Pressing tools and method for mounting a screw rotor

Abstract

A pressing tool (210; 310) for mounting a screw rotor (200) in an axial inlet bearing (201) of a screw element for compressing a gas with a predefined maximum head clearance (X'; X"), characterized in that the pressing tool (210; 310) comprises a group of first support points and a group of second support points, wherein the first support points are positioned such that, when mounting the screw rotor (200), they contact a head face (205) of the screw rotor (200) and exert pressure on the head face (205) in a direction towards the axial inlet bearing (201), wherein the second support points are positioned such that, upon completion of mounting the screw rotor (200), they contact a first coupling surface (212) of a housing of the screw element, and wherein the first support points and the second support points are positioned relative to each other such that, upon completion of mounting the screw rotor (200), the head face (205) and the high-pressure end face (207) are at a perpendicular distance from each other, equal to the maximum head clearance (X'; X").

Description

[0001] Pressing tools and method for mounting a screw rotor .

[0002] The present invention relates to a pressing tool and a method for mounting a screw rotor in an axial inlet bearing of a screw element for compressing a gas .

[0003] In the context of the present invention, a screw element for compressing a gas may mean a screw compressor element , a screw blower element or a screw vacuum pump element .

[0004] More specifically, the present invention relates to a pressing tool for mounting a screw rotor into an axial inlet bearing of a screw element for compressing a gas , wherein the pressing tool is configured to mount the screw rotor with a predefined maximum head clearance between

[0005] - on the one hand, a head face of a profile body of the screw rotor; and

[0006] - on the other hand, a high-pressure end face of a compression space , located within a housing of the screw element and configured to accommodate the profile body of the screw rotor, wherein the housing is configured to be composed of two parts having mutually corresponding coupling surfaces .

[0007] Traditionally, an axial bearing for supporting a screw rotor is provided in a housing of a screw element for compressing a gas on an outlet side of the screw element .

[0008] Here , the outlet side of the screw element is a part of the housing, adj acent to a high-pressure end face of a compression space of the screw element , while an inlet side of the screw element is a part of the housing, adj acent to a low-pressure end face of the compression space .

[0009] The axial bearing can absorb axial forces that act on a profile body of the screw rotor in the compression space during operation of the screw element .

[0010] These axial forces are caused by the screw element , in operation, by the compression of the gas in the compression space , whereby a pressure gradient in the compression space is created from the high-pressure end face to the low-pressure end face , wherein the high- pressure end face is at a higher pressure than the low- pressure end face .

[0011] The axial bearing determines a head clearance between

[0012] - on the one hand, a head face of a profile body of the screw rotor , facing the outlet side of the screw element ; and

[0013] - on the other hand, the high-pressure end face of the compression space .

[0014] Depending on the tolerances of the axial bearing , different methods can be used to mount the screw rotor with a certain maximum head clearance in the axial bearing .

[0015] A first method involves using a universally matchable bearing with a limited axial stand-in / stand-out deviation between the inner and outer rings , of typically only 3 micrometres . This allows the universally matchable bearing, with a predetermined axial offset between the inner and outer rings , to be mounted as an axial bearing on an axle j ournal of the screw rotor on the outlet side of the screw element .

[0016] However , such universally fitting axial bearings are characterised by a higher cost than conventional axial bearings with a larger axial stand-in / stand-out deviation of typically 200 micrometres .

[0017] In addition, when using the axial bearing on the outlet side of the screw element , there will be a variation in the final head clearance due to the bearing tolerances and a bearing fit .

[0018] As an alternative method to avoid this variation in the final head clearance , the screw rotor can be mounted in the axial bearing in at least two pressing steps : a . First , an axle j ournal of the screw rotor is pressed into the axial bearing and a radial bearing by means of a master tool , thus forming a master press piece with a relatively large maximum master head clearance .

[0019] If necessary, the profile body of the screw rotor can be pushed against the high-pressure end face . b . A dial gauge is placed on the end of the axle j ournal and set to a zero distance . c . The profile body of the screw rotor is then moved maximally away from the high-pressure end face , thereby causing a master head clearance between the head face and the high-pressure end face to be set at a value equal to the maximum master head clearance , and the dial gauge displays a value indicative of this maximum master head clearance . d . Next , a suitable spacer is selected to press the axle j ournal of the screw rotor , in combination with the master tool , into the axial bearing and radial bearing, in such a way that a final maximum head clearance is set , which final maximum head clearance is smaller than the maximum master head clearance . e . To check the final maximum head clearance , steps b and c must be repeated .

[0020] This method is always time-consuming and requires , among other things , that an operator selects the correct press piece, correctly positions the dial gauge on the end of the axle j ournal and sets the dial gauge to the zero distance at the correct moment . As a result , many things can go wrong during this procedure , making it necessary to reassemble the screw element .

[0021] The present invention aims to provide a solution to at least one of the said and / or other disadvantages .

[0022] More specifically, the invention aims to provide a pressing tool and method for mounting a screw rotor in an axial inlet bearing of a screw element for compressing a gas , whereby the screw rotor is mounted in the screw element with a maximum head clearance between

[0023] - on the one hand, a head face of a profile body of the screw rotor facing the outlet side of the screw element ; and

[0024] - on the other hand, a high-pressure end face of a compression space , located within a housing of the screw element and configured to accommodate the profile body of the screw rotor, in an accurate and fast manner , at a limited cost and independently of any bearing tolerances , bearing fit and / or internal variations of the head clearance when the screw rotor is mounted in the screw element .

[0025] To this end, the present invention relates to a pressing tool for mounting a screw rotor in an axial inlet bearing of a screw element for compressing a gas , wherein the pressing tool is configured to mount the screw rotor with a predefined maximum head clearance between

[0026] - on the one hand, a head face of a profile body of the screw rotor; and

[0027] - on the other hand, a high-pressure end face of a compression space , located within a housing of the screw element and configured to accommodate the profile body of the screw rotor, wherein the housing is configured to be composed of two parts having mutually corresponding coupling surfaces , of which two parts a first part with a first coupling surface of the mutually corresponding coupling surfaces contains the axial inlet bearing, characterized in that the pressing tool comprises a group of first support points and a group of second support points , wherein the first support points are positioned such that , when mounting the screw rotor , they contact the head face and exert pressure on the head face in a direction towards the axial inlet bearing , wherein the second support points are positioned such that , upon completion of mounting the screw rotor, they contact the first coupling surface , and wherein the first support points and the second support points are positioned relative to each other such that , upon completion of mounting the screw rotor , the head face and the high-pressure end face are at a perpendicular distance from each other, equal to the maximum head clearance .

[0028] Here , the term ' inlet bearing ' in the context of the invention means a bearing which, in the case of the screw element with the mounted screw rotor , is located over an axle j ournal of the screw rotor, facing an inlet side of the screw element .

[0029] Furthermore , the term ' high-pressure end face ' has the same meaning as in the already known state of the art , as explained above .

[0030] The advantage of this pressing tool is that the screw rotor can be mounted directly in a single pressing step , independently of any bearing tolerances or bearing fit and without the use of a special universal-fit axial bearing , precisely with the predefined maximum head clearance in the screw element by applying pressure with the first support points on the screw rotor in the direction of the axial inlet bearing until the second support points contact the first coupling surface of the first part of the housing .

[0031] There is a technical prej udice that mounting the screw rotor in the screw element in this way would not be possible due to excessive thermal expansion of the screw rotor when the compressor element is in operation, whereby an initial head clearance between, on the one hand, the head face of the profile body of the screw rotor, facing the outlet side of the screw element and, on the other hand, the high-pressure end face , would be reduced too much .

[0032] However , within the scope of the invention, it is surprisingly observed that with recent screw elements that are smaller than long-known screw elements and which aim to minimize costs rather than maximize operating efficiency, this is no longer an insurmountable problem, partly due to the limited length of the screw element .

[0033] When, according to common practice , the axial bearing is located on the outlet side of the screw element , such thermal expansion of the screw rotor will also occur during operation . In that case , however, the thermal expansion will occur in a direction toward the inlet side of the screw element , such that a second head clearance between, on the one hand, the screw rotor head face , facing the inlet side of the screw element and, on the other hand, the low-pressure end face will decrease . A size of this second head clearance has a less critical impact on the operating efficiency of the screw element , such that this second head clearance can initially be set larger than the said first head clearance , and the ris k of an excessive reduction in the second head clearance during operation of the screw element is therefore lower . For this reason, a person s killed in the art of compressor technology will be reluctant to move the axial bearing from the outlet side to the inlet side of the screw element . A further advantage of the pressing tool according to the invention is that no high-precision positioning means for axially positioning the pressing tool relative to the first part of the housing are required for mounting the screw rotor in the axial inlet bearing with the predefined maximum head clearance , since the axial positioning of the pressing tool , when completing mounting of the screw rotor, can be relied upon to rely on the relative positioning of the first and second support points and on the contact of the first and second support points with the head face and first coupling surface , respectively .

[0034] In a preferred embodiment of the pressing tool according to the invention, the pressing tool has a stepped pressing surface , wherein the first support points are located on a first plane level of the stepped pressing surface and the second support points are located on a second plane level of the stepped pressing surface , and wherein the first plane level and the second plane level are parallel and are located at a perpendicular distance from each other, at least equal to the maximum head clearance .

[0035] This provides the pressing surface or working surface of the pressing tool with a simple geometry with two flat levels that can be formed easily, yet accurately, using standard production techniques such as , for example , milling .

[0036] With the pressing tool according to this preferred embodiment , it is possible to mount the screw rotor directly in a single pressing step with the predefined maximum head clearance in the screw element if the first coupling surface lies in the same plane as the high- pressure end face .

[0037] Preferably, the perpendicular distance between the first plane level and the second plane level is equal to the maximum head clearance increased by a stiffness correction factor .

[0038] By means of the stiffness correction factor , a stiffness of components of the screw element that influence the maximum head clearance during screw rotor installation, for example bearing stiffness , can be taken into account . This stiffness leads to a reduction of the maximum head clearance when, upon completion of mounting the screw rotor, the pressure of the first support points of the pressing tool on the screw rotor is released by removing the pressing tool .

[0039] Alternatively or additionally, the pressing tool according to the invention comprises a separately removable attachment for providing at least the first flat level of the stepped pressing surface .

[0040] This allows the perpendicular distance between the first plane level and the second plane level to be adj usted easily and quickly by changing the pressing tool attachment .

[0041] In a further preferred embodiment of the pressing tool according to the invention, the first support points are positionally distributed such that the said pressure , exerted on the screw rotor , when mounting the screw rotor, is rotationally symmetrically distributed over the head face according to an axis of rotation of the screw rotor .

[0042] Preferably, the first support points are uniformly positionally distributed according to a circle or ring .

[0043] Thereby, the first support points may exert a uniform pressure on the head face of the screw rotor , when mounting the screw rotor .

[0044] In a further preferred embodiment of the pressing tool according to the invention, the pressing tool has a recess , which recess is configured such that the pressing tool , when mounting the screw rotor, accommodates at least a portion of an axle j ournal of the screw rotor protruding from the head face .

[0045] This provides the pressing tool with a shape that allows the pressing tool to move over and / or around the axle j ournal or portion of the axle j ournal to bring the initial contact points into contact with the head face of the screw rotor .

[0046] In practice , the pressing tool may comprise two or more mutually separable parts for forming the recess , wherein the two or more mutually separable parts enclose the recess .

[0047] Thereby, it is easy to form the recess in the pressing tool and it is easy to assemble the pressing tool around the axle j ournal or the portion of the axle j ournal . Alternatively or additionally, the recess preferably has a shape , corresponding to the axle j ournal or the portion of the axle j ournal .

[0048] Preferably, this shape is a cylindrical shape .

[0049] If the first support points of the pressing tool according to the invention are uniformly positionally distributed according to a circle or ring , even more preferably, a centre of the circle or ring is located on a symmetrical axis of the cylindrical shape .

[0050] This allows the first support points to apply uniform pressure around the axle j ournal or portion of the axle j ournal to the head face of the screw rotor when mounting the screw rotor .

[0051] Furthermore , the present invention also relates to a method for mounting a screw rotor in an axial inlet bearing of a screw element for compressing a gas , characterized in that the screw rotor is mounted with the aid of a pressing tool according to any one of the preceding embodiments with a predefined maximum head clearance between

[0052] - on the one hand, a head face of a profile body of the screw rotor; and

[0053] - on the other hand, a high-pressure end face of a compression space , located within a housing of the screw element and configured to accommodate the profile body of the screw rotor, wherein the housing comprises two parts with mutually corresponding coupling surfaces , of which two parts a first part with a first coupling surface of the mutually corresponding coupling surfaces comprises the axial inlet bearing , wherein the method comprises the following consecutive steps :

[0054] - contacting the head face of the screw rotor with the first support points of the pressing tool ;

[0055] - pressing the screw rotor into the axial inlet bearing by applying pressure from the first support points of the pressing tool onto the head face in a direction towards the axial inlet bearing until the second support points of the pressing tool contact the first coupling surface .

[0056] It goes without saying that such a method enj oys the same advantages as the above-described embodiments of a pressing tool according to the invention, since in such a method the screw rotor is mounted in an axial bearing on the inlet side of the screw element and since such a method can only be carried out with the aid of such a pressing tool .

[0057] Finally, the invention relates to a screw element for compressing a gas , comprising

[0058] - a screw rotor with a profile body; and

[0059] - a housing containing a compression space, which compression space contains the profile body of the screw rotor ,

[0060] - wherein the housing is composed of two parts , connected to each other at mutually corresponding coupling surfaces , of which two parts a first part with a first coupling surface of the mutually corresponding coupling surfaces contains an axial inlet bearing, characterized in that the screw rotor is mounted in the axial inlet bearing using the method described above , such that a head face of the profile body and a high- pressure end face of the compression space are located at a perpendicular distance from each other, equal to a maximum head clearance .

[0061] It goes without saying that such a screw element enj oys the same advantages with regard to the mounting of its screw element in the axial inlet bearing as the method according to the invention described above .

[0062] Preferably, the first coupling surface is located at the high-pressure end face .

[0063] This has the advantage that mounting the screw rotor in the axial inlet bearing can be done with a smaller tolerance and therefore greater accuracy, since it is known in advance that the second support points of the pressing tool will be at the level of the high-pressure end face , when completing the mounting of the screw rotor .

[0064] With the view to better demonstrate the features of the invention, hereinafter, by way of example but not by way of limitation, some preferred applications of a pressing tool and method according to the invention for mounting a screw rotor in an axial inlet bearing of a screw element for compressing a gas are described, with reference to the accompanying drawings , in which : Figure 1 shows an already known conventional method for mounting a screw rotor in an axial bearing of a screw element ;

[0065] Figure 2 shows a method according to the invention for mounting a screw rotor in an axial inlet bearing of a screw element ;

[0066] Figure 3 shows a pressing tool according to the invention for mounting a screw rotor in an axial inlet bearing of a screw element ;

[0067] Figure 4 shows a cross-section of the pressing tool in Figure 3 along line IV-IV;

[0068] Figure 5 shows in more detail the part marked F5 in Figure 4 ; and

[0069] Figure 6 shows in more detail the part indicated by

[0070] F6 in Figure 2 .

[0071] In a first step a of a conventional method for mounting a screw rotor 100 into an axial outlet bearing 101 of a screw element as shown in Figure 1 , in a first pressing step , an axle j ournal 102 of the screw rotor 100 is pressed by means of a master tool ( not shown in the figure ) into the axial outlet bearing 101 and a radial outlet bearing 103 ( shown by means of hollow arrows o) , whereby a master press piece 104 with a relatively large maximum master head clearance X is formed .

[0072] In this case , a head face 105 of a profile body 106 of the screw rotor 100 is pressed against a high-pressure end face 107 of a compression space of the screw element ( shown by the upward arrow o ) , thereby completely eliminating any master head clearance between the head face 105 and the high-pressure end face 107 . In a second step b of this conventional method, a dial gauge 108 is placed on the end of the axle j ournal 102 and set to a zero distance .

[0073] In a third step c of the conventional method, the profile body 106 of the screw rotor 100 with the head face 105 is then moved maximally away from the high-pressure end face 107 , as a result of which the master head clearance is set to a value equal to the maximum master head clearance X, and the dial gauge 108 shows a value indicative of this maximum master head clearance X .

[0074] In a fourth step d of the conventional method, a suitable spacer is then selected to further press the axial outlet bearing 101 over the axle j ournal 102 in a second pressing step in combination with the master tool , such that a final maximum head clearance is set ( indicated by means of hollow arrows 5 ) , which final maximum head clearance is smaller than the maximum master head clearance X .

[0075] In an optional fifth step ( not shown in Figure 1 ) of the conventional method, previous steps b and c are repeated to check the final maximum head clearance .

[0076] Consequently, in the conventional method, the axial outlet bearing 101 is always pressed over the axle j ournal 102 in at least two pressing steps , namely the first pressing step in the first step a , and the second pressing step in the fourth step d . Figure 2 shows a method according to the invention for mounting a screw rotor 200 in an axial inlet bearing 201 of a screw element .

[0077] In this method according to the invention, the screw rotor 200 is mounted using a pressing tool 210 according to the invention with a predefined maximum head clearance X ' ( shown in Figure 6 ) between

[0078] - on the one hand, a head face 205 of a profile body 206 of the screw rotor 200 ; and

[0079] - on the other hand, a high-pressure end face 207 of a compression space , located within a housing of the screw element and configured to accommodate the profile body 206 of the screw rotor 200 .

[0080] The housing of the screw element comprises two parts with corresponding coupling surfaces , in this case at the high-pressure end face 207 , of which two parts a first part 211 with a first coupling surface 212 of the corresponding coupling surfaces contains the axial inlet bearing 201 . In this case , the first coupling surface 212 is preferably located at the high-pressure end face 207 .

[0081] In a first step a ' of the method according to the invention,

[0082] - the screw rotor 200 placed in the compression space ; and

[0083] - the head face 205 of the screw rotor 200 is contacted with a group of first support points of the pressing tool 210 , in the case of Figure 2 by placing a recess 213 in the pressing tool 210 over and around an axle j ournal 214 of the screw rotor 200 , extending from the head face 205 .

[0084] In a second step b ' of the method according to the invention, the screw rotor 200 is pressed into the axial inlet bearing 201 by exerting pressure of the pressing tool 210 on the head face 205 in a direction towards the axial inlet bearing 201 until a group of second support points of the pressing tool 210 contacts the first coupling surface 212 .

[0085] After the method according to the invention for mounting the screw rotor 200 in the axial inlet bearing 201 , in an optional third step c ' , the pressing tool 210 can then be removed from the first part 211 of the housing of the screw element with the mounted screw rotor 200 by breaking off the contact between the first support points of the pressing tool 210 and the head face 205 of the screw rotor 200 . After this , the two parts of the housing can then be coupled to each other according to their mutually corresponding coupling surfaces ( not shown in Figure 2 ) .

[0086] Figures 3 , 4 and 5 show at least part of a pressing tool 310 according to the invention for mounting the screw rotor 200 in the axial inlet bearing 201 of the screw element with a predefined maximum head clearance X" .

[0087] Figure 3 shows an isometric view of the pressing tool 310 , while Figure 4 shows a cross-section of the pressing tool 310 , taken along line IV-IV in Figure 3 . Figure 5 shows in more detail an enlargement of the part of the cross-section of the pressing tool 310 , designated with F5 in Figure 4 .

[0088] In order to mount the screw rotor 200 in the axial inlet bearing 201 of the screw element with a predefined maximum head clearance X" , the pressing tool 310 comprises

[0089] - a group of first support points , wherein the first support points are positioned such that , when the screw rotor 200 is mounted, they contact the head face 205 and exert pressure on the head face 205 in a direction toward the axial inlet bearing 201 ; and

[0090] - a group of second support points , wherein the second support points are positioned such that , upon completion of mounting of the screw rotor 200 , they contact the first coupling surface 212 of the first portion 211 of the housing of the screw element , wherein the first support points and the second support points are positioned relative to each other such that , upon completion of mounting of the screw rotor 200 , the head face 205 and the high-pressure end face 207 are at a perpendicular distance from each other , equal to the maximum head clearance X" .

[0091] Preferably, and in the case of Figures 3 , 4 and 5 , the pressing tool 310 has a stepped pressing surface , wherein the first support points are located on a first plane level 315 of the stepped pressing surface and the second support points are located on a second plane level 316 of the stepped pressing surface , and wherein the first plane level 315 and the second plane level 316 are parallel and at a perpendicular distance from each other, at least equal to the maximum head clearance X" . Within the scope of the invention, it is not excluded that the pressing tool has a pressing surface with a different geometry, as long as the first support points and the second support points are positioned relative to each other in such a way that, when mounting the screw rotor is completed, the head face and the high-pressure end face are at a perpendicular distance from each other, equal to the maximum head clearance .

[0092] Preferably, the first plane level 315 and the second plane level 316 are located at a perpendicular distance from each other, equal to the maximum head clearance X" , increased with a stiffness constant . As a result , during mounting of the screw rotor 200 in the axial inlet bearing 201 , for example a bearing stiffness of the axial inlet bearing 201 is taken into account .

[0093] In this case , the stepped pressing surface with the first plane level 315 and the second plane level 316 is integrally provided in the pressing tool 310 .

[0094] However , it is not excluded within the scope of the invention that the pressing tool comprises a separately removable attachment for providing at least the first flat level of the stepped pressing surface .

[0095] Preferably, the first support points are positionally distributed such that the pressure , exerted by the pressing tool 310 on the screw rotor 200 , when mounting the screw rotor 200 , is rotationally symmetrically distributed over the head face 205 along an axis of rotation of the screw rotor 200 . More preferably, the first support points are uniformly positionally distributed according to a circle or ring . It will be clear that , in Figure 3 , the first plane level 315 constitutes an annular surface with uniformly distributed first support points .

[0096] Furthermore , preferably and also in the case of Figures 3 and 4 , the pressing tool 310 has a recess 313 , which recess 313 is configured such that , when mounting the screw rotor 200 , the pressing tool 310 accommodates at least a portion of the axle j ournal 214 of the screw rotor 200 which extends from the head face 205 .

[0097] In this case , the pressing tool 310 is provided as one integral piece .

[0098] However , it is not excluded within the scope of the invention that the pressing tool comprises two or more mutually separable parts for forming a recess , whereby the two or more mutually separable parts then enclose the recess .

[0099] Preferably, the recess 313 has a shape , preferably a cylindrical shape , corresponding to the axle j ournal 214 or the portion of the axle j ournal 214 , as also shown in Figures 3 and 4 .

[0100] In this case , a centre of the annular first surface level 315 of the pressing tool 310 in Figure 3 lies on a symmetrical axis of the cylindrical shape . Figure 6 shows in more detail the part labelled F6 in Figure 2 .

[0101] As can be seen in Figure 6 , here too, the pressing tool

[0102] 210 has a stepped pressing surface , wherein the first support points are located on a first plane level 215 of the stepped pressing surface and the second support points are located on a second plane level 216 of the stepped pressing surface , and wherein the first plane level 215 and the second plane level 216 are parallel and at a perpendicular distance from each other, at least equal to the maximum head clearance X ' .

[0103] In this manner, the screw rotor 200 can be mounted with the predefined maximum head clearance X ' in the axial inlet bearing 201 of the first part 211 of the screw element housing by exerting pressure on the head face 205 of the screw rotor 200 with the first support points on the first plane level 215 of the pressing surface of the pressing tool 210 until the second support points on the second plane level 216 of the pressing surface contact the first coupling surface 212 of the first part

[0104] 211 of the screw element housing .

[0105] The present invention is by no means limited to the pressing tools and the method for mounting a screw rotor in an axial inlet bearing of a screw element for compressing a gas as described by way of example and shown in the figures , but a pressing tool according to the invention can be realized in all kinds of shapes and dimensions and a method according to the invention can be realized in all kinds of variants without departing from the scope of protection of the invention as defined in the claims .

Claims

Claims .1.- A pressing tool for mounting a screw rotor (200) in an axial inlet bearing (201) of a screw element for compressing a gas, wherein the pressing tool (210; 310) is configured to mount the screw rotor (200) with a predefined maximum head clearance (X'; X") between- on the one hand, a head face (205) of a profile body (206) of the screw rotor (200) ; and- on the other hand, a high-pressure end face (207) of a compression space, located within a housing of the screw element and configured to accommodate the profile body (206) of the screw rotor (200) , wherein the housing is configured to be composed of two parts having mutually corresponding coupling surfaces, of which two parts a first part (211) with a first coupling surface (212) of the mutually corresponding coupling surfaces contains the axial inlet bearing (201) , characterized in that the pressing tool (210; 310) comprises a group of first support points and a group of second support points, wherein the first support points are positioned such that, when mounting the screw rotor (200) , they contact the head face (205) and exert pressure on the head face (205) in a direction towards the axial inlet bearing (201) , wherein the second support points are positioned such that, upon completion of mounting the screw rotor (200) , they contact the first coupling surface (212) , andwherein the first support points and the second support points are positioned relative to each other such that, upon completion of mounting the screw rotor (200) , the head face (205) and the high-pressure end face (207) are at a perpendicular distance from each other, equal to the maximum head clearance (X' ; X") .2.- The pressing tool according to claim 1, characterised in that the pressing tool (210; 310) has a stepped pressing surface, wherein the first support points are located on a first plane level (215; 315) of the stepped pressing surface and the second support points are located on a second plane level (216; 316) of the stepped pressing surface, and wherein the first plane level (215; 315) and the second plane level (216; 316) are parallel and are located at a perpendicular distance from each other, at least equal to the maximum head clearance (X'; X") .3.- The pressing tool according to claim 2, characterised in that the perpendicular distance between the first plane level (215; 315) and the second plane level (216; 316) is equal to the maximum head clearance (X'; X") , increased by a stiffness correction factor.4.- The pressing tool according to claim 2 or 3, characterised in that the pressing tool (210; 310) comprises a separately removable attachment for providing at least the first flat level (215; 315) of the stepped pressing surface.5.- The pressing tool according to any one of the preceding claims, characterised in that the firstsupport points are positionally distributed such that the said pressure, exerted on the screw rotor (200) , when mounting the screw rotor (200) , is rotationally symmetrically distributed over the head face (205) according to an axis of rotation of the screw rotor(200) .6.- The pressing tool according to claim 5, characterized in that the first support points are uniformly positionally distributed according to a circle or ring.7.- The pressing tool according to any one of the preceding claims, characterised in that the pressing tool (210; 310) has a recess (213; 313) , which recess (213; 313) is configured such that the pressing tool (210; 310) , when mounting the screw rotor (200) , accommodates at least a portion of an axle journal (214) of the screw rotor (200) protruding from the head face (205) .8.- The pressing tool according to claim 7, characterised in that the pressing tool (210; 310) comprises two or more mutually separable parts for forming the recess (213; 313) , wherein the two or more mutually separable parts enclose the recess (213; 313) .9.- The pressing tool according to claim 7 or 8, characterised in that the recess (213; 313) has a shape, corresponding to the axle journal (214) or the portion of the axle journal (214) .10.- The pressing tool according to claim 9, characterized in that the said shape is a cylindrical shape .11.- The pressing tool according to claims 6 and 10, characterised in that a centre of the circle or ring is located on a symmetrical axis of the cylindrical shape.12.- A method for mounting a screw rotor (200) in an axial inlet bearing (201) of a screw element for compressing a gas, characterized in that the screw rotor (200) is mounted with the aid of a pressing tool (210, 310) according to any of the preceding claims with a predefined maximum head clearance (X' , X") between- on the one hand, a head face (205) of a profile body (206) of the screw rotor (200) ; and- on the other hand, a high-pressure end face (207) of a compression space, located within a housing of the screw element and configured to accommodate the profile body (206) of the screw rotor (200) , wherein the housing comprises two parts with mutually corresponding coupling surfaces, of which two parts a first part (211) with a first coupling surface (212) of the mutually corresponding coupling surfaces contains the axial inlet bearing (201) , wherein the method comprises the following consecutive steps : a' . contacting the head face (205) of the screw rotor (200) with the first support points of the pressing tool (210; 310) ;b' . pressing the screw rotor (200) into the axial inlet bearing (201) by applying pressure from the first support points of the pressing tool (210; 310) onto the head face (205) in a direction towards the axial inlet bearing (201) until the second support points of the pressing tool (210; 310) contact the first coupling surface (212) .13.- A screw element for compressing a gas, comprising- a screw rotor (200) with a profile body (206) ; and- a housing containing a compression space, which compression space contains the profile body (206) of the screw rotor (200) , wherein the housing is composed of two parts, connected to each other at mutually corresponding coupling surfaces, of which two parts a first part (211) with a first coupling surface (212) of the mutually corresponding coupling surfaces contains an axial inlet bearing (201) , characterized in that the screw rotor (200) is mounted in the axial inlet bearing (201) using the method according to claim 12, such that a head face (205) of the profile body (206) and a high-pressure end face (207) of the compression space are located at a perpendicular distance from each other, equal to a maximum head clearance (X'; X") .

14. The screw element according to claim 13, characterized in that the first coupling surface (212) is located at the high-pressure end face (207) .

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