A METHOD FOR TREATING A WORKPIECE FOR A FLUID ENERGY MACHINE

Abstract

 The present invention relates to a method for treating a workpiece (100) for a fluid energy machine, especially a shaft (100) for a fluid energy machine, comprising the steps of performing a first heat treatment process on the workpiece (100), the first heat treatment process comprising a first solution treatment process at a first predetermined temperature, a first quenching process, and at least one first tempering process at a second predetermined temperature; and performing a second heat treatment process on one or more sections (110) of the workpiece (100), the second heat treatment process comprising at least one second tempering process at a fourth predetermined temperature or the second heat treatment process comprising a second solution treatment process at a third predetermined temperature, a second quenching process, and the at least one second tempering process at the fourth predetermined temperature.

Description

[0001] The present invention relates to a method for treating a workpiece for a fluid energy machine as well as to a workpiece for a fluid energy machine.

Background of the invention

[0002] Fluid energy machines are machines or devices, in which mechanical work is exchanged with a fluid, i.e. a gas and/or liquid. A fluid energy machine thus either transfers work from the outside to the fluid (working machine) or extracts energy from the fluid (prime mover), which is then delivered to the outside as mechanical work. A turbomachinery is a working machine, which transfers energy between a rotor and a fluid. A turbomachinery can be a turbine or a compressor. While a turbine transfers energy from a fluid to a rotor, a compressor transfers energy from a rotor to a fluid.

[0003] In a fluid energy machine of that kind, impellers can be arranged on a rotating shaft. For example, in a compressor like a cryogenic radial turbo-compressor, an expander impeller and a compressor impeller can be fixed on both ends of a steel shaft. This shaft has to sustain a high torque created by the fluid flow through the impellers. For example in cryogenic applications, the process fluid, which flows through the impellers, may reach temperatures down to 50 K at expander outlet and/or at compressor inlet. The shaft rotation can be guided by magnetic bearings, which can comprise a pair of radial bearings, a pair of auxiliary bearings and axial bearings. Axial bearings can directly interact with an axial thrust disk which can be part of the shaft, wherein the shaft is ferromagnetic. A (high-speed) motor or generator can for example also be installed in the centre part of the shaft, in conjunction to magnetic bearings or with oil bearings. A high level of ferromagnetism can then also be required in the centre part of the shaft. A temperature gradient can occur along the shaft axis. The experienced temperatures can depend on the limit conditions of the rotor.

[0004] In some cryogenic applications, the shaft material may have to combine firstly a high impact toughness at one or two of its ends and at the coldest temperature it experiences, that can be 77 K, i.e. -196°C, or even less, and secondly a high magnetic induction to sustain high axial thrusts and/or to allow a high-speed motor or generator operation. A combination of that kind of high impact toughness and high magnetic induction can be difficult to achieve since highly ferromagnetic steels are usually unsuitable for very cold cryogenic temperatures whereas cryogenic steels exhibit a poor ferromagnetism and are usually magnetically soft materials. Alloys used for shafts in cryogenic applications down to 77 K and less can be optimised for impact toughness, but typically are poorly ferromagnetic, because ferromagnetism and impact toughness are negatively correlated. Therefore, axial thrust of extremely cold expanders or compressors might have to be limited, which might not allow to work at a maximum efficiency. Further, the use of a high-speed motor or generator may not be possible. Conversely, if a high axial thrust shall be sustained or if a high-speed motor or generator shall be used, the minimum temperature of a corresponding process gas might be limited because of the use of magnetically hard materials, which might restrain the use to mild cold applications.

[0005] It is therefore desirable, to improve workpieces for fluid energy machines, especially shafts for fluid energy machines.

Disclosure of the invention

[0006] The present invention refers to a method for treating a workpiece for a fluid energy machine as well as to a workpiece for a fluid energy machine with the features of the independent claims. Embodiments and advantages form the subject-matter of the dependent claims and of the subsequent description.

[0007] The corresponding fluid energy machine can expediently be provided for cryogenic applications, especially for temperatures down to 77 K or even less. The workpiece is particularly a shaft, expediently a shaft for a rotor of the corresponding fluid energy machine, on which one or more impellers can be arranged, e.g. at one or both axial ends of the shaft. Particularly, the workpiece is made of a material with one single chemical composition. The workpiece is particularly made in one piece. The workpiece can expediently be an axisymmetric workpiece, especially with respect to a main axis or rotation axis. A length in an axial direction of the workpiece can particularly be larger than a maximum diameter in a radial direction of the workpiece.

[0008] According to the present invention, a first heat treatment process is performed on the entire workpiece, wherein this first heat treatment process comprises a first solution treatment process at a first predetermined temperature, a subsequent first quenching process, and subsequently at least one first tempering process at a second predetermined temperature. Each one of these first tempering processes can be performed at a different, individually predetermined second temperature. Expediently, these first tempering processes can be separated by air cooling.

[0009] A second heat treatment process is performed on one or more sections or segments of the workpiece, especially on one or more axial sections with a predetermined length in axial direction. This section or these sections shall hereafter also be referred to as one or more first sections, i.e. at least one first section. In particular, all these (first) sections together expediently only form a part of the entire workpiece. Therefore, the sum of all these first sections, on which the second heat treatment is performed, particularly does not correspond to or add up to the entire workpiece. The sum of all these sections is expediently smaller than the entire workpiece. The second heat treatment process is therefore not performed on the entire workpiece, but only on a part of the workpiece.

[0010] This second heat treatment process comprises at least one second tempering process at a fourth predetermined temperature. Alternatively, the second heat treatment process comprises a second solution treatment process at a third predetermined temperature, a subsequent second quenching process, and subsequently the at least one second tempering process at the fourth predetermined temperature. Each one of these second tempering processes can be performed at a different, individually predetermined fourth temperature. The second tempering processes can be separated by air cooling.

[0011] The corresponding first and second solution treatment process is particularly to be understood as a heating of the workpiece material to the corresponding predetermined temperature, especially such that one or more constituents of the workpiece material enter into a solid solution.

[0012] The corresponding first and second quenching process is particularly to be understood as a rapid cooling of the workpiece material after the corresponding solution treatment process, especially a cooling in air. By means of this quenching process, the corresponding material constituents particularly retain the properties of the solution.

[0013] The corresponding first and second tempering process is particularly to be understood as a heating of the workpiece material to the corresponding temperature, which expediently lies below a critical point in the phase equilibrium curve of the corresponding material. Subsequently, the workpiece material is allowed to cool, e.g. in still air.

[0014] Since the first heat treatment process is performed on the entire workpiece, mechanical, physical, or magnetic properties can be homogenously be influenced throughout the entire workpiece. With the second heat treatment process being performed not on the entire workpiece but only on the specific first section or sections of the workpiece, mechanical, physical, or magnetic properties in these first sections can individually be influenced, particularly independently of the rest or the remaining sections of the workpiece. By means of this spatially restricted second heat treatment process, the workpiece can therefore selectively be heat-treated, especially selectively tempered. Therefore, properties in the different workpiece sections can be adjusted individually and independently of each other and can expediently be optimised for the specific application of the corresponding fluid energy machine. If in this specific application there are different demands for different kinds of properties, like impact toughness and magnetic induction, e.g. in cryogenic application, selectively tempering the workpiece expediently allows to meet these demands. The invention therefore allows to significantly improve the workpiece for the desired application of the fluid energy machine.

[0015] The invention further refers to a workpiece for a fluid energy machine, especially a shaft of a fluid energy machine, which has been treated according to an embodiment of method of the present invention. Embodiments and advantages of the workpiece according to the invention and of the method according to the invention shall arise from the present description in an analogue manner.

[0016] According to an embodiment, the first heat treatment process and the second heat treatment process are performed such that a first quantity or property or variable, especially a magnetic quantity, in the one or more (first) sections of the workpiece lies within a first predetermined value range and such that a second quantity or property or variable, especially a magnetic quantity, in at least one other second section of the workpiece lies within a second predetermined value range. Expediently, this at least one second section corresponds to that part of the workpiece, on which the second heat treatment process is not performed. In accordance with the first section or first sections, each of these second sections is particularly also an axial section with a predetermined length in axial direction. The first and second sections can be axially adjacent to each other. Expediently, the first and second sections do not overlap in axial direction. There can be an axial transition section between adjacent first and second sections.

[0017] Particularly, by means of the second heat treatment process, which is performed only on the first section(s), the first quantity in this first section(s) can be influenced and a specific value of this first quantity can be adjusted to be in the first value range. By means of the first heat treatment process, which is performed on the entire workpiece, i.e. also on the second section(s), the second quantity in the second section(s) is particularly influenced and a specific value of this second quantity is expediently adjusted to be in the corresponding second value range. Therefore, after treating the workpiece by means of the first and second heat treatment process, different axial sections of the workpiece have different, individual mechanical, physical and/or magnetic properties. In particular, in these different first and second sections of the workpiece, the respective quantity or property can individually be adjusted and optimised for the specific application of the corresponding fluid energy machine. The corresponding first or second quantity can expediently be homogeneous in the corresponding first or second section in a radial direction, i.e. especially homogeneous from a surface to a centre of the corresponding first or second section.

[0018] According to an embodiment, the first heat treatment process and the second heat treatment process are performed such that an impact toughness as the first quantity in the one or more first section of the workpiece lies within the first predetermined value range and such that a magnetic induction as the second quantity in the at least one second section of the workpiece lies within the second predetermined value range. Impact toughness and magnetic induction are usually negatively correlated with respect to the temperature of the heat treatment process. That is, the lower the temperature of the heat treatment process, the higher the magnetic induction that can be achieved. In contrast to that, the higher the temperature of the heat treatment process, the higher the achieved impact toughness. However, by means of performing the first and second heat treatment processes, the impact toughness and the magnetic induction can be adjusted individually and independently of each other in the different sections of the workpiece. In particular, by means of the first heat treatment process, the magnetic induction in the second section(s) can be adjusted to be in the second predetermined value range. By means of the second heat treatment process, the impact toughness in the first section(s) can be adjusted to be in the corresponding first predetermined value range. Expediently, a high impact toughness and a high ferromagnetism can be combined in the same workpiece, particularly made of one single chemical composition and in one piece. Selectively tempering the workpiece during the second heat treatment process particularly allows to combine high impact toughness or ductility and ferromagnetism in the workpiece.

[0019] Expediently, the final tempering process or processes of the second heat treatment process tune the final mechanical properties in the first section(s). If several second tempering processes are performed during the second heat treatment process, these subsequent second tempering processes are particularly performed with decreasing tempering temperatures, i.e. with decreasing fourth temperature. The higher the tempering temperature, the lower is the achieved strength of workpiece material and furthermore, the higher is the ductility and the impact toughness. That is, after a tempering process with a higher temperature, the workpiece material is e.g. softer than after a tempering process with a lower temperature. Particularly, in order to achieve optimum impact toughness properties, the first section(s) of the workpiece can be double tempered in the second heat treatment process, i.e. two second tempering processes can subsequently be performed with decreasing fourth temperature.

[0020] Expediently, if the correspondingly treated workpiece is provided as a shaft, the shaft can withstand high torques, also at cryogenic temperatures down to 77 K or less, particularly because of its strength, expediently because of its yield stress and ultimate tensile strength. The high impact toughness can expediently prevent brittle failure of the shaft in case of a shock in operation. In cryogenic applications, independent from their actual strength, materials should demonstrate enough impact toughness to prevent the catastrophic failure. An impeller can expediently be provided in a corresponding first section of the shaft with high impact toughness. Further, the high magnetic induction allows the use of magnetic bearings to guide the shaft at the correspond second section(s). The high magnetic induction further allows to install a (high-speed) motor or generator in the correspond second section(s). In particular, the shaft can be treated to have high impact toughness at one or two of its axial ends and at the coldest temperature it experiences, e.g. 77 K or less, and to have high magnetic induction to sustain high axial thrusts and/or to allow a high-speed motor or generator operation. Therefore, the axial thrust on the shaft expediently does not have to be limited and the fluid energy machine can particularly be operated with high or even maximum efficiency. Further, the minimum temperature of a corresponding process gas particularly does not have to be limited either.

[0021] According to an embodiment, the first predetermined value range for the impact toughness lies between 10 J at 77 K and 20 J at 77 K, especially between 10 J at 20 K and 20 J at 20 K. Particularly, the impact toughness in the first section(s) is adjusted to be essentially 15 J at 77 K. Alternatively or additionally, a lower limit of the second predetermined value range for the magnetic induction is 1.48 T at a magnetic field of 20 kA/m. Alternatively or additionally, an upper limit of the second predetermined value range is 5.00 T at a magnetic field of 20 kA/m.

[0022] According to an embodiment, during the second heat treatment process, a cooling process is performed on at least one transition section to a predetermined fifth temperature, e.g. 200°C or lower. This at least one transition section is located between the one or more first sections and the at least one second section. Expediently, a transition section of that kind is located between axially adjacent first and second sections. The cooling process can e.g. be performed by means of an air flow or by an helicoidal coil containing a water stream. By means of this cooling process it can especially be prevented that properties of the second section(s), which were adjusted during the first heat treatment process, are influenced during second heat treatment process. An intensity of the corresponding cooling during the cooling process can especially allow to minimise a length of the corresponding transition section in axial direction and further to expediently enlarge a length of the first and second sections in axial direction. For example, the lengths of the various sections can be adjusted in order to install a high-speed motor or generator in the middle of the shaft. The cooling process might not be necessary when the shaft is designed for a magnetic axial thrust bearing where in that case, only the central disk shall be strongly magnetic. Further, if the shaft ends are smaller in diameter than the middle portion of the shaft, the temperature increase will also be limited due to conductive heat transfer.

[0023] According to an embodiment, at least one temperature sensor is provided at a predetermined position on a surface of the workpiece and/or inside the workpiece. A temperature at the corresponding predetermined position is monitored by means of the at least one temperature sensor during the first heat treatment process and/or the second heat treatment process. For example, the corresponding temperature sensors can be welded to the workpiece surface at the corresponding positions. For providing the corresponding temperature sensors inside the workpiece, these sensors can e.g. be inserted through holes drilled from the surface of the workpiece to the corresponding position. The temperature at the corresponding positions can particularly be monitored in order to conduct the second heat treatment process properly. During the second heat treatment process, temperatures at different positions on the workpiece surface in the first section(s) should particularly have the same value or at least essentially the same value within a predetermined tolerance margin. Temperature sensors inside the workpiece can especially be used during a development or calibration phase for calibrating a corresponding device with which the second heat treatment process is performed. After the second heat treatment process, the temperature sensors can be removed from the workpiece. For example, Type K thermocouples can be used as the temperature sensors. A Type K thermocouple is a temperature sensor with conductors made of the alloys Chromel and Alumel. Requirements for these Type K thermocouples are defined in the standard ANSI/ASTM E230 or IEC 60584.

[0024] According to an embodiment, at least one set of temperature sensors is provided at a predetermined axial position of the workpiece, i.e. a predetermined position in axial direction, each set of temperature sensors comprising at least two temperature sensors provided at predetermined, especially equidistant distances in a circumferential direction on the surface of the workpiece. Each set of temperature sensors is therefore expediently uniformly distributed around the circumference of the workpiece at a specific axial position, e.g. to monitor whether the temperature of the workpiece surface is constant along the circumference during the second heat treatment process. For example, each set of temperature sensors can comprise especially four temperature sensors, which allows efficient, precise monitoring of the surface temperature at the corresponding axial position.

[0025] Alternatively or additionally, at least one temperature sensor is provided inside the workpiece on a main axis or rotational axis of the workpiece at a predetermined axial position of the workpiece. These sensors can especially be provided by insertion in thin holes drilled radially from the surface to the axis. These temperature sensors on the workpiece axis can especially be used during the development or calibration phase for calibrating the corresponding device for performing the second heat treatment process.

[0026] According to an embodiment, a first set of temperature sensors is provided at a first axial position corresponding to a first axial end of the one or more first sections in axial direction. Alternatively or additionally, a second set of temperature sensors is provided at a second axial position corresponding to a second axial end of the one or more first sections in axial direction. This second end is therefore especially opposite to the first end in axial direction. This second axial end particularly corresponds to an interface between the corresponding first section and the corresponding transition section, which is located between the corresponding first section and the adjacent second section. A third set of temperature sensors is expediently provided at a third axial position between the first axial position and the second axial position, especially in the middle between the first axial position and the second axial position. During the second heat treatment process, all these temperature sensors of the first, second and third set of sensors should particularly show the same temperature value or at least essentially the same temperature value within a predetermined tolerance margin. Alternatively or additionally, a fourth set of temperature sensors can be provided at an interface between the at least one transition section and the at least one second section. The temperature measured with the sensors of this fourth set should particularly be below the aforementioned fifth predetermined temperature, e.g. below 200°C.

[0027] According to an embodiment, the second heat treatment process is performed on one or more end sections of the workpiece, especially on one or more end sections extending from an axial end of the workpiece with a predetermined length in axial direction. In this case, the workpiece comprises especially one second section. This second section can e.g. extend axially between two end sections. If only one end section is treated during the second heat treatment process, the second section can be adjacent to this corresponding first section and can axially extend to the other axial end of the shaft. In case of a shaft, these end section(s) can expediently be treated in the second heat treatment process to have high impact toughness and to have high strength such that one or several impellers can be arranged in these end section(s) and such that the shaft can withstand high torque created by the impeller(s) and brittle failure is prevented. Both end sections can e.g. identically be treated during the second heat treatment process. It is also possible to vary the corresponding third and fourth temperatures of the corresponding second heat treatment processes performed on the different axial end sections. Therefore, the two axial end sections can individually be treated to have an individual impact toughness.

[0028] According to an embodiment, the third predetermined temperature is identical or at least essentially identical to the first predetermined temperature. Therefore, the first solution treatment process and the second solution treatment process are especially performed at the same or at least essentially the same temperature. For example, the first and third predetermined temperature differ from each other no more than 10°C, especially no more than 5°C, especially no more than 1°C.

[0029] According to an embodiment, the first heat treatment process is performed using a heat treatment furnace. The workpiece can be arranged entirely inside this heat treatment furnace such that the entire workpiece can uniformly be heated during the first solution treatment process and the at least one first tempering process.

[0030] According to an embodiment, the second heat treatment process is performed using an induction furnace and/or an induction local heating device and/or a radiation furnace and/or a cooling device. The radiation furnace can especially comprise a predetermined number of bulbs, e.g. four or six bulbs. By means of the induction furnace, the induction local heating device and/or the radiation furnace, the first section(s) can locally be heated, especially without heating the second section(s). By means of the cooling device, the at least one transition section between the first and second section(s) can particularly be cooled during the second heat treatment process.

[0031] According to an embodiment, the workpiece is made of a martensitic stainless steel (MSS) or a precipitation hardening stainless steel (PHSS). Martensitic stainless steel is a stainless-steel alloy having a martensite crystal structure. Precipitation hardening stainless steel is a corrosion resistant stainless-steel alloy, which can comprise copper, molybdenum, aluminium, titanium or a combination thereof. These kinds of materials are heat treatable alloys, whose final properties particularly depend on the solution treating temperature and the (single or dual) tempering temperature.

[0032] According to an embodiment, the fluid energy machine is a working machine, i.e. a machine that transfers work from the outside to a fluid. In particular, the fluid energy machine is as a rotating turbomachinery, especially a compressor or a turbo compressor or a cryogenic turbo compressor, especially for transferring energy from a rotor to a fluid. The fluid energy machine particularly comprises a rotor, wherein the shaft can be provided for this rotor of the fluid energy machine. The fluid energy machine is particularly provided for cryogenic applications, especially for temperatures down to 77 K or even less. The fluid energy machine can particularly be a turbo compressor with at least a cryogenic turbine side working at a process temperature of 77 K or less, or with both cryogenic turbine and compressor, equipped with axial magnetic bearings and/or high-speed motor or generator. Treating the workpiece according to an embodiment of the present invention particularly allows to operate the corresponding fluid energy machine with a process fluid in deep cryogenic conditions down to 77 K or even down to 20 K and take advantage of the high ferromagnetism of the shaft centre part. This allows the possibility to compensate high axial thrusts with magnetic bearings and/or to add a high-speed motor or a high-speed generator to the fluid energy machine with.

[0033] Further advantages and developments of the invention are specified in the description and the associated drawings.

[0034] It goes without saying, that the features named above and still to be explained below can be used not only in the combination indicated respectively, but also in other combinations or in a stand-alone manner, without going beyond the scope of the present invention.

[0035] The invention is illustrated schematically in the drawings on the basis of exemplary embodiments and will be described in detail in the following with reference to the drawings.

Description of drawings

[0036] 

Fig. 1

schematically shows a workpiece in a side view, which can be treated according to an embodiment of the method according to the present invention.

Fig. 2

schematically shows a workpiece in a side view (Fig. 2a) and a front view (Fig. 2b), which can be treated according to an embodiment of the method according to the present invention.

Fig. 3

schematically shows an embodiment of the method according to the present invention as a block diagram.

Detailed description of the drawings

[0037] Fig. 1 schematically shows a workpiece 100 in a side view, in particular a shaft to be used as a rotor in a fluid energy machine, e.g. a turbomachinery, e.g. a compressor for cryogenic applications, e.g. a cryogenic turbo compressor.

[0038] The shaft 100 is axisymmetric relative to a main axis or rotation axis 105. A length of the shaft 100 in an axial direction is larger than a maximum diameter in radial direction. The shaft 100 is made of a material with one single chemical composition and is made in one piece.

[0039] The shaft comprises a first axial end 101 and an opposite, second axial end 102. An impeller shall be arranged on a first section 110 of the shaft 100, especially at an end section extending from the first axial end 101 with a predetermined length in axial direction. In this axial end section 110, the shaft 100 shall have a high impact toughness and high strength in order to prevent brittle failure and to withstand high torques created by the impeller.

[0040] In a second section 120 axially adjacent to the first section 110, the shaft 100 shall have high magnetic induction, e.g. to enable the use of magnetic bearings and/or to add a high-speed motor or a high-speed generator. The first section 110 and the second section 120 do not overlap but are separated by a transition section 130.

[0041] The shaft 100 shall be treated according to an embodiment of the method according to the present invention in order to adjust its mechanical and magnetic properties. In particular, the shaft 100 shall be treated to have high impact toughness in the first section 110 and high magnetic induction in the second section 120 at cryogenic temperatures down to 77 K, especially down to 20 K.

[0042] Before treating the shaft 100 accordingly, a number of temperature sensors, e.g. Type K thermocouples, are provided at predetermined positions on a surface of the workpiece and inside the workpiece, as shall now be explained with reference to Fig. 2.

[0043] Fig. 2a shows a part of the shaft 100 in a side view. Fig. 2b shows the first section 110 of the shaft 100 in a front view.

[0044] As shown in Fig. 2a and 2b, several sets 210, 220, 230, 240 of temperature sensors are provided at predetermined axial positions of the workpiece, wherein each set of temperature sensors comprises several temperature sensors provided at predetermined, equidistant distances in a circumferential direction on the surface of the shaft.

[0045] In particular, a first set 210 comprising four temperature sensors 211, 212, 213, 214 is provided at a first axial position 201 corresponding to a first axial end of the first section 110, i.e. corresponding to the first axial end 101 of the shaft. As can be seen in Fig. 2b, these four temperature sensors 211, 212, 213, 214 are uniformly distributed around the circumference of the shaft 100.

[0046] A second set 220 of temperature sensors also comprises four temperature sensors. In Fig. 2a, only three of these sensors 221, 222, 223 of the second sensor set 220 can be seen. This second set 220 is provided at a second axial position 202 corresponding to a second axial end of the first section 110 corresponding to an interface between the first section 110 and the transition section 130. In accordance with first sensor set 210 as shown in Fig. 2b, the four sensors of the second sensor set 220 are uniformly distributed around the circumference of the shaft 100.

[0047] A third set 230 of temperature sensor also comprises four temperature sensors, although only three of these sensors 231, 232 and 233 can be seen in Fig. 2a. The third sensor set 230 is provided at a third axial position 203 between the first axial position 201 and the second axial position 202, especially in the middle between the first axial position 201 and the second axial position 202, and hence especially in the middle of the first section 110. In accordance with first sensor set 210 as shown in Fig. 2b, the four sensors of the third sensor set 230 are uniformly distributed around the circumference of the shaft 100.

[0048] A fourth set 240 of temperature sensor also comprises four temperature sensors, wherein only three of these sensors 241, 242 and 243 can be seen in Fig. 2a. This fourth sensor set 240 is provided at a fourth axial position 204 corresponding to an interface between the transition section 130 and the second section 120. In accordance with first sensor set 210 as shown in Fig. 2b, the four sensors of the fourth sensor set 240 are uniformly distributed around the circumference of the shaft 100.

[0049] Further, a number of temperature sensors is provided inside the shaft 100 on the main axis 105 at predetermined axial positions.

[0050] Fig. 2b shows a temperature sensor 250 of that kind, which is provided on the main axis 105 at the first axial position 201. Correspondingly, one temperature sensor of that kind is provided on the main axis 205 at each of the second axial position 202, the third position 203, and the fourth axial position 204. These sensors are provided by insertion in holes drilled radially from the surface to the axis 105.

[0051] By means of all these temperature sensors provided on the surface and on the main axis 105 of the shaft 100, a corresponding temperature is monitored during the treatment of the shaft according to an embodiment of the present invention.

[0052] The treatment of the shaft 100 will now be explained with reference to Fig. 3, which shows an embodiment of the method according to the present invention as a schematic block diagram.

[0053] In a first step 301, the various temperature sensors are provided to the shaft as explained above. In step 302, a calibration of furnaces and devices used for the shaft treatment is performed in dependence of temperature values measured with the temperature sensors 250 provided inside the shaft 100 on the main axis 105.

[0054] In step 310, a first heat treatment process is performed on the entire shaft 100, e.g. using a heat treatment furnace. During this first heat treatment process 310, a first solution treatment process at a first predetermined temperature T1 is performed in step 311, i.e. the entire shaft 100 is heated to this first predetermined temperature T1. Subsequently, a first quenching process, e.g. in air, is performed in step 312, wherein the shaft 100 is rapidly cooled after the first solution treatment process 311.

[0055] Subsequently, in step 313, a first tempering process is performed on the entire shaft 100 at a predetermined second temperature T2, wherein the shaft 100 is heated to the corresponding second temperature T2, which lies below a critical point in the phase equilibrium curve of the workpiece material. It is also possible to perform several first tempering processes of that kind with cooling periods in between, wherein during each of these several first tempering processes, the shaft 100 is heated to an individual second temperature T2.

[0056] By means of this first heat treatment process 310, the magnetic induction in the second section 120 is adjusted to be in a predetermined value range, e.g. between 1.48 T and 5.00 T at a magnetic field of 20 kA/m. Expediently, the lower the second predetermined temperature T2, the higher the magnetic induction that can be achieved in the second section 120.

[0057] For example, the material of the shaft 100 can be a precipitation hardening stainless steel (PHSS), e.g. stainless steel 1.4542, i.e. X5CrNiCuNb16-4. In this case, the first predetermined temperature T1 of the first solution treatment process 311 can be between 1030°C and 1050°C. The predetermined second temperature T2 of the first tempering process 313 can be e.g. 620°C or 590°C or 550°C.

[0058] Alternatively, the material of the shaft 100 can e.g. be a martensitic stainless steel (MSS), e.g. stainless steel 1.4313, i.e. X3CrNiMo13-4. In this case, the first predetermined temperature T1 of the first solution treatment process 311 can be between 950°C and 1050°C. The predetermined second temperature T2 of the first tempering process 313 can e.g. be 550°C or 520°C.

[0059] After the first heat treatment process 310, a second heat treatment process 320 is performed on the first section 110 of the shaft 100, e.g. using an induction furnace, an induction local heating device or a radiation furnace. During this second heat treatment process 320, in step 321, a second solution treatment process at a third predetermined temperature T3 is performed, wherein the first section 110 is heated to this third predetermined temperature T3. In step 322, a second quenching process is performed, wherein the first section 110 is rapidly cooled in air after the second solution treatment process 321.

[0060] Subsequently, in step 323, at least one second tempering process is performed on the first section 110 at a predetermined fourth temperature T4, wherein the first section 110 is heated to the corresponding fourth temperature below the critical point of the shaft material. Expediently, several second tempering process of that kind are performed with cooling periods in between, wherein the first section 110 is heated to an induvial fourth temperature T4 during each of these second tempering processes. Alternatively, the second solution treatment process 321 and the second quenching process 322 can also be omitted such that only the second tempering process or processes 323 are performed.

[0061] By means of the second heat treatment process 320, especially by means of the second tempering process or processes 323, the impact toughness in the first section 110 is adjusted to be in a corresponding value range, e.g. between 10 J at 77 K and 20 J at 77 K, especially between 10 J at 20 K and 20 J at 20 K. In particular, the higher the tempering temperature T4, the lower the achieved strength and the higher the achieved ductility and the higher the achieved impact toughness.

[0062] For example, if the shaft material is the precipitation hardening stainless steel stainless steel 1.4542, i.e. X5CrNiCuNb16-4, the third predetermined temperature T3 of the second solution treatment process 221 can be between 1030°C and 1050°C, accordingly to the first predetermined temperature T1. In this case, the first section 110 can be double tempered with two subsequent second tempering processes 323. A first one of these double tempering processes 323 can be performed at a corresponding fourth temperature T4 of e.g. 760°C. A subsequent second one of these double tempering processes 323 can then be performed at a corresponding fourth temperature T4 of e.g. 620°C.

[0063] If the shaft material is for example the martensitic stainless steel 1.4313, i.e. X3CrNiMo13-4, the third predetermined temperature T3 of the second solution treatment process 221 can be between 950°C and 1050°C, accordingly to the first temperature T1. Also in this case, the first section 110 can be double tempered with two subsequent second tempering processes 323. The first one of these double tempering processes 323 can be performed at a corresponding fourth temperature T4 e.g. between 650°C and 670°C. The subsequent second one of these double tempering processes 323 can then be performed at a corresponding fourth temperature T4 between e.g. 600°C and 620°C.

[0064] During the second heat treatment process 320, especially during the second solution treatment process 321 and the second tempering process(es) 323, a cooling process is performed on the transition section 130, such that the temperature of the transition section 130 stays below a predetermined fifth temperature T5 of e.g. 200°C. This cooling process can e.g. be performed by means of an air flow or by an helicoidal coil containing a water stream. By means of this cooling process it can be prevented that the magnetic induction of the second section 130, as it was adjusted during the first heat treatment process 310, is influenced by means of the second heat treatment process 320.

[0065] During the second heat treatment process 320, the temperatures measured by the temperature sensors of the first sensor set 210, the second sensor set 220, the third sensor set 230 and the fourth sensor set 240 are monitored. Expediently, all the temperature sensors of the first sensor set 210, the second sensor set 220 and the third sensor set 230 should show the same temperature value or at least essentially the same temperature value within a predetermined tolerance margin. That is, the first section 110 should be homogeneously and uniformly be heated during the second heat treatment process 320. The temperature measured with the sensors of the fourth sensor set 240 shall be below the fifth predetermined temperature T5, e.g. below 200°C.

[0066] After the second heat treatment process 320, the treated shaft can be used as rotor in the corresponding turbomachinery. The present invention therefore allows to adjust the impact toughness and the magnetic induction individually and independently of each other in the different sections of the shaft 100 made of one single chemical composition and in one piece. The shaft 100 can therefore be optimised for the specific cryogenic application of the corresponding turbomachinery.

List of reference signs

[0067] 

100

shaft

101

first axial end

102

second axial end

105

main axis, rotation axis

110

first section

120

second section

130

intermediate section

201

first axial position

202

second axial position

203

third axial position

204

fourth axial position

210

first set of temperature sensors

211

temperature sensor of the first set

212

temperature sensor of the first set

213

temperature sensor of the first set

214

temperature sensor of the first set

220

second set of temperature sensors

221

temperature sensor of the second set

222

temperature sensor of the second set

223

temperature sensor of the second set

230

third set of temperature sensors

231

temperature sensor of the third set

232

temperature sensor of the third set

233

temperature sensor of the third set

240

fourth set of temperature sensors

241

temperature sensor of the fourth set

242

temperature sensor of the fourth set

243

temperature sensor of the fourth set

250

temperature sensor provided on the main axis

301

providing temperature sensors

302

calibration of furnaces and devices

310

first heat treatment process

311

first solution treatment process

312

first quenching process

313

at least one first tempering process

320

second heat treatment process

321

second solution treatment process

322

second quenching process

323

at least one second tempering process

Claims

1. A method for treating a workpiece (100) for a fluid energy machine, especially a shaft (100) for a fluid energy machine, comprising the steps of:

performing a first heat treatment process (310) on the workpiece (100), the first heat treatment process (310) comprising a first solution treatment process (311) at a first predetermined temperature, a first quenching process (312), and at least one first tempering process (313) at a second predetermined temperature; and

performing a second heat treatment process (320) on one or more sections (110) of the workpiece (100), the second heat treatment process (320) comprising at least one second tempering process (323) at a fourth predetermined temperature or the second heat treatment process (320) comprising a second solution treatment process (321) at a third predetermined temperature, a second quenching process (322), and the at least one second tempering process (323) at the fourth predetermined temperature.

2. The method according to claim 1, further comprising:
performing the first heat treatment process (310) and the second heat treatment process (320) such that a first quantity, especially a magnetic quantity, in the one or more sections (110) of the workpiece (100) lies within a first predetermined value range and such that a second quantity, especially a magnetic quantity, in at least one other second section (120) of the workpiece (100) lies within a second predetermined value range.

3. The method according to claim 2, further comprising:
performing the first heat treatment process (310) and the second heat treatment process (320) such that an impact toughness in the one or more sections (110) of the workpiece (100) lies within the first predetermined value range and such that a magnetic induction in the at least one other second section (120) of the workpiece (100) lies within the second predetermined value range.

4. The method according to claim 3, wherein the first predetermined value range for the impact toughness lies between 10 J at 77 K and 20 J at 77 K, especially between 10 J at 20 K and 20 J at 20 K, and/or wherein a lower limit of the second predetermined value range for the magnetic induction is 1.48 T at a magnetic field of 20 kA/m, and/or wherein an upper limit of the second predetermined value range for the magnetic induction is 5.00 T at a magnetic field of 20 kA/m.

5. The method according to any one of claims 2 to 4, further comprising:
performing a cooling process on at least one transition section (130) between the one or more sections (110) and the at least one other second section (120) to a fifth predetermined temperature during the second heat treatment process (320).

6. The method according to any one of the preceding claims, further comprising:

providing at least one temperature sensor (211, 212, 213, 214, 221, 222, 223, 231, 232, 233, 241, 242, 243, 250) at a predetermined position (201, 202, 203, 204) on a surface of the workpiece (100) and/or inside the workpiece (100), and

monitoring a temperature at the corresponding predetermined position (201, 202, 203, 204) by means of the at least one temperature sensor (211, 212, 213, 214, 221, 222, 223, 231, 232, 233, 241, 242, 243, 250) during the first heat treatment process (310) and/or the second heat treatment process (320).

7. The method according to claim 6, wherein providing the at least one temperature sensor (211, 212, 213, 214, 221, 222, 223, 231, 232, 233, 241, 242, 243, 250) comprises:

providing at least one set (210, 220, 230, 240) of temperature sensors at a predetermined axial position (201, 202, 203, 204) of the workpiece (100), each set (210, 220, 230, 240) of temperature sensors comprising at least two temperature sensors provided at predetermined, especially equidistant distances in a circumferential direction on the surface of the workpiece; and/or

providing at least one temperature sensor (250) inside the workpiece on a main axis (105) or rotational axis (105) of the workpiece (100) at a predetermined axial position (201, 202, 203, 204) of the workpiece (100).

8. The method according to claim 7, wherein

a first set (210) of temperature sensors (211, 212, 213, 214) is provided at a first axial position (201) corresponding to a first axial end of the one or more sections (110) in axial direction; and/or

a second set (220) of temperature sensors (221, 222, 223) is provided at a second axial position (202) corresponding to a second axial end of the one or more sections (110) in axial direction; and/or

a third set (230) of temperature sensors (231, 232, 233) is provided at a third axial position (203) between the first axial position (201) and the second axial position (202), especially in the middle between the first axial position (201) and the second axial position (202); and/or

wherein a fourth set (240) of temperature sensors (241, 242, 243) is provided at an interface between the at least one transition section (130) and the at least one second section (120).

9. The method according to any one of the preceding claims, wherein the second heat treatment process (230) is performed on one or more end sections (110) of the workpiece (100), especially on one or more end sections extending from an axial end (101) of the workpiece with a predetermined length in axial direction.

10. The method according to any one of the preceding claims, wherein the third predetermined temperature is identical or at least essentially identical to the first predetermined temperature.

11. The method according to any one of the preceding claims, wherein the first heat treatment process (310) is performed using a heat treatment furnace.

12. The method according to any one of the preceding claims, wherein the second heat treatment process (320) is performed using an induction furnace and/or an induction local heating device and/or a radiation furnace and/or a cooling device.

13. The method according to any one of the preceding claims, wherein the workpiece (100) is made of a martensitic stainless steel or a precipitation hardening stainless steel.

14. The method according to any one of the preceding claims, wherein the fluid energy machine is a working machine, especially a turbomachinery, especially a rotating turbomachinery, especially a compressor or a turbo compressor or a cryogenic turbo compressor.

15. A workpiece (100) for a fluid energy machine, especially a shaft (100) of a fluid energy machine, treated according to a method of any one of the preceding claims.

Drawing