Turbomolecular vacuum pump

Abstract

Turbomolecular vacuum pump (1) comprising at least one heating rod (20) comprising at least one holding part (20a) and one heating part (20b) by Joule effect when the heating rod (20) is electrically powered, the holding part (20a) forming a sheath for the electrical wires supplying the heating part (20b), at least one connection conduit (21) being arranged at least in part in a high-pressure stator (19) of the vacuum pump (1) for the passage of the holding part (20a), the heating part (20b) being received along at least one helical groove (14) of the high-pressure stator (19). Abstract figure: figure 1

Description

Title of the invention: Turbomolecular vacuum pump Technical field of the invention

[0001] The present invention relates to a turbomolecular vacuum pump. Technical background

[0002] Generating a high vacuum in an enclosure requires the use of turbomolecular vacuum pumps consisting of a stator in which a rotor is driven in rapid rotation, for example rotation at more than ninety thousand revolutions per minute.

[0003] In certain processes in which turbomolecular vacuum pumps are used, such as semiconductor or LED manufacturing processes, a deposition layer may form in the vacuum pump.

[0004] It is known to heat the stator by an external heating belt to prevent condensation of reaction products in pumps. However, new generations of processes produce more and more condensable by-products. In some cases, conventional heating is no longer sufficient to prevent the formation of by-products and it is not possible to further increase the temperature of the stator without risking mechanically weakening the aluminum rotor. Deposits can then appear on the stator of the high-pressure compression stage, known as Holweck, where the functional clearances with the rotor of a few tenths of a millimeter are relatively small, the rotor being little exposed because its rotation prevents the adhesion of deposits.If no preventive maintenance is done, the deposit can thicken and contact can be created between the rotor and the stator, leading to an immediate crash of the pump due to the high rotational speed of the rotor and its kinetic energy. Such destruction of the vacuum pump in a semiconductor manufacturing process can lead, in addition to the complete destruction of the pump, to the destruction of the batch of wafers being manufactured and immobilization of the manufacturing equipment for several days. The financial losses can be considerable.

[0005] In order to limit the risks of accumulation of deposits in these critical clearances, one solution could be to heat the Holweck compression stage to temperatures above 200°C, such as 300°C or 400°C, quickly, i.e. in a time of less than two minutes, so as not to heat the entire body of the pump, with the minimum of thermal inertia, by heating mainly the condensable deposit without heating the stator or the rotor and by avoiding creating cold zones in the Holweck compression stage.

[0006] Document FR3101115A1 thus proposes to arrange a heating device under vacuum, in the path of the pumped gases to better localize the heating inside the vacuum pump. The heating device includes heating resistors and insulating layers interposed between the Holweck stator and the heating resistors. The heating resistors can be energized punctually, for example for one second at 500°C, to avoid overheating the rotor. These high temperatures of the heating elements make it possible to volatilize or decompose the solid reaction products that have deposited on the heating elements or near the heating elements, without heating the rotor. However, this technology requiring in particular the deposition of insulating layers on the stator can be complex to implement and therefore expensive. Furthermore, the electrical power supply of the heating elements arranged under vacuum, in the gas flow path of the turbomolecular vacuum pump, can also be difficult to implement.In fact, the sheaths of electrical cables, the tin of solders, and even the protective resin of the solder can be damaged by infrared heating in a vacuum produced by the heating elements. Summary of the invention

[0007] One of the aims of the present invention is to propose a turbomolecular vacuum pump which at least partially resolves a drawback of the state of the art.

[0008] For this purpose, the subject of the invention is a turbomolecular vacuum pump comprising a stator and a rotor configured to rotate in the stator, helical grooves being provided in a high-pressure stator of the stator opposite a Holweck skirt of the rotor, characterized in that the vacuum pump further comprises at least one heating rod comprising at least one holding part and one heating part by Joule effect when the heating rod is electrically powered, the holding part forming a sheath for the electrical wires supplying the heating part, at least one connection conduit being at least partly provided in the high-pressure stator for the passage of the holding part, the heating part being received along at least one helical groove of the high-pressure stator.

[0009] In operation, the heating parts radiate in the infrared at temperatures greater than or equal to 200°C in the gas pumping path when they are electrically powered. The internal surfaces of the vacuum pump in the pumped gas path, generally reflective, reflect the radiated heat in the absence of deposits while the deposits, generally made of organic material and with a higher emissivity, greater than 0.5, absorb the heat. The deposits therefore absorb more heat and their temperature rises more than the walls of the vacuum pump. The heat reflected by the internal walls of the vacuum pump also returns to the heating parts of the heating rods or to the deposits. The deposits heated at high temperature can then be evaporated and entrained in gaseous form towards the outlet orifice without overheating the rotor or the internal walls of the stator. As soon as the thickness of the deposit is sufficiently low to no longer absorb infrared radiation, it is reflected by the walls of the vacuum pump. The removal of deposits can therefore be carried out automatically, without controlling or cycling the heating which can remain at high temperature. The heating is also targeted and therefore effective, without being harmful to the integrity of the rotor.

[0010] The arrangement of the heating parts of the heating rods in the helical grooves allows the deposits to be heated by radiation and to evaporate well before the high-pressure stator heats up. The heating parts of the heating rods are furthermore located on the high-pressure side of the vacuum pump stator in the direction of gas flow, i.e. in a location where the pressure is highest and where the risk of deposit is greater. The heating parts take up little space in the helical grooves and do not disturb molecular pumping because they follow the curvature of the helical grooves. Only the heating parts heat up in the area in which the pumped gases circulate. The holding parts received in the connection conduits are not heated and are therefore not likely to cause melting or damage to the electrical supply wires due to high temperatures.It is then possible to guarantee good mechanical strength of the high pressure stator and sufficient thermal insulation to allow the heating rods to heat up and radiate into the flow path of the pumped gases.

[0011] The turbomolecular vacuum pump may further comprise one or more of the features described below, taken alone or in combination.

[0012] The vacuum pump comprises, for example, between one and twelve heating rods.

[0013] Each heating rod is formed with at least one holding portion at one end, attached to a heating part. The holding part is “non-heating”, that is to say it is configured to have a temperature lower than 150°C when the heating rod is electrically powered. The heating part comprises an electrical resistor configured to have a surface temperature greater than or equal to 200°C when the heating rod is electrically powered.

[0014] The heating rods comprise, for example, a sheath made of a material resistant to potentially corrosive pumped gases, such as an alloy sheath, such as stainless steel or a nickel sheath.

[0015] The electrical supply wires can only be connected on one side of the heating rod, on the side of the holding part. The end of the heating part is then left free, or in other words, is not electrically connected, the electrical resistance forming a loop in the sheath connected to the electrical supply wires. on the side of the holding part.

[0016] Alternatively, the power supply wires may be connected to both sides of the heating rod, each end of the heating rod having a holding portion. In this case, only the central heating portion can effectively heat its surroundings by infrared radiation.

[0017] The connection conduit(s) is / are for example arranged in one end of the high-pressure stator, for example on a flat annular periphery of the high-pressure stator, for example on the side of the inlet of the high-pressure stator where the gases to be pumped enter. When there are several connection conduits, they are for example regularly distributed on the periphery of this end of the high-pressure stator.

[0018] According to an exemplary embodiment, the vacuum pump comprises at least as many heating rods as the high-pressure stator comprises helical grooves, at least one heating portion being received in a respective associated helical groove.

[0019] According to another exemplary embodiment, the heating part is received along at least two helical grooves.

[0020] The heating portion preferably extends beyond the helical groove of the high-pressure stator, into an annular discharge space located between an outlet of the high-pressure stator and a discharge orifice of the vacuum pump and / or into a turbomolecular stage of the vacuum pump. It is then possible to also heat the annular discharge space and / or the turbomolecular stage, by radiative radiation.

[0021] The vacuum pump may also comprise at least one additional heating rod comprising at least one holding portion and one Joule heating portion when the additional heating rod is electrically powered, the holding portion forming a sheath for the electrical wires supplying the heating portion. The holding portion of the additional heating rod is located in at least one connection duct, the heating portion being received in the annular discharge space located between an outlet of the high-pressure stator and a discharge orifice of the vacuum pump and / or in a turbomolecular stage of the vacuum pump. For example, provision is made for the holding portions of at least one heating rod and at least one additional heating rod to be received in the same connection duct.

[0022] A groove may be provided in a bottom of the helical groove to receive the heating part.

[0023] The heating rod may be preformed in the shape of a connection conduit and an associated helical groove. The heating rods comprise, for example, cold-formable resistors. The heating rod may thus be connected by only a few attachment zones to the high-pressure stator (two or three) and conduct very little heat by conduction in favor of infrared radiation.

[0024] The stator may further comprise a first annular fixing plate fixed to one end of the high-pressure stator in which the connection conduit is at least partially arranged, to close the connection conduit(s) and retain the holding part(s), the connection conduit(s) being arranged in the end of the high-pressure stator closed by the first fixing plate and / or in the first fixing plate.

[0025] The stator may further comprise a second annular fixing plate, fixed to the opposite end of the high pressure stator, for retaining the end(s) of the heating part(s) or another holding part(s). The other holding part is located at the other end of the heating rod if applicable.

[0026] According to another example, the connection duct(s) is / are provided at least in part in one end of the high-pressure stator opposite a stage of fins of the stator, the connection duct(s) being closed by a crown of the stage of fins and provided in the crown and / or in the end of the high-pressure stator.

[0027] The heating part is preferably kept mainly without contact in the helical groove of the high pressure stator.

[0028] For this purpose, the vacuum pump may include thermally insulating spacers arranged in the helical groove.

[0029] Alternatively or additionally, the heating part can be held in the helical groove by two orifices provided in a side wall of the helical groove.

[0030] According to an exemplary embodiment, the vacuum pump further comprises a purge gas supply configured to inject a purge gas into the connection duct(s). The purge gas is under overpressure in the connection duct relative to the interior of the high-pressure stator, thus creating a dynamic barrier for the pumped gases. The connection duct, thus located between a zone crossed by the potentially aggressive pumped gases and a zone still under vacuum, not very tight in itself but mechanically and thermally solid, is protected from the potentially corrosive pumped gases by the flow of purge gas sweeping it. The part(s) holding the heating rod(s) is (are) thus protected from the pumped gases and infrared radiation. The vacuum pump can then comprise conventional sealed connectors, remote from the very hot zones.The use of high-temperature sealed passages to be made around the heating rod(s) is avoided, which would require the use of materials capable of withstanding high temperatures for the seals, up to 200°C near the heating rod(s), capable of resisting differential thermal expansion between the heating rod(s) and the high-pressure stator and capable of resisting the aggression of sometimes very corrosive gases. All the connections can be . purged while preventing pumped gases from entering.

[0031] The purge gas supply comprises, for example, a common conduit in communication with an annular space surrounding the high-pressure stator in communication with the connection conduit(s).

[0032] The annular space surrounding the high-pressure stator may also be connected to an annular groove interposed between the high-pressure stator and a high-pressure casing of the stator, the high-pressure casing surrounding the high-pressure stator and connecting the high-pressure stator with the discharge port. The annular groove allows the passage of the purge gas around the entire circumference of the two parts. As in the connecting conduit(s), the purge gas injected into the annular groove is at an overpressure relative to the annular discharge space, thus creating a dynamic barrier for the pumped gases, making it possible to avoid the use of a seal in the annular groove.

[0033] The purge gas supply may comprise an additional conduit connecting the annular space with a seal groove of the stator receiving a seal. In addition to allowing the supply of the purge gas over the entire circumference between the high-pressure stator and the high-pressure casing, the annular space allows the purge gas to be supplied in the additional conduit as far as the seal groove. It is thus possible, at lower cost, to protect the seals from corrosive gases, which allows the use of seal materials that are less chemically resistant and therefore less expensive.

[0034] Furthermore, the internal walls of the stator and the walls of the rotor intended to be in communication with the pumped gases have, for example, an emissivity of less than or equal to 0.2, called low emissivity. They are for example metallic, made of aluminum or stainless steel material or have a low emissivity coating such as comprising nickel. The walls can be polished. These low emissivity surfaces have the advantage of reflecting infrared radiation, which makes it possible on the one hand to avoid heating the internal walls of the stator and the walls of the rotor intended to be in communication with the pumped gases, and on the other hand to concentrate the heat on the deposits which in general are organic deposits having an emissivity higher than that of the low emissivity surfaces.This takes advantage of the fact that the walls of the stator and rotor in communication with the pumped gases, made of aluminum, stainless steel or coated steel or aluminum, are made of low-emissivity materials to provide resistance to corrosion. These low-emissivity properties help to prevent the vacuum pump from heating while promoting the heating of unwanted deposits.

[0035] The turbomolecular vacuum pump may further comprise an external stator heating device, such as a resistive heating belt, for heating the stator to a set temperature, for example above 80°C, such as 100°C. Heating by the heating rods is then complementary to the external heating device of the stator.

[0036] The turbomolecular vacuum pump may also comprise a cooling device, in particular for cooling the first stages of fins of the turbomolecular stage. The cooling device makes it possible, for example, to control the temperature at a temperature less than or equal to 75°C, such as 70°C, for example by circulating water at ambient temperature. Brief description of the figures

[0037] Other advantages and characteristics will appear on reading the following description of a particular embodiment of the invention, but in no way limiting, as well as the appended drawings in which:

[0038] [Fig-1] [Fig.l] shows an axial sectional view of a turbocharged vacuum pump lecular according to a first example of realization.

[0039] [Fig.2] [Fig.2] shows a sectional view (along two radial planes) of elements of the turbomolecular vacuum pump of [Fig.l] with a first fixing plate shown in dotted lines.

[0040] [Fig.3] [Fig.3] shows an axial sectional view of the elements of [Fig.2] with a detail seen enlarged.

[0041] [Fig.4] [Fig.4] shows a disassembled view of the elements of [Fig.2].

[0042] [Fig.5] [Fig.5] is an axial sectional view of a portion of the vacuum pump of the [Fig.l] with a first and second detail seen enlarged.

[0043] [Fig.6] [Fig.6] shows a view similar to [Fig.3] for a second exemplary embodiment.

[0044] [Fig.7] [Fig.7] shows a sectional view of elements of the turbocharged vacuum pump lecular for a third example of realization.

[0045] In these figures, identical elements have the same reference numbers. Detailed description

[0046] The following embodiments are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment, or that the features apply only to a single embodiment. Single features of different embodiments may also be combined or interchanged to provide other embodiments.

[0047] “Upstream” means an element which is placed before another in relation to the direction of circulation of the pumped gases FL. Conversely, “downstream” means an element placed after another in relation to the direction of circulation of the pumped gases FL.

[0048] [Fig.l] illustrates an example of a turbomolecular vacuum pump 1.

[0049] The vacuum pump 1 comprises a stator 2 in which a rotor 3 is configured to to rotate at high speed in axial rotation, for example, rotation at more than ninety thousand revolutions per minute.

[0050] The gases enter through a suction port 6 of the vacuum pump 1, first pass through a turbomolecular stage 4, then a molecular stage 5, to then be evacuated towards a discharge port 7 of the vacuum pump 1 intended to be connected to a primary pumping. An annular inlet flange 8 surrounds for example the suction port 6 to connect the vacuum pump 1 to an enclosure whose pressure is to be lowered. In operation, the gases are entrained in the direction of circulation of the pumped gases F1 going from the suction port 6 towards the discharge port 7.

[0051] In the turbomolecular stage 4, the rotor 3 comprises at least two stages of blades 9 and the stator 2 comprises at least one stage of fins 10. The stages of blades 9 and fins 10 follow one another axially along the axis of rotation II of the rotor 3. The rotor 3 comprises, for example, more than four stages of blades 9, such as, for example, between four and twelve stages of blades 9.

[0052] Each stage of blades 9 of the rotor 3 comprises inclined blades which extend in a substantially radial direction from a hub 11 of the rotor 3 fixed to a drive shaft 12 of the vacuum pump 1, for example by screwing. The blades are distributed regularly around the periphery of the hub 11.

[0053] Each stage of fins 10 of the stator 2 comprises a crown from which extend, in a substantially radial direction, inclined fins, distributed regularly around the inner periphery of the crown. The fins of a stage of fins 10 of the stator 2 engage between the blades of two successive stages of blades 9 of the rotor 3. The blades 9 of the rotor 3 and the fins 10 of the stator 2 are inclined to guide the pumped gas molecules towards the molecular stage 5.

[0054] In the molecular stage 5, the rotor 3 comprises a Holweck skirt 13 downstream of the at least two blade stages 9, formed by a smooth cylinder, which rotates opposite helical grooves 14 arranged in a part of the stator 2 called the Holweck stator or high-pressure stator 19 (Figures 2 and 3). The high-pressure stator 19 comprises a plurality of helical grooves 14 arranged one above the other. There are for example between three and ten helical grooves 14, such as six. The high-pressure stator 19 is for example made of aluminum material and may have a low-emissivity nickel-type coating. The high-pressure stator 19 is intended to increase the compression ratio of the vacuum pump 1 for so-called intermediate pressures. The helical grooves 14 allow the pumped gases to be compressed and guided towards the discharge port 7.

[0055] The rotor 3 is configured to be driven in rotation in the stator 2 by an internal motor 16 of the vacuum pump 1. The motor 16 is for example arranged in a bell 17 of the stator 2, itself arranged under an internal bowl 15 of the rotor 3, the drive shaft 12 of the rotor 3 passing through the bell 17 of the stator 2.

[0056] The rotor 3 is guided laterally and axially by magnetic bearings 18 or mechanical bearings supporting the drive shaft 12 of the rotor 3, located in the stator 2.

[0057] The vacuum pump 1 may comprise a cooling device received in the stator 2, for example in the bell 17 or in thermal contact with the bell 17, such as a hydraulic circuit, to continuously cool the bell 17 and the elements that it contains such as in particular the bearings 18, the motor 16 and other electrical or electronic components in order to allow their operation, and / or to cool the first stages of fins 10 of the turbomolecular stage 4. The cooling device makes it possible, for example, to control the temperature at a temperature less than or equal to 75°C, such as 70°C, for example by circulating water at ambient temperature.

[0058] The vacuum pump 1 may further comprise a purge device 25 comprising an inlet conduit 26 configured to be connected to a source of purge gas in order to introduce a purge gas into the gap located between the bell 17 of the stator 2 and the internal bowl 15 of the rotor 3. The circulation of the purge gas is shown diagrammatically by arrows f2 in [Fig.l]. The purge gas is preferably air or nitrogen, but may also be another neutral gas such as helium or argon. The purge gas flow rate is low.

[0059] The vacuum pump 1 further comprises at least one heating rod 20, for example between one and twelve heating rods 20, here six ([Fig.4]).

[0060] Each heating rod 20 comprises at least one holding part 20a and one heating part 20b by Joule effect when the heating rod 20 is electrically powered.

[0061] Each heating rod 20 is formed of at least one holding portion 20a at one end, attached to a heating portion 20b. The holding portion 20a is “non-heating”, that is to say that it is configured to have a temperature lower than 150°C when the heating rod 20 is electrically powered. The heating portion 20b comprises an electrical resistance configured to have a temperature greater than or equal to 200°C when the heating rod 20 is electrically powered.

[0062] The heating rods 20 comprise, for example, a sheath made of a material resistant to potentially corrosive pumped gases, such as an alloy sheath, such as stainless steel or a nickel sheath.

[0063] The heating rods 20 are for example supplied with 140V to obtain a surface temperature of the heating parts 20b close to 400°C under vacuum, making it possible to heat the environment by infrared radiation while maintaining an acceptable lifespan.

[0064] The heating rods 20 may be electrically connected to each other in series or in parallel. All of the heating rods 20, or at least one group of heating rods 20, may be powered synchronously. Alternatively, the heating rods 20 may be powered asynchronously, in groups or individually. The heating rods 20 may be powered continuously or cyclically, i.e. by alternating on-times with off-times. A cycle may be more or less rapid, i.e. have a cycle duration of between a few milliseconds and several minutes.The control of the power supply can take into account the temperature of the heating rods 20, the temperature of the high pressure stator 19, the temperature of the rotor 3, the motor torque 16 or the signal of another sensor of the vacuum pump 1, such as a deposit sensor or a pressure sensor arranged in the gas flow path.

[0065] The sections of the heating rods 20 may be round, ovoid, square, rectangular or flat. The heating rods 20 have, for example, a round section with a diameter between 2 mm and 5 mm, such as 3.7 mm.

[0066] The holding portion 20a has for example a length greater than 100 mm, such as 150 mm. This holding portion 20a forms a sheath for the electrical wires supplying the heating rod 20.

[0067] The electrical supply wires can only be connected on one side of the heating rod 20, on the side of the holding part 20a. The end of the heating part 20b is then left free, or in other words, is not electrically connected, the electrical resistance forming a loop in the sheath connected to the electrical supply wires on the side of the holding part 20a.

[0068] As an alternative solution, the electrical supply wires can be connected to two sides of the heating rod 20, each end of the heating rod 20 comprising a holding portion 20a. Only the central heating portion 20b then effectively heats its environment by infrared radiation.

[0069] At least one connection conduit 21 is provided at least in part in the high pressure stator 19 for the passage of the holding part 20a ([Fig.4]).

[0070] The connection conduits 21 are for example at least partly arranged in one end of the high pressure stator 19, for example on a flat annular periphery of the high pressure stator 19, for example on the side of the inlet of the high pressure stator 19 where the gases to be pumped enter. These connection conduits 21 are for example regulated They are widely distributed on the periphery of this end of the high pressure stator 19. They have a respective section substantially greater than the section of the heating rods 20, for example 4mm x 4mm for a heating rod 20 of 3.7mm diameter, so as to form a low conductance which, as will be seen later, makes it possible in particular to limit the outlet of the purge gas.

[0071] The heating part 20b has for example a length greater than 200mm, such as between 250mm and 1700mm.

[0072] The heating part 20b is received along at least one helical groove 14 of the high pressure stator 19, for example in the middle of the helical groove 14 (Figures 2, 3) or near a side wall 14a of the helical groove 14 ([Fig.7]).

[0073] A groove 22, with dimensions slightly larger than those of the heating rod 20, may further be provided in the bottom of the helical groove 14, in each groove 14, for example in the middle of the groove 14, to receive the heating part 20b ([Fig.3]). The shape of the section of the groove 22 may be square, rectangular, round, or any other machinable shape. The groove 22 may be centered in the groove 14 or offset relative to the middle towards one of the side walls.

[0074] The vacuum pump 1 comprises, for example, at least as many heating rods 20 as the high-pressure stator 19 comprises helical grooves 14, and therefore connection conduits 21, at least one heating part 20b being received in a respective associated helical groove 14.

[0075] The vacuum pump 1 may have more heating rods 20 than the high-pressure stator 19 has helical grooves 14. In particular, the vacuum pump 1 may have more than one heating rod 20 in each helical groove 14, for example two.

[0076] The helical grooves 14 extend along the high-pressure stator 19, from one end to the other. They open on the one hand into the connection conduits 21 at one end of the high-pressure stator 19 and can on the other hand open into the annular discharge space 34 located between the outlet of the high-pressure stator 19 at the opposite end, and the discharge orifice 7. The connection conduits 21 are for example linear and oriented in the continuity of the angle given by the associated helical grooves 14.

[0077] The heating parts 20b of the heating rods 20 may extend beyond the helical grooves 14 of the high-pressure stator 19, for example into the annular discharge space 34, or even beyond the discharge orifice 7 and / or into the turbomolecular stage 4. It is then possible to also heat the annular discharge space 34 and / or the turbomolecular stage 4 by radiative radiation.

[0078] When the vacuum pump 1 comprises several heating rods 20, several ends of heating parts 20b may protrude into the annular space of re crowding 34 around the high pressure stator 19. There are for example six ends of heating parts 20b projecting into the annular discharge space 34, regularly distributed around the high pressure stator 19 ([Fig.2]).

[0079] The heating parts 20b are preferably kept mainly without contact in the helical groove 14 of the high-pressure stator 19, or in the groove 22 of the helical groove 14 if applicable, to avoid heating the stator 2 by conduction. Although the heating rod 20 can have several point contacts with the high-pressure stator 19, the heat transmitted by conduction in primary vacuum remains very low.

[0080] For this, the heating rods 20 can be preformed, that is to say shaped beforehand, before being mounted in the high-pressure stator 19, according to the shapes of the connection conduits 21 and the shapes of the associated helical grooves 14, and where appropriate of the grooves 22. The heating rods 20 comprise, for example, cold-formable resistors. The heating rod 20 can thus be connected by only a few attachment zones to the high-pressure stator 19 (two or three) and conduct the heat only very little by conduction in favor of infrared radiation.

[0081] The stator 2 may further comprise a first annular fixing plate 23 fixed to the end of the high-pressure stator 19, for example by screwing, the connection conduits 21 being arranged in the end of the high-pressure stator 19 and / or in the first fixing plate 23, the first fixing plate 23 closing the connection conduits 21 and retaining the holding parts 20a in the connection conduits 21 (figures 2 and 4).

[0082] The stator 2 may also comprise a second annular fixing plate 24, here made in several segments, fixed to the opposite end of the high-pressure stator 19, for example by screwing, to retain the ends of the heating parts 20b or the holding parts 20a located at the other end of the heating rods 20 when the heating rods 20 comprise a holding part 20a at each end. The fixing plates 23, 24 participate in holding the heating rods 20 in the helical grooves 14, in particular in the case of preformed heating rods 20.

[0083] According to another example, the connection conduits 21 are arranged at least in part in one end of the high-pressure stator 19 opposite a stage of fins 10 of the stator 2, the connection conduits 21 being closed by the crown of the stage of fins 10 and arranged in the crown and / or in the end of the high-pressure stator 19.

[0084] Other embodiments making it possible to maintain the heating parts 20b in the helical grooves 14 mainly without contact will be described later with reference to FIGS. 6 and 7.

[0085] In operation, the heating parts 20b radiate in the infrared at temperatures greater than or equal to 200°C, such as for example 300°C, and for example less than 700°C, in the gas pumping path when they are supplied. The internal surfaces of the vacuum pump 1 in the pumped gas path, generally reflective, reflect the radiated heat in the absence of deposits while the deposits, generally made of organic material and with a higher emissivity, greater than 0.5, absorb the heat. The deposits therefore absorb more heat and their temperature rises more than the walls of the vacuum pump 1. The heat reflected by the internal walls of the vacuum pump 1 also returns to the heating parts 20b of the heating rods 20 or to the deposits. The deposits heated to high temperature can then be evaporated and entrained in gaseous form towards the outlet orifice 7 without overheating the rotor 3 or the internal walls of the stator 2.As soon as the thickness of the deposit is sufficiently low to no longer absorb infrared radiation, it is reflected by the walls of the vacuum pump 1. The removal of deposits can therefore be carried out automatically, without controlling or cycling the heating, which can remain at a high temperature. The heating is also targeted and therefore effective, without being harmful to the integrity of the rotor 3.

[0086] The internal walls of the stator 2 and the walls of the rotor 3 intended to be in communication with the pumped gases have, for example, an emissivity of less than or equal to 0.2, called low emissivity. The internal walls of the stator 2 and the walls of the rotor 3 intended to be in communication with the pumped gases of low emissivity are, for example, metallic, made of aluminum or stainless steel material or have a low emissivity coating such as comprising nickel. The walls can be polished. These low emissivity surfaces have the advantage of reflecting infrared radiation, which makes it possible, on the one hand, to avoid heating the internal walls of the stator 2 and the walls of the rotor 3 intended to be in communication with the pumped gases, and on the other hand to concentrate the heat on the deposits which in general are organic deposits having an emissivity higher than that of the low emissivity surfaces.This takes advantage of the fact that the walls of the stator 2 and the rotor 3 in communication with the pumped gases, made of aluminum, stainless steel or coated steel or aluminum, are made of low-emissivity materials to enable them to resist corrosion. These low-emissivity properties help to prevent the vacuum pump 1 from heating while promoting the heating of unwanted deposits.

[0087] The arrangement of the heating parts 20b of the heating rods 20 in the helical grooves 14 makes it possible to heat the deposits by radiation and to evaporate them well before heating the high-pressure stator 19. The heating parts 20b of the heating rods 20 are furthermore located on the high-pressure side of the stator 2 of the vacuum pump 1 in the direction of gas circulation, i.e. in an em placement where the pressure is highest and where the risk of deposit is greater. The heating parts 20b take up little space in the helical grooves 14 and do not disturb molecular pumping because they follow the curvature of the helical grooves 14. Only the heating parts 20b heat up in the area in which the pumped gases circulate. The holding parts 20a received in the connection conduits 21 are not heated and are therefore not likely to cause melting or damage to the electrical supply wires due to high temperatures. It is then possible to guarantee good mechanical strength of the high-pressure stator 19 and sufficient thermal insulation to allow the heating rods 20 to rise in temperature and radiate into the flow path of the pumped gases.

[0088] The turbomolecular vacuum pump 1 may further comprise an external heating device for the stator 2, such as a resistive heating belt, for heating the stator 2 to a set temperature, for example greater than 80°C, such as 100°C. The heating by the heating rods 20 is then complementary to the external heating device for the stator 2.

[0089] According to an exemplary embodiment, the vacuum pump 1 comprises a purge gas supply 27 configured to inject a purge gas into the connection conduits 21. The purge gas supply 27 connects, for example, the inlet conduit 26 of the purge device 25 of the vacuum pump 1 to the connection conduits 21. According to another example, the purge gas supply 27 connects an additional purge gas inlet conduit to the connection conduits 21, this additional inlet conduit being independent of the inlet conduit 26 of the purge device 25.

[0090] The purge gas supply 27 comprises for example a common conduit 27a, in communication with an annular space 27b surrounding the high-pressure stator 19, itself in communication with the connection conduits 21. The common conduit 27a is for example in communication with the inlet conduit 26 of the purge device 25 or in communication with the additional inlet conduit. This purge gas supply 27 is for example arranged in a high-pressure casing 29 of the stator 2 surrounding the high-pressure stator 19 and connecting the high-pressure stator 19 with the discharge orifice 7 to put the pumped gases leaving the high-pressure stator 19 in communication with the discharge orifice 7.

[0091] In operation, the purge gas enters the purge gas supply 27, the common duct 27b and then the annular space 27b. The purge gas extends into the annular space 27b surrounding the high-pressure stator 19, then into the connection duct(s) 21 closed by the first closure plate 23, passes through the connection duct(s) 21 and is entrained with the pumped gases towards the discharge orifice 7. The purge gas is under overpressure in the connection ducts 21 relative to inside the high pressure stator 19, thus creating a dynamic barrier for the pumped gases.

[0092] The connection conduit 21, thus located between a zone crossed by the potentially aggressive pumped gases and a zone always under vacuum, not very tight in itself but mechanically and thermally solid, is protected from the potentially corrosive pumped gases by the flow of purge gas sweeping it. The holding parts 20a of the heating rods 20 are thus protected from the pumped gases and from infrared radiation. The vacuum pump 1 can then comprise conventional sealed connectors, offset at a distance from the very hot zones.The use of high-temperature sealed passages to be made around the heating rods 20 is avoided, which would require the use of materials capable of withstanding high temperatures for the seals, up to 200°C near the heating rods 20, capable of resisting differential thermal expansions between the heating rods 20 and the high-pressure stator 19 and capable of resisting the attacks of sometimes very corrosive gases. All the connections can be purged while preventing the pumped gases from entering.

[0093] According to an exemplary embodiment, the annular space 27b surrounding the high-pressure stator 19 is connected to an annular groove 28 interposed between the high-pressure stator 19 and the high-pressure casing 29 of the stator 2 (top detail in [Fig.5]). The annular groove 28 may be provided in the high-pressure casing 29 or the high-pressure stator 19.

[0094] In operation, the purge gas is introduced into the purge gas supply 27, into the common conduit 27b then into the annular space 27b, into the connection conduit(s) 21 and into the annular groove 28 between the high-pressure stator 19 and the high-pressure casing 29. The annular groove 28 allows the passage of the purge gas around the entire circumference of the two parts. As in the connection conduits 21, the purge gas injected into the annular groove 28 is at overpressure relative to the annular discharge space 34, thus creating a dynamic barrier for the pumped gases, making it possible to avoid the use of a seal in the annular groove 28.

[0095] According to an exemplary embodiment, the purge gas supply 27 comprises an additional conduit 32 placing the annular space 27b in communication with a seal groove 30 of the stator 2 receiving a seal 33.

[0096] For example, the additional conduit 32 connects the annular groove 28 or the annular space 27b with a seal groove 30 of a discharge connection 31 of the stator 2 (bottom detail in [Fig.5]). The seal groove 30 is provided between the discharge connection 31 and a main body of the high-pressure casing 29 in which the purge gas supply 27 is provided. The discharge connection discharge 31 comprises a tube and a flange for connecting the discharge port 7 of the vacuum pump 1 which are standardized for vacuum.

[0097] In operation, the purge gas is introduced into the purge gas supply 27, into the common conduit 27b then into the annular space 27b, into the connection conduit(s) 21 and into the additional conduit 32 up to the seal groove 30, protecting the seal 33 from potentially aggressive pumped gases. In addition to allowing the purge gas to be supplied over the entire circumference between the high-pressure stator 19 and the high-pressure casing 29, the annular space 27b allows the purge gas to be supplied into the additional conduit 32 which descends to the seal groove 30. It is thus possible, at lower cost, to protect the seals 33 from corrosive gases, which allows the use of less chemically resistant and therefore less expensive materials for the seals 33.

[0098] According to another example, the additional conduit (not shown) connects the annular groove 28 or the annular space 27b with a seal groove 36 located between the high pressure casing 29 and a low pressure casing 37 of the vacuum pump 1. The low pressure casing 37 carries the crowns of the vane stage 10 of the stator 2 ([Fig. 1]). As described in the previous example, the purge gas makes it possible to avoid the use of special materials for the seal 33 received in the seal groove 36.

[0099] Other embodiments are possible for the heating rods 20.

[0100] In particular, the heating part 20b of a heating rod 20 can be received along at least two helical grooves 14. The heating part 20b descends for example along a first helical groove 14 and rises along an adjacent second helical groove 14. The vacuum pump 1 can then comprise fewer heating rods 20 than the high-pressure stator 19 comprises helical grooves 14, the same heating rod 20 having a heating part 20b running one after the other through two or more helical grooves 14.

[0101] The heating part 20b of the heating rod 20 extending in several helical grooves 14 can extend beyond the helical grooves 14 of the high-pressure stator 19, for example into the annular discharge space 34 and / or into the turbomolecular stage 4, or even beyond the discharge orifice 7.

[0102] The vacuum pump 1 may comprise a single heating rod 20 extending in all the helical grooves 14, the heating rod 20 successively passing, rising then descending, through all the helical grooves 14 (not shown). This configuration is particularly advantageous for a heating rod 20 comprising two holding parts 20a for the electrical connection, on each side of the heating part 20b.

[0103] [Fig.6] shows a second example of embodiment.

[0104] In this example, the turbomolecular vacuum pump 1 comprises thermally insulating spacers 35, for example two or three, arranged in each helical groove 14 to keep the heating rod 20 away from the high-pressure stator 19. There is for example at least one spacer 35 arranged at the inlet of the helical groove 14 and one spacer arranged at the outlet of the helical groove 14. The spacers 35 are for example made of ceramic material and have a cylindrical orifice complementary to the section of the heating rod 20. This limits the thermal contact between the heating part 20b of the heating rod 20 and the high-pressure stator 19, and therefore heating of the stator 2.

[0105] Several shapes are possible for the spacers 35. They can for example have a block shape ([Fig.6]) or a ring shape or other. These spacers can also have shapes cooperating with complementary shapes of the helical groove 14, such as rails.

[0106] The other characteristics of this example are similar to the first embodiment.

[0107] [Fig.7] shows a third example of embodiment.

[0108] In this example, the heating parts 20b are held mostly without contact in the helical groove 14 of the high-pressure stator 19 by two orifices provided in a side wall 14a of the helical groove 14. There is for example an orifice provided in the side wall 14a at the inlet of the helical groove 14 and an orifice provided in the side wall 14a at the outlet of the helical groove 14 in the direction of gas circulation. Here it is the helical groove 14 which holds the heating part 20b in position in the helical groove 14 mostly without contact with the helical groove 14.

[0109] The other characteristics of this example are similar to the first two embodiments.

Claims

Claims

1. Turbomolecular vacuum pump (1) comprising a stator (2) and a rotor (3) configured to rotate in the stator (2), helical grooves (14) being provided in a high-pressure stator (19) of the stator (2) opposite a Holweck skirt (13) of the rotor (3), characterized in that the vacuum pump (1) further comprises at least one heating rod (20) comprising at least one holding portion (20a) and one heating portion (20b) by Joule effect when the heating rod (20) is electrically powered, the holding portion (20a) forming a sheath for the electrical wires supplying the heating portion (20b), at least one connection conduit (21) being at least partly provided in the high-pressure stator (19) for the passage of the holding portion (20a), the heating portion (20b) being received along at least one of the following: less than one helical groove (14) of the high pressure stator (19).

2. Vacuum pump (1) according to claim 1, characterized in that the vacuum pump (1) comprises at least as many heating rods (20) as the high-pressure stator (19) comprises helical grooves (14), at least one heating part (20b) being received in a respective associated helical groove (14).

3. Vacuum pump (1) according to claim 1, characterized in that the heating part (20b) is received along at least two helical grooves (14).

4. Vacuum pump (1) according to one of the preceding claims, characterized in that the heating part (20b) extends beyond the helical groove (14) of the high-pressure stator (19), into an annular discharge space (34) located between an outlet of the high-pressure stator (19) and a discharge orifice (7) of the vacuum pump (1) and / or into a turbomolecular stage (4) of the vacuum pump (1).

5. Vacuum pump (1) according to one of the preceding claims, characterized in that a groove (22) is provided in a bottom of the helical groove (14) to receive the heating part (20b).

6. Vacuum pump (1) according to one of the preceding claims, characterized in that the heating rod (20) is preformed in the shape of a connection conduit (21) and an associated helical groove (14).

7. Vacuum pump (1) according to one of the preceding claims, characterized in that the stator (2) comprises a first annular fixing plate (23) fixed to one end of the high-pressure stator. (19) in which the connection conduit (21) is at least partially arranged, to close the connection conduit (21) and retain the holding part (20a).

8. Vacuum pump (1) according to the preceding claim, characterized in that the stator (2) comprises a second annular fixing plate (24), fixed to the opposite end of the high pressure stator (19), to retain the end of the heating part (20b) or another holding part (20a).

9. Vacuum pump (1) according to one of the preceding claims, characterized in that the heating part (20b) is held predominantly without contact in the helical groove (14) of the high-pressure stator (19).

10. Vacuum pump (1) according to the preceding claim, characterized in that it comprises thermally insulating spacers (35) arranged in the helical groove (14).

11. Vacuum pump (1) according to one of claims 9 or 10, characterized in that the heating part (20b) is held in the helical groove (14) by two orifices provided in a side wall (14a) of the helical groove (14).

12. Vacuum pump (1) according to one of the preceding claims, characterized in that it comprises a purge gas supply (27) configured to inject a purge gas into the connection conduit(s) (21).

13. Vacuum pump (1) according to the preceding claim, characterized in that the purge gas supply (27) comprises a common conduit (27a) in communication with an annular space (27b) surrounding the high pressure stator (19) in communication with the connection conduit(s) (21).

14. Vacuum pump (1) according to claim 13, characterized in that the annular space (27b) surrounding the high pressure stator (19) is connected to an annular groove (28) interposed between the high pressure stator (19) and a high pressure casing (29) of the stator (2), the high pressure casing (29) surrounding the high pressure stator (19) and connecting the high pressure stator (19) with the discharge port (7).

15. Vacuum pump (1) according to one of claims 13 or 14, characterized in that the purge gas supply (27) comprises an additional conduit (32) putting the annular space (27b) into communication with a seal groove (30; 36) of the stator (2) receiving a seal gasket (33).

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