GB2569996A

GB2569996A - Heated vacuum system

Info

Publication number: GB2569996A
Application number: GB1800311.1A
Authority: GB
Inventors: Charles Lamb Peter; Glyn Horler Richard
Original assignee: Edwards Ltd
Current assignee: Edwards Ltd
Priority date: 2018-01-09
Filing date: 2018-01-09
Publication date: 2019-07-10
Also published as: WO2019138218A1; GB201800311D0; JP3230119U; CN214381456U; DE212019000162U1

Abstract

A heated vacuum system and, in particular, a multilayer heater coating 9 for a vacuum system or a component thereof, such as a conduit or a rotor chamber 10 of a pump, comprises an inner insulation layer bonded to a surface of the component, a heater layer coating an outer surface of the inner insulation layer and an outer insulation layer coating an outer surface of the heater layer. A sealing layer may further be provided coating an outer surface of the outer insulation layer. The outer insulation layer may be less thermally conductive than the inner insulation layer. Electrical connection to the heater layer may be provided by a detachable connector part 15 comprising two connectors 13, 14 which selectively engage copper alloy plates 11, 12 formed on the heater layer. The invention further relates to a method of manufacturing a multilayer heater coating for a vacuum system, and vacuum systems and components thereof.

Description

HEATED VACUUM SYSTEM

Field of the Invention [001] The present invention relates to a heated vacuum system and, in particular, a multilayer heater coating for a vacuum system or a component thereof. The invention further relates to a method of manufacturing a multilayer heater coating for a vacuum system, and vacuum systems and components thereof.

Background to the Invention [002] When objects are placed under vacuum, gas embedded within the material and on the surface, evolves from their surfaces. The generation of gas by this process is known as outgassing. Outgassing becomes a progressively significant proportion of the total gas load once a vacuum chamber is roughed down to below 0.1 mbar. For ultra-high vacuum systems (10-7 mbar or less), outgassing is the most important factor influencing degassing and the time to ultimate pressure.

[003] Outgassing can be reduced by eliminating elastomer, hydrocarbon oil and greases from the vacuum pumps; avoiding other materials known to have poor outgassing performance, such as mild steel or porous surfaces; and using clean-room techniques to avoid contamination.

[004] In addition, to reduce the time taken to achieve ultimate pressure in ultra-high vacuum systems it is normal practice to raise the temperature of the vacuum chamber and pump to improve the rate of evolution from their surfaces.

[005] Similarly, vacuum pumps and their components may also be heated in industrial manufacturing settings, such as semiconductor processing. In these processes, maintaining a high pump temperature may prevent the condensation and/or sublimation of liquids and/or solids from a gas stream and thereby prevent the pump and/or pipe work from having to handle particulates and allow the gas molecules to be more readily pumped.

[006] Traditional heat sources may comprise wire heating elements built into the vacuum system or a component thereof or tapes, cables and bands that are attached to or wound round the system’s external surfaces, which are in turn covered in lagging or other insulation.

[007] Traditional heating methods of this type have been found to present certain disadvantages. For instance, when a heating cable is employed it may be difficult to achieve uniform contact between heat source and the surface: resulting in variable surface temperatures and poor heat transfer.

[008] As will be appreciated, depending on the specifics of the system, cold spots may not degas adequately, or conversely may facilitate condensation or sublimation, which in turn may have a deleterious effect on the overall system pressure and/or performance. Quilted jacket heaters ameliorate some of these problems; however, they are bespoke manufactured and therefore often prohibitively expensive.

[009] The present invention addresses, to at least an extent, these and other problems associated with the prior art.

Summary of the Invention [010] Accordingly, in a first aspect, the invention provides a multilayer heater coating for heating a vacuum system or component thereof. The multilayer heater coating comprises an inner insulation layer bonded to a surface of the vacuum system or component thereof; a heater layer coating an outer surface of the inner insulation layer, and an outer insulation layer comprising a ceramic or glass coating an outer surface of the heater layer. The inner and outer insulation layers each have a greater electrical resistance than the heater layer. The outer insulation layer is less thermally conductive than the inner insulation layer. Optionally, the multilayer heater coating may comprise a sealing layer at least partially coating an outer surface of the outer insulation layer.

[011] Preferably the ceramic inner and outer layers each have an electrical resistance at least about 1x1010 times greater than the heater layer, preferably at least about 1x1012 times greater, preferably from about 1x1010 times greater to about 1x1016 times greater. Preferably the heater layer has a resistance of from about 0.005 Ω m to about 0.1 Ω m, preferably from about 0.01 Ω m to about 0.05 Ω m, 0.02 Ω m being an example. Preferably the inner and outer insulation layers each have an electrical resistance of from about 1χ109Ω m to about 1χ1015Ω m, preferably from 1χ101θ Ω m to about 1x1012 Ω m, 1x1011 Ω m being an example. Electrical resistance may be measured according to ASTM D2149 -13.

[012] Additionally, or alternatively, the thermal conductivity of the inner insulation layer is at least about five times higher, more preferably from about five times to about twenty times higher than the outer insulation layer. The inner insulation layer may have a thermal conductivity of from about 10 W/m-K to about 50 W/m-K, preferably from about 20 W/m-K to about 40 W/m-K, 30 W/m-K being an example. Additionally, or alternatively, the outer insulation layer may have a thermal conductivity of from about 0.5 W/m-K to about 10 W/m-k, preferably from about 1 W/m-K to about 5 W/m-K, 3 W/m-K being an example. Thermal conductivity may be measured according to ASTM C1470.

[013] Advantageously, because the outer insulation layer comprises a ceramic or glass, the multilayer heater coatings according to the invention are able to operate at higher temperatures than are appropriate with polymer insulation layer or lagging. Moreover, a ceramic outer insulation layer may have the further advantage of being relatively tough, thereby resisting scratching during mishandling which could damage the top coat and expose the electrical layer. Furthermore, because the outer insulation layer is different to the inner insulation layer, the thermal performance can be better tailored to the specific requirements of the component and/or system.

[014] Typically, an uninsulated portion of a surface of the heater layer is not covered by an insulation layer and is configured such that in use an electrical current from a non-permanent electrical connector may be passed through said uninsulated portion. Typically, the uninsulated portion is a minor portion of the outer surface of the heater layer that is not covered by the outer insulation layer.

[015] Accordingly, in a further aspect, the present invention provides a multilayer heater coating for heating a vacuum system or a component thereof. The multilayer heater coating comprises an inner insulation layer bonded to a surface of the vacuum system or component thereof; a heater layer coating an outer surface of the inner insulation layer; and an outer insulation layer coating an outer surface of the heater layer. An uninsulated portion, typically a minor portion, of an outer surface of the heater layer is not covered by an outer insulation layer and is configured such that in use an electrical current from a non-permanent electrical connector may be passed through said uninsulated portion. Typically, the uninsulated portion is an outer surface of the heater layer that is not covered by the outer insulation layer. The multilayer heater coating may comprise an optional sealing layer coating an outer surface of the outer insulation layer.

[016] As in the previous aspect of the invention, the inner and outer insulation layers are typically more electrically resistive than the heater layer, and the outer insulation layer is less thermally conductive than the inner insulation layer.

[017] An electrical connector may be selectively coupled to, and decoupled from, the multilayer heater coating to provide electrical power to the heater layer via the uninsulated portion. Typically, the electrical connector is magnetically and/or mechanically coupled to the multilayer heater coating, preferably the heater layer. The means for coupling the connector to the heater layer is preferably reversible, i.e. non-permanent. Advantageously, employing such reversible attachment provides a more durable apparatus, compared to those with permanent, e.g. soldered, connections.

[018] Typically, the electrical connector is configured to directly engage, i.e. touch, the uninsulated portion of the heater layer, or a conductive material in electrical contact with said heater layer. The conductive material may be, for instance, a protective metallic plate, e.g. a copper plate, that may be bonded to the surface of the heater layer, preferably at least substantially covering the uninsulated portion. Preferably the conductive material is thermally sprayed, or otherwise deposited, directly onto the heater layer. Advantageously, employing a protective plate provides a more robust apparatus. Thermally spraying the protective plates directly onto the heater layer avoids the need for a separate bonding material, e.g. solder; thereby further increasing robustness, particularly at higher temperatures (greater than about 300 °C), where solder may typically begin to soften and limit the operating envelope of the heater.

[019] The electrical connector preferably comprises a member or members for engaging the uninsulated portion of the heater layer, or protective metallic plate. For instance, the electrical connector may comprise a sprung or flexible connector, for instance a pogo connector, spring loaded connector, button connector, battery contact or leaf spring connector, typically two pogo connectors are employed. Pogo connectors are preferred because they can accommodate slight variations in the position, height or roughness of the contact area.

[020] In a further aspect, the present invention provides a vacuum system or component thereof comprising a multilayer heater coating. The multilayer heater coating comprises: an inner insulation layer bonded to a surface of the pump, a heater layer coating an outer surface of the inner insulation layer, an outer insulation layer coating an outer surface of the heater layer, and an electrical connector coupled to the vacuum system or component thereof for providing electrical power to the multilayer heater coating. The electrical connector may comprise a first part coating a surface of the vacuum system or component thereof and a detachable second part which is configured to selectively engage the first part to provide an electrical connection therewith. Typically, the first part comprises the heater layer or a conductive material bonded thereto, such as a protective metal plate. The detachable second part may comprise a sprung or flexible connector, preferably a pogo connector, typically two pogo connectors.

[021] In a further aspect, the present invention provides a method of manufacturing a vacuum system or component thereof comprising a multilayer heater coating. Typically, the method comprises the steps of bonding an inner insulation layer to a surface of the vacuum system or component thereof, coating an outer surface of the inner insulation layer by thermally spraying a heater layer thereon, and at least partially coating an outer surface of the heater layer by thermally spraying an outer insulation layer onto a portion of the outer surface of the heater layer, the outer insulation layer preferably comprising a ceramic or glass. The method may further comprise the step of coating an outer surface of the outer coating with a sealing layer.

[022] Advantageously, a sealing layer may cover imperfections or porosity within the outer insulation layer, which could otherwise lead to electrical breakdown in high humidity or corrosive external environmental conditions.

[023] Unless otherwise stated, the following preferred features may be employed in all aspects of the invention.

[024] In use, the inner insulation layer prevents the heater layer from earthing through the remainder of the vacuum system or component thereof. Advantageously, the inner insulation layer may comprise a material selected from the group consisting of a ceramic or a polymer, preferably a ceramic.

[025] Where the inner insulation layer comprises a ceramic, the ceramic may be selected from the group consisting silicon carbide, boron nitride, alumina, and aluminium nitride. Alumina is particularly preferred because it is resistant to high thermal temperatures and so will resist damage when subsequent layers are applied through plasma deposition, where the temperature may exceed 5000°C.

[026] Additionally, or alternatively, the inner insulation layer may be a polymer.

[027] When present, the polymer may typically be selected from group consisting of thermoplastic materials or thermosets. Thermoplastic materials are preferred and particularly those classified as high performance thermoplastic materials as a result of their thermal properties.

[028] Preferably, the polymer has a melting temperature above about 250 °C, more preferably above about 300 °C, even more preferably above about 400 °C.

[029] Preferred thermoplastics are selected from the group consisting of liquid crystal polymers, including aromatic polyamides and aromatic polyesters, aromatic polyimides, polyamides, polysulpones, polyethylenimines, and polyether ether ketone (PEEK), or derivatives or copolymers thereof.

[030] A preferred polyimide may comprise poly(4,4'-oxydiphenylene-pyromellitimide). Alternatively, polyamide nylon resins or polybutylene terephthalate resins may be selected.

[031] The polymers may additionally include one or more from the group consisting antistatics, antioxidants, mould release agents, flameproofing agents, lubricants, colorants, flow enhancers, fillers, including nanofillers, light stabilizers and ultraviolet light absorbers, pigments, and plasticisers.

[032] In embodiments, the polymer may be a composite comprising a polymer matrix and a dispersed phase which increases the temperature resistance of the polymer matrix: glass fibre reinforced polymers and carbon fibre reinforced polymers are particularly preferred.

[033] When the inner insulation layer comprises a polymer, the heater layer, outer insulation layer and, optional, sealing layer may be sequentially coated onto the polymer before the polymer is bonded to the vacuum system or component thereof.

[034] Once a multilayer heater coating so assembled is placed on the portion of the vacuum system or component thereof to be heated, the first heating cycle of the multilayer heater coating may be used to bond the multilayer heater coating permanently to the vacuum system or component thereof. Advantageously, this allows the multilayer heater coating to be applied in situ and/or retrofitted to an existing vacuum system or component thereof.

[035] Alternatively, the inner insulation layer, heater layer, and/or outer insulation layer are sequentially thermally sprayed, or otherwise deposited, over an outer surface of the vacuum system or component thereof. This is particularly preferred when the inner insulation layer is ceramic.

[036] The inner insulation layer may be permanently affixed to the surface of the vacuum system or component thereof.

[037] Thermal spraying is typically a coating process in which melted or heated material is sprayed onto a surface where it solidifies to form a layer. The coating precursor is typically heated by electrical (plasma or arc) or chemical means (combustion flame).

[038] Thermal spraying techniques suitable for use in the invention include plasma spraying, wire arc spraying, flame spraying, high velocity oxygen fuel coating spraying (HVOF), high velocity air fuel (HVAF), warm spraying and cold spraying. The skilled person may select an appropriate technique depending upon the specific coating and substrate. Preferably, the inner insulation layer, heater layer and outer insulation layer are applied using the same thermal spraying technique.

[039] Typically, a fixed torch is used and the vacuum system or component thereof component is moved. However, for more complex shapes the component may itself be fixed and the torch may be moved relative thereto. The skilled person will choose a process depending upon the specific component in question.

[040] Additionally, or alternatively, the inner insulation layer, heater layer and/or outer insulation layer are deposited using one or more of the techniques selected from the group consisting of high velocity oxygen fuel (HVOF), electrophoretic deposition (EPD), low temperature deposition (LPD), electron beam physical vapour deposition (EBPVD), air plasma spray (APS), electrostatic spray assisted vapour deposition (ESAVD), direct vapour deposition, and combinations thereof.

[041] Typically, the inner insulation layer has a thickness of from about 20 pm to about 500 pm, more preferably from about 50 pm to about 250 pm. 100 pm being an example. Advantageously, insulation layers of this thickness have been found to provide good coverage without undesirable thermal restriction between the heater layer and the substrate to be heated. Contact between the heater layer and the substrate may breakdown electrical continuity and prevent the heater from working.

[042] In an example, the inner layer comprises alumina and has a thickness of from about 50 pm to about 200 pm, preferably about 100 pm.

[043] Typically, when the outer layer insulation is a ceramic the outer insulation layer comprises a material selected from the group consisting of zirconia, alumina zirconia, Yttria-stabilised zirconia, magnesium-stabilised zirconia, or silica. Alumina zirconia or zirconia are particularly preferred because of its combination of hardness and insulation properties. Alternatively, where the outer insulation layer is a glass, the glass comprises silica. Fused silica is particularly preferred.

[044] Preferably the outer insulation layer has a Mohr scale hardness of about 7 or greater, preferably about 8 or greater, preferably from about 9 being an example.

[045] The outer insulation layer may be the external surface coating, and is typically a thermal and electrical insulator, reducing heat loss to the environment and preventing short-circuiting as a result external contact. The outer layer thereby improves thermal efficiency of heating and provides a safe external layer for the user.

[046] Typically, the heater layer is electrically insulated from the vacuum system or component thereof, which may itself be metallic. Preferably, substantially all of the inner surface of the heater layer is separated from the outer surface of the vacuum system or component thereof by at least the inner insulation layer. This will stop the adjacent heater layer shorting to earth on the surface of the vacuum system or component thereof but still enable the generated heat to be transferred to the pump surface. Typically, the heater layer is coated directly onto the inner insulation layer, which may in turn be coated directly onto the surface of the vacuum system or component thereof.

[047] Typically, the outer insulation layer is coated directly onto the heater layer. Preferably the outer insulation layer is applied by thermal spraying. In embodiments, only a portion of the heater layer may be covered by the outer insulation layer. For instance, a portion of the heater layer may be left uncoated for use with an electrical connector. A stencil, masking tape or similar may be used during spraying, and the subsequently removed, to provide an uncoated portion of heater layer.

[048] Typically, the outer insulation layer has a thickness of from about 50 pm to about 500 pm, more preferably from about 75 pm to about 200 pm. 100 pm being an example.

[049] The heater layer comprises a resistive heating material that increases in temperature as an electrical current is passed through it. The heater layer may be metallic or ceramic.

[050] When the heater layer is metallic it may comprise a material selected from the group consisting of nichrome, titanium alloys, kanthal, cupronickel, platinum, iridium, rhenium, palladium, rhodium, gold, copper, silver, tungsten and alloys of thereof. Titanium nickel chromium alloys are particularly preferred because of their low electrical resistance, allowing relatively thin layers to be employed. 150 pm being an example.

[051] Alternatively, when the heater layer is ceramic it may be comprise a material selected from the group consisting of molybdenum disilicide or positive temperature coefficient ceramics, such as barium titanate, lead titanate, titanium nitride, zirconium nitride and titanium boride.

[052] Typically, the heater layer has a thickness of from about 50 pm to about 500 pm, more preferably from about 75 pm to about 250 pm. 150 pm being an example.

[053] The thickness of the heater layer may be uniform or vary, for instance within an individual multilayer heater element on a vacuum system or component thereof. By uniform thickness it is meant the thickness varies by no more than ± 2%.

[054] Additionally, or alternatively, individual multilayer heating elements, of the same or different thicknesses, may be employed on a single vacuum system or component thereof. Again, the individual multilayer heating elements may themselves be of uniform or varying thickness. Typically, thinner portions of heater layer will have a higher resistance and therefore heat more readily, whereas a thicker heater layer will have a lower resistance and therefore heat comparatively less readily. Advantageously, by varying the thickness of the heater layer, different parts of the vacuum system, or component thereof, may be heated at different rates and/or to different temperatures using a single multilayer heater coating.

[055] The sealing layer may typically comprise a polymer or ceramic glaze coated over the outer insulation layer, typically over the whole of the external surface of the remainder of the multilayer heater coating.

[056] Typically, the sealing layer will comprise a polymer. Typically, the polymer will comprise a material selected from the group consisting of a urethane liquid, phenolic liquid or silicone resin.

[057] The outer sealing layer protects the remainder of the multilayer heater coating from the surrounding environment. This may be particularly advantageous when the surrounding environment comprises corrosive material or wherein one or more of the components is sensitive to moisture.

[058] Typically, the sealing layer has a thickness of from about 50 pm to about 500 pm, more preferably from about 100 pm to about 200 pm. 150 pm being an example.

[059] An electrical connector will typically be coupled to the vacuum system or component thereof and provide electrical power to the multilayer heater coating. Preferably the electricity supply is less than about 250 V, more preferably from about 12 V to about 60 V. 24 V is an example.

[060] Preferably the multilayer heater coating may heat at least the area of the vacuum system or component thereof covered by the heater layer to a temperature of greater than 70 °C, preferably greater than about 200 °C, preferably greater than about 300 °C, preferably from about 200 °C to about 450 °C.

[061] Preferably the multilayer heater coating has a power output from about 0.5 W per cm2 to about 4 W per cm2, more preferably from about 1 W per cm2 to about 1.5 W per cm2.

[062] Preferably the outer surface of the portion of the vacuum system or component thereof to which the inner insulation layer is bonded has a surface roughness, Ra, of greater than about 1.5 pm, preferably from about 1.5 pm to about 10 pm, more preferably from about 1.5 pm to about 3.5 pm. 1.6 pm is an example. It has been found that surfaces of this roughness provide improved bonding and prevents the bond breaking down at higher temperatures, particularly when the inner insulation layer is itself coated onto the surface of the vacuum system or component thereof.

Brief Description of the Figures [063] Preferred features of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Fig. 1 shows a schematic representation of a multilayer heater coating.

Fig. 2 shows a multilayer heater coating and electrical connector.

Figs. 3 and 4 show prototype multilayer heater coatings

Fig. 5 shows the results of a heat cycling experiment performed using a prototype multilayer heater coating.

Detailed Description of the Invention [064] The present invention provides a vacuum system or component thereof comprising a multilayer heater coating (1).

[065] As illustrated in Fig. 1, the multilayer heater coating (1) may comprise an inner insulation layer (2), such as Mulite™, bonded to a surface of the pump (3), a heater layer (4) coating an outer surface (5) of the inner insulation layer (2), an outer insulation layer (6) coating an outer surface (7) of the heater layer (4), and, optionally, a sealing layer (not shown) coating an outer surface (8) of the outer insulation layer (6). As illustrated, the multilayer heater coating (1) also includes a power supply for providing electrical power to the heater layer (4).

[066] For the purpose of the invention, inner, innermost, and lower each refer to a surface or surfaces on the device-side of a layer; whereas outer, outermost and upper refer to a surface or surfaces on the non-device side.

[067] For the purposes of the invention vacuum system or component thereof may include any component of the vacuum system, including the vacuum chamber, pipe and duct work, exhaust system, and the pumping mechanism itself, including for instance the rotor chamber. Preferably, the multilayer heater coating may be applied to a vacuum chamber wall and/or rotor chamber wall and/or exhaust pipe or duct work walls.

[068] The multilayer heater coating may be employed in the heating of both high pressure and exhaust sections of a vacuum system, and/or low pressure, higher vacuum parts of the vacuum system. The multilayer heater coating may be applied to external and/or internal surfaces of the vacuum system or component thereof, for instance the external and/or internal surfaces of the vacuum chamber, rotor chamber, and/or piping or duct work.

[069] Vacuum systems suitable (or components thereof) for use in the invention may be dry pumps and include positive displacement and momentum transfer pumps, and/or getter pumps such as cryogenic, ion and non-evaporable getter pumps. Preferred positive displacement pumps may include scroll pumps, screw pumps, roots pumps, lobe pumps, rotary vane, liquid ring, and oil diffusion pumps, particularly those manufactured by Edwards Vacuums™. Preferred momentum transfer pumps may include turbomolecular pumps, particularly those manufactured by Edwards Vacuums™ under the trade names EXT™ or nEXT™.

[070] Where the multilayer heater coating is used to assist degassing an ultrahigh vacuum system or component thereof, typically the heating multilayer heater coating will be applied to or adjacent to those parts of the pump system exposed to the ultrahigh vacuum. For instance, heating the rotor chamber of a turbomolecular pump and/or the vacuum chamber associated therewith. The multilayer heater coating may for instance be coated onto an outer surface of the rotor chamber housing or the vacuum chamber housing.

[071] Alternatively, where the multilayer heater coating is used to reduce deposition of condensates on pump components, typically the multilayer heater coating will be applied to those parts of the pump that would otherwise be sufficiently cool for condensation and/or sublimation to occur. For instance, in pipe and/or duct work and/or rotor chamber.

[072] Multilayer heater coatings according to the invention have been found to be particularly effective in preventing deposition within vacuum pump exhausts systems, and components thereof, including deposition on the internal surfaces of exhaust system ducting and pipe work.

[073] Accordingly, in a further aspect, the invention provides a vacuum system comprising a vacuum chamber and a vacuum pump configured to pump gas from within the vacuum chamber to a location external to the vacuum chamber, wherein gas exits the vacuum pump into an exhaust management system and wherein the exhaust management system comprises a multilayer heater coating comprising an inner insulation layer bonded to a surface of the exhaust system; a heater layer coating an outer surface of the inner insulation layer, and an outer insulation layer coating an outer surface of the heater layer, wherein the inner and outer insulation layers each have a greater electrical resistance than the heater layer, and wherein the outer insulation layer is less thermally conductive than the inner insulation layer.

[074] Typically, the inner insulation layer is bonded to ducting and/or pipe work forming a part of the exhaust management system, preferably an outer surface thereof.

[075] In a further aspect, the invention provides a vacuum system comprising a vacuum chamber and a pumping system comprising one or more vacuum pumps configured to pump gas from within the vacuum chamber to a location external to the vacuum chamber. The pumping system may comprise a conduit for directing gas either from the vacuum chamber to one or more of the vacuum pumps, or from a first vacuum pump to a second vacuum pump within the vacuum system, the conduit having a surface comprising a multilayer heater coating comprising an inner insulation layer bonded to the surface of the conduit; a heater layer coating an outer surface of the inner insulation layer, and an outer insulation layer coating an outer surface of the heater layer, wherein the inner and outer insulation layers each have a greater electrical resistance than the heater layer, and wherein the outer insulation layer is less thermally conductive than the inner insulation layer.

[076] The pumping system may comprise two or more pumps in series and/or two or more pumps in parallel. Typically, the coated surface is an outer surface of the conduit.

[077] To improve fatigue resistance, it is preferable for the multilayer heater coating to be applied to flat or gently profiled surface. Therefore, where the shape requiring heating is complex blended radii and smooth transitions should ideally be employed, whereas sharp edges or rapid changes in profile may be avoided.

[078] Preferably the multilayer heater coating has a fatigue life of at least a thousand heating cycles.

[079] Figure 2 shows a section through a rotor chamber of vacuum system or component thereof (10) comprising a multilayer heater coating (9). Although not visible, the multilayer heater coating (9) comprises an inner insulation layer coated to a surface of the pump envelope, and a heater layer coating an outer surface of the inner insulation layer.

[080] Preferably, to reduce the incidence of shorting, the heater layer may not completely cover the inner insulation layer. Preferably, the area of the heater layer is smaller than the area of inner insulation, such that the inner insulation layer surrounds the peripheral edge of the heater layer. Preferably, the heater layer is surrounded by a border of inner insulation layer having a width of from about 1 mm to about 10 mm, preferably about 5 mm.

[081] The vacuum system or component thereof (10) further comprises an electrical connector coupled to the vacuum system or component thereof (10) that is used to provide electrical power to the multilayer heating coating. In the illustrated example, the electrical connector comprises a first part comprising two copper alloy plates (11, 12) thermally sprayed directly onto the heater layer and a detachable second part (15) comprising two pogo connectors (13, 14) which selectively engage the copper plates (11, 12) to provide an electrical connection therewith and the heater layer located below.

[082] As illustrated in Figure 2, when a multilayer heater coating extends around an outer surface of a component, for instance the circumference of a generally tubular body, a gap (18) is typically included between either end of a multilayer heater coating (9). In use, this gap (18) will result in a relatively cooler patch and so ideally the gap (18) is kept as narrow as practicable. Considerations when configuring size of the gap (18) may include the manufacturing method used for depositing the multilayer heater coating layers: for instance, when layers are thermally sprayed using masks as shielding, said layers may ‘bleed’ under the edge of the masks. Accordingly, an uncoated gap of from about 2 mm to about 10mm may surround the edge of a multilayer heater coating according to the invention. A 5mm gap is particularly preferred.

[083] As the skilled person will appreciate there is in theory no limit on the size of the heater layer that can be employed; however, as the size increases the performance of the heater will alter as the power density will change. Therefore, in practice, a plurality of separate multilayer heater coatings may be used to simultaneously heat larger components.

[084] For the purpose of the invention, separate multilayer heater coatings may each be referred to as an individual multilayer heater element. A vacuum system, or component thereof, may therefore comprise one or more individual multilayer heater elements, each comprising a single multilayer heater coating.

[085] As illustrated in Figure 2, the outer insulation layer (16) coats substantially all of the outer surface of the heater layer except for where the two metallic plates (11, 12) are situated.

[086] The pogo connectors are screwed into a connector housing (17), which housing reversibly couples to the vacuum system or component thereof (10) to hold the pogo connectors (13, 14) in electrical contact with the metal plates (11, 12). A magnet may be used to couple the housing (17) to the vacuum system or component thereof (10), alternatively a mechanical coupling or strap may be employed. Multilayer heater coatings according to the invention thereby avoid the need for soldering an electrical connection to the heater layer. The invention thereby provides a more robust electrical connection which can be used at higher temperatures.

[087] The pogo connectors (13, 14) are typically connected to a 24V electricity source.

[088] The invention will now be demonstrated by the following non-limiting example.

Example [089] To demonstrate the capability of multilayer heater coatings according to the invention, prototype parts as illustrate in Figure 3 were produced.

[090] The prototypes comprised a three-layer multilayer heater coating (9) applied to a steel band (19). The steel band is 120mm diameter, 50mm tall, with a substantially uniform wall having thickness of 3 mm.

[091] The three layers were: i) a 100 pm uniform thickness alumina inner insulation layer (silicon carbide, and aluminium nitride, of the same thickness were separately tested successfully); ii) a 150 pm uniform thickness titanium nickel chromium heater layer (50 pm, 100 pm, 150 pm and 200 pm were all successfully tested); and iii) a 100 pm uniform thickness outer layer of zirconia oxide.

[092] All three layers were applied using High Velocity Oxygen Fuel (HVOF) deposition. In the employed method, the material for coating was provided as ground powder (median particle size from 20 pm to 50 pm measured using laser diffraction) and fed into the path of a heated gas stream. The heated gas stream includes oxygen and fuel which is combusted and passed through a converging-diverging nozzle. In this example, kerosene was used as the fuel.

[093] As will be appreciated by the skilled reader, in HVOF methods heated gas at temperatures of several thousand degrees centigrade and travelling at supersonic speed is used to deposit the material on the substrate. As a result of the material being deposited in molten form, a substantially even and low porosity coating can be achieved. The porosity of a coating may be varied by altering the particle size of the ground powder to be deposited; generally, employing a lower particle size provides a higher density coating.

[094] The HVOF nozzle can either be fixed and the substrate moved relative thereto (e.g. rotated) to enable an even coverage, or the nozzle itself can be moved by a robot arm. The latter is preferred for complex components. For the example a stationary nozzle was employed.

[095] When manufacturing the prototypes, masking tape was used to protect areas of substrate where the coating layer was not required. For example, following its deposition, the peripheral edge of the inner insulation layer was masked to ensure the subsequently deposited heater layer did not directly contact the steel band. High-temperature resistant tape was used to manufacture the prototypes. Steel masks may be used instead of tape masking. Advantageously, steel masks may be reused multiple times.

[096] As illustrated in Figure 4, two copper conductor pads (20, 21) were deposited using HVOF on the heater layer to provide power terminal points. Power input wires (24, 25) were soldered (22, 23) onto the copper conductor pads (20, 21). To avoid the solder melting heating was limited to 250°C with a 24V input.

[097] As illustrated in Fig. 5, cyclic thermal testing of a prototype demonstrated that the multilayer heater coatings may be successfully operated.

[098] The multilayer heater coatings enable a rapid increase in temperature once activated. The multilayer heater coatings were robust and not easily susceptible to being scratched or scuffed. Thermal performance of 1 W/cm2 was achieved and thermal imaging confirmed a consistent thermal output from the multilayer heater coating with even coverage.

[099] It will be appreciated that various modifications may be made to the embodiments shown without departing from the spirit and scope of the invention as defined by the accompanying claims as interpreted under patent law.

Reference Numeral Key 1 Multilayer Heater Coating 2 Inner Insulation Layer 3 Pump/Component 4 Heater Layer 5 Outer Surface of the Inner Insulation Layer 6 Outer Insulation Layer 7 Outer Surface of the Heater Layer 8 Outer Surface of the Outer Insulation Layer 9 Multilayer Heater Coating 10 Vacuum System or Component 11 Copper Alloy Plate (1) 12 Copper Alloy Plate (2) 13 Pogo Connector (1) 14 Pogo Connector (2) 15 Detachable Second Part 16 Outer Insulation Layer 17 Connector Housing 18 Gap 19 Steel Band 20 Copper Conductor Pad (1) 21 Copper Conductor Pad (2) 22 Solder (1) 23 Solder (2) 24 Power Input Wire (1) 25 Power Input Wire (2)

Claims

1. A multilayer heater coating for heating a vacuum system or a component thereof, wherein the multilayer heater coating comprises: an inner insulation layer bonded to a surface of the vacuum system or a component thereof, a heater layer coating an outer surface of the inner insulation layer, and an outer insulation layer comprising a ceramic or glass coating an outer surface of the heater layer, and, optionally, a sealing layer coating an outer surface of the outer insulation layer, wherein the inner and outer insulation layers each have a greater electrical resistance than the heater layer, and wherein the outer insulation layer is less thermally conductive than the inner insulation layer.

2. The multilayer heater coating according to claim 1 wherein an uninsulated portion of a surface of the heater layer is not covered by an insulation layer and is configured such that in use an electrical current from a non-permanent electrical connector may be passed through said uninsulated portion.

3. A multilayer heater coating for heating a vacuum system or a component thereof, wherein the heating multilayer heater coating comprises: an inner insulation layer bonded to a surface of the vacuum system or a component thereof, a heater layer coating an outer surface of the inner insulation layer, and an outer insulation layer coating an outer surface of the heater layer, and, optionally, a sealing layer coating an outer surface of the outer insulation layer, wherein an uninsulated portion of the outer surface of the heater layer is not covered by the outer insulation layer and is configured such that in use an electrical current from a non-permanent electrical connector may be passed through said uninsulated portion.

4. A multilayer heater coating according to claim 3 wherein the inner and outer insulation layers each have a higher electrical resistance than the heater layer, and wherein the outer insulation layer is less thermally conductive than the inner insulation layer.

5. A multilayer heater coating according any preceding claim wherein the inner insulation layer comprises a material selected from the group consisting of a ceramic, a polymer or a polymer matrix composite, preferably a ceramic.

6. A multilayer heater coating according to claim 5 wherein the inner insulation layer comprises a ceramic selected from the group consisting silicon carbide, boron nitride, alumina, aluminium nitride, Spinel, mullite, preferably alumina.

7. A multilayer heater coating thereof according to any preceding claim wherein the inner insulation layer, heater layer and/or outer insulation layer are deposited using one or more of the techniques selected from the group consisting of high velocity oxygen fuel (HVOF), electrophoretic deposition (EPD), low temperature deposition (LPD), electron beam physical vapour deposition (EBPVD), air plasma spray (APS), electrostatic spray assisted vapour deposition (ESAVD), direct vapour deposition, and combinations thereof.

8. A multilayer heater coating according to any preceding claim wherein the outer insulation layer comprises a material selected from the group consisting of alumina zirconia, zirconia, Yttria-stabilized zirconia or silica.

9. A multilayer heater coating according to any preceding claim wherein the heater layer is metallic or ceramic.

10. A multilayer heater coating according to claim 9 wherein the heater layer is metallic and comprises an alloy selected from the group consisting of cupronickel, a titanium alloy or a chromium alloy: including nichrome; an iron chromium aluminium alloy; a titanium, nickel and a chromium alloy; a titanium, nickel and chromium alloy; preferably a titanium, nickel and chromium alloy.

11. A multilayer heater coating according to claim 9 wherein the heater layer is ceramic and selected from the group consisting of molybdenum disilicide or a positive temperature coefficient ceramic, such as barium titanate or lead titanate.

12. A multilayer heater coating according to any preceding claim wherein the thickness of the heater layer and/or inner insulation layer varies, and/or wherein the inner insulation layer comprises one or more distinct areas, each distinct area comprising a different material.

13. A multilayer heater coating according to any one of claims 2 to 12 further comprising an electrical connector non-permanently coupled to the uninsulated portion of the heater layer to provide electrical power to the heater layer.

14. A multilayer heater coating according to claim 13 wherein the electrical connector is magnetically and/or mechanically coupled to the multilayer heater coating.

15. A multilayer heater coating according to claim 13 or 14 wherein the electrical connector is configured to directly engage the uninsulated portion of the heater layer or a conductive material in electrical contact with said heater layer.

16. The multilayer heater coating according to any one of claims 13 to 15 wherein the electrical connector comprises a flexible or sprung connector, preferably a button connector, battery connector, leaf spring, or a pogo connector.

17. A method of manufacturing a vacuum system or a component thereof comprising a multilayer heater coating, the method comprising the steps of: a) bonding an inner insulation layer to a surface of the vacuum system, b) coating an outer surface of the inner insulation layer with a heater layer, and c) at least partially coating an outer surface of the heater layer with an outer insulation layer, the outer insulation layer preferably comprising a ceramic or glass, and d) optionally, coating an outer surface of the outer insulation layer with a sealing layer.

18. A multilayer heater coating for a vacuum system or component thereof, wherein the multilayer heater coating comprises: a) an inner insulation layer bonded to a surface of the vacuum system; b) a heater layer coating an outer surface of the inner insulation layer, c) an outer insulation layer coating an outer surface of the heater layer, and d) an electrical connector coupled to the vacuum system and configured to provide electrical power to the heater layer, wherein the electrical connector comprises a first part coating a surface of the vacuum system and a detachable second part which selectively engages the first part to provide an electrical connection therewith, and wherein the first part comprises the heater layer or a conductive material bonded thereto.

19. A vacuum system comprising a vacuum chamber and one or more vacuum pumps configured to pump gas from within the vacuum chamber to a location external to the vacuum chamber, wherein as gas exits one or more of the vacuum pumps it enters an exhaust management system and wherein the exhaust management system comprises a multilayer heater coating comprising an inner insulation layer bonded to a surface of the exhaust management system; a heater layer coating an outer surface of the inner insulation layer, and an outer insulation layer coating an outer surface of the heater layer, wherein the inner and outer insulation layers each have a greater electrical resistance than the heater layer, and wherein the outer insulation layer is less thermally conductive than the inner insulation layer.

20. A vacuum system according to claim 19 wherein the surface of the exhaust management system is a surface of a conduit through which gas from the vacuum pump is directed, typically an outer surface of the conduit.

21. A vacuum system comprising a vacuum chamber and a pumping system comprising one or more vacuum pumps configured to pump gas from within the vacuum chamber to a location external to the vacuum chamber, wherein the pumping system comprises a conduit configured to direct gas either from the vacuum chamber to one or more of the vacuum pumps, or from a first vacuum pump to a second vacuum pump within the pumping system, the conduit having a surface comprising a multilayer heater coating comprising an inner insulation layer bonded to the surface of the conduit; a heater layer coating an outer surface of the inner insulation layer, and an outer insulation layer coating an outer surface of the heater layer, wherein the inner and outer insulation layers each have a greater electrical resistance than the heater layer, and wherein the outer insulation layer is less thermally conductive than the inner insulation layer.

22. The vacuum system according to claim 21 wherein the pumping system comprises two or more pumps in series and/or two or more pumps in parallel.

23. The vacuum system according to claim 21 or 22 wherein the surface is an outer surface of the conduit.

24. A vacuum system or component thereof, or a multilayer heater, according to the figures and examples.

24. The vacuum system according to any one of claims 19 to 23 wherein the vacuum pump is a turbomolecular pump or a dry pump.

25. A vacuum system or component thereof comprising a multilayer heater coating according to any one of claims 1 to 16 or 18.

26. A vacuum system according to claim 25 comprising a turbomolecular pump or a dry pump.