CN112004626B

CN112004626B - Method for producing spiral body

Info

Publication number: CN112004626B
Application number: CN201980025300.6A
Authority: CN
Inventors: 马提亚斯·布塞; 弗朗兹-约瑟夫·沃斯特曼
Original assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Current assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Priority date: 2018-04-12
Filing date: 2019-04-11
Publication date: 2023-12-08
Anticipated expiration: 2039-04-11
Also published as: US20210121960A1; CN112004626A; EP3774123A1; DE102018205588A1; WO2019197584A1

Abstract

The application relates to a method for producing a hollow spiral conductor (1), wherein a spiral core (8) is produced from a core material that is liquefiable or vaporizable under the influence of heat, and is then coated with a first powder layer (3, 3') of an at least partially electrically conductive first powder by means of a powder coating method, and the spiral core with the first powder layer is then heated to a first temperature, wherein the core is liquefied or converted into a gaseous state and the first powder layer is at least partially cured in a porous form, wherein the core material escapes from the space enclosed by the powder coating, and wherein after the core material escapes from the space enclosed by the first powder layer is further sintered, in particular by heating the first powder layer to a second temperature that is higher than the first temperature. The application also relates to the screw.

Description

Method for producing spiral body

Technical Field

The application belongs to the field of machine manufacturing, and more specifically belongs to the technical field of casting. It relates to a method for producing a spiral, such as a coil or a spring. Such a body is understood to mean in particular a strand-like body which is curved such that it extends in a spiral form. For example, such a screw may be used as an electrical coil, and is particularly advantageous for certain applications when the screw itself is hollow. In this case, a current of a large amperage can flow through the spiral and be cooled from the inside by the liquid flowing through the cavity. However, other applications of such hollow spirals are also contemplated.

Background

If such a screw, for example in the form of a coil, is used, a higher power density can be achieved than if a solid coil is used, without the risk of overheating. Thereby, space utilization can be made more efficient. However, the formation of such spiral hollow bodies has only been possible with great effort to date.

Furthermore, the use of such spirals may also reduce the effect of the skin effect (i.e. forcing the current to move towards the surface of the conductor).

The object of the present application is therefore to create a method for producing hollow spiral conductors, which is implemented in a simple manner and which allows low production costs for such bodies.

Disclosure of Invention

According to the application, the object is achieved by a method having the features described below. The following relates to possible embodiments of such a method.

The application therefore relates to a method for producing a hollow spiral conductor. The application also relates to a corresponding screw. Possible embodiments of the screw are described below.

In particular, the method provides that a spiral core is first produced from a core material that is liquefiable or vaporizable under the influence of heat, and then is coated with a first powder layer of an at least partially electrically conductive first powder by a powder coating method, and then the spiral core with the first powder layer is heated to a first temperature, wherein the core is liquefied or converted into a gaseous state and the first powder layer is at least partially cured in a porous form, wherein the core material escapes from the space enclosed by the powder coating, and wherein after the core material escapes from the space enclosed by the first powder layer, the first powder layer is further sintered, in particular by heating the first powder layer to a second temperature that is higher than the first temperature.

Thus, the method is as follows: first, the spiral core is produced, for example, from expanded plastics, in particular from EPS plastics (expanded polystyrene). The body thus produced defines the geometry of the screw produced. Such molded cores may also be produced with waxy fusible materials as alternatives to foam materials.

The core may be connected to one or more connection accessories, which in turn will be further processed with the core.

The core realized in this way is then coated with an electrically conductive first powder, for example a metal powder. This coating step can be achieved in known powder coating methods. The powder used is a sinterable powder which can be sintered by achieving the corresponding physical conditions, in particular heating to the necessary sintering temperature. In this way, the powder layer is hardened while adhering to the core. At the same time, the core material is melted or gasified and can escape. It is particularly advantageous that the powder is sintered only to such an extent that the produced solid remains porous, so that the material of the core can escape at least partly through the pores of the sintered powder layer. As material for the first layer, all sinterable materials, in particular sinterable metal powders, can be used.

After the core material escapes, the powder layer may be further sintered, for example by heating to a second temperature higher than the first temperature. In addition, other physical parameters, such as pressure, may be varied to facilitate further sintering. The first powder can thus be sintered to such an extent that it is sufficiently solidified, in particular also to such an extent that the pores are closed. The temperature may be selected according to the typical sintering temperature of the materials used.

The connection fitting (if present) may be coated with the core and in this way become part of the screw.

Hereby is achieved a screw which essentially takes the shape of a screw core. In particular, the latter spiral conductor has a cavity in its interior which completely conforms to the shape of the spiral core in which it is initially located. The powder layer is self-supporting, whereby a stable spiral conductor is formed from the powder layer.

The spiral core and the powder layer defining the cavity may be formed in the method in such a way that the cavity in the spiral to be produced forms a fluid channel, which has one or more openings, for example, at one or more predetermined locations, in particular at least one end of the spiral. For example, the powder layers may each have an interruption at one or more predetermined locations, thereby exposing the core there. The interruption may be introduced separately, for example, by not applying powder to the respective location (e.g. by covering the location and then removing the covering), or by removing previously applied powder in a post-treatment step, for example by shearing one section of the core. However, it is also possible to produce a screw with a closed cavity and to introduce openings in the post-treatment step after sintering.

The geometry of the core may be chosen such that the gap between the spirals of the conductor achieved is minimized and thus an optimal space filling/space utilization, e.g. a space filling higher than 95%, is achieved with spiral conductors.

As described above, the sintering may be controlled such that the first powder layer is sintered at a first temperature, thereby solidifying the first powder layer, but wherein the porosity is maintained such that the liquefiable or vaporizable core material may escape through the sintered powder layer.

However, it is also conceivable to sinter the first powder layer in a single step or continuously, in particular if it is ensured that the material of the core can escape at one end of the core/coil to be realized. This is possible, in particular, if one or more openings of the above-mentioned fluid channels are already defined by the powder layer applied on the spiral core before heating, i.e. if the powder layer has a corresponding interruption, for example at one end of the core or at both ends of the core.

Sintering the first powder layer at a second temperature, whereby the first powder layer becomes dense and thus liquid-tight, in particular also gas-tight, may be advantageous, in particular for current carrying capacity and achieving low electrical resistance.

It can also be provided that the first powder layer is formed in the form of a plurality of successive sub-layers of the first powder. The thickness of the powder layer can thus be controlled well, in particular the sub-layers can also be applied successively in this way, which can each be dried at least stepwise or partially cured, in particular also partially sintered, before the next layer is applied.

It is also conceivable to apply at least one second powder layer of the second powder on the first powder layer, in particular before or after the first sintering step. In this way, it is also possible to suitably form the sintered layer, and the resulting coil body can be provided with a desired conductor cross section. Different powder layers may also be applied sequentially to achieve a certain current distribution or other desired electrical properties.

For example, if multiple powder layers are provided, all powder layers may have the above-described discontinuities to create openings in the cavity. In the method, one or more interruptions may be provided in the powder coating with the first and/or one second powder layer to create one or more openings for cavities defined by the spiral core, which cavities are delimited by the powder coating and then extend in the produced spiral.

It may be provided that the second powder is made of an electrically insulating material and that an insulating layer is formed after sintering. Typically, a sinterable ceramic powder or other electrically insulating sinterable powder may be used as the material of the second powder layer. In this case, the body can be produced as a whole as a screw/coil body with a successful and insulating function. It can be provided that the second powder layer is sintered at the same time as the first powder layer or after it. However, another way of curing the second layer, such as drying or bonding, may also be selected.

In the case of powder coating by means of the first layer or one second layer or other layers, it can be provided that powder coating is carried out with the first and/or one second powder layer by spraying, immersion or using a fluidized powder bed or by means of a plurality of different successive coating types. By the above-mentioned coating type, the entire surface of the spiral body of the core can be uniformly coated even if the distance between adjacent spirals of the spiral is small. In this way, the spirals can be made with a minimum distance between the individual spirals as a whole.

It may also be provided that the powder coating is carried out with a powder slurry and/or a powder raw material. Powder slurry is understood to be a pasty mass comprising a powder in a carrier liquid to which a viscous binder is added. A powder raw material is understood to be a homogeneous mixture of powder and binder, which enables particularly good dimensional stability during sintering.

All known and suitable sintering methods for each of the powders used can be considered as sintering methods, for example also suitable gas atmospheres or protective gas atmospheres. In particular, metal powders or metal alloy powders or mixtures of different metal powders or metal alloy powders can be used as sintering materials.

In the production of the core, it can be provided in particular that the spiral core is produced in a casting process or in a foaming process, wherein the core in particular consists of a plurality of parts. It is thereby also possible to easily produce cores of complex shape, such as the shape of a coil spring or spiral spring. The foam may be foamed in a mold or may be produced by extrusion and subsequent setting.

It is also conceivable that the core is produced as a blank and then brought into a spiral shape by manufacturing a spiral-shaped hollow. For example, the blank may be cylindrical or cube-shaped, wherein the blank may have a cylindrical, prismatic, or cube-shaped cavity therethrough that passes completely through the blank from a first end to a second end. For example, the blank may thus have the shape of a hollow cylinder.

It may also be provided that said helical recess is produced in the core by a tool that rotates about an axis passing through the core and simultaneously advances continuously along said axis. The axis of the core about which the tool rotates may pass through both the blank and the cavity therein, thereby causing the tool to at least partially rotate within the cavity and penetrate and remove material from the blank at the radially outer end thereof. For example, the axis about which the tool rotates may be the longitudinal axis of the hollow cylinder forming the blank. The tool can then be rotated about the axis to introduce a recess in the wall of the hollow cylinder, for example by cutting, milling or sawing. For example, the tool may be configured in the form of a knife or saw or file. The tool may also be rotated about its own longitudinal axis during machining or may perform sawing, swinging or vibrating movements along its longitudinal axis. The tool may also be heated to melt the material of the blank.

In addition to the rotary turning movement of the tool, it is also possible to advance continuously parallel to the longitudinal axis of the blank, so that the tool creates a helical recess in the blank, thereby converting the blank at least partially into a helix.

Obviously, the application also requires protection of the screw produced in the manner described. The screw has a cavity. As mentioned above, the cavity is produced by means of a core, the dimensions of the cavity being defined by the dimensions of the core.

The screw has in one embodiment a fluid channel as a cavity, the fluid channel having at least one, preferably at least two openings. For example, the openings may be provided at opposite ends of the screw. Openings may also be provided in addition or in addition, which are not at the ends of the spiral, but for example at the sides of the winding.

The fluid channel may have a constant or variable cross section in its longitudinal direction. The core may be designed with a constant or variable thickness accordingly for creating the fluid channel.

The external dimensions of the screw may be, for example, in the range of centimeters to decimeters. As mentioned above, the body may be cylindrical or cubical, i.e. may have a circular or rectangular bottom surface and a height extending in the direction of the cavity and the longitudinal axis. For example, the body may also be narrowed in its height direction so that it has, for example, a truncated cone shape or a truncated pyramid shape. The outer dimension in each spatial direction may be, for example, between 3cm and 1m, i.e. the bottom surface may have, for example, a diameter or a lateral dimension (e.g. side length) between 3cm and 1 m. For example, the height may be between 3cm and 1 m.

For example, the cross-section of the fluid channel may be polygonal or elliptical, in particular rectangular or circular. The cross-section of the fluid passage may be otherwise sizedExternally or additionally, for example in the range of a few millimeters to a few centimeters. The cross-sectional area may be about 10mm ² To 50cm ² Between them. In one example, the dimension, e.g. the diameter or side length of the cross section of the fluid channel, may be at least 5mm and/or at most 5cm, depending on the geometry it has. For example, the wall thickness of the material surrounding the cavity made of the first powder layer or the first and second powder layers may be between 1mm and 20 mm.

It should be emphasized that only the features described in connection with the method may be required for the device and vice versa.

Drawings

The application will be illustrated and described with reference to the embodiments shown in the drawings. Wherein:

figure 1 shows a perspective view of a screw/coil,

figure 2 shows a cross section of the windings of a coil/spiral,

figure 3 shows a cross section of a winding of another spiral,

figure 4 shows an enlarged schematic view of a cross section of a powder coated spiral surface,

figure 5 shows a device for producing a spiral core and a core in which a hollow is partly introduced,

fig. 6 to 10 show the parts of the screw with the current and/or fluid connection in different views.

Detailed Description

Fig. 1 shows in perspective view an electrically conductive coil 1 as a spiral, which is formed from a spiral, insulated, strand-shaped electrical conductor 2. The illustration of fig. 1 shows a coil with a quadrangular, in particular square, cross section, wherein the conductors constituting the coil themselves also have a rectangular cross section. The spiral layers of the conductor are rectangular and are stacked on top of each other at small intervals.

The screw has an outer dimension corresponding to a cuboid having a rectangular (square) bottom surface of a×b and a height h, the cavity extending in the height direction. For example, the body may also have other floors and/or taper in its height direction, so that it has, for example, a truncated cone shape or a truncated pyramid shape. The external dimensions a, b and h are between 3cm and 1m, respectively.

Fig. 2 illustrates a cross section of an insulated conductor, such as may be used in the manufacture of a coil, as shown in fig. 1. In fig. 2, the hollow outer part formed by the sintered powder is marked 3, and also shown within the powder coating 3 is a core 4, which is made of foam, in particular EPS, for example. The situation shown in fig. 2 is for example created directly after coating the spiral core 4 with the first powder. The powder is configured to be at least partially conductive and is composed of a conductive material such as a metal or metal alloy. It may also consist of a mixture of two or more powders, which are preferably all electrically conductive.

In the case shown, the coated core 4 may be heated to a temperature below the melting temperature of the first powder, at which temperature the material of the core 4 either gasifies or liquefies. The material of the core may then escape at one end of the layer/coating or through the coating itself, so that only the coating which is simultaneously sintered and thus cured remains. The sintering process is generally controlled in such a way that, in the first stage of sintering, if the first powder layer is still gas-or fluid-permeable, the core is liquefied or made gas-permeable, so that, for example, it can also escape through the coating/powder layer.

After the material of the core 4 has escaped, the sintering process can continue, either by holding the temperature steady for an additional period of time, or by raising the temperature slightly. This may continue until the first powder layer becomes dense and thus gas/fluid impermeable. For example, the sintering process may be performed in a protective atmosphere.

The cavity defined by the core 4 then forms a fluid channel, which in this embodiment is present at the opposite end of the coil. For example, the cross-sectional area p×q of the rectangular fluid passage in the present embodiment is 10mm ² And 50cm ² Between them. In an embodiment, the side lengths p and q of the cross-sectional area of the channel, corresponding to the cross-sectional area, may be several millimeters to several centimeters. For example, material (bag) surrounding the cavityIncluding the first powder layer) may be between 1mm and 20 mm.

It is also possible to provide additionally or alternatively openings for the fluid channels, which openings are not at the ends of the spiral, but for example at the sides of the windings.

The fluid channel may have a constant or variable cross section in its longitudinal direction.

Fig. 3 shows the case of a core 4 'with a circular cross section, which is 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 surrounding the first powder layer 3' consists of or is made of an electrically insulating material, for example a sinterable ceramic powder or other sinterable electrically insulating powder.

During co-sintering of the first and second powder layers, two hard, self-supporting layers are formed, wherein the inner layer is conductive and forms the conductor of the spiral, and the outer layer forms the outer insulation of the conductor. The powder layers 3' and 5 can also be applied and sintered successively. Since the space required for the powder coating using a conventional powder coating method such as immersion or spray coating is very small, even closely spaced coil windings (as shown in fig. 1) can be uniformly covered with a powder layer, which is then solidified by sintering. In this way, a spiral conductor can be produced in a simple manner, with little space requirements and with little gaps between the windings and optionally also with insulation. By means of such a screw, coils or springs can be produced with optimal space utilization.

In this case, the cross section of the round core 4 or the fluid channel has a radius r of, for example, between 5mm and 5cm. For example, the area may alternatively or additionally be 10mm ² And 50cm ² Between them. The wall thickness w' of the material surrounding the cavity (comprising the first and second powder layers) may for example be between 1mm and 20 mm.

Fig. 4 shows the first powder layer 3 as well as the core 4 in an enlarged schematic view, wherein individual particles of the powder layer can be distinguished. The material of the core is gasified or liquefied and can pass through the pores of the first powder layer 3 according to arrows 6, 7 as long as the material of the first powder layer has not yet been sintered to a fluid tight state.

In fig. 5 a hollow cylinder 8 is shown, which is used as a blank for producing the core. The blank 8 may for example consist of a foam material, but may also consist of wax or a similar meltable substance. The cylinder 8 has a cylindrical cavity 9, so that it is generally configured as a hollow cylinder with a hollow cylindrical wall 10. The longitudinal axis of the hollow cylinder is designated 11.

Below the hollow cylinder 8, a device for introducing a spiral hollow into the hollow cylinder 8 is shown, which device has a vertically arranged shaft 12 which is mounted on a support 17 rotatably about its longitudinal axis. On the shaft 12 a tool 13 is arranged, which extends perpendicularly from the shaft 12. The tool 13 is connected to the shaft 12 by a vibration or saw drive 14. The drive 14 can cause the tool 13 to perform a swinging movement in the direction of the double arrow 15. Instead of the vibration drive 14, a heater for the tool 13 may also be provided.

If the shaft 12 is driven in rotation, the tool 13 moves on a circular orbit around the shaft 11 and if the tool moves along the orbit through the cylinder wall 10, the hollow cylinder 8 is cut. This may be achieved, for example, by a rasping or sawing motion, provided that the tool 13 has serrations. The tool 13 may also be heated to such an extent that the material of the hollow cylinder 8 melts. The tool 13 is axially advanced in the direction of the shaft 11, for example at a constant speed, while being moved rotationally about the shaft 11. However, the propulsion speed may also be varied to produce different sections with different pitches. The helical recess 16 is introduced into the hollow cylinder 8 by a combination of a rotational movement and a pushing movement of the tool 13. The portion of the hollow cylinder 8 left between the individual spirals of the continuous hollow 16 is also helical. This body can be used as a core for the spiral to be produced and is then covered with a first powder layer. After sintering the first powder layer and removing the core material, a hollow coil-like spiral conductor remains.

Fig. 6 shows an end section of the hollow screw 1 in a perspective view. The spiral may be a coiled shape having a diameter that decreases or increases between windings of the spiral, but may also be a spiral shape having a constant diameter. The screw 1 has at one or both ends a connection fitting 20 in the form of a sleeve, in particular a cylindrical sleeve. The sleeve 20 may be made of metal, such as iron, steel, stainless steel, copper, or brass. The sleeve 20 may have a metal connection tab 21 to establish an electrically conductive connection.

Fig. 7 shows that the core 4 is connected to the attachment 20 during the manufacturing process, and that both are then coated with the powder layer 3, 3'. This is indicated by arrow 22.

Fig. 8 shows that the core 4 ends at the accessory 20 when the core 4 is connected to the accessory, and that the accessory may be attached to the core.

Fig. 9 shows that the core 4 may also extend into the passage hole 20a of the accessory. For this purpose, the core 4 can be cast onto and into the accessory 20 during its manufacture.

Fig. 8 and 9 show that the coating 23 is applied on both the core 4 and the sleeve 20, so that the sleeve 20 is connected with the part of the spiral 1 formed by the coating 23 without further measures being taken after removal of the core. Such a connection may be provided at both ends of the body 1.

In addition to electrical connections, the sleeve 20 may also form a connection accessory for connecting fluid lines for cooling. For this purpose, the sleeve may also have a thread 24 (see fig. 10) and/or a bayonet lock and/or a seal and/or a sealing seat.

By means of the application, a hollow screw with low space requirements and high space utilization can be realized, which can be used very effectively as an electrical coil, since internal cooling is possible.

Claims

1. Method for producing a hollow spiral electrical conductor (1), wherein a spiral core (4, 4', 8) is first produced from a core material that is liquefiable or vaporizable under the influence of heat, and is then coated with a first powder layer (3, 3') of an at least partially electrically conductive first powder by means of a powder coating method, and the spiral core with the first powder layer is then heated to a first temperature, wherein the core is liquefied or converted into a gaseous state and the first powder layer is at least partially cured in a porous form, wherein the core material escapes from the space enclosed by the powder coating, and wherein after the core material has escaped from the space enclosed by the first powder layer is further sintered,

wherein the first powder layer (3, 3') is sintered at the first temperature, such that the first powder layer is solidified, but wherein a porosity is maintained such that the liquefiable or vaporizable core material can escape through the sintered powder layer,

wherein the first powder layer (3, 3') is sintered at a second temperature higher than the first temperature, whereby the first powder layer becomes dense, rendering it liquid impermeable,

and wherein a second powder layer (5) of at least one second powder is applied on the first powder layer (3, 3'), in particular before or after the first sintering step; the second powder is composed of an electrically insulating material and forms an insulating layer after sintering.

2. Method according to claim 1, characterized in that the first powder layer (3, 3') is constituted in the form of a plurality of successively applied sub-layers of the first powder.

3. Method according to claim 1, characterized in that powder coating with the first and/or one second powder layer (3, 3', 5) is performed by spraying, immersing or using a fluidized powder bed or by a plurality of different successive coating types.

4. A method according to any one of claims 1 to 3, characterized in that powder coating is performed with a powder slurry and/or a powder raw material.

5. A method according to any one of claims 1-3, characterized in that the spiral core (4, 4', 8) is produced in a casting method or a foaming method, wherein the core in particular consists of a plurality of parts.

6. A method according to claim 5, characterized in that the core (4, 4', 8) is produced as a blank and then brought into a spiral shape by creating a spiral recess (16).

7. A method according to claim 6, characterized in that the spiral recess (16) is produced in the core (4, 4', 8) by means (13) rotating around an axis (11) passing through the core and advancing continuously along the axis (11) at the same time.

8. A method according to any one of claims 1 to 3, characterized in that at least one interruption is provided in the powder coating with the first and/or one second powder layer (3, 3', 5) to create an opening for a cavity defined by the spiral core, which cavity is delimited by the powder coating.

9. Screw, characterized in that it has a cavity and is manufactured in a method according to one of the preceding claims.

10. The screw of claim 9, wherein the cavity is configured as a fluid channel and has at least one opening.

11. A screw according to claim 9 or 10, characterized in that the external dimensions of the screw are between 3cm and 1m in each spatial direction.

12. A screw according to claim 9 or 10, wherein the wall thickness of the material surrounding the cavity is between 1mm and 20 mm.

13. Screw according to claim 9 or 10, characterized in that the cavity formed as a fluid channel is polygonal or elliptical in cross-section and has a cross-section of 10mm ² And 50cm ² Cross-sectional area therebetween.