TW202319650A - Turbomolecular vacuum pump - Google Patents

Abstract

Turbomolecular vacuum pump (1) comprising at least one heating rod (20) having at least one holding part (20a) and a heating part (20b) utilizing the Joule effect when the heating rod (20) is electrically powered, the holding part (20a) forming a sheath for the electrical supply wires to the heating part (20b), at least one connection duct (21) being at least partially arranged 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).

Description

Turbo Molecular Vacuum Pump

The present invention relates to turbomolecular vacuum pumps.

The generation of high vacuum in the enclosure requires the use of a turbomolecular vacuum pump, which consists of a stator in which a rotor is driven in rapid rotation, for example at a rate of more than 90,000 revolutions per minute.

In certain processes using turbomolecular vacuum pumps, such as semiconductor or LED manufacturing processes, deposited layers may be formed in the vacuum pump.

It is known to heat the stator by means of external heating strips in order to prevent condensation of reaction products in the pump. However, new generation processes produce more and more condensable by-products. In some cases, conventional heating methods are no longer sufficient to prevent the formation of by-products and it is not possible to further increase the temperature of the stator without the risk of mechanically weakening the aluminum rotor. Deposits can then show up on the stator of the high pressure compression or Holwerk stage, where the functional clearance to the rotor (tens of millimeters in total) is quite small and the rotor is hardly exposed since its rotation prevents deposition of deposits. If preventive maintenance is not performed, deposits can become thicker and contact between the rotor and stator can occur, causing immediate failure of the pump due to the high rotation rate of the rotor and its kinetic energy. During the manufacture of semiconductors, such failure of a vacuum pump can result in the destruction of a batch of wafers being manufactured and the immobilization of the manufacturing equipment for several days, as well as complete failure of the pump. Financial losses can be substantial.

To limit the risk of deposits accumulating in these critical gaps, one solution could be to rapidly heat the Holwerk compression stage to a temperature above 200°C, such as 300°C or 400°C, i.e. in less than two minutes time period so as not to heat the entire pump body and have a minimum thermal inertia, mainly heat the condensable deposits without heating the stator, and avoid the establishment of cold zones in the Holwerk compression stage.

Therefore, document FR3101115A1 proposes to arrange the vacuum heating device in the path of the pumped gas in order to better position the heating inside the vacuum pump. The heating unit consists of a heating resistor and an insulating layer inserted between the Holwerk stator and the heating resistor. The heating resistors may be energized briefly, for example to 500° C. for one second, so as not to overheat the rotor. These high temperatures of the heating elements allow for the evaporation or decomposition of solid reaction products that have deposited on or next to the heating elements without the need to heat the rotor. However, this technique - which requires, inter alia, the deposition of an insulating layer on the stator - can prove complex to implement and therefore costly. Furthermore, in the flow path of the gas of the turbomolecular vacuum pump, the power supply to the heating elements disposed in the vacuum can also prove difficult to implement. In fact, the sheathing of the cable, the tin of the solder or even the protective resin of the solder can be damaged by infrared heating under the vacuum created by the heating element.

One of the objects of the present invention is to propose a turbomolecular vacuum pump which at least partially solves the disadvantages of the prior art.

For this purpose, the invention relates to a turbomolecular vacuum pump comprising a stator and a rotor, the rotor being constructed to rotate in the stator, the helical grooves being arranged in the high-voltage stator of the Holwerk skirt of the stator facing the rotor, characterized in that The vacuum pump also comprises at least one heating rod having at least one holding part and a heating part utilizing the Joule effect when the heating rod is energized, the holding part forming a sheath for the power line to the heating part, at least one connecting duct system Arranged at least partially in the high voltage stator for the passage of a holding element, the heating element is received along at least one helical groove of the high voltage stator.

During operation, the heating element, when energized, radiates infrared rays at a temperature greater than or equal to 200°C in the pumping path of the gas. In the path of the pumped gas, the usually reflective internal surfaces of the vacuum pump reflect the radiated heat in the absence of deposits, which instead - usually organic materials with high emissivity, greater than 0.5 - absorb heat. Consequently, these deposits absorb more heat and their temperature rises above the temperature of the walls of the vacuum pump. The heat reflected by the inner wall of the vacuum pump also reaches the heating parts or deposits of the heating rod. The deposits heated to high temperature can then be vaporized and driven in gaseous form towards the outlet orifice without overheating the inner walls of the rotor or stator. Once the thickness of the deposit is small enough to no longer absorb infrared radiation, the latter is reflected by the walls of the vacuum pump. Thus, deposits can be eliminated automatically without controlled or cyclic heating, which can be maintained at high temperature. This heating system is also targeted and thus effective without harming the integrity of the rotor.

The arrangement of the heating elements of the heating rods in the helical grooves allows heating of the deposit by radiation and vaporization of it prior to heating of the high voltage stator. The heating part of the heating rod is also located on the high-pressure side of the vacuum pump's stator in the direction of gas circulation, that is, at the position where the pressure system is the highest and the risk of deposition is greater. The heating elements take up little space in the helical groove and do not disrupt molecular pumping because they follow the curvature of the helical groove. In the area where the pumped gas circulates, only the heating parts are heated. The holding parts accommodated in the connecting duct are not heated, and therefore it is impossible to melt or damage the power cord due to high temperatures. It is then possible to ensure good mechanical strength of the high voltage stator and sufficient thermal insulation to allow the temperature of the heating rods to rise and radiate into the flow path of the pumped gas.

A turbomolecular vacuum pump may also include one or more of the features described below, either alone or in combination.

The vacuum pump contains, for example, between 1 and 12 heating rods.

Each heating rod is formed at one end by at least one retaining element attached to the heating element. The holding part is "non-heated", that is, when the heating rod is energized, its temperature is designed to be lower than 150°C. The heating part contains a resistor, and when the heating rod is energized, its surface temperature is designed to be greater than or equal to 200°C.

For example, the heating rod comprises a sheath made of a material resistant to the potentially corrosive pumped gas, such as an alloy sheath, such as stainless steel or a nickel sheath.

The power lead may be attached to only one side of the heating rod, on the side of the holding part. Then, the end of the heating part is free, or in other words, has no electrical connection, with the resistance forming a loop in the sheath connected to the power line on the side of the holding part.

In an alternative solution, the power cord may be connected to both sides of the heating rod, at each end of the heating rod comprising a holding part. In this case, only the middle heating element can effectively heat its environment by means of infrared radiation.

A connecting duct is arranged, for example, at one end of the high-pressure stator, for example above the flat annular circumference of the high-pressure stator, for example on the inlet side of the high-pressure stator, for the input of the gas to be pumped. When there are several connecting ducts, they are for example regularly distributed over the periphery of this end of the high voltage stator.

In an exemplary embodiment, the vacuum pump comprises at least as many heating rods as the high voltage stator, comprising helical grooves, at least one heating element being received in each associated helical groove.

In another exemplary embodiment, the heating element is accommodated along at least two spiral grooves.

The heating element preferably extends beyond the helical groove of the high pressure stator, into the annular return space between the outlet of the high pressure stator and the return orifice of the vacuum pump, and/or into the turbomolecular stage of the vacuum pump. It is then also possible to heat the annular recirculation space and/or the turbomolecular stage by means of radiative heating.

The vacuum pump may also comprise at least one additional heating rod having at least one holding part and a heating part utilizing the Joule effect when the additional heating rod is energized, the holding part forming a sheath for the power cord for heating the part. At least one additional rod holding part is located in at least one connecting duct, the heating part is accommodated in the annular return space between the outlet of the high-pressure stator and the return orifice of the vacuum pump, and/or the turbomolecular of the vacuum pump stage. For example, it is provided that the holding parts of at least one heating rod and at least one additional heating rod are accommodated in the same connecting duct.

Channels may be provided in the base of the helical groove for receiving heating elements.

The heating rods may be pre-formed in the shape of the connecting pipes and associated helical grooves. The heating rod comprises, for example, a resistance which may be cold formed. Thus, the heating rods may be connected via only a few areas (two or three) for attachment to the high voltage stator, so very little heat is transferred by conduction, mostly by infrared radiation.

The stator may also comprise a first annular fixing plate fixed to the end of the high-voltage stator in which the connecting duct is arranged at least partially in order to close the connecting duct and retain the holding part, the connecting duct being arranged by means of the first In the end of the high voltage stator closed by the fixing plate and/or in the first fixing plate.

The stator may also comprise a second annular fixing plate fixed to the opposite end of the high voltage stator in order to retain the end of the heating part or another holding part or parts. Another retaining part (where provided) is located at the other end of the heating rod.

According to another example, connecting ducts are arranged at least partially in the end of the high-pressure stator facing the vane stage of the stator, the connecting ducts are closed by the ring of the vane stage and are arranged in this ring and/or In the end of the high voltage stator.

The heating elements are preferably held mainly contact-free in the helical grooves of the high-voltage stator.

To this end, the vacuum pump may comprise thermally insulating spacers arranged in the helical grooves.

Alternatively or additionally, the heating element may be held in the helical groove via two apertures arranged in the side walls of the helical groove.

According to an exemplary embodiment, the vacuum pump also comprises a purge gas input for injecting purge gas into the connecting pipe. The purge gas system is under higher pressure in the connecting piping than inside the high-pressure stator, thus creating a dynamic barrier for the pumped gas. Therefore, the connecting duct between the area through which the potentially corrosive pumped gas passes and the area which is always under vacuum is not itself sealed, but is mechanically and thermally robust and is secured by the sweeping flow of purge gas. Protected from potentially corrosive pumped gases. Thus, the holding parts of the heating rod are protected from the pumped gas and from infrared radiation. The vacuum pump may then incorporate conventional hermetic connectors placed at a distance from very hot areas. This avoids creating a temperature-tight passage around the heating rod, which would require the use of materials that can withstand temperatures up to 200°C close to the heating rod for the sealing fittings, be able to withstand the differential thermal expansion between the heating rod and the high voltage stator, and be able to Resistant to the attack of highly corrosive gases in some cases. The entire connection can be purged while preventing the ingress of pumped gas.

The purge gas input comprises, for example, a common duct communicating with the annular space surrounding the high-voltage stator, the common duct communicating with the connecting duct.

The annular space surrounding the high voltage stator may also be connected to an annular channel inserted between the high voltage stator and the high voltage housing of the stator, which surrounds the high voltage stator and connects the high voltage stator to the return orifice. The annular channel allows the purge gas to pass over the entire circumference of the two parts. As in the connection piping, the purge gas system injected into the annular channel is at a higher pressure relative to the annular return space, thus creating a dynamic barrier for the pumped gas and allowing the use of sealing fittings to be avoided in the annular channel.

The purge gas input may comprise an additional conduit which communicates the annulus with the seal passage of the stator housing the seal fitting. In addition to allowing the purge gas to be supplied over the entire circumference between the high pressure stator and the high pressure housing, this annular space allows the purge gas to enter the additional duct up to the sealing channel. Thus, the sealing fittings can be protected from corrosive gases at low cost, which allows the use of less chemically resistant materials for the sealing fittings and thus reduces the price.

The inner walls of the stator and the walls of the rotor for communicating with the pumped gas also have emissivity less than or equal to 0.2, known as low emissivity, for example. For example, they are metallic, made of aluminum or stainless steel material, or have a low emissivity coating, such as containing nickel. The walls may be polished. These surfaces with low emissivity have the advantage of reflecting infrared radiation, which firstly allows avoiding heating of the inner walls of the stator and of the walls of the rotor intended to communicate with the pumped gas, and secondly concentrates the heat on the deposits, which deposits Deposits are largely organic deposits with higher emissivity than low emissivity surfaces. This takes advantage of the fact that the walls of the stator and rotor are made of materials with low emissivity, especially allowing corrosion resistance, these walls communicate with the pumped gas and are made of aluminum, stainless steel material or coated steel or aluminum . These low emissivity properties help avoid vacuum pump heating while promoting heating of unwanted deposits.

The turbomolecular vacuum pump may also comprise external heating means of the stator, such as heating resistance bands, for heating the stator to a reference temperature, eg greater than 80°C, such as 100°C. The heating by the heating rods then supplements the external heating of the stator.

The turbomolecular vacuum pump may also comprise cooling means, especially for cooling the first vane stage of the turbomolecular stage. For example, by circulation of water at the ambient temperature, the cooling device allows this temperature to be controlled to a temperature less than or equal to 75°C, for example 70°C.

The following examples are exemplary. Although this description refers to more than one embodiment, this does not necessarily mean that each reference is to the same embodiment, or that these features are only applicable to a single embodiment. Individual features of different embodiments can also be combined or interchanged in order to provide other embodiments.

The term "upstream" means an element placed before another element with respect to the circulation direction F1 of the pumped gas. In contrast, the term "downstream" means an element placed behind another element with respect to the circulation direction F1 of the pumped gas.

FIG. 1 illustrates an exemplary turbomolecular vacuum pump 1 .

The vacuum pump 1 comprises a stator 2, wherein a rotor 3 is designed to rotate at a high axial rotational rate, for example more than ninety thousand revolutions per minute.

The gas enters through the intake port 6 of the vacuum pump 1 , first passes through the turbo molecular stage 4 , then the molecular stage 5 , and is then evacuated towards the return port 7 of the vacuum pump 1 for connection to the main pump. For example, an annular inlet flange 8 surrounds the inlet orifice 6 in order to connect the vacuum pump 1 to the enclosure to be decompressed. In operation, the gas system is driven from the inlet orifice 6 to the return orifice 7 in the circulation direction F1 of the pumped gas.

In the turbomolecular stage 4 , the rotor 3 contains at least two blade stages 9 and the stator contains at least one blade stage 10 . The vane stage 9 and the vane stage 10 are arranged axially in sequence along the rotation axis I-I of the rotor 3 . The rotor 3 comprises for example more than four vane stages 9 , for example between four and twelve vane stages 9 .

Each vane stage 9 of the rotor 3 comprises angled vanes extending in a substantially radial direction from a hub 11 of the rotor 3 which is fixed to the drive shaft of the vacuum pump 1, for example by means of screw fittings 12. The fins are regularly distributed around the periphery of the hub 11 .

Each blade stage 10 of the stator 2 comprises a circular ring from which angled blades regularly distributed around the inner periphery of the ring extend in a substantially radial direction. The vanes of the vane stage 10 of the stator 2 mesh between the vanes of two successive vane stages 9 of the rotor 3 . The vanes 9 of the rotor 3 , and the blades 10 of the stator 2 are angled in order to direct the molecules of the pumped gas to the molecular stage 5 .

In the molecular stage 5, the rotor 3 comprises a Holwerk skirt 13 downstream of at least two airfoil stages 9 and is formed as a smooth cylinder arranged opposite to what is known as a Holwerk stator or high pressure The helical groove 14 in a part of the stator 2 of the stator 19 (see Figs. 2 and 3) rotates. The high-voltage stator 19 includes a plurality of spiral grooves 14 arranged one above the other. For example, there are between three and ten helical grooves 14, such as six. The high-voltage stator 19 is made, for example, of aluminum material and may have a low-emissivity nickel-type coating. The high pressure stator 19 is designed in order to increase the compressibility of the vacuum pump 1 for so-called intermediate pressures. The helical groove 14 allows the pumped gas to be compressed and directed towards the return orifice 7 .

The rotor 3 is designed to be driven in rotation in the stator 2 by the internal motor 16 of the vacuum pump 1 . The motor 16 is arranged, for example, in the bell-shaped housing 17 of the stator 2 , which is itself arranged below the inner bowl 15 of the rotor 3 through which the drive shaft 12 of the rotor 3 passes.

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

The vacuum pump 1 may comprise cooling means housed in the stator 2, for example in the bell housing 17, or in thermal contact with the bell housing 17, such as a hydraulic circuit, for the continuous cooling of the bell housing 17 and the elements contained therein, such as In particular the bearings 18 , the motor 16 and other electrically related or electronic components in order to allow them to function and/or to cool the first blade stage 10 of the turbomolecular stage 4 . This cooling device allows the temperature to be controlled to a temperature less than or equal to 75° C., for example 70°, for example by circulation of water at ambient temperature.

The vacuum pump 1 may also comprise a purge device 25 comprising an inlet duct 27 designed to be connected to a source of purge gas in order to direct the purge gas into the gap between the bell-shaped housing 17 of the stator 2 and the inner bowl 15 of the rotor 3 gap. The circulation of the purge gas is indicated schematically by the arrow f2 on FIG. 1 . The purge gas is preferably air or nitrogen, but could also be another inert gas such as helium or argon. The flow of purge gas is slight.

The vacuum pump 1 also comprises at least one heating rod 20 , for example between 1 and 12 heating rods 20 , here 6 ( FIG. 4 ).

Each heating rod 20 includes at least one holding part 20a and a heating part 20b, which utilize the Joule effect when the heating rod 20 is energized.

Each heating rod 20 is formed by at least one holding part 20a attached at one end to a heating part 20b. The holding part 20a is "non-heated", ie designed to have a temperature below 150°C when the heating rod 20 is energized. The heating part 20b includes a resistance designed to have a temperature greater than or equal to 200°C when the heating rod 20 is energized.

For example, the heating rod 20 comprises a sheath made of a material resistant to potentially corrosive pumped gases, such as an alloy sheath, such as stainless steel or nickel sheath.

For example, the heating rod 20 is powered at 140 V to obtain a surface temperature of the heating part 20b close to 400° C. under vacuum, allowing the environment to be heated by infrared radiation while retaining a containable service life.

The heating rods 20 may be electrically connected together in series or in parallel. All heating rods 20, or at least one group of heating rods 20, may be supplied synchronously. Alternatively, the heating rods 20 may be supplied asynchronously, in groups or individually. The heating rod 20 can be supplied continuously or in a cyclic manner, that is, energized periods and non-energized periods are performed alternately. A cycle can be of variable length, ie have a cycle duration between milliseconds and minutes. The electrical control system may take into account the temperature of the heating rods 20, the temperature of the high voltage stator 19, the temperature of the rotor 3, the torque of the motor 16, or another sensor from the vacuum pump 1, such as deposits disposed in the flow path of the gas sensor or pressure sensor signal.

The cross-section of the heating rod 20 can be circular, oval, square, rectangular or flat. For example, the heating rod 20 has a circular cross-section with a diameter between 2 mm and 5 mm, such as 3.7 mm.

The holding part 20a has, for example, a length greater than 100 mm, such as 150 mm. This retaining part 20 a forms a sheath for the power cord of the heating rod 20 .

The power cord can be connected only to one side of the heating rod 20, on the side of the holding part 20a. The ends of the heating part 20b are then left free, or in other words not electrically connected, with the resistance forming a loop in the sheath of the power line connected to the side of the holding part 20a.

Alternatively, the power cord may be connected to both sides of the heating rod 20, each end of the heating rod 20 comprising a retaining part 20a. Only the middle heating element 20b then effectively heats its environment by means of infrared radiation.

At least one connecting duct 21 is arranged at least partially in the high-voltage stator 19 for the passage of the retaining part 20a ( FIG. 4 ).

The connecting duct 21 is for example arranged at least partially at the 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 at the inlet of the gas to be pumped. These connecting ducts 21 are distributed regularly over the circumference, for example at this end of the high-voltage stator 19 . They have respective cross-sections which are substantially larger than the cross-section of the heating rod 20, for example 4 mm x 4 mm for a heating rod 20 with a diameter of 3.7 mm, in order to create a low conductivity, as As will be seen below, it limits, among other things, the outflow of purge gas.

For example, the heating element 20b has a length exceeding 200 mm, such as between 250 mm and 1700 mm.

The heating element 20b is accommodated along at least one helical groove 14 of the high voltage stator 19, for example in the middle of the helical groove 14 (FIG. 2, 3), or close to the side wall 14a of the helical groove 14 (FIG. 7).

Channels 22 with dimensions slightly larger than those of the heating rods 20 may also be arranged in the base of the helical grooves 14, in each groove 14, for example in the middle of the grooves 14, for receiving heating elements 20b (FIG. 3) . The cross-sectional shape of the channel 22 can be square, rectangular, circular or any other manufacturable form. Channel 22 may be located in the center of trench 14, or offset from the center toward one of the sidewalls.

The vacuum pump 1 comprises, for example, as many heating rods 20 as high-voltage stators 19 , with helical grooves 14 and thus connecting ducts 21 , wherein at least one heating element 20 b is housed in the associated respective helical groove 14 .

The vacuum pump 1 may comprise more heating rods 20 than the high voltage stator 19 and has helical grooves 14 . In particular, the vacuum pump 1 may include more than one heating rod 20 , for example two, in each spiral groove 14 .

The helical groove 14 extends from one end to the other along the high voltage stator 19 . They open firstly into the connecting duct 21 at one end of the high-pressure stator 19 and secondly into an annular return space 34 between the outlet of the high-pressure stator 19 and the return opening 7 at the opposite end. The connecting ducts 21 are for example linear and oriented in a succession of angles given by the associated helical grooves 14 .

The heating element 20 b of the heating rod 20 can extend beyond the helical groove 14 of the high-voltage stator 19 , for example into the annular return space 34 , or even beyond the return orifice 7 and/or into the turbomolecular stage 4 . It is then possible to heat the annular return space 34 and/or the turbomolecular stage 4 also by means of radiant heat.

When the vacuum pump 1 comprises several heating rods 20 , several ends of the heating element 20 b can protrude into the annular return space 34 surrounding the high-pressure stator 19 . For example, six ends of the heating element 20b protrude into the annular return space 34, distributed regularly around the high voltage stator 19 (Fig. 2).

The heating element 20b is preferably mainly held contactlessly in the helical groove 14 of the high voltage stator 19, or in the channel 22 of the helical groove 14 provided, in order to avoid heating of the stator 2 by conduction. Although the heating rods 20 may have several points of contact with the high voltage stator 19, the heat transfer by conduction under the primary vacuum remains very low.

For this purpose, the heating rods 20 can be preformed, that is to say follow the shape of the connecting duct 21 and the shape of the associated helical groove 14 and - where provided - the shape of the channel 22 , before being installed in the high voltage stator 19 . The shape is preformed. The heating rod 20 comprises, for example, a cold-formable resistor. Thus, the heating rod 20 can be connected by only a few areas (two or three) for attachment to the high voltage stator 19, so very little heat is transferred by conduction, mostly by infrared radiation.

The stator 2 may also comprise a first annular fixing plate 23 fixed, for example by means of screw fittings, to the end of the high voltage stator 19, the connecting duct 21 being arranged in the end of the high voltage stator 19 and/or in the first fixing plate 23 , the first fixing plate 23 closes the connecting duct 21 and retains the holding part 20a in the connecting duct 21 (Figs. 2 and 4).

The stator 2 may also comprise a second annular fixing plate 24, here made of several segments, and fixed, for example by means of screw fittings, to the opposite ends of the high voltage stator 19, so that when the heating rods 20 comprise retaining plates at each end When the component 20a is used, the heating component 20b or the end of the holding component 20a located at the other end of the heating rod 20 remains. The fixing plates 23 , 24 help to retain the heating rod 20 in the helical groove 14 , especially in the case of pre-shaped heating rods 20 .

In another example, a connecting duct 21 is arranged at least partially in the end of the high-voltage stator 19 facing the vane stage 10 of the stator 2, the connecting duct 21 being closed by the ring of the vane stage 10 and arranged in this circle In the ring and/or in the end of the high voltage stator 19 .

Further exemplary embodiments will be described below with reference to FIGS. 6 and 7 , which allow the heating element 20 b to remain in the helical groove 14 mainly in a contactless manner.

In operation, the heating element 20b, when energized, radiates infrared rays at a temperature greater than or equal to 200°C, such as 300°C, and for example less than 700°C, in the pumping path of the gas. In the path of the pumped gas, the internal surfaces of the vacuum pump 1 are usually reflective, reflecting the radiated heat in the absence of deposits, which instead - usually organic materials with a high emissivity greater than 0.5 - absorb the heat . Therefore, the deposit absorbs more heat and the temperature rises faster than the wall of the vacuum pump 1 . The heat reflected by the inner wall of the vacuum pump 1 also reaches the heating part 20b of the heating rod 20 or the deposit. The deposits heated to a high temperature can then evaporate and be driven in gaseous form towards the outlet orifice 7 without overheating the inner walls of the rotor 3 or stator 2 . Once the thickness of the deposit is low enough that the infrared radiation is no longer absorbed, it is reflected by the walls of the vacuum pump 1 . Thus, deposits can be eliminated automatically without controlled or cyclic heating, which can remain at high temperatures. Again, this heating is targeted and thus effective without harming the integrity of the rotor 3 .

The inner wall surface of the stator 2 and the wall surface of the rotor 3 for communicating with the pumped gas have emissivity less than or equal to 0.2, which is known as low emissivity. The inner walls of the stator 2 and the walls of the rotor 3 for communication with the pumped gas and having a low emissivity are eg metallic, made of aluminum or stainless steel material, or have a low emissivity coating, such as containing nickel. Wall surfaces can be polished. These surfaces with low emissivity have the advantage of reflecting infrared radiation, which allows avoiding, firstly, the heating of the inner walls of the stator 2 and the walls of the rotor 3 intended to communicate with the pumped gas, and secondly the concentration of heat on the deposits, etc. Deposits are usually organic deposits that have higher emissivity than low emissivity surfaces. This takes advantage of the fact that the walls of the stator 2 and rotor 3, which communicate with the pumped gas and are made of aluminium, stainless steel material or coated steel or aluminium, are made of a material with a low emissivity, which in particular allows corrosion resistance . These properties of low emissivity help avoid heating of the vacuum pump 1 while promoting heating of unwanted deposits.

The arrangement of the heating elements 20 b of the heating rods 20 in the helical groove 14 allows reheating and likewise vaporizing the deposits by means of radiation before heating the high voltage stator 19 . The heating elements 20b of the heating rods 20 are also located in the gas circulation direction on the high-pressure side of the stator 2 of the vacuum pump 1, ie at locations where the pressure is highest or the risk of deposits is greater. The heating elements 20 b occupy little space in the helical groove 14 and do not disrupt molecular pumping because they follow the curvature of the helical groove 14 . Only the heating element 20b is heated in the region in which the pumped gas circulates. The holding part 20a accommodated in the connection duct 21 is not heated, and therefore it is unlikely that the power cord will be melted or damaged due to high temperature. It is then possible to ensure good mechanical strength of the high voltage stator 19 and sufficient thermal insulation to allow the temperature of the heating rods 20 to rise and radiate into the flow path of the pumped gas.

The turbomolecular vacuum pump 1 may also comprise external heating means of the stator 2, such as a heating resistance band, for heating the stator 2 to a reference temperature, eg greater than 80°C, such as 100°C. The external heating of the stator 2 is then supplemented by the heating of the heating rods 20 .

According to an exemplary embodiment, the vacuum pump 1 comprises a purge gas input 27 designed for injecting purge gas into the connecting conduit 21 . For example, a purge gas input 27 connects the inlet line 26 of the purge device 25 of the vacuum pump 1 to the connecting line 21 . According to another example, the purge gas input 27 connects to this connection conduit 21 an additional purge gas inlet conduit which is independent of the inlet conduit 26 of the purge device 25 .

The purge gas input 27 comprises, for example, a common duct 27a communicating with the annular space 27b surrounding the high-pressure stator 19 , which itself communicates with the connecting duct 21 . The common conduit 27a communicates, for example, with the inlet conduit 26 of the purging device 25, or with an auxiliary inlet conduit. This purge gas input 27 is arranged, for example, in the high-pressure housing 29 of the stator 2, which surrounds the high-pressure stator 19 and connects the high-pressure stator 19 to the return orifice 7, so that the pumped gas leaving the high-pressure stator 19 is connected to the return flow. The orifices 7 communicate with each other.

In operation, purge gas enters this purge gas input 27, then enters common conduit 27a, and then enters annular space 27b. The purge gas enters the annular space 27b surrounding the high pressure stator 19 and then enters the connecting duct 21 closed by the first closing plate 23 , passes through the connecting duct 21 and is driven towards the return orifice 7 with the pumping gas. The purge gas system is under a higher pressure in the connection duct 21 relative to the interior of the high pressure stator 19, thereby creating a dynamic barrier for the pumped gas.

The connecting duct 21 between the area through which the possibly corrosive pumped gas passes and the area which is always under vacuum is therefore not sealed per se, but is mechanically and thermally robust and is ventilated by the purge gas. The swept flow is used to protect it from potentially corrosive pumped gases. Thus, the holding part 20a of the heating rod 20 is protected from the pumped gas and from infrared radiation. The vacuum pump 1 may then comprise conventional sealed connectors arranged at a distance from very hot areas. This avoids the establishment of a temperature-tight passage around the heating rod 20, which would require the use of a material capable of withstanding high temperatures of up to 200° C. close to the heating rod 20 as a sealing fitting, and capable of withstanding the difference between the heating rod 20 and the high voltage stator 19. Thermal expansion and resistance to gases that can in some cases be highly corrosive. The entire connection can be purged while preventing the ingress of pumped gas.

According to an exemplary embodiment, the annular space 27b surrounding the high voltage stator 19 is connected to an annular channel 28 inserted between the high voltage stator 19 and the high voltage housing 29 of the stator 2 (detail at the top of FIG. 5 ). The annular channel 28 can be arranged in the high-voltage housing 29 or in the high-voltage stator 19 .

In operation, purge gas enters purge gas input 27 , common conduit 27 a , and then annular space 27 b , connecting conduit 21 and annular passage 28 between high pressure stator 19 and high pressure housing 29 . Annular channel 28 allows the passage of purge gas over the entire circumference of the two parts. As in connecting duct 21 , the purge gas system injected into annular channel 28 is under higher pressure relative to annular return space 34 , thus creating a dynamic barrier for the pumped gas and avoiding the use of sealing fittings in annular channel 28 .

According to an exemplary embodiment, the purge gas input 27 comprises an additional duct 32 bringing the annular space 27b into communication with the sealing channel 30 of the stator 2 housing the sealing fitting 33 .

For example, an additional duct 32 brings the annular channel 28 or the annular space 27b into communication with the sealing channel 30 of the return connection 31 of the stator 2 (detail at the bottom of FIG. 5 ). A sealing channel 30 is arranged between the return connection 31 and the body of the high pressure housing 20 in which the purge gas input 27 is arranged. The return connection 31 comprises a pipe and flange for connection to the return orifice 7 of the vacuum pump 1 , which are standard for vacuum.

In operation, purge gas enters purge gas input 27, common conduit 27a and then into annular space 27b, connection conduit 21 and additional conduit 32 to seal passage 30, thereby protecting seal fitting 33 from potentially corrosive pumped gas. Influence. As well as allowing the purge gas to be directed over the entire circumference between the high pressure stator 19 and the high pressure housing 29 , the annular space 27 b allows the purge gas to be delivered to the additional duct 32 down to the sealed channel 30 . Thus, the sealing fitting 33 can be protected against corrosive gases at low cost, which allows the use of less chemically resistant and thus inexpensive materials for the sealing fitting 33 .

According to another example, an additional conduit (not shown) brings the annular channel 28 or the annular space 27b into communication with the sealed channel 36 between the high pressure housing 29 and the low pressure housing 37 of the vacuum pump 1 . The low pressure housing 37 carries the rings of the vane stages 10 of the stator 2 ( FIG. 1 ). As described in the previous example, for the sealing fitting 33 housed in the sealing channel 36, the purge gas allows avoiding the use of special materials.

Other embodiments for the heating rod 20 are possible.

In particular, the heating part 20 b of the heating rod 20 can be accommodated along at least two spiral grooves 14 . For example, the heating element 20b descends along a first helical groove 14 and ascends along an adjacent second helical groove 14 . Then, the vacuum pump 1 may include fewer heating rods 20 than the high-voltage stator 19, and include spiral grooves 14, wherein the same heating rod 20 has heating elements 20b passing through more than two spiral grooves 14 in sequence.

The heating elements 20b of the heating rods 20 extending in several helical grooves 14 can extend beyond the helical grooves 14 of the high-voltage stator 19, for example into the annular return space 34 and/or into the turbomolecular stage 4, even beyond the return orifice 7 .

The vacuum pump 1 may comprise a single heating rod 20 extending in all the helical grooves 14, the heating rod 20 ascending and then descending through all the helical grooves 14 in sequence (not shown). This configuration is particularly suitable for a heating rod 20 comprising two holding elements 20a for electrical connection, one on each side of the heating element 20b.

Figure 6 shows a second exemplary embodiment.

In this example, the turbomolecular vacuum pump 1 comprises thermally insulating spacers 35 , for example two or three, arranged in each helical groove 14 in order to hold the heating rod 20 spaced apart from the high voltage stator 19 . For example, at least one spacer 35 is arranged at the entrance of the helical groove 14 and one spacer is arranged at the exit from the helical groove 14 . The spacer 35 is for example made of ceramic material and has a cylindrical opening complementary to the cross-section of the heating rod 20 . This limits the thermal contact between the heating element 20 b of the heating rod 20 and the high voltage stator 19 and thus limits the heating of the stator 2 .

Several forms are possible for the spacer 35 . They may, for example, have the form of blocks ( FIG. 6 ) or have the form of rings or the like. For example, the spacer may also have a shape that cooperates with the complementary shape of the helical groove 14, such as a rail.

Other features of this example are similar to those of the first exemplary embodiment.

Fig. 7 shows a third exemplary embodiment.

In this example, the heating element 20 b is held contactlessly in the helical groove 14 of the high voltage stator 19 mainly via two openings arranged in the side wall 14 a of the helical groove 14 . For example, one orifice is arranged in the side wall 14a at the entrance to the helical groove 14 and one orifice is arranged in the side wall 14a at the outlet from the helical groove 14 in the gas circulation direction. Here, it is the helical groove 14 holding the heating element 20b in place in the helical groove 14 , mainly not in contact with the helical groove 14 .

Other features of this example are similar to those of the previous two exemplary embodiments.

1: Turbo molecular vacuum pump 2: Stator 3: rotor 4: Turbomolecular stage 5: Molecular stage 6: Air inlet orifice 7: Return orifice 8: Entrance flange 9:Foil stage 10: Blade stage 11: hub 12: Drive shaft 13: Holwick Skirt 14: spiral groove 14a: side wall 15: inner bowl 16: Motor 17: bell shell 18: Magnetic bearing 19:High voltage stator 20: heating rod 20a: Holding parts 20b: Heating parts 21: Connect the pipes 22: channel 23: Fixed plate 24: Fixed plate 25: Purging device 26: Inlet pipe 27: Purge gas input 27a: Public plumbing 27b: Annular space 28: Ring channel 29: High pressure housing 30: sealed channel 31: Return connector 32: Additional pipes 33:Sealing accessories 34: Return space 35: spacer 36: sealed channel 37: High pressure housing F1: circulation direction of gas f2: arrow I: Shaft

Further advantages and features will become apparent from reading the following description of specific embodiments of the invention, and from the accompanying drawings, which are by no means limiting, in which:

[ Fig. 1 ] An axial sectional view showing a turbomolecular vacuum pump according to a first embodiment.

[ FIG. 2 ] Shows a cross-sectional view (along two radial planes) of elements of the turbomolecular vacuum pump from FIG. 1 , with the first fixed plate depicted in dotted lines.

[ FIG. 3 ] shows an axial cross-sectional view of the element from FIG. 2 with enlarged details.

[ Fig. 4 ] An exploded view showing the element from Fig. 2 .

[ FIG. 5 ] is an axial cross-sectional view of a part of the vacuum pump from FIG. 1 , with first and second enlarged details.

[ Fig. 6 ] A view similar to Fig. 3 is shown for the second embodiment.

[ Fig. 7 ] A sectional view showing elements used in a turbomolecular vacuum pump of a third exemplary embodiment.

In these figures, identical elements bear the same reference symbols.

1: Turbo molecular vacuum pump

2: Stator

3: rotor

4: Turbomolecular stage

5: Molecular stage

6: Air inlet orifice

7: Return orifice

8: Entrance flange

9:Foil stage

10: Blade stage

11: hub

12: Drive shaft

13: Holwick Skirt

14: spiral groove

15: inner bowl

16: Motor

17: bell shell

18: Magnetic bearing

19:High voltage stator

20: heating rod

25: Purging device

26: Inlet pipe

27: Purge gas input

27a: Public plumbing

27b: Annular space

28: Ring channel

29: High pressure shell

30: sealed channel

31: Return connector

33:Sealing accessories

34: Return space

36: sealed channel

37: High pressure shell

F1: circulation direction of gas

f2: arrow

I: Shaft

Claims (15)

A turbomolecular vacuum pump (1), comprising a stator (2) and a rotor (3) configured to rotate in the stator (2), a helical groove (14) is arranged on the stator (2) facing the rotor (3) ) in the high voltage stator (19) of the Holvik skirt (13) is characterized in that the vacuum pump (1) also comprises at least one heating rod (20) having at least one holding part (20a) and when The heating element (20b) utilizing the Joule effect when the heating rod (20) is energized, the holding element (20a) forms a sheath for the power line to the heating element (20b), at least one connecting duct (21) is at least partially Arranged in the high voltage stator (19) for the passage of the holding part (20a), the heating part (20b) is housed along at least one helical groove (14) of the high voltage stator (19). The vacuum pump (1) of claim 1, wherein the vacuum pump (1) includes at least as many heating rods (20) as the high-voltage stator (19), the high-voltage stator includes spiral grooves (14), at least one heating element ( 20b) are accommodated in respective associated helical grooves (14). The vacuum pump (1) according to claim 1, wherein the heating element (20b) is accommodated along at least two spiral grooves (14). The vacuum pump (1) according to any one of claims 1 to 3, wherein the heating element (20b) extends beyond the spiral groove (14) of the high-voltage stator (19) into the outlet and the outlet of the high-voltage stator (19) The annular recirculation space (34) between the recirculation orifices (7) of the vacuum pump (1), and/or into the turbomolecular stage (4) of the vacuum pump (1). The vacuum pump (1) according to claim 1, 2 or 3, wherein the channel (22) is arranged in the base of the spiral groove (14) for accommodating the heating element (20b). The vacuum pump (1) according to claim 1, 2 or 3, wherein the heating rod (20) is preformed in the shape of the connecting pipe (21) and associated helical groove (14). As the vacuum pump (1) of claim 1, 2 or 3, wherein the stator (2) includes a first annular fixing plate (23) fixed to an end of the high-voltage stator (19), the connecting pipe (21) is It is at least partially arranged in the end so as to close the connecting duct (21) and retain the retaining part (20a). The vacuum pump (1) as claimed in claim 7, wherein the stator (2) includes a second annular fixing plate (24) fixed to the opposite end of the high voltage stator (19) so as to retain the heating element (20b) or another An end of a retaining part (20a). The vacuum pump (1) according to claim 1, 2 or 3, wherein the heating element (20b) is mainly held in the spiral groove (14) of the high voltage stator (19) in a non-contact manner. The vacuum pump (1) according to claim 9, wherein the vacuum pump comprises a thermal insulation spacer (35) arranged in the spiral groove (14). The vacuum pump (1) according to claim 9, wherein the heating element (20b) is held in the spiral groove (14) via two openings arranged in the side wall (14a) of the spiral groove (14). The vacuum pump (1) of claim 1, 2 or 3, wherein the vacuum pump comprises a purge gas input (27) designed for injecting purge gas into the connecting pipe (21). The vacuum pump (1) as claimed in claim 12, wherein the purge gas input (27) includes a common pipeline (27a) communicating with the annular space (27b), and the annular space surrounds the high-voltage stator communicating with the connecting pipeline (21) ( 19). The vacuum pump (1) as claimed in claim 13, wherein the annular space (27b) surrounding the high-voltage stator (19) is linked to the high-pressure housing (29) inserted between the high-voltage stator (19) and the stator (2) An annular channel (28), the high voltage housing (29) surrounds the high voltage stator (19) and connects the high voltage stator (19) to the return orifice (7). The vacuum pump (1) of claim 13, wherein the purge gas input (27) includes an additional conduit (32) that seals the annular space (27b) with the stator (2) that houses the sealing fitting (33) The channels (30; 36) communicate with each other.

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