load contact with the wire 310 by means of one or more rubber rings 432 or other suitable means. The wire contact tip 422 is made of high electrically conducting material. As the wire 310 exits the wire contact tip 422, it enters a wire guide tip 330 for guiding the wire 310 into a desired alignment with the axial centerline 76 of the constricting orifice 224. The wire guide tip 330 can be supported in a wire guide tip block within an insulating block 434 which provides electrical insulation between the torch body 202, which is held at a negative electrical potential, while the wire guide tip block 332 and the wire contact tip 422 are held at a positive potential. In other embodiments, the wire guide tip 330 can be structurally integral with the nozzle 220. A small port 536 in the insulator block 434 allows a small amount of secondary gas 518 to be diverted through the wire guide tip block 332 in order to provide heat removal from the block 332. This can also be done via a bleed gas 510 around or through the nozzle 220. In some embodiments, the wire guide tip block 332 can be maintained in pressure contact with the plasma nozzle 222 to provide an electrical connection between the plasma nozzle 222 and the wire guide tip block 332. Electrical connection is made to the torch body 202 and thereby to the cathode subassembly 210 (which includes the cathode 212) through the cathode holder 214 from the negative terminal of the power supply 410. In some embodiments, the power supply 410 may contain both a pilot power supply and a main power supply operated through isolation contactors. Positive electrical connection can be made to the wire contact tip 422 from the positive terminal of the power supply 410. Wire 310 is fed toward the axial centerline 76 of the constricting orifice 224, which is also the axis of the plasma plume 62. Concurrently, the cathode subassembly 210 is electrically energized with a negative charge and the wire 310, as well as the plasma nozzle 222 although the plasma nozzle 222 can be isolated, it can be electrically charged with a positive charge. The wire guide tip 330 and wire 310 can be positioned relative to the plasma nozzle 222 by many different methods. In one embodiment, the plasma nozzle 222 itself can have features for holding and positioning of the wire guide tip 330. The torch body 202 may be desirably mounted on a power rotating support (not shown) which revolves the torch around the wire axis to coat the interior of bores.
To initiate operation of the apparatus 110, plasma gas 512 at an inlet gas pressure of between 35 and 140 psig is caused to flow through the plasma gas ports 532, typically creating a vortex flow of the plasma gas 512 about the inner surface of the plasma nozzle 222 and then, after an initial period of time of typically two seconds, high-voltage DC power or high frequency power is connected to the electrodes creating the plasma arc 60. Wire 310 is fed by means of wire feed rollers 340 into the plasma arc 60 sustaining it even as the free end 370 is melted off by the intense heat of the plasma arc 60 and its associated plasma 68 which surrounds the plasma arc 60. Molten metal particles can be formed on the free end 370 of the wire 310 which are then atomized into fine, particles 74 by the viscous shear force established between the high velocity, ionized plasma gas 516 and the initially, stationary molten droplets. The molten particles can be further atomized and accelerated by the much larger mass flow of secondary gas 518 through passageway 540 which converge at a location or zone beyond the melting of the wire free end 370, now containing the finely atomized particles 74, which are propelled to the substrate surface 80 to form a deposit 82 on a desired substrate 84.
The wire 310 can be melted with the particles 70 being carried and accelerated by vector forces 66 in the same direction as the plasma arc 60. A uniform dispersion 70 of fine particles 74, without aberrant globules 72, can be obtained. The vector forces 66 are the axial force components of the plasma arc energy and the high level converging secondary gas 518 streams. However, under some conditions, instabilities occur where particles from the melted wire free end 370 are not uniformly melted as the cathode subassembly 210 is rotated around the rotational centerline 206 of the wire 310 whereby some part of the wire free end 370 is accelerated away from the free end 370 in larger droplets 72 which are not atomized into fine particles 74. These large particles or droplets 72 are propelled as large agglomerate masses toward the substrate 84 and are included into the coating (i.e. deposit 82) as it is being formed, resulting in coating of poor quality.
As indicated earlier, high velocity secondary gas 518 is released from typically equi-angularly spaced bores 556 to project a curtain of secondary gas 518 streams about the plasma arc 60. The supply 524 of secondary gas 518, such as air, is introduced into the chamber 550 under high flow, with a pressure of about 20-120 psi. The chamber 550 (i.e. gas manifold 550) acts as a plenum to distribute the secondary gas 518 to the series of typically equi-angularly spaced passageways 540 which direct the secondary gas 518 as a concentric converging stream which assists the atomization and acceleration of the particles 70. Each passageway 540 can have an internal diameter of about 0.040-0.090 inches and projects a high velocity air flow at a flow rate of about 10-60 scfm from the total of all of the passageway 540 combined. The plurality of passageways 540, typically ten in number, are located concentrically around the constricting orifice 224, and are radially and substantially equally spaced apart. To avoid excessive cooling and turbulence in the arc zone at the plasma arc 60, these streams are typically radially located so as not to impinge directly on the wire free end 370. The passageways 540 are spaced angularly apart so that the wire free end 370 is centered midway between two adjacent passageways 540, when viewed along the axial centerline 76 of the constricting orifice 224. Thus, as shown in
A cathode assembly 210 includes the cathode holder 214 which secures the position of the cathode 212. Down from the opening 224 in the nozzle 220 (the plasma nozzle 222) is the wire 310 which moves through the guide tip 330. The free end 370 of the wire 310. The center vector 78 is illustrated as a dotted line bisecting the cathode 212 down to the free end 370 of the wire 310
The system 100 can be implemented with respect to virtually any prior art apparatus 50. The system 100 can be implemented using a wide variety of different assemblies, components, and component configurations. The system 100 can also be implemented using a variety of different non-symmetrical passageway configurations 549 to deflect the particle stream 70 in a horizontal and/or vertical manner.
No patent application can disclose through text descriptions or graphical illustrations all of the potential embodiments of an invention. In accordance with the provisions of the patent statutes, the principles and modes of operation of the system are explained and illustrated with respect to certain preferred embodiments. However, it must be understood that the components, configurations, and methods described above and below may be practiced otherwise than is specifically explained and illustrated without departing from its spirit or scope. Each of the various components, assemblies, and other elements described in the glossary set forth in Table 1 above can be implemented in a variety of different ways while still being part of the spirit and scope of the invention.
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