Square-pressed litz wire production process

Abstract

The invention provides a squaring litz wire production process, and relates to the technical field of cables, and the squaring litz wire production process comprises the following steps: twisting a plurality of copper wires with insulating layers to form a circular multi-strand wire, carrying out spiral winding treatment on the circular multi-strand wire to obtain a film-coated multi-strand wire, and then carrying out heat treatment on the film-coated multi-strand wire to obtain a squaring litz wire. The method comprises the following steps: carrying out back-twisting treatment on a film-coated multi-strand wire in a wrapping tape softening state to eliminate the back-twisting stress of the film-coated multi-strand wire, carrying out online straightening treatment on the wire rod, carrying out square pressing on the film-coated multi-strand wire after back-twisting straightening, and cooling to obtain the square pressing litz wire. The fabric has the advantages of high dimensional stability and the like.

Description

Technical Field

[0001] This invention relates to the field of cable technology, and in particular to a stress-relief process for producing square-faced Litz wire. Background Technology

[0002] Litz wire is a conductor structure made of multiple independently insulated conductors twisted or braided together. It is mainly used in high-frequency electromagnetic equipment to reduce losses caused by the skin effect and proximity effect. Typical applications include inductor coils, wireless charging devices, and high-frequency transformers.

[0003] Since ordinary Litz wire is only stranded, when the wire is wound onto the spool and then coiled, it needs to be cut. At this time, the beginning and end are relatively loose, and the loose part cannot be used. It needs to be cut off after the coil is wound, which wastes materials and requires a wire cutting process, increasing production costs. Therefore, the existing technology wraps the stranded wire bundle to enhance the bundle's cohesion and integrity, as disclosed in Chinese Patent Application No. 202411664195X and Chinese Patent Application No. 2019100816690.

[0004] However, the aforementioned prior art is only suitable for single-turn use (equivalent to multiple wires connected in parallel) or multi-turn shaping use (with gaps between adjacent turns). The application documents of the aforementioned patents also reflect its application scenarios in this way. This is because, on the one hand, the resulting wire harness does not have good flexibility and good winding characteristics, and on the other hand, they do not have good shape retention and high temperature resistance.

[0005] Specifically, Chinese patent application number 202411664195X discloses a method for manufacturing Litz wire coils. It first twists thousands of copper wires into a circle, then flattens them to obtain a single bundle of multi-strand wire suitable for the iron core slot, and finally wraps it with an insulation layer. From its detailed process, the diameter of the semi-finished round wire is on the order of centimeters or more, and the resulting wire bundle clearly lacks conventional flexibility, meaning it does not possess conventional winding characteristics. Essentially, it is a custom-made wire, its length and other parameters manufactured according to the needs of the motor stator, not a conventional general-purpose wire (i.e., not used for winding into coils). From the method of application, this prior art applies a film after flattening; this film is essentially an insulating protection between the "wire bundles," not wrapped before flattening, and therefore cannot provide a binding function for flattening, nor can it effectively and tightly wrap the Litz wire. Its single wires are relatively thick (above 0.2mm), and have good plasticity, making it suitable for high-frequency electronic products. The Litz wire used in the magnetic induction coils of this product has a single wire diameter of less than 0.05mm and is formed through multiple consecutive drawing processes. As is well known, during cold working processes such as drawing, as the wire diameter decreases, the dislocation density increases, leading to an increase in tensile strength, hardness, and toughness, but a decrease in ductility. Therefore, the copper wire used in the magnetic induction coils of high-frequency electronic products, after multiple cold drawing processes, has poorer ductility than the large-diameter copper wires in the aforementioned prior art. After stranding, it cannot naturally maintain its stranded shape and will quickly untwist (increase torque) after the forced stranding force is lost. The existing technology described in the aforementioned patent, which involves stranding small-diameter single wires to produce Litz wire, cannot meet the requirements and cannot achieve square-forming. The circular shape formed after wrapping with the insulation layer exerts a binding force on the stranded wire; that is, the stranded wire under the insulation layer's constraint has mechanical stress (untwisting). Direct square-forming maintains this mechanical stress, preventing the square-formed Litz wire from being straight (it becomes spiral-shaped under natural traction). Under tension, it exhibits a tendency to self-twist. Therefore, when used as a wire harness requiring multiple turns, it lacks good flexibility and tight winding. Furthermore, the outer wrapping film cannot provide adequate protection. The effective bonding of the Litz wire outline means that the rotational torque cannot maintain the rectangular shape of the film; instead, the film's plasticity causes it to be "stretched" by the rotational torque of the wire harness. Furthermore, as a refinement of this patent, it involves baking after pressing, causing the self-adhesive individual wires to unravel under the mechanical stress of unwinding after heating. In this process, maintaining the rectangle relies on the constraint of the outer insulation layer. While some stress is released after the pressed rectangular stranded wire unravels, new stress is also generated. This stress, after removing the outer insulation layer, makes the square stranded wire even looser and less flexible, and the individual wires inevitably experience linear tensile stress. It is clear from the patent application documents that the Litz wire obtained by this process is a type of wire bundle, a finished wire harness with multiple individual wires bound by the outer insulation layer. It is unsuitable for winding and for flat multi-turn winding. The stress release after the outer insulation layer deforms due to heat obviously causes deformation and disorder in the wire harness, resulting in poor heat resistance.

[0006] Chinese patent application number 2019100816690 discloses a double-stranded Litz wire for medium and high frequency electrical applications. The process involves manufacturing a multi-strand Litz wire, where multiple electromagnetic wires are spirally twisted together to form each Litz wire strand; these strands are then spirally twisted together to form a core; the core is then squared while wrapped, making its cross-section approximately rectangular; the wrapping layer is removed, and the squared core is spirally wrapped with DuPont paper. From the description in this patent application, it is clear that this is an irregularly squared Litz wire. Due to its double twisting, the number of Litz strands is relatively large. The strands are few and have gaps between them. After pressing, the outer rectangular shape is irregular. After twisting, there is still untwisting mechanical stress. The application documents do not describe whether stress is released during the process of removing the outer insulation layer and rewinding DuPont paper. However, even if the untwisting mechanical stress is released after removing the outer insulation layer, it will change its original roughly rectangular shape. If the untwisting mechanical stress is not released, it has the same defect as Chinese patent application number 202411664195X, that is, the DuPont paper will break and fall apart (the DuPont paper that is wound breaks apart loses all binding force on the strands).

[0007] In summary, the Litz square wires obtained in the above-mentioned prior art are finished wire harnesses, not general-purpose wires, or in other words, they are shaped Litz wires, not stress-relieved Litz wires. Based on this, this application is proposed. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention proposes a production process for press-formed Litz wire with stable performance.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: a process for producing square-faced Litz wire, characterized by comprising the following steps: stranding multiple copper wires with insulating layers to form a circular multi-strand wire; spirally winding the circular multi-strand wire to obtain a film-coated multi-strand wire; heat-treating the film-coated multi-strand wire; un-twisting the film-coated multi-strand wire in a softened state to eliminate the torsional stress of the film-coated multi-strand wire; straightening the wire online; and finally square-faceting the un-twisted and straightened film-coated multi-strand wire and cooling it to obtain the square-faced Litz wire.

[0010] Furthermore, the baking temperature is controlled between 80 and 100°C, and the continuous online heating time is controlled between 3 and 5 hours.

[0011] Furthermore, the degree of untwisting should be controlled between 10% and 40%, ideally so that the free end of the wire can be in a naturally straight state after pressing. The untwisting rate is the ratio of the amount of reverse rotation of the pay-off reel to the amount of twisting rotation.

[0012] Furthermore, the copper wire used for stranding is self-adhesive enameled wire.

[0013] Furthermore, the diameter of the copper wire used for stranding is 0.05–0.50 mm.

[0014] Furthermore, the number of strands is 10 to 10,000.

[0015] Furthermore, the long side of the resulting compressed Litz wire cross section is less than 10 mm; the aspect ratio is greater than 1 and less than 3.

[0016] Furthermore, the resulting pressed Litz wire has a conductive area accounting for over 70%. This is the ratio of the sum of the cross-sectional areas of the copper wires to the cross-sectional area of ​​the pressed Litz wire.

[0017] Furthermore, the outer wrapping film of the circular multi-strand wire is a polyimide film with high temperature resistance.

[0018] The compressed Litz line obtained by this method has the following advantages:

[0019] 1. High dimensional stability, which comes from the elimination and weakening of the rotational stress of the strands by untwisting, the mutual adhesion of the self-adhesive copper wires after the adhesive film is cured, and the straightening treatment as needed. In essence, the initial stranding is "over-stretching" of the wire, that is, the torque of the stranded wire bundle formed by the initial stranding is smaller than the torque of the set Litz wire, which can make the wire "over-bend". After untwisting, the single wire tends to be in a natural bending state. The torque after untwisting is slightly larger than before. The torque after untwisting is the design torque.

[0020] 2. Uniform size, regular and flat outer shape, soft thread bundle, straight and without twist in its natural state;

[0021] 3. Higher temperature resistance (up to 240℃). In existing technologies, the increase in temperature will cause the stranded wire to unravel and twist, which will damage the outer insulation layer.

[0022] 4. Stable electrical performance: Existing square-pressed Litz wires have negative effects on physical and electrical properties when heated. Torsional stress can easily cause cross-flow between individual wires, which is especially noticeable after bending. After being heated and dissipated, individual wires will also generate tensile stress. Untwisted round wires are prone to compressing individual wires during square pressing, causing local insulation damage and unstable electrical performance. In particular, when square-pressed Litz wires are wound in multiple turns or have long-distance conduction, the probability and risk of wire breakage are greater.

[0023] 5. High fill factor, which benefits from the stability of wire size and profile, and also depends on the high heating temperature that maintains size and shape.

[0024] 6. This solution involves wrapping the outer film before pressing, so that the film and the wire are fused together under the dual action of extrusion and heat fusion. It is not a bonding but an adhesion, resulting in a smooth outer contour of the Litz wire. The outer contours of the film and the wire are consistent in cross-section, which increases the density of the "film-coated wire bundle" and is conducive to improving the filling density. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the main wire shapes used in the fabrication of this square Litz wire.

[0026] Figure 2 This is a flow chart of the production process of the Litz press line;

[0027] Figure 3 This is a picture of the finished product of this pressed Litz wire (the image has been color-processed).

[0028] Legend: 1. Circular multi-strand yarn; 2. Film-coated multi-strand yarn; 3. Pressed Litz yarn. Detailed Implementation

[0029] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0030] like Figure 1 and Figure 2 As shown, the process includes the following steps: Multiple copper wires to be stranded are simultaneously unwound, with the wires having insulating varnish or self-adhesive insulating varnish, and a single wire diameter of 0.05–0.50 mm. The copper wires are then stranded, with 10–10,000 strands forming a circular multi-strand wire 1. This circular multi-strand wire 1 is then spirally wound to obtain a film-coated multi-strand wire 2. The wrapping material is a high-temperature resistant polyimide film. The film-coated multi-strand wire 2 is then heat-treated continuously during the winding process. The baking temperature is 80–100°C, and the heating time is controlled between 3–5 hours to ensure the wrapping tape softens and the bonding force between the strands weakens. The film-coated multi-strand wire is then heat-treated while the wrapping tape is softened. 2. Perform untwisting treatment to eliminate the torsional stress of the membrane-coated multi-strand wire 2. After heating, the membrane-coated multi-strand wire 2 exhibits good outer film plasticity during untwisting, and the adhesion of the single-strand paint film is weakened, avoiding wear between single strands during the untwisting process. At the same time, the wire bundle is always in a pre-tightened and straightened state to avoid uneven untwisting and to prevent uneven contraction and expansion of the outer film. If necessary, the wire can be straightened online. Generally speaking, truss surfaces with a long side less than 2mm do not require straightening and can be shaped during the untwisting process under tension, maintaining a straight finished product. However, thicker square wires require an additional straightening system for online straightening. Finally, the untwisted and straightened membrane-coated multi-strand wire 2 is squared, and after cooling, the squared Litz wire 3 is obtained and wound up to become the base wire. Figure 3 As shown.

[0031] The degree of untwisting should be controlled between 10% and 40%, ideally so that the free end of the square wire can be in a naturally straight state after crimping. The untwisting rate is the ratio of the amount of reverse rotation of the pay-off reel to the amount of twisting rotation. The longer side of the resulting square-crimped Litz wire 3 cross-section should be less than 10mm; the aspect ratio should be greater than 1 and less than 3; and the conductive area of ​​the resulting square-crimped Litz wire 3 should account for more than 70%. The ratio of the sum of the cross-sectional areas of the copper wires to the cross-sectional area of ​​the square-crimped Litz wire 3 is also considered.

[0032] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A process for producing pressed Litz wire, characterized in that, The process includes the following steps: twisting multiple copper wires with insulating layers together to form a circular multi-strand wire (1), spirally winding the circular multi-strand wire (1) to obtain a membrane-coated multi-strand wire (2), then heat-treating the membrane-coated multi-strand wire (2), and un-twisting the membrane-coated multi-strand wire (2) in a softened state to eliminate the torsional stress of the membrane-coated multi-strand wire (2). Finally, the un-twisted and straightened membrane-coated multi-strand wire (2) is pressed square and cooled to obtain the pressed Litz wire (3).

2. The production process for pressed Litz wire according to claim 1, characterized in that, The wire is straightened online before pressing and after heating.

3. The production process for pressed Litz wire according to claim 2, characterized in that, The degree of untorture should be controlled between 10% and 40%, so that the free end of the pressed line can be in a naturally straight state.

4. The production process for pressed Litz wire according to claim 2, characterized in that, The copper wire used for stranding is self-adhesive enameled wire.

5. A process for producing pressed Litz wire according to any one of claims 1 to 4, characterized in that, The diameter of the copper wire used for stranding is 0.05 to 0.50 mm.

6. A process for producing pressed Litz wire according to any one of claims 1 to 4, characterized in that, The number of strands is 10 to 10,000.

7. A process for producing pressed Litz wire according to any one of claims 1 to 4, characterized in that, The long side of the resulting compressed Litz wire cross section is less than 10 mm; the aspect ratio is greater than 1 and less than 3.

8. A process for producing pressed Litz wire according to any one of claims 1 to 4, characterized in that, The resulting pressed Litz wire has a conductive area accounting for more than 70%.

9. A process for producing pressed Litz wire according to any one of claims 1 to 4, characterized in that, The outer wrapping film of the circular multi-strand wire is a high-temperature resistant polyimide film.

10. A process for producing pressed Litz wire according to any one of claims 1 to 4, characterized in that, The heating temperature is controlled between 80 and 100°C, and the continuous online heating time is controlled between 3 and 5 hours.

Images