System and method for treating surfaces of components

A system (10) for coating surfaces of a workpiece (12) comprises a biasing system (242) for connection to said workpiece (12) and an anode (76) such as to negatively bias the workpiece relative to the anode and a vacuum source (42, 44) for evacuating an interior of the workpiece (12). A gas supply (224, 226, 228) is employed for introducing a gas containing a treatment material to said workpiece and a control system (244) controls the biasing system (242), the vacuum source (42, 44) and the gas supply (224, 226, 228) so as to establish a hollow cathode effect within the workpiece (12). A pair of coupling heads (16, 18) are supported on articulated arms (22, 24, 26) movable in one or more of three axes and include removable shields (78) to protect the heads (16, 18) and an anode mount (74) for receiving an anode (76). The articulated arms allow the system to accommodate a plurality of different shaped and different sized workpieces while the shields protect the coupling heads during a deposition process.

TECHNICAL FIELD

The present invention relates to a system and method for treating surfaces of components and relates particularly but not exclusively to such systems for use in coating or modifying the internal surfaces of components such as pipes with complex shapes and the like.

BACKGROUND ART

“Plasma enhanced chemical vapor deposition” (or PECVD) is a known technique used to form films on various substrates. For example, Felts et al., U.S. Pat. No. 5,224,441, describes an apparatus for rapid plasma deposition. In the plasma enhanced chemical vapor deposition of silicon oxide, a gas stream including components such as a volatilized organosilicon compound, oxygen, and an inert gas such as helium or argon, is sent into an enclosed chamber at reduced pressure and a glow discharge plasma is established from the gas stream or its components. A silicon oxide layer is deposited upon the substrate when it is positioned near the plasma. In such a system, the pressure is typically reduced from atmospheric pressure by a vacuum pumping system. Electrode surfaces are in electrical communication with the gases introduced into the system such that an electrical discharge or plasma is formed. The purpose of this discharge is to excite moieties in the system and cause them to be deposited onto the workpiece or substrate to be coated.

The use of the “hollow cathode effect” is known from published international patent application No. W0 2006/019565 which is owned by the assignee of the present application, in which the internal surface of tubes and pipes are modified by a treatment process in which the workpiece itself forms the deposition chamber. Treatment is effected within the workpiece by applying a biasing voltage between an electrode within the workpiece, or just at the exterior of the workpiece, and the workpiece itself while passing a treatment gas through the workpiece and maintaining the interior of the workpiece at a reduced pressure. The treatment gas contains the element to be deposited or implanted and the pressure is low enough to establish and maintain the “hollow cathode effect” in which the electron mean free path is slightly less than the diameter of the workpiece, thus causing electron oscillation and implantation or deposition of the desired element below or onto the surface of the component itself.

Plasma deposition systems (either PVD or CVD) generally employ a vacuum chamber of fixed size, with the workpiece to be coated placed in the chamber. The chamber is pumped down before a gas is introduced, and a plasma is generated by applying electrical power between electrodes in the chamber. Different size workpieces can be coated externally as long as the part does not exceed the size limitations of the chamber. However, the ability to coat internal surfaces is very limited. Published international patent application No. W0 2006/019565, which is owned by the assignee of the present application, discloses an arrangement which lends itself to the treatment of internal surfaces. In this arrangement, the pipe is sealed at either end to create a sealed volume that can be evacuated and into which can be passed a treatment gas prior to the application of a bias voltage between anodes positioned outside of the pipe and the pipe itself so as to create the plasma necessary for coating. While this arrangement provides a perfectly acceptable system for treating long components in the field, it is not easy to employ it in the treatment of complex shapes or to accommodate components of differing sizes or to accommodate component apertures of different sizes. Additionally, the anodes themselves are subjected to the coating effect and their performance deteriorates with time.

SUMMARY OF THE INVENTION

The present invention provides a system for treating a workpiece such as a pipe or the like which comprises a biasing system, for connection to a workpiece and an anode such as to negatively bias a workpiece relative to an anode; a vacuum source, for evacuating an interior of a workpiece; a gas supply, for introducing a gas containing a treatment material to said workpiece; a control system for controlling the biasing system, the vacuum source and the gas supply; and a coupling head comprising: a casing, having an inlet for receiving gas from said gas supply and an outlet for connecting with a workpiece to be treated; and a removable shield, at least partially shielding said casing from any gas introduced thereto.

In an alternative form of the present invention, there is provided a system for treating a workpiece comprising a biasing system, for connection to a workpiece and an anode such as to negatively bias a workpiece relative to an anode; a vacuum source, for evacuating an interior of a workpiece; a gas supply, for introducing a gas containing a treatment material to said workpiece; a control system for controlling the biasing system, the vacuum source and the gas supply; a pair of coupling heads comprising: an input coupling head having a casing, said casing having an inlet for receiving gas from said gas supply and an outlet for connecting with a workpiece to be treated; an output coupling head having a casing, said casing having an inlet for connection to a workpiece and for receiving gas from said workpiece and an outlet for connection with said vacuum source; and a removable shield, at least partially shielding a casing from gas introduced thereto.

Preferably, the shield comprises a circular shield having an inlet therein for receiving gas into the interior thereof and an outlet for coupling to the outlet of the coupling head. It may also include an anode aperture for receiving an anode when inserted into said casing. The casing may include an anode mounting for receiving an anode within the interior of said casing and the mount may comprise an external mount through which said anode may be inserted so as to protrude into said casing.

In order to accommodate workpieces having differing aperture sizes, one may provide a size adjustable coupling for coupling said coupling head to a plurality of different sized workpieces. Such a coupling may include an ultra-torr type fitting, which is easily altered to accommodate a number of different sized workpieces.

A further degree of adjustment is provided by way of an adjustable mount onto which said coupling head is positioned such as to allow adjustment in one or more of three axes. In one arrangement, this adjustable mount comprises a linear track, while in another arrangement it comprises an articulated arm arrangement. In a still further arrangement, the adjustable mount comprises the combination of an articulated arm and a linear track. When the adjustable mount is provided in the form of an articulated arm, it may comprise a plurality of pivotal arms, one or more of which is mounted about a substantially vertical axis for pivotal movement relative to an adjacent arm. Such an arrangement allows for the rapid alteration of the position of the coupling head, so as to speedily accommodate a change between workpieces of differing sizes. The articulated arms may be provided with an external gas supply passageway or, as described in a preferred arrangement, an internal passageway may be formed within the arms themselves such as to facilitate the passage of gas to and from the mounting heads. The use of internal passageways reduces the possibility of supply pipes becoming kinked or broken as a result of excessive arm movement and generally reduces clutter in the working environment. When provided with internal gas passageways, the arms include inlets and outlets for communication with adjacent arms, and further include a gas seal between the arms themselves, so as to ensure that gas does not escape to atmosphere. This gas seal can be differentially pumped to ensure leak integrity.

The coupling head is preferably provided with a closable opening or door through which the shield may be inserted and in which there may be positioned a viewing window so as to allow the observation of the plasma generation within the workpiece itself and to monitor the condition of the anode. A portion of the closable opening may be provided with a location surface for cooperation with a corresponding location flange provided on the shield itself so as to, at least partially, locate the shield within the housing. In order to more accurately locate the shield, it may be desirable to employ a second location surface on the head for location with a second location flange or portion on the shield itself.

In a preferred arrangement, the system comprises a pair of coupling heads substantially as described above, such as to accommodate a workpiece therebetween and for coupling to apertures on said workpiece itself. This arrangement is particularly advantageous when it is desired to process at high speed a number of different sized and different shaped workpieces.

The above system may be further provided with a cross-linking duct between the coupling heads and include two vacuum pumps provided in association with each coupling head. The cross linking allows for the use of both vacuum pumps in combination when reducing the pressure within the workpiece and separately when drawing gas through the workpiece.

It has been found that benefit can be gained from employing one or more plasma reflectors between the coupling head or heads and the workpiece itself. Such reflectors help ensure the plasma is fully developed before it enters the workpiece, and this helps ensure a more even application of the treatment to the surface thereof.

Gas may be generated or introduced in a number of different ways. For example, one may employ a pressurized source of gas, in which case a simple pressure regulator and a Mass Flow Controller (MFC) may be used between the gas source and the head. Alternatively, one may employ a gas bubbler or an evaporator.

In the above arrangements, the biasing system is configured such as to apply a voltage sufficient to generate a plasma within the workpiece and the vacuum source is configured such as to establish a hollow cathode effect.

The system employs removable anodes and shields, but may be provided with these components fitted.

According to a still further aspect of the present invention, there is provided a method of operating the system described above comprising the steps of: connecting a workpiece to said coupling head such that the outlet of said coupling head is in flow communication with an interior of said workpiece; reducing the pressure within the interior of said workpiece and applying a biasing voltage between the workpiece and the anode such as to establish a hollow cathode effect and generate a plasma within said workpiece; and introducing a gas containing a treatment material into said coupling head and passing it into said workpiece such as to allow for the deposition or implantation of treatment material.

DETAILED DESCRIPTION

Referring now to the drawings in general but particularly toFIG. 1, a system10for modifying the surface of a workpiece12comprises a base portion14upon which is mounted a first coupling head16and an optional second coupling head18. One or more of the heads16,18are mounted for relative movement on an articulated arm20(not labelled) for movement in one or more of three axes X, Y, Z. The arms themselves20comprise a plurality of pivotal arms22,24,26, each of which is pivotable about an axis A, B, C such as to accommodate movement within axes Y and Z and are each preferably provided with an internal passageway extending from inlets28to outlets30such as to form a gas passageway, the function of which will be described in detail later herein. Optionally, gas may be supplied via an external gas supply pipe shown schematically by dotted lines32. The arms are mounted to each other by means of a bearing mount which incorporates a gas seal and the arrangement allows the arms to pivot relative to each other whilst preventing gas escaping to atmosphere. The arrangement is best seen by referring toFIGS. 9 and 10described in detail later herein. One end of the arm assembly is provided with a “rise and fall” mechanism shown schematically at38which allows the entire arm to be moved in the Z axis. Referring now toFIGS. 1 and 2in combination, it will be appreciated that the otherwise free end of the arms is provided with the coupling heads16,18which are each mounted in bearing mounts52,54for rotational movement about axis D. The combination of movement about axes A to D allows the coupling heads to be speedily repositioned between desired positions and facilitates the coupling to workpieces of various shapes. A cross-linking duct40is provided within the base portion and acts to connect the arms to vacuum pumps42,44provided within the base itself. Isolators46,48,50allow the pumps to be used together or individually to draw a vacuum from either or both ends of a workpiece12positioned on the system10.

Referring now toFIGS. 1 to 6in general, the coupling heads themselves are substantially the same and, consequently, like reference numerals will be used to denote the same components. The heads16,18include an outer casing56having a first opening58connected to the gas passageway in the arms and a second opening60for connection with a workpiece12positioned between the heads. A door62over a further opening64is mounted by hinge66and provided with a locking mechanism68and seal70to facilitate access to the interior of the coupling head16,18while also facilitating maintenance of a vacuum when required. An optional transparent window72may be provided in the door62so as to allow observation of any plasma created within the workpiece. The casing56is further provided with a mounting point74for receiving an anode76which extends through the casing and into the interior of the coupling head itself such that it is positioned adjacent the opening communicating with a workpiece12. A shield78(best seen inFIGS. 3 and 5) is removably mounted within the head16,18by means of flanged location surface80which engages with a corresponding location surface82provided on the opening portion of the head itself. The end of the shield78remote from flange80is provided with a second location flange or portion84which engages with a corresponding location surface86on the head16,18.FIG. 6illustrates the shield in more detail, and further illustrates an aperture88for allowing treatment gas to enter the head and a further aperture90through which the anode76may be inserted.

Referring now particularly toFIG. 3, a further component of the system includes an adjustable coupling92in the form of, for example, a KF100™ (4″ diameter) type fitting94to the head16,18and a 4″ ultra-torr type fitting96to the workpiece. Other diameter workpieces (smaller or larger) can be accommodated by using a connector with different diameter Ultra-Torr™ fittings that adapt up or down to the KF100™ fitting to the head. A centering ring98within the KF100™ fitting is made of an insulating material, such as ceramic, to provide electrical isolation between the pipe which is biased as the cathode and the heads16,18. A further ceramic piece100can also be inserted between the outer diameter of the pipe and the inner diameter of the anode housing to prevent the formation of stray plasma on the outside of the pipe.

FIG. 7illustrates an alternative system200in which the coupling heads16,18are each mounted on a linear track arrangement202by means of a rise and fall mechanism shown schematically at204. The details of the coupling heads16,18and the sealing mechanism remain as described above except for the deletion of the coupling arms22,24,26.

FIG. 8illustrates the gas supply and electrical connections by way of a schematic layout. The workpiece12is connected to the gas supply by means of connections220,222which in turn are connected to the various gas supply arrangements shown generally at224,226and228. The vacuum pumps42,44are shown connected to cross-linking duct40. While it will be appreciated that various forms of gas supply may be employed, the readers' attention is drawn to an evaporator arrangement at224in which an evaporator230is provided to evaporate a source of liquid diamond like component from injection mechanism232. This injection mechanism supplies a small amount of liquid which is completely vaporized in the heated flash evaporator224. An inert carrier gas such as argon or nitrogen can be added to help transport the vaporized liquid to the chamber. Item226illustrates a heater arrangement234in which a precursor liquid is heated to a temperature where it has a certain vapor pressure. A carrier gas is then “bubbled” through the heated liquid such that the gas bubble picks up an amount of precursor liquid as the ratio of the vapour pressure of the liquid at that temperature and pressure over the total pressure in the bubbler. A sublimer can also be used in the case of a solid precursor. In this case, the solid is heated to generate a certain vapor pressure and a carrier gas is used to move the precursor gas to the chamber. Item228discloses a still further arrangement in which sources of pressurized gas shown generally at238is supplied via Mass Flow controllers shown generally at240and then directed to connections220and/or222. A biasing system is shown generally at242and includes a source of DC power and a pulsing mechanism connected to the workpiece12and anode76as shown diagrammatically inFIG. 1. A control computer or CPU is shown schematically at244and is connected to the gas and electrical supply components in order to control said components as necessary during the treatment process. The control computer includes a sequencing control for controlling the selection of supply according to a desired or preprogrammed control sequence.

The operation of the above-mentioned requires the connection of a workpiece12to the coupling heads16,18such that said heads16,18are in flow series therewith and reduce the pressure within the interior of said workpiece to a desired pressure by operating vacuum pumps42,44. A biasing voltage is then applied between the workpiece and the cathode by means of biasing system242such as to establish a hollow cathode effect and generate a plasma within said workpiece itself. The control computer244is configured to control the application of the biasing voltage, the vacuum pumps and the gas supply so as to provide the required conditions for creating the hollow cathode effect and for deposition or implantation of treatment material. A series of gas treatment steps is then performed as necessary in order to facilitate implantation or deposition of treatment material into or onto the surface of the workpiece itself. Such processes are described in detail in published international application WO 2006/019565 and are, therefore, not described in further detail herein.

Referring now toFIGS. 9 and 10which illustrate a coupling assembly300provided between arms22,24,26, and from which it will be appreciated that the assembly comprises an upper and a lower portion302,304, respectively. The upper portion includes an outer surface306having three circumferentially extending grooves308,310and312which house seals314and316on either side of a bearing shown schematically at318. The upper portion302is assembled into the lower portion of the assembly such that seals314,316and bearing318engage with an inner surface320on lower portion304and provide a gas-tight seal on either side of a bearing surface which allows one portion to rotate relative to the other so as to facilitate articulation of the arms22,24,26. Also shown inFIGS. 9 and 10are additional seals322and324provided on upper and lower surfaces326and328, respectively, which, in operation, act to seal the ends of the coupling relative to the arm portion to which it is secured. In order to facilitate securing of the coupling, one may provide a series of holes330on a flange332of the lower portion304for receiving bolts (not shown) which may be secured into threaded holes (FIG. 12) in a lower arm. The upper portion may be provided with corresponding threaded holes334for receiving bolts (not shown) bolted through from an internal portion of an upper arm. Of particular interest inFIG. 10is the evacuation outlet shown generally at336and which comprises a hole338extending through portion304and communicating at an inner end with the groove312in which the bearing318is situated. A portion of the hole is provided with a screw thread340for receiving a pipe fitting342having a corresponding thread portion344provided at one end and a flexible tube346on an otherwise free end. The flexible tube346is, in turn, operably connected to an evacuation pump42,44ofFIG. 1or a separate pump (not shown). A series of coupling bearings may be linked by means of a manifold tube system (not shown). In operation, a reduced pressure is maintained between the seals314and316such as to purge any treatment gas passing through the arms and escaping into the bearing portion of the coupling. Such a system is also referred to herein as being “differentially pumped”.

FIG. 11illustrates an alternative to the coupling92shown inFIG. 3. In this alternative, the walls318taper between the fittings94,96which allows for the plasma created therein to fully develop before it enters the component to be coated. In effect, the walls act like deflectors funnelling the created plasma as it passes through this section.FIG. 12provides a perspective view of the arm arrangement22,24,26and illustrates the bolting positions360provided to allow the portions304,306of the coupling member300ofFIGS. 9 and 10to be secured to their respective arm portions.