A coiled body and method for its manufacture

Description

[0001] The invention lies in the field of mechanical engineering, and more specifically in the field of foundry technology. It relates to a method for manufacturing a helical body, for example, a coil or a spring. Such a body is understood to be, in particular, a strand-like body that is curved in such a way that it runs in the form of a helix. Such helical bodies can be used, for example, as electrical coils and are particularly advantageous for certain purposes when the helical body itself is hollow. In this case, the helix can be subjected to a high current and cooled from the inside by a liquid flowing through the cavity. However, other applications for such hollow helical bodies are also conceivable.

[0002] Using such a helical body, for example in the form of a coil, allows for higher power densities without the risk of overheating compared to solid coils. This enables more efficient use of space. However, forming such helical hollow bodies has so far only been possible with considerable effort.

[0003] Furthermore, with such a helical / coiled body, the effects of the skin effect, i.e. the displacement of the current towards the surface of a conductor, can also be reduced.

[0004] Various manufacturing processes for bodies with cavities are known from the prior art.

[0005] Document JP 2005 310694 A describes a process for manufacturing a helical body, which also involves a sintering process of particles in a paste. The document provides for individual, separate cavities within the particles, which are components of the paste.

[0006] Document JP 2017 048439 A describes a method for manufacturing an electrically conductive coil inside a soft magnetic body for a motor.

[0007] The document describes a process for manufacturing an electrically conductive coil. A metal powder or slurry is placed in a mold and encased in a binder. A coiled tube is used as the mold.

[0008] Document JP 2005 294725 A discloses a method for producing a laminated ceramic body with an integrated electrically conductive coil former, wherein the coil former is composed of windings on individual ceramic laminate bodies which is sintered.

[0009] Document US 2 695 230 A discloses a method for manufacturing metal objects in which a metal powder is pressed and sintered in a mold, optionally with a core.

[0010] Document US 2018 / 009032 A1 discloses a manufacturing process for metal objects in which a metal powder in the form of slurry is filled into a mold and subsequently sintered.

[0011] Document US 8 852 498 B1 discloses a process for manufacturing pellets for fusion reactors, wherein the pellets are produced by coating small organic nuclei and then sintering them.

[0012] Document US 7 776 255 B1 discloses a process for producing hollow metallic bodies by preforming a core, coating the core, extruding the core by pyrolysis, and sintering the remaining shell.

[0013] Document US 4 917 857 A discloses a process for producing hollow metallic bodies by preforming a core, for example from a foam, coating the core with a metal oxide powder or ceramic powder, removing the core by pyrolysis and sintering the shell.

[0014] Document JP H09 74037 A discloses a method for manufacturing a winding conductor for a rotating electrical machine using pyrolysis and sintering.

[0015] According to document US 2002 / 173429 A1, an item to be manufactured is used as a core, and this core is coated.

[0016] The document "3-D numerical and experimental analysis of a built-in motorized high-speed spindle with helical water cooling channel", Applied Thermal Engineering, Pergamon, Oxford, GB, Vol 28, No. 17-18, 1 Dec 2008, pages 2327-2336, describes a helical fluid channel in association with a spindle.

[0017] Against the background of the prior art, the present invention is therefore based on the objective of creating a method for producing a hollow helical, electrically conductive body that can be carried out with simple means and allows for the cost-effective production of such bodies.

[0018] According to the invention, the problem is solved by a method having the features of claim 1. Claims 2 to 11 relate to possible embodiments of such a method.

[0019] Accordingly, the invention relates to a method for manufacturing a hollow, helical, electrically conductive body. Furthermore, the invention relates to the corresponding helical body according to claim 11.

[0020] Possible embodiments of the helical body are described in claim 12.

[0021] The process is as follows: first, a coiled core, for example made of a foamed plastic, in particular EPS (expanded polystyrene), is produced. This core defines the geometry of the resulting coiled body. This core, which acts as a model, can alternatively be made of a wax-like, easily meltable material instead of foam.

[0022] The core can be connected to one or more connection fittings, which will be discussed further below in connection with the core.

[0023] The core created in this way is then coated with an electrically conductive first powder, for example, a metal powder. This coating step can be carried out using a known powder coating process. The powder used is a sinterable powder that can be sintered by creating appropriate physical conditions, in particular by heating it to the necessary sintering temperature. The powder layer thus hardens as it adheres to the core. At the same time, the core material is melted or vaporized and can escape. It is particularly advantageous if the powder is sintered only to the extent that the resulting solid remains porous, allowing the core material to escape at least partially through the pores of the sintered powder layer. Any sinterable material, especially sinterable metallic powders, can be used as the material for the first layer.

[0024] After the core material emerges, the powder layer can be further sintered, for example, by heating it to a second temperature higher than the first. Other physical parameters, such as pressure, can also be changed to promote further sintering. This allows the initial powder to be sintered sufficiently to solidify, particularly to close the pores. The temperatures can be selected according to the typical sintering temperatures for the materials used.

[0025] The connecting fittings, if present, can be coated together with the core and thus become part of the coiled body.

[0026] This creates a coiled body that essentially takes on the shape of the coiled core. Specifically, the resulting coiled, electrically conductive body has a cavity inside that corresponds exactly to the shape of the coiled core initially contained within it. The powder layer is self-supporting, so that a stable, coiled, electrically conductive body is formed from the powder layer.

[0027] The coiled core, which defines the cavity, and the powder layer are formed in the process such that the cavity in the coiled body to be produced forms a fluid channel, which, for example, has one or more openings at one or more predefined locations, in particular at least at one end of the coiled body. For example, the powder layer can have a break at each of the one or more predefined locations, so that the core is exposed there. The break can be introduced, for example, by not applying powder to the corresponding location (e.g., by covering the location and subsequently removing the cover), or by removing previously applied powder in a post-processing step, e.g., by cutting off a section of the core.However, it is also possible to produce the coiled body with a closed cavity and to introduce the openings in a post-processing step after sintering.

[0028] The geometry of the core can be chosen so that the spaces between the individual coils of the created electrically conductive body are minimized, thus achieving optimized space filling / utilization with the coiled electrically conductive body, for example with a space filling above 95%.

[0029] As mentioned above, the sintering process can be controlled in such a way that at the first temperature, the first powder layer is sintered, thereby solidifying the first powder layer, while remaining porous enough to allow the liquefiable or vaporizable core material to escape through the sintered powder layer.

[0030] However, it is also conceivable to sinter the first powder layer in a single step or continuously, especially if it is ensured that the core material can exit at one end of the core / coil to be created. This is particularly possible if the opening or openings of the fluid channels described above are already defined by the powder layer applied to the coiled core before heating; that is, if the powder layer has the corresponding breaks—for example, at the end(s) of the core.

[0031] It can be particularly advantageous for current-carrying capacity and the creation of low electrical resistance that at the second temperature a sintering of the first powder layer takes place, whereby the first powder layer is compacted in such a way that it becomes impermeable to liquids and especially also to gases.

[0032] Furthermore, it can be provided that the first powder layer is formed in the form of several successively applied partial layers of the first powder. This allows for good control of the powder layer thickness, and in particular, it also allows for the successive application of partial layers, each of which can be at least gradually dried or partially solidified, and especially partially sintered, before the application of the next layer.

[0033] It is also conceivable that at least one second powder layer of a second powder is applied to the first, particularly before or after a first sintering step. In this way, the sintered layer can also be suitably shaped, and the resulting coil former can be provided with the required conductor cross-section. Different powder layers can also be applied successively to achieve a specific current distribution or other desired electrical properties.

[0034] If multiple powder layers are used, all powder layers can, for example, have the interruptions described above to create openings in the cavity. Thus, in this process, one or more interruptions can be provided in the powder coating with the first and / or a second powder layer to create one or more openings for the cavity defined by the coiled core, which is bounded by the powder coating and then extends into the manufactured coiled body.

[0035] It is possible for the second powder to consist of an electrically insulating material and to form an insulating layer after sintering. Typically, sinterable ceramic powders or other electrically insulating sinterable powders can be used as the material for the second powder layer. In this case, the entire body can be manufactured as a functional and insulated helical body / coil body. The second powder layer can be sintered simultaneously with or after the first powder layer. However, a different solidification method for the second layer, such as drying or setting, can also be chosen.

[0036] In powder coating, the first, second, or subsequent layers can be applied by spraying, dipping, using a fluidized powder bed, or by several different, sequential coating methods. These coating methods allow for uniform coating of the entire surface of the coiled core, even if the spacing between adjacent coils is small. This enables the production of a coiled core with minimal spacing between individual coils.

[0037] It is also possible for the powder coating to be carried out using powder slurry and / or a powder feedstock. Powder slurry is understood to be a paste-like mass consisting of powder in a carrier liquid with the addition of a viscous binder. Powder feedstock is understood to be a homogeneous mixture of powder and binder that enables particularly good dimensional stability during sintering.

[0038] All known sintering processes suitable for the specific powder used are eligible, including those using a suitable gas atmosphere or protective gas atmosphere. Suitable sintering materials include, in particular, metal powders, metal alloy powders, or mixtures of different metal powders or metal alloy powders.

[0039] The core manufacturing process can be carried out using either a casting or a foaming process, with the core being composed of several parts. This allows for the easy production of cores in complex shapes, such as helical or spiral springs. The foam can be produced by foaming it in a mold or by extrusion followed by shaping.

[0040] It is also conceivable that the core is manufactured as a blank and then shaped into a helix by creating a helical cavity. The blank can, for example, have a cylindrical or cuboid shape, and may contain a cylindrical, prismatic, or cuboid cavity extending completely through it from one end to the other. For example, the blank could thus have the shape of a hollow cylinder.

[0041] It can also be provided that the helical recess in the core is created by a tool rotating around an axis passing through the core and simultaneously being continuously advanced along that axis. The core's axis around which the tool rotates can penetrate both the blank and the cavity within it, so that the tool rotates at least partially within the cavity and, at its radially outer end, penetrates and removes material from the blank. For example, the axis around which the tool rotates can be the longitudinal axis of a hollow cylinder forming the blank. The tool, which creates a recess in the wall of the hollow cylinder, for example by cutting, milling, or sawing, can then rotate around this axis. The tool can be designed, for example, like a knife, a saw, or a rasp.The tool can also rotate around its own longitudinal axis during the machining process or perform a sawing, oscillating, or vibrating motion along its longitudinal axis. The tool can also be heated to melt the material of the workpiece.

[0042] In addition to the rotating pivoting movement of the tool, it can be continuously advanced parallel to the longitudinal axis of the blank, so that the tool creates a helical recess in the blank and thus transforms the blank into a body that is at least partially helical.

[0043] It is understood that the present application also claims protection for the helical body produced in the manner described. The helical body has a cavity. The cavity is produced with the aid of the core as described above, and the dimensions of the cavity are defined by the dimensions of the core.

[0044] In the present invention, the helical body comprises a fluid channel as a cavity with at least one, preferably at least two, openings. The openings can be provided, for example, at opposite ends of the helical body. Alternatively or additionally, openings can also be provided that are not located at the ends of the helical body but, for example, laterally along the turns.

[0045] The fluid channel can have a constant or variable cross-section along its length. The core can be designed accordingly for the manufacture of the fluid channel, by having a constant or variable thickness.

[0046] The spiral body has external dimensions that can range, for example, from centimeters to decimeters. As mentioned, the body can be cylindrical or cuboid, meaning it has a round or rectangular base and a height extending along the cavity and longitudinal axis. However, the body can also taper towards its height, resulting in a truncated cone or pyramid shape, for example. The external dimensions in any spatial direction can range, for example, from 3 cm to 1 m; that is, the base can have a diameter or lateral dimensions (e.g., side lengths) of between 3 cm and 1 m. The height can also range, for example, from 3 cm to 1 m.

[0047] The cross-section of the fluid channel can be, for example, polygonal or elliptical, and in particular rectangular or circular. The dimensions of the fluid channel's cross-section can alternatively or additionally range from a few millimeters to a few centimeters. The cross-sectional area can be between approximately 10 mm² and 50 cm². For example, the dimensions—such as the diameter or side length of the fluid channel's cross-sectional area, depending on its geometry—can be at least 5 mm and / or at most 5 cm. The wall thickness of the material surrounding the cavity, which consists of the first powder layer or of the first and second powder layers, can be, for example, between 1 mm and 20 mm.

[0048] It should be emphasized that features described only in connection with the method can also be claimed for the device and vice versa.

[0049] The invention is shown below with reference to exemplary embodiments in figures of a drawing and is subsequently explained. Fig. 1 a perspective view of a helical body / coil, Fig. 2 a turn of a coil / helical body in cross-section, Fig. 3 a helix of another helical body in cross-section, Fig. 4 in schematically enlarged form the powder-coated surface of a helical body in cross-section, Fig. 5 a device for producing a helical core and a core into which a recess has been partially made, Figs. 6 to 10 in different views parts of a helical body with a power connection and / or a fluid connection.

[0050] Figure 1The figure shows, in perspective, an electrically conductive coil 1 as a helical body formed by a helical, insulated, strand-shaped electrical conductor 2. In the representation of the Figure 1 Figure 1 shows a coil with a rectangular, specifically square, cross-section, where the conductor forming the coil also has a rectangular cross-section. The various helical layers of the conductor are rectangular in shape and stacked on top of each other with small gaps.

[0051] The spiral body has external dimensions corresponding to a cuboid, with a rectangular (square) base axb and a height h, along which the cavity extends. However, the body can also have a different base shape and / or taper towards its height, resulting in, for example, a truncated cone or a truncated pyramid shape. The external dimensions a, b, and h are each between 3 cm and 1 m.

[0052] Figure 2 shows an example of the cross-section of an insulated conductor, which can be used, for example, to manufacture a coil, as is the case in Figure 1 is shown. Figure 2 The hollow outer part, formed from a sintered powder, is designated 3, and the core 4, which consists, for example, of a foam, in particular EPS, is shown within the powder coating 3. The in Figure 2The illustrated configuration arises, for example, directly after the helical core 4 is coated with a first powder 3. The powder 3 is at least partially electrically conductive and consists of an electrically conductive material, for example, a metal or a metal alloy. It can also consist of a mixture of two or more powders, preferably all of which are electrically conductive.

[0053] In the illustrated configuration, the coated core 4 can be heated to a temperature below the melting point of the first powder, causing the core material to either evaporate or liquefy. The core material can then escape at one end of the layer / coating or through the coating itself, leaving only the coating, which is simultaneously sintered and thus solidified. The sintering process is typically controlled such that, in an initial phase of sintering while the first powder layer 3 is still permeable to gas or fluid, the core is liquefied or made gaseous, allowing it to escape, for example, through the coating 3 / powder layer 3.

[0054] After the material from core 4 has emerged, sintering can continue, either by maintaining a stable temperature for a longer period or by slightly increasing the temperature to accelerate the sintering process. This can continue until the first powder layer has compacted to the point of being gas / fluid impermeable. The sintering process can, for example, take place in a protective atmosphere.

[0055] The cavity defined by core 4 then forms a fluid channel, which in this example emerges at opposite ends of the coil. The cross-sectional area pxq of the rectangular fluid channel in this example is, for instance, between 10 mm² and 50 cm². The side lengths p and q of the channel's cross-sectional area can range from a few millimeters to several centimeters, depending on the cross-sectional area. The wall thickness w of the material surrounding the cavity, which comprises the first powder layer, can, for example, range from 1 mm to 20 mm.

[0056] Alternatively or additionally, openings in the fluid channel can be provided that are not located at the ends of the helical body but, for example, laterally on the windings.

[0057] The fluid channel can have a constant or a variable cross-section along its length.

[0058] In Figure 3Figure 1 shows a configuration with a core 4' that is round in cross-section and surrounded by a first powder layer 3' and an outer second powder layer 5. The first powder layer 3' consists of an electrically conductive powder, for example, a metal powder, while the second powder layer 5, which surrounds the first powder layer 3', consists of or is made of an electrically insulating material, such as a sinterable ceramic powder or another sinterable electrically insulating powder.

[0059] When the first and second powder layers are sintered together, two hard, self-supporting layers are formed. The inner layer 3' is electrically conductive and forms the conductor of the coiled body, while the outer layer 5 provides external insulation for the conductor 3'. The powder layers 3' and 5 can also be applied and sintered sequentially. Since powder coating using common methods such as dipping or spraying requires very little space, even closely spaced coil windings, as in [reference to diagram], can be coated. Figure 1The coil is uniformly covered with a layer of powder, which is then solidified by sintering. This allows for the simple production of a helical, electrically conductive body with a small footprint and minimal space between the individual turns, optionally with insulation. Such a helical body can be used to manufacture a coil or spring with optimal space utilization.

[0060] The cross-sectional area of ​​the round core 4, or fluid channel, has a radius r, which is, for example, between 5 mm and 5 cm. Alternatively or additionally, the area can be, for example, between 10 mm² and 50 cm². The wall thickness w' of the material surrounding the cavity, which comprises the first and second powder layers, can be, for example, between 1 mm and 20 mm.

[0061] Figure 4Figure 1 shows an enlarged schematic representation of a first powder layer 3 and a core 4, where individual grains of the powder layer are distinguishable. The core material is vaporized or liquefied and can pass through the pores of the first powder layer 3 according to arrows 6 and 7, as long as the material of the first powder layer has not yet been sintered to a fluid density.

[0062] In Figure 5 Figure 1 shows a hollow cylinder 8, which serves as a blank for manufacturing the core. This blank 8 can be made of, for example, a foam, but also of wax or a similarly fusible material. The cylinder 8 has a cylindrical cavity 9, so that it is designed as a hollow cylinder with a hollow cylinder wall 10. The longitudinal axis of the hollow cylinder is labeled 11.

[0063] Below the hollow cylinder 8, a device for creating a helical recess in the hollow cylinder 8 is shown. This device has a vertically arranged shaft 12, which is rotatably mounted on a holder 17 about its longitudinal axis. A tool 13 is arranged on the shaft 12 and projects perpendicularly from the shaft 12. The tool 13 is connected to the shaft 12 by means of a vibration or saw drive 14. This drive 14 can cause an oscillating movement of the tool 13 in the direction of the double arrow 15. Instead of the vibration drive 14, a heating element for the tool 13 can also be provided.

[0064] When the shaft 12 is driven in a rotating direction, the tool 13 moves in a circular path around the axis 11, thereby cutting the hollow cylinder 8 as it cuts a path through the cylinder wall 10. This can be achieved, for example, by a rasping or sawing motion, provided the tool 13 has teeth. The tool 13 can also be heated to the point where it melts the material of the hollow cylinder 8. Simultaneously with the rotational movement around the axis 11, the tool 13 is fed axially in the direction of the axis 11, for example, at a constant speed. However, the feed rate can also be varied to produce different sections with varying pitches. The combination of the rotational and feed movements of the tool 13 creates a helical recess 16 in the hollow cylinder 8.The portion of the hollow cylinder 8 remaining between the individual axes of the continuous recess 16 also has the form of a helix. This section can be used as a core for the helical body to be produced and later covered with a first layer of powder. After sintering the first powder layer and removing the core material, a hollow, helical, electrically conductive body in the form of a coil remains.

[0065] Fig. 6Figure 1 shows an end section of a hollow, helical body 1 in a perspective view. The helical body can have the form of a spiral with a diameter that decreases or increases from turn to turn of the helix, or it can have the form of a screw with a constant diameter. The helical body 1 has a connecting fitting 20 at one or both ends, which takes the form of a sleeve, in particular a cylindrical sleeve. The sleeve 20 can be made of a metal, for example, iron, steel, stainless steel, copper, or brass. The sleeve 20 can have a metallic connecting tab 21 for creating an electrically conductive connection.

[0066] The Fig. 7 Figure 22 shows that in the manufacturing process, the core 4 is connected to the connecting fitting 20 and then both are coated together with a powder layer 3, 3'. This is indicated by the arrows 22.

[0067] The Fig. 8shows that when connecting the core 4 with the fitting 20, the core 4 can end at the fitting and the fitting can be attached to the core.

[0068] The Fig. 9 This shows that the core 4 can also extend into a through-opening 20a of the fitting. The core 4 can be cast into and onto the fitting 20 during its manufacture.

[0069] The Fig. 8 and 9 Show that the coating 23 is applied to both the core 4 and the sleeve 20, so that, without further measures, the sleeve 20 is connected to the parts of the coiled body 1 formed by the coating 23 after the core is removed. Such a connection can be provided at both ends of the body 1.

[0070] The sleeve(s) 20 can / can form not only an electrical connection but also a connection fitting for attaching a fluid line for cooling. For this purpose, a sleeve can also have a screw thread 24 (see...). Fig. 10) and / or have a bayonet fitting and / or a seal and / or a sealing seat.

[0071] The invention makes it possible to create a hollow, coiled body with a small footprint and high space utilization, which can be used very efficiently as an electrical coil due to the possibility of internal cooling.

Claims

1. A method of producing a hollow, helical, electrically conducting body, wherein a cavity in the helical body to be produced forms a channel for a fluid, in which first a helical core (4, 4', 8), made of a core material that can be liquefied or evaporated under the action of heat, is produced, and thereafter is coated with a first powder layer (3, 3') of an at least partially electrically conducting powder using a powder coating method, and in which the helical core comprising the first powder layer is then heated to a first temperature, at which the core is liquefied or converted into a gaseous state and at which the first powder layer is at least partially solidified in porous form, the core material exiting the space surrounded by the powder coating, and, after the core material has exited the space surrounded by the first powder layer, the first powder layer is sintered further, wherein the first powder layer is heated to a second temperature, which is higher than the first temperature, and sintering of the first powder layer (3,3') takes place at the second temperature, causing the first powder layer to become compacted so as to become impermeable to liquids.

2. The method according to claim 1, characterized in that the first powder layer (3, 3') is formed in the form of multiple consecutively applied sub-layers of the first powder.

3. The method according to any one of claims 1 or 2, wherein at least one second powder layer (5) of a second powder is applied to the first powder layer (3, 3'), in particular prior to or after a first sintering step.

4. The method according to claim 3, wherein the second powder is made of an electrically insulating material, and forms an insulating layer after sintering.

5. The method according to any one of claims 1 to 4, wherein the powder coating by way of the first and / or a second powder layer (3, 3', 5) is carried out by spraying, dipping or using a fluidizing powder bed, or by several different consecutive ones of the aforementioned coating manners.

6. The method according to any one of claims 1 to 5, wherein the powder coating is carried out using a powder slurry and / or a powder feedstock.

7. The method according to any one of claims 1 to 6, wherein the helical core (4, 4', 8) is produced in a casting process or a foaming process, the core being in particular assembled from multiple parts.

8. The method according to claim 7, wherein the core (4, 4', 8) is produced as a blank, and thereafter is brought into the shape of a helix by creating a helical recess (16).

9. The method according to claim 8, wherein the helical recess (16) is created in the core (4, 4', 8) using a tool (13) that rotates about an axis (11) which extends through the core and, at the same time, is steadily advanced along the axis (11).

10. The method according to any one of the preceding claims, wherein at least one interruption is provided in the powder coating comprising the first and / or a second powder layer (3, 3' 5), so as to create an opening for a cavity defined by the helical core, the cavity being delimited by the powder coating.

11. A helical, electrically conducting body comprising a first sintered powder layer and a cavity, wherein the cavity in the helical body forms a fluid channel and has at least one opening, and is produced in a method according to any one of the preceding claims.

12. The helical body according to claim 11, wherein outer dimensions of the body are between 3 cm and 1 m in each spatial direction and / or a wall thickness of a material surrounding the cavity is between 1 mm and 20 mm and / or a cross-section of the cavity designed as a fluid channel is polygonal or elliptical and has a cross-sectional surface area of between 10 mm2 and 50 cm2.