Methods of manufacturing toroids

Abstract

A method of manufacturing a toroid is disclosed. The method comprises unspooling a strip (210) from a first spool (202). The strip (210) has a longitudinal axis. The method comprises, during unspooling, cutting the strip (210) into a first oval having one axis of symmetry, wherein the one axis of symmetry is parallel to the longitudinal axis of the strip (210). The method comprises winding the first oval onto a second spool (204) to form the toroid.

Description

METHODS OF MANUFACTURING TOROIDSTechnical Field

[0001] The following disclosure relates to methods of manufacturing toroids and in particular but not exclusively, to methods of manufacturing toroids for magnetic cores.Background

[0002] Magnetic cores are utilised across a range of electromagnetic devices such as transformers, electric motors, generators, and inductors. Magnetic cores may have a toroidal (i.e. ring, doughnut or bagel) shape. Magnetic cores typically comprise thin sheets of material with high magnetic permeability in a laminated arrangement to minimise energy losses from internal eddy currents.

[0003] Toroidal magnetic cores are normally wound with several stepped widths of electrical steel, in a stop-start process, to achieve an approximately round crosssection of the torus. For each stepping, the process gets interrupted, the steel strip gets cut, a new spool of steel gets hooked up, the end of the steel strip already on the toroid gets spot-welded to the new strip, and then the winding process continues. Disclosed herein are improved methods of manufacturing toroids.Summary

[0004] There is provided a method of manufacturing a toroid. The method comprises unspooling a strip from a first spool. The strip has a longitudinal axis. The method comprises, during unspooling, cutting the strip into a first oval having one axis of symmetry, wherein the one axis of symmetry is parallel to the longitudinal axis of the strip. The method comprises winding the first oval onto a second spool to form the toroid.

[0005] Winding the first oval onto the second spool may be carried out contemporaneously with cutting the strip.

[0006] The method may comprise, during unspooling, cutting the strip into a second oval having one axis of symmetry, wherein the one axis of symmetry of the second oval is parallel to the longitudinal axis of the strip. The method may comprise winding1L_LIVE_EMEA1 :101600433v1the second oval onto a third spool. The second oval may have the same shape as the first oval.

[0007] The first oval and the second oval may be tessellated from the strip to minimise unused portion of the strip to reduce waste material from the strip. For example, the second oval may be offset from the first oval and a mirror image of the first oval in a direction perpendicular to the longitudinal axis of the strip. The toroid may be a first toroid, and the method may comprising unspooling the second oval from the third spool onto a fourth spool to form a second toroid. This is because if the second oval is a mirror image of the first oval, when the second oval is wound on the third spool, the outer layer of the second oval would be the inside of the second toroid. Hence the second oval can be wound onto the fourth spool from the third spool to form the second toroid.

[0008] Alternatively, the first and second ovals may have the same orientation on the strip. In this case, the toroid may be a first toroid, and winding the second oval onto the third spool may form a second toroid.

[0009] The strip may be a strip of material with high magnetic permeability such as ferromagnetic metals or ferrimagnetic compounds. The strip may comprise a surface which is coated in an electrically insulating material. The electrically insulating material may be curable.

[0010] The strip may be coated with glue prior to, or after, unspooling from the first spool.

[0011] The method may further comprise the step of placing one or more excitation coils around the toroid and delivering an excitation current to the one or more coils above the nominal range of the toroid; wherein the excitation current is controlled to achieve a target temperature in the toroid for a target time period.

[0012] The method may further comprise applying clamps to the toroid to achieve a required bonding pressure of the glue.

[0013] The method may further comprise applying an insulating cover to the toroid during the heating process.

[0014] There is also disclosed a method of manufacturing a toroid, the method comprising winding a strip of electrical steel coated with glue onto a second spool to form the toroid; placing one or more excitation coils around the toroid; delivering an excitation current to the one or more coils above a nominal range of the toroid;wherein the excitation current is controlled to achieve a target temperature in the toroid for a target time period.

[0015] The method may further comprise applying clamps to the toroid to achieve the required bonding pressure of the glue.

[0016] The method may further comprise applying an insulating cover to the toroid during the heating process.

[0017] The method may further comprise unspooling the strip from a first spool, wherein the strip has a longitudinal axis; and during unspooling, cutting the strip into a first oval having one axis of symmetry, wherein the one axis of symmetry is parallel to the longitudinal axis of the strip.

[0018] Winding the first oval onto the second spool may be carried out contemporaneously with cutting the strip.

[0019] The method may further comprise during unspooling, cutting the strip into a second oval having one axis of symmetry, wherein the one axis of symmetry of the second oval is parallel to the longitudinal axis of the strip; and winding the second oval onto a third spool.

[0020] There is also disclosed a method of manufacturing a toroid, the method comprising unspooling a strip from a first spool, wherein the strip has a longitudinal axis; during unspooling, cutting the strip in two locations parallel to the longitudinal axis; periodically adjusting the two locations to two new locations, at the location at which the two locations are adjusted making cuts in the strip between respective previous locations and new locations perpendicular to the longitudinal axis of the strip; and winding the strip onto a second spool to form a toroid; wherein the adjustments of the locations are selected to achieve a toroid with a stepped cross section that approximates a circle.

[0021] Winding the strip onto the second spool may be carried out contemporaneously with cutting the strip.

[0022] The strip may be a strip of material having high magnetic permeability.

[0023] There is also disclosed a toroid manufactured using the methods described here.Brief description of the drawings

[0024] Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. Elements in the figures areillustrated for simplicity and clarity and have not been drawn to scale. Like reference numerals have been included in the respective drawings to ease understanding:Figure 1 A is a schematic perspective view of a toroid;Figure 1 B is a schematic side view of the toroid of Figure 1 A;Figure 1 C is a schematic side view of a cross-section A-A of the toroid of Figure 1 A;Figure 1 D is a schematic side view of a cross-section B-B of the toroid of Figure 1 A;Figure 2 is a schematic view of a strip used to form the toroid of Figure 1 A;Figure 3A is a schematic perspective view of an apparatus for manufacturing a toroidFigure 3B is a schematic side view of the apparatus of Figure 3A;Figure 4 is a schematic top view of a strip used to form a plurality of toroids;Figure 5 is a flowchart of a process for manufacturing a toroid; Figures 6A to 6C are schematic views of a magnetic core; and Figure 7 shows a method of manufacture of a magnetic core.Detailed description

[0025] Figures 1 A to 1 D show a toroid 100. The words toroid and toroidal will be used herein to describe a shape approximating that formed by rotating a closed curve around an axis which lies in the same plane as the curve but does not intersect it. The closed curve may be a circle, oval, or other shape suitable for the intended use. The word oval is used herein to refer to a mathematical oval, but also to include shapes which approximate a mathematical oval where appropriate. For example, shapes with a generally oval shape but which have flattened or truncated ends falls within the meaning of oval As will be apparent from the following description the cross-section of manufactured toroids may vary somewhat around the toroid due to the manufacturing process and are not perfect toroids but approximate that shape. The toroid 100 comprises a planar elongate oval 102 wound in a spiral. The toroid 100 may be suitable for use as a magnetic core, and therefore, the elongate oval 102 may be made of a material which has high magnetic permeability such as ferromagnetic metals or ferromagnetic compounds. For example, the elongate oval 102 may be made of steel. The elongate oval 102 has a length in the direction of winding, and a width which is perpendicular to the length and which varies along the length to form the stepped widths of the cross-section A-A. The width of the elongateoval 102 is narrower at each of an inner end WPA 104 of the elongate oval 102 and at an outer end 106 of the elongate oval 102.

[0026] Figure 2 illustrates a representation of the elongate oval 102 if it were unwound from forming the toroid 100. The elongate oval 102 has one axis of symmetry 150. The elongate oval 102 is widest at a position 160 between the inner end 104 and the outer end 106. The position 160 is closer to the inner end 104 than the m idpoint between the inner end 104 and the outer end 106 since the outer circumference of the spiral increases as the elongate oval 102 is wound. The toroid 100 is formed by winding the elongate oval 102 into a spiral.

[0027] With reference to Figures 3A and 3B, an apparatus 200 for manufacturing a toroid, such as the toroid 100, comprises a first spool 202, a second spool 204, and a set of cutters 206. The set of cutters 206 may comprise, for example, one or more laser cutters, such as fibre laser cutters, one or more water jets, or one or more cutting blades.

[0028] The first spool 202 comprises a strip 210 which is wound on the first spool 202. The strip 210 is an elongate strip having a longitudinal axis. The strip 210 is wound around the first spool 202. The strip 210 can be unwound from the first spool 202 and passed through the set of cutters 206. The set of cutters 206 is configured to cut the strip 210 into an elongate oval 212. For example, by either moving a single cutter or varying a distance between adjacent cutters to be the width of the elongate oval corresponding to the position along the length of the elongate oval. The elongate oval 212 emerging from the set of cutters 206 can be wound onto the second spool 204 to form a toroid 214. The offcuts 216, being the remains of the strip 210 after the oval 212 has been cut from the strip 210, may also be wound onto the second spool 204 or one or more other spools. This can aid in collecting this waste material for reuse or recycling.

[0029] In the example apparatus 200, one oval 212 is cut from the strip 210 using the set of cutters 206. In other examples, the set of cutters 206 can be configured to cut a plurality of ovals from the strip 210, for example in a tessellated pattern shown in Figure 4 to minimise the amount of material in the offcuts. The tessellated pattern may comprise ovals 212 which are oriented on the strip in different directions relative to each other. For example, a first oval may be a mirror image of a second oval on the same strip. The ovals in the tessellated pattern may be the same shape and size, or may be different shapes and sizes to maximise material usage.

[0030] A method 500 of manufacturing a toroid such as the toroid 100 using the apparatus 200 is discussed with reference to Figure 5. At step 502, the strip 210 is unspooled from the first spool 202 and fed towards the set of cutters 206. At step 506, while the strip 210 is being unspooled, the strip 210 is cut by the set of cutters 206 into one or more ovals 212. Each oval has one axis of symmetry which is parallel to the longitudinal axis of the strip 210. At step 510, the one or more ovals 212 emerging from the set of cutters 206 are wound onto one or more spools such as the second spool 204. Ovals where the outer end 106 is the outermost layer of the spiral form toroids. Step 510 may be carried out contemporaneously to unspooling and cutting, or may be carried out once complete ovals are cut from the strip 210. Tension may be applied via the second spool 204 to the strip and / or the second oval 214 as it is being wound onto the second spool 204 to ensure a tight spiral minimising space or gaps between layers. This tension may also assist in keeping the second oval 214 centred on the second spool 204.

[0031] Optionally, at step 514, ovals which are wound backwards, i.e. where the inner end 104 is the outermost layer of the spiral, may be unspooled and then contemporaneously wound, at step 518 onto another spool to form toroids.

[0032] Optionally, glue may be applied to a top surface and / or a bottom surface of the strip 210 after unwinding from the first spool 202, but before winding onto the second spool 204. The glue may be applied before the strip 210 has passed through the set of cutters 206 or after the strip 210 has passed through the set of cutters 206. The glue may be a two-part adhesive, with one part applied to the top surface of the strip 210 and the second part applied to the bottom surface of the strip 210. Once the one or more ovals 212 formed from the strip 210 have been wound onto the second spool 204 (or another spool, if subsequent unspooling and winding is required) to form toroids, the glue may be cured by heating the toroids. The heating may be performed by an induction heater, oven, or any other suitable means.

[0033] Alternatively, the toroid & glue can be heated by placing one or more coils around the toroid and then delivering an excitation signal through the coils that generates an alternating magnetic field above the nominal range of the magnetic core. The resulting hysteresis and eddy current losses from the repeated magnetisation and demagnetisation of the steel generates heat evenly throughout the core to heat and cure the glue. An insulating material (such as fiberglass) can be placed around thetoroid to aid retaining heat during the heating process. Additionally, clamps may be applied to the toroid to achieve the necessary bonding pressure for the glue.

[0034] In an alternate method of manufacturing a toroid during unspooling the strip is cut at two locations parallel to the longitudinal axis of the strip. At defined locations along the strip the two cutting locations are changed such that the distance between the locations changes and the width of the cut strip is changed. When the cutting locations are changed a cut is made perpendicular to the longitudinal axis to connect the previous and new locations. The resulting strip therefore has a “stepped” shape which approximates a smooth shape. When wound into a toroid the toroid has a stepped shape which approximates a circular shape.

[0035] The distance between the locations, and the points at which that distance change, are defined such that the resulting toroid has the desired shape. PCT Publication W02023 / 073203, incorporated herein by reference, describes a stepped toroid. The distances and points of change may be predefined during the design process and communicated to the apparatus controlling implementation of themethod during manufacturing.

[0036] The process of cutting and winding the strip 210 to form the toroid 100 may impair the magnetic properties of the grain-oriented electrical steel. In particular, the orientation of the magnetic domains may be affected in the rolling direction. In order to rectify this, the toroid 100 may be annealed after winding, so as to allow the disturbed domains to realign themselves.

[0037] The toroid 100 may include a surface coating of electrically-insulating material which, may be curable, such as a varnish or paint. The surface coating may be applied before or after annealing of the core. Where a curable surface coating is utilised that curing is performed in the appropriate manner, for example by heating the coated toroid in an autoclave.

[0038] An example three-phase magnetic core of PCT patent application published as W02023 / 073203A1 is described in brief with reference to Figures 6A to 6C. Magnetic core 600 comprises three arc-shaped limbs 602 which are evenly spaced around a central axis 604. Each limb 602 is substantially identical. The arc-shaped limbs 602 are 180 degree arcs and are substantially semi-toroidal in shape. Each limb 602 has a first end and a second end. Each first end has a first edge which lies along the central axis 604. Each second end has a second edge which lies along the central axis. Each limb 602 may be wound with one or more of a primary, a secondary and amodulating winding on one or more bobbins (not illustrated in Figures 6A to 6C). Each limb 602 may comprise a plurality of electrical steel strips that are laminated together. The use of thin steel laminations reduces power losses caused by eddy currents induced when sinusoidal voltage is applied to the windings. The width of the laminated electrical steel strips may be different in an arrangement that leads to the limbs 602 having a cross section that approximates a circle.

[0039] The first ends 606 of each limb 602 are securely held or clamped together, and the second ends 608 of each limb 602 are securely held or clamped together, such that the ends of the limbs are in direct or close contact with each other for optimum electromagnetic performance of the core.

[0040] Toroids manufactured using the apparatus 200 may be used to form substantially semi-toroidal limbs for three-phase magnetic cores such as limbs 602. A method of manufacturing a three-phase magnetic core such as the core 600 using toroids manufactured using the apparatus 200 is discussed with reference to Figure 7. At step 652, two identical toroids such as toroid 214 are each cut into two equal halves, thereby forming four identical halves.

[0041] At step 654, each end of three of the four toroid halves is machined to produce three limbs with angled ends. The spare fourth half toroid may be used toward the manufacture of another three-phase magnetic core. The ends may be machined to an angle of 120 degrees to allow the ends of the limbs to closely mate with each other. The machining may include one or more of sanding, grinding, milling, and cutting, such as waterjet cutting or laser cutting. In some examples, the ends of the limbs may be machined to produce lap joints which allow the limbs to mate tightly with each other.

[0042] At step 658, one or more of a primary winding, a secondary winding and modulating windings may be applied to each limb. Applying windings to the limbs may be carried out at any point before both ends of each limb are connected together at step 662, in other words, when there is at least one open end. Applying windings around the limbs may include winding wire around a limb to form the winding.Alternatively, applying windings around the limbs may include spinning a wire onto a bobbin and inserting the limb into the bobbin. The winding process is simplified by winding the limbs prior to joining the limbs together. The windings may be distributed on the limbs with or without spacers.

[0043] At step 662, the three limbs are positioned around a central axis. The first ends of the three limbs are connected to each other, and the second ends of the three limbsare connected to each other. Connecting the ends of the limbs together may include using an adhesive such as a metal-to-metal structural adhesive. Alternatively or additionally to connecting using an adhesive, connecting the ends of the limbs together may include clamping the limbs together.

[0044] Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognise that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term “comprising” or “including” does not exclude the presence of other elements.

Claims

Claims1 . A method of manufacturing a toroid, the method comprising: unspooling a strip from a first spool, wherein the strip has a longitudinal axis; during unspooling, cutting the strip into a first oval having one axis of symmetry, wherein the one axis of symmetry is parallel to the longitudinal axis of the strip; and winding the first oval onto a second spool to form the toroid.

2. The method of claim 1 , wherein winding the first oval onto the second spool is carried out contemporaneously with cutting the strip.

3. The method of any preceding claim, comprising: during unspooling, cutting the strip into a second oval having one axis of symmetry, wherein the one axis of symmetry of the second oval is parallel to the longitudinal axis of the strip; and winding the second oval onto a third spool.

4. The method of claim 2, wherein the toroid is a first toroid, the method comprising unspooling the second oval from the third spool onto a fourth spool to form a second toroid.

5. The method of claim 2, wherein the toroid is a first toroid, and wherein winding the second oval onto the third spool forms a second toroid.

6. The method of any preceding claim, wherein the strip is a strip of material having high magnetic permeability.

7. The method according to any preceding claim, wherein the strip is coated with glue prior to, or after, unspooling from the first spool.

8. The method according to claim 7, further comprising the step of placing one or more excitation coils around the toroid and delivering an excitation current to the one or more coils above the nominal range of the toroid; wherein the excitation current is controlled to achieve a target temperature in the toroid for a target time period.

9. The method of claim 7 or claim 8, further comprising applying clamps to the toroid to achieve a required bonding pressure of the glue.

10. The method of claim 8 or claim 9 further comprising applying an insulating cover to the toroid during the heating process.

11. A toroid manufactured using the method of any one of claims 1 to 6.

12. A method of manufacturing a toroid, the method comprising: winding a strip of electrical steel coated with glue onto a second spool to form the toroid; placing one or more excitation coils around the toroid; delivering an excitation current to the one or more coils above a nominal range of the toroid; wherein the excitation current is controlled to achieve a target temperature in the toroid for a target time period.

13. The method of claim 12, the method further comprising: applying clamps to the toroid to achieve the required bonding pressure of the glue.

14. The method of claim 12 or claim 13, the method further comprising: applying an insulating cover to the toroid during the heating process.

15. The method of any of claims 12 to 14, the method further comprising: unspooling the strip from a first spool, wherein the strip has a longitudinal axis; and during unspooling, cutting the strip into a first oval having one axis of symmetry, wherein the one axis of symmetry is parallel to the longitudinal axis of the strip.

16. The method of any of claims 12 to 15, wherein winding the first oval onto the second spool is carried out contemporaneously with cutting the strip.

17. The method of any of claims 12 to 16, comprising:during unspooling, cutting the strip into a second oval having one axis of symmetry, wherein the one axis of symmetry of the second oval is parallel to the longitudinal axis of the strip; and winding the second oval onto a third spool.

18. A toroid manufactured using the method of any one of claims 12 to 17.

19. A method of manufacturing a toroid, the method comprising: unspooling a strip from a first spool, wherein the strip has a longitudinal axis; during unspooling, cutting the strip in two locations parallel to the longitudinal axis; periodically adjusting the two locations to two new locations, at the location at which the two locations are adjusted making cuts in the strip between respective previous locations and new locations perpendicular to the longitudinal axis of the strip; and winding the strip onto a second spool to form a toroid; wherein the adjustments of the locations are selected to achieve a toroid with a stepped cross section that approximates a circle.

20. The method of claim 19, wherein winding the strip onto the second spool is carried out contemporaneously with cutting the strip.

21. The method of any claim 19 or claim 20, wherein the strip is a strip of material having high magnetic permeability.

22. A toroid manufactured using the method of any one of claims 19 to 21 .

Images